Latest results of a phase 2 study of IMM01 combined with azacitidine (AZA) as the first-line treatment in adults with higher risk myelodysplastic syndromes (MDS).

6510 Background: Patients diagnosed with higher-risk myelodysplastic syndrome (MDS) have poor prognosis. Azacitidine (Aza) has been shown to prolong survival in patients with treatment-naive, higher-risk MDS compared to a menu of standard of care options. IMM01 is a fusion protein comprising a recombinant signal regulatory protein α (SIRPα) and IgG1, exerting anti-tumor effects by inhibiting the "Don't eat me" signal and activating the "Eat me" signal, leading to robust antibody-dependent cellular phagocytosis (ADCP). Methods: This is an open-label, multi-center, phase 2 study (NCT05140811) that evaluated safety and efficacy of IMM01 in combination with AZA as the first-line treatment for patients with untreated higher-risk MDS. Enrolled patients were aged ≥18 years with intermediate to very high risk MDS, as defined by the Revised International Prognostic Scoring System (IPSS-R) score >3.5, and were not eligible for stem cell transplant or intensive chemotherapy. Patients were received intravenous IMM01 at a dosage of 2.0mg/kg/week and subcutaneous AZA at a dosage of 75 mg/m 2 on days1-7 per 28-day cycle. Results: By the cutoff-day of Dec 22, 2023, 57 patients were enrolled in the study. The median age was 64 (30-83) years, with 41 (71.9%) being male, and 55 (96.5%) having an ECOG of ≥1. Based on risk classification per IPSS-R, 43.9% were high risk (HR) and 31.6% were very high risk (vHR). At baseline, the median levels of blood counts were 69 (35-136)g/L for hemoglobin, 43 (2-409)×10 9 /L for platelets and 0.8 (0.1-8.6)×10 9 /L for neutrophils. The median duration of follow-up was 12.8 months (95%CI:9.7-15.3). Among the 51 efficacy evaluable patients, overall response rate (ORR) was 64.7%, including 29.4% complete response (CR) rate, 15.7% marrow CR (mCR) with hematologic improvement (HI), 5.9% HI and 13.7% mCR alone. The median time to response (TTR) was 1.9 months (95%CI:1.8-2.8) and the median duration of response (DoR) was not reached(NR). The median of progression-free survival (PFS) was not reached, with an estimated 12-month PFS of 54.4% (95% CI, 31.4-72.6). NGS analysis identified common mutations in DNMT3A, ASXL1, U2AF1 and RUNX1. Notably, NPM1 mutations significantly correlate with treatment response, particularly achieving CR. The most common ≥G3 treatment related adverse events (TRAEs) (≥10%) included leukopenia (78.9%), thrombocytopenia (66.7%), neutropenia (66.7%), lymphopenia (56.1%), anemia (43.9%), infection (15.8%) and pneumonia (10.5%). Without using of a low priming dose, the Grade ≥3 hemolysis was rare (only 1.8%). Conclusions: IMM01 (without low-dose priming) combined with AZA were well tolerated and showed exciting efficacy results in patients with treatment-naive higher-risk MDS. Clinical trial information: NCT05140811 .