Abstract 6161: HER3 expression is associated with cold tumor immune microenvironment and the regulation of its signal in humanized breast cancer patient derived xenograft models converts to hot tumor
Authors: Tanaka Sunao , Suzuki Eiji , Kotake Takeshi , Kawaoka Shinpei , Kawaguchi Kosuke , Nishimura Tomomi , Pu Fengling , Toi Masakazu 
Published: June 2022

Abstract
Background: HER3 signal pathways in cancer cells are thought to be involved in up-regulation of PD-L1 expression, resulting in “cold” tumor immune microenvironment (TIME). However, little is known on the association of HER3 expression and immune related molecular network in breast cancer and the functional role of HER3 signals in antitumor immune responses.
Methods: The dataset of the TCGA study was analyzed to determine the correlation of HER3 expression and antitumor immune molecules. Two breast cancer patient-derived xenograft (PDX) models were treated with patritumab (anti-HER3 antibody), polyclonal activated autologous T cells (PATCs) or a combination of patritumab and PATCs (P-PATCs) in order to test immunological modulation by the regulation of HER3 signals. RT-PCR, immunohistochemical staining and CyTOF were performed in tumors or liver tissue for CD3, CD4, CD8a, CD137, CD134/OX40, CD80, IFN-γ and PD-L1, LAG3, TIM3, FOXP3. In addition, HER3-knockdown human breast cancer cell lines and PBMC were co-cultured and comprehensive cytokine expression in supernatant was analyzed by bioplex.
Results: In TCGA dataset analysis, HER3 expression was inversely corelated with expression of CD4, CD8A, IFN-γ, granzyme A/B. In humanized PDX models, although treatment of PATCs or patritumab alone showed limited anti-tumor effects, P-PATCs treatment showed a significantly greater anti-tumor response. Interestingly, the proportion of CD137 expressing T cell infiltration and mRNA expression of CD137 was significantly higher in P-PATCs group compared to patritumab or the PATCs group, while the proportion of CD4/8 T cell infiltration was also higher in the P-PATCs group. CyTOF revealed that the proportion of CD137 and CD134/OX40 expressing cells was higher in P-PATCs group compared to the PATCs group. In co-culture of PBMC with HER3 knockdown cancer cells, the secretion level of immune stimulatory factors (IL2, IFN-g, TNF-a) increased and immune inhibitors (IL6, IL10) decreases.
Conclusions: These data suggest that HER3 expression in breast cancer associated with “cold” TIME and the regulation of its signal converts “cold” TIME to “hot”. Thus, inhibition of HER3 signal might be of interesting concept for both regulation of oncologic signal and immunological modulation in HER3-expressing breast cancer. Further HER3 related immune modulation exploration in breast cancer treatment strategy needs to be clarified in the future.
Citation Format: Sunao Tanaka, Eiji Suzuki, Takeshi Kotake, Shinpei Kawaoka, Kosuke Kawaguchi, Tomomi Nishimura, Fengling Pu, Masakazu Toi. HER3 expression is associated with cold tumor immune microenvironment and the regulation of its signal in humanized breast cancer patient derived xenograft models converts to hot tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6161.