Trial Watch

Abstract

Adoptive cell transfer (ACT) represents a prominent form of immunotherapy against malignant diseases. ACT is conceptually distinct from dendritic cell-based approaches (which de facto constitute cellular vaccines) and allogeneic transplantation (which can be employed for the therapy of hematopoietic tumors) as it involves the isolation of autologous lymphocytes exhibiting antitumor activity, their expansion/activation ex vivo and their reintroduction into the patient. Re-infusion is most often performed in the context of lymphodepleting regimens (to minimize immunosuppression by host cells) and combined with immunostimulatory interventions, such as the administration of Toll-like receptor agonists. Autologous cells that are suitable for ACT protocols can be isolated from tumor-infiltrating lymphocytes or generated by engineering their circulating counterparts for the expression of transgenic tumor-specific T-cell receptors. Importantly, lymphocytes can be genetically modified prior to re-infusion for increasing their persistence in vivo, boosting antitumor responses and minimizing side effects. Moreover, recent data indicate that exhausted antitumor T lymphocytes may be rejuvenated in vitro by exposing them to specific cytokine cocktails, a strategy that might considerably improve the clinical success of ACT. Following up the Trial Watch that we published on this topic in the third issue of OncoImmunology (May 2012), here we summarize the latest developments in ACT-related research, covering both high-impact studies that have been published during the last 13 months and clinical trials that have been initiated in the same period to assess the antineoplastic profile of this form of cellular immunotherapy.

Keywords: :

• chimeric antigen receptor
• cyclophosphamide
• FOXP3⁺ regulatory T cells
• lymphodepletion
• T-cell receptor
• tumor-infiltrating lymphocytes

Introduction

During the past three decades, it has become clear that the immune system does not constitute a mere bystander of oncogenesis, tumor progression and response to treatment, a conceptual shift that has driven the development and clinical evaluation of several forms of anticancer immunotherapy.^1-5 These include relatively unspecific approaches, such as the administration of immunostimulatory cytokines like interleukin-2 (IL-2) or immunological checkpoint blockers like anti-CTLA4 antibodies (i.e., ipilimumab),^6-11 as well as precisely targeted interventions, encompassing anticancer vaccines^12-14 and adoptive cell transfer (ACT).^1-3,15

ACT involves the re-infusion into a lymphodepleted patient of large numbers (often up to 10¹¹) of lymphocytes with antitumor activity,^1-5 hence constituting one—but not the only—form of cell-based anticancer therapy. ACT should indeed be conceptually discriminated from dendritic cell (DC)-based approaches, which de facto constitute anticancer vaccines (and are never performed in the context of lymphodepletion),^12,16-18 as well as from allogeneic hematopoietic stem cell transplantation (HSCT), a therapeutic option for patients affected by hematological malignancies that relies on the elimination of most tumor cells by lymphoablating regimens followed by the re-establishment of an allogenic (and hence potentially tumor-reactive) immune system.^19,20

In a few settings, i.e., melanoma and renal cell carcinoma patients, the starting material for ACT is a surgical specimen or tumor biopsy, from which tumor-infiltrating lymphocytes (TILs) are isolated and sometimes selected for T-cell receptor (TCR) specificity.²¹ Prior to re-infusion, these lymphocytes are expanded ex vivo in the presence of appropriate growth factors (e.g., IL-2), and optionally activated with agonistic anti-CD3 antibodies, alone or combined with tumor-associated antigen (TAAs).²² In the majority of cases, however, this approach cannot be undertaken, as (1) surgical/biopsic material is not available or (2) tumor lesions contain reduced number of TILs. In these cases, ACT protocols can be implemented starting from circulating lymphocytes that are genetically engineered for the expression of tumor-reactive TCRs.¹ Importantly, genetic engineering can also be used to endow lymphocytes with several other features,²³ including (but not limited to) an increased proliferative potential,^24,25 a prolonged in vivo persistence,²⁶ the capacity to self-provide immunostimulatory cytokines and/or growth factors,²⁴ an improved capacity to migrate to tumor tissues^27,28 and robust cytotoxic functions.²⁹ Finally, so-called chimeric antigen receptors (CARs) can be employed as valid alternatives to TCRs. CARs recognize TAAs through antibody-derived complementarity-determining regions, yet rely on TCR-associated signal transducers, de facto triggering the activation of T cells even when TAA are not presented in complex with MHC molecules.^30,31 Obviously, the efficacy (and safety) of ACT is dramatically influenced (if not entirely dictated) by the specificity of re-infused cells. We have extensively discussed all these aspects one year ago, in the first Trial Watch of the series dealing with ACT,¹⁵ and more recently, in three distinct Trial Watches dealing with anticancer vaccines.^12-14

Initially, autologous TILs expanded and activated ex vivo were administered to virtually untreated patients, an approach that was episodically associated with measurable, though not durable, clinical responses.³² This was likely due to the facts that (1) upon re-infusion, TILs normally fail to persist for long periods in vivo;^33,34 (2) the antineoplastic activity of re-infused TILs is rapidly annihilated by local and systemic immunosuppressive networks, such as those established by myeloid-derived suppressor cells (MDSCs)^35-37 and FOXP3⁺ regulatory T cells (Tregs);^38-42 and (3) endogenous immune effector cells, including T, B and natural killer (NK) lymphocytes, might enter in competition with re-infused TILs for key cytokines such as IL-7 and IL-15, a phenomenon that is known as “cytokine sink.”^43,44 To circumvent these issues, various lymphodepleting regimens have been developed, mostly relying on combinations of high-dose cyclophosphamide (an alkylating agent currently approved for the treatment of several cancers), fludarabine (a nucleoside analog often employed against hematological neoplasms) and total body irradiation.⁴⁵ Since the intensity of lymphodepletion has been clearly correlated with the clinical efficacy of ACT, preconditioning lymphodepletion is now part of standard ACT protocols.⁴⁵

Along similar lines, it is relatively common to reintroduce TILs into lymphodepleted patients together with high doses of IL-2,^46,47 even though this approach is being increasingly questioned owing to its potential immunosuppressive side effects.^48-50 Several alternative agents have been investigated for their capacity to potentiate the clinical efficacy of ACT, including (1) immunostimulatory cytokines other than IL-2, such as IL-7, IL-12, IL-15 and interferon (IFN)γ;^51-54 (2) inhibitors of angiogenesis, which facilitate the homing to TILs to neoplastic lesions;^55,56 (3) Toll-like receptor (TLR) agonists, as they exert potent adjuvant effects and limit endogenous immunosuppression;^57-60 and (4) a wide panel of immunostimulatory chemotherapeutics, encompassing (but not limited to) metronomic cyclophosphamide, gemcitabine (a nucleoside analog that is used for the treatment of various carcinomas and some forms of lymphoma) and several anthracyclines.^61-63

Importantly, although the efficacy of ACT is generally attributed to CD8⁺ T cells, the administration of CD4⁺ T cells alone has also been shown to induce durable clinical responses in melanoma patients.⁶⁴ Moreover, at least theoretically, immune effector cell types other than T lymphocytes, including B and NK cells, can be used in ACT protocols. So far, the adoptive transfer of autologous B cells has only been investigated at the preclinical level.⁶⁵ This is presumably linked to the fact that B cells are known to mediate immunosuppressive effects and sustain tumor growth, at least in some models of carcinogenesis.^66,67 Conversely, NK cell-based ACT strategies have already been evaluated in clinical trials, with relatively deceiving results.^68,69 This is at odds with encouraging preclinical observations as well as with the established efficacy of allogeneic NK cells against acute myeloid leukemia (AML).^70-72 Promising results have been obtained with “young TILs,” i.e., minimally cultured, bulk TILs that can be generated in a relatively inexpensive and rapid manner that does not entail individualized tumor-reactivity screening steps.^73-75 By abating the costs that are associated with the generation of ACT-compatible TILs, this technology may significantly increase the number of centers that will offer ACT immunotherapy to eligible patients in the near future. As it stands, however, there are no ACT protocols approved by the US FDA or other international regulatory agencies for use in cancer patients (source www.fda.gov).

Along the lines of our monthly Trial Watch series,^{9-15,57,59,76-79} here we will summarize the latest advances in the use of ACT as an active immunotherapeutic strategy against cancer, focusing on high-impact studies that have been published and clinical trials that have been launched during the last 13 mo.

Literature Update

Since the submission of our previous Trial Watch on this topic (January 2012),¹⁵ the results of no more than 10 clinical trials investigating the therapeutic potential of ACT in cancer patients have been published (source www.ncbi.nlm.nih.gov/sites/entrez/). Six of these studies involved individuals bearing hematological (most often B-cell) malignancies,^80-85 especially in settings of post-HSCT relapse.^80,81,83,85 The remaining 4 trials investigated the clinical potential of ACT in patients with neuroblastoma, nasopharyngeal carcinoma, melanoma or recurrent ovarian carcinoma.^86-89 The clinical protocols employed in some of these studies were relatively conventional, such as (1) the infusion of autologous T cells expanded and activated ex vivo to pediatric neuroblastoma patients early after HSCT;⁸⁶ (2) the administration of autologous TILs in combination with low-dose IL-2 to lymphodepleted metastatic melanoma patients,⁸⁷ (3) the infusion of autologous T cells genetically modified for the expression of a HA-1-specific TCR to leukemia patients relapsing upon HSCT;⁸³ (4) the administration of originally allogeneic T lymphocytes isolated from B-cell malignancies that failed to respond to HSCT (upon expansion and activation ex vivo with anti-CD3/anti-CD28-coated beads);⁸⁰ (5) the infusion of autologous peripheral blood mononuclear cells (PBMCs) expanded ex vivo in the presence of Epstein-Barr virus (EBV)-infected cells to individuals affected by EBV-associated nasopharyngeal carcinoma;⁸⁹ and (6) the administration of cytokine-induced killer (CIK) cells, i.e., an heterogeneous population of T lymphocytes and CD3⁺CD56⁺, non-MHC-restricted cells exhibiting a mixed T-cell/NK-cell phenotype,⁹⁰ to patients with hematological malignancies relapsing upon HSCT.⁸⁵

Alongside, four studies evaluated the clinical profile of CAR-based ACT immunotherapy.^81,82,84,88 Thus, the groups of Steven Rosenberg (National Cancer Institute, Bethesda, MD) and George Coukos (University of Pennsylvania, Philadelphia, PA) independently investigated (in Phase I clinical trials) the safety and efficacy of autologous T cells genetically modified to express an anti-CD19 CAR in patients bearing advanced B-cell malignancies, either upon a course of conventional chemotherapy⁸² or during HSCT.⁸¹ Along similar lines, Oliver Press and collaborators (Fred Hutchinson Cancer Research Center, Seattle, WA) conducted a Phase I clinical trial to preliminarily assess the clinical potential of autologous T cells stably expressing a CD20-specific CAR in indolent B-cell or mantle cell lymphoma patients previously subjected to lymphodepletion with cyclophosphamide.⁸⁴ Finally, Coukos and colleagues tested the safety and activity of autologous T cells engineered to express a folate receptor α (FRα)-targeting CAR in (lymphodepleted) patients affected by recurrent ovarian cancer.⁸⁸ Taken together, the results of these studies corroborate the notion that the re-administration of autologous T cells genetically engineered for the expression of TAA-specific TCRs or CARs to cancer patients is generally safe¹⁵ and drives robust tumor-specific immune responses that—at least in a fraction of patients—translate into measurable clinical benefits.^1,5,91 Of note, Carl June and collaborators (University of Pennsylvania, Philadelphia, PA) have recently reported the results of a decade-long safety assessment of an ACT protocol involving the administration of T lymphocytes expressing a gp120-specific CAR to HIV-1 patients.⁹² This study demonstrates that the use of retroviral transduction to generate CAR-expressing T cells is associated with stable engraftment and durable safety, implying that previously reported side effects linked to insertional mutagenesis^93,94 are either stem cell- or transgene-intrinsic and hence do not constitute a relevant issue for ACT immunotherapy.⁹²

During the last 13 months, an intense wave of (preclinical) investigation has focused on the characterization of novel factors that may influence the clinical efficacy of ACT as well as on the refinement of protocols for the isolation, expansion and activation of clinical-grade material for this immunotherapeutic regimen. Moreover, considerable efforts have been dedicated at the identification of maneuvers that may improve the persistence of re-infused lymphocytes and boost their antineoplastic activity while keeping potential side effects at bay.

The refinements of expansion/activation protocols that have recently been suggested to quantitatively and/or qualitatively improve cellular preparations for ACT include, but are not limited to: (1) the addition of an in vitro re-stimulation step with relevant peptides prior to expansion, resulting in an increased proportion of tumor-specific T cells among cultured PBMCs;⁹⁵ (2) the use of IL-12 or IFNγ for the priming of TILs with TAA-derived peptides, resulting in increased antitumor activity in vivo;^96,97 (3) the use of low-dose IFNγ as a pre-treatment for autologous cancer (melanoma) cells employed to activate TILs in co-culture settings, de facto boosting their cytotoxic activity;⁹⁸ (4) the use of an antigen-presenting cell (APC) platform engineered for the expression of the co-stimulatory molecule 4–1BBL and the secretion of IL-21, resulting in the superior expansion of T cells that exhibit a “young” CD27⁺CD28⁺ phenotype and increased cytotoxic functions, but not of Tregs;⁹⁹ (5) the treatment of T cells with the selective A3 adenosine receptor agonist Cl-IB-MECA prior to infusion, resulting in increased tumor necrosis factor α (TNFα) secretion and hence superior cytotoxic potential in vivo;¹⁰⁰ (6) the use of CD8⁺ T cell-specific lentiviral vectors (as opposed to vector that unselectively target T cells) for the transduction of TAA-targeting TCR-coding genes, resulting in increased granzyme B levels and CD8 expression by a subpopulation of transfected cells and hence in improved antineoplastic effects in vivo;¹⁰¹ (7) the downregulation of the E3 ubiquitin ligase Casitas B-lineage lymphoma B (CBLB) in T cells prior to infusion, de facto limiting their sensitivity to immunosuppressive signals such as those delivered by transforming growth factor β (TGFβ);¹⁰² (8) the downregulation of protein tyrosine phosphatase, non-receptor type 6 (PTPN6, also known as SHP1), resulting in a superior short-term accumulation of T cells upon re-infusion and increased therapeutic activity;¹⁰³ (9) the transgene-driven expression of an ubiquitination-resistant linker for activation of T cells (LAT), resulting in increased TCR signaling and cytotoxic potential;¹⁰⁴ (10) the expression of a constitutively active form of signal transducer and activator of transcription 5 (STAT5), significantly boosting the proliferative potential of TAA-experienced T cells;¹⁰⁵ (11) the expression of a co-receptor-independent TCR, resulting in a increased fraction of cytotoxic CD3⁺ cells (including CD4^-CD8^- cells);¹⁰⁶ (12) the expression of single-chain IL-12, resulting in the local self-provision of immunostimulatory signals that appear to be required for the clinical efficacy of CAR-expressing T cells in several mouse tumor models;¹⁰⁷ and (13) the depletion of CD137⁺CD44^highCD4⁺ cells prior to infusion, as these cells de facto constitute a subpopulation of highly activated CD25⁺FOXP3⁺ Tregs.¹⁰⁸ Moreover, Somanchi et al. have shown that trogocytosis, the process whereby T, B and NK lymphocytes can acquire transmembrane proteins from APCs,^109,110 can be efficiently used to engineer cells for ACT prior to re-infusion. Thus, NK cells exposed to CCR7-expressing K562 leukemia cells ex vivo have been shown to efficiently take up CCR7 and express it at their own membrane, resulting in increased homing to lymph nodes upon re-infusion.¹¹¹

The study of Chinnasamy and colleagues mentioned above deserves a special mention as the authors not only showed that the local production of IL-12 dictates the efficacy of CAR-transduced T cells, but also demonstrated that T lymphocytes expressing a vascular endothelial growth factor receptor 2 (VEGFR2)-specific CAR mediate antineoplastic effects both as they inhibit angiogenesis and as they target VEGFR2⁺ MDSCs (in situ and systemically).¹⁰⁷ Along similar lines, we have found of particular interest a recent work from Kloss and colleagues, who proposed a combinatorial strategy whereby CAR-expressing T cells can be rendered truly specific for a given tumor.¹¹² This is particularly relevant when CARs are designed to target so-called “shared” TAAs—that is, TAAs that are also expressed (generally to low levels) by normal cells—as CAR-engineered T cells are extremely sensitive to cognate antigens and hence may damage non-neoplastic tissues.^113,114 To minimize this possibility, Kloss et al. engineered T cells for the co-expression of a CAR that provides suboptimal activation upon binding to one antigen and a chimeric co-stimulatory receptor (CCR) that recognizes a second antigen, resulting in a significant improvement in T-cell selectivity.¹¹²

Besides these improvements in the protocols whereby autologous tumor-reactive lymphocytes are isolated, expanded and activated, several strategies have been proposed as possible means to ameliorate the efficacy of ACT immunotherapy at a later stage, that is, at or post re-infusion. These approaches encompass, but are not limited to: (1) the combination of ACT with agonistic anti-CD40 and anti-CD137 monoclonal antibodies (in the latter case at a specific time point upon infusion), both of which are known to mediate potent co-stimulatory signals;^115,116 (2) the co-administration of ACT with 6-gingerol, a capsaicin-like component of ginger that seems to promote the proliferation of TIL in vivo and their ability to infiltrate neoplastic lesions;¹¹⁷ (3) the administration of ACT together with monoclonal antibodies specific for the immunosuppressive receptor PD-1,⁷ resulting in increased IFNγ production at the tumor site and superior antineoplastic activity;¹¹⁸ (4) the combination of ACT with oncogene-targeting agents, such as compound that specifically inhibit mutant BRAF, which have recently been shown to improve tumor-infiltration by adoptively transferred T cells as well as antitumor responses in murine models of mutant BRAF-expressing melanoma.^119,120

During the past 13 months, important insights have been gained into the mechanisms that underpin the efficacy of ACT in vivo. For example, it has been demonstrated that (1) the T-cell transcription factor NFAT1 plays a prominent role in the tumor-induced anergy of CD4⁺ T cells;¹²¹ (2) the absence of functional ligands for L-, P- and E-selectins (adhesion molecules that are involved in leukocyte rolling along high endothelial venules) as well as the dysfunction of the NK-cell activating receptor NKG2D compromises the antineoplastic activity of adoptively transferred CD8⁺ T cells, in mice;^122,123 (3) the survival of memory CD8⁺ T cells in the absence of CD4⁺ T-cell help relies on CD27-transduced signals that result in the expression of the IL-7 receptor;¹²⁴ (4) memory T cells that can self-renew upon adoptive transfer to cancer patients respond to antigenic stimuli by producing IL-2- and IFNγ-coding mRNAs in a stoichometrically defined ratio;¹²⁵ (5) IL-15, but not IL-2, relieves the immunosuppressive impact of Tregs on adoptively transferred CD8⁺ T cells, hence favoring their survival, proliferation and effector functions;¹²⁶ and (6) one of the mechanisms whereby melanoma cells become refractory to ACT immunotherapy involves a TNFα-dependent inflammatory response that results in the selective loss of melanocytic (but not non-melanocytic) antigens.¹²⁷ The results of these studies are highly relevant for the development of novel ACT strategies that exert superior antineoplastic activity. Along similar lines, the discovery that γδ T cells also mediate potent antitumor effects upon re-infusion (following “conventional” expansion/activation only or in combination with the retroviral transduction of CD8 plus a tumor-reactive αβ TCR) paves an interesting avenue for the development of innovative ACT protocols.^128-131

This said, perhaps the most exciting progress for ACT achieved during the last 13 months relates to the possibility of “rejuvenating” T cells.¹³² Indeed, the TAA-specific T cells that are employed in ACT protocols are often highly differentiated, in particular if TILs are used as starting material, as they have been exposed to chronic inflammation and prolonged antigenic stimulation in vivo. Moreover, expansion procedures generally engender (at least some degree of) terminal differentiation, loss of proliferative capacity and exhaustion/senescence.^133,134 To circumvent this issue, protocols that allow for the selective expansion of early-differentiated, stem-cell memory T (T_SCM) cells have been developed.^133,135 These cells constitute the most undifferentiated human T-cell compartment exhibiting bona fide memory functions, virtually generating all memory cell subsets, display superior persistence and expansion capabilities in vivo and survive for extended periods even after the loss of cognate antigens.^136,137 In addition, the induced pluripotent stem cell (iPSC) technology has been successfully applied to antigen-experienced T cells, allowing for the generation of mature, rejuvenated T cells that maintain the original rearrangement of TCR-coding genes, produce IFNγ in response to antigenic stimulation, exhibit long telomeres (which are indicative of a high replicative potential), are capable of expanding to considerable extents in vitro, express higher levels of cytotoxic molecules than the T-cell clones they derive from and lack the expression of the exhaustion marker PD-1.^138-140 We firmly believe that the use of rejuvenated T cells will considerably expand the therapeutic potential of ACT.

Update on Clinical Trials

When our latest Trial Watch dealing with ACT anticancer immunotherapy was submitted to OncoImmunology for publication (January 2012), official sources listed no more than 35 recent (started after January 1, 2008), ongoing (not withdrawn, terminated or completed by the day of submission) clinical trials that would assess the safety and efficacy of ACT in cancer patients.¹⁵ The status of 28 of these studies has remained unchanged since, whereas 4 trials (NCT00720031; NCT00730613; NCT00815321; NCT01118091) have been completed, 2 have been terminated (NCT00924001; NCT01212887, the latter of which due to safety concerns and lack of efficacy) and 1 has been suspended (NCT01477021). Of note, only the results of NCT00815321, testing the administration of CIK expanded/activated ex vivo with standard protocols to patients with hematological malignancies relapsing upon HSCT, have already been published (see above).⁸⁵

At present (February 2013), official sources list no less than 27 clinical trials launched after February 1, 2012, that would investigate the safety and efficacy of ACT in oncological indications (source www.clinicaltrials.gov). This rate is strikingly higher than that observed in the previous 4-y period, corroborating the notion that ACT immunotherapy is nowadays considered as one of the most promising strategies against cancer. A majority of ongoing clinical studies involve patients bearing hematological malignancies encompassing (but not limited to) acute lymphocytic leukemia (ALL), myelodysplastic syndrome (MDS) and several forms of myeloma (10 trials) or skin cancers, such as melanoma and Merkel cell carcinoma (7 trials). Taken together, the remaining 10 studies are performed in a relatively heterogeneous group of patients, including individuals affected by esophageal cancer (2 trials), breast carcinoma (1 trial), mesothelioma (1 trial), cholangiocarcinoma (1 trial) as well as unspecified solid tumors (5 trials) (Table 1). Although not always specified at www.clinicaltrials.gov, most (if not all) of these trials involve patient pre-conditioning, which is often achieved with cyclophosphamide and fludarabine optionally combined with one or more cytotoxic chemotherapeutics, as well as the administration of IL-2 upon re-infusion (for the reasons discussed above).

Table 1. Recent clinical trials assessing the safety and efficacy of ACT immunotherapy in cancer patients*

Type	Indication(s)	Phase	Status	Note(s)	Ref.
Engineered T cells	Advanced solid tumors	I	Active, not recruiting	MAGE-A4-specific TCR-expressing T cells	NCT01694472
		II	Recruiting	T cells expressing an NY-ESO-1-specific TCR plus NY-ESO-1-pulsed DCs	NCT01697527
		II	Recruiting	CEA-specific CAR-expressing T cells, as a standalone intervention	NCT01723306
	AML CML	I/II	Recruiting	T cells expressing a WT1-specific TCR, as a standalone intervention	NCT01621724
	AML MDS MM	I	Active, not recruiting	T cells expressing a CAR specific for the Lewis Y carbohydrate antigen	NCT01716364
	B-cell ALL	I	Recruiting	CD19-specific CAR-expressing T cells, in pediatric patients with relapsing disease	NCT01683279
	CLL	I	Not yet recruiting	CD19-specific CAR-expressing T cells	NCT01653717
		II	Recruiting	CD19-specific CAR-expressing T cells, in patients with relapsed/refractory disease	NCT01747486
	Leukemia Lymphoma	I	Recruiting	CD20-specific CAR-expressing T cells, in patients with chemorefractory disease	NCT01626495
		n.a.	Not yet recruiting	CD20-redirected T cells, in patients with chemorefractory disease	NCT01735604
		I	Recruiting	CD19-redirected T cells, in children and young adults failing conventional therapies	NCT01593696
	Mesothelioma	I	Not yet recruiting	FAP-specific CAR-expressing T cells, in patients with FAP^+ pleural disease	NCT01722149
	Mesothelioma Pancreatic carcinoma	I/II	Recruiting	T cells expressing a CAR specific for mesothelin, as a standalone intervention	NCT01583686
	Melanoma	I	Recruiting	T cells expressing a tyrosinase-specific, co-receptor-independent TCR	NCT01586403
		I/II	Not yet recruiting	CXCR2- or NGFR-expressing T cells, in patients with metastatic disease	NCT01740557
	Ovarian carcinoma	I/II	Active, not recruiting	T cells expressing a TCR specific for NY-ESO-1 or MAGE-A3/A6/B18	NCT01567891
Unmodified T cells	Breast carcinoma	II	Recruiting	Activated T cells armed with a bispecific antibody targeting CD3 and ERBB2	NCT01658969
	HPV^+ carcinoma	II	Recruiting	Young TILs as a standalone intervention	NCT01585428
	Lymphoproliferative disorders	I	Not yet recruiting	EBV-specific cytotoxic T lymphocytes	NCT01555892
	Melanoma	n.a.	Recruiting	Conventional TILs plus ipilimumab	NCT01701674
		I	Recruiting	Young TILs combined with vemurafenib	NCT01585415
		II	Recruiting	Conventional TILs plus vemurafenib	NCT01659151
	Merkel cell carcinoma	I/II	Not yet recruiting	Autologous polyclonal CD8^+ TILs plus local irradiation or intralesional IFNβ	NCT01758458
Other cell types	Cholangiocarcinoma	I	Recruiting	CIK cells as a standalone intervention	NCT01573455
	Esophageal carcinoma	n.a.	Recruiting	CIK cells plus radiotherapy and conventional chemotherapy	NCT01691625
		n.a.	Recruiting	CIK cells plus radiotherapy	NCT01691664
	Myeloma	I/II	Not yet recruiting	Umbilical cord blood-derived NK cells plus chemotherapy and ASCT	NCT01729091

ACT, adoptive cell transfer; ALL, acute lymphocytic leukemia; AML, acute myeloid leukemia; ASCT, autologous stem cell transplantation; CAR, chimeric antigen receptor; CEA, carcinoembryonic antigen; CIK, cytokine-inducer killer; CLL, chronic lymphocytic leukemia; CML, chronic myeloid leukemia; CXCR2, chemokine (C-X-C motif) receptor 2; DC, dendritic cell; EBV, Epstein-Barr virus; FAP, fibroblast activation protein; HPV, human papillomavirus; IFN, interferon; MAGE; melanoma-associated antigen; MDS, myelodysplastic syndrome; MM, multiple myeloma; n.a., not available; NGFR, nerve growth factor receptor; NK, natural killer; TCR, T-cell receptor; TIL, tumor-infiltrating lymphocyte; WT1, Wilms tumor 1. *Started after January 31, 2012.

In a majority of cases, the infused material consists of genetically engineered lymphocytes, mostly for the expression of TAA-specific CARs (10 studies) or TCRs (5 studies). Thus, T cells expressing a CD19-specific CAR are being tested (1) in pediatric patients with relapsed B-cell ALL (NCT01683279); (2) children and young adults affected by ALL, B-cell leukemia, large cell lymphoma or non-Hodgkin lymphoma who have failed conventional therapies (NCT01593696); (3) patients with relapsed or refractory chronic lymphocytic leukemia (NCT01747486; NCT01653717); and (4) subjects suffering from not better defined variants of CD19⁺ leukemia or lymphoma (NCT01626495). Moreover, (1) T cells expressing a CD20-directed CAR are being tested in patients affected by a large variety of hematological neoplasms (NCT01735604); (2) T lymphocytes engineered for the expression of a CAR targeting the Lewis Y carbohydrate antigen are being assessed as a therapeutic intervention in AML, MDS and multiple myeloma patients (NCT01716364); (3) T cells expressing a fibroblast activation protein (FAP)-specific CAR are being evaluated in patients with malignant pleural mesothelioma (NCT01722149); (4) the antineoplastic activity of mesothelin-redirected T cells is being assessed in metastatic mesothelioma and pancreatic carcinoma patients (NCT01583686); and (5) T lymphocytes redirected against the carcinoembryonic antigen (CEA) by means of a specific CAR are investigated as a therapeutic option for subjects affected by metastatic carcinomas (NCT01723306). The safety and preliminary efficacy of T lymphocytes engineered to express TCRs that recognize NY-ESO-1 (a cancer-testis antigen),¹⁴¹ tyrosinase and various other melanoma-associated antigens (MAGEs) or Wilms tumor 1 (WT1, a TAA overexpressed by various hematological and renal tumors)¹⁴² are being investigated in cohorts of patients affected by AML or chronic myeloid leukemia (NCT01621724), melanoma (NCT01586403), ovarian carcinoma (NCT01567891), as well as advances solid tumors (NCT01694472; NCT01697527). Finally, T cells co-expressing nerve growth factor receptor (NGFR) or chemokine (C-X-C motif) receptor 2 (CXCR2), improving their ability to proliferate in vivo and to migrate to neoplastic lesions, are being tested as a standalone therapeutic intervention in melanoma patients (NCT01740557).

The remaining clinical studies involve genetically unmodified cells. In particular: (1) TILs isolated and amplified with conventional protocols are being assessed, in combination with either the BRAF-specific inhibitor vemurafenib^143,144 or the anti-CTL4 monoclonal antibody ipilimumab,^9,10,145 for the treatment of metastatic melanoma patients (NCT01659151; NCT01701674); (2) young TILs, alone or combined with vemurafenib, are being assessed in cohort of patients affected by human papillomavirus (HPV)⁺ tumors (mainly oropharyngeal, cervical, vaginal and anal carcinoma) and melanoma, respectively (NCT01585428; NCT01585415); (3) autologous polyclonal CD8⁺ TILs specific for a Merkel cell polyomavirus-associated antigen are being tested, in combination with local irradiation or intralesional IFNβ, in subjects bearing metastatic Merkel cell carcinomas (NCT01758458);¹⁴⁶ (4) the safety and therapeutic potential of EBV-specific cytotoxic T lymphocytes are being evaluated in patients with various forms of EBV⁺ lymphomas and lymphoproliferative disorders (NCT01555892); and (5) activated T cells armed with a bispecific antibody simultaneously targeting CD3 and ERBB2, a TAA that is often overexpressed in breast carcinoma,¹⁴⁷ are being tested in combination with conventional chemotherapeutic regimens for the treatment of resectable Stage II-III breast cancer (NCT01658969). In addition, (1) CIK cells are being investigated as a standalone intervention for the therapy of cholangiocarcinoma patients (NCT01573455) or combined with conventional chemotherapy and/or radiation in subjects bearing esophageal carcinomas (NCT01691625; NCT01691664); and (2) the safety and efficacy of umbilical cord blood-derived NK cells are being assessed in a cohort of myeloma patients concomitantly subjected to chemotherapy and autologous stem cell transplantation (NCT01729091).

Concluding Remarks

As detailed above, no less than 27 new clinical trials that would evaluate the safety and efficacy of ACT immunotherapy in cancer patients have been launched during the past 14 months. By comparison, only 35 of such studies were launched from January 1, 2008, and January 31, 2012, reflecting the interest that this immunotherapeutic modality has generated among clinicians. Along similar lines, the molecular and cellular circuitries that may influence the clinical efficacy of ACT are being intensively investigated, as demonstrated by the constantly increasing amount of high quality scientific publications dealing with topics (source www.ncbi.nlm.nih.gov/pubmed/).

As it stands, CAR-based approaches are on the limelight, at least in part due to the development of “third-generation” molecules that contain multiple intracellular signaling domains, including CD3ζ-, CD28- and OX40- or 4–1BB-derived modules, and hence exert robust antineoplastic effects.^148-150 In addition, Carl June and collaborators have recently reported that the administration of CAR-expressing T cells to HIV-1 patients is associated with a stable engraftment (CAR⁺ cells could be detected as long as 11 y after infusion), even in the absence of lymphodepleting regimens, but (1) no severe side effects and (2) no evidence of insertional mutagenesis.⁹² It will be interesting to see whether these observations hold true in cancer patients, in particular in view of the fact that both HIV-1 infection and cancer are expected to induce (at least some extent of) immunosuppression, though by distinct mechanisms. In this setting, approaches in which T cells are engineered for the expression of suicide proteins, such as an inducible variant of caspase-9,¹⁵¹ should provide an additional level of security for the development of novel and safe immunotherapeutic protocols based on ACT. Future will tell whether the great expectations that are being generated by ACT immunotherapy will ever translate into a clinical reality.

Abbreviations:
ACT	=	adoptive cell transfer
ALL	=	acute lymphocytic leukemia
AML	=	acute myeloid leukemia
APC	=	antigen-presenting cell
CAR	=	chimeric antigen receptor
CBLB	=	Casitas B-lineage lymphoma B
CCR	=	chimeric co-stimulatory receptor
CEA	=	carcinoembryonic antigen
CIK	=	cytokine-induced killer
CLL	=	chronic lymphocytic leukemia
CXCR2	=	chemokine (C-X-C motif) receptor 2
DC	=	dendritic cell
EBV	=	Epstein-Barr virus
FAP	=	fibroblast activation protein
FRα	=	folate receptor α
HPV	=	human papillomavirus
HSCT	=	hematopoietic stem cell transplantation
IFN	=	interferon
IL	=	interleukin
LAT	=	linker for activation of T cells
iPSC	=	induced pluripotent stem cell
MAGE	=	melanoma-associated antigen
MDS	=	myelodysplastic syndrome
MDSC	=	myeloid-derived suppressor cell
NGFR	=	nerve growth factor receptor
NK	=	natural killer
PBMC	=	peripheral blood mononuclear cell
PTPN6	=	protein tyrosine phosphatase, non-receptor type 6
STAT5	=	signal transducer and activator of transcription 5
TAA	=	tumor-associated antigen
TCR	=	T-cell receptor
TGFβ	=	transforming growth factor β
TIL	=	tumor-infiltrating lymphocyte
TLR	=	Toll-like receptor
TNFα	=	tumor necrosis factor α
Treg	=	FOXP3+ regulatory T cell
TSCM	=	stem-cell memory T
VEGFR2	=	vascular endothelial growth factor receptor 2
WT1	=	Wilms tumor 1

Acknowledgments

Authors are supported by the European Commission (ArtForce); Agence National de la Recherche (ANR); Ligue contre le Cancer (Equipe labelisée); Fondation pour la Recherche Médicale (FRM); Institut National du Cancer (INCa); LabEx Immuno-Oncologie; Fondation de France; Fondation Bettencourt-Schueller; AXA Chair for Longevity Research; Cancéropôle Ile-de-France and Paris Alliance of Cancer Research Institutes (PACRI).

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Notes

† These authors share senior co-authorship.