Murine pre–B-cell ALL induces T-cell dysfunction not fully reversed by introduction of a chimeric antigen receptor

Abstract

Adoptive transfer of patient-derived T cells modified to express chimeric antigen receptors (CARTs) has demonstrated dramatic success in relapsed/refractory pre-B-cell acute lymphoblastic leukemia (ALL), but response and durability of remission requires exponential CART expansion and persistence. Tumors are known to affect T-cell function, but this has not been well studied in ALL and in the context of chimeric antigen receptor (CAR) expression. Using TCF3/PBX1 and MLL-AF4-driven murine ALL models, we assessed the impact of progressive ALL on T-cell function in vivo. Vaccines protect against TCF3/PBX1.3 but were ineffective when administered after leukemia injection, suggesting immunosuppression induced early during ALL progression. T cells from leukemia-bearing mice exhibited increased expression of inhibitory receptors, including PD1, Tim3, and LAG3, and were dysfunctional following adoptive transfer in a model of T-cell receptor (TCR)-dependent leukemia clearance. Although expression of inhibitory receptors has been linked to TCR signaling, pre-B-cell ALL induced inhibitory receptor expression, at least in part, in a TCR-independent manner. Finally, introduction of a CAR into T cells generated from leukemia-bearing mice failed to fully reverse poor in vivo function.

Perforin-deficient CAR T cells recapitulate late-onset inflammatory toxicities observed in patients

“…Here, we examined the role of granule-mediated cytotoxicity in CAR T cell responses and toxicity by evaluating the function of perforin-deficient CAR T cells in a syngeneic murine model of anti-CD19 CAR T cell therapy against pre-B cell acute lymphoblastic leukemia (pre-B ALL) (23)(24)(25)(26). We found that perforin was not required for leukemia clearance by CAR T cells but was critical for CAR T cell cytotoxic potency.…”

“…The need for perforin-deficient donor T cells to model HLH-like toxicities may reflect a limitation of the syngeneic murine model using mice in a stardard clean facility: the vast majority of nonmodified T cells in laboratory mice are naive and their myeloid cells are less activated (67), which does not mimic a human who has been exposed to numerous antigens (67)(68)(69). Patients with multiply relapsed leukemia also have been exposed to numerous chemotherapies, corticosteroids, and other immunosuppressants, and their T cells are probably dysfunctional (25). We hypothesize that perforindeficient CAR T cells with a decreased ability to control leukemia at early time points may more accurately reflect the human CAR T cells derived from patients who have suboptimal T cell function.…”

Differential Depletion of Bone Marrow Resident B-ALL after Systemic Administration of Endosomal TLR Agonists

“…The low mutation burden and poor antigen presentation capacity of ALL blasts, in concert with a rapid induction of T cell dysfunction by progressive leukemia may contribute to the failure of immune therapy in many ALL patients [22,24,28,29,38]. Our results indicate that TLR agonists, in particular CpG ODN, can exert sufficient immunomodulatory activity to overcome these inhibitory mechanisms to eliminate primary B-ALL cells in the absence of a strong rejection antigen.…”

A good response of refractory mantel cell lymphoma to haploidentical CAR T cell therapy after failure of autologous CAR T cell therapy

“…CAR T cells from complete-responding patients with CLL were enriched in memory-related genes, including IL-6/STAT3 signatures, whereas T cells from non-responders upregulated programs involved in effector differentiation, glycolysis, exhaustion and apoptosis. T cells from leukemia-bearing mice presented increased expression of inhibitory co-receptors including programmed cell death protein 1 (PD1), Tim3 and LAG3, and introduction of a CAR into these T cells failed to fully reverse poor in vivo function [11]. However, T cells from a haplo-source of healthy donor were not affected by leukemia before infusion and may express lower levels of the inhibitory molecules than T cells from the lymphoma patient.…”