Transfusion of autologous cytotoxic cells leads to failure of unrelated, DLA-nonidentical marrow grafts.

Dogs conditioned with 9.2 Gy total body irradiation (TBI) and given histoincompatible marrow transplants have a high rate of graft failure. Engraftment can be achieved by using 18 Gy fractionated TBI as preparative regimen. In this study, we tested the effects of infusing, at the time of histoincompatible marrow transplantation, autologous cells that had been stored before beginning high-dose (18 Gy) TBI. Our aim was to identify the peripheral blood mononuclear cells (PBMC) that contribute to failure of marrow grafts. Marrow graft failure was observed in three of three dogs receiving a mean of 2.1 x 10(8) unfractionated autologous PBMC/kg body weight as well as in two of two dogs receiving a mean dose of 0.075 x 10(8) PBMC/kg. When the dose of PBMC was decreased to 0.01 x 10(8)/kg, engraftment was seen in two of two dogs. These experiments thus established a cell dose response for causing marrow graft failure; further studies evaluated which subset of cells mediated this effect. Infusion of 0.09 x 10(8) nylon wool-nonadherent, plastic-nonadherent PBMC/kg was effective in causing marrow graft failure in three of three dogs. In contrast, infusion of 0.03 x 10(8) autologous monocytes/kg, enriched threefold above the number contained in the lower dose of PBMC causing graft failure, was associated with engraftment in four of six dogs. Infusion of 0.13 x 10(8) PBMC/kg treated with L-leucyl-L-leucine methyl ester (Leu-Leu-OMe), a drug that depletes canine cytotoxic T-lymphocytes (CTL), natural killer (NK) cells, and monocytes, permitted engraftment in three of four dogs. These data suggest that cytotoxic lymphocytes mediate failure of histoincompatible marrow grafts.