Mitigation of Graft-versus-host disease in mice with xenogeneic antithymocyte serum and complement

In vitro treatment of parental C57BL/6 lymphohematopoietic cell grafts with unabsorbed guinea pig anti-mouse thymocyte serum (ATS) and guinea pig complement (GPC), prior to inoculation into lethally irradiated B6D2F hybrid hosts, has proven to be of value in terms of mitigating graft-versus-host disease (GvHD). However, the beneficial effect of such a pregrafting procedure is limited to the prevention of acute GvHD. The late GvHD remains a continuing problem, and is probably due to the graft-versus-host activity (GvHA) of newly produced nontolerant lymphocytes from lymphoid precursors resistant to ATS. Possible ways to render these precursors sensitive to ATS and complement are discussed. The potential significance of thymic hormones and cyclic AMP in achieving this is emphasized.