Inclusion criteria :

          -  Confirmed diagnosis of Acute Myeloblastic leukemia (AML) (except acute promyelocytic
             leukemia), or myelodysplastic syndrome (MDS) with a risk category of intermediate or
             higher. Patients must have exhausted available treatment options and must not be
             eligible for any treatment known to provide clinical benefit.

          -  Patients with AML must have relapsed or refractory disease that has been resistant to
             available therapies.

          -  Patients with B-ALL (B acute lymphoid leukemia) in second or subsequent relapse:
             should have completed previously ≥1 cycle of a salvage regimen. Patients must have
             exhausted available treatment options and must not be eligible for any treatment known
             to provide clinical benefit.

          -  Patients with HR-MDS (high risk myelodysplastic syndrome) must have >10% blasts in the
             bone marrow at the time of enrollment and fit one of the following categories: Not
             eligible for induction therapy and having completed ≥2 cycles of therapy or not
             eligible for allogeneic stem cell transplant and having completed ≥1 course of
             induction therapy.

          -  Signed written informed consent.

        Exclusion criteria:

          -  Age <16 years old.

          -  Eastern Cooperative Oncology Group (ECOG) performance status >2.

          -  Patients with inadequate biological tests.

          -  White blood cell count > 30,000/mm3

          -  History of active or chronic autoimmune conditions that has required or requires
             therapy.

          -  Graft-versus-host disease following allogeneic stem cell transplantation requiring
             treatment with more than 10 mg of oral prednisone or equivalent daily. The stem cell
             transplant and/or donor lymphocyte infusion should have been performed more than 3
             months before study treatment start.

          -  Second primary malignancy that requires active therapy. Adjuvant hormonal therapy is
             allowed.

          -  Previous treatment with radiotherapy or immunotherapeutic agents in the 4 weeks prior
             to investigational medicinal product (IMP) administration.

          -  Previous treatment with any other investigational agent in the 4 weeks prior to IMP
             administration.

          -  Receiving, at the time of first IMP administration, of concurrent steroids >10 mg/day
             of oral prednisone or the equivalent for ≥3 months.

          -  Requirement for tocilizumab for any other diagnosis.

          -  Evidence of active central nervous system leukemia at the time of enrollment.

          -  Acquired immunodeficiency syndrome (AIDS-related illnesses) or HIV (human
             immunodeficiency virus) disease requiring antiretroviral treatment or having active
             Hepatitis B viral infection or Hepatitis C viral infection.

          -  Women of childbearing potential, male with a partner of childbearing potential who do
             not agree to use effective methods of birth control.

          -  Any clinically significant, uncontrolled medical conditions that, in the
             Investigator's opinion, would expose excessive risk to the patient or may interfere
             with compliance or interpretation of the study results.

        The above information is not intended to contain all considerations relevant to a patient's
        potential participation in a clinical trial.