Calcitriol and Tacalcitol Modulate Th17 Differentiation Through Osteopontin Receptors: Age-Dependent Insights from a Mouse Breast Cancer Model.

Purpose: Beyond its direct anticancer effects in breast cancer (BC), vitamin D₃ (VD₃) also modulates tumor progression and metastasis through immune mechanisms. T-helper 17 (Th17) cells may play a key role in these effects. This study investigates how VD₃ influences Th17 differentiation in 4T1 and 67NR murine BC models.

Methods: Calcitriol or tacalcitol was administered to young and aged mice bearing 4T1 or 67NR tumors. Tumor growth, angiogenesis, and metastasis were evaluated. CD4⁺ lymphocytes isolated from tumors and other tissues were analyzed by flow cytometry for IL-17 and osteopontin (OPN, Spp1) receptors. CD4⁺ splenocytes were separated; gene expression was assessed using qPCR, and protein levels by Western blotting, ELISA. CD3⁺CD4⁺ splenocytes were ex vivo differentiated into Th17 cells with blockade of CD29, CD51, and CD44, followed by flow cytometric analysis of IL-17 and IFNγ expression.

Results: Tacalcitol increased metastasis in young mice but decreased it in aged mice with 4T1 tumors. Th17 cell levels in the lungs increased in young mice treated with tacalcitol but declined in aged counterparts. IL-17⁺ and IFNγ⁺ Th17 cells increased upon differentiation from splenocytes of treated mice. CD29 promoted IL-17 expression in tacalcitol-treated mice, while CD51 and CD44 had opposing effects. CD51 blockade reduced IFNγ⁺ Th17 cells in both treatment groups. Spp1 expression increased in CD4⁺ lymphocytes, and OPN levels were elevated in induced Th17 cells from tacalcitol-treated young mice, suggesting a role in Th17 activation.

Conclusion: CD29 stimulates IL-17 expression in response to tacalcitol, while CD51 and CD44 exert opposing effects. CD51 also mediates IFNγ expression. VD₃-induced modulation of IL-17 and IFNγ in Th17 cells may influence their pro- or anticancer function.