A specific CD4 epitope bound by tregalizumab mediates activation of regulatory T cells by a unique signaling pathway

CD4+CD25+ regulatory T cells (Tregs) represent a specialized subpopulation of T cells, which are essential for maintaining peripheral tolerance and preventing autoimmunity. The immunomodulatory effects of Tregs depend on their activation status. Here we show that, in contrast to conventional anti-CD4 monoclonal antibodies (mAbs), the humanized CD4-specific monoclonal antibody tregalizumab (BT-061) is able to selectively activate the suppressive properties of Tregs in vitro. BT-061 activates Tregs by binding to CD4 and activation of signaling downstream pathways. The specific functionality of BT-061 may be explained by the recognition of a unique, conformational epitope on domain 2 of the CD4 molecule that is not recognized by other anti-CD4 mAbs. We found that, due to this special epitope binding, BT-061 induces a unique phosphorylation of T-cell receptor complex-associated signaling molecules. This is sufficient to activate the function of Tregs without activating effector T cells. Furthermore, BT-061 does not induce the release of pro-inflammatory cytokines. These results demonstrate that BT-061 stimulation via the CD4 receptor is able to induce T-cell receptor-independent activation of Tregs. Selective activation of Tregs via CD4 is a promising approach for the treatment of autoimmune diseases where insufficient Treg activity has been described. Clinical investigation of this new approach is currently ongoing

Dysregulated Lymphoid Cell Populations in Mouse Models of Systemic Lupus Erythematosus.

International audienceBiases in the distribution and phenotype of T, B, and antigen-presenting cell populations are strongly connected to mechanisms of disease development in mouse models of systemic lupus erythematosus (SLE). Here, we describe longitudinal changes in lymphoid and antigen-presenting cell subsets in bone marrow, blood and spleen from two lupus-prone strains (MRL/lpr and B6.Sle1.Sle2.Sle3 tri-congenic mice), and how they integrate in our present understanding of the pathogenesis of the disease. In particular, we focus on (autoreactive) T cell activation patterns in lupus-prone mice. Break of T cell tolerance to chromatin constituents (histone peptides) is key to the development of the disease and is related to T cell intrinsic defects, contributed by genetic susceptibility factors and by extrinsic amplificatory mechanisms, in particular over-stimulation by antigen-presenting cells. We also describe shifts in B cell sub-populations, going from skewed immature B cell populations as an indication of disturbed central and peripheral tolerance checkpoints, to enriched long-lived plasma cells, which are key to persistent autoantibody production in the disease. B cell activation mechanisms in SLE are both T cell-dependent (break of tolerance and production of specific autoantibodies) and -independent (polyclonal B cell activation, production of autoantibodies by long-lived plasma cells). By providing a comprehensive evaluation of B and T cell surface markers in two major mouse models of SLE and a description of their changes before and after disease onset, this review illustrates how the study of lymphoid cell phenotype delivers key information regarding pathogenic pathways and supplies tools to assess the beneficial effects of novel therapeutic interventions