Immunotherapy highlights from the 2011 meeting of the American Society of Hematology

Abstract

The world’s largest hematology society, the American Society for Hematology, meets annually, gathering physicians, scientists, administrators, medical students, graduate students, allied health professionals and exhibitors. The meeting this year was held in San Diego, CA, USA, and included a plethora of basic, translational and clinical research.

Keywords::

• cancer
• cord blood
• cytomegalovirus
• graft-versus-host disease
• hematology
• immunotherapy
• T cell

Every year, the American Society of Hematology (ASH) hosts the largest gathering of hematologists in the world. In the past 5 years, the meeting has hosted between 20,000 and 25,000 attendees, drawing from over 100 countries. ASH invited participants to submit abstracts that were reviewed by a panel of experts and selected for poster or oral presentations. One well-attended oral abstract session was ‘Adoptive immunotherapy: T lymphocytes’. Some of the abstracts from this session, as well as other abstracts related to immunotherapy, are highlighted in this report.

Improving T-cell function & persistence

In the past 10 years, investigators have shown that there is limited persistence of ex vivo-expanded and infused tumor-specific T cells when compared with the success and persistence of virus-specific cytotoxic T lymphocytes (CTLs) expanded using similar methodologies [1–3]. Hasan et al. tried to address this dichotomy by separately generating tumor (WT-1)-specific and virus (cytomegalovirus [CMV])-specific CTLs, and testing the ability of each of these CTLs to control endogenously expressing WT-1 human colon carcinoma cells that were genetically modified to express CMV pp65 (coca pp65). Coca pp65 cells were transferred to NOD/SCID-IL2Rgc-KO/J mice and allowed to grow for 5 days before NOD/SCID-IL2Rgc-KO/J mice were treated with WT-1 CTLs and CMV-CTLs and their in vivo efficacy was then compared. Interestingly, CMV-CTL were better at lysing coca pp65 tumors than WT-1 CTL [4].

Gerdemann et al. also used genetic manipulation to improve the persistence of tumor-specific CTLs. T cells recognized tumor antigens via their native T-cell receptors (TCRs) and were also modified to express the IL-7α receptor, which is typically expressed on naive T cells but is downregulated after activation. By expressing the IL-7α receptor, transduced CTL had improved persistence and expansion in response to IL-7 [5].

Hudecek et al. evaluated the use of naive CD4+ T cells modified with a chimeric antigen receptor (CAR) targeting ROR1 to provide anti-tumor activity and support for CD8+ ROR-CAR T cells. In brief, CD4+ T cells derived from the naive population exhibited the strongest cytotoxicity, exhibited the best expansion and produced the most Th1 cytokines, leading to an optimal environment for functional CD8+ ROR-CAR T cells [6]. These results – limited to CD4+ T cells – support what Hinrichs and colleagues have shown for CD8+ murine T cells [7], but contrast sharply with what Berger and colleagues have shown, where central memory-derived CD8+ T cells persist the longest in primates [8]. Whether the discrepancy is attributed to the difference between the CD4+ T cells and CD8+ T cells will hopefully be elucidated in the forthcoming manuscript.

Targeting tumor antigens & preventing graft-versus-host disease

In the same session, Ochi presented work from the Yasukawa group in Japan showing that CD4+ T cells could be redirected using TCR gene transfer of a WT-1-specific TCR. Redirected cells expressed very low FoxP3, but released IL-2, IFN-γ and TNF-α in response to WT-1 peptide. When redirected CD4+ T cells (but not nonredirected CD4+ T cells) were combined with redirected CD8+ T cells, there was an increase in WT-1-specific cytotoxicity and cytokine release [9].

Similar to Yasukawa, Bonini et al. presented an abstract in which they identified a high avidity TCR that recognized an epitope of WT-1. This TCR was exogenously transferred to nonspecifically activated CD3+ T cells in the presence of zinc finger nucleases to prevent mispairing [10] – a common problem when transferring exogenous TCRs [3]. After selection, only T cells bearing the exogenous WT-1 TCR survived and expanded. They were not alloreactive, and when transferred to mice, these T cells were able to engraft without causing graft-versus-host disease (GVHD) [10].

Donor lymphocyte infusion (DLI) has shown promise in clinical trials [11], but the risk of GVHD has limited the usefulness of such an approach [12]. To overcome this limitation, Ghosh et al. have developed a method of suppressing GVHD but retaining the graft versus leukemia (GVL) effect by eliminating alloreactive T cells and host antigen-presenting cell (APC). In a murine model, splenocyte-derived T cells were transduced with a lentiviral vector encoding the apoptosis-inducing molecule TNF-related apoptosis inducing ligand (TRAIL). When T cells were transferred to T-cell-depleted B6 mice with LB27.4 tumors, TRAIL-transduced T cells exhibited significantly greater anti-tumor immunity in the absence of GVHD. The elimination of LB27.4 tumors was mediated by the TRAIL ligand death receptor 5 (DR5). Interestingly, DR5 was shown to be high on host APCs as well as activated alloreactive CD25+ T cells, and the authors suggest that the lack of GVHD is a result of TRAIL-transduced T cells forcing DR5+ host APCs and alloreactive T cells to undergo apoptosis [13].

Yet another strategy for preventing GVHD but enhancing GVL was presented by Stevanovic et al. from The Netherlands. In this abstract, nonobese diabetic/severe combined immunodeficient mice were engrafted with B-ALL or CML-BP tumors and treated with HLA-matched and HLA Class I-matched/Class II-mismatched DLI. The HLA-matched DLI delayed tumor growth, but was not able to eliminate the tumor. By contrast, the HLA Class I-matched/Class II-mismatched DLI rapidly cleared the leukemic cells [14]. This study implies that an HLA Class II mismatch may be favored for GVL effect, but how to balance the GVL effect with the increased risk for GVHD remains to be elucidated.

Cord blood transplantation (CBT) is becoming increasingly popular worldwide as an alternative donor source for patients who do not have matched related or unrelated donors available. One problem that arises after CBT is an increase in viral infection due to a delay in the recovery of virus-specific T cells post-transplantation [15]. Hanley et al. presented an abstract about immunotherapy with cord blood (CB)-derived virus-specific CTL [16]. In the setting of CBT, the enrolled patients received 80% of a fractionated CB unit for transplantation and 20% of the CB was reserved for CTL generation. Despite the delayed engraftment associated with CBT, transferring only 80% of the CB unit did not further delay engraftment, with a median time-to-neutrophil engraftment of 20 days. CTLs were transferred to four patients (median days post-CBT: 84) and in all patients virus-specific CTLs were detectable postinfusion. One of the four patients had CMV reactivation/infection and in this patient there was a concomitant rise in CMV pp65-specific CTLs that were not present before CTLs infusion [17]. As this is the first trial of antigen-specific CTLs derived from CB, it will be interesting to evaluate whether CB-derived CTLs (which are derived from naive T cells and not memory T cells) are as efficacious as peripheral blood-derived CTLs.

Despite the apparent interest in T-cell immunotherapy, abstracts were not limited to T cells with at least three natural killer (NK) cell abstracts earning oral presentations in the ‘Exploiting innate and adaptive immunity’ and ‘Graft characterization and manipulation’ sessions. One abstract by Reger et al. evaluated the use of bortezomib to sensitize a variety of tumors to NK cells that were expanded ex vivo and adoptively transferred. Patients received either a single dose of NK cells (5 × 10⁶ to 1 × 10⁸/kg) or one dose of NK cells on day 0 (1 × 10⁸/kg) and an escalating dose on day 5 (5 × 10⁷ and 1 × 10⁸/kg) following a second dose of bortezomib. No infused NK cell-related Grade II–IV toxicities were observed. Of 20 patients receiving NK cell therapy, six had progressive disease, ten had stable disease and four had a minor response [18].

Summary & future direction of immunotherapy

Based on the ASH abstracts selected for oral and poster presentations, it is obvious that translational research and cell-based immunotherapy, in particular, is a growing therapy for hematologic malignancies. One of the greatest challenges ahead for immunotherapists is expanding immune system cells that target self-antigens such as tumor antigens. By definition, self-antigens are difficult to target because of the negative selection of T cells in the thymus that target such cells, leaving low avidity T cells in circulation. Ways to circumvent the use of these low-avidity T cells include utilizing redirected TCRs that are transduced with zinc finger nucleases to prevent TCR mispairing [19], using chimeric antigen receptors [20] and expanding only high avidity T cells from tumors [21]. However, with few exceptions, these cells have lacked clinical efficacy, mostly due to their lack of persistence in vivo. Using genetic modifications such as overexpressing TRAIL or the IL-7R on T cells are ways to improve persistence.

Another challenge facing stem cell transplantation is the balance of retaining GVL yet minimizing GVHD. Abstracts in this meeting aimed at focusing on GVL by overexpressing TRAIL or mismatching HLA Class II but not Class I antigens. Di Stasi et al. and other groups have also reported strategies to maximize the GVL effect with T-cell therapy while preventing the morbidity of GVHD by transducing the infused cells with a suicide gene. At the onset of GVHD, the suicide gene is triggered by a small molecule or drug and, in the case of the trial by Di Stasi et al., the GVHD resolves within minutes [22]. The use of CB as an alternative stem cell source is another option because it is associated with less GVHD but similar relapse rates to similarly mismatched peripheral blood and bone marrow transplants [23].

Finally, immunotherapy is trending towards a multifaceted approach. Whether it be with adjuvants, cytokines, chemotherapeutic agents or a combined vaccine/T-cell therapy/antibody approach [24,25], infusing T cells or NK cells alone no longer seems to be the most effective way of treating evasive tumors; these seminal studies are still important for elucidating how to better manipulate the immune system, but combining modalities is becoming the future of adoptive immunotherapy.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or mater ials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.