Pretransplant tumor antigen-specific immunization of allogeneic bone marrow transplant donors enhances graft-versus-tumor activity without exacerbation of graft-versus-host disease.

Allogeneic bone marrow transplantation (BMT) causes a beneficial graft-versus-tumor (GVT) immune response that is often associated with graft-versus-host disease (GVHD). There is substantial interest in developing therapeutic strategies that augment GVT without GVHD. We have demonstrated recently that immunization of BMT donors with cellular tumor vaccines leads to curative GVT but induces unacceptable GVHD because of the presence of recipient minor histocompatibility antigens (mHAgs) in whole-cell tumor vaccines. This study tested the hypothesis that immunization of BMT donors against a defined tumor-specific antigen with a vaccine not containing recipient mHAgs would help to separate the two responses by enhancing GVT activity without exacerbating GVHD, even when cellular vaccines were used after BMT. Recipient strain C57BL/6 fibrosarcoma cells engineered to express the well-characterized model tumor antigen, influenza nucleoprotein (NP), were used in these studies. C3H.SW donors were immunized against NP prior to BMT, and cytolytic T cells were transferred along with bone marrow into irradiated H-2-matched, mHAg-mismatched C57BL/6 recipients with established micrometastatic 205-NP tumors. Donor immunization led to a significant increase in GVT activity, as measured by reduction in tumor growth and enhanced survival. However, deaths in recipients of tumor antigen-specific immune BMT ultimately occurred because of the growth of antigen-loss variants; such tumor growth did not occur in animals receiving BMT from donors treated with whole-cell vaccines. Donor immunization did not lead to an exacerbation of GVHD, even when BMT recipients received additional immunization after BMT with a 205-NP "whole" tumor cell vaccine (which was shown to induce fatal GVHD when used for donor immunization). In conclusion, immunization of allogeneic BMT donors against a tumor-specific antigen significantly enhances GVT activity without an associated exacerbation of GVHD.