Part A Inclusion Criteria

          -  Participants with cytologically/histologically confirmed myelodysplastic syndrome
             (MDS) according to the 2016 World Health Organization (WHO) classification with the
             following:

               -  Measurable disease per WHO MDS with excess blasts criteria as defined either:

                    -  5%-9% blasts in the bone marrow or 2%-4% blasts in the peripheral blood or

                    -  10%-19% blasts in the bone marrow or 5%-19% blasts in the peripheral blood

               -  MDS that is relapsed or refractory and must not have other therapeutic options
                  known to provide clinical benefit in MDS available.

               -  Treatment failure after prior hypomethylating agent (HMA) therapy for MDS,
                  defined as one of the following:

                    -  Progression (per 2006 International Working Group [IWG] criteria) at any
                       time after initiation of HMA therapy.

                    -  Lack of response (failure to achieve complete remission [CR], partial
                       response [PR], or hematologic improvement [HI] per 2006 IWG criteria) after
                       at least 6 cycles of azacitidine (or equivalent HMA) or 4 cycles of
                       decitabine (or equivalent HMA).

                    -  Relapse after achievement of CR, PR, or HI (per 2006 IWG criteria).

                    -  Intolerance of HMA (Grade 3 or higher non-hematologic toxicity leading to
                       treatment discontinuation).

                    -  Participants with isolated 5q-/5q- syndrome must have progressed, failed,
                       relapsed, or not tolerated lenalidomide in addition to HMA.

          -  Must be off HMA therapy ≥ 2 weeks and must be off any other treatments for MDS for ≥ 4
             weeks prior to first dose of SEA-CD70; growth factors and transfusions are allowed
             before and during the study as clinically indicated

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0-1

        Part B Inclusion Criteria

          -  Participants with cytologically/histologically confirmed MDS according to the WHO
             classification with the following:

               -  Measurable disease per WHO MDS with excess blasts (MDS-EB) criteria as defined
                  either:

                    -  5%-9% blasts in the bone marrow or 2%-4% blasts in the peripheral blood, or

                    -  10%-19% blasts in the bone marrow or 5%-19% in the peripheral blood

               -  MDS that is relapsed or refractory and must not have other therapeutic options
                  known to provide clinical benefit in MDS available.

               -  Treatment failure after prior HMA therapy for MDS defined as one of the
                  following:

                    -  Progression (per 2006 IWG criteria) at any time after initiation of HMA
                       therapy.

                    -  Lack of response (failure to achieve CR, PR, or HI per 2006 IWG criteria)
                       after at least 6 cycles of azacitidine or 4 cycles of decitabine.

                    -  Relapse after achievement of CR, PR, or HI (per 2006 IWG criteria).

                    -  Intolerance of HMA (Grade 3 or higher non-hematologic toxicity leading to
                       treatment discontinuation).

                    -  Participants with isolated 5q-/5q- syndrome must have progressed, failed,
                       relapsed, or not tolerated lenalidomide in addition to HMA.

          -  Must be off HMA therapy ≥ 2 weeks and must be off any other systemic treatments for
             MDS for ≥ 4 weeks prior to first dose of SEA-CD70; growth factors (e.g., G-CSF,
             erythropoietin and thrombopoietin) and transfusions are allowed before and during the
             study as clinically indicated.

          -  ECOG Performance Status of 0-2

        Part C Inclusion Criteria

          -  Participants with relapsed or refractory acute myeloid leukemia (AML) according to the
             WHO 2016 classification (except for acute promyelocytic leukemia [APL]):

               -  Who have received either 2 or 3 previous regimens to treat active disease.
                  Post-remission treatments, intrathecal chemotherapy, and radiotherapy are not
                  considered previous regimens.

               -  Who have received 1 previous regimen to treat active disease and have at least
                  one of the following:

                    -  Age > 60 and ≤75 years.

                    -  Primary resistant AML (defined as failure to achieve CR after 1-2 courses of
                       induction therapy)

                    -  First CR duration <6 months

                    -  Adverse-risk per European Leukemia Net (ELN) genetic risk stratification

                    -  Secondary AML (prior history of MDS or therapy-related)

          -  Age 18-75 years

          -  ECOG performance status of 0-2

        Exclusion Criteria (All Parts)

          -  History of another malignancy within 3 years before the first dose of study drug or
             any evidence of residual disease from a previously diagnosed malignancy. Exceptions
             are malignancies with a negligible risk of metastasis or death.

          -  Previous exposure to CD70-targeted agents

          -  Prior allogeneic hematopoietic stem cell transplant, for any condition

          -  Central nervous system leukemia based on imaging or documented positive cytology in
             cerebral spinal fluid

          -  History of clinically significant sickle cell anemia, autoimmune hemolytic anemia, or
             idiopathic thrombocytopenic purpura