Perforin Is Required for Innate and Adaptive Immunity Induced by Heat Shock Protein Gp96 of CD8 CTL in response to heat shock protein gp96- peptide comlexes, indicating an essential function for perforin-mediated lysis in the nascent NK and CD8 CTL

trauma, infection, or necrosis (Basu et al., 2000; Berwin Tumor-secreted gp96-Ig is highly immunogenic and et al., 2001). Gp96-peptide complexes bind to CD91 and triggers CD8 T cell-mediated tumor rejection. In vivo other receptors on dendritic cells (Basu et al., 2001; secreted gp96-Ig and gp96-myc cause NK activation Berwin et al., 2002; Binder et al., 2000), mediate endocyand clonal expansion of specific CD8 CTL in wildtosis and dendritic cell maturation (Singh-Jasuja et al., type and in Fas-ligand-deficient (gld) mice but not in 2000), and chaperone peptides into class I MHC of denperforin(PKO) or IFN-deficient (GKO) mice. Transdritic cells and macrophages (Arnold et al., 1995; Udono fer of perforin-competent NK cells restores the ability and Srivastava, 1993). It has been postulated that activaof PKO mice to clonally expand CD8 CTL in response tion of APC by gp96 is responsible for the subsequent to gp96-Ig. The data demonstrate an essential role for CTL response in vivo. perforin-mediated functions in the activation of innate In previous studies we generated a secreted form of and adaptive immunity by heat shock protein gp96gp96, gp96-Ig, by deletion of the endoplasmic reticulum peptide complexes. Crosspresentation of antigens by retention signal and replacement with the Fc portion of heat shock proteins seems to require a perforinmurine IgG1. When transfected into tumor cells and used dependent positive feedback loop between NK and for immunization of mice, secreted gp96-Ig generated DC for both sustained NK activation and clonal CTL a protective and specific immune response against subexpansion. The studies also explain how depressed sequent challenge with the same tumor (Yamazaki et NK activity in patients with tumors or after viral infecal., 1999). Immune rejection was dependent on CD8 cells tions could diminish CTL responses. and did not require CD4 help, supporting the concept that