| Summary: | Abstract Immune checkpoint pathways active in Acute Myeloid Leukemia (AML) patients, especially during the course of remission induction chemotherapy, have not been well studied. Although dominant in mediating T cell dysfunction in cancer, it is now well-accepted that interruption of PD-1/PD-L1 axes alone does not always completely restore T cell function, indicating the involvement of additional negative regulatory pathways, such as TIM-3/Gal-9, in promoting T cell exhaustion. Here, we characterized these pathways in AML patients enrolled in a phase I dose escalation trial that combined Selinexor, a Selective Inhibitor of Nuclear Export (SINE), with high-dose cytarabine (HiDAC) and mitoxantrone (Mito) (NCT02573363) as induction therapy. To monitor changes in expression of immune checkpoint receptors, multi-parameter flow cytometry was performed on peripheral blood and bone marrow biopsy specimens at diagnosis and following induction therapy in 26 AML patients. Expression of CD47, PD-L1, PD-L2 and Gal9 was assessed on CD34+ AML blasts, as well as on CD34− cell populations. In parallel, we evaluated expression of inhibitory (PD1, CTLA4, LAG3, TIM-3) and stimulatory (CD28, ICOS, CD137, OX40, CD40L, HLA-DR) co-receptors on CD4+ and CD8+ T cell subsets. Compared to baseline, the frequency of Gal9+ CD34− cells was significantly higher in patients with treatment failure (TF) than in those in complete remission (CR), and this finding correlated with increased TIM-3 expression on marrow-resident T cells in TF patients. Moreover, when we measured the expression level of PD-1 and TIM-3 in bone marrow samples compared to peripheral blood, TIM-3 was significantly higher in BM specimens. Our results suggest that targeting the Gal9/Tim-3 axis could be effective in combination with induction chemotherapy to increase the likelihood of complete remission in AML patients.
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