Impaired Metabolic Fitness in T Cells in Chronic Lymphocytic Leukemia

Quiescent T cells primarily use oxidative phosphorylation (OXPHOS) to generate ATP, while in response to activation T cells switch to high rates of aerobic glycolysis, also known as the Warburg effect. While less efficient in overall ATP production, this switch to aerobic glycolysis is essential to produce cellular biomass needed for proliferation, and is required for T cell effector functions. In chronic lymphocytic leukemia (CLL) acquired T cell dysregulation occurs independent of treatment with functional impairment and exhaustion of T cells. As tumor-imposed metabolic restrictions in mouse models can mediate T cell hyporesponsiveness during cancer, we hypothesized that in the context of CLL T cell metabolism might be altered.

Comparison of gene expression profiles of T cells from patients with CLL and age-matched healthy donors (HD) revealed a highly significant increase in the expression of genes in the OXPHOS pathway (P=3.4*10^-15) in the CD8 T cell compartment. In corroboration with these array results, we found that in naïve CD8 T cells in CLL, mitochondrial mass and respiration were significantly increased. In addition, increased mitochondrial ROS production was observed in the naïve CD8 T cell subset.

Using Seahorse EFA technology on sorted CD8 T cells from CLL and age-matched HD, we found increased oxygen consumption rates in CLL derived CD8 T cells, indicating increased OXPHOS, while the spare respiratory capacity was lower in these cells, indicating impeded ability to cope with cellular stress. Extracellular acidification rates (ECAR; indicating glycolysis), and uptake of fluorescently labeled glucose were similar in CD8 T cells from CLL patients and HD.

Next, we studied the metabolic plasticity of CLL derived T cells by stimulation of PBMCs from CLL patients and age-matched HD using anti-CD3/CD28 antibodies. Two days after stimulation, CLL derived T cells had diminished expression of activation markers CD25 and CD38, which correlated with reduced uptake of fluorescently labeled glucose. Moreover, preliminary Seahorse analysis of the immediate response to stimulation with anti-CD3/CD28 showed a reduced increase in ECAR in CLL derived CD8 T cells, indicating an impairment of the glycolytic switch in these cells.

Taken together, these results demonstrate that the metabolic fitness of CD8 T cells is impaired in CLL at resting state and after activation. Boosting T cell metabolism in CLL might therefore improve existing immunotherapies in CLL such as CAR-T cell therapy.

This work is funded by VENI and VIDI grants from the Dutch Organisation for Scientific Research, and a Marie Curie Career Integration Grant from the European Union.