Abstract 5015: Tumor dependence on HER2 signaling as a player in immune infiltration required for trastuzumab activity
Authors: Triulzi Tiziana , Regondi Viola , De Cecco Loris , Ghedini Gaia , Carcangiu Maria Luisa , Pupa Serenella M. , Tagliabue Elda 
Published: August 2015

Abstract
The identification of a robust clinical or molecular predictor of trastuzumab benefit has proven challenging. Recent clinical studies have shown that either tumor dependence on HER2 signaling or the presence of high levels of tumor-infiltrating lymphocytes is predictive of trastuzumab sensitivity. Preclinical data suggest that only a fraction of the HER2+ breast carcinoma (BC) cells are truly addicted to the oncogene and that innate and adaptive immune cells contribute substantially to the therapeutic effect of trastuzumab. Based on these data, we aimed to determine whether tumor cells addicted to HER2 guide the development of tumor immune cell infiltration required for trastuzumab cytotoxic activity.
Gene expression profile analysis of 53 HER2+ BC patients treated with adjuvant trastuzumab and chemotherapy identified a 41-gene classifier able to predict tumor relapse risk in both adjuvant and neoadjuvant settings. Tumors classified as low-risk presented high HER2 mRNA levels and were mainly HER2-enriched based on PAM50 signature (p&lt;0.0001); these tumors showed significantly enhanced immune cell pathways and T cell infiltration as compared with high-risk samples. Gene-set enrichment analysis identified chemokine and cytokine ligands and receptor pathways enriched in low-risk patients (ES = 0.63, p&lt;0.0001, FDR&lt;0.0001), with CXCL9, CXCL10, CXCL11 and CX3CL1 also significantly (p&lt;0.05) associated with low relapse risk. The high CXCL9 expression in low-risk tumors was validated by immunohistochemistry on FFPE tumor slides. PD-L1 expression levels were also significantly higher in low- than in high-risk tumors (p = 0.0014). Mean expression levels of relevant chemokines in human HER2+ BC cell lines as analyzed by qRT-PCR were 3- to 30-fold higher in HER2-addicted lines HER2 (ZR75.30, SKBr3 and BT474) than in non-addicted lines (MDAMB361 and MDAMB453). Similarly, murine CXCL10 and CX3CL1 levels were 2- and 10-times higher, respectively, in murine MI6 mammary carcinoma cells than in wild-type (WT) HER2 cells derived from mice transgenically expressing human delta16-HER2, which develop HER2-addicted tumors, or human WT-HER2, which develop non-addicted mammary tumors. Analysis of PBMC migration induced by tumor cells showed a higher recruitment of immune cells by HER2-addicted than non-addicted cells in vitro.
Overall, our results support the notion that the activated HER2 oncogene induces production of chemokines/cytokines that recruit the immune infiltrate favorable to trastuzumab activity. Moreover, it seems likely that tumor cells themselves exert a PD-L1-dependent immunosuppressive activity that trastuzumab reverts to anti-tumor immunity.
Supported by AIRC and Fondazione Pezcoller.
Citation Format: Tiziana Triulzi, Viola Regondi, Loris De Cecco, Gaia Ghedini, Maria Luisa Carcangiu, Serenella M. Pupa, Elda Tagliabue. Tumor dependence on HER2 signaling as a player in immune infiltration required for trastuzumab activity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5015. doi:10.1158/1538-7445.AM2015-5015