This is a non-randomized, open-label, Phase 1 study of atezolizumab (anti programmed
death-ligand 1 [anti-PD-L1] monoclonal antibody) in intermediate/high/very high-risk
myelodysplastic syndromes (MDS) participants, as evaluated by the International Prognostic
Scoring System-Revised (IPSS-R). Eligible participants will either have never received
treatment with hypomethylating agent(s) (HMAs) or have relapsed or are refractory (R/R) to
prior HMA therapy. The primary objectives of this study are to determine the safety and
feasibility of atezolizumab therapy in these participant populations, including treatment in
combination with azacitidine.

Phase 1 will investigate maximum tolerated dose of OXi4503 as a single agent and in
combination with intermediate-dose cytarabine in subjects with relapsed/refractory AML or
MDS.

Phase 2 will investigate overall response rate of OXi4503 in combination with
intermediate-dose cytarabine in 1) subjects with MDS after failure of 1 prior
hypomethylating agent (Arm A) and 2) subjects with relapsed and refractory AML after
treatment failure of up to 1 prior chemotherapy regimen (Arm B).