CD28-B7 blockade after alloantigenic challenge in vivo inhibits Th1 cytokines but spares Th2.

Abstract

SummaryBlocking the CD28-B7 T cell costimulatory pathway with the fusion protein CTLA4Ig inhibits alloimmune responses in vitro and in vivo and induces tolerance to cardiac allografts in mice and rats, but the mechanisms mediating the tolerant state in vivo are unknown. Here, we report the effects and potential mechanisms of CTLA4Ig in the rat renal allograft model. LEW rats were nephrectomized and received renal allografts from major histocompatibility complex-incompatible WF rats. While all untreated and control immunoglobulin (Ig)-treated animals acutely rejected their allografts and died, 86% of rats that received a single injection of CTLA4Ig on day 2 after transplantation had prolonged survival (>60-100 days) with preserved renal function. By contrast, only 29% of animals that received CTLA4Ig on the day of engraftment had prolonged survival. Long-term survivors (>100 days) exhibited donor-specific tolerance, accepting donormatched WF but acutely rejecting third-party BN cardiac allografts. Immunohistological analysis of grafts sampled at 1 week after transplantation showed that both control and CTLA4Ig-treated animals had mononuclear cell infiltrates, with a higher percentage of CD4 + cells in the CTLA4Ig-treated group. However, while this was associated with vasculitis and tubulitis in control grafts, there was no evidence of tissue injury in CTLA4Ig-treated animals. The immune response leading to graft rejection in control animals was characterized by expression of the T helper (Th) type 1 cytokines interleukin (IL)-2 and interferon-% In contrast, the persistent CD4 § infiltrate without graft rejection in CTLA4Ig-treated animals was associated with increased staining for the Th2-related cytokines IL-4 and Ibl0. Furthermore, grafts from CTLA4Ig-treated animals had marked upregulation of intragraft staining for IgG1, but not IgG2a or IgG2b. Administration of riD2 to CTLA4Ig-treated animals restored allograft rejection in 50% of animals tested. These results confirm that blockade of the CD28-B7 pathway after alloantigenic challenge induces donor-specific acceptance of vascularized organ allografts, and indicates in this model that CTLA4Ig inhibits Thl but spares Th2 cytokines in vivo.

Adenoviral delivery of CTLA4Ig into myeloid dendritic cells promotes their in vitro tolerogenicity and survival in allogeneic recipients

“…24 In this study, we have shown that myeloid DC propagated in vitro with GM-CSF + IL-4 can be transduced using a replication-deficient Ad vector to express the gene encoding CTLA4Ig. This chimeric fusion protein is a potent immunosuppressant that blocks the expression of B7 costimulatory molecules on APC [5][6][7] and that suppresses both experimental allograft rejection [12][13][14][15] and autoimmune disease. 16 The data also reveal that CTLA4Ig-transduced DC have markedly impaired ability to induce T cell proliferation and CTL generation.…”

“…5,6 It prolongs allograft survival in experimental animals and in some cases, may induce transplantation tolerance. [12][13][14][15] Ex vivo treatment of APC with CTLA4Ig and autoantigen can prevent the development of experimental autoimmune disease in rodents. 16 In this study, we genetically modified BM-derived myeloid DC with an adenoviral (Ad) vector encoding cDNA for CTLA4Ig.…”

CTLA4 Silencing with siRNA Promotes Deviation of Th1/Th2 in Chronic Hepatitis B Patients

“…Upon B7-1 or B7-2 engagement, CTLA4 expressed on the surface of activated T lymphocytes signals for cell-cycle arrest and attenuating the function of effectors (2,3). Previous studies have demonstrated that blockage of signaling transduction between CD28 and CTLA4-Ig inhibited the response of T cells and prolonged the allograft survival in several rodent and organ transplantation models (4)(5)(6)(7). On the other hand, it was found that the blockage of CTLA4 in previously vaccinated cancer patients increased T cell response and was associated with objective tumor regression (8)(9)(10), although in some cases it was accompanied by serious side effects, including hypophysitis and enterocolitis.…”

Feasibility of CTLA4Ig gene delivery and expression in vivo using retrovirally transduced myeloid dendritic cells that induce alloantigen-specific T cell anergy in vitro

“…38 There is also evidence that CTLA4Ig may divert host immune responses toward a Th2 pathway. 39 Newell et al 40 reported recently that blockade of the B7-CD28 pathway had inhibitory effects on CD4 + but not CD8 + T cells, and that inhibition of CD4 + T cell-mediated allograft rejection might be related to down-regulation of Th1 cytokines, and/or up-regulation of Th2 cytokines. The present findings with CTLA4Ig-gene-transduced DC, including the greater suppression of proliferative compared with cytotoxic T cell responses following exposure to these cells, are compatible with the latter observations.…”

“…[38][39][40] We therefore examined the cytokine profiles of draining (popliteal) lymph node lymphocytes from mice injected s.c. in one hind footpad with CTLA4Ig-transduced DC. When compared with those from animals given control (Zeo)-transduced DC, lymphocytes from mice given CTLA4Ig-transduced DC exhibited markedly reduced production of IFN-␥, but enhanced secretion of IL-4 and IL-10 in response to restimulation with allogeneic splenocytes (Figure 7).…”