INFLUENCE OF DONOR LYMPHOCYTES ON THE INCIDENCE OF PRIMARY GRAFT FAILURE AFTER ALLOGENEIC BONE-MARROW TRANSPLANTATION IN A MURINE MODEL

We used a murine model to determine the impact of donor lymphocyte subsets on the incidence of primary marrow graft failure after transplantation of lymphocyte-depleted bone marrow. After lethal irradiation with 7.5 Gy, Balb/c mice received 1 x 10(5) to 4 x 10(7) GvH-nonreactive (C57 x Balb)F1 or GvH-reactive C57Bl/6 marrow cells. Pretreatment with anti-Thy-1.2, anti-CD4/CD8, anti-asialo-GM1 or L-leucyl-L-leucine methyl ester (Leu-Leu-OMe) was employed to eliminate T lymphocytes and/or natural killer cells, Primary graft failure was defined as death with neutrophils < 0.5 x 10(9)/l. To assess long-term chimaerism, the percentage of H-2(b)-positive spleen cells was determined. Pretreatment with anti-Thy-1.2, anti-CD4/CD8 or Leu-Leu-OMe successfully eliminated GvHR-induced mortality. Graft failure rates gradually declined from 88% after transplantation of 1 x 10(5) cells to 0% after transplantation of 4 x 10(7) C57Bl/6 cells. The incidence of graft failure, however, was not altered by T-celI depletion, provided that the unspecific loss of marrow cells was compensated for. After transplantation of GvH-nonreactive (C57 x Balb)F1 bone marrow, neither ex-vivo treatment with anti-Thy-1.2 and anti-asialo GM1 nor addition of 1 x 10(7) donor thymocytes to the allograft significantly influenced engraftment. The data obtained in our animal model suggest that the total number of marrow cells is of critical importance for successful marrow engraftment and not the presence or absence of T cells, NK cells or GVHR.