Immunization with inactivated autoreactive T cells (T cell vaccination) selected from individual's own T cell repertoire provides a unique in vivo setting for testing immune regulation that is known to involve interactions of a variety of related surface molecules (1). It induces regulatory immune responses that closely resemble the in vivo situation where the immune system is challenged by clonal activation and expansion of given T cell populations in various autoimmune diseases. T cell vaccination provides a powerful means of eliciting natural reactions of the immune system in response to clonal expansion of T cells, which can be used as a therapeutic approach to suppress or eliminate specific pathogenic autoreactive T cells in autoimmune conditions. Clinical trials using T cell vaccination to deplete autoreactive T cells in human autoimmune conditions have begun to reveal the pathologic relevance of various autoimmune T cell populations in the disease processes, providing a unique opportunity to test the autoimmune theories in a clinical setting.