fludarabine + cytarabine + busulfan + anti-thymocyte immunoglobulin

This is a multi-agent conditioning regimen used primarily before allogeneic hematopoietic stem cell transplantation (HSCT), especially in patients with hematologic malignancies such as acute leukemia and lymphoid malignancies. The combination includes: - Fludarabine, a purine analog that inhibits DNA synthesis and has potent immunosuppressive properties. - Cytarabine (AraC), a pyrimidine nucleoside analog that interferes with DNA synthesis, mainly used for its antileukemic effects. - Busulfan, an alkylating agent that causes cross-linking of DNA strands leading to cell death; it is myeloablative and immunosuppressive. - Anti-thymocyte immunoglobulin (ATG), a polyclonal antibody preparation targeting human T cells, providing additional immunosuppression to prevent graft rejection and reduce the risk of graft-versus-host disease. This regimen aims to achieve sufficient myeloablation and immune suppression for successful engraftment while reducing toxicity compared to more intensive regimens. It is considered an intensified or reduced-intensity conditioning protocol depending on dosing[1][2][3][4].