P612: CHRONIC LYMPHOCYTIC LEUKEMIA (CLL)-DERIVED T-CELLS HAVE DISTURBED FATTY ACID METABOLISM, POSSIBLY CONTRIBUTING TO T-CELL DYSFUNCTION

Abstract

Background: T-cells from CLL patients are dysfunctional and display reduced activation, proliferation and cytotoxicity upon in-vitro activation. Whilst the role of glucose metabolism in activated T cells is extensively studied, the contribution of other energy sources is less clear. Fatty acid (FA) and lipid uptake in T cells involves the scavenger membrane transporter CD36. CD36-mediated lipid transport has been identified to (metabolically) modulate intratumoral T cells (both Treg and cytotoxic CD8+ T cells). However, lipid metabolism and a potential role for CD36 has not been studied in the context of T cell dysfunction in CLL Aims: To examine the role of FA metabolism and the fatty acid transporter CD36 in acquired T-cell dysfunction in CLL. Methods: Untreated CLL patients with a white blood cell count (WBC) greater than 20×109 cells/L and, as control, age-matched healthy donors (HD) were studied. T cells were analyzed by flow cytometry, confocal microscopy or extracellular flux analysis (Seahorse), either directly after thawing or after a 2 day culture with or without αCD3/αCD28 antibodies. Results: Analysis of CD36+ vs CD36- CD4 and CD8 T-cells from HD revealed that CD36+ cells had higher long-chain fatty acid (LCFA) and glucose uptake, and higher expression of the glucose transporter GLUT-1 and the rate-limiting mitochondrial FA transporter CPT1α (Fig. 1A). The cells expressing CD36 were also more likely to increase their CD25 expression and mitochondrial mass upon stimulation, indicating a metabolic and functional advantage potentially conferred by the surface expression of CD36. The absolute amount and percentage of T cells (CD4 and CD8) expressing FA transporter CD36 was lower in CLL T-cells as compared to HD (Fig. 1B). The levels of LCFA uptake and expression of CPT1α were comparable, indicating that the lower amount of CD36 might successfully cater to the FA demands of resting CLL T cells(Fig. 1C). However, while stimulation of HD T-cells markedly upregulated CD36 abundance, LCFA uptake and CPT1α, concomitantly with the activation marker CD25, CLL-derived T-cells failed to mount a similar response (Fig. 1D). This lack of induction of CD36 expression was also observed in CLL-derived T cells that increased CD25, which implies that this response is independent of T-cell activation. The transcription factors peroxisome proliferator-activated receptors (PPAR) α and γ are important regulators of FA metabolism. We observed reduced expression of these transcription factors in resting CLL T cells. However, distinct from CD36, CLL T cells were indistinguishable from HD T-cells in their ability to increase levels of both PPARα and PPARγ upon stimulation, indicating that alternative mechanisms might be implicated in the regulation of CD36 and FA metabolism in CLL T cells. Image:Summary/Conclusion: Collectively, our results show that disturbances in FA metabolism are present on multiple levels in CLL T cells and that lack of LCFA uptake into CLL T-cells could represent a limiting step in FA metabolism. We also highlight CD36+ cells as a metabolically distinct T-cell subtype that is largely absent in CLL T-cells, independently of their activation status. We are currently investigating strategies to increase CD36 expression and FA metabolism in general in CLL T cells, which could ameliorate CLL T cell dysfunction and provide targets to improve autologous T cell therapies.