Immunomodulatory Macrophages Enable E-MNC Therapy for Radiation-Induced Salivary Gland Hypofunction

A newly developed therapy using effective-mononuclear cells (E-MNCs) is reportedly effective against radiation-damaged salivary glands (SGs) due to anti-inflammatory and revascularization effects. However, the cellular working mechanism of E-MNC therapy in SGs remains to be elucidated. In this study, E-MNCs were induced from peripheral blood mononuclear cells (PBMNCs) by culture for 5-7 days in medium supplemented with five specific recombinant proteins (5G-culture). We analyzed the anti-inflammatory characteristics of macrophage fraction of E-MNCs using a co-culture model with CD3/CD28-stimulated PBMNCs. To test therapeutic efficacy in vivo, either E-MNCs or E-MNCs depleted of CD11b-positive cells were transplanted intraglandularly into mice with radiation-damaged SGs. Following transplantation, SG function recovery and immunohistochemical analyses of harvested SGs were assessed to determine if CD11b-positive macrophages contributed to tissue regeneration. The results indicated that CD11b/CD206-positive (M2-like) macrophages were specifically induced in E-MNCs during 5G-culture, and Msr1- and galectin3-positive cells (immunomodulatory macrophages) were predominant. CD11b-positive fraction of E-MNCs significantly inhibited the expression of inflammation-related genes in CD3/CD28-stimulated PBMNCs. Transplanted E-MNCs exhibited a therapeutic effect on saliva secretion and reduced tissue fibrosis in radiation-damaged SGs, whereas E-MNCs depleted of CD11b-positive cells and radiated controls did not. Immunohistochemical analyses revealed HMGB1 phagocytosis and IGF1 secretion by CD11b/Msr1-positive macrophages from both transplanted E-MNCs and host M2-macrophages. Thus, the anti-inflammatory and tissue-regenerative effects observed in E-MNC therapy against radiation-damaged SGs can be partly explained by the immunomodulatory effect of M2-dominant macrophage fraction.