The development of
immune checkpoint inhibitors represents a major breakthrough in the field of
cancer therapeutics. Pursuant to their success in
melanoma and numerous solid
tumor malignancies, these agents are being investigated in
hematological malignancies including
acute myelogenous leukemia (AML) and
myelodysplastic syndromes (MDS). Although AML/MDS have traditionally been considered to be less immunogenic than solid
tumor malignancies, recent pre-clinical models suggest a therapeutic role for
immune checkpoint inhibition in these diseases. CTLA-4 inhibition may be especially effective in treating late post-allogeneic stem cell transplant relapse of AML in patients with limited or no
graft versus host disease.
Immune checkpoint inhibition, specifically PD-1 inhibition, demonstrated limited single agent efficacy in patients with relapsed AML and with MDS post-hypomethylating
therapy. Rationally designed combinations of
PD-1 inhibitors with standard anti-leukemic
therapy are needed. Hypomethylating agents such as
azacitidine, up-regulate PD-1, PD-L1, and PD-L2 in patients with AML/MDS and up-regulation of these genes was associated with the emergence of resistance. The combination of
azacitidine and PD-1/PD-L1 inhibition may be a potential mechanism to prevent or overcome resistance to 5-azacitidine. A number of such combinations are being evaluated in clinical trials with early encouraging results.
Immune checkpoint inhibition is also an attractive option to improve relapse-free survival or eliminate
minimal residual disease post induction and consolidation by enhancing T-cell surveillance in patients with high-risk AML. The ongoing clinical trials with checkpoint inhibitors in AML/MDS will improve our understanding of the immunobiology of these diseases and guide us to the most appropriate application of these agents in the
therapy of AML/MDS.