Abstract
Background: The murine 4T1.2 triple-negative breast cancer model is widely used, but is poorly immunogenic with no defined tumor-associated antigens. A modified 4T1.2 model has been developed that stably expresses a surrogate tumor antigen, human epidermal growth factor receptor-2 (HER2). The goal of the current study was to characterize host immune responses in the 4T1.2-HER2 tumor model, focusing on the tumor microenvironment (TME) during the early stage of tumor development. Methods: Female BALB/c mice were orthotopically inoculated with 4T1.2-HER2 tumor cells and sacrificed at day (D) 6, 9, 12, 15 and 18 post tumor inoculation. The phenotype and function of tumor-infiltrating immune cells were assessed. Results: 4T1.2 and 4T1.2-HER2 tumor cells had similar proliferation rates in vitro. In contrast to the rapid progression of the parental 4T1.2 model, the 4T1.2-HER2 model demonstrated initial tumor growth followed by spontaneous tumor regression by D18 post tumor inoculation, which was not observed in scid mice. Following tumor regression, mice demonstrated either a second phase of tumor outgrowth or complete tumor rejection. Within the TME, the percentage of T cells was reduced at D9 and increased during tumor regression through D18 (p<0.05), whereas the percentage of myeloid-derived suppressor cells (MDSCs) increased during the initial tumor growth and was reduced by D18 (p<0.01). There was a stepwise increase in the percentage of IFNg+, IL-2+ and perforin+ T cells and NK cells peaking at D12-15. Furthermore, tumor regression occurred concurrently with HER2-specific IFNg production from tumor-infiltrating immune cells at D12 and D15 (p<0.05). During the second phase of 4T1.2-HER2 tumor growth, tumor volume was negatively correlated with immune infiltration (r=0.662, p=0.052). Conclusions: These results suggest that the integration of a surrogate tumor antigen, human HER2, into the clinically relevant, yet poorly immunogenic 4T1.2 breast cancer model enhanced its immunogenicity and induced HER2-specific immune responses.
Association of cathepsin E with tumor growth arrest through angiogenesis inhibition and enhanced immune responses