Mesenchymal Stem Cells in Fungal Infections: Immunomodulation, Direct Antifungal Activity, and the Promise of the Secretome.

Mesenchymal stem/stromal cells (MSCs) are widely recognized as potent modulators of inflammation and immune function in bacterial and viral infections. However, their roles in fungal disease remain comparatively under-defined despite the growing clinical burden of invasive and opportunistic mycoses. This Feature Review synthesizes emerging evidence that MSCs influence antifungal outcomes through two complementary axes: (i) host-directed effects, including modulation of immune responses, particularly macrophage responses, and tissue/barrier conditioning; and (ii) fungus-directed effects (direct antifungal activity mediated by contact-dependent mechanisms and secreted antimicrobial factors). We will summarize how MSCs reshape cytokine and chemokine networks and tune innate immune effector functions, with emphasis on macrophage polarization, pattern-recognition receptor signaling, and downstream phagocytic and fungicidal pathways. In parallel, we will review data suggesting that MSCs can interact more directly with fungal pathogens through sensing, physical engagement, and secretion of antimicrobial mediators while highlighting mechanistic uncertainties and model-dependent limitations. A dedicated section will address MSC-derived secretome products (conditioned media, extracellular vesicles) as a cell-free strategy to enhance antifungal immunity. We will critically evaluate conflicting findings across studies, highlighting that outcomes depend on pathogen and host context. Clarifying these context dependencies is essential to rationally develop MSC or secretome-based interventions that are safe, reproducible, and tailored to specific fungal pathogens and patient populations.