Abstract P4-04-05: Listeria monocytogenes-based bivalent Lm-LLO immunotherapy for the treatment of HER2/neu positive and triple negative breast cancer and its impact on immunosuppression

Abstract

Abstract Overexpression of tumor associated antigens (TAA) such as HER2/neu and high molecular weight melanoma associated antigen (HMW-MAA) are associated with aggressive high-grade tumors leading to disease progression and reduced survival. HMW-MAA has been reported as a TAA in triple negative breast tumors and is also expressed at high levels by activated pericytes and pericytes in tumor angiogenic vasculature that are associated with neovascularization in vivo. Previously published reports have shown that bioengineered Listeria monocytogenes (Lm) secreting either a chimeric HER2/neu antigen (cHER2), or HMW-MAA fragment, fused to a truncated highly immunogenic fragment of the adjuvant protein listeriolysin O (LLO) were found to impact the growth of both transplantable and transgenic mouse breast tumor models. Therefore, we hypothesized that an Lm-LLO immunotherapy capable of delivering two different antigens would likely have a synergistic effect of decreasing tumor growth by targeting two independent mechanisms that support tumor growth; 1) tumor angiogenesis, and 2) tumor cell surface marker, thus improving the therapeutic efficacy of the agent. Here we report the construction of a bivalent recombinant Lm-LLO immunotherapy that expresses and secretes both the cHER2 and HMW-MAA antigens concomitantly as fusion proteins. Initial characterization of the bivalent immunotherapy indicates that both the antigens cHER2 and HMW-MAA are stably expressed and secreted after two in vivo mouse passages. Preliminary studies support the hypothesis that bivalent immunotherapy causes efficient reduction of tumor growth in both HER2 expressing and triple negative breast tumors. Further, mechanistic studies demonstrate that treatment with Lm-LLO immunotherapy resulted in a decreased proportion of regulatory T cells (Tregs) as well as Myeloid Derived Suppressor Cells (MDSC) particularly in the tumor microenvironment and not in spleen, tumor draining lymph nodes, or peripheral blood. Interestingly, both residual Tregs and MDSCs isolated from the tumor microenvironment were found to have a decreased ability to suppress the division of T cells after Lm-LLO immunotherapy, a finding which warrants further investigation. We will present data on the efficacy of bivalent Lm-LLO immunotherapy and the mechanisms that are likely responsible for the observed tumor regression. Currently Lm-LLO immunotherapies are being evaluated in Phase 2 clinical trials for HPV-associated dysplasia and malignancies such as CIN2/3, cervix cancer and head & neck cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-04-05.