Manufacture of CD22 CAR T cells following positive versus negative selection results in distinct cytokine secretion profiles and γδ T cell output

Chimeric antigen receptor T cells (CART) have demonstrated curative potential for hematological malignancies, but the optimal manufacturing has not yet been determined and may differ across products. The first step, T cell selection, removes contaminating cell types that can potentially suppress T cell expansion and transduction. While positive selection of CD4/CD8 T cells after leukapheresis is often used in clinical trials, it may modulate signaling cascades downstream of these co-receptors; indeed, the addition of a CD4/CD8-positive selection step altered CD22 CART potency and toxicity in patients. While negative selection may avoid this drawback, it is virtually absent from good manufacturing practices. Here, we performed both CD4/CD8-positive and -negative clinical scale selections of mononuclear cell apheresis products and generated CD22 CARTs per our ongoing clinical trial (NCT02315612NCT02315612). While the selection process did not yield differences in CART expansion or transduction, positively selected CART exhibited a significantly higher in vitro interferon-γ and IL-2 secretion but a lower in vitro tumor killing rate. Notably, though, CD22 CART generated from both selection protocols efficiently eradicated leukemia in NSG mice, with negatively selected cells exhibiting a significant enrichment in γδ CD22 CART. Thus, our study demonstrates the importance of the initial T cell selection process in clinical CART manufacturing.

CD19/22 CAR T cells in children and young adults with B-ALL: phase 1 results and development of a novel bicistronic CAR

Remission durability following single-antigen targeted chimeric antigen receptor (CAR) T-cells is limited by antigen modulation, which may be overcome with combinatorial targeting. Building upon our experiences targeting CD19 and CD22 in B-cell acute lymphoblastic leukemia (B-ALL), we report on our phase 1 dose-escalation study of a novel murine stem cell virus (MSCV)-CD19/CD22-4-1BB bivalent CAR T-cell (CD19.22.BBζ) for children and young adults (CAYA) with B-cell malignancies. Primary objectives included toxicity and dose finding. Secondary objectives included response rates and relapse-free survival (RFS). Biologic correlatives included laboratory investigations, CAR T-cell expansion and cytokine profiling. Twenty patients, ages 5.4 to 34.6 years, with B-ALL received CD19.22.BBζ. The complete response (CR) rate was 60% (12 of 20) in the full cohort and 71.4% (10 of 14) in CAR-naïve patients. Ten (50%) developed cytokine release syndrome (CRS), with 3 (15%) having ≥ grade 3 CRS and only 1 experiencing neurotoxicity (grade 3). The 6- and 12-month RFS in those achieving CR was 80.8% (95% confidence interval [CI]: 42.4%-94.9%) and 57.7% (95% CI: 22.1%-81.9%), respectively. Limited CAR T-cell expansion and persistence of MSCV-CD19.22.BBζ compared with EF1α-CD22.BBζ prompted laboratory investigations comparing EF1α vs MSCV promoters, which did not reveal major differences. Limited CD22 targeting with CD19.22.BBζ, as evaluated by ex vivo cytokine secretion and leukemia eradication in humanized mice, led to development of a novel bicistronic CD19.28ζ/CD22.BBζ construct with enhanced cytokine production against CD22. With demonstrated safety and efficacy of CD19.22.BBζ in a heavily pretreated CAYA B-ALL cohort, further optimization of combinatorial antigen targeting serves to overcome identified limitations (www.clinicaltrials.gov #NCT03448393).

Abstract LB103: Novel DNA-based-T-cell-activation for the generation of chimeric antigen receptor T cells with enhanced anti-leukemia cytotoxicity

Chimeric antigen receptor (CAR)-T cell therapy has shown remarkable results in the treatment of hematological malignancies. However, several challenges remain, including achieving predictable efficacy and safety profiles and extending this approach to solid tumors. As such, the development of approaches that generate engineered T cells with superior persistence and efficacy are needed. Currently, the generation of CAR-T requires that they be activated and expanded ex vivo, generally via beads coated with anti-CD3/anti-CD28 mAbs. T cell activation provides three fundamental signals; (i) primary triggering of TCR signals; (ii) secondary co-stimulatory signals and, (iii) synthesis of cytokines to direct T cell expansion and differentiation. We hypothesize that a CAR-T response can be modulated by tuning the: (i) pattern, (ii) magnitude and, (iii) duration of the input T cell activation signals. To this end, we used a novel, soluble, tunable activation platform based on DNA hybridization - utilizing concatenated single stranded DNA (ssDNA) polymers to cluster complementary oligonucleotide-modified antibodies targeted at T-cell surface receptors. This DNA-Based-T-cell-Activation (DBTA) platform was compared with conventional bead-bound CD3/CD28 antibodies (Dynabead) in the generation and function of T cells engineered to express a CD19-targeted CAR harboring a 4-1BB co-stimulatory domain. The two methods did not result in any significant differences in CAR-T expansion nor in memory/activation phenotypes. Notably, though, these cells exhibited higher cytokine secretion in response to CAR stimulation, and in vitro killing of DBTA-generated CART was significantly higher than that of bead-activated CART. Indeed, only the former showed cytotoxicity against Nalm6 leukemic cells expressing low levels of the CD19 target antigen CART. Furthermore, in an in vivo NSG model with Nalm6 leukemia, the adoptive transfer of low numbers of DBTA-generated CART (2e6) resulted in leukemia eradication and delayed leukemia relapse. Mechanistically, the enhanced function of DBTA-generated CAR was associated with increased metabolic activity in the pre-infusion product. These results suggest that calibrating the activation potential of CAR-T cells can result in the generation of a product with enhanced therapeutic potential.

Citation Format: Mehdi Benzaoui, Sooraj R. Achar, Vandana Keskar, Anup Sood, Brian M. Davis, Steven L. Highfill, Grégoire Altan-Bonnet, Christopher D. Chien, Naomi Taylor. Novel DNA-based-T-cell-activation for the generation of chimeric antigen receptor T cells with enhanced anti-leukemia cytotoxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB103.