Therapeutic Effect of Anti-CD52 Monoclonal Antibody in Multiple Sclerosis and Its Animal Models Is Mediated via T Regulatory Cells

The objective of this study is to determine the mechanism of action of anti-CD52 mAb treatment in patients with relapsing-remitting multiple sclerosis (RRMS). Experimental autoimmune encephalomyelitis (EAE), an animal model of the disease, was used to address the role of T regulatory cells (Tregs) in the anti-CD52 mAb-induced suppression of the disease. In vitro studies on PBMCs from RRMS patients and matched healthy controls determined the effect of IL-7 on the expansion of CD4⁺CD25⁺CD127^- Tregs and induction of their suppressive phenotype. This study using EAE animal models of MS has shown that mouse anti-CD52 mAb suppression of clinical disease was augmented by coadministration of IL-7 and partially reversed by anti-IL-7 mAb. In vitro human studies showed that IL-7 induced expansion of CD4⁺CD25⁺CD127^- Tregs and increased their FOXP3, GITIR, CD46, CTLA-4, granzyme B, and perforin expression. Anti-CD52 mAb treatment of mice with relapsing-remitting EAE induced expansion of Foxp3⁺CD4⁺ Tregs and the suppression of IL-17A⁺CD4⁺ and IFN-γ⁺CD4⁺ cells in peripheral immune organs and CNS infiltrates. The effect was detected immediately after the treatment and maintained over long-term follow-up. Foxp3⁺CD4⁺ Treg-mediated suppression of IL-17A⁺CD4⁺ and IFN-γ⁺CD4⁺ cells in the spinal cord infiltrates was reversed after inducible Foxp3 depletion. Our results demonstrated that the therapeutic effect of U.S. Food and Drug Administration-approved anti-CD52 mAb is dependent on the presence of Tregs.