Obesity Attenuates CAR T-Cell Function in Pediatric B-Cell Acute Lymphoblastic Leukemia

Obesity is associated with higher rates of relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) in part due to tumor-promoting inflammation, altered drug pharmacokinetics/pharmacodynamics, and increased treatment-related adverse events in patients with increased adiposity. Therefore, a large number of patients with this cancer-promoting comorbidity will be eligible for immunotherapy. Given the substantial immunological changes associated with obesity, research focusing on the impact of obesity on cancer immunotherapy is steadily increasing. These efforts have birthed the concept of the “obesity paradox” where obesity has been shown to increase the efficacy of immunotherapy in preclinical and clinical studies. However, these studies largely focused on how obesity impacts immune checkpoint blockade therapy targeting solid cancers; whereas, its impact on other forms of cancer immunotherapies is still heavily understudied. Here we show that obesity-induced functional defects in T-cells that affect the functionality of engineered chimeric antigen receptor (CAR) T-cells in the context of targeting B-ALL.

Transcriptomic analysis of T-cells derived from pediatric patients with obesity and B-ALL revealed that T-cells express significantly lower levels of genes encoding T-cell receptor components, coreceptors (CD4 and CD8), T-cell receptor associated tyrosine kinases (FYN), and cytolytic genes (PRF1) compared to results obtained from healthy donors and lean pediatric donors with B-ALL. These transcriptional signatures translated to dysfunctional pediatric patient-derived T-cells from donors with obesity, where we observed that ex vivo stimulation resulted in defective cytokine production (IFN-γ/TNF-α) and attenuated upregulation of cytolytic proteins (perforin/granzyme B).

Engineering CAR T-cells from pediatric donors with B-ALL revealed that the body mass index (BMI) of the patient did not impact the post-transduction viability of CAR T-cells nor the percentage of CAR-expressing CAR T-cells. However, CAR T-cells generated from patients with obesity expressed higher surface levels of immune checkpoint proteins (Tim-3/Lag-3/Pd-1) and failed to consume glycine and alanine, which are amino acids critical for T-cell proliferation and function. Furthermore, co-culturing patient-derived CAR T-cells with human B-ALL cell lines revealed that CAR T-cells generated from pediatric donors with obesity expressed lower protein levels of granzyme B which correlated with a reduction in the killing efficiency of leukemia cells at all effector to target (E:T) cell ratios tested. These results may explain our previously reported retrospective results, where pediatric and young adult patients with obesity and relapsed/refractory B-ALL experienced significant reductions in progression-free survival and overall survival when treated with commercially manufactured Tisagenlecleucel (Ross et al., 2022 ASH Conference). However, obesity may further complicate the efficacy of CAR T-cell therapy in pediatric patients due to our observation that the obese bone marrow microenvironment reduces CD19 surface expression on human B-ALL cells.

Importantly, we were able to recapitulate these findings using murine models of diet-induced obesity. In these studies, CAR T-cells engineered from obese compared to lean mice displayed the same phenotypes as the patient-derived samples including no changes in CAR T-cell viability, similar CAR expression in engineered products, and defective cytolysis of leukemia cells in co-culture assays with CAR T-cells and murine B-ALL cells, particularly at higher E:T ratios. In syngeneic studies conducted in lean mice transplanted with B-ALL cells, we found treatment with CAR T-cells engineered from lean mice conferred complete protection from B-ALL; whereas, treating lean mice with CAR T-cells made from obese mice resulted in over 60 percent of the mice succumbing to disease within 2 months.

Overall, our clinical and pre-clinical findings demonstrate that obesity impairs CD19-directed CAR T-cell therapy in pediatric B-ALL largely due to cell autonomous defects in T-cells which cannot by overcome by the introduction of CD3/CD28-expressing CARs. Furthermore, the efficacy of CAR T-cell therapy is negatively impacted by adipocyte-mediated downregulation of CD19 on bone marrow-derived human B-ALL cells.