Unfractionated spleen cells but not natural killer (NK) cells from RFM donors prevent the progression of host-versus-graft disease in murine RFM/(T6 x RFM)F1 chimeras.

Host-versus-graft (HVG) syndrome is the fatal allogenic disease which develops in susceptible strains of inbred mice following their perinatal inoculation with related F1 hybrid spleen cells. Deaths are caused by pathogenic immune complexes. It is thought that the antibody components of these complexes are produced by F1 donor B cells stimulated by the allogenic HVG reaction. To complement previous work that showed that lethal disease could be prevented if the HVG response was suppressed, the present studies tested whether or not it could also be prevented by augmenting HVG reactivity with the adoptive transfer of spleen cells syngenic with the host. The data show that unfractionated RFM spleen cells given on Days 13-14 prevented lethal disease in 86% of RFM/(T6 x RFM)F1 chimeras. Successful therapy was associated with the suppression of formation of nephropathic-immune complexes, and with the rejection of F1 donor cells or their gradual replacement by host cells. RFM spleen cells enriched for NK activity by a new improved method not only failed to prevent HVG disease but appeared to exacerbate it. This was also true of spleen cells that had been activated in vitro for 3 days with IL-2, a procedure that greatly enhanced their cytolytic activity against YAC-1 targets. It is suggested that therapy with NK cells failed, even after IL-2 activation, because they had no effect on proliferating and antibody-forming F1 donor cells that had engrafted in large numbers in the lymph nodes of the RFM hosts.