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Immunosenescence describes the gradual remodeling of immune responses, leading to disturbed immune homeostasis and increased susceptibility of older adults for infections, neoplasia and autoimmunity. Decline in cellular immunity is associated with intrinsic changes in the T cell compartment, but can be further pushed by age-related changes in cells regulating T cell immunity. Myeloid-derived suppressor cells (MDSCs) are potent inhibitors of T cell activation and function, whose induction requires chronic inflammation. Since aging is associated with low grade inflammation (inflammaging) and increased myelopoiesis, age-induced changes in MDSC induction and function in relation to T cell immunity were analyzed. MDSC numbers and functions were compared between “healthy” young and old adults, who were negatively diagnosed for severe acute and chronic diseases known to induce MDSC accumulation. MDSCs were either isolated from peripheral blood or generated in vitro from blood-derived CD14 cells. Aging was associated with significantly increased MDSC numbers in the monocytic- (M-) and polymorphonuclear (PMN-) MDSC subpopulations. MDSCs could be induced more efficiently from CD14 cells of old donors and these MDSCs inhibited CD3/28-induced T cell proliferation significantly better than MDSCs induced from young donors. Serum factors of old donors supported MDSC induction comparable to serum factors from young donors, but increased immunosuppressive activity of MDSCs was only achieved by serum from old donors. Elevated immunosuppressive activity of MDSCs from old donors was associated with major metabolic changes and increased intracellular levels of neutral and oxidized lipids known to promote immunosuppressive functions. Independent of age, MDSC-mediated suppression of T cell proliferation required direct MDSC– T cell contact. Besides their increased ability to inhibit activation-induced T cell proliferation, MDSCs from old donors strongly shift the immune response towards Th2 immunity and might thereby further contribute to impaired cell-mediated immunity during aging. These results indicate that immunosenescence of innate immunity comprises accumulation and functional changes in the MDSC compartment, which directly impacts T cell functions and contribute to age-associated impaired T cell immunity. Targeting MDSCs during aging might help to maintain functional T cell responses and increase the chance of healthy aging. The online version contains supplementary material available at 10.1186/s12979-025-00524-w.

Dendritic cell (DC)-based immunotherapy has potential for treating infections and malignant tumors, but the functional capacity of DC must be assessed in detail, especially maturation and Ag-specific CTL priming. Recent reports suggest that DC that are provided with continuous maturation signals in vivo after transfer into patients are required to elicit the full DC functions. We demonstrate in this study that the rSendai virus vector (SeV) is a novel and ideal stimulant, providing DC with a continuous maturation signal via viral RNA synthesis in the cytosol, resulting in full maturation of monocyte-derived DC(s). Both RIG-I-dependent cytokine production and CD4 T cell responses to SeV-derived helper Ags are indispensable for overcoming regulatory T cell suppression to prime melanoma Ag recognized by T cell-1-specific CTL in the regulatory T cell abundant setting. DC stimulated via cytokine receptors, or TLRs, do not show these functional features. Therefore, SeV-infected DC have the potential for DC-directed immunotherapy.