Graft-versus-host resistance induced by class II major histocompatibility complex-specific T cell clones

A small population of vasculitogenic T cells expands and has skewed T cell receptor usage after culture with syngeneic smooth muscle cells

Adoptive transfer of lymphocytes co-cultured with syngeneic smooth muscle (SM) cells to healthy recipient mice results in vasculitic lesions predominantly in post-capillary venules. The present study focuses on the mechanisms by which the disease-inducing CD4(+) T cells are generated in co-culture of lymphocytes with SM cells. Microvascular SM cells provide survival signals to both CD4(+) and CD8(+) naïve syngeneic T cells and can activate only a limited range of CD4(+) T lymphocytes in culture. Additionally, approximately 0.4% of the original CD4(+) T cells divide at least twice in co-culture with SM cells. Survival of CD4(+) T cells in co-culture is dependent on a TCR mediated process, since transgenic CD4 (+)cells with a unique specificity for a non-murine peptide do not survive in culture with SM. Analysis of TCR Vbeta shows no superantigen activation of T cells following co-culture with SM cells. Spectratype analysis of TCR Vbeta Jbeta segment usage reveals a skewage in the TCR repertoire of T cells co-cultured with SM, and also of T cells from vasculitic lung. These results are consistent with a specific immune response of pathogenic T cells against one or more activating antigenic determinants of the microvascular SM cells, in contrast to non-specific cytokine activation.

Mutual tolerance after liver and not after heart transplantation? Evaluation of patient-anti-donor and donor-anti-patient responses by mixed lymphocyte culture

The ultimate goal in organ transplantation is the induction of donor-specific transplantation tolerance. The fact that in some patients it is possible to withdraw immunosuppressive therapy completely, suggests that immunological adaptation or donor-specific nonresponsiveness can occur following transplantation. In earlier studies we have shown that after blood transfusion, the mixed lymphocyte reactivity of the donor against patient peripheral blood mononuclear lymphocytes taken after blood transfusion gradually decreased with time. This may reflect the induction of an immunoregulatory mechanism, which protects the recipient against an immune reaction of the donor, enhancing a state of mixed chimerism. A similar phenomenon might also play a role in the immunological mechanism leading to transplantation tolerance. Therefore, we studied responses in patients with a well-functioning liver and heart transplant using a primed lymphocyte test (PLT) and a mixed lymphocyte culture (MLC). Two years after liver transplantation the PLT and MLC responses of patient against donor were decreased significantly compared to the situation before transplantation. The response of donor against patient was also lower two years after transplantation. The decreased responses were donor-specific since responses to third-party cells generally remained unchanged. In heart transplant recipients we could not detect a donor-specific downregulation. The reversed response, of donor against patient, was not different from responses of third-party against patient cells. Therefore, we conclude that donor-specific nonresponsiveness is not induced in patients with well-functioning heart transplants. In contrast, after a successful liver transplantation the response of patient against donor is decreased, as is the reversed response. It may be valuable to test whether in liver transplant patients withdrawing or reducing of maintenance immunosuppression is permitted for patients who appear to have developed two-way donor-specific hyporeactivity.

Transfusion-associated graft-versus-host disease in immunocompetent patients: a self-protective mechanism

Transfusion-associated graft-versus-host disease (TA-GVHD) is a rare but hazardous complication caused by transfusion of leucocyte-containing blood. It is not clear why some patients are at risk for TA-GVHD, but others are not. We studied TA-GVHD in immunocompetent individuals by looking at donor-anti-host reactivity after transfusion of leucocyte-containing blood. We tested reactivity in 62 donor-recipient combinations in vitro before and at different times after blood transfusion with mixed lymphocyte culture. One patient was studied in more detail. Reactivity of blood donors against hosts gradually decreased after blood transfusion. This decrease significantly correlated with time (p < 0.001). Studies in a single patient showed that absence of donor-host reactivity was due to host T cells that inhibited the response. These data indicate that an active mechanism exists in immunocompetent individuals which inhibits the graft-versus-host reaction of the donor against the host. This mechanism might be exploited in organ transplantation by pre-transplant blood transfer.

Anti-idiotypic antibody to T-cell receptor in multiply transfused patients may play a role in resistance to graft-versus-host disease

Most patients who receive multiple blood or platelet transfusions do not develop graft-versus-host disease (GVHD) in spite of the transfusion of donor white cells--cells that are capable of engraftment and subsequent GVHD. The object of this study was to search for the factors responsible for resistance to GVHD in such patients. Some sera from patients who have received multiple platelet transfusions inhibit the proliferation of alloreactive T-cell clones that function as an in vitro model of donor-derived proliferating T cells recognizing recipient alloantigens. The humoral factor in such sera was capable of binding to the T-cell clones, but not to stimulator cells. Further analysis revealed that the humoral factor in such sera was IgG, which specifically bound to membrane molecules of the T-cell clones. The antibody competed with WT31, a monoclonal antibody (MoAb) to T-cell receptor (TCR), in binding to TCR of the T-cell clones. It did not compete with CD3 or CD2 MoAb. These observations strongly favor the view that the antibody against TCR exists in the sera of multiple transfusion recipients. It is suggested that the TCR antibody binds to TCR of the T-cell clones, thus blocking the interaction of the T-cell clone with alloantigens of stimulator cells and resulting in inhibition of the proliferation of T-cell clones. Furthermore, in view of T-cell clone-specific binding of the antibody in sera, it might be concluded that the antibody is anti-idiotypic.