title: Coexpression and functional cooperation of CTLA-4 and CD28 on activated T lymphocytes.
abstract: T cell costimulation by molecules on the antigen presenting cell (APC) is required for optimal T cell proliferation. The B7 molecule on APC binds the T lymphocyte receptor CD28, triggering increased interleukin 2 (IL-2) production and subsequent T cell proliferation. CTLA-4 is a predicted T cell membrane receptor homologous to CD28, which also binds the B7 counter receptor, but whose distribution and function are unknown. Here we have developed monoclonal antibodies (mAbs) specific for CTLA-4 and have investigated these questions. mAbs were produced that bound CTLA-4 but not CD28, and that blocked binding of CTLA-4 to B7. CTLA-4 expression as measured by these mAbs was virtually undetectable on resting T cells, but was increased several hundred-fold during T cell activation. On activated lymphocytes, CTLA-4 was expressed equally on CD4+ and CD8+ T cell subsets and was coexpressed with CD25, CD28, and CD45RO. CTLA-4 expression was lower than that of CD28, reaching a maximum of approximately 1/30-50 the level of CD28. Despite its lower expression, CTLA-4 was responsible for much of the B7 binding by large activated T cells. Anti-CTLA-4 mAb 11D4 and anti-CD28 mAb 9.3 acted cooperatively to inhibit T cell adhesion to B7, and to block T cell proliferation in primary mixed lymphocyte culture. When coimmobilized with anti T cell receptor (TCR) mAb, anti-CTLA-4 mAbs were less effective than anti-CD28 mAb 9.3 at costimulating proliferation of resting or activated T cells. However, coimmobilized combinations of anti-CD28 and anti-CTLA-4 were synergistic in their ability to augment anti-TCR-induced proliferation of preactivated CD4+ T cells. These results indicate that CTLA-4 is coexpressed with CD28 on activated T lymphocytes and cooperatively regulates T cell adhesion and activation by B7.
authors.affiliation: Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, Washington 98121.
authors.forename: P S
authors.initials: PS
authors.lastname: Linsley
authors.forename: J L
authors.initials: JL
authors.lastname: Greene
authors.forename: P
authors.initials: P
authors.lastname: Tan
authors.forename: J
authors.initials: J
authors.lastname: Bradshaw
authors.forename: J A
authors.initials: JA
authors.lastname: Ledbetter
authors.forename: C
authors.initials: C
authors.lastname: Anasetti
authors.forename: N K
authors.initials: NK
authors.lastname: Damle
mesh_terms: D000069594:Abatacept; D000818:Animals; D000911:Antibodies, Monoclonal; D000938:Antigen-Presenting Cells / Q000276:immunology*; D015703:Antigens, CD / Q000032:analysis / Q000096:biosynthesis* / Q000276:immunology; D000943:Antigens, Differentiation / Q000032:analysis / Q000096:biosynthesis* / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis / Q000096:biosynthesis* / Q000276:immunology; D018106:CD28 Antigens; D015704:CD4 Antigens / Q000032:analysis / Q000276:immunology; D016466:CHO Cells; D060908:CTLA-4 Antigen; D002448:Cell Adhesion / Q000276:immunology; D002478:Cells, Cultured; D006224:Cricetinae; D018796:Immunoconjugates; D007700:Kinetics; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C / Q000276:immunology; D010957:Plasmids; D011956:Receptors, Cell Surface / Q000032:analysis / Q000096:biosynthesis / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D014162:Transfection
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D000945:Antigens, Differentiation, T-Lymphocyte; D018106:CD28 Antigens; D015704:CD4 Antigens; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D011956:Receptors, Cell Surface; D000069594:Abatacept