Abstract: An antigen-specific T-cell response to alloantigen, tissue-specific antigen (e.g., islet antigen or other autoantigens involved in autoimmune disease), or self (or host) antigen is detected at an early stage of graft rejection or recurrent autoimmunity. An increase in cytotoxic lymphocyte gene (CLG) expression in peripheral blood is a risk factor for development of deleterious immune responses, which may be confirmed by functional assays. For example, the distinction between production of regulatory or inflammatory cytokines by T cells may dissect the type of immune response which is being induced: the survival of transplanted islet cells used to treat type 1 diabetes may be monitored, loss of the transplant by graft rejection (i.e., an alloantigen target) may be distinguished from autoimmune disease (i.e., a self or host antigen target).