Identification of Immunoreactive Tumour Antigens Using Free and Exosome-Associated Humoral Responses

Abstract

Altered tumour antigens can initiate cellular and humoral immune responses; however, they often fail to eliminate tumours. In humans, the presence of cancer is generally associated with the suppression of T cell activation and effector responses, characterized as a Th1 to Th2 biased response. This Th2 response leads to the production of tumour-reactive antibodies. Further, neoplastic lesions and biological fluids of cancer patients contain an abundance of tumour-derived exosomes (TDE) expressing tumour antigens. Expression of tumour antigens on TDE may represent an antibody target and serve to block antibody binding to the tumour, implicating a role for these nanovesicles in tumour survival. In this study, ovarian tumour cell proteins were separated by two-dimensional electrophoresis (2-DE) and patient-derived antibodies were used to analyse immunoreactivity. Common immunoreactive proteins among ovarian cancer patients were identified by mass spectrometry and six proteins were selected based on recognition and correlation 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-derived ovarian tumour exosomes was defined. Analysis of the TDE demonstrated bound tumour-reactive immunoglobulins, exhibiting immunoreactivity with specific antigens, suggesting that patient-derived antibodies recognize tumour antigens on circulating exosomes.