A prospective, open-label, phase 2a study, to evaluate the pharmacokinetic (PK) profile, safety, and efficacy of multiple doses of Cannabidiol (CBD) in participants Graft-Versus-Host Disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT)

The study contains 3 cohorts of 12 participants each: All participants will be orally administered for 105 days with CBD at doses of 75, 150 or 300 mg (PO) BID for the prevention of acute GVHD (aGVHD) following allogeneic HSCT.

In addition to the study drug, all participants will receive standard aGVHD prophylaxis consisting of a calcineurin inhibitor (cyclosporine or tacrolimus) and a short course of methotrexate (MTX). After completion of 105 treatment days, the participant will be followed-up until day 180.

Inclusion Criteria:

1. Any malignant hematological disease in CR or Myelodysplastic Syndrome (MDS)
2. Age ≥ 18 years
3. Karnofsky Score (KS) ≥ 60%
4. HSCT-Comorbidity Index (HSCT-CI) score ≤ 3
5. No major organ dysfunction
6. Myeloablative or reduced intensity conditioning regimen
7. Matched (7/8 or 8/8) unrelated donor
8. Peripheral blood stem cell graft
9. Female subjects of childbearing potential must use a medically accepted method of contraception and must agree to continue use of this method for the duration of the study and for the follow-up time period. Acceptable methods of contraception include abstinence, barrier method with spermicide, intrauterine device (IUD), or steroidal contraceptive (oral, transdermal, implanted, and injected) in conjunction with a barrier method.
10. Male subjects with partners of childbearing potential must agree to use adequate contraception (barrier method or abstinence) during the study.
11. Subject's written informed consent

Exclusion Criteria:

1. Malignant hematological disease other than MDS, not in CR
2. Myelofibrosis
3. Allogeneic transplantation from a matched or mismatched sibling donor
4. Cord blood transplantation
5. Positive serology for HIV
6. Serious psychiatric or psychological disorders
7. Any uncontrolled infection at time of registration
8. Active consumption of illicit drugs (such as: Crack cocaine, Heroin, Methamphetamines, Cocaine, Bath Salts, Amphetamines, Methadone, Benzodiazepine, Ecstasy)
9. Use of Cannabis and/or its derivatives fourteen days prior to HSCT and for the duration of study participation
10. Uncontrolled hepatitis B or active hepatitis C infection.
11. QTc>450ms per Fridericia's correction and Impaired cardiac function or clinically significant cardiac diseases
12. Inadequate renal function defined as measured creatinine clearance > 2.0 mg/dl
13. Liver enzymes: ALT and AST > 3x upper limit of normal
14. Pregnancy or breastfeeding ((positive serum β-HCG 7 days before first dose)
15. Treatment with another investigational drug, biological agent, or device within 30 days of first dose, or investigational cell therapy within 6 months of first dose