Abstract 2421: An adenoviral vaccine encoding full-length inactivated human HER2 exhibits potent immunogenicity and enhanced therapeutic efficacy without oncogenicity
Authors: Hartman Zachary C. , Wei Jun-Ping , Glass Oliver , Yang Xiao-Yi , Lei Gang-jun , Morse Michael , Lyerly Herbert K. , Clay Timothy M. 
Published: February 2011

While HER2 oncogene directed therapies such as lapatinib and trastuzumab confer clinical benefits, a majority of metastatic HER2+ patients eventually experience progressive disease; however, their tumors remain strongly HER2+. Thus, current therapeutic limitations combined with continued HER2 expression in patients makes immunotherapeutic vaccination against HER2 an attractive strategy. But as HER2 is an oncogene, it is imperative to develop HER2 vaccines with maximal immunologic potential, but minimal oncologic potential. To address these issues, we created recombinant adenoviral vectors expressing the extracellular domain of HER2 (Ad-HER2-ECD), ECD plus the transmembrane domain (Ad-HER2-ECD-TM) and full length HER2 inactivated for kinase function (Ad-HER2-ki) and determined their relative immunogenicity, anti-tumor effectiveness, as well as their oncogenic potential.

As an immunotherapeutic vaccine, we found that that both Ad-HER2-ki and Ad-HER2-ECD-TM were highly effective in eliciting significant T-cell and antibody responses to HER2 in naïve mouse models compared to plasmid vaccination with HER2-ki constructs, thus validating the immunologic efficacy of the adenoviral platform. In contrast, we did not observe any induction of HER2 specific T-cell or antibody responses in HER2-ECD vaccinated animals. While the strong immune responses from both Ad-HER2-ki and Ad-HER2-ECD-TM vectors translated into significantly retarded tumor growth in naïve animals, our studies revealed that Ad-HER2ki vaccinated animals had the most significant HER2-specific T-cell responses as well as the most significant anti-tumor response. When a HER2+ tolerant mouse model was used, we observed that direct Ad-HER2-ki vaccination elicited only slightly diminished T-cell and antibody responses compared to HER2 naïve mice. Most significantly, we were able to demonstrate that Ad-HER2-ki vaccination of HER2+ tolerant mice elicits significant anti-HER2+ tumor responses.

Subsequent investigation into the oncogenicity associated with strong overexpression of HER2-ki revealed no evidence for its oncogenic functionality in terms of phosphorylation or transcriptional signature in primary human cells. We also found no evidence for its oncogenicity in enabling enhanced cellular proliferation, anchorage-independent growth, or transformation in vivo.

In sum, we found that vaccination with mutationally inactivated, non-oncogenic Ad-HER2-ki results in robust polyclonal immune responses to HER2 in tolerant models, which translate into strong and effective anti-tumor responses in vivo. Ad-HER2-ki is thus a safe and promising vaccine for evaluation in clinical trials.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2421.