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Free keywords:
Anti-CD4; YTS177.9; Foxp3; Tolerance; Autoimmunity; DEREG
Abstract:
CD4+ helper T cells orchestrate protective immunity against pathogens, yet can also induce undesired pathologies including allergies, transplant rejection and autoimmunity. Non-depleting CD4-specific antibodies such as clone YTS177.9 were found to promote long-lasting T cell tolerance in animal models. Thus, \CD4\} blockade could represent a promising therapeutic approach for human autoimmune diseases. However, the mechanisms underlying anti-CD4-induced tolerance are incompletely resolved. Particularly, multiple immune cells express \{CD4\} including Foxp3+ regulatory T cells (Tregs) and dendritic cells (DCs), both controlling the activation of CD4+Foxp3− helper T cells. Utilizing mixed leukocyte reactions (MLRs) reflecting physiological interactions between T cells and DCs, we report that anti-CD4 treatment inhibits CD4+Foxp3− T cell proliferation in an IL-2-independent fashion. Notably, YTS177.9 binding induces a rapid internalization of \{CD4\} on both CD4+Foxp3− T cells and Foxp3+ Tregs. However, no expansion or activation of immunosuppressive CD4+Foxp3+ Tregs was observed following anti-CD4 treatment. Additionally, cytokine production, maturation and T cell priming capacity of \{DCs\} are not affected by anti-CD4 exposure. In line with these data, the selective ablation of Foxp3+ Tregs from \{MLRs\} by the use of diphtheria toxin (DT)-treated bacterial artificial chromosome (BAC)-transgenic \{DEREG\} mice completely fails to abrogate the suppressive activity of multiple anti-CD4 antibodies. Instead, tolerization is associated with the defective expression of various co-stimulatory receptors including \{OX40\} and CD30, suggesting altered signaling through the \{TCR\ complex. Consistent with our findings in mice, anti-CD4 treatment renders human CD4+ T cells tolerant in the absence of Tregs. Thus, our results establish that anti-CD4 antibodies can directly tolerize pathogenic CD4+Foxp3− helper T cells. This has important implications for the treatment of human inflammatory diseases.
