Abstract 4079: Reversal of immune evasion mediated by HER2 requires both humoral and cellular HER-2 targeted immune interventions

Objectives: HER2 over-expression in breast cancer is associated with a poor prognosis and HER2 is an intense target of immunotherapy with both humoral and T cell -base approaches. HER2 expression is also known to facilitate the escape of tumor cells from immune surveillance by down-regulating MHC class I, resulting in a reduced sensitivity to CTL lysis. Restoring tumor cell MHC Class I expression and reversing their immune evasion are therefore important strategies in the design of immunotherapy against HER2 expressing tumors. In this study we investigated the effects of monoclonal antibody trastuzumab and T help-1 associated cytokines IFN-γ and TNF-A on HLA Class I expression and the susceptibilities to CTL lysis of human HER2 expressing tumor cell lines. Methods: Breast cancer cell lines MCF7, SKBR3, BT474 and ovarian cancer cell line SKOV3 were treated with trastuzumab only, combination of IFN-γ and TNF-A or trastuzumab with IFN-γ and TNF-A. Cell surface expressions of HLA ABC were examined by flow cytometric analysis. The susceptibility of tumor cells to HER2 specific CD8+ T cell recognition and CTL lysis were assessed by measurement of CD8+ T cell IFN-γ secretion and flow cytometric analysis respectively. Results: Th1 cytokines IFN-γ and TNF-A dramatically increased HLA ABC expressions on all tumor lines compared to untreated cells, [ MCF7 (p=0.04); SKBR3 (p=0.02); SCOV3 (p=0.02) and BT474 (p=0.04)], while trastuzumab alone showed little impact on HLA ABC up-regulation. When treated with a combination of trastuzumab, IFN-γ and TNF-A tumor cells displayed synergistically enhanced HLA ABC expression [MCF7 (p=0.02); SKBR3 (p=0.004); SKOV3 (0.006) and BT474 (p=0.03)]. We observed that IFN-γ and TNF-A treatment was able to remarkably increase CD8+ T cell recognition and CTL lysis of low and intermediate HER2 expressing tumors [ MCF7(p=0.03) and SKOV3(0.02)], but not High HER2 tumor[ SKBR3(p=0.07)]. Only a combined treatment of trastuzumab, IFN-γ and TNF-A rendered SKBR3 susceptible to a significant killing by CTL (p=0.02). To investigate the impact of other HER family members EGFR and HER3 on MHC class I expression , HER2 over-expressing breast cancer cell lines BT474 and SKBR3 were pre-treated with EGF or Heregulin, then subjected to IFN-γ and TNF-A treatments. Activation of HER1 and HER3 signaling made HER2 over-expressing cells resistant to the effect of MHC class I up-regulation by IFN-γ and TNF-A. Conclusion: Both humoral and cellular immune HER-2 targeted interventions are required to reverse immune escape mediated by HER2; in addition to targeting HER2, targeting HER1 and HER3 signaling elements should also be included in order to abrogate the cross talk between HER family members and more effectively inhibit the HER2 signaling pathway. Citation Format: Shuwen Xu, Jessica Cintolo, Jashodeep Datta, Cinthia Rosemblit, Erik Berk, Julia Terhune, Elizabeth Fitzpatrick, Brian Czerniecki. Reversal of immune evasion mediated by HER2 requires both humoral and cellular HER-2 targeted immune interventions. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4079. doi:10.1158/1538-7445.AM2014-4079