Inclusion Criteria:

          -  Confirmed diagnosis of relapsed or refractory acute leukemia (acute myeloid leukemia,
             acute lymphoblastic leukemia, blast crisis of chronic myeloid leukemia [CML],
             secondary AML from prior myelodysplastic syndrome [MDS] / myeloproliferative neoplasm
             [MPN]); minimum of 5% blasts in the bone marrow or 10% blasts in circulation

          -  Patients with Philadelphia chromosome (Ph)+ ALL or blast crisis of CML must be
             refractory (not intolerant) to at least 2 second/third generation ABL kinase
             inhibitors (TKI)

          -  For AML: patients must belong to one of the following ?high risk? categories:

               -  Primary induction failure (PIF) as defined by failure to achieve at least a 50%
                  reduction in bone marrow blasts after one cycle of high intensity, anthracycline
                  containing induction regimen or failure to achieve complete response
                  (CR)/complete remission with incomplete blood count recovery (CRi) after two
                  cycles of high intensity chemotherapy

               -  First early relapse as defined by an initial remission duration of fewer than 6
                  months

               -  Second or subsequent relapse regardless of remission duration, or

               -  Relapse after allogeneic or autologous stem cell transplantation (first relapse
                  after stem cell transplant would be eligible, regardless of prior duration of
                  remission)

          -  Patients with MDS who transform to AML while on hypomethylator agents or patients with
             AML who progress on hypomethylator agents could be considered for arm A of this trial
             if

               -  They choose not to be treated on or are ineligible for the investigator's
                  competing trial of sEPHB4-HSA + hypomethylator (9L-16-6)

               -  They are appropriate for high dose cytarabine treatment

          -  For ALL: patients must belong to one of the following ?high risk? categories:

               -  Primary refractory as defined by failure to achieve CR after induction and at
                  least one salvage therapy

               -  Second or subsequent relapse

               -  Relapse after allogeneic or autologous stem cell transplantation (requirement for
                  second relapse does not apply post-transplant)

               -  All variants of ALL including T-ALL, B / myeloid, lymphoblastic leukemia lymphoma
                  are eligible

          -  Patients with myeloid diseases (AML, myeloid blast crisis of CML) will be eligible for
             arm A with cytarabine; patients with lymphoid diseases (ALL, lymphoid blast crisis of
             CML) will be eligible for arm B with liposomal vincristine; patients with leukemia of
             ambiguous lineage or bi-phenotypic leukemia (e.g. B/myeloid) may be treated on either
             arm A or B, at discretion of treating physician

          -  Performance status Eastern Cooperative Oncology Group (ECOG) 0 to 2

          -  Life expectancy > 2 months

          -  Total bilirubin ? 3 X upper limit of normal (ULN), unless attributable to Gilbert
             syndrome

          -  Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT]) /
             alanine transaminase [ALT] (serum glutamic pyruvic transaminase [SPGT]) ? 5 X
             institutional upper limit of normal

          -  Creatinine: glomerular filtration rate (GFR) > 30 as calculated by modification of
             diet in renal disease (MDRD) equation

          -  Women of child-bearing potential and men must agree to use adequate contraception
             (hormonal or barrier method of birth control; abstinence) prior to study entry, for
             the duration of study participation, and for 90 days following completion of therapy;
             should a woman become pregnant or suspect she is pregnant while participating in this
             study, she should inform her treating physician immediately

          -  A female of child-bearing potential is any woman (regardless of sexual orientation,
             having undergone a tubal ligation, or remaining celibate by choice) who meets the
             following criteria:

               -  Has not undergone a hysterectomy or bilateral oophorectomy; or

               -  Has not been naturally postmenopausal for at least 12 consecutive months (i.e.,
                  has had menses at any time in the preceding 12 consecutive months)

          -  No major surgery within 4 weeks of first dose of sEPHB4

          -  Peripheral blood blast count ? 30,000 at time of eligibility assessment (within 7 days
             of start of therapy); blast counts that increase beyond 30,000 after a patient is
             deemed eligible will not disqualify the patient

          -  For subjects with prior allogeneic stem cell transplant, no evidence of active
             graft-versus host disease (GVHD), and must be ? 2 weeks off immunosuppressive therapy

          -  Ability to understand and the willingness to sign a written informed consent

        Exclusion Criteria:

          -  Diagnosis of acute promyelocytic leukemia (M3 classification)

          -  ALL patient refractory to their first induction only or their first relapse, will be
             excluded; they must be refractory to at least one salvage therapy, or relapse after
             first salvage, to be eligible

          -  ALL patients refractory to liposomal vincristine as defined by progression while on
             therapy or relapse within 3 months of completion of therapy with liposomal vincristine

          -  Prior malignancy requiring therapy within the last 12 months (excluding non-melanoma
             skin cancer); hormone therapy for prostate cancer or adjuvant endocrine therapy for
             breast cancer would not be excluded

          -  Patient is receiving other investigational agents

          -  Active central nervous system (CNS) disease

               -  Definition: any patient receiving active CNS therapy (defined as more than 1
                  intrathecal treatment per week or current radiation therapy to brain); if patient
                  has a history of CNS disease: must have cerebrospinal fluid (CSF) sampling within
                  28 days of enrollment that is negative for leukemia; intrathecal chemotherapy for
                  patients without active CNS disease is allowed (e.g., ongoing primary or
                  secondary prophylaxis for patients who cleared the CSF prior to study
                  enrollment); CSF sample is not required for enrollment for patients with no
                  history of CNS disease

          -  Chemotherapy within 2 weeks of first dose of sEPHB4-HSA (minimum of 6 weeks for
             nitrosoureas and 8 weeks for bone marrow transplantation) with the following
             exceptions:

               -  Hydroxyurea allowed prior to, and up to day +5 of cycle 0 of treatment (max 100
                  mg/kg/day)

               -  Corticosteroids allowed until day -3 (max dexamethasone 20mg/day)

               -  Maintenance chemotherapy for ALL allowed one week prior to start of treatment
                  (e.g., POMP)

          -  Grade ? 2 toxicity (other than alopecia) continuing from prior anticancer therapy,
             including radiation

          -  Patients with Charcot-Marie-Tooth disease or other demyelinating diseases are excluded
             from the liposomal vincristine containing arm

          -  New York Heart Association class 3 or 4 heart failure; myocardial infarction, acute
             coronary syndrome, diabetes mellitus with ketoacidosis, or chronic obstructive
             pulmonary disease (COPD) requiring hospitalization in the preceding 6 months; or any
             other intercurrent medical condition that contraindicates treatment with sEPHB4-HSA or
             places the patient at undue risk for treatment related complications

          -  Uncontrolled active systemic infections

          -  Known history of human immunodeficiency virus (HIV) or active infection with hepatitis
             C virus (HCV) or hepatitis B virus (HBV); patients with HBV and/or HCV sero-positivity
             only will be eligible, if nucleic acid amplification testing (NAT) is negative

          -  Warfarin (any dose) or full-dose anticoagulation with other agents (low molecular
             weight heparin, antithrombin agents, anti-platelet agents and full dose aspirin)
             within 7 days prior to first dose of study drug; patients on prophylactic doses of
             low-molecular weight heparin are allowed