EFFECT OF A NOVEL IMMUNOSUPPRESSANT, ST1959, ON ALLOGENEIC IMMUNE RESPONSE AND RENAL ALLOGRAFT SURVIVAL IN RATS

P1133 3,5-Diaryl-s-triazoles belong to a new class of contragestional agents with also, among other properties, immunosuppressant activity. A previous study showed that a compound from this class, 3-(2-ethylphenyl)-5-(3-methoxyphenyl)-1H-1.2,4-triazole, DL111-IT (recoded ST1959), inhibits both humoral and cellular immune responses by a non-cytotoxic mechanism. To find new immunosuppressive therapies based on more selective and less toxic agents, we investigated the effects of ST1959 on allogeneic immune response and on renal allograft survival in rats. In the first part of the study, two groups of Lewis rats received ST1959 (0.5 mg/Kg, subcutaneously) for 6 days, with or without infusion of 10 x 106 splenocytes from Brown Norway rats on day one to induce sensitization. Control groups received vehicle alone with or without alloantigens. At the end of treatment, all rats were sacrificed and thymus, spleen, lymph nodes, bone marrow, and blood were harvested. Cell number, leukocyte subpopulations (by FACS analysis) and T cell alloreactivity (by MLR) were evaluated. The direct effect of ST1959 on T cell proliferation was evaluated by adding the drug to MLR from allosensitized rats treated with vehicle. Three additional groups of Lewis rats underwent an allogeneic kidney transplant (from BN rats): two groups received ST1959 (0.5 mg/Kg, subcutaneously daily until death or for 6 days and then twice every week) and the third one received vehicle. Renal function was monitored until death. In naïve rats, ST1959 reduced thymus weight and cellularity, lowering the percentage of CD4+CD8+ thymocytes (74.2 ± 2.7 vs. vehicle: 89.1 ± 1.1 %; p<0.05), and reduced cellularity in spleen and lymph nodes and lymphocyte % in blood. This was not associated with myelosuppressive effect, since bone marrow cellularity was not affected by ST1959. In lymph nodes of allosentized rats, ST1959 completely normalized the increased % of activated CD4+ T cells (CD4+CD25+), while the drug had no effect on the % of CD4+CD25+ cells in naïve rats. Consistently, the stimulation indexes (SI) of MLR from allosensitized animals treated with ST1959 were significantly lower than those recorded in MLR from allosensitized rats treated with vehicle (SI:6.9 ± 1.7 vs. 17.3 ± 2.6; p<0.05). In vitro addition of ST1959 to MLR from allosensitized rats significantly reduced the SI (7.6 ± 3.4 vs. 17.3 ± 2.6; p<0.05). In renal allografts recipients, ST1959 significantly prolonged survival in comparison to vehicle (12 ± 1 vs. 7.4 ± 0.5 days; p < 0.001). Consistently, serum creatinine levels at day 7 post-transplant were significantly lower in recipient rats given ST1959 as compared with rats treated with vehicle alone (1.85 ± 0.39 vs. 2.62 ± 0.49 mg/dl; p < 0.05). These results show that ST1959 has immunomodulatory activity and significantly prolongs survival of renal allografts in rats. Preliminary results indicate that it acts both centrally by reducing CD4+CD8+ thymocytes and in periphery by preventing T cell activation. Further studies are requested to better understand its mechanism of action.