Abstracts

Cancer Immunotherapy using adjuvant-free, fusion protein encoding M. bovis BCG hsp65 and HPV16 E7

Abstract presented at Cancer Vaccine Week 1998  -  New York, NY  October 5-9, 1998

Chu NR, Wu B, Bantroch S, Boux L, Siegel M, Mizzen LA, Wu TC

Human papillomavirus type 16 (HPV16) infection has been linked to the development of cervical dysplasia and cervical cancer.  A hallmark of persistent infection is the continuous expression of HPV16 E6 (E6) and HPV16 E7 (E7) in the epithelial cells of the cervix.  Because of their sustained levels of expression and their integral roles in perpetuating malignancy, E6 and E7 are ideal candidates as tumor antigens for immunotherapy.  Using the TC-1 tumor cell line, (cotransformed by Ha-ras and HPV16 E6/E7), as a model for cervical cancer, we have studied the efficacy of a novel immunogen, Hsp65E7, on TC-1 tumor rejection.  Hsp65E7 is a recombinant fusion protein consisting of M. bovis BCG hsp65 covalently linked to HPV16 E7.  In vivo, subcutaneous (s.c.) injection with Hsp65E7 in saline prophylactically protects C57BL/6 mice against subcutaneous tumor challenge as well as therapeutically to induce regression of pre-existing subcutaneous tumor.  Cytokine release assays show that splenocytes from animals primed with Hsp65E7 produce IFN-gamma but no IL-4 upon restimulation.  Furthermore, the amount of IFN-gamma release in vitro correlates with the dose of Hsp65E7 used for in vivo injection.  E7 peptide-specific CTL activity is also recovered from mice primed with Hsp65E7.  Additional in vivo studies reveal that a single s.c. injection with Hsp65E7 can completely regress s.c. tumor in a dose-dependent manner and more significantly, this therapeutic treatment may be delayed for at least 21 days post tumor implantation and still induce tumor regression.  Lastly, the anti-tumor effect of Hsp65E7 treatment is associated with the fusion protein itself and not the individual moieties as s.c. injection with either Hsp65, E7 or the admixture does not prime for in vitro IFN-gamma release nor regress TC-1 tumor.  Taken together, these findings suggest that s.c. administration of adjuvant-free, Hsp65E7 fusion protein induces cellular anti-tumor immunity which results in the regression of an established E7-expressing tumor.