GLUT1 Overexpression Enhances 19-28z CAR-T Cell Expansion and Metabolic Fitness

The tumor microenvironment presents many obstacles to effective CAR T cell therapy. One of these obstacles is glucose competition from tumor and myeloid cells to the detriment of CAR T cells. We hypothesize here that CAR T cells with elevated levels of glucose transporter are better fit under such conditions, which will result in improved therapeutic efficacy.

We overexpressed either GLUT1 or GLUT3 in CD19-targeted CAR T cells engineered with a clinically validated CAR (19-28z). GLUT1 is ubiquitously expressed in tissues and GLUT3 has a higher affinity for glucose. Upon in vitro antigen stimulation, 1928z-GLUT1 and 1928z-GLUT3 showed greater enrichment of CAR+ T cells and underwent more cell divisions than control 1928z-LNGFR under glucose-limiting conditions. In repetitive antigen stimulation assays, 1928z-GLUT1 expanded significantly more than 1928z-LNGFR cells in 10 mM or 5 mM glucose medium. Surprisingly, 1928z-GLUT3 CAR T cells faired markedly less well than 1928z-LNGFR controls, associated with reduced viability of 1928z-GLUT3 CAR T cells after 2 or 3 exposures to antigen. In the NALM6 acute lymphoblastic leukemia model, low-dose CAR T cell treatment with 1928z-LNGFR and 1928z-GLUT3 did not curtail rapid tumor progression, while 1928z-GLUT1 CAR T cells significantly increased survival. More abundant CAR+ T cells were found in the bone marrow and spleen of 1928z-GLUT1-treated mice. Interestingly, we observed consistent increases in CD62L+CD45RA+ Tscm population in 1928z-GLUT1 cells, including both CD8 and CD4 T cells. We flow-sorted CAR T cells from treated mice and performed SMARTer RNA-seq. GLUT1, but not GLUT3, significantly upregulated TCF7 and genes encoding glycolytic enzymes and electron transport chain, indicating that GLUT1 overexpression enhances both glycolysis and oxidative phosphorylation.

To further test GLUT1-CAR-T function in tumor lines with high levels of glucose transporter, we generated a renal cell carcinoma (RCC) patient-derived xenograft (PDX) with ectopic expression of human CD19. CAR-T cells were repetitively stimulated with the RCC PDX under titrated glucose concentrations. 1928z-GLUT1 significantly improved CAR T cell viability compared to 1928z-LNGFR in low glucose conditions. The expansion of GLUT1 CAR-T cells in 10 mM and 5 mM glucose also surpassed that of LNGFR CAR-T cells. In vivo, 1928z-GLUT1-treated mice showed significantly less tumor burden than 1928z-LNGFR-treated mice.

Overall, we developed a novel strategy for enhancing the metabolic fitness of 1928z CAR-T cells by constitutively overexpressing GLUT1. GLUT1 but not GLUT3 enhances glycolysis and oxidative phosphorylation in CAR-T cells, which sustains T-cell expansion and increases therapeutic efficacy. This strategy is under investigation with other CAR formats.