Introduction: The importance of epithelial-stromal interactions for tissue homeostasis and maintenance is well documented. We have recently provided evidence that two distinct fibroblast lineages in the human breast stroma, lobular and interlobular, respectively, can be prospectively isolated and stably propagated in serial-passage subculture. The aim of the present study was to generate immortalized and stable cell lines derived from lobular and interlobular fibroblasts with preserved lineage identity and functionality. The availability of such cell lines will allow for an as of yet unprecedented detailed characterization of mammary fibroblast lineages including their specific interactions with normal and malignant breast epithelium.

Results: Lobular- and interlobular-derived fibroblast cell strains in passage 8 were immortalized by retroviral introduction of human telomerase reverse transcriptase (hTERT) followed by neomycin selection. At abstract submission deadline, lobular and interlobular hTERT expressing fibroblasts had reached passage 56 corresponding to 60 and 100 population doublings, respectively, while mock-transfected controls had seized proliferating in passage 21. Lineage restriction of immortalized cells was maintained as lobular fibroblasts express higher levels of CD105 than interlobular fibroblasts. Also, lobular fibroblasts are able to undergo adipogenic and osteogenic differentiation upon relevant induction in culture, but fail to generate bone in an in vivo ectopic bone formation model, thus functionally distinguishing lobular fibroblasts from bone marrow-derived mesenchymal/skeletal stem cells. Upon co-culture with primary breast luminal progenitors, lobular fibroblasts support epithelial growth and branching morphogenesis, including correct apical-basal polarization.

Conclusion: Lobular and interlobular fibroblasts have been successfully immortalized while preserving both lineage restriction and functional characteristics of their primary counterparts. With 80% of breast cancers arising in lobular epithelium, these established fibroblast models may prove instrumental to unravel such focal susceptibility to breast cancer development.

Citation Format: Mikkel Morsing, Abbas Jafari, Moustapha Kassem, Ole William Petersen, Lone Rønnov-Jessen. Establishing lobular-like and interlobular-like fibroblast cell lines from human breast reduction mammoplasties [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1010.