A phase 1 study of IO-202, an anti-LILRB4 antibody, in chronic myelomonocytic leukemia and acute myeloid leukemia.

IO-202 is a humanized immunoglobulin G1 monoclonal antibody with high affinity and specificity for leukocyte immunoglobulin-like receptor B4 (LILRB4; ILT3), which is predominantly expressed in monocytes and monocytic blasts. IO-202 induces antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis in vitro and in patients with leukemia. Herein, we present the phase 1a dose escalation data of IO-202 as monotherapy and in combination with azacitidine (AZA) in patients with relapsed/refractory (R/R) acute myeloid leukemia (AML) and R/R chronic myelomonocytic leukemia (CMML), and the phase 1b dose expansion data of IO-202 combined with AZA for the treatment of hypomethylating agent (HMA)-naïve CMML. IO-202 was well tolerated as monotherapy and in combination with AZA. Patients with R/R monocytic AML expressing high LILRB4 on leukemia blasts demonstrated clinical activity, including a complete response (CR) in dose escalation with IO-202 + AZA. In patients with HMA-naïve CMML, IO-202 + AZA led to a 27.8% CR rate and 66.7% overall response rate, based on the 2015 International Working Group response criteria for myelodysplastic/myeloproliferative neoplasms. All 18 efficacy-evaluable patients with HMA-naïve CMML (100%) achieved some form of investigator-assessed clinical benefit, including symptomatic improvement, a decrease in transfusions, reduced blasts and/or monocytes, and resolution of thrombocytopenia. Seven patients (38.9%) proceeded to allogeneic hematopoietic cell transplantation. Translational data suggest that efficacy favors patients with high LILRB4 expression, supporting the mechanism of action of IO-202. Overall, the data support a future pivotal study of IO-202 + AZA in patients with HMA-naïve CMML. This trial was registered at www.clinicaltrials.gov as #NCT04372433.