Heterogeneous CD3 expression levels in differing T cell subsets correlate with the in vivo anti-CD3-mediated T cell modulation

The tolerogenic anti-CD3ε monoclonal Abs (anti-CD3) are promising compounds for the treatment of type 1 diabetes. Anti-CD3 administration induces transient T cell depletion both in preclinical and in clinical studies. Notably, the said depletion mainly affects CD4⁺ but not CD8⁺ T cells. Moreover, type 1 diabetes reversal in preclinical models is accompanied by the selective expansion of CD4⁺Foxp3⁺ T regulatory (Treg) cells, which are fundamental for the long-term maintenance of anti-CD3-mediated tolerance. The mechanisms that lead to this immune-shaping by affecting mainly CD4⁺ T effector cells while sparing CD4⁺Foxp3⁺ Treg cells have still to be fully elucidated. This study shows that CD3 expression levels differ from one T cell subset to another. CD4⁺Foxp3^- T cells contain higher amounts of CD3 molecules than do CD4⁺Foxp3⁺ and CD8⁺ T cells in both mice and humans. The said differences correlate with the anti-CD3-mediated immune resetting that occurs in vivo after anti-CD3 administration in diabetic NOD mice. Additionally, transcriptome analysis demonstrates that CD4⁺Foxp3⁺ Treg cells are significantly less responsive than are CD4⁺Foxp3^- T cells to anti-CD3 treatment at a molecular level. Thus, heterogeneity in CD3 expression seems to confer to the various T cell subsets differing susceptibility to the in vivo tolerogenic anti-CD3-mediated modulation. These data shed new light on the molecular mechanism that underlies anti-CD3-mediated immune resetting and thus may open new opportunities to improve this promising treatment.