Wound healing‐like immune program facilitates postpartum mammary gland involution and tumor progression

Abstract

Women diagnosed with breast cancer within 5 years postpartum have poor survival rates. The process of postpartum mammary gland involution, whereby the lactating gland remodels to its pre-pregnant state, promotes breast cancer progression in xenograft models. Macrophage influx occurs during mammary gland involution, implicating immune modulation in the promotion of postpartum breast cancer. Herein, we characterize the postpartum murine mammary gland and find an orchestrated influx of immune cells similar to that which occurs during wound healing. Further, the normal involuting gland may be in an immunosuppressed state as discerned by the transient presence of Foxp3+ regulatory T cells and IL-10+ macrophages with T cell suppressive function. To determine the influence of the postpartum immune microenvironment on mammary tumor promotion, we developed an immune-competent model. In this model, mammary tumors in the involution group are six-fold larger than nulliparous group tumors, have decreased CD4+ and CD8+ T cell infiltrates and contain a greater number of macrophages with the ability to inhibit T cell activation. Targeting involution with a neutralizing antibody against the immunosuppressive cytokine IL-10 reduces tumor growth in involution group mice but not in nulliparous mice, implicating the involution microenvironment as the primary target of αIL-10 treatment. Relevance to women is implicated, as we find post-lactational human breast tissue has transient high IL-10+ and Foxp3+ immune cell infiltrate. These data show an immune modulated microenvironment within the normal involuting mammary gland suggestive of immunosuppression, that when targeted reduces tumor promotion, revealing possible immune-based strategies for postpartum breast cancer.

Physiologically activated mammary fibroblasts promote postpartum mammary cancer

“…The induction of Cxcl12 in PGE2-treated fibroblasts ( Figure 4A) supports the hypothesis that PGE2-activated fibroblasts may mediate chemotaxis of monocyte-derived cells, an immune cell abundantly present in the involuting mammary gland (7). To begin to test this hypothesis, we utilized a modified cell migration assay, in which collagen pads containing fibroblasts were separated from fluorescently labeled bone marrow-derived monocytes by a membrane with 5-μm pores.…”

“…Rather, data implicate a unique biology of the postpartum breast in the promotion of postpartum breast cancer. Specifically, weaning-induced mammary gland involution is implicated because, in rodents, the tissue microenvironment of the involuting mammary gland enhances tumor growth, local tumor cell dissemination, and distant metastasis (5)(6)(7).…”

“…Involution can be separated broadly into an initial phase of secretory epithelial cell death followed by a stromal remodeling phase that reestablishes the adipocytes and connective tissue as dominant constituents of the nonlactating gland (8,14). The stromal remodeling phase of involution shares numerous attributes with wound healing (15)(16)(17), including lymphangiogenesis (6), orchestrated immune cell infiltration, immune suppression (7,12), and deposition of a fibrotic-like extracellular matrix (ECM), mainly the fibrillar collagens (9,12). The mechanistic links between wound healing and cancer (18,19) and the known role of fibroblasts in these processes (20)(21)(22)(23) identify the mammary fibroblast as a potential mediator of postpartum breast cancer progression.…”

A Portal Vein Injection Model to Study Liver Metastasis of Breast Cancer

“…These mammary tumor lines were selected based on their characterized behavior in mammary fat pad models and include the highly aggressive and metastatic 4T1 cell line, the less aggressive metastatic D2A1 line, and the low/non-metastatic D2.OR line 37,61,73,74 . 2,000 and 10,000 cells per injection were tested with no notable differences in the time to development of overt metastasis with these low cell concentrations.…”

A Hormone-responsive 3D Culture Model of the Human Mammary Gland Epithelium

“…The hormone-sensitive 3D culture model described herein also allows for the addition of cell types considered of relevance in breast tissue morphogenesis, such as fibroblasts, adipocytes and circulating blood cells 6,8,10 . Finally, testing of hormonal influence on the breast epithelium in this 3D culture model is not limited to endogenous hormones alone.…”