BACKGROUND.T cells expressing antigen-specific chimeric antigen receptors (CARs) improve outcomes for CD19-expressing B cell malignancies. We evaluated a human application of T cells that were genetically modified using the Sleeping Beauty (SB) transposon/transposase system to express a CD19-specific CAR. METHODS.T cells were genetically modified using DNA plasmids from the SB platform to stably express a second-generation CD19-specific CAR and selectively propagated ex vivo with activating and propagating cells (AaPCs) and cytokines. Twenty-six patients with advanced non-Hodgkin lymphoma and acute lymphoblastic leukemia safely underwent hematopoietic stem cell transplantation (HSCT) and infusion of CAR T cells as adjuvant therapy in the autologous (n = 7) or allogeneic settings (n = 19).RESULTS. SB-mediated genetic transposition and stimulation resulted in 2,200-to 2,500-fold ex vivo expansion of genetically modified T cells, with 84% CAR expression, and without integration hotspots. Following autologous HSCT, the 30-month progression-free and overall survivals were 83% and 100%, respectively. After allogeneic HSCT, the respective 12-month rates were 53% and 63%. No acute or late toxicities and no exacerbation of graft-versus-host disease were observed. Despite a low antigen burden and unsupportive recipient cytokine environment, CAR T cells persisted for an average of 201 days for autologous recipients and 51 days for allogeneic recipients.CONCLUSIONS. CD19-specific CAR T cells generated with SB and AaPC platforms were safe, and may provide additional cancer control as planned infusions after HSCT. These results support further clinical development of this nonviral gene therapy approach.

Genetic modification of clinical-grade T cells is undertaken to augment function, including redirecting specificity for desired antigen. We and others have introduced a chimeric antigen receptor (CAR) to enable T cells to recognize lineage-specific tumor antigen, such as CD19, and early-phase human trials are currently assessing safety and feasibility. However, a significant barrier to next-generation clinical studies is developing a suitable CAR expression vector capable of genetically modifying a broad population of T cells. Transduction of T cells is relatively efficient but it requires specialized manufacture of expensive clinical grade recombinant virus. Electrotransfer of naked DNA plasmid offers a cost-effective alternative approach, but the inefficiency of transgene integration mandates ex vivo selection under cytocidal concentrations of drug to enforce expression of selection genes to achieve clinically meaningful numbers of CAR +

Improving the therapeutic efficacy of T cells expressing a chimeric antigen receptor (CAR) represents an important goal in efforts to control B-cell malignancies. Recently an intrinsic strategy has been developed to modify the CAR itself to improve T-cell signaling. Here we report a second extrinsic approach based on altering the culture milieu to numerically expand CAR+ T cells with a desired phenotype. For, the addition of IL-21 to tissue culture improves CAR-dependent T-cell effector functions. We used electrotransfer of Sleeping Beauty (SB) system to introduce a CAR transposon and selectively propagate CAR+ T cells on CD19+ artificial antigen-presenting cells (aAPC). When IL-21 was present, there was preferential numeric expansion of CD19-specific T cells which lysed and produced IFN-γ in response to CD19. Populations of these numerically expanded CAR+ T cells displayed an early memory surface phenotype characterized as CD62L+CD28+ and a transcriptional profile of naïve T cells. In contrast, T cells propagated with only exogenous IL-2 tended to result in an overgrowth of CD19-specific CD4+ T cells. Furthermore, adoptive transfer of CAR+ T cells cultured with IL-21 exhibited improved control of CD19+ B-cell malignancy in mice. To provide coordinated signaling to propagate CAR+ T cells, we developed a novel mutein of IL-21 bound to the cell surface of aAPC that replaced the need for soluble IL-21. Our findings demonstrate that IL-21 can provide an extrinsic reprogramming signal to generate desired CAR+ T cells for effective immunotherapy.

Adoptive transfer of T cells expressing a CD19-specific chimeric antigen receptor (CAR) is being evaluated in multiple clinical trials. Our current approach to adoptive immunotherapy is based on a second generation CAR (designated CD19RCD28) that signals through a CD28 and CD3-ζ endodomain. T cells are electroporated with DNA plasmids from the Sleeping Beauty (SB) transposon/transposase system to express this CAR. Stable integrants of genetically modified T cells can then be retrieved when co-cultured with designer artificial antigen presenting cells (aAPC) in the presence of interleukin (IL)-2 and 21. Here, we reveal how the platform technologies of SB-mediated transposition and CAR-dependent propagation on aAPC were adapted for human application. Indeed, we have initiated clinical trials in patients with high-risk B-lineage malignancies undergoing autologous and allogeneic hematopoietic stem-cell transplantation (HSCT). We describe the process to manufacture clinical grade CD19-specific T cells derived from healthy donors. Three validation runs were completed in compliance with current good manufacturing practice for Phase I/II trials demonstrating that by 28 days of co-culture on γ-irradiated aAPC ∼1010 T cells were produced of which >95% expressed CAR. These genetically modified and propagated T cells met all quality control testing and release criteria in support of infusion.

Nonviral integrating vectors can be used for expression of therapeutic genes. piggyBac (PB), a transposon= transposase system, has been used to efficiently generate induced pluripotent stems cells from somatic cells, without genetic alteration. In this paper, we apply PB transposition to express a chimeric antigen receptor (CAR) in primary human T cells. We demonstrate that T cells electroporated to introduce the PB transposon and transposase stably express CD19-specific CAR and when cultured on CD19 þ artificial antigen-presenting cells, numerically expand in a CAR-dependent manner, display a phenotype associated with both memory and effector T cell populations, and exhibit CD19-dependent killing of tumor targets. Integration of the PB transposon expressing CAR was not associated with genotoxicity, based on chromosome analysis. PB transposition for generating human T cells with redirected specificity to a desired target such as CD19 is a new genetic approach with therapeutic implications.

The Sleeping Beauty (SB) transposon/transposase DNA plasmid system is used to genetically modify cells for long-term transgene expression. We adapted the SB system for human application and generated T cells expressing a chimeric antigen receptor (CAR) specific for CD19. Electro-transfer of CD19-specific SB DNA plasmids in PBMC and propagation on CD19+ artificial antigen presenting cells (aAPC) was used to numerically expand CD3+ T cells expressing CAR. By Day 28 of co-culture >90% of expanded CD3+ T cells expressed CAR. CAR+ T cells specifically killed CD19+ target cells and consisted of subsets expressing biomarkers consistent with central memory, ieffector memory, and effector phenotypes. CAR+ T cells contracted numerically in the absence of CD19 antigen, did not express SB11 transposase, and maintained a polyclonal TCRVα and TCRVβ repertoire. Quantitative fluorescence in situ hybridization (Q-FISH) revealed that CAR+ T cells preserved telomere length. Quantitative PCR (Q-PCR) and FISH showed CAR transposon integrated on average once per T-cell genome. CAR+ T cells in peripheral blood can be detected by Q-PCR at a sensitivity of 0.01%. These findings lay the groundwork as the basis of our first-in-human clinical trials of the non-viral SB system for the investigational treatment of CD19+ B-cell malignancies (currently under three INDs #: 14193, 14577, and 14739).

The potency of clinical-grade T cells can be improved by combining gene therapy with immunotherapy to engineer a biologic product with the potential for superior (i) recognition of tumor-associated antigens (TAAs), (ii) persistence after infusion, (iii) potential for migration to tumor sites, and (iv) ability to recycle effector functions within the tumor microenvironment. Most approaches to genetic manipulation of T cells engineered for human application have used retrovirus and lentivirus for the stable expression of CAR [1][2][3] . This approach, although compliant with current good manufacturing practice (GMP), can be expensive as it relies on the manufacture and release of clinical-grade recombinant virus from a limited number of production facilities. The electro-transfer of nonviral plasmids is an appealing alternative to transduction since DNA species can be produced to clinical grade at approximately 1/10 th the cost of recombinant GMP-grade virus. To improve the efficiency of integration we adapted Sleeping Beauty (SB) transposon and transposase for human application [4][5][6][7][8] . Our SB system uses two DNA plasmids that consist of a transposon coding for a gene of interest (e.g. 2 nd generation CD19-specific CAR transgene, designated CD19RCD28) and a transposase (e.g. SB11) which inserts the transgene into TA dinucleotide repeats [9][10][11] . To generate clinically-sufficient numbers of genetically modified T cells we use K562-derived artificial antigen presenting cells (aAPC) (clone #4) modified to express a TAA (e.g. CD19) as well as the T cell costimulatory molecules CD86, CD137L, a membrane-bound version of interleukin (IL)-15 (peptide fused to modified IgG4 Fc region) and CD64 (Fc-γ receptor 1) for the loading of monoclonal antibodies (mAb) 12 . In this report, we demonstrate the procedures that can be undertaken in compliance with cGMP to generate CD19-specific CAR + T cells suitable for human application. This was achieved by the synchronous electro-transfer of two DNA plasmids, a SB transposon (CD19RCD28) and a SB transposase (SB11) followed by retrieval of stable integrants by the every-7-day additions (stimulation cycle) of γ-irradiated aAPC (clone #4) in the presence of soluble recombinant human IL-2 and IL-21 13. Typically 4 cycles (28 days of continuous culture) are undertaken to generate clinically-appealing numbers of T cells that stably express the CAR. This methodology to manufacturing clinical-grade CD19-specific T cells can be applied to T cells derived from peripheral blood (PB) or umbilical cord blood (UCB). Furthermore, this approach can be harnessed to generate T cells to diverse tumor types by pairing the specificity of the introduced CAR with expression of the TAA, recognized by the CAR, on the aAPC.

4291 Natural Killer (NK) cells have important and potent innate immunoregulatory and immune surveillance functions against tumor. The paradoxical coexistence of tumors and anti-tumor immune cells (“Hellstrom Paradox”) may in part be explained by the pathophysiology of the “hostile” tumor microenvironment which suppress immune-cell function, such as hypoxia, low pH, low tissue glucose, and the presence of immunosuppressive cytokines and metabolites. However, the effect of the malignant environment on the ability of NK cells to infiltrate tumor and exhibit effector function is largely unknown. Therefore, we investigated the ability of NK cells to operate under conditions of hypoxia. Importantly, NK cells showed a 1,000-fold reduction in proliferative capacity when grown under chronic hypoxia (4 weeks of 1% O2). In addition, there was a corresponding decrease in cytotoxicity as revealed by chromium release assay. This was in contrast to autologous T cells which could numerically expand under corresponding growth conditions. Expression profiling uncovers profound upregulation of hypoxia-inducible genes such as EGLN1(9.9x), EGLN3(52x), LDHA(11.5x), SLC2A1(30.5x), PDK1(16.8x), VEGFA(286x) and BNIP3(138x) in hypoxic NK cells. Protein expression confirmed these changes, as NK cells under normoxic culture produced 520 nmoles/million cells of ATP, while those under hypoxic culture managed only 100 nmoles/million cells. This is consistent with a bioenergetic switch from oxidative phosphorylation to glycosis resulting from PDK1 upregulation. NK cells in hypoxia produced 61 pg/mL of VEGF compared to 1480 pg/mL for NK cells in normoxia (20% O2), as determined by ELISA. The inability of NK cells to propagate under conditions of hypoxia may be due to a drop in mitochondrial content we observed when cells were exposed to chronic hypoxia, a potential mitophagic effects of BNIP3 upregulation. In addition to the poor proliferative capacity of NK cells under hypoxia, we also noted the loss of CD56 expression on hypoxic NK cells which is associated with loss of cytotoxicity. Sequence analysis reveals that miR-210 can bind to the 3′UTR of CD56 mRNA, targeting it for degradation. Therefore, we investigated whether miR-210 levels are upregulated in hypoxic NK cells and found that increased presence correlated with loss of CD56 expression. This leads to the conclusion that NK-cell immunotherapy may be improved by downregulating miR-210 levels. Indeed, our findings help shape strategies for obtaining robust and sustained NK-cell effector function for adoptive immunotherapy in the hypoxic tumor microenvironment. Disclosures: No relevant conflicts of interest to declare.