Downregulated ATP6V1B1 expression acidifies the intracellular environment of cancer cells leading to resistance to antibody-dependent cellular cytotoxicity.

Among several mechanisms for the resistance of human epidermal growth factor receptor 2-overexpressing (HER2 +) cancer cells to trastuzumab, little is known regarding the mechanism underlying the resistance to trastuzumab-mediated antibody-dependent cellular cytotoxicity (ADCC). Cell death due to ADCC is caused by apoptosis of target cells induced by granzymes released from natural killer cells. Because optimal granzyme physiological activity occurs at neutral pH, we assumed that the pH of the intracellular environment influences the cytotoxic effects of granzymes. We established ADCC-resistant cells and compared them with wild-type cells in terms of the expression of intracellular pH-regulating genes. The expression of ATP6V1B1, which encodes a component of vacuolar ATPases, was downregulated in the ADCC-resistant cells. Thus, to functionally characterize ATP6V1B1, we used a CRISPR/Cas9 system to generate ATP6V1B1-knockout SKBR3 and JIMT-1 cells (both HER2 + human breast cancer cell line). The resulting cells exhibited significantly less ADCC than the control SKBR3 and JIMT-1 cells. The intracellular pH of the ATP6V1B1-knockout SKBR3 and JIMT-1 cells was significantly lower than control SKBR3 and JIMT-1cells. An analysis of granzyme dynamics during the ADCC reaction in cancer cells revealed that granzymes degraded intracellularly in the control SKBR3 and JIMT-1 cells and accumulated in ATP6V1B1-knockout cells, but were not cytotoxic. These findings suggest that decreased vacuolar ATPase activity alters the cytoplasmic pH of cancer cells to create an environment that is less suitable for granzyme bioactivity, which adversely affects the induction of apoptosis of cancer cells by NK cells.

Downregulation of neuropilin-1 on macrophages modulates antibody-mediated tumoricidal activity.

Neuropilin-1 (NRP-1)-expressing macrophages are engaged in antitumor immune functions via various mechanisms. In this study, we investigated the role of NRP-1 on macrophages in antibody-mediated tumoricidal activity. Treatment of macrophages with NRP-1 knockdown or an anti-NRP-1-neutralizing antibody significantly suppressed antibody-dependent cellular cytotoxicity and modulated cytokine secretion from macrophages in vitro. Furthermore, in vivo studies using a humanized mouse model bearing human epidermal growth factor receptor-2 (HER2)-positive breast cancer xenografts showed that antibody-mediated antitumor activity and tumor infiltration of CD4+ T lymphocytes were significantly downregulated when peripheral blood mononuclear cells in which NRP-1 was knocked down were co-administered with an anti-HER2 antibody. These results revealed that NRP-1 expressed on macrophages plays an important role in antibody-mediated antitumor immunity. Taken together, the induction of NRP-1 on macrophages may be a therapeutic indicator for antibody treatments that exert antibody-dependent cellular cytotoxicity activity, although further studies are needed in order to support this hypothesis.

Trogocytosis-mediated expression of HER2 on immune cells may be associated with a pathological complete response to trastuzumab-based primary systemic therapy in HER2-overexpressing breast cancer patients.

BACKGROUND: Trogocytosis is defined as the transfer of cell-surface membrane proteins and membrane patches from one cell to another through contact. It is reported that human epidermal growth factor receptor 2 (HER2) could be transferred from cancer cells to monocytes via trogocytosis; however, the clinical significance of this is unknown. The aim of this study is to demonstrate the presence and evaluate the clinical significance of HER2(+) tumor-infiltrated immune cells (arising through HER2 trogocytosis) in HER2-overexpressing (HER2+) breast cancer patients receiving trastuzumab-based primary systemic therapy (PST). METHODS: To assess the trogocytosis of HER2 from cancer cells to immune cells, and to evaluate the up- and down-regulation of HER2 on immune and cancer cells, peripheral blood mononuclear cells from healthy volunteers and breast cancer patients were co-cultured with HER2+ and HER2-negative breast cancer cell lines with and without trastuzumab, respectively. The correlation between HER2 expression on tumor-infiltrated immune cells and a pathological complete response (pCR) in HER2+ breast cancer patients treated with trastuzumab-based PST was analyzed. RESULTS: HER2 was transferred from HER2+ breast cancer cells to monocytes and natural killer cells by trogocytosis. Trastuzumab-mediated trogocytosed-HER2(+) effector cells exhibited greater CD107a expression than non-HER2-trogocytosed effector cells. In breast cancer patients, HER2 expression on tumor-infiltrated immune cells in treatment naïve HER2+ tumors was associated with a pCR to trastuzumab-based PST. CONCLUSIONS: HER2-trogocytosis is visible evidence of tumor microenvironment interaction between cancer cells and immune cells. Given that effective contact between these cells is critical for immune destruction of target cancer cells, this interaction is of great significance. It is possible that HER2 trogocytosis could be used as a predictive biomarker for trastuzumab-based PST efficacy in HER2(+) breast cancer patients.

Alteration of specific cytokine expression patterns in patients with breast cancer.

Systemic inflammation has been associated with aggressive tumor growth, invasion, and metastasis. Here we performed a comprehensive analysis of 26 kinds of inflammatory cytokine expression patterns among 185 patients with breast cancer and 54 healthy volunteers followed by chemometric analysis. We identified the specific cytokine expression patterns of breast cancer patients compared to healthy volunteers with (1) VEGF, IL-9, GM-CSF, IL-13, IL-4, and IFNγ, (2) IL-8, IL-10, IL-12, IL-5, IL-7, IL-1α, GCSF, IL-1ß, and TNFα and (3) IL-2, Eotaxin, MIP1ß, MIP1α, IL-17, and bFGF. Among the patients with breast cancer, we identified the specific cytokine signature of metastatic patients compared to non-metastatic patients. We also established a mathematical model for distinguishing patients with breast cancer from healthy volunteers and metastatic patients from non-metastatic patients. This cytokine network analysis could provide new insights into early intervention and effective therapeutic strategy for patients with breast cancer.

Gene expression profile of peripheral blood mononuclear cells may contribute to the identification and immunological classification of breast cancer patients.

BACKGROUND: It has been reported that the gene expression profile of peripheral blood mononuclear cells (PBMCs) exhibits a unique gene expression signature in several types of cancer. In this study, we aimed to explore the breast cancer patient-specific gene expression profile of PBMCs and discuss immunological insight on host antitumor immune responses. METHODS: We comprehensively analyzed the gene expression of PBMCs by RNA sequencing in the breast cancer patients as compared to that of healthy volunteers (HVs). Pathway enrichment analysis was performed on MetaCoretm to search the molecular pathways associated with the gene expression profile of PBMCs in cancer patients compared with HVs. RESULTS: We found a significant unique gene expression signature, such as the Toll-like receptor (TLR) 3- and TLR4-induced Toll/interleukin-1 receptor domain-containing adapter molecule 1 (TICAM1)-specific signaling pathway in the breast cancer patients as compared to that of healthy volunteers. Distinctive immunological gene expression profiles also showed the possibility of classifying breast cancer patients into subgroups such as T-cell inhibitory and monocyte-activating groups independent of known phenotypes of breast cancer. CONCLUSIONS: These preliminary findings suggest that evaluation of gene expression patterns of PBMCs might be both a less invasive diagnostic procedure and a useful way to reveal immunological insight of breast cancer, including biomarkers for cancer immunotherapy, such as immune checkpoint inhibitor therapy.