Anti-tumor effects of anti-T-cell globulin.

In vivo T-cell depletion using anti-T-cell antibodies is a standard procedure during allogeneic hematopoietic stem cell transplantation (allo-HSCT). Clinical data demonstrate that in vivo T-cell depletion with the anti-CD52 monoclonal antibody Alemtuzumab is associated with increased relapse rates of hematologic malignancies after allo-HSCT, underlining the importance of donor T cells for graft versus tumor activity. In contrast, recent results suggest that in vivo T-cell depletion with rabbit anti-T-cell globulin (ATG) Fresenius is not associated with tumor relapse after allo-HSCT, raising the possibility that ATG mediates antitumor effects. However, data on ATG's ability to bind to tumor cells and on its effect on the induction of antibody-dependent cellular cytotoxicity (ADCC) are lacking. We used ATG Fresenius, which contains polyclonal rabbit IgG directed against the human T-lymphoma cell line Jurkat, to study relevant mechanisms of ATG-mediated antitumor effects, including ADCC, complement-dependent cytotoxicity, and induction of apoptosis. Based on the knowledge that Jurkat cells aberrantly express myeloid markers and B-cell markers, we hypothesized that rabbit ATG Fresenius binds to a variety of hematologic malignancies. We found that ATG specifically binds to a variety of hematologic malignancies including acute myeloid leukemia and B-cell lymphoma in a concentration-dependent manner. We demonstrate that ATG mediates antitumor activity, including induction of ADCC, complement-dependent cytotoxicity, and apoptosis, toward different hematologic malignancies. Our results contribute to a better understanding of the effects of ATG on posttransplant immunology in patients undergoing allo-HSCT.