Relative diabetogenic properties of islet-specific Tc1 and Tc2 cells in immunocompetent hosts

CD8(+) T cells are important effecters, as well as regulators, of organ-specific autoimmunity. Compared with Tc1-type CD8(+) cells, Tc2 cells have impaired anti-viral and anti-tumor effector functions, although no data are yet available on their pathogenic role in autoimmunity. Our aim was to explore the role of autoreactive Tc1 and Tc2 cells in autoimmune diabetes. We set up an adoptive transfer model in which the recipients were transgenic mice expressing influenza virus hemagglutinin (HA) specifically in their pancreatic beta islet cells (rat insulin promoter-HA mice) and islet-specific Tc1 and Tc2 cells were generated in vitro from HA-specific CD8(+) cells of TCR transgenic mice (CL4-TCR mice). One million Tc1 cells, differentiated in vitro in the presence of IL-12, transferred diabetes in 100% of nonirradiated adult rat insulin promoter-HA recipients; the 50% diabetogenic dose was 5 x 10(5), Highly polarized Tc2 cells generated in the presence of IL-4, IL-10, and anti-IFN-gamma mAb had a relatively low, but definite, diabetogenic potential. Thus, 5 x 10(6) Tc2 cells caused diabetes in 6 of 18 recipients, while the same dose of naive CD8(+) cells did not cause diabetes. Looking for the cause of the different diabetogenic potential of Tc1 and Tc2 cells, we found that Tc2 cells are at least as cytotoxic as Tc1 cells but their accumulation in the pancreas is slower, a possible consequence of differential chemokine receptor expression. The diabetogenicity of autoreactive Tc2 cells, most likely caused by their cytotoxic activity, precludes their therapeutic use as regulators of autoimmunity.