CLINICAL TRIAL / NCT02942290

Inclusion Criteria: - Participant must have documented diagnosis of untreated de novo MDS with: - International Prognostic Scoring System (IPSS) risk categories Int-2 or High (minimum IPSS overall score of 1.5) OR Revised IPSS (IPSS-R) categories intermediate, high or very high (score of > 3) and - Presence of less than 20% bone marrow blasts per bone marrow biopsy/aspirate. - Eastern Cooperative Oncology Group (ECOG) performance score of less than or equal to 2. Exclusion Criteria: - Participant has received prior therapy for MDS. (Prior supportive care in form of transfusions or growth factors, etc., is not considered prior therapy). - Participant has received prior therapy with a BCL-2 Homology 3 (BH3) mimetic. - Participant has a diagnosis other than previously untreated de novo MDS (as defined in the protocol) including: - MDS with IPSS risk categories Low or Int-1 (overall IPSS score < 1.5) - Therapy-related MDS (t-MDS). - MDS evolving from a pre-existing myeloproliferative neoplasm (MPN). - MDS/MPN including chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (CML), juvenile myelomonocytic leukemia (JMML) and unclassifiable MDS/MPN. - Participant has received allogeneic Hematopoietic Stem Cell Transplantation (HSCT) or solid organ transplantation. - Participant has received a live attenuated vaccine within 4 weeks prior to the first dose of study drug.