Title

Roles of the cell surface expression of an ER-resident heat shock protein gp96 in anti-tumor immunity and autoimmunity

Date of Completion

January 2006

Keywords

Health Sciences, Pathology|Health Sciences, Immunology

Degree

Ph.D.

Abstract

Endoplasmic reticulum (ER)-resident heat shock protein gp96, derived from tumor cells, is now being tested in several clinical trials against human malignancies. Mechanistically, gp96 is able to interact with antigen presenting cells (APCs) through a receptor(s)-dependent manner, leading to cross-presentation of gp96-associated antigens to MHC molecules and activation of APCs to initiate adaptive immunity. Without tissue stress or necrotic death, these intracellular molecules are not accessible to their receptors on the surface of APCs. I hypothesized that an uncontrolled extracellular export of gp96 in vivo could possibly break the immunological tolerance. To test this hypothesis, gp96 was targeted onto tumor cell surface (96tm). The surface expression of gp96 on progressive tumor cells rendered them regressive, which was dependent on CD4+ and CD8+ T-lymphocytes. It was revealed that 96tm+ tumor cells potentiated the cross-priming of naïve CD8+ T cells. Therefore, the maneuver of the localization of intracellular heat shock proteins could provide a new therapeutics for cancer immunotherapy. The hypothesis was further tested in 96tm transgenic mice, in which gp96 is ubiquitously expressed on the cell surface. Transgenic mice spontaneously developed lupus-like autoimmunity, which was dependent on CD4+ T cells and B cells. By using a novel conditional DC knockout mouse and macrophage (M&phis;)-specific depletion reagents, it was demonstrated that DCs but not M&phis;s were necessary for the initiation of lupus-like autoimmunity. Moreover, pro-inflammatory cytokine IL-12 but not IL-23 was essential for the development of autoimmunity. The roles of regulatory T cells (Treg) were also investigated because the loss of self-tolerance could be due to the defects of Treg's inhibitory functions. It was found that Tregs from transgenic mice exerted significantly increased suppressive function in vitro and in vivo, which was dependent on Toll-like receptor-4. This transgenic mouse model established at the cellular and molecular levels that an uncontrolled access of gp96 to DCs in vivo could be a pathological cause of spontaneous autoimmune diseases. Taken together, my thesis work provided strong evidence that the cell surface expression of gp96 has profound impacts on both the innate and the adaptive immunity against tumor and self antigens. ^