T. N. Augustine1, R. Duarte2, G. P. Candy2 1School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa 2School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
Immune infiltration is a fundamental determinant of tumour progression and response to therapy, with interactions between immune, and tumour cells mediated by cytokines. In advanced breast cancer, a dominance of regulatory T (TREG) lymphocytes and the scarcity natural killer (NK) cells may reflect the primacy of adaptive immunity in the induction of tumour tolerance. We thus developed 3-dimensional (3D) models of the tumour microenvironment to determine induced cytokine profiles under immune-mediation.
Three-dimensional culture models were established by co-culturing CD4+CD25+ TREG lymphocytes and NK cells with hormone-dependent MCF-7 or hormone-independent MDA-MB-231 cell lines in growth factor reduced-Matrigel. Cytokine production was measured using a multiplex cytokine assay. Multivariate analyses were used to determine significant differences in cytokine production, and to explore associations between cytokines.
The results show that cytokine secretions in a 3D simulated breast tumour microenvironment are associated with the hormone-dependency of tumours. The effects of NK cell-mediation induced a significant increase in CCL2, CCL4 and CXCL8 secretion in the MCF-7 culture model. In the MDA-MB-231 culture model NK cells alone induced a significant increase in IL-12 and CCL2 inferring the dominance of TREG cell-mediation of cytokine secretion. Cluster analysis and principal components analysis indicate that IL-6 plays a significant role in the induction of a chemokine cascade in both culture models, with IL-1β implicated in the induction of proinflammatory environment in the MDA-MB-231 culture model.
The cytokine data suggests that hormone-dependent MCF-7 cells, as a weakly metastatic cell line, are capable of subverting cytokine secretion of NK cells and TREG lymphocytes to enhance their invasive potential. In contrast, hormone-independent MDA-MB-231 cells, a more aggressive phenotype, subvert TREG cell-mediated cytokine secretion for the maintenance of a proinflammatory microenvironment for tumour progression. Further, the data suggests a role for IL-6 and IL-1β in promoting such immune evasion and tissue invasion.