anti-thymocyte globulin + PCV13

**Anti-thymocyte globulin + PCV13** is a combination regimen used in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients, where anti-thymocyte globulin (ATG), a polyclonal antibody preparation targeting T-lymphocytes, is administered as part of immunosuppressive conditioning to prevent graft-versus-host disease (GvHD), and PCV13 (13-valent pneumococcal conjugate vaccine, branded as Prevenar13®) is given as part of a vaccination schedule to prevent pneumococcal infections. ATG works by depleting T-cells through complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity, reducing acute rejection and GvHD risk in transplant settings. PCV13 induces T-cell-dependent humoral immunity against 13 Streptococcus pneumoniae serotypes (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 23F) by conjugating capsular polysaccharides to a diphtheria CRM197 carrier protein, though responses are diminished in ATG-exposed, immunosuppressed patients.[1]