A recombinant humanized anti-CD52 monoclonal antibody (biologic immunosuppressant) administered subcutaneously as part of conditioning for allogeneic hematopoietic cell transplantation. It binds CD52 on mature lymphocytes and other immune cells, depleting them via complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity to reduce donor–recipient alloreactivity and graft-versus-host disease risk.