Synergy between cyclosporin A and a monoclonal antibody to B7 in blocking alloantigen-induced T-cell activation

Abstract

Costimulatory signals are absolutely required for T-cell activation after T-cell receptor/major histocompatibility complex-peptide interaction. So far, the best-known candidate essential costimulatory signal is mediated by interaction of CD28 on T cells with B7 on antigen- presenting cells. Using an allogeneic B7+ Epstein-Barr virus- transformed B-cell line as stimulator, we found that addition of a monoclonal antibody (MoAb) to B7 that efficiently blocks B7-CD28 interaction only partially inhibited proliferation and interleukin-2 (IL-2) production in primary and secondary mixed lymphocyte reactions (MLR), whereas the generation of cytotoxic T lymphocytes (CTL) was not affected. Inhibition of primary or secondary MLR-induced T-cell activation with cyclosporin A (CsA) at nontoxic concentrations also was never complete. However, the combination of CsA and anti-B7 MoAb B7–24 synergistically blocked allogeneic B cell-induced T-cell proliferation, IL-2 production, and CTL generation. These data suggest that the mere blockage of B7-CD28 interaction during allotransplantation will be insufficient to prevent rejection or graft-versus-host disease. However, low CsA concentrations, when combined with an agent blocking B7-CD28 interaction, can potentially achieve complete immunosuppression.

T Helper‐Independent Activation of Human CD8+ Cells: the Role of CD28 Costimulation

“…In vivo experiments in mice confirmed that CD80 costimulation was sufficient for activation of tumour antigen-specific CD8 T cells [14,15]. In previous studies, we and others demonstrated generation of CTL activity in cultures of human T cells by stimulation with anti-CD3 and CD80-transfected mouse cells [23,24] and with allogeneic B-cell lines [25]. More recent data in humans showed in vitro activation of isolated CD8 cells (proliferation and CTL generation) through costimulation by CD80 [26].…”

“…By bridging the effector CTL to the target cell FcR with anti-CD3 MoAb, this anti-CD3-redirected cytotoxicity system permits detection of CTL activity regardless of antigen specificity of the CTL [23]. In some experiments, CTL activity was also tested as the alloantigen-specific 4 h target cell lysis of the stimulator cell line [25,32]. One million targets were incubated for 1 h with 200…”

“…The cytolytic assays were performed in a 96-well V-bottomed microtitre plate at an effector:target (E:T) ratio of 10 or 20. Cytotoxic activity was calculated as described previously [23,25,32] and is expressed as total 51 Cr release (TR%) or specific 51 Cr release (SR%).…”

“…We previously reported a synergy between CsA and a blocking anti-B7 MoAb in inhibiting alloantigen-induced T-cell activation and CTL generation in cultures of T cells stimulated with ARC cells [25]. We then analysed the blocking capacity of CsA together with anti-CD80 MoAb or with CTLA-4Ig during the…”

Recent advances in graft‐versus‐host disease (GVHD) prevention

“…For example, van Gool and colleagues have shown that the combination of CsA and CTLA4-Ig blocked the generation of alloantigen-specific CTL precursors, whereas reactivity to a third-party stimulator remained intact (122), Non-responsiveness could be reversed by culture in IL-2, indicating that clonal deletion did not occur. The combination of an anti-B7 mAb with low-dose CsA synergistically blocked T-cell proliferation and IL-2 production in response to alloantigen expressed on EBV-transformed B-cell lines in pri-mary as well as secondary MLR cultures (123). In contrast, in a different ex vivo culture system in which the frequency of alloreactive precursor T lymphocytes are measured in response to host or third party stimulators.…”