Date on Master's Thesis/Doctoral Dissertation

12-2014

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Committee Chair

Suttles, Jill

Committee Co-Chair (if applicable)

Mitchell, Tom

Committee Member

Chesney, Jason

Committee Member

Bodduluri, Haribabu

Subject

Ovaries--Cancer; Immune complexes; Cancer--Immunological aspects; Tumor antigens

Abstract

The pathogenesis of epithelial ovarian cancer is complicated by its diagnosis during the latter stages of the disease resulting from lack of symptoms or from presence of symptoms that mimic other conditions. Because of the often fatal prognosis by the time of actual detection, efforts are being made to better understand the host immune response to ovarian cancer. In this study, the contributions of the humoral immune response were investigated by focusing on the role of tumor-derived exosomes and their ability to modulate humoral immune responses. First, ovarian cancer patient-derived free circulating antibodies were investigated for immunoreactivity to patient antigen. The immunoreactivity allowed for the mass spectrometry identification of six proteins which have been shown to be correlated with cancer pathogenesis. The identity of these proteins were confirmed by immunoreactivity of patient-derived antibodies with recombinant proteins and their presence on in vivo and in vitro ovarian tumor-derived exosomes (TDE) was defined. Analysis of the TDE demonstrated bound tumor-reactive immunoglobulin (predominantly IgG1 and IgG2) that exhibited immunoreactivity with the identified antigens. Direct effects of the TDE on the B cell were investigated by coculture of B cells with patient TDE at different concentrations and time points. Surprisingly, B cells were induced to undergo apoptosis, with the greatest cell death seen at the latter time points and with the higher concentrations of exosomes. Apoptosis as the mechanism of cell death was confirmed by Western blot analysis with common apoptotic markers, PARP and caspase-3, and DNA fragmentation analysis using agarose gels. Further analysis of the supernatant from the B cell/TDE cocultures revealed increases in three proteins (PAI-1, IL-16, and sICAM-1). Collectively, data from this study suggests that ovarian patient-TDE express immunogenic antigen that binds IgG as a mechanism to divert the humoral antitumor response away from the tumor, while utilizing different subclasses to mediate strength of the antitumor response. Furthermore, ovarian patient-TDE induce apoptosis of B cells to diminish production of antitumor antibodies and promote secretion of proteins to assist the ovarian tumor in immune escape and promote its survival.

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