INDUCTION OF NONSPECIFIC X-IRRADIATION-RESISTANT SUPPRESSOR-CELL ACTIVITY IN-VIVO AND PROLONGATION OF VASCULARIZED ALLOGRAFT SURVIVAL BY SK-AND-F-105685, A NOVEL IMMUNOMODULATORY AZASPIRANE

SK&F 105685 is a novel azaspirane with immunosuppressive activity in a nimal models of autoimmune disease. This study evaluates the efficacy and mechanism of action of the compound in rat recipients of cardiac a llografts. Short-term SK&F 105685 therapy (20 mg/kg/day by gavage) pro ved effective both in the pretreatment (days -14 to -8 or -7 to -1; al lograft at day 0) and treatment (days 0 to 6) protocols, with cardiac allograft survival prolonged to 14-17 days (acute rejection = 7 days; P<0.001). SK&F 105685 pretreatment exerted at least additive effects w ith subtherapeutic CsA (1.5 mg/kg/day x7 days i.m.) given after transp lantation, with 50% of allografts surviving >50 days. SK&F 105685 ther apy diminished the immunohistological features of acute rejection, wit h the cellular infiltrate suppressed and the induction of IL-2/transfe rrin receptors, and elaboration of IL-2/IFN-gamma essentially abolishe d, as compared with the grafts in untreated hosts. These correlated wi th normal frequency of CD4, CD5, CD8 phenotype subsets and B cells in recipient lymphoid organs, as shown by flow microfluorimetry. Adoptive transfer of untreated or x-irradiated (2000 rads) spleen cells from S K&F 105685-modulated hosts significantly prolonged the survival of don or-specific or third-party test cardiac allografts to 10-15 days, sugg esting the presence of nonspecific x-irradiation-resistant suppressor cells in the transferred inoculum. Their activity could be enriched by Percoll density centrifugation and screened by the ability to inhibit Con A-driven proliferation of normal cells in the coculture assay. Th e light-density x-irradiation-resistant spleen cell fraction (1.07 g/m l) was consistently and significantly more suppressive than the heavy- density (1.09 g/ml) interface, or the corresponding unseparated cells. Thus SK&F 105685 therapy abrogates rejection response and significant ly prolongs the survival of vascularized cardiac allografts in rats. T his effect is associated with selective depression of host alloreactiv ity/immune activation at the graft site, and simultaneous induction of suppressor cells in recipient spleen, comparable to natural or non-sp ecific suppressor cells generated by TLI. This unique activity profile is consistent with the concept that SK&F 105685 should be considered as a critical chemical adjunct in novel therapeutic strategies represe nting TLI-equivalent.