Prevention of acute murine cardiac allograft rejection: anti-CD4 or anti-vascular cell adhesion molecule one monoclonal antibodies block acute rejection but permit persistent graft-reactive alloimmunity and chronic tissue remodelling.

We treated C57BL/6 mouse recipients of DBA/2 cardiac allografts with anti-CD4 monoclonal antibodies (mAb) or anti-vascular cell adhesion molecule 1 mAb to promote long-term allograft survival and subjected both the recipient animals and the long-surviving allografts to a battery of histologic and immunologic tests. The results were similar regardless of the mAb used for antirejection therapy. At all tested times after transplantation, the allografts displayed histologic evidence of ongoing microvascular endothelial activation and interstitial leukocytic infiltration. Reverse transcription polymerase chain reaction analyses revealed continuous intragraft expression of messenger RNA for interleukin 1, interleukin 2, interleukin 4, interleukin 6, tumor necrosis factor, interferon gamma, and transforming growth factor beta. All grafts had histologic evidence of ongoing vascular and parenchymal tissue remodeling, including interstitial fibrosis and vascular neointimal hyperplasia. The graft recipients retained limiting dilution analysis--detectable, donor-reactive cytolytic T lymphocyte, and helper T lymphocyte in their spleens and produced high liters of donor-reactive alloantibodies. Variable amounts of allogeneic microchimerism were detectable in some, but not all of the long-surviving graft recipients. In general, these observations indicate that (1) a similar immune status is achieved in long-surviving allografts and their recipients when either anti-CD4 mAb or anti-vascular cell adhesion molecule-1 mAb was used for antirejection therapy, in spite of the major differences in lineage and distribution of cells targeted by these two mAbs, (2) this immune status is characterized by continuous, long-term inflammatory and immune processes very similar to those observed during acute allograft rejection, and (3) in spite of these processes the allografts continue to function, although they invariably develop a chronic rejection-like histopathologic condition that may ultimately limit graft function. In this regard, the recipients of long-surviving allografts do not seem to be tolerant of their graft alloantigens.