Direct evidence for clonal destruction of allo-reactive T cells in the mice treated with cyclophosphamide after allo-priming.

It has previously been reported that a single i.p. injection of 200 mg/kg cyclophosphamide (CP) 2 days after priming with 10(8) donor spleen cells (SC) leads to donor-specific skin allograft tolerance in H-2 compatible, multiminor antigen incompatible murine strain combinations. It is speculated that the i.v. injection of donor cells may result in synchronized proliferation of donor-reactive host T cells and subsequently administered CP may specifically destroy these proliferating T cells in the periphery. Although this unique action of CP is considered to be a principal mechanism in this method, direct evidence has not yet been obtained. In the present article, this in vivo destructive effect of CP is clearly demonstrated by assessing detailed kinetics of host-derived blastoid T cells and donor (Mls-1a)-reactive V beta 6+ T cells in the model system of C3H mice rendered tolerant to AKR. Frequencies of the blastoid cells and V beta 6+ cells, which increased as a result of AKR priming, decreased rapidly with the administration of CP. C3H mice, which received AKR SC alone, also exhibited partial deletion of V beta 6+ T cells, but both tempo and magnitude of decrease in the frequency of V beta 6+ cells were quite different from those of the C3H mice given AKR SC and CP, which showed more rapid and profound elimination of V beta 6+ T cells. In accordance with these kinetic studies, in vitro proliferative response to Mls-1a antigens was greatly impaired in mice treated with SC and CP, whereas a low but appreciable response was detected in mice given SC alone.(ABSTRACT TRUNCATED AT 250 WORDS)