Preclinical models have shown that blocking PD-1/PD-L1 pathways enhances antileukemic responses. Azacitidine upregulates PD-1 and IFNγ signaling. We therefore conducted this single-arm trial, in which patients with relapsed/refractory (R/R) acute myeloid leukemia (AML) were treated with azacitidine 75 mg/m² days 1 to 7 intravenously or subcutaneously with nivolumab 3 mg/kg intravenously on days 1 and 14, every 4 to 6 weeks. For the seventy patients who were treated, the median age was 70 years (range, 22–90) and the median number of prior therapies received was 2 (range, 1–7). The overall response rate (ORR) was 33%, including 15 (22%) complete remission/complete remission with insufficient recovery of counts, 1 partial response, and 7 patients with hematologic improvement maintained >6 months. Six patients (9%) had stable disease >6 months. The ORR was 58% and 22%, in hypomethylating agent (HMA)–naïve (n = 25) and HMA-pretreated (n = 45) patients, respectively. Grade 3 to 4 immune-related adverse events occurred in 8 (11%) patients. Pretherapy bone marrow and peripheral blood CD3 and CD8 were significantly predictive for response on flow cytometry. CTLA4 was significantly upregulated on CD4⁺ Teff in nonresponders after 2 and 4 doses of nivolumab. Azacitidine and nivolumab therapy produced an encouraging response rate and overall survival in patients with R/R AML, particularly in HMA-naïve and salvage 1 patients. Pretherapy bone marrow aspirate and peripheral blood CD3 percentage may be biomarkers for patient selection.

Azacitidine in combination with nivolumab appeared to be a safe and effective therapy in patients with AML who were salvage 1, prior hypomethylator-naïve, or had increased pretherapy CD3⁺ bone marrow infiltrate by flow cytometry or IHC. Bone marrow CD3 and CD8 are relatively simple assays that should be incorporated to select patients in future trials.

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