A single center, prospective, one arm clinical study to assess the tolerance and effectiveness of total body irradiation and cladribine in adult patients diagnosed with AML( acute myeloid leukemia) and myelodysplastic syndromes.

Inclusion Criteria:

1. Age between 18 and 60 years.
2. Patient is a candidate for allogeneic hematopoietic cell transplantation due to acute myeloid leukemia(intermediate or high risk acute myeloid leukemia in complete remission, low risk with positive Minimal residual disease) or high risk myelodysplastic syndrome.
3. Demonstration of chemosensitivity in the case of treatment regimens with cladribine in induction therapy.
4. Patient signed informed consent form prior to any study related screening procedures are performed.
5. Patient has Eastern Cooperative Oncology Group performance status score of 0 or 1.
6. Patient is a candidate for allogeneic hematopoietic cell transplantation from sibling or unrelated donor (full matched or 9/10 mismatched) or from haploidentical donor.

Exclusion Criteria:

1. Has received more than 1 allogeneic hematopoietic cell transplantation.
2. Presence of active uncontrolled infection (i.e. sepsis, new symptoms, worsening physical signs or radiographic findings attributable to infection).
3. Known active human immunodeficiency virus, hepatitis B virus or hepatitis C virus infection (positive polymerase chain reaction test) or risk of hepatitis B virus reactivation (Hepatitis B surface antigen positive).
4. Presence of active disease in acute myeloid leukemia patients.
5. History or current diagnosis for uncontrolled or significant cardiac or pulmonary disease.
6. Presence of severe renal or liver dysfunction (creatinine, alanine aminotransferase,aspartate aminotransferase or bilirubin concentration > 3.0 upper limit of normal
7. Currently pregnancy or breast feeding.
8. Treatment of any other investigational agent in the same time as this study.
9. Known allergies, hypersensitivity, or intolerance to cladribine or similar compounds.
10. Women of childbearing potential who do not agree to use two effective methods of contraception.