Abstract A041: CD19-targeting third generation CAR T cells for relapsed and refractory lymphoma and leukemia – report from the Swedish phase I/IIa trial

Chimeric antigen receptor (CAR) T cells have shown promising results in patients with B cell malignancy. In preclinical studies we showed that CD19-targeting third generation (3G) CAR T cells containing signaling domains from both CD28 and 4-1BB as co-stimulatory molecules have a higher activation status and greater proliferation in response to antigens. Herein we report initial results from a phase I/IIa study (NCT:02132624) using these 3G CAR T cells. Patients with relapsed or refractory CD19+ B-cell malignancy were eligible, provided there was no other curative treatment available. Of the first eleven patients reported, nine had lymphoma and two patients had acute lymphoblastic leukemia (ALL). Autologous CAR T cells were manufactured using a gamma retrovirus encoding the CAR and expanded by αCD3/αCD28/IL2. During CAR T cell production, all lymphoma patients received treatment to control tumor burden (-90 to -3 days before T cell infusion). Type of treatment depended on the type of lymphoma and previous treatments. In addition, prior to T cell infusion (day -2 to -1) patients #6-11 received cyclophosphamide (500mg/m2) and fludarabine (25mg/m2) as preconditioning to decrease immunosuppressive cells.

The patients received one infusion of CAR T cells starting at a dose of 2x107 cells/m2 (patients 1 and 2), 1x108 (patients 4, 5, 7, 8, 9) and 2x108 (patients 6, 10, 11, 12). Patient #1 (DLBCL) had a mild cytokine release syndrome (CRS) after four weeks (never requiring treatment), followed by a complete response of his lymphoma. A relapse and a second CRS occurred after six weeks and he was treated with prednisone with good symptomatic effect and reduction of tumor size. The patient progressed after three months. Patients #2, 4, 5 (CLL, MCL, MCL) all progressed after 2, 1, and 3 months, respectively. Patient #6 (DLBCL) responded to treatment (CR) prior to T cell infusion and remained in complete remission for 6 months post T cell infusion. Patient #7 (CLL) and #9 (DLBCL) also responded to treatment prior to T cell infusion and remains in complete remission (>3 months). The CLL patient has a tumor negative bone marrow. Patient #8 (FL-DLBCL) progressed after 1 month but had a mild CRS. Patient #10 (ALL) experienced transient CNS toxicity followed by a complete response. However, at 3 months the patient relapsed with a CD19 negative ALL, accompanied by increased levels of immunosuppressive cells. Patient #11 (ALL) is in complete remission after a CRS (>1 month) and patient #12 (FL/Burkitt) had a major CRS requiring intensive care but is too early to evaluate. The CAR transgene could be detected in blood at the time of patient response.

In summary, eleven patients have been treated with increasing doses of CAR T cells in Sweden. All treatments were given as out-patients. The conditioning has been relatively mild as compared to previous published studies. Six patients had complete remission, or complete clinical responses, at the time of evaluation of which two relapsed later. Four patients did not respond to treatment and progressed early; and 1 is still too early to evaluate. Correlations between the levels of immunosuppressive cells and patient response are currently under investigation.

Citation Format: Gunilla Enblad, Hannah Karlsson, Kristina I. Wikstrom, Magnus Essand, Barbara Savoldo, Malcolm K. Brenner, Gianpietro Dotti, Martin Hoglund, Hans Hagberg, Angelica Loskog. CD19-targeting third generation CAR T cells for relapsed and refractory lymphoma and leukemia – report from the Swedish phase I/IIa trial. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A041.

Abstract IA22: Immunotherapy with virus-specific T cells

Epstein-Barr virus (EBV) reactivation post allogeneic hematopoietic stem cell transplantation (HSCT) can lead to the outgrowth of EBV-infected B cells and the development of post-transplant lymphoproliferative disease (EBV-PTLD). Since 1993 our group has used adoptive transfer of in vitro expanded EBV-specific T cells as a means to prevent or treat these EBV-driven lymphomas. In a series of Phase I and II clinical trials we have assessed the safety and clinical benefit associated with these transferred cells in allogeneic HSCT recipients. The T cell products infused were generated using 3 different manufacturing methodologies - [(i) EBV-transformed lymphoblastoid cell lines (EBV-LCLs) (~12 weeks manufacturing time), (ii) plasmid-nucloefected dendritic cells (DCs) (17 day manufacturing) and (iii) direct stimulation of PBMCs using overlapping peptide libraries (10 day manufacturing)] and were administered to either prevent (n=162) or treat (n=47) EBV reactivation/disease in a total of 209 allogeneic HSCT recipients ranging in age from 6 months to 63 years. Of 162 patients infused prophylactically only 1 (0.6%) developed EBV-PTLD, which occurred following the administration of steroids 3 weeks-post VST infusion. However, this patient responded to a second VST infusion after the steroids. 31 of 36 (86%) patients with elevated viral load (n=21) or biopsy-proven/probable LPD (n=15) achieved durable complete remissions and the infused cells persisted long term as demonstrated in 26 patients who received gene-marked VSTs that were detectable for up to 9 years post-infusion.

To extend the approach to additional viruses we initially developed methodology for using genetically modified antigen presenting cells approach to generate VSTs from donor peripheral blood that target CMV, EBV and adenovirus and showed that adoptively transferred donor-derived VSTs can reconstitute antiviral immunity to all three viruses and effectively treat established infections. However, the time taken to prepare patient-specific products and the lack of virus-specific memory T cells in cord blood and seronegative donors restricts application. More recently we have evaluated whether T-cell lines manufactured using overlapping peptide pools and extended the specificity to include HHV6 and BK. When administered to 11 recipients of allogeneic transplants, 8 of whom had up to four active infections with the targeted viruses, these VSTs proved safe in all subjects and produced an overall 94% virological and clinical response rate that was sustained long-term.

Another means of avoiding growing CTLs for individual patients is to bank lines that are then available as an off the shelf product of most closely HLA-matched allogeneic cytotoxic T lymphocyte lines. We evaluated this strategy in a multicenter study through the NHLBI Specialized Centers for Cell-Based Therapy (SCCT) program in HSCT recipients who had viral reactivation or infection refractory to standard therapy. The overall cumulative incidence of first CR/PR in 50 patients based on viral load by day 42 was 74.0% (73.9% for CMV, 66.7% for EBV and 77.8% for adenovirus). In a follow up study using the peptide induced VSTs that recognize 5 viruses, based on viral load measurements by quantitative PCR a single VST infusion successfully controlled active infections in 19/21 evaluable patients. These results demonstrate the feasibility and safety of 3rd party multivirus-directed VSTs, generated by direct stimulation of PBMCs with synthetic peptides and administered as an off the shelf product.

Citation Format: Helen E. Heslop, Ifigenia Tzannou, Bilal Omer, Malcolm K. Brenner, Ann M. Leen, Cliona M. Rooney. Immunotherapy with virus-specific T cells. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr IA22.

Clonal Dynamics In Vivo of Virus Integration Sites of T Cells Expressing a Safety Switch

Safety switches are becoming relevant for the clinical translation of T-cell-based immunotherapies. In patients receiving an allogeneic hematopoietic stem cell transplant, the inducible caspase-9 gene (iC9) safety switch expressed by donor-derived T lymphocytes efficiently controls acute graft versus host disease (GvHD). However, in vivo elimination of iC9-T cells by the chemical inducer of dimerization (CID) that activates the iC9 protein is incomplete. To study this effect, we characterized the clonal diversity and dynamics of vector insertion sites (VIS) in iC9-T cells pre- and post-CID administration in four patients who developed GvHD. We identified 3,203 VIS among four patients and followed their in vivo clonal dynamics up to 161 days post-CID. VIS were categorized by their proximity to host genome elements, gene associations, and cis-modulatory relationship to mapped promoters. We found that VIS are preferentially located near open chromatin and promoter regions; furthermore, there was no evidence for selection bias among VIS surviving the CID treatment. The majority of iC9-T cells with high normalized VIS copy number at the time of GvHD onset were eliminated by CID, while iC9-T cells detectable post-CID generally have low normalized VIS copy number. We propose that suboptimal iC9 transgene expression is responsible for the incomplete elimination of iC9-T cells and illustrate here by simple model how cis-modulatory influences of local genome context and T-cell receptor activation status at time of CID treatment contribute to stochastic sparing of iC9-T cells.

A Safeguard System for Induced Pluripotent Stem Cell-Derived Rejuvenated T Cell Therapy

The discovery of induced pluripotent stem cells (iPSCs) has created promising new avenues for therapies in regenerative medicine. However, the tumorigenic potential of undifferentiated iPSCs is a major safety concern for clinical translation. To address this issue, we demonstrated the efficacy of suicide gene therapy by introducing inducible caspase-9 (iC9) into iPSCs. Activation of iC9 with a specific chemical inducer of dimerization (CID) initiates a caspase cascade that eliminates iPSCs and tumors originated from iPSCs. We introduced this iC9/CID safeguard system into a previously reported iPSC-derived, rejuvenated cytotoxic T lymphocyte (rejCTL) therapy model and confirmed that we can generate rejCTLs from iPSCs expressing high levels of iC9 without disturbing antigen-specific killing activity. iC9-expressing rejCTLs exert antitumor effects in vivo. The system efficiently and safely induces apoptosis in these rejCTLs. These results unite to suggest that the iC9/CID safeguard system is a promising tool for future iPSC-mediated approaches to clinical therapy.

CAR-T Cell Therapy for Lymphoma

Lymphomas arise from clonal expansions of B, T, or NK cells at different stages of differentiation. Because they occur in the immunocyte-rich lymphoid tissues, they are easily accessible to antibodies and cell-based immunotherapy. Expressing chimeric antigen receptors (CARs) on T cells is a means of combining the antigen-binding site of a monoclonal antibody with the activating machinery of a T cell, enabling antigen recognition independent of major histocompatibility complex restriction, while retaining the desirable antitumor properties of a T cell. Here, we discuss the basic design of CARs and their potential advantages and disadvantages over other immune therapies for lymphomas. We review current clinical trials in the field and consider strategies to improve the in vivo function and safety of immune cells expressing CARs. The ultimate driver of CAR development and implementation for lymphoma will be the demonstration of their ability to safely and cost-effectively cure these malignancies.

Abstract 4703: Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer

Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). T cells expressing this CAR were able to kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-)293T cells (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n = 3). Although these CAR-T cells had potent anti-tumor activity, pancreatic tumors employ immune evasion strategies such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when we examined the serum of patients with pancreatic cancer (n = 8) we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect our CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n = 4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n = 3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand (increase from 2×10e6 cells on day 0 to 5.53±8.46×10e10 cells on day 28), unlike unmodified CAR-PSCA T cells which plateaued at 3.84±5.43×10e8 cells (n = 4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28; n = 4). However, even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent. In conclusion, CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.

Citation Format: Somala Mohammed, Sujita Sukumaran, Pradip Bajgain, Usanarat Anurathapan, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4703. doi:10.1158/1538-7445.AM2015-4703

Abstract B63: Improving CAR T cell function by reversing the immunosuppressive tumor environment of pancreatic cancer

Background: Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. Although these CAR-T cells have potent anti-tumor activity in vitro and in vivo, pancreatic tumors employ immune evasion mechanisms, such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function.

Methods: To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). We also engineered a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Expansion and selection profiles and short- and long-term anti-tumor activity of these transgenic T cells were assessed.

Results: T cells expressing CAR-PSCA kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-) targets, such as 293T (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n=3). Although these CAR-T cells had potent anti-tumor activity in vitro and in vivo, pancreatic tumors employ immune evasion mechanisms, such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when the serum of patients with pancreatic cancer (n=8) was examined, we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect the CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n=4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n=3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand unlike unmodified CAR-PSCA T cells (from 2x106 cells on day 0 to 5.53x1010±8.46x1010 cells (CAR-PSCA 4/7R ChR) on day 28, in comparison to CAR-PSCA T cells that reached only 3.84x108±5.43x108 cells, n=4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28, n=4), but even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent.

Conclusions: CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.

Citation Format: Somala Mohammed, Sujita Sukumaran, Usanarat Anurathapan, Pradip Bajgain, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor environment of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B63.

Mesenchymal Stromal Cells for Linked Delivery of Oncolytic and Apoptotic Adenoviruses to Non-small-cell Lung Cancers

Oncolytic adenoviruses (OAdV) represent a promising strategy for cancer therapy. Despite their activity in preclinical models, to date the clinical efficacy remains confined to minor responses after intratumor injection. To overcome these limitations, we developed an alternative approach using the combination of the OAdv ICOVIR15 with a replication incompetent adenoviral vector carrying the suicide gene of inducible Caspase 9 (Ad.iC9), both of which are delivered by mesenchymal stromal cells (MSCs). We hypothesized that coinfection with ICOVIR15 and Ad.iC9 would allow MSCs to replicate both vectors and deliver two distinct types of antitumor therapy to the tumor, amplifying the cytotoxic effects of the two viruses, in a non-small-cell lung cancer (NSCLC) model. We showed that MSCs can replicate and release both vectors, enabling significant transduction of the iC9 gene in tumor cells. In the in vivo model using human NSCLC xenografts, MSCs homed to lung tumors where they released both viruses. The activation of iC9 by the chemical inducer of dimerization (CID) significantly enhanced the antitumor activity of the ICOVIR15, increasing the tumor control and translating into improved overall survival of tumor-bearing mice. These data support the use of this innovative approach for the treatment of NSCLC.

Human Epidermal Growth Factor Receptor 2 (HER2) -Specific Chimeric Antigen Receptor-Modified T Cells for the Immunotherapy of HER2-Positive Sarcoma

PURPOSE

The outcome for patients with metastatic or recurrent sarcoma remains poor. Adoptive therapy with tumor-directed T cells is an attractive therapeutic option but has never been evaluated in sarcoma.

PATIENTS AND METHODS

We conducted a phase I/II clinical study in which patients with recurrent/refractory human epidermal growth factor receptor 2 (HER2) -positive sarcoma received escalating doses (1 × 10(4)/m(2) to 1 × 10(8)/m(2)) of T cells expressing an HER2-specific chimeric antigen receptor with a CD28.ζ signaling domain (HER2-CAR T cells).

RESULTS

We enrolled 19 patients with HER2-positive tumors (16 osteosarcomas, one Ewing sarcoma, one primitive neuroectodermal tumor, and one desmoplastic small round cell tumor). HER2-CAR T-cell infusions were well tolerated with no dose-limiting toxicity. At dose level 3 (1 × 10(5)/m(2)) and above, we detected HER2-CAR T cells 3 hours after infusion by quantitative polymerase chain reaction in 14 of 16 patients. HER2-CAR T cells persisted for at least 6 weeks in seven of the nine evaluable patients who received greater than 1 × 10(6)/m(2) HER2-CAR T cells (P = .005). HER2-CAR T cells were detected at tumor sites of two of two patients examined. Of 17 evaluable patients, four had stable disease for 12 weeks to 14 months. Three of these patients had their tumor removed, with one showing ≥ 90% necrosis. The median overall survival of all 19 infused patients was 10.3 months (range, 5.1 to 29.1 months).

CONCLUSION

This first evaluation of the safety and efficacy of HER2-CAR T cells in patients with cancer shows the cells can persist for 6 weeks without evident toxicities, setting the stage for studies that combine HER2-CAR T cells with other immunomodulatory approaches to enhance their expansion and persistence.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

Activity of broad-spectrum T cells as treatment for AdV, EBV, CMV, BKV, and HHV6 infections after HSCT

It remains difficult to treat the multiplicity of distinct viral infections that afflict immunocompromised patients. Adoptive transfer of virus-specific T cells (VSTs) can be safe and effective, but such cells have been complex to prepare and limited in antiviral range. We now demonstrate the feasibility and clinical utility of rapidly generated single-culture VSTs that recognize 12 immunogenic antigens from five viruses (Epstein-Barr virus, adenovirus, cytomegalovirus, BK virus, and human herpesvirus 6) that frequently cause disease in immunocompromised patients. When administered to 11 recipients of allogeneic transplants, 8 of whom had up to four active infections with the targeted viruses, these VSTs proved safe in all subjects and produced an overall 94% virological and clinical response rate that was sustained long-term.

Early transduction produces highly functional chimeric antigen receptor-modified virus-specific T-cells with central memory markers: a Production Assistant for Cell Therapy (PACT) translational application

BACKGROUND

Virus-specific T-cells (VSTs) proliferate exponentially after adoptive transfer into hematopoietic stem cell transplant (HSCT) recipients, eliminate virus infections, then persist and provide long-term protection from viral disease. If VSTs behaved similarly when modified with tumor-specific chimeric antigen receptors (CARs), they should have potent anti-tumor activity. This theory was evaluated by Cruz et al. in a previous clinical trial with CD19.CAR-modified VSTs, but there was little apparent expansion of these cells in patients. In that study, VSTs were gene-modified on day 19 of culture and we hypothesized that by this time, sufficient T-cell differentiation may have occurred to limit the subsequent proliferative capacity of the transduced T-cells. To facilitate the clinical testing of this hypothesis in a project supported by the NHLBI-PACT mechanism, we developed and optimized a good manufacturing practices (GMP) compliant method for the early transduction of VSTs directed to Epstein-Barr virus (EBV), Adenovirus (AdV) and cytomegalovirus (CMV) using a CAR directed to the tumor-associated antigen disialoganglioside (GD2).

RESULTS

Ad-CMVpp65-transduced EBV-LCLs effectively stimulated VSTs directed to all three viruses (triVSTs). Transduction efficiency on day three was increased in the presence of cytokines and high-speed centrifugation of retroviral supernatant onto retronectin-coated plates, so that under optimal conditions up to 88% of tetramer-positive VSTs expressed the GD2.CAR. The average transduction efficiency of early-and late transduced VSTs was 55 ± 4% and 22 ± 5% respectively, and early-transduced VSTs maintained higher frequencies of T cells with central memory or intermediate memory phenotypes. Early-transduced VSTs also had higher proliferative capacity and produced higher levels of TH1 cytokines IL-2, TNF-α, IFN-γ, MIP-1α, MIP-1β and other cytokines in vitro.

CONCLUSIONS

We developed a rapid and GMP compliant method for the early transduction of multivirus-specific T-cells that allowed stable expression of high levels of a tumor directed CAR. Since a proportion of early-transduced CAR-VSTs had a central memory phenotype, they should expand and persist in vivo, simultaneously protecting against infection and targeting residual malignancy. This manufacturing strategy is currently under clinical investigation in patients receiving allogeneic HSCT for relapsed neuroblastoma and B-cell malignancies (NCT01460901 using a GD2.CAR and NCT00840853 using a CD19.CAR).

iCaspase 9 Suicide Gene System

Although cellular therapies may be effective in cancer treatment, their potential for expansion, damage of normal organs, and malignant transformation is a source of concern. The ability to conditionally eliminate aberrant cells in vivo would ameliorate these concerns and broaden the application of cellular therapy. We devised an inducible T-cell safety switch that can be stably and efficiently expressed in human T cells without impairing phenotype, function, or antigen specificity. This system is based on the fusion of human caspase 9 to a modified human FK-binding protein, allowing conditional dimerization using a small-molecule drug. When exposed to a synthetic dimerizing drug, the inducible caspase 9 (iC9) becomes activated and leads to the rapid apoptosis of cells expressing this construct. We have demonstrated the clinical feasibility and efficacy of this approach after haploidentical hematopoietic stem cell transplant (haplo-HSCT). A single dose of a small-molecule drug (AP1903) eliminated more than 90 % of the modified T cells within 30 min after administration and symptoms resolved without recurrence. This system has the potential to broaden the clinical applications of cellular therapy.