Acute and Chronic Lymphocytic Leukemia Induces Exhaustion and Suppresses Metabolic Reprogramming in T Cell Activation

Background. Cancer cells in both hematopoietic and non-hematopoietic malignancies can suppress anti-tumor immunity by inducing a state of T cell exhaustion and hypo-responsiveness. Indeed, T cells in patients with leukemia, such as chronic lymphocytic leukemia (CLL) and acute lymphocytic leukemia (ALL) express exhaustion markers such as PD-1 or TIM-3 and can be poorly responsive. As a result, the T cells not only fail to engage the leukemic cells, but render the host susceptible to infections. The cause of the T cell defect is not known. We have previously shown that T cell metabolism is tightly regulated and sought here to test if chronic T cell stimulation through leukemic cells in human and murine leukemia modulates T cell metabolism to suppress T cell function.

Methods. We established in vitro and in vivo T cell stimulation models using syngeneic pro-B-cell BCR/ABL+ mouse lymphocytic leukemia. We also analyzed freshly collected peripheral blood from 18 CLL patients and from blood or bone marrow aspirates of 3 patients with BCR/ABL+ ALL. Using flow cytometry and radiometric assays, we measured T cell proliferation, IL-2 and IFNγ production, expression of the activation and exhaustion markers CD25, CD71 and PD-1 and changes in T cell glucose metabolism. Lastly, the role of altered glucose uptake was tested using mice with T cell-specific transgenic expression of the glucose transporter 1 (Glut1).

Results. Our studies showed that murine and human lymphocytic leukemia induces chronic T cell stimulation and exhaustion as measured by increased expression of PD-1 and TIM-3. Following T cell receptor stimulation, T cells from leukemic mice and human patients had impaired up regulation of surface activation molecules. Production of IL-2 and IFNγ was reduced and proliferation of leukemia-associated T cells was impaired. Importantly, recruitment of key metabolic genes such as Glut1 was inhibited in both murine and human leukemia-associated T cells. The mechanism of T cell exhaustion was unclear, but additionally to the effects of persistent stimulation, T cells expressed inhibitory receptors and inhibitory ligands were found in the leukemic microenvironment. The nutrient profile of conditioned media from leukemia cells was markedly altered, and the conditioned media prevented mouse T cell activation and proliferation. Next we questioned whether altered glucose metabolism contributed to T cell functional defects in lymphoid leukemia. We used mice expressing transgenic Glut1 in T cells to determine the effects of chronic stimulation through leukemia cells on the phenotypes of T cells. These Glut1-transgenic T cells resisted exhaustion and partially maintained function despite the presence of leukemia.

Conclusion. Results of our studies indicate that lymphocytic leukemia induces a chronic stimulation leading to T cell exhaustion and impaired T cell function in part through inhibition of glucose metabolism.