Cells mediating graft rejection in the mouse. IV. The Ly-5, 6, and 8 effector cell phenotype

“Pruning” of Alloreactive CD4+T Cells Using 5- (and 6-)Carboxyfluorescein Diacetate Succinimidyl Ester Prolongs Skin Allograft Survival

Removal of alloreactive cells by either thymic deletion or deletion/anergy in the periphery is regarded as crucial to the development of tolerance. Dyes, such as CFSE, that allow monitoring of cell division suggest that in vitro proliferation could be a used as a way of "pruning" alloreactive cells while retaining a normal immune repertoire with retention of memory to previously encountered pathogens. This would overcome the problems occurring as a result of therapies that use massive depletion of T cells to allow acceptance of organ transplants or bone marrow grafts. We therefore used a skin graft model of CD4-mediated T cell rejection across a major H-2 mismatch (C57BL/6 (H-2(b)) to BALB/c (H-2(d)) mice) to evaluate whether nondividing CD4(+) T cells derived from a mixed lymphocyte culture would exhibit tolerance to a skin graft from the initial stimulator strain. We demonstrate that selective removal of dividing alloreactive CD4(+) T cells resulted in marked specific prolongation of allogeneic skin graft survival, and that the nondividing CD4(+) T cells retained a broad TCR repertoire and the ability to maintain memory. This novel way of depleting alloreactive T cells may serve as a useful strategy in combination with other mechanisms to achieve transplant tolerance.

Cellular basis of allograft rejection

In summary, we currently hypothesize that systemic immunization within the lymphoid tissue is amplified by a sequence of specific and non-specific immunological interactions which lead to enrichment of specifically sensitized T-cells at the graft site. Nascent sensitized cells enter the graft via non-specific attractants generated by the healing response. The interaction of alloantigen with responder T-cells bearing specific alloantigen receptor results in production of lymphokines which increase blood flow and vascular permeability, and which are chemotactic for circulating lymphocytes. These events and other non-specific events recruit circulating cells regardless of the specificity of their sensitization. The state of activation of these cells may control their presence within the circulation. Cells which are more activated are released more readily from the lymphoid depots into the circulation so that relatively more specifically sensitized (though not necessarily mature cytotoxic cells) cells would enter the circulation and be recruited to the graft. At the allograft, there is an escalating sequence of lymphokine production and non-specific recruitment. II-1 has been demonstrated to be capable of mediating such recruitment. A second phase of amplication occurs at the graft site where precytotoxic (x-ray-sensitive) cells mature and expand into cytotoxic (x-ray-resistant) cells. These cells may be important effector cells of allograft rejection in concert with many unsensitized cells which can participate in non-specific attacks on graft viability. The essential point made from the studies summarized here is the consideration that trafficking patterns of lymphocytes and recruitment of lymphocytes and other inflammatory cells are in essential component to the local mechanism of graft rejection. The relative importance of specificity of response has not been defined.