Safety of MT-401-OTS in Patients With Relapsed AML or MDS

This study is a Phase 1 multicenter, open-label study evaluating the safety and efficacy of escalating doses of MT-401-OTS in 2 participant populations: 1) Those with intermediate or high-risk AML per 2022 ELN criteria who have evidence of MRD and/or \</= 10% blast following prior induction therapy or at least 4 cycles of nonintensive therapy and 2) those with high- or very-high-risk MDS per 2023 IWG criteria and who have residual disease with \</= 10% blasts following treatment with an HMA-based therapy. Participants must meet all eligibility criteria. Once a suitable MT-401-OTS product is confirmed, the participant will receive a lymphodepleting conditioning regimen consisting of fludarabine and cyclophosphamide daily from Day -7 to Day -5. Bendamustine (administered on Days -6 and -5) may be used for participants with underlying toxicities or if lack of availability precludes the use of fludarabine and/or cyclophosphamide. Two standard doses of an HMA (azacitidine or decitabine) will be administered on Day -4 to -3. MT-401-OTS will be administered IV over 10 minutes on Day 0. Safety evaluations will be performed throughout the study. Disease assessments will be performed at regular intervals based on 2022 ELN criteria for AML and the 2023 response criteria for higher-risk MDS. The dose escalations will begin with Cohort 1 which a single MT-401-OTS dose administered at a flat dose of 100 X 10\^6 cells). Dose escalations will proceed using the modified 3+3 design up to the highest single flat dose of 400 x 10\^6 cells. If a clinical safety issue should arise in Cohort 1, a lower DL may be explored. Additionally, Cohort 4 is an optional cohort that may be considered based on the cumulative data from Cohorts 1 through 3 to asses alternative dosing schedules (split dosing) of 400 X 10\^ 6 cells or without lymphodepletion and/or HMA.