Immune approaches beyond traditional immune checkpoint inhibitors for advanced renal cell carcinoma

ABSTRACT

Renal cell carcinoma (RCC), especially clear cell RCC, is generally considered an immunotherapy-responsive cancer. Recently, the prognosis for patients with locally advanced and metastatic RCC has significantly improved with the regulatory approvals of anti-PD-1/PD-L1/CTLA-4 immune checkpoint inhibitor (ICI)-based regimens. Yet in most cases, RCC will remain initially unresponsive to treatment or will develop resistance over time. Hence, there remains an unmet need to understand what leads to ICI resistance and to develop novel immune and nonimmune treatments to enhance the response to ICIs. In this review, we highlight recently published studies and the latest clinical studies investigating the next generation of immune approaches to locally advanced and metastatic RCC beyond traditional ICIs. These trials include cytokines, gut microbiota-based therapies, novel immune checkpoint agents, vaccines, and chimeric antigen receptor T cells. These agents are being evaluated as monotherapy or in combination with traditional ICIs and will hopefully provide improved outcomes to patients with RCC soon.

KEYWORDS:

• Immunotherapy
• gut microbiota
• cytokine
• interleukin
• immune checkpoint inhibitor
• vaccine
• CAR T-cell therapy

Introduction

Renal cell carcinoma (RCC), especially of the clear cell subtype, has long been considered a cancer susceptible to immune-based treatments. Prior to the year 2000, high-dose systemic interleukin-2 (IL-2) and interferon alfa were both approved in the setting of metastatic RCC (mRCC) because some patients had complete responses to cytokine infusions for several decades.¹ However, these cases were not common, and the associated side effects from cytokines were numerous. Starting in the year 2015 with the approval of nivolumab as second-line therapy in mRCC, immune checkpoint inhibitors (ICIs) (specifically anti-CTLA-4, PD-1 and PD-L1 monoclonal antibodies) have revolutionized the management of RCC including in the frontline metastatic setting and as adjuvant therapy in the localized setting (specifically pembrolizumab for intermediate-high or high-risk of recurrence).² Unfortunately, many patients with RCC either do not respond to anti-CTLA-4/PD-1/PD-L1 ICIs or develop ICI resistance. Hence, more novel methods and agents are needed. This review provides an overview of the promising upcoming immunotherapeutic agents for locally advanced and mRCC, focusing on cytokine-based therapies, the gut microbiota, novel immune checkpoint agents, vaccines, and chimeric antigen receptor (CAR) T cells that are currently being evaluated in clinical trials.

Cytokines

Cytokines continue to remain of interest in mRCC after the success of systemic interleukin-2 and interferon-alfa for some patients despite the high toxicities. The cytokines that are under current clinical investigation are engineered to minimize toxicities seen with systemic high-dose IL-2 while preserving antitumor immunity. These include IL-2, IL-12, IL-15, and IL-27. Table 1 summarizes the latest clinical trials involving these cytokines.

Table 1. Current active and recruiting clinical trials evaluating engineered interleukins in metastatic RCC.

Trial number	Interleukin target	Agent(s)	Setting	Primary outcome measures
NCT04540705	IL-2	Bempegaldesleukin, nivolumab, and TKI vs. nivolumab and TKI	Frontline	AEs, DLT
NCT02799095	IL-2	Nemvaleukin-alfa alone and with pembrolizumab	Refractory or intolerant to approved therapies	AEs, ORR
NCT04235777	IL-12	Bintrafusp alfa with NHS-IL-12	Refractory or intolerant to approved therapies	Safety and tolerability
NCT04234113	IL-15	Nanrilkefusp alfa alone and with pembrolizumab	Refractory or intolerant to approved therapies	AEs, DLT
NCT03228667	IL-15	N-803 with anti-PD-1/PD-L1 ICIs and PD-L1 targeting high-affinity NK cells	Refractory to prior ICI	ORR
NCT04628780	IL-15	PF-07209960	Progressed on at least 2 prior lines of therapy	AEs, DLT, ORR
NCT04374877	IL-27	SRF388	Prior treatment with VEGF-targeted therapy and ICI	AEs, DLT, ORR

TKI = tyrosine kinase inhibitor, AEs = adverse events, DLT = dose-limiting toxicities, ORR = objective response rate, ICI = immune checkpoint inhibitor, VEGF = vascular endothelial growth factor.

IL-2

While systemic IL-2 continues to be used in clinical trials, such as in combination with pembrolizumab or nivolumab (e.g., NCT03991130, NCT05155033, NCT03260504, NCT02964078), novel engineered cytokines using the IL-2 pathway while mitigating toxicity are being explored. The engineered cytokines being evaluated in mRCC include bempegaldesleukin (NKTR-214) and nemvaleukin-alfa (ALKS 4230).

Bempegaldesleukin consists of an IL-2 protein bound to releasable polyethylene glycol (PEG) chains; when IL-2 is bound to PEG, it remains inactive. Bempegaldesleukin selectively activates the IL-2 receptors of cytotoxic T cells over helper T regulatory cells, theoretically maximizing antitumor effects and minimizing toxicities.³ The combination of bempegaldesleukin and nivolumab was evaluated in 557 patients with various solid tumors in the PIVOT-02 phase 1/2 trial (NCT02983045). PIVOT-02 involved a cohort of 49 patients with mRCC receiving this combination as frontline therapy, and results for this cohort were published.⁴ After a median follow-up of 32.7 months, the objective response rate (ORR) was 34.7% (17/49 patients) and the median progression-free survival (PFS) was 7.7 months (95% CI, 3.8–13.9). Every patient except for one had a treatment-emergent adverse event (TEAE), including 38.8% with grade 3/4 events. The combination overall demonstrated safety and efficacy, leading to the PIVOT-09 open-label phase 3 study (NCT03729245) that randomized 623 patients to either bempegaldesleukin/nivolumab or the investigator’s choice of sunitinib or cabozantinib as frontline therapy in mRCC. Unfortunately, the experimental arm did not meet the prespecified boundary for statistical significance compared to the control arm, so the trial was discontinued.⁵ Overall, the combination of bempegaldesleukin with nivolumab has been a disappointment, as the PIVOT IO 001 trial for frontline metastatic melanoma also did not meet the primary endpoint.⁶ As a result, most clinical trials involving this combination for various cancers have been discontinued. While doublet treatments were ineffective, triplet therapy is being evaluated in the PIVOT IO 011 phase 1 trial (NCT04540705). This trial assesses 30 patients with previously untreated mRCC to receive the combination of bempegaldesleukin and nivolumab with either cabozantinib or axitinib.⁷

Nemvaleukin-alfa binds with intermediate affinity to the IL-2 receptor while sparing high-affinity IL-2 receptors to minimize toxicities.⁸ ARTISTRY-1 is a phase 1/2 trial (NCT02799095) involving 243 patients with advanced solid tumors including RCC refractory to or intolerant of approved therapies, receiving either nemvaleukin-alfa as monotherapy or in combination with pembrolizumab. Preliminary data presented at the 2022 ASCO Annual Meeting showed tolerability and durable antitumor activity for both nemvaleukin-alfa monotherapy and the combination with pembrolizumab.⁹ Nemvaleukin-alfa monotherapy was also shown to induce a robust expansion of cytotoxic T cells and NK cells with minimal effect on regulatory T cells. The data is promising and warrants further investigation of nemvaleukin-alfa with ICIs.

IL-12

IL-12 is a pro-inflammatory cytokine involved in cell-mediated immunity with the potential to reverse tumor-induced immunosuppression, but it previously failed in clinical trials due to systemic toxicities including death.¹⁰ Localized and targeted IL-12 therapies are being designed. There is an ongoing phase 1 trial (NCT04235777) of bintrafusp alfa and NHS-IL12 with or without stereotactic body radiation therapy for 66 patients with metastatic non-prostate genitourinary cancers.¹¹ Bintrafusp alfa is a bifunctional antibody that inhibits both PD-L1 and tumor growth factor-beta, which are both immunosuppressive.¹² NHS-IL12 is a fusion protein of two molecules of IL-12 with an antibody (NHS76) to single- and double-stranded DNA, targeting necrotic tumor with DNA exposure.¹³ In preclinical models, these two agents had synergistic activity, inducing both adaptive and innate tumor immunity and generating tumor antigen-specific immune memory.¹⁴

IL-15

IL-15 is another novel cytokine target being investigated in RCC. It is structurally like IL-2 due to sharing the common gamma chain.¹⁵ It has been shown to stimulate cytotoxic T cells and NK cells and promotes memory cytotoxic T-cell survival, while having no effect on regulatory T cells.¹⁶ IL-15 itself has a half-life of less than one hour, so its direct use as a cancer therapy is limited, but its components and receptor are being investigated in clinical trials. Nanrilkefusp alfa (SO-C101, SOT101) is an IL-15 superagonist being evaluated for safety and preliminary efficacy as monotherapy or in combination with pembrolizumab in the AURELIO-03 phase 1/1b trial (NCT04234113) in 200 patients with relapsed/refractory metastatic solid tumors including RCC. Preliminary data reported at the 2022 ASCO Annual Meeting showed a favorable safety profile and early signs of efficacy for nanrilkefusp alfa as monotherapy and in combination with ICIs.¹⁷ N-803, an IL-15 superagonist fusion protein, is being evaluated in QUILT-3.055, a phase 2 trial (NCT03228667), in combination with different anti-PD-1/PD-L1 ICIs and PD-L1 targeting high-affinity NK cells in 147 patients with metastatic solid tumors including RCC who have progressed on prior anti-PD-1/PD-L1 ICIs. Preliminary data suggests N-803 has minimal toxicity and provides promising efficacy.¹⁸ PF-07209960, an anti-PD-1 targeting IL-15 fusion protein, is being evaluated as monotherapy in a phase 1 trial (NCT04628780) in 37 patients with metastatic solid tumors including RCC who have progressed on two prior lines of therapy.

IL-27

IL-27 is a member of the IL-12 family of cytokines¹⁹; however, it has primarily been shown to be anti-inflammatory and represses anti-tumor immunity.²⁰ Increased IL-27 transcript expression is associated with a poor prognosis in RCC.²¹ SRF388 is a monoclonal antibody that blocks the interaction of IL-27 with its receptor. SRF388 is being evaluated in a phase 1/1b trial (NCT04374877) as either monotherapy or in combination with pembrolizumab in 220 patients with metastatic solid tumors, including patients with RCC who have previously received vascular endothelial growth factor-targeted therapy and ICI. Preliminary results reported at the 2022 ASCO Annual Meeting suggested SRF388 as monotherapy had good tolerability with preliminary evidence of antitumor activity, including 1 of 10 patients with RCC achieving a partial response, warranting further evaluation in a phase 2 trial.²²

STING

Stimulator of Interferon Genes (STING) is a cytosolic DNA-sensing protein critical for activating the release of inflammatory cytokines, which upregulate the innate immunity to destroy pathogens.²³ STING agonists are being designed as novel agents to stimulate their release to activate the innate immune response against tumor cells.²⁴ STING agonists are being combined with traditional ICIs in clinical trials to upregulate both the adaptive and innate immunity and to provide synergy to destroy tumor cells. TAK-500 is a STING agonist being evaluated as monotherapy and in combination with pembrolizumab in a phase 1 trial (NCT05070247) for patients with metastatic solid tumors including mRCC. IMSA101, a STING agonist injected intratumorally, is being assessed with an ICI and personalized ultra-fractionated stereotactic adaptive radiotherapy (PULSAR) in patients with oligometastatic RCC compared to a control arm of ICI and PULSAR in a phase 2 trial (NCT05846646).

Gut microbiota and traditional immune checkpoint inhibitors

There is growing evidence that the gut microbiota, which refers to the trillions of microbes (bacteria, fungi, viruses, archaea) that colonize the human gut, are one of the key host factors associated with response to ICI therapies in a variety of solid tumors including RCC.^25–31 This observation was first made by noting a correlation between a poor response to ICIs when cancer patients were exposed to antibiotics.³² Specific bacteria have been demonstrated to be potential biomarkers of response to ICIs. However, only recently have we begun to understand the mechanisms by which the gut microbiota directly enhances the ICI anti-tumor response through direct/indirect interactions between microbes and the immune system, the tumor microenvironment, and tumor cells themselves.³³ Therefore, there are now clinical trials investigating microbiota-derived therapies (such as probiotics and fecal microbiota transplants [FMT]) to enhance ICI efficacy in a variety of solid tumors including RCC.

A prospective cohort biomarker study of patients with solid tumors treated with either nivolumab or pembrolizumab also had their short chain fatty acids (SCFAs) concentration analyzed from fecal and plasma samples, and high fecal SCFA concentrations were associated with a statistically significantly longer PFS.³⁴ In addition, recent antibiotic use, which disturbs the gut flora, has been associated with a decreased overall survival (OS), PFS, and response rate for cancer patients on ICIs.³⁵ For RCC, bacterial species such as Akkermansia muciniphila and Bifidobacterium spp. have been positively associated with ICI response, while the Enterocloster genus has been linked to lack of ICI response.³⁶

The promising gut microbiota-based therapy under investigation for RCC is CBM588. CBM588 is a live bacterial product that contains the probiotic Clostridium butyricum, which produces butyric and acetic acids³⁷ and promotes expansion of Bifidobacterium spp. which have been shown to correlate with response to ICI in patients with RCC.³⁸ CBM588 was previously demonstrated in a retrospective study to improve both PFS and OS for patients with metastatic non-small cell lung cancer (NSCLC) receiving ICIs compared to patients who did not receive C. butyricum.³⁹ In RCC, a phase 1 trial (NCT03829111) enrolled 30 patients with metastatic disease and no prior ICIs to receive either CBM588 (taken 80 mg orally twice daily) with ipilimumab/nivolumab versus ipilimumab/nivolumab alone in a 2:1 ratio.⁴⁰ Although the primary endpoint of the change in Bifidobacterium spp. at baseline to 12 weeks was not met, the patients receiving CBM588 had a significantly prolonged median PFS (12.7 months vs. 2.5 months, HR 0.15; 95% CI, 0.05–0.47; p = 0.001) and a trend toward higher response rate (58% vs. 20%, p = 0.06). This trial suggests the importance of incorporating the gut microbiota into future clinical trials involving ICIs. In a similar trial design, CBM588 is being assessed in another phase 1 trial (NCT05122546), as 30 patients received CBM588 with nivolumab/cabozantinib versus nivolumab/cabozantinib alone in a 2:1 ratio. Preliminary results reported at the 2023 ASCO Annual Meeting showed benefit of the CBM588 cohort, with the median PFS not reached compared to 5.8 months in the nivolumab/cabozantinib cohort (p = 0.03) and response rates of 63% versus 33%, respectively.⁴¹

Outside of probiotics, FMT are currently under clinical investigation to improve ICI response in RCC. FMT-based clinical trials utilize donor stool from patients who have responded to ICI and transplant them into patients about to receive ICI. This has shown remarkable efficacy in refractory metastatic melanoma patients^42,43 and has even been used to treat ICI-induced colitis.⁴⁴ In RCC, the TACITO phase 1/2 trial (NCT04758507) is evaluating whether FMT from donors who have had excellent responses to ICIs can enhance ICI efficacy in treatment-naïve patients. In this quadruple-blinded placebo-controlled trial, a total of 50 patients with RCC being treated with ICIs will be randomized to receive either donor FMT versus placebo FMT via colonoscopy infusions and then oral frozen fecal or placebo capsules at 90 or 180 days after the first FMT.⁴⁵ Another phase 1 trial (NCT05354102) is enrolling 12 patients with either NSCLC, melanoma, or RCC who have progressed on prior PD-1/PD-L1 ICIs to receive BMC128 (oral capsule composed of a live bacterial consortium of four bacterial strains) with nivolumab.⁴⁶ Outside of probiotics and FMT, there are several promising microbiota-based therapeutics in the preclinical pipeline which will be evaluated in the clinical trial setting soon.

Novel immune checkpoint targets

The first ICIs targeting the PD-1/PD-L1 or CTLA-4 proteins on T cells have revolutionized the care of cancer patients. However, there are other novel immune checkpoints under clinical investigation.⁴⁷ These novel targets are not only expressed on CD4 or CD8 T cells but also aim to enhance ICI efficacy by targeting other cells within the tumor microenvironment such as myeloid cells. This section focuses on the checkpoint proteins, both inhibitory and stimulatory, with antibodies under investigation in clinical trials that include patients with RCC. A summary of the active and recruiting novel immune checkpoint clinical trials described in this section is provided in Table 2.

Table 2. Current active and recruiting clinical trials evaluating novel immune checkpoint targets involving patients with metastatic RCC.

Trial number	Immune checkpoint target(s)	Agent(s)	Setting	Primary outcome measures
NCT05805501	LAG-3 and TIGIT	RO7247669 and axitinib with or without tiragolumab	Frontline	PFS
NCT03744468	TIM-3, LAG-3, and PD-L1	BGB-A425, tislelizumab, and LBL-007	Locally advanced unresectable or metastatic	ORR
NCT03977467	TIGIT and PD-L1	Tiragolumab and atezolizumab	Progression on prior anti-PD-1 inhibitor	ORR
NCT04913337	ILT2, ILT4, and PD-1	NGM707 alone and with pembrolizumab	Refractory or intolerant to approved therapies	DLT, AEs, DoR, PFS, OS
NCT05215574	ILT3 and PD-1	NGM831 alone and with pembrolizumab	No prior ILT3 inhibition	DLT, AEs, ORR
NCT04691375	TREM2 and PD-1	PY314 alone and with pembrolizumab	Refractory to or relapsed on approved therapies	AEs, DLT
NCT05864144	VISTA and PD-1	SNS-101 alone and with cemiplimab	Refractory to or relapsed on approved therapies	AEs, recommended phase 2 dose, ORR
NCT04773951	BTLA	Icatolimab	Refractory to or relapsed on approved therapies	Safety, tolerability, MTD
NCT05789069	BTLA and PD-1	HFB200603 alone and with tislelizumab	Refractory to at least 2 lines of therapy	AEs, DLT
NCT05229601	OX-40	HFB301001	Progression on at least 2 lines of therapy	AEs, recommended phase 2 dose
NCT05661955	OX-40 and PD-1	BGB-A445 alone and with tislelizumab	Progression on one to three lines of therapy	ORR
NCT04198766	OX-40 and PD-1	INBRX-106 alone and with pembrolizumab	Refractory to or relapsed on approved therapies	AEs, MTD, recommended phase 2 dose
NCT03894618	OX-40 and PD-1	SL-279252	Refractory to or relapsed on approved therapies	AEs, MTD
NCT03809624	4–1BB and PD-1	INBRX-105 alone and with pembrolizumab	Traditional immune checkpoint therapy naïve and refractory allowed	AEs, MTD, recommended phase 2 dose
NCT04895748	A2AR and PD-1	Taminadenant, spartalizumab, and DFF332	Refractory to or relapsed on approved therapies	AEs, DLT
NCT04969315	A2AR	TT-10	Refractory to or relapsed on approved therapies	DLT, recommended phase 2 dose
NCT03454451	CD73, A2AR, and PD-1	Mupadolimab alone, with ciforadenant, and with ciforadenant and pembroliuzmab	Progression on up to 5 prior lines of therapy	DLT, AEs

PFS = progression-free survival, ORR = objective response rate, MTD = maximum tolerated dose, DLT = dose-limiting toxicities, AEs = adverse events, DoR = duration of response.

LAG-3

Lymphocyte-activation gene 3 (LAG-3) is an inhibitory coreceptor that becomes expressed on T cells and other immune cells upon antigen stimulation, and it binds to major histocompatibility complex (MHC) II. By binding MHC II, LAG-3 prevents presentation of tumor antigens to T cells leading to diminished anti-tumor immunity.⁴⁸ There are two monoclonal antibodies targeting LAG-3 under clinical investigation in RCC, relatlimab (BMS-986016) and ieramilimab (LAG525). Of note, relatlimab was recently approved by the United States Food and Drug Administration in March 2022 for frontline therapy of metastatic melanoma in combination with nivolumab, after this combination showed a greater PFS benefit compared to nivolumab alone in RELATIVITY-047 (NCT03470922).⁴⁹ The FRACTION-RCC phase 2 trial (NCT02996110) evaluated various arms of combination ICIs, including relatlimab/nivolumab, with ipilimumab/nivolumab as the control arm for patients who had progressed on or after prior ICI; the results from the relatlimab/nivolumab arm have not yet been reported.

A phase 1/2 study (NCT02460224) evaluated ieramilimab with spartalizumab (PDR001, an anti-PD-1 agent) in 255 patients with metastatic solid tumors with progression on prior therapy, including 11 patients with mRCC (7 received ieramilimab alone and 4 received combination therapy).⁵⁰ Overall, ieramilimab alone or with spartalizumab was well tolerated in this patient population, with no specific details reported for RCC. Antitumor activity was stronger in the combination arm over ieramilimab alone, as 10% of patients had either a complete or partial response to the treatment combination.

In addition, RO7247669 is an anti-PD-1/anti-LAG-3 bispecific antibody delivering dual checkpoint inhibition. In a phase 2 trial (NCT05805501), RO7247669 is being combined with axitinib alone or with axitinib/tiragolumab (another novel ICI, as explained later) as frontline options in 210 patients with mRCC, compared to the control arm of pembrolizumab/axitinib.

TIM-3

T-cell immunoglobulin mucin-3 (TIM-3) is expressed on many immune cells and plays an important role in the inhibition of T cell responses. High levels of TIM-3 expression are correlated with T-cell exhaustion.⁵¹ There was a phase 1/2 trial (NCT02608268) evaluating sabatolimab (MBG453), an anti-TIM-3 monoclonal antibody, with and without spartalizumab in metastatic solid tumors including RCC that progressed or were intolerant to standard therapies. The phase 1/1b portion included 219 patients (6 RCC) and results showed that sabatolimab alone did not result in tumor response, and the combination of sabatolimab/spartalizumab resulted in some patients with partial responses.⁵² The trial was terminated due to business reasons.

BGB-A425 is another anti-TIM-3 monoclonal antibody. Tislelizumab is a novel anti-PD-1 antibody designed to minimize binding to macrophages in order to minimize potential resistance to anti-PD-1 therapy.⁵³ LBL-007 is an anti-LAG-3 monoclonal antibody. These three drugs, in various combinations, are being evaluated in a phase 1/2 trial (NCT03744468) for patients with advanced solid tumors. In the phase 2 dose expansion arm, this triplet combination is being evaluated in a cohort of multiple cancers including RCC.

TIGIT

T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is another novel immune checkpoint protein expressed on both T cells and natural killer (NK) cells. It plays an important role by directly inhibiting T- and NK-cell effector function and elimination of tumor cells by binding to CD155 on tumor cells.⁵⁴ Tiragolumab is an anti-TIGIT antibody, and it received breakthrough designation in February 2021 for its improved PFS and ORR for previously untreated metastatic NSCLC in combination with atezolizumab compared to placebo/atezolizumab in the CITYSCAPE phase 2 trial (NCT03563716).⁵⁵ A phase 2 trial (NCT03977467) is evaluating tiragolumab/atezolizumab in 80 patients with advanced malignancies (including approximately 15 patients with RCC) with progression after frontline PD-1 inhibition.

ILT2–4

Immunoglobulin-like transcripts 2, 3, and 4 (ILT2, ILT3, and ILT4) are expressed on immune cells, and when they bind to their ligands, they contribute to immune evasion by tumor cells.⁵⁶ Both ILT2 and ILT4 bind to human leukocyte antigen-G on tumor cells, assisting with tumor escape.⁵⁷ NGM707 is a humanized monoclonal antibody against both ILT2 and ILT4.⁵⁸ NGM707 is being evaluated with and without pembrolizumab in a phase 1/2 trial (NCT04913337) involving 179 patients with metastatic solid tumors including RCC that progressed or were intolerant to all prior available therapies. ILT3 is expressed on select myeloid antigen-presenting cells,⁵⁹ including myeloid-derived suppressor cells (MDSCs) which accumulate in the tumor microenvironment, inhibiting the antitumor immune response and encouraging tumor growth.⁶⁰ The interaction of ILT3 with fibronectin was found to promote an immunosuppressive state.⁶¹ NGM831, an ILT3 antibody, is being evaluated as monotherapy and in combination with pembrolizumab in a phase 1/2 trial (NCT05215574) involving 179 patients with metastatic solid tumors including RCC.

TREM2

Triggering receptor expressed on myeloid cells-2 (TREM2) is expressed on some myeloid cells including macrophages and dendritic cells (DCs), and high expression of TREM2-positive cells leads to decreased antitumor immunity including the inhibition of T-cell proliferation.⁶² TREM2 is expressed on tumor-associated macrophages, which are linked to tumor growth, immune evasion, and overall poor prognosis for cancer patients.⁶³ TREM2 has also been associated as an oncogenic factor in the development of RCC, as TREM2 expression was abnormally high in RCC tumor tissues in vivo, and silencing TREM2 inhibited tumor cell growth.⁶⁴ PY314 is a TREM2 monoclonal antibody, and it is being assessed either alone or in combination with pembrolizumab in a phase 1 trial (NCT04691375) in 288 patients with refractory/relapsed metastatic solid tumors including RCC to standard therapies.⁶⁵

VISTA

V-domain Ig suppressor of T-cell activation (VISTA) is expressed on both myeloid cells and T cells, and it generally acts as an inhibitory immune checkpoint for many cancers and downregulates T-cell activity.⁶⁶ VISTA has been found to be highly expressed in clear cell RCC tumors,⁶⁷ and high expression of VISTA on tumor-associated immune cells has been associated with a worse prognosis for patients with clear cell RCC with venous tumor thrombus.⁶⁸ Therefore, this makes VISTA an attractive target for patients with RCC.

CA-170 is an oral PD-L1, PD-L2, and VISTA antagonist that rescued the proliferation and effector function of T cells resulting in significant antitumor activity in preclinical models.⁶⁹ In a phase 1 trial of CA-170 for patients with advanced solid tumors including three patients with mRCC that were naïve to ICI therapy, the drug was well tolerated with evidence of antitumor activity.⁷⁰

SNS-101 is a conditionally active antibody that selectively targets the active form of VISTA with potent tumor inhibition but also minimizes the risk of cytokine release syndrome. A phase 1/2 trial (NCT05864144) is evaluating the safety and efficacy of SNS-101 as monotherapy or in combination with cemiplimab in advanced solid tumors refractory or intolerant to standard of care therapies.

BTLA

B- and T-lymphocyte attenuator (BTLA), a member of the CD28 superfamily and is structurally similar to PD-1 and CTLA-4, is an inhibitory immune checkpoint that is expressed on many immune cells including lymphocytes, macrophages, and DCs.⁷¹ Icatolimab (JS004) is an anti-BTLA monoclonal antibody being evaluated for safety and tolerability as monotherapy in a phase 1 trial (NCT04773951) for patients with advanced solid tumors, including RCC, refractory to standard of care therapies. HFB200603 is another anti-BTLA antibody being evaluated as monotherapy and in combination with tislelizumab in a phase 1 trial (NCT05789069) for patients with advanced solid tumors including RCC refractory to at least two lines of therapy.

OX40 and 4–1BB

OX40 (CD134, also known as tumor necrosis factor receptor superfamily [TNFRSF], member 4) is a co-stimulatory molecule expressed on activated T cells, and it induces expression of anti-apoptotic proteins and cell-cycle progression, upregulating the immune system against tumor cells.⁷² Similarly, 4–1BB (CD37, also known as TNFRSF, member 9) is expressed on the surface of T cells after activation and promotes anti-tumor activity.⁷³ Hence, antibodies that stimulate OX40 and 4–1BB signaling may enhance the immune response against tumors.

INCAGN01949, an anti-OX40 agonist, was evaluated in a phase 1/2 trial (NCT02923349) as monotherapy for patients with 87 metastatic solid tumors including RCC previously treated with available therapies. INCAGN01949 monotherapy had no major safety concerns; however, just one patient achieved a partial response, and 23 had stable disease.⁷⁴ INCAGN01949 did not enhance proliferation or activation of T cells and did not reduce circulation of regulatory T cells. A phase 1/2 trial (NCT02737475) of BMS-986178 (anti-OX40 agonist) monotherapy (20 patients) or in combination with ipilimumab and/or nivolumab (165 patients) was reported, which included eight patients with mRCC (with one to at least three lines of standard therapy and no prior ICI exposure) who received BMS-986178/nivolumab/ipilimumab every 3 weeks for four cycles followed by maintenance BMS-986178/nivolumab.⁷⁵ One patient with RCC had a partial response, three had stable disease, and three had progressive disease. Five of the eight patients with RCC experienced treatment-related adverse events (none grade 3/4). Ivuxolimab (PF-04518600, another anti-OX40 agonist) was evaluated in combination with axitinib against axitinib alone in a phase 2 randomized double-blind trial (NCT03092856) for patients with mRCC with prior ICI exposure. Unfortunately, preliminary data presented at the 2022 ASCO Annual Meeting, which analyzed 29 patients receiving the axitinib/ivuxolimab combination and 30 patients receiving axitinib/placebo, revealed no difference in the median PFS (13.1 vs. 8.5 months, HR 0.85, p = 0.61), and the study was closed to further accrual.⁷⁶

More novel anti-OX40 agonistic antibodies with possibly better efficacy are being actively evaluated in phase 1 clinical trials. HFB301001 is a second-generation anti-OX40 agonist that binds to a unique epitope on OX40 that does not bind to the endogenous OX40 ligand (OX40L), allowing for a more agonistic effect compared to prior OX40 agonists which often do interact with OX40L.⁷⁷ HFB301001 is being evaluated as monotherapy in a phase 1 dose-escalation trial (NCT05229601) in 84 patients with metastatic solid tumors, including patients with RCC, who have received at least two lines of therapy. Similarly, BGB-A445 is an anti-OX40 agonist that also does not interact with the OX40–OX40L axis directly.⁷⁸ BGB-A445 is being evaluated as monotherapy or in combination with tislelizumab (anti-PD-1 antibody) in a phase 1/2 trial (NCT05661955) that has two cohorts (monotherapy and combination) enrolling patients with previously treated RCC (1–3 prior lines). INBRX-106, a hexavalent OX40 agonist which has superior activity compared to bivalent agonists,⁷⁹ is being evaluated as either monotherapy or in combination with pembrolizumab in a phase 1/2 trial (NCT04198766) enrolling 333 patients with metastatic tumors who have progressed on all standard therapies including ICIs. SL-279252 (PD1-Fc-OX40L), a PD-1 and OX40L bifunctional fusion protein, is being evaluated in a phase 1 trial (NCT03894618) for 87 patients with advanced solid tumors including RCC. Preliminary results showed SL-279252 was well tolerated with some observed durable anti-tumor activity.⁸⁰

Utomilumab (PF-05082566) is a 4–1BB agonist that was evaluated in a dose-escalation phase 1b trial (NCT02179918) in combination with pembrolizumab in 23 patients with metastatic solid tumors who progressed on standard therapies, including five patients with RCC.⁸¹ Overall, the combination was safe and tolerable. For the patients who responded to the combination, there was a trend toward high levels of activated memory and effector cytotoxic T cells. Ivuxolimab as monotherapy and in combination with utomilumab was evaluated in a phase 1 trial (NCT02315066) involving 174 patients with metastatic solid tumors including RCC who progressed or were intolerant to standard therapies including traditional ICIs. An analysis of the ivuxolimab monotherapy cohort (52 patients, including 9 with RCC) showed ivuxolimab to be well tolerated and have increased immune cell infiltrate on tumor biopsies.⁸² An analysis of the dose-escalation and dose-expansion cohorts of the combination (total of 87 patients) was reported, which did not include any patients with RCC.⁸³ The combination was found to be well tolerated with some antitumor activity, warranting further investigation of various combinations of these immune checkpoint approaches.

INBRX-105 is a bispecific antibody targeting PD-L1 and 4–1BB. It is being evaluated in a phase 2 trial (NCT03809624) as monotherapy and in combination with pembrolizumab for different metastatic solid tumors including RCC. Patients with tumors that have progressed on traditional ICIs as well as tumors that are ICI-naïve are being enrolled.

CD27 and CD70

CD27 (also known as TNFRSF7), like OX40 and 4–1BB, is expressed on naïve lymphocytes and plays a role in B- and T-cell costimulation when activated.⁸⁴ The natural ligand of CD27 is CD70, which is highly expressed on some activated immune cells. Normally, CD27/70 binding activates the immune system. However, CD70 is also frequently expressed in malignancies including RCC.⁸⁵ Paradoxically, the CD27/CD70 interaction allows for tumor cells to evade the immune system, leading to tumor cell proliferation.⁸⁵ CD27/CD70 may also play a role in the apoptosis of lymphocytes in patients with RCC.⁸⁶ Hence, both the tumor-promoting and tumor-evading effects of CD27/CD70 make these targets of significant clinical interest.

Varlilumab is a CD27 agonist, and it was evaluated in combination with nivolumab in 175 patients with refractory metastatic solid tumors who have received up to five lines of treatment without prior anti-PD-1/PD-L1 agent in a phase 1/2 study (NCT02386111).⁸⁷ A phase 2 cohort evaluating ORR included 14 patients with RCC. Nine patients developed TEAEs. Of 12 patients who were evaluable for objective response, none had a complete or partial response, while five had stable disease. Overall, the combination of varlilumab and nivolumab was well tolerated, but the treatment efficacy of the combination was not much better than expected compared to nivolumab alone. There are currently no active trials with other CD27 agonists in patients with RCC.

Because of the high expression of CD70 on the surface of RCC tumor cells, there are various RCC trials targeting CD70 as an RCC tumor marker for tumor cell destruction. These trials mostly involve antibody-drug conjugates (beyond the scope of this review) and CAR T cells. The CAR T cells targeting CD70 will be discussed in a later section.

A2AR and CD73

When adenosine binds to adenosine-A2A receptor (A2AR), it triggers a complex signaling cascade that protects the normal cells from autoimmunity, and tumor cells can use this pathway to inhibit the immune response and to promote tumor immune escape.⁸⁸ CD73 is a checkpoint protein found on the surface of cells including endothelium, lymphocytes, and some tumors. CD73 has many roles, including the synthesis of adenosine, angiogenesis in the tumor microenvironment, and cancer cell proliferation.⁸⁹

In a phase 1/1b trial (NCT02655822) of 502 refractory solid tumor patients including 68 patients with refractory RCC (including with anti-PD-1/PD-L1 ICIs), ciforadenant (CPI-444, an A2AR small molecule antagonist) was evaluated as monotherapy or in combination with atezolizumab.⁹⁰ One in 33 receiving monotherapy and 4 of 35 patients receiving combination achieved a partial response, and the median PFS was 4.1 months and 5.8 months, respectively. The trial noted an association with cytotoxic T-cell infiltration into the tumor with prolonged disease control. Patients after treatment also had an increase in T-cell receptor diversity. Importantly, patients who responded to treatment had an adenosine-regulated gene expression signature in pre-treatment tumor biopsies, suggesting a possible predictive biomarker for A2AR inhibition.

Taminadenant (PBF509/NIR178) is an oral selective A2AR antagonist. It is being combined with spartalizumab and DFF332 (a hypoxia-inducible factor 2 alpha inhibitor) in a phase 1 trial (NCT04895748) for patients with RCC and other solid tumors refractory to all approved standard therapies. Similarly, TT-10 is another oral A2AR antagonist being evaluated in a phase 1/2 trial (NCT04969315) as monotherapy for patients with metastatic solid tumors including RCC refractory to standard of care therapies.

Mupadolimab (CPI-006) is an anti-CD73 antagonist that has been shown to activate B cells and stimulate antibody production.⁹¹ Mupadolimab is being evaluated as monotherapy or with ciforadenant alone, pembrolizumab alone, and the combination of ciforadenant and pembrolizumab in 378 patients with incurable solid tumors including RCC in a phase 1/1b trial (NCT03454451). Preliminary data presented at the 2019 ASCO Annual Meeting for 17 patients showed mupadolimab monotherapy induces rapid lymphocyte redistribution and early evidence of antitumor activity.⁹²

Summary of novel immune checkpoint targets

Novel immune checkpoints including both activators (particularly the tumor necrosis factor receptor superfamily) and inhibitors of the immune system are of major interest. Many of the trials have evaluated these drugs in combination with traditional ICIs. Some of these trials have been completed, which have not overwhelmingly shown to be of major benefit for patients over current ICIs. None of the agents have reached phase 3 clinical trials yet for mRCC. However, the clinical trials of these novel immune checkpoints show enough promising results for further studies to continue. In addition, novel immune checkpoints are also of interest in the localized setting. For example, the NESCIO phase 2 trial (NCT05148546) is evaluating relatlimab/nivolumab in one experimental arm (other arms include ipilimumab/nivolumab and nivolumab alone) as neoadjuvant therapy in high-risk localized RCC.

With these novel immune checkpoints, there is an urgent need to determine predictive biomarkers. Currently, high tumor mutational burden (TMB), microsatellite instability, deficient mismatch repair systems, and PD-L1 expression all have their limits in accurately predicting tumor response to traditional ICIs.⁹³ Furthermore, mRCC frequently has low TMB and low microsatellite instability.⁹⁴ Genes on chromosome 3p that are frequently mutated in clear cell RCC, including BAP1, PBRM1, and SETD2, have been studied as potential predictive biomarkers. BRCA-1-associated protein-1 (BAP1) is a tumor suppressor, and its loss is associated with PD-L1 expression, inflammation, and abundant infiltration of immune cells.^95,96 Mutations in PBRM1, which encodes a protein important in chromatin remodeling, have been shown to be associated with positive outcomes in pan-cancer patients receiving ICIs,⁹⁷ although there is also conflicting data suggesting PBRM1 mutations may lead to ICI resistance.⁹⁸ SETD2 encodes a histone methyltransferase critical to maintaining genomic integrity and stability, and mutations in SETD2 have been linked to higher TMB and microsatellite instability and therefore more favorable clinical outcomes to ICIs.⁹⁹ The association of these gene mutations with ICI response needs to be further validated. Because definitive predictive biomarkers for ICIs remain elusive, evaluating the genomic profile of tumors that have a good response to novel immune checkpoint agents is necessary.

Vaccines

Tumor vaccines that aim to enhance intrinsic immune responses against tumor cells have been studied for at least the past 20 y in patients with RCC. Although they were determined to be safe and tolerable, most were not very effective, so none led to regulatory approval.¹⁰⁰ However, cancer vaccine technology has continued to improve and remains of significant interest for RCC because of the inherent immunogenicity of RCC tumors. Currently, more vaccine trials for mRCC are underway, which include peptides and personalized neoantigens, DCs, and viruses. Table 3 summarizes the clinical trials involving RCC vaccines.

Table 3. Current active and recruiting clinical trials evaluating vaccines in metastatic RCC.

Trial number	Type of vaccine	Agent(s)	Setting	Primary outcome measures
NCT05329532	Peptide	Modi-1 alone and with pembrolizumab or nivolumab	Prior treatment with anti-angiogenic therapy	AEs, cellular immune response
NCT02950766	Personalized neoantigen	Neovax and ipilimumab	No prior immunotherapy	DLT
NCT05641545	Personalized neoantigen	IVAC-RCC-001 with ipilimumab and nivolumab	No prior systemic therapy	Toxicities and T-cell response
NCT05269381	Personalized neoantigen	Personalized neoantigen vaccine with pembrolizumab	Prior systemic therapy allowed	AEs
NCT03289962	Personalized neoantigen	Autogene cevumeran alone and with atezolizumab	No prior immunotherapy for patients with RCC	DLT, AEs, recommended phase 2 dose
NCT04203901	DC	CMN-001 with ipilimumab and nivolumab vs. ipilimumab and nivolumab	Frontline	OS
NCT00458536	DC-tumor fusion	DC-tumor fusion vaccine alone and with GM-CSF	No prior systemic therapy	AEs
NCT03294083	Virus	Pexastimogene devacirepvec with cemiplimab	Both frontline and prior systemic therapy allowed	MTD, AEs, ORR
NCT02432963	Virus	p53MVA with pembrolizumab	Prior systemic therapy allowed	Tolerability

AEs = adverse events, DLT = dose-limiting toxicities, DC = dendritic cell, OS = overall survival, GM-CSF = granulocyte macrophage colony-stimulating factor, MTD = maximum tolerated dose, ORR = objective response rate.

Peptides and neoantigens

Peptide vaccines are generally designed to be 20–30 amino acids long containing specific immunogenic epitopes. Peptide vaccines are overall safer and cheaper than the other types of cancer vaccines. To improve efficacy, peptide vaccines can include epitopes that stimulate cytotoxic T cells and other epitopes that stimulate helper T cells to promote both a humoral and cell-mediated immune response.¹⁰¹ The vaccines have also been given in combination with traditional ICIs to prevent T-cell exhaustion. As the technology of next-generation sequencing has improved, there are opportunities to identify tumor-specific mutations in different patients and to develop personalized neoantigen-based therapeutic vaccines. Advantages of this vaccine over a traditional peptide vaccine include a more tumor-specific T-cell response sparing normal cells and a decrease in a T-cell central tolerance, while disadvantages include higher financial costs and production delays.¹⁰²

IMA901 is a peptide-based vaccine consisting of 10 different tumor-associated peptides (nine binding to HLA class I and one binding to HLA class II) that were strongly overexpressed in RCC compared to normal cells. In the phase 3 trial IMPRINT (NCT01265901), the combination of IMA901 with sunitinib was compared to sunitinib alone in 339 treatment-naïve mRCC, and patients were randomly assigned in a 2:1 ratio to combination versus monotherapy.¹⁰³ The study did not meet its primary endpoint, as the median OS for the combination therapy did not differ significantly between the two groups (HR 1.34; 95% CI, 0.96–1.86; p = 0.087). More grade 3 or higher TEAEs were present in the combination group (57% vs. 47%).

Modi-1 is a peptide combination vaccine based on citrullinated vimentin and enolase peptides that stimulates tumor-infiltrating helper T cells.¹⁰⁴ The Modi-1 peptides are linked to a toll-like receptor ligand 1/2 adjuvant to enhance the immune response by several fold. ModiFY (NCT05329532) is a phase 1/2 trial evaluating Modi-1 alone or in combination with pembrolizumab or nivolumab in 144 patients with advanced solid tumors including RCC. RCC inclusion criteria in the study includes prior anti-angiogenic therapy and favorable/intermediate risk disease. Primary endpoints include adverse events and cellular immune response measured on the IFN-gamma ELISpot assay.

There are two phase 1 trials evaluating personalized RCC protein neoantigen cancer vaccines (NeoVax and IVAC-RCC-001), recruiting patients with advanced mRCC who have undergone resection of their tumors. NeoVax is being used in combination with ipilimumab in 19 patients (NCT02950766). Patients may not have received prior immunotherapy; prior systemic therapy excluding immunotherapy is allowed if given prior to six months before the first injection NeoVax. The primary endpoint is dose-limiting toxicity. Similarly, IVAC-RCC-001 will be used in combination with ipilimumab/nivolumab in 10 patients (NCT05641545). Patients may not have received prior systemic therapy. The primary endpoint is treatment success, defined as a vaccine-specific T-cell responses without unacceptable toxicities. PNeoVCA (NCT05269381) is another phase 1 trial using a personalized neoantigen peptide-based vaccine in combination with pembrolizumab for patients with advanced solid tumors.

Autogene cevumeran (RO7198457), a personalized mRNA-based neoantigen vaccine delivered via lipoplex nanoparticles intravenously, is being evaluated in several metastatic solid tumors in a phase 1 trial (NCT03289962) either as monotherapy or in combination with atezolizumab.¹⁰⁵ Preliminary results reported an ICI-naïve cohort of nine patients with mRCC with one prior line of therapy receiving the combination of autogene cevumeran with atezolizumab had an ORR of 22% (2 patients) in the dose-expansion phase.

Dendritic cell vaccines

DCs are the professional antigen-presenting cells of the immune system. DCs express high amounts of the costimulatory molecules CD40, CD80, and CD86 as well as high levels of MHCII, and it is becoming increasingly recognized that DCs are essential for anti-tumor immunity by initiating T-cell priming and through production of key cytokines such as interferon-gamma and IL-12.¹⁰⁶ Autologous DC vaccines expose tumor antigens to DCs in hopes of stimulating a tumor-specific immune response.

Rocapuldencel-T is a mature monocyte-derived DC that is coelectroporated with amplified autologous RCC tumor RNA (isolated from nephrectomy) and CD40L RNA. In the pre-ICI era, it was tested in combination with standard-of-care sunitinib in the phase 3 trial ADAPT (NCT01582672), which enrolled 462 patients with mRCC to receive either rocapuldencel-T with sunitinib or sunitinib alone.¹⁰⁷ The combination was unsuccessful, as the median OS was 27.7 months compared to 32.4 months with sunitinib alone (HR 1.10, 95% CI, 0.83–1.40), and the trial was terminated early. The study did show that patients with high numbers of regulatory T cells and IL-12 levels could be survival-predictive biomarkers for patients receiving rocapuldencel-T.

Now in the ICI era, a phase 2 trial (NCT01876212) for patients with ICI-refractory metastatic melanoma determined that a DC vaccine targeting tumor blood vessel antigens in combination with dasatinib could improve clinical outcomes.¹⁰⁸ A phase 2 trial (NCT04203901) is evaluating CMN-001 (an autologous, tumor antigen-loaded DC vaccine) in combination with ipilimumab/nivolumab against the control arm of ipilimumab/nivolumab in intermediate/poor risk patients with mRCC. Patients who progress in either cohort will be switched to lenvatinib/everolimus. Notably, the primary outcome measure of this trial is OS.

DCs and tumor cells can be fused together to become a heterokaryon that expresses both MHC Class I and II molecules, co-stimulatory molecules, and tumor-associated antigens. DC-cell tumor fusions can become a potent activator of the immune system and can induce strong anti-tumor immune responses over tumor cells alone as tumor cells themselves lack immune costimulatory molecules.¹⁰⁹ There is an active phase 1/2 trial (NCT00458536) for 38 patients with mRCC who have undergone a debulking nephrectomy and no prior systemic therapy, testing the safety of a DC-tumor fusion vaccine with granulocyte macrophage colony stimulating factor (GM-CSF). Patients receive three subcutaneous vaccinations of fused cells every 3 weeks. Six patients received only the vaccine, and the other patients received the study vaccine with GM-CSF.

Notably, there is a phase 2 trial (NCT05127824) for patients with localized RCC, in which 21 patients will be enrolled to receive neoadjuvant autologous tumor blood vessel antigen DC vaccine injections intradermally with cabozantinib prior to surgical resection, and they will be compared with 21 controls without RCC that will receive no intervention. The primary outcome measure is the probability of a CD8 T-cell immune response for the combination treatment.

Oncolytic viruses

Oncolytic viruses are designed to cause selective replication and lysis of cancer cells while sparing normal cells, and the release of immunogenic tumor proteins ideally provides tumor-associated antigens for APCs to stimulate the immune system to further destroy cancer cells.¹¹⁰ Talimogene laherparepvec (T-VEC), the only regulatory-approved oncolytic immunotherapy which selectively replicates within tumors and secretes GM-CSF, is used to treat advanced melanoma, based on the findings from the successful phase 3 trial OPTiM (NCT00769704).¹¹¹ A phase 1/2 trial (NCT03294083) has enrolled 89 patients with mRCC (both frontline and refractory to anti-PD-1/PD-L1 therapy settings allowed) to evaluate safety and efficacy of Pexastimogene devacirepvec (Pexa-Vec, a modified version of the vaccinia virus with the GM-CSF gene and deletion of thymidine kinase gene) in combination with cemiplimab. Both intravenous infusion as well as direct intratumoral injection of Pexa-Vec are used.¹¹²

The p53–expressing modified vaccinia Ankara (p53MVA) virus delivers the full-length p53 to antigen-presenting cells which can reactivate or generate de novo effector and memory T cell responses against numerous antigenic p53 epitopes, as many cancer cells express p53 variants on the cell surface while normal cells do not.¹¹³ Aphase 1 trial (NCT02432963) is evaluating p53MVA in combination with pembrolizumab for patients with advanced solid tumors including RCC. Preliminary results of this trial of 11 patients (RCC not included) suggested this combination is feasible and safe.¹¹³

CAR T-cell therapy

CAR T-cell therapy has received regulatory approval in various hematologic malignancies (in the autologous setting), and its use has begun to expand to metastatic solid tumors. There remain several challenges and setbacks to CAR T-cell therapy, not limited to on-target/off-tumor effects, immune effector cell-associated neurotoxicity, cytokine release syndrome, financial costs, and complex manufacturing requirements.¹¹⁴ However, the main setback for CAR T cells in solid tumors is the lack of a ubiquitously expressed tumor antigen that the CAR T cells can target. CAR T-cell therapies for RCC have failed in the past, using the targets carbonic anhydrase IX (CAIX) due to liver toxicity (as CAIX is expressed on the bile duct epithelium creating on-target/off tumor effects),¹¹⁵ and vascular endothelial growth factor receptor 2 (VEGFR2) due to no objective responses resulting in termination (NCT01218867). Despite these setbacks, there are several ongoing trials of CAR T cells designed to treat mRCC refractory to approved therapies. Some of the CAR T cells being used in RCC trials involve allogeneic CAR T cells, which decreases the manufacturing time for patients compared to autologous CAR T cells. RCC targets in current clinical trials include CAIX, CD70, ROR2, and AXL. A summary of these clinical trials is provided in Table 4.

Table 4. Current active and recruiting clinical trials CAR T-cell therapy in metastatic RCC.

Trial number	Target	Agent(s)	Setting	Primary outcome measures
NCT04969354	CAIX	CAIX-targeted CAR T cell	Up to 2 prior lines of treatment including anti-PD-1/PD-L1 agents	AEs, ORR
NCT04438083	CD70	CTX130	Refractory to all SoC therapies	AEs, ORR
NCT04696731	CD70	ALLO-316	Refractory to prior ICI and VEGF-TKI	DLT
NCT05420519	CD70	CD70–targeted CAR T cell	Refractory to all SoC therapies	AEs, MTD
NCT05518253	CD70	CD70–targeted CAR T cell	Refractory to all SoC therapies	AEs, MTD
NCT05468190	CD70	CD70–targeted CAR T cell	Refractory to all SoC therapies	AEs, MTD
NCT05420545	CD70	CD70–targeted CAR T cell	Refractory to all SoC therapies	AEs, MTD
NCT02830724	CD70	CD70–targeted CAR T cell	Refractory to at least one line of therapy	AEs, ORR
NCT05795595	CD70	CTX131	Refractory to SoC therapies	AEs, ORR
NCT03393936	ROR2 and AXL	CCT301–59 for ROR2, and CCT301–38 for AXL	Refractory to SoC therapies	DLT, ORR

CAIX = carbonic anhydrase IX, AEs = adverse events, ORR = objective response rate, SoC = standard of care, ICI = immune checkpoint inhibitor, VEGF-TKI = vascular endothelial growth factor tyrosine kinase inhibitor, DLT = dose-limiting toxicities, MTD = maximum tolerated dose.

CAIX

Carbonic anhydrase IX (CAIX) is a transmembrane protein that normally is upregulated in hypoxic stress in normal kidney cells. CAIX can become highly expressed on the surface of clear cell RCC tumor cells even in normal oxygen conditions, and its downstream effects ultimately lead to tumor progression.¹¹⁶ CAIX is being actively studied as a target not just for CAR T-cell therapy but also in the field of theranostics. Girentuximab is a monoclonal antibody targeting CAIX. ⁸⁹Zr-DFO-girentuximab (TLX250–CDx) PET/CT imaging is being evaluated in the phase 3 trial ZIRCON (NCT03849118), and data reported at the 2023 ASCO Genitourinary Cancers Symposium suggests it can accurately detect RCC for patients with indeterminate renal lesions.¹¹⁷ The currently recruiting phase 2 trial STARLITE 2 (NCT05239533) is evaluating the combination of the radiopharmaceutical ¹⁷⁷Lu-girentuximab and nivolumab in patients with mRCC who have failed prior treatment with an anti-PD-1/PD-L1 ICI.¹¹⁸

As mentioned above, a prior experience with CAIX-directed CAR T cells for 12 patients with CAIX-expressing mRCC was disappointing because of liver toxicity.¹¹⁹ A phase 1 trial (NCT04969354) is enrolling 20 patients with mRCC refractory to prior therapies (including up to two regimens of systemic treatments including anti-PD-1/PD-L1 ICIs) to receive CAIX-targeted CAR T cells, with primary outcome measures of adverse events and ORR. Prior to CAR T-cell infusion, patients receive a CAIX monoclonal antibody injected into the hepatic artery to minimize liver toxicity.

CD70

As mentioned in a prior section, CD70 interacts with CD27 to activate B and T cells in normal circumstances. However, for cancer cells, CD70 can be aberrantly expressed, which paradoxically facilitates immune evasion and tumor growth. CD70 is known to be highly expressed in some malignancies including RCC while having limited expression in normal tissue,¹²⁰ making it a promising target for CAR T-cell therapy. There are three trials dedicated to evaluating CD70–targeting CAR T cells for patients with RCC, and more that are evaluating CD70–targeting CAR T cells in solid tumors expressing CD70.

CTX130 is an allogeneic CAR T cell that was evaluated in the phase 1 trial COBALT-RCC (NCT04438083), which is enrolling 107 patients with mRCC who have failed all standard of care treatments. Patients receive the CTX130 infusion after lymphodepleting chemotherapy. Preliminary data presented at the 2022 SITC Annual Meeting showed that for 13 evaluable patients, the disease control rate (DCR) was 77%.¹²¹ The ORR was 8% (one patient), but this patient developed a complete response by 3 months that was maintained at 18 months. Overall, the results were encouraging with a good safety profile and encouraging antitumor activity.

Similarly, ALLO-316 is an allogeneic CAR T cell that was evaluated in the phase 1 trial TRAVERSE (NCT04696731), which is enrolling 120 patients with mRCC who have progressed on prior ICI and tyrosine kinase inhibitor. Patients received a lymphodepleting deconditioning regimen prior to infusion with ALLO-316. Preliminary results presented at the 2023 AACR Annual Meeting revealed that for 18 evaluable patients, the ORR was 17%, DCR was 89%, while for 10 patients with CD70+ RCC, three patients achieved a partial response and the DCR was 100%.¹²² Importantly, the safety profile was consistent with autologous CAR T-cell therapy. ALLO-316 also eliminated CD70+ host T cells, which prevented allorejection and preserved treatment efficacy.

Another phase 1 trial (NCT05420519) is enrolling 24 patients with mRCC who have failed all standard of care treatments to receive CD70–targeted CAR T cells, with primary endpoints of a maximum tolerated dose and to determine the incidence of adverse events. There are other phase 1 trials underway enrolling patients with CD70+ metastatic solid tumors including RCC (e.g., NCT05518253, NCT05468190, NCT05420545). The primary outcome measures of all these studies are adverse events and maximum tolerated dose. Two phase 1/2 trials (NCT02830724 and NCT05795595) are enrolling patients with relapsed and refractory CD70+ metastatic solid tumors to receive allogeneic CAR T cells, with primary outcome measures to include adverse events and ORR.

ROR2 and AXL

Receptor tyrosine kinase-like orphan receptor 2 (ROR2) is a tumor-associated kinase that has been associated with RCC tumor growth and migration, with high expression associated with poor outcomes.^123,124 AXL is a receptor tyrosine kinase overexpressed in many cancers, and its expression on RCC is much higher than for normal kidney tissue,¹²⁵ and high expression of AXL in patients with RCC treated with sunitinib led to worse outcomes.¹²⁶ A phase 1/2 trial (NCT03393936) is evaluating autologous CAR T cells after lymphodepletion in 66 patients with mRCC refractory to standard therapies. Patients with RCC expressing ROR2 will receive CCT301–59 T cells, and patients with RCC expressing AXL will receive CCT301–38 T cells. The primary outcome measures are dose-limiting toxicity and ORR.

Conclusions

RCC continues to be a difficult malignancy to treat despite all the success of traditional immune checkpoint inhibitor therapies targeting CTLA-4, PD-1 and PD-L1. Many promising clinical trials are underway for RCC, evaluating novel immune approaches for both frontline and refractory/relapsed patients as either monotherapy or in combination with already approved agents. Given the adverse effects of the currently approved ICIs for solid tumors, the safety of these immunotherapies will be heavily scrutinized. Fortunately, many agents being evaluated that have demonstrated efficacy also appear to be safely tolerated. With more experience, the design of these novel therapies will further improve the clinical outcomes of patients with advanced RCC and will hopefully become more widely available to patients in the near future.

Disclosure statement

Jonathan E. Shoag received personal fees from Fortec Medical and grants from BMS Foundation. Jorge A. Garcia received personal fees from Pfizer, Aptitude Health, and the US Food and Drug Administration. Tian Zhang received research funding from Acerta, Novartis, Merrimack, AbbVie/StemCentrx, Merck, Regeneron, Mirati Therapeutics, Janssen, AstraZeneca, Pfizer, OmniSeq, Personal Genome Diagnostics, Astellas, and Eli Lilly, served as advisory board member and consultant for Merck, Exelixis, Sanofi-Aventis, Janssen, AstraZeneca, Pfizer, Amgen, BMS, Pharmacyclics, SeaGen, Calithera, QED Therapeutics, Eisai, Aveo, Eli Lilly, Bayer, and Aravive, and received honoraria from MJH Associates, Vaniam, Aptitude Health, and PeerView. Pedro C. Barata received personal fees from BMS, Merck, and EMD Serono, grants from Roche, personal fees from Eisai, Exelixis, Pfizer, Caris Life Sciences, Myovant, and UroToday, and nonfinancial support from Guardant360. All the other authors declare no conflict of interest.

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Funding

The author(s) reported that there is no funding associated with the work featured in this article.