Targeting LFA-1 and CD154 Suppresses the In Vivo Activation and Development of Cytolytic (CD4-Independent) CD8+ T Cells

Abstract

Short-term immunotherapy targeting both LFA-1 and CD40/CD154 costimulation produces synergistic effects such that long-term allograft survival is achieved in the majority of recipients. This immunotherapeutic strategy has been reported to induce the development of CD4+ regulatory T cells. In the current study, the mechanisms by which this immunotherapeutic strategy prevents CD8+ T cell-dependent hepatocyte rejection in CD4 knockout mice were examined. Combined blockade of LFA-1 and CD40/CD154 costimulation did not influence the overall number or composition of inflammatory cells infiltrating the liver where transplanted hepatocytes engraft. Expression of T cell activation markers CD43, CD69, and adhesion molecule CD103 by liver-infiltrating cells was suppressed in treated mice with long-term hepatocellular allograft survival compared to liver-infiltrating cells of untreated rejector mice. Short-term immunotherapy with anti-LFA-1 and anti-CD154 mAb also abrogated the in vivo development of alloreactive CD8+ cytotoxic T cell effectors. Treated mice with long-term hepatocyte allograft survival did not reject hepatocellular allografts despite adoptive transfer of naive CD8+ T cells. Unexpectedly, treated mice with long-term hepatocellular allograft survival demonstrated prominent donor-reactive delayed-type hypersensitivity responses, which were increased in comparison to untreated hepatocyte rejectors. Collectively, these findings support the conclusion that short-term immunotherapy with anti-LFA-1 and anti-CD154 mAbs induces long-term survival of hepatocellular allografts by interfering with CD8+ T cell activation and development of CTL effector function. In addition, these recipients with long-term hepatocellular allograft acceptance show evidence of immunoregulation which is not due to immune deletion or ignorance and is associated with early development of a novel CD8+CD25high cell population in the liver.

Disparate Primary and Secondary Allospecific CD8+ T Cell Cytolytic Effector Function in the Presence or Absence of Host CD4+ T Cells

“…1b). These studies expand upon our previous observations that CD8 ϩ GICs in hepatocyte rejectors express a CTL phenotype (CD8 ϩ CD43 ϩ ) (47) and that the detection of in vivo allocytotoxicity correlates with graft survival status (46,47).…”

“…One study of cardiac allografts reported that host CD4 ϩ T cells are necessary to license dendritic cells for CD8 ϩ T cell activation, CTL function, and CD4-dependent graft rejection (45). However, the development of CTL effectors under CD4-independent conditions in response to allograft tissues such as skin, intestine, and hepatocytes has not been investigated, except for reports by our group showing that the rejection of allogeneic liver parenchymal cells in the absence of CD4 ϩ T cells is accompanied by in vivo cytotoxic effector function (46,47).…”

“…ϩ GICs in CD4 KO hepatocyte rejectors expresses the IL-2R␣ (CD25), implicating a role for local IL-2 in (CD4-independent) CD8 ϩ T cell alloimmunity (46,47). To address the possibility of enhanced CD8 ϩ T cell proliferation in the presence of CD4 ϩ T cells, we analyzed in vivo proliferation of allospecific TCR transgenic Des ϩ CD8 ϩ T cells in CD4-sufficient and CD4-deficient conditions.…”

“…Detection of in vivo cytolytic T cell function through clearance of CFSEstained allogeneic and syngeneic target cells was modified from published methods (49,50), and has been previously described (47) …”

“…26) and stimulate the accumulation of GICs in the recipient liver (47). To retrieve GICs, recipient mice were euthanized for excision of the liver.…”