Inclusion Criteria:

          1. Male or female age ≥18 years old;

          2. Signed informed consent form

          3. One of the two following:

             i) AML either de novo or secondary [any subtype except acute promyelocytic leukemia
             (APL)] who either:

               1. are in relapse to standard therapy following an initial response

               2. failed primary induction therapy with no CR (failed ≥2 courses of intensive
                  induction therapy. Intensive chemotherapy defined as an intensity of ≥ 5+2)

               3. newly diagnosed untreated AML in patients ≥ 65 years of age with high risk
                  cytogenetics, if they are not candidates for standard available induction
                  chemotherapy

               4. AML secondary to MDS, either relapsed or refractory, previously treated with
                  hypomethylating agents for at least 4 cycles;

               5. Relapsed or refractory AML unfit for intensive chemotherapy previously treated
                  with a low intensity regimen (e.g. low dose Ara-c, hypomethylating agent, etc.)
                  including Venetoclax for at least 2 cycles;

             OR ii) MDS patients who meet the following criteria: very high-risk disease (IPSS-R
             score > 6, Greenberg et al., 2012), either relapsed or refractory, previously treated
             with hypomethylating agents for at least 4 cycles;

          4. Must have baseline BM sample taken by BMA/BMB within 28 days prior to first dose of
             MCLA-117 for CLEC12A detection;

          5. Estimated life expectancy of at least 8 weeks;

          6. Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2;

          7. Significant toxicities incurred as a result of previous anti-cancer therapy resolved
             to ≤ Grade 1 (NCI-CTCAE version 4.03);

          8. Acceptable laboratory values at screening;

          9. Male patients must agree to use an adequate and medically accepted method of
             contraception throughout the study and for at least 6 months after if their sexual
             partners are women of child bearing potential (WOCBP).

         10. WOCBP must be using highly effective and medically accepted method of contraception to
             avoid pregnancy throughout the study and for at least 6 months after the study ;

         11. WOCBP must have a negative serum or urine pregnancy test within 72 hours prior to the
             start of study drug.

         12. Peripheral blast count </= 30,000/mm3 at the time of initiation of infusion on Cycle 1
             Day 1.

         13. Able and willing to comply with all study procedures.

        Exclusion Criteria:

          1. Diagnosis of chronic myelogenous leukemia in blast crisis;

          2. Prior hematopoietic stem cell transplantation (this exclusion applies for dose
             escalation Part 1 and Cohort A of Part 2);

          3. For patients in Cohort B of Part 2, prior hematopoietic stem cell transplantation is
             allowed under certain circumstances.

          4. Treatment with anticancer medications, investigational drugs or radiotherapy is
             allowed within 2 weeks or 5 half-lives prior to start of MCLA-117;

          5. Previous receipt of live vaccines in the 4 weeks prior to study drug administration;

          6. Chronic concurrent need of use of corticosteroids > 10 mg/day of oral prednisone or
             the equivalent, except topical preparations (e.g., topical creams, steroid inhaler,
             nasal spray or ophthalmic solution);

          7. Use of immunosuppressant medications within 4 weeks of MCLA-117 administration;

          8. Clinically active central nervous system (CNS) leukemia;

          9. Patients who are pregnant or lactating;

         10. Patients with an active infection or with an unexplained fever during screening or on
             the first scheduled day of dosing;

         11. Patients with known hypersensitivity to any of the components of MCLA-117 or who have
             had prior hypersensitivity reactions to human or humanized monoclonal antibodies;

         12. Patients with known HIV, hepatitis B or C;

         13. Patients with New York Heart Association Class III or IV congestive heart failure or
             left ventricular ejection fraction (LVEF) < 50%, or significant uncontrolled cardiac
             disease, current diagnosis of unstable angina, uncontrolled congestive heart failure,
             new myocardial infarction, or ventricular arrhythmia requiring medication;

         14. Prior malignancy (other than basal cell carcinoma and cervical in situ carcinoma)
             unless treated with a curative intend and without evidence of malignant disease for 1
             year before screening. Patients with prior hematologic malignancies that have
             progressed to AML (such as Myelodysplastic syndrome, myeloproliferative neoplasms,
             bi-phenotypic leukemias, AcuteLymphocyticLeukemia) or AML that has relapsed are
             eligible;

         15. Urinary protein >2+ possibly indicative of renal disease. If the 24 hours urine
             protein shows a result of < 100 mg protein, subject can be eligible;

         16. Patients with any other medical or psychological condition deemed by the Investigator
             to be likely to interfere with a patient's ability to sign informed consent, cooperate
             and participate in the study, or interfere with the interpretation of the results;

         17. WOCBP or males with a WOCB partners not willing to use highly effective and medically
             accepted methods of contraception for 6 months after last study drug administration.

         18. Need for concurrent other cytoreductive chemotherapy.