The D665monoclonal antibody reacts with mouse CD28，a45kDa costimulatory receptor and a member of the Ig superfamily.CD28is expressed by thymocytes，most peripheral T cells，and NK cells.CD28is a receptor forCD80（B7-1）and CD86（B7-2）。Signaling through CD28induces IL-2and IL-2receptor expression and T cell proliferation.The D665 antibody is a CD28superagonist and is most commonly used to induce the expansion of Treg cellsin vivoin various mouse models of disease。
Win，S.J.，et al.（2016）。“In vivo activation of Treg cells with a CD28 superagonist prevents and ameliorates chronic destructive arthritis in mice”Eur J Immunol46（5）：1193-1202。PubMed
Although regulatory T（Treg）cells are necessary to prevent autoimmune diseases，including arthritis，whether Treg cells can ameliorate established inflammatory disease is controversial.Using the glucose-6-phosphate isomerase（G6PI）-induced arthritis mol miin，we aimed to determine the therapeutic efficacy of increasing Treg cell number and function during chronic destructive arthritis.Chronic destructive arthritis was induced by transient depletion of Treg cells prior to immunization with G6PI.At different time points after disease induction，mice were treated with a CD28superagonistic antibody（CD28SA）。CD28SA treatment during the induction phase of arthritis ameliorated the acute signs of arthritis and completely prevented the development of chronic destructive arthritis.CD28SA treatment of mice with fully developed arthritis induced a significant reduction in clinical and histological signs of arthritis of arthritis structive phase of arthritis，56days after disease induction，CD28SA treatment resulted in a modest reduction of clinical signs of arthritis and a reduction in histopathological signs of joint inflammation.Our data show that increasing the number and activation of Treg cells by a CD28 therapeutically exectime。
in vivoT cell stimulation/activation
Schmidt，T.，et al.（2016）。“Induction of Tregulatory cells by the superagonistic anti-CD28antibody D665leads to decreased pathogenic IgG autoantibodies against desmogein3ina HLA-transgenic mouse model of pemphigus vulgaris”Exp Dermatol25（4）：293-298。PubMed
Pemphigus vulgaris（PV）is a potentially life-threatening autoimmune disease of the skin and mucous membranes。Its pathogenesis is based on IgG autoantibodies that target the desmosomal cadherins，desmoglein3（Dsg3）and desmoglein1（Dsg1）and induce intra-epidermal loss of adhesion。Although the PV pathogenesis is well-understood，therapeutic options are still limited to immunosuppressive drugs，particularly corticosteroids，which are associated with significant side effects.Dsg3-reactive Tregulatory cells（Treg）have been previously iden and herried LA class II alleles。Ex vivo，Dsg3-specific Treg cells down-regulated the activation of pathogenic Dsg3-specific T-helper（Th）2cells。In this study，in a HLA-DRIB1*04:02 transgenic mouse model of PV，peripheral Treg cells were modulated by the use of Treg-depleting or expanding monoclonal antibodies，respectively.Our findings show that，in vivo单击功能区上，although not statistically significant，Treg cells exert a clear down-regulatory effect on the Dsg3-driven T-cell response and，accordingly，the formation of Dsg3-specific IgG antibodies.These observations confirm the powerful immune regulatory functions of Treg cells and identify Traptions ators in PV。
in vivoT cell stimulation/activation
Schuhmann，M.K.，et al.（2015）。“CD28 superagonist-mediated boost of regulatory T cells increases thrombo-inflammation and ischemic neurodegeneration during the acute phase of experimental stroke”J Cereb Blood Flow Metab35（1）：6-10。PubMed
While the detrimental role of non-regulatory T cells in ischemic stroke is meanwhile unequivocally recognized，there are controversies about the properties of regulatory T cells（Treg）。The aim of this study was to elucidate the role of Treg by applying superagonistic anti-CD28antibody expansion of Treg.Stroke outcome，thrombus formation，and brain-infiltrating cells were determined on day1after transient middle cerebral artery occlusion.Antibody-mediated expansion of Treg enhanced stroke size and worsened functional outcome.Mechanistically，Treg increased thrombus formation in the cerebral microvasculature.These findings confirm that Treg promote thrombo-inflammatory lesion growth during the acute stage of ischemic stroke。
in vitroT cell stimulation/activation
Dennehy，K.M.，et al.（2006）。“Cutting edge:monoverency of CD28 maintains the antigen dependence of T cell costimulatory responses”J Immunol176（10）：5725-5729。PubMed
CD28and CTLA-4are the major costimulatory receptors on naive T cells.But it is not clear why CD28is monoverent whereas CTLA-4is bivalent for their shared ligands CD80/86.We generated bivalent CD28constructs by fusing the extracellular domains of CTLA-4 or CD80with the intraclullar domaint CD 28 S wereligated with recombinant ligands with or without TCR coligation.Monovalent CD28ligation did not induce responses unless the TCR was coligated.By contrast，bivalent CD28ligation induced responses in the absence of TCR engagement.To extend these findings to primary cells，we used novel superagonistic and conventional CD28Abs.superagonistic Ab D665，but not conventional Ab E18，predominantly ligates CD28bivalently at low CD28/Ab ratios and induces Ag-indent T cell proliferation.Monovalency of CD28forits natural ligands is thus essential to provide costimulation without inducing responses in the absence of TCR engagement。
