Impact of Fetal Umbilical Cord Blood CD34+ Cells on Breast Cancer Cell Lines: A Mechanism of Fetal Microchimerism.

Introduction: Fetal microchimerism could be involved in the regulation of breast cancer oncogenesis. CD34+ cells could be of a particular interest as up to 12% of the CD34+ population in maternal blood are of fetal origin. The aim of this research was to analyze the impact of umbilical cord blood (UCB) CD34+ on MCF-7 and MDA-MB-231 breast cancer cell lines, in order to uncover novel biological mechanisms and suggest novel treatment options for breast cancer.

Methods: UCB CD34+ cells were obtained from healthy women at full-term delivery. Direct cultures were grown with MCF-7 and MDA-MB-231 cells. Proliferation, migration, invasion, and transcriptomic analysis of breast cancer cell lines were compared between cultures exposed and nonexposed to UCB CD34+ cells. Interactions between UCB CD34+ and breast cancer cells were analyzed under fluorescent microscopy. Functional analyses were generated with QIAGEN's Ingenuity Pathway Analysis (IPA) and Gene Set Enrichment Analysis (GSEA).

Results: Direct contact between UCB CD34+ and breast cancer cell lines induced a reduction in the proliferative capacities of MCF-7 and MDA-MB-231 and diminished the migration abilities of MDA-MB-231 cells. In 3D coculture, UCB CD34+ cells were attracted by tumor spheroids and incorporated into tumor cells. These cell-to-cell interactions were responsible for transcriptome modifications coherent with observed functional modifications. Among the cytokines secreted by UCB CD34+, IFN-γ was identified as a potential upstream regulator responsible for the molecular modifications observed in transcriptomic analysis of MCF-7 breast cancer cells exposed to UCB CD34+ cells, as was IL-17A in MDA-MB-231 cells.

Conclusion: Direct cell-to-cell contact induced functional modifications in breast cancer cells. Interactions between UCB CD34+ and breast cancer cells could induce cell fusion and signal transmission via cytokines. Further analysis of direct cell-to-cell interactions should be performed at a molecular level to further understand the potential role of fetal CD34+ cells in breast cancer.