Dose-dependent enhancing and inhibitory effects of A77 1726 (leflunomide) on cytotoxic T lymphocyte induction

Abstract

Leflunomide is an immunosuppressive prodrug which prevents allograft rejection in several animal model systems and may, therefore, have clinical application in organ transplant recipients. Although cytotoxic T lymphocytes (CTL) are an important component of the allograft rejection response, the effect of leflunomide on CTL development has not been thoroughly explored. In this study we have determined the effect of A77 1726, the active metabolite of leflunomide, on CTL induction in C57BL/6 mouse T cell cultures stimulated with anti-CD3 monoclonal antibody. Conjugate formation with P815 target cells, granzyme B enzymatic activity in CTL lysates, and P815 cytolysis in a 51Cr-release assay were used as determinants of in vitro CTL function. At high concentrations (10–20 μM), A77 1726 strongly inhibited CTL generation. In contrast, a low concentration (0.5 μM) of A77 1726 promoted CTL development. These dose-dependent opposing effects of A77 1726 on CTL induction could not be attributed to alterations in CD8 + lymphocyte percentages, interleukin-2 or CD25 expression, or the ability to conjugate with P815 target cells. However, both interferon- γ and granzyme B expression were significantly decreased when CTL were induced in the presence of 10-20 μM A77 1726, and were slightly, but not always significantly, elevated in the presence of 0.5 μM A77 1726. We conclude that at high concentrations A77 1726 is a potent inhibitor of CTL induction, but a low concentration of A77 1726 enhances CTL development.