Immunosuppression by blocking alpha 4-integrins/VCAM-1 adhesion

Immunologic Pathways in a Quantitative Model of Immunosuppression Based on Rejection of an Allogeneic or Xenogeneic Tumor Graft

BACKGROUND

A quantitative model of immunosuppression was previously developed based on the rejection of the allogeneic A/J murine tumor sarcoma 1 (Sa1) in immunocompetent mice. Here, the model is used to evaluate the immunologic mechanisms of graft rejection and to determine the potential of this model to detect synergistic effects of combined immunosuppressive therapies.

METHODS

Wild-type, genetically-deficient, or drug-treated mice were used. Mice were challenged subcutaneously with the allogeneic murine tumor cell line, Sa1, or with the xenogenic human tumor, MDA435. Tumor growth was monitored with time, with increasing tumor size reflecting greater immunosuppression. In some cases, the mice were presensitized with either Sa1 or with A/J splenocytes.

RESULTS

In naïve recipient mice, studies in major histocompatibility complex (MHC)-I-deficient mice and with depleting anti-CD8 monoclonal antibody (mAb) demonstrate that CD8 T cells are important for Sa1 rejection. A modest role for perforin but not for Fas/Fas ligand could be demonstrated. Blockade of CD4 T cells was more effective with decreasing histocompatibility barriers. In contrast, CD4 T cells were critical in second-set rejections, but CD8 T cells were not. Rejection of xenogeneic tumors was also T-cell dependent as demonstrated by anti-CD3 mAb, dependent on both CD4 and CD8 T cells as demonstrated using MHC-I- and MHC-II-deficient mice, but was more vigorous as demonstrated by the lack of effectiveness of immunosuppressive drugs in this model.

CONCLUSIONS

This model can be used to define dominant and partial effects of immunologic pathways as well as synergistic interactions of agents to develop immunosuppressive strategies.

New approaches to the management of acute and chronic cardiac allograft rejection

There are still many problems to be faced in the field of heart transplantation. Acute and chronic rejection are still the major medical obstacles. In this review, we describe recent research in this field undertaken in our laboratory. The induced intercellular adhesion molecule-1 (ICAM-1) and MHC class II antigen resulting from rejection can be visualized in vivo by radioimmunoscintigraphy. This non-invasive method is sensitive for detecting early rejection and allows quantitative assessment of rejection. Short-term administration of monoclonal antibodies to ICAM-1 and leukocyte function-associated antigen-1 (LFA-1) results in an indefinite acceptance of cardiac allografts by induction of antigen-specific tolerance, as evidenced by acceptance of the secondary skin allografts. The characteristics and possible mechanisms of this tolerance induction are discussed. Immunohistopathologic features of graft coronary arteriopathy are shown. Adhesion molecules, cytokines, and growth factors are associated with intimal hyperplasia and phenotypic transformation of smooth muscle cells in the allograft coronary arteries. Dramatic reduction in this intimal hyperplasia was demonstrated by antisense gene therapy targeting cyclin-dependent kinase 2 kinase. We hope that these investigations will contribute to the improvement of the management of patients who undergo heart transplantation.