rituximab + fludarabine + cyclophosphamide + siplizumab

This is a combination regimen consisting of four agents: - **Rituximab** is a monoclonal antibody targeting CD20 on B lymphocytes, leading to their depletion via complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity, and direct induction of apoptosis. - **Fludarabine** is a purine analog that inhibits DNA synthesis by interfering with DNA polymerase and ribonucleotide reductase, resulting in inhibition of cell proliferation. - **Cyclophosphamide** is an alkylating agent that crosslinks DNA strands, leading to cell death. - **Siplizumab** is a humanized monoclonal antibody targeting CD2 on T cells and natural killer (NK) cells, resulting in immunosuppression through T-cell depletion. This combination represents an investigational chemoimmunotherapy regimen. The FCR (fludarabine, cyclophosphamide, rituximab) backbone has established efficacy in chronic lymphocytic leukemia (CLL) and follicular lymphoma. Siplizumab has been studied as part of conditioning regimens for hematopoietic stem cell transplantation due to its T-cell depleting properties[1][3]. The addition of siplizumab aims to further modulate immune responses or enhance engraftment in transplant settings.