Leflunomide to Prevent Cytomegalovirus Reactivation in Stem Cell Transplant Patients

Patients undergoing half-matched hematopoietic stem cell transplantation (HSCT) are at high risk of viral reactivation after bone marrow transplantation (BMT). The purpose of this study is to evaluate whether leflunomide can prevent cytomegalovirus (CMV) reactivation in these patients and to assess its safety. The main questions it aims to answer are - 1. Does leflunomide prevent cytomegalovirus (CMV) related organ damage? 2. Does leflunomide prevent a rise in cytomegalovirus (CMV) copy number to more than 2000 copies/ml? 3. Does leflunomide prevent the need to start pre-emptive therapy for cytomegalovirus (CMV)? 4. Is it safe to use in bone marrow transplant ( BMT) patients? 5. Does leflunomide prevent other viral reactivations - like Adeno virus and BK virus? 6. Does leflunomide affect the risk of acute graft-versus-host disease ( acute GVHD) after bone marrow transplant (BMT)? What medicine will the patients receive? Patients in study shall receive loading dose of Tab. Leflunomide 100 mg daily for 3 days followed by 20 mg daily orally. Leflunomide will be given till day +180 post transplant or till patient is on immunosuppressant medicines.