Restoration of LAT signaling via the ALA-CART platform promotes metabolic resiliency and persistence of AML CAR T cells

Despite therapeutic advancements, the majority of patients with relapsed and/or refractory (r/r) acute myeloid leukemia (AML) have very poor prognoses and limited treatment options. While Chimeric Antigen Receptor (CAR) T cell therapy has transformed the treatment of r/r B-cell acute lymphoblastic leukemia (ALL), inducing remissions in up to 90% of patients, yet clinical trials of 2 nd generation CAR T cells for patients with r/r AML have not replicated this success. Post-CAR T cell relapses in ALL are common and limit the long term efficacy of this therapy. Mechanisms driving ALL relapses after CAR T cells, such as short duration of activity and antigen modulated escape, have illuminated vulnerabilities of 2 nd generation CAR T cells, such as exhaustion, poor persistence, and low antigen sensitivity. The mechanisms underlying AML progression after CAR T cells are not well defined, however, it is likely that similar barriers must be overcome to improve CAR T cell responses in patients with r/r AML. We recently demonstrated the Linker for Activation of T cells (LAT) is inefficiently engaged in ALL-directed CAR T cells, particularly when antigen levels are low. Through a novel Adjunctive LAT-Activating CAR T (ALA-CART) platform, LAT activity and downstream signaling were restored and ALA-CART cells demonstrated enhanced potency, expansion, and persistence. We hypothesized that CD33-directed ALA-CART cells would similarly show improved potency and persistence in pre-clinical models of AML. Despite exhibiting decreased effector function in vitro, 33ALA-CART cells demonstrated increased efficacy in multiple AML xenograft models. 33ALA-CART cells had greater in vivo expansion and were effective at lower doses than CD33BBz CAR T cells. 33ALA-CART cells showed similar potency as CD33-28z CAR T cells, however, demonstrated enhanced persistence relative to both CD33BBz and CD33-28z CAR T cells. In rechallenge experiments, 33ALA-CART cells demonstrated enhanced expansion and leukemia clearance. Interestingly, the enhanced persistence of 33ALA-CART was strongly correlated with increased mitochondrial activity, a feature associated with long-lived memory T cell subsets and persistence. Consistent with this, RNA-sequencing analysis demonstrates that ALA-CART cells have increased potential for mitochondrial biogenesis and a reduced capacity for glycolysis relative to 2 nd generation CAR T cells. Together, these data suggest that increased signaling through LAT results in enhanced metabolic capacity, potentially contributing to the enhanced proliferative, functional, and persistence capacity of 33ALA-CART cells in vivo. Through restoring LAT activity and downstream signaling, the ALA-CART platform provides a rational strategy to enhance multiple facets of CAR T cell function and represents a promising approach to improve the efficacy of AML-directed CAR T cell therapy.