GMCSF-neuroantigen vaccines engender FOXP3(+) regulatory T cell responses through low-efficiency self-antigen recognition events integrated through diminished CD40L-CD40 signaling

Abstract Neuroantigen (NAg)-specific tolerogenic vaccines that induce myelin-specific FOXP3+ regulatory T cells (Tregs) may be an effective treatment for Multiple Sclerosis. Previous studies showed that fusion proteins comprised of GM-CSF and NAg (GMCSF-NAg) are potent tolerogens that inhibit several rodent models of experimental autoimmune encephalomyelitis. GMCSF-NAg-induced T cell responses were investigated in vivo by use of 2D2-FIG mice, which have a FOXP3 GFP reporter (FIG) and a transgenic TCR (2D2) which recognizes myelin oligodendrocyte glycoprotein peptide 35–55 (MOG) as a low-efficiency antigen and neurofilament medium peptide 13–37 (NFM) as a high-efficiency antigen. A single subcutaneous vaccination of 2D2-FIG mice with GMCSF-MOG resulted in high numbers and percentages of Tregs in the blood, spleen, and lymph nodes, whereas GMCSF-NFM elicited a dominant conventional T cell (Tcon) response. To determine how low and high-efficiency TCR responses regulate cell lineage fate, we investigated TCR-induced CD40L expression. GMCSF-NFM, but not GMCSF-MOG, induced significant CD40L expression when cultured with 2D2 responder T cells. Pretreatment of 2D2-FIG mice with an agonistic anti-CD40 monoclonal antibody prevented GMCSF-MOG induction of Tregs and favored Tcon responses. MOG35–55 was a partial TCR antagonist that blocked NFM stimulation of CD40L expression in 2D2 T cell cultures. Similarly, GMCSF-MOG was functionally dominant and induced Tregs in 2D2-FIG mice when mixed with an equimolar dose of GMCSF-NFM. These data indicated that low-efficiency antigen recognition is a key parameter for the induction of Treg responses and is in part controlled through CD40L-CD40 signaling pathways to determine T cell lineage fate.