title: Synergistic effects of CTLA-4 blockade with tremelimumab and elimination of regulatory T lymphocytes in vitro and in vivo.
abstract: Anti-CTLA-4 monoclonal antibodies (mAb) that block the interaction of CTLA-4 with CD80 and CD86 such as tremelimumab and ipilimumab are currently being tested in the clinic for cancer treatment exploiting their properties to de-repress tumor-specific cellular immunity. Addition of the fully human anti-CTLA-4 (tremelimumab) to cultures of human T cells with allogenic dendritic cells (DCs) did not increase proliferation. Magnetic bead-mediated elimination of CD4(+) CD25(+) regulatory T cells (T(reg)) before setting up those alloreactive cultures also largely failed to increase primary proliferation. In contrast, predepletion of CD4(+) CD25(+) T(reg) and culture in the presence of tremelimumab synergistically resulted in increased proliferation and DC:T-cell aggregation. These effects were much more prominent in CD4 than in CD8 T cells. The synergy mechanism can be traced to enhanced CTLA-4 expression in effector cells as a result of T(reg) elimination, thereby offering more targets to the blocking antibody. Human T cells and allogenic DCs (derived both from healthy donors and advanced cancer patients) were coinjected in the peritoneum of Rag2(-/-) IL-2Rγ(-/-) mice. In these conditions, tremelimumab injected intravenously did not significantly enhance alloreactive proliferation unless T(reg) cells had been predepleted. Synergistic effects in vivo were again largely restricted to the CD4 T-cell compartment. In addition, T(reg) depletion and CTLA-4 blockade synergistically enhanced specific cytotoxicity raised in culture against autologous EBV-transformed cell lines. Taken together, these experiments indicate that tremelimumab therapy may benefit from previous or concomitant T(reg) depletion.
authors.affiliation: Biochemistry Department, Clínica Universidad de Navarra, Pamplona, Spain.
authors.forename: Natalia
authors.initials: N
authors.lastname: Suarez
authors.forename: Carlos
authors.initials: C
authors.lastname: Alfaro
authors.forename: Juan
authors.initials: J
authors.lastname: Dubrot
authors.forename: Asis
authors.initials: A
authors.lastname: Palazon
authors.forename: Elixabet
authors.initials: E
authors.lastname: Bolaños
authors.forename: Lorena
authors.initials: L
authors.lastname: Erro
authors.forename: Sandra
authors.initials: S
authors.lastname: Hervas-Stubbs
authors.forename: Ivan
authors.initials: I
authors.lastname: Martinez-Forero
authors.forename: Aizea
authors.initials: A
authors.lastname: Morales-Kastresana
authors.forename: Salvador
authors.initials: S
authors.lastname: Martin-Algarra
authors.forename: Bruno
authors.initials: B
authors.lastname: Sangro
authors.forename: Fernando
authors.initials: F
authors.lastname: Lecanda
authors.forename: Jose L
authors.initials: JL
authors.lastname: Perez-Gracia
authors.forename: Alvaro
authors.initials: A
authors.lastname: Gonzalez
authors.forename: Ignacio
authors.initials: I
authors.lastname: Melero
mesh_terms: D000818:Animals; D019138:Antibodies, Blocking; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D015703:Antigens, CD / Q000276:immunology*; D060908:CTLA-4 Antigen; D049109:Cell Proliferation / Q000187:drug effects; D017690:Cell Transplantation; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000637:transplantation; D006801:Humans; D007155:Immunologic Factors / Q000494:pharmacology*; D051379:Mice; D008822:Mice, Transgenic; D013601:T-Lymphocytes / Q000276:immunology / Q000637:transplantation; D050378:T-Lymphocytes, Regulatory / Q000187:drug effects / Q000276:immunology*
chemical_list: D019138:Antibodies, Blocking; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D015703:Antigens, CD; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C556707:Ctla4 protein, mouse; D007155:Immunologic Factors; C520704:tremelimumab