Characterization of tumor growth, immune and metastatic outcomes in the 4T1.2-HER2 mammary tumor model
Open Access
- Author:
- Ravichandran, Abirami
- Graduate Program:
- Integrative and Biomedical Physiology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 09, 2021
- Committee Members:
- Connie Jo Rogers, Thesis Advisor/Co-Advisor
Margherita Teresa-Anna Cantorna, Committee Member
Donna Korzick, Program Head/Chair
Robert Paulson, Committee Member - Keywords:
- mouse mammary tumor model
triple-negative breast cancer
breast cancer
immune response
antigen-specific immune response
tumor immunology - Abstract:
- In 2020, breast cancer surpassed lung cancer to become the most prevalent type of cancer worldwide. Breast cancer is the leading cause of cancer-related mortality in women. The main contributing factor for death in breast cancer is metastatic disease. Mouse models are an excellent tool for mechanistic studies pertaining to breast cancer. 4T1.2 mouse mammary tumor model with triple-negative phenotype and clinically relevant metastatic properties has been used in many preclinical breast cancer studies. However, 4T1.2 has no known tumor antigens and is poorly immunogenic, limiting the use of this model in immunological studies. To overcome this drawback, in the 4T1.2-HER2 tumor cell, the parental 4T1.2 tumor cell has been modified to stably express the surrogate antigen, HER2. HER2 is used as the tumor antigen in this breast cancer model. When implanted in vivo in BALB/c mice, tumor growth of the 4T1.2-HER2 tumor was significantly different from the parental tumor model. It exhibited a short period of initial tumor growth followed by spontaneous tumor regression, which was dependent on the adaptive immune response. Following the regression phase, in the third phase, a subset of mice demonstrated tumor outgrowth, whereas others rejected the tumor. Experiments were undertaken in our laboratory to characterize the immune responses in the early phases of tumor growth and regression. In the early phases, tumor growth was associated with a decrease in T cells and an increase in myeloid-derived suppressor cells (MDSCs), whereas tumor regression was associated with an increase in T cells and a decrease in MDSCs in the spleen and tumor. Moreover, HER2-specific IFNγ secretion from splenic and tumor-infiltrating immune cells was evident during the tumor regression period. The goal of the present study was to characterize the tumor growth, immune responses, and metastatic outcomes in the 4T1.2-HER2 mammary tumor model during the late stages of tumor growth. In the 4T1.2-HER2 tumor model, considerable heterogeneity was observed in the tumor volume of mice during the third phase of tumor growth. Since the mice had varying tumor volumes in the third phase of tumor growth, for aim 1, we wanted to determine if tumor volume was associated with immune cell populations in the spleen and tumor. In the spleen, the percentage of dendritic cells and Tregs were negatively associated, and the percentage of MDSCs and monocytic MDSCs were positively associated with tumor volume. In the tumors, the percentage of CD4, NK cells, Tregs, and central memory T cells were negatively associated with tumor volumes, whereas MDSCs, effector memory cells, and memory precursor effector cells were positively associated with tumor volume. Subsequently, we wanted to examine if the tumor volume was associated with antigen-specific immune responses against HER2 in the spleen and tumor. Stimulation of immune cells from spleen and tumor using H-2Kd-restricted HER2 peptide induced IFNγ secretion from the tumor-infiltrating lymphocytes (TILs) but not from the splenocytes. Further, IFNγ secretion from the TILs was significant only in smaller-sized tumors. For aim 3, we wanted to determine if tumor volume was associated with lung metastatic burden. Using the gene expression of gp70, we observed that all the mice had lung metastasis. However, no significant difference was seen in the lung metastatic burden between the mice with larger tumor volumes and smaller tumor volumes. From this study, we observed associations between the immune cell populations in the spleen and tumor and the tumor volume. Further, we could also observe a significant HER2-specific immune response in smaller tumors. In conclusion, with the introduction of the surrogate tumor antigen, HER2, in the 4T1.2 tumor cells, in vivo immunogenicity is increased, and HER2-specific immune responses are induced in the tumor. These immune features are highly preferred in a tumor model for immunological studies. This model would be an ideal experimental system for exploring questions related to the effect of interventions on antigen-specific immune responses against tumors in a preclinical setting.