Background: The introduction of checkpoint inhibitors in solid cancer therapy showed successful results. The role of Programmed Death-1/Programmed Death-Ligand 1 (PD1/PD-L1) in hematologic malignancies is currently being investigated and clinical trials are ongoing. Preliminary findings showed conflicting results. In this study, we examined the degree of PD-L1 and PD-L2 expression in primary acute leukemia patients.
Methods: Flow cytometry expression of PD-L1 and PD-L2 was evaluated in de novo acute leukemia in the collaborating institutions between 2018 - 2020.
Results: One hundred forty patients were identified. PD-L1 was positive in 34/70 (49%) of AML, 25/50 (50%) of B-ALL, and none (0/20) of T-ALL patients. In contrast, PD-L2 was solely expressed in eight (19%) AML patients. The expression of PD-L1 showed statistically significant correlation with the type of acute leukemia (AML and B-ALL > T-ALL, p < 0.001) and with age group (adults > children, p = 0.048), but not with blast count, immunophenotype or cytogenetic mutations. The positivity for PD-L1 was associated with worse overall survival in AML, but not in B-ALL.
Conclusions: The expression of PD-L1 is common among newly diagnosed AML and B-ALL patients and is not restricted to relapsed cases as previously described. PD-L2 is less commonly expressed and is accompanied by PD-L1 expression. Positive PD-L1 patients may benefit from treatment with immune checkpoint inhibitors, especially in AML. Further studies are recommended.