PS1134 CHRONIC LYMPHOCYTIC LEUKEMIA CELLS IMPAIR MITOCHONDRIAL FITNESS IN T CELLS AND IMPEDE CAR T CELL EFFICACY
Authors: Van Bruggen J.A. C. , Martens A.W. J. , Fraietta J.A. , Hofland T. , Tonino S. , Eldering E. , Levin M.‐D. , Siska P.J. , Endstra S. , Rathmell J.C. , June C.H. , Porter D.L. , Melenhorst J.J. , der van Windt G.J. W. , Kater A.P. 
Published: June 2019

Background:Chronic lymphocytic leukemia (CLL) patients acquire T cell dysfunction through a yet unresolved mechanism, impeding efficacy of immunotherapeutic strategies. As T cell function and development share an intricate relationship with T cell metabolism, we hypothesized that CLL cells impose a reduction in mitochondrial fitness and altered glucose metabolism on T cells, which may underlie the acquired T cell dysfunction.Aims:We aim to elucidate the underlying mechanism of T cell dysfunction in CLL and intend to resolve metabolic dysfunction via pharmacological intervention.Methods:We selected untreated CLL patients with a WBC greater than 20 × 109 cells/L. Age‐matched healthy donors (HD) were used as controls. CAR T cells were obtained from the University of Pennsylvania, generated from relapsed/refractory (R/R) CLL patients enrolled in two clinical trials of single‐agent CTL019 therapy (registered at clinicaltrials.gov; NCT01029366, and NCT01747486). We either directly analyzed T cells by flow cytometry or XF96 Seahorse, or after a 2 day culture with or without CD3 and CD28 antibodies.Results:We have previously shown that stimulated CLL derived CD8+ T cells had reduced expression of activation markers, increased expression of PD‐1 and reduced expression of glucose transporter GLUT‐1, coinciding with reduced glucose uptake. In addition we observed that mitochondrial biogenesis is impaired in CLL derived CD8+ T cells. Clinical significance of this data was further demonstrated by analyzing mitochondrial mass of CAR T cells from CLL patients showing complete response (CR) versus patients with no response (NR). Patients with CR had higher mitochondrial mass compared to NR. These findings support our hypothesis that CLL cells reprogram T cell metabolism, in particular mitochondrial fitness and biogenesis (Blood 2018, 132:235).In this follow up study we investigated (A) whether metabolic reprogramming is a pan T cell phenomenon or CD8 specific, (B) upstream signaling leading to metabolic reprogramming, and (C) if pharmacological intervention can boost T cell metabolism and thereby function. We found that (A) CD4 T cells share most metabolic alterations with CD8 T cells in CLL, and that (B) AKT signaling is disturbed in CLL T cells. For the metabolic interventions studies (C) we are currently exploring the effects of manipulating mitochondrial ROS or respiration, and blocking immune‐suppressive cytokines. Results of both approaches will be presented at the conference.Summary/Conclusion:We found that metabolic impairment in CLL T cells is not restricted to CD8 T cells, but also applies to CD4 T cells, and that impaired AKT signaling is at least part of the upstream bottleneck. We are currently investigating the use of compounds and metabolites in order to improve mitochondrial fitness of T cells for CLL patients to benefit autologous immunotherapies.