Towards the definition of a chimpanzee and human conserved CD6 domain 1 epitope recognized by T1 monoclonal antibody.
ABSTRACT Scavenger receptor cysteine-rich (SRCR) domains are evolutionally conserved modules that display complex structures stabilized by key amino acids, while some other residues have evolved with a relative independence, thus allowing the functional diversity of these receptors. CD6, a highly glycosylated membrane protein predominantly expressed on lymphocytes, contains three SRCR domains. The lack of CD6 domain crystal structure has limited the characterization of the binding sites for the interacting molecules. The interaction between CD6 and its ligand, activated leukocyte-cell adhesion molecule (ALCAM)/CD166, through the membrane-proximal SRCR3 domain, has low affinity and involves conserved sites in both molecules mediating a cross-species binding. The CD6-ALCAM interaction has been involved in cell adhesion, maturation, regulation of activation, and survival processes, suggesting the potential relevance of this target for therapeutic interventions. Several anti-CD6 monoclonal antibodies (MAb) have been described but their affinity and epitope definition remain unclear. We found the murine and humanized T1 MAb versions have similar CD6 recognition profiles and affinity constants of about 6 x 10(8). These antibodies do not block the CD6-ALCAM interaction and recognize a conformational epitope independent of the CD6 N-glycosylation. This epitope was additionally found in the chimpanzee and contains an RXE/Q consensus motif located in the membrane-distal SRCR1. These results, together with the therapeutic evidence previously obtained with these MAbs, suggest a differential contribution of CD6 domains to lymphocyte biology. Potential mechanisms for T1 MAb therapeutic effect different from CD6-CD166 interaction blocking would be dissected.
SourceAvailable from: Patricia Hernandez[Show abstract] [Hide abstract]
ABSTRACT: Psoriasis is a chronic inflammatory disease with a prevalence of approximately 2-3% in the general population. The majority of diagnosed patients have plaque psoriasis, and about 20% have moderate-to-severe disease. Itolizumab, a new monoclonal antibody specific for the CD6 molecule mainly expressed on T lymphocytes, has demonstrated to inhibit in vitro ligand-induced proliferation and pro-inflammatory cytokine production. We assessed the immunological and histopathological effect of the antibody using clinical samples taken from 26 patients with moderate-to-severe psoriasis included in a clinical trial. The precursor frequency of lymphocytes activated with anti-CD2/CD3/CD28 beads, as well as the number of interferon (IFN)-γ-secreting T cells after stimulation, were measured at different time points of the study. Serum cytokine levels and anti-idiotypic antibody response to itolizumab were also evaluated. Additionally, lymphocyte infiltration and epidermis hyperplasia were studied in five patients. A significant reduction in T cell proliferation capacity and number of IFN-γ-producing T cells was found in treated patients. Serum levels of interleukin-6, tumor necrosis factor and IFN-γ showed an overall trend toward reduction. No anti-idiotypic antibody response was detected. A significant reduction in the epidermis hyperplasia was observed in analyzed patients. These results support the relevance of the CD6 molecule as a therapeutic target for the treatment of this disease.mAbs 03/2014; 6(3). DOI:10.4161/mabs.28376 · 4.73 Impact Factor
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ABSTRACT: CD6 is a cell surface receptor expressed on the majority of T cells and a subset of B cells. When expressed, CD6 contributes to lymphocyte activation through its extracellular domain 1, while adhesion and cellular migration are related to the extracellular scavenger receptor cysteine-rich domain (SRCR-D)-3 of CD6. Itolizumab, clone T1h, is a newly developed humanized IgG1 monoclonal antibody that targets CD6 SRCR-D1 and blocks immune activation. Itolizumab has been proposed to be effective in autoimmune diseases such as rheumatoid arthritis, Sjögren's syndrome and multiple sclerosis. In Sjögren's syndrome, the utilization of itolizumab as therapeutic option is reinforced by our recent observation that ALCAM, the CD6 ligand, is overexpressed and that CD6-positive T and B cells are detected within salivary glands from Sjögren's syndrome patients. In this study, itolizumab-positive target cells were characterized within both peripheral blood and salivary glands in order to provide rational for anti-CD6 treatment in Sjögren's syndrome.Immunologic Research 04/2013; 56(2-3). DOI:10.1007/s12026-013-8423-x · 3.53 Impact Factor
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ABSTRACT: Itolizumab, a humanized monoclonal antibody to CD6, is a novel therapeutic agent evaluated in chronic plaque psoriasis. We sought to assess the safety and efficacy of itolizumab in moderate to severe chronic plaque psoriasis. A total of 225 patients were randomized (2:2:1) to 2 different itolizumab arms (A or B; A = 4-week loading dose of 0.4 mg/kg/wk followed by 1.6 mg/kg every 2 weeks; B = 1.6/mg every 2 weeks) or placebo. At week 12, the placebo arm was switched to 1.6 mg/kg itolizumab every 2 weeks. The primary end point was the proportion of patients with at least 75% improvement in Psoriasis Area and Severity Index score at week 12. At week 12, 27.0% in arm A (P = .0172 vs placebo), 36.4% in B (P = .0043 vs placebo), and 2.3% in the placebo arm had at least 75% improvement in Psoriasis Area and Severity Index score. At week 28, the proportion with at least 75% improvement in Psoriasis Area and Severity Index score was comparable: 46.1%, 45.5%, and 41.9% for A, B, and placebo, respectively. In weeks 1 to 12, the incidence of all adverse events was comparable across arms (A, 43%; B, 38%; placebo, 47%) and the incidence of infections was not greater than placebo (11.1%, 8.9%, and 18.6% for A, B, and placebo). No active comparator is a limitation. Itolizumab is an effective and well-tolerated novel biological therapy in moderate to severe psoriasis.Journal of the American Academy of Dermatology 04/2014; 71(3). DOI:10.1016/j.jaad.2014.01.897 · 5.00 Impact Factor