CD11b-positive macrophages among human E-MNCs attenuate cellular senescence and promote tissue regeneration in radiation-damaged salivary glands

No definitive treatment options are currently available for radiation-damaged salivary glands (SGs). We developed novel therapeutic cells designated as “effective-mononuclear cells (E-MNCs)”, which consist of a heterogeneous cell population including abundant M2 macrophages and proliferated Th2 lymphocytes. Our previous studies using mouse E-MNCs indicated that the therapeutic effects associated with tissue regeneration were primarily mediated by macrophages within the cell population. In anticipation of future clinical applications, this study specifically focused on CD11b-positive macrophages, which constitute approximately 20–30% of human E-MNCs, and directly evaluated their role and underlying mechanism as the principal therapeutic component of E-MNC therapy. Human E-MNCs and CD11b-positive macrophages were administered locally to immunodeficient nude mice with radiation-damaged submandibular glands. The effects of human E-MNCs and CD11b-positive macrophages on inhibiting radiation-induced cellular senescence in cultured SG epithelial cells were also examined. Administration of CD11b-positive cells significantly suppressed the expression of genes and proteins associated with cellular senescence and inflammatory cytokines, while markedly increased the expression of genes related to M2 macrophages and those involved in functional recovery. CD11b-positive cells inhibited tissue fibrosis and acinar cell atrophy, as well as the accumulation of senescent cells and senescence-associated secretory phenotype (SASP) factors in ductal regions. These effects were comparable to those observed with E-MNC administration, suggesting that CD11b-positive macrophages function as a crucial therapeutic component of E-MNCs. Our findings demonstrate that human E-MNCs, particularly the subpopulation of CD11b-positive macrophages, effectively attenuate cellular senescence in radiation-damaged SGs and may play a pivotal role in tissue regeneration of atrophic SGs.