Prevention of GvHD by a lymphokine

T lymphocytes which are capable of preventing GvHD when mixed with GvHD inducing cells before grafting and of inhibiting MLR, have been demonstrated in spleen and thymus of neonatal mice and rats. The supernatant of short term cultures of neonatal thymus and spleen contains a factor termed SUF, that produces the same suppressions. SUF has been produced by a number of hybridoma cell lines, that were obtained by fusion of a T lymphoma cell line with neonatal spleen cells. SUF does not reduce CFU-S upon incubation with mouse bone marrow. Suppression by SUF in MLR is not mediated via a cytotoxic mechanism, neither does SUF inhibit proliferation of normal and malignant lymphocytes. Preliminary data suggest that SUF interferes with the action of IL-2 on T effector lymphocytes.