Effect of posttransplantation administration of peripheral blood lymphocytes in skin-grafted mice treated with antilymphocyte serum or antilymphocyte serum plus bone marrow.

Posttransplantation administration of donor-specific bone marrow cells to ALS-treated allograft recipients produces graft survival that is greater than that produced by ALS treatment alone. We have now studied the effect of peripheral blood lymphocytes (PBLs) in a mouse skin allograft model using this protocol (C3H skin grafted to B6AF1 mice, day 0; i.p. ALS on days -1 and +2; i.v. bone marrow days +6 or +7). When PBLs are injected in place of bone marrow cells, graft survival is extended beyond that noted for control mice given ALS only. The timing and specificity of this phenomenon suggest that it resembles the effect produced by posttransplant bone marrow administration and not that associated with pretransplant blood transfusion. The PBLs active in graft prolongation are Thy-1-negative and display a density in Percoll gradients similar to that of the active marrow cells. In contrast, when PBLs are injected in combination with bone marrow cells, the length of graft survival is shortened in comparison with that produced by bone marrow alone. The cells associated with this partial abrogation of the effectiveness of bone marrow appear to be mature T cells; this abrogation cannot be produced by PBLs treated with anti-Thy-1 plus complement or by thymocytes, but it is a property of lymph node cells enriched for T cells by nylon-wool fractionation. This study suggests that clinical application of this posttransplantation induction of specific allograft unresponsiveness can be facilitated by the use of peripheral blood lymphocytes rather than marrow, sparing a living organ donor from having to undergo bone marrow harvest. Additionally, the data indicate that contamination of marrow with blood lymphocytes should be minimized. However, the density gradient fractionation method that we have found to be effective in preparing the graft prolonging bone marrow cells simultaneously removes the PBLs deleterious to graft survival.