Examination of the clonal deletion hypothesis following transfusions in rat cardiac transplants

Inhibition of chronic vascular rejection by donor-specific blood transfusion is associated with a reduction in transforming growth factor-beta1 expression

BACKGROUND

Concentric intimal thickening and the infiltration of inflammatory cells in cardiac allografts are the pathological hallmark characteristics of chronic vascular rejection (CVR), the leading cause of long-term graft failure. The precise mechanisms involved in the development and pathogenesis of CVR remain elusive. In the PVG-R23 to PVG-RT1u rat model of CVR, prior administration of a donor-specific transfusion (DST) was previously shown to prolong graft survival indefinitely and abolish the vascular lesions associated with CVR. The present study investigates in more depth the underlying mechanisms involved in the subsequent prolongation of allograft survival and inhibition of CVR by DST.

METHODS

R23 heart grafts were monitored in nontransfused and transfused RT1u recipients injected 2 weeks before transplantation with 1.5 ml of R23 blood. Severity of arteriosclerosis, transplant infiltrate, transforming growth factor (TGF)-beta1 protein expression within the graft, plasma TGF-beta1 levels, class II MHC expression, tenascin protein expression, and serum alloantibody levels were measured.

RESULTS

There was no significant difference in donor MHC class II, myocardial TGF-beta1, or tenascin expression between DST and non-DST-treated recipients. However, DST-pretreated recipients showed greatly reduced histological evidence of CVR and had lower titers of R23-specific IgG subclasses. Furthermore, DST-treated allograft recipients showed significant decreases in circulating TGF-beta1 levels and a reduction in TGF-beta1 and tenascin expression within coronary arteries of the allografts.

CONCLUSION

The results suggested that DST inhibited CVR by altering and regulating the expression of TGF-beta1, thereby preventing the fibrogenic effects associated with TGF-beta1.

Advantages of donor-specific blood transfusion in the rat via the portal vein for renal transplantation

It is well known that blood transfusion can promote immune unresponsiveness to a renal allograft in both animals and humans. The present study examined the differences between either portal venous (PV) or intravenous (IV) donor-specific transfusion (DST) alone on the survival of rat renal allografts without other immunosuppression. Seven days before LEW (RT1(1)) renal transplantation, recipient WKA rats (RT1u) were inoculated with graded doses (1.0 to 0.0001 mL) of LEW whole blood through either the portal vein or the tail vein. A dose of 0.001 mL whole blood PV resulted in significantly greater prolongation of renal allograft survival than occurred with IV preimmunization (38.5 +/- 10.6 days v 12.5 +/- 2.7 days). Although recipient survival was not significantly different for the two routes for a lower dose (0.1 mL) of whole blood preimmunization 7 days before transplantation, azotemia and rejection were prevented when the PV route, but not the IV route, was used. However, when 0.1 mL of whole blood was administered 5 days before transplantation, survival was prolonged only in animals preimmunized by the PV route (54.7 +/- 14.0 days v 14.3 +/- 4.0 days). In the stronger reciprocal combination of WKA to LEW, there was an advantage of PV with 0.1 mL whole blood, but not with 1 mL. These results indicate that the beneficial effects of DST on renal allograft survival can be obtained when a smaller volume of blood is given via the PV rather than the IV route and a shorter interval elapses between preimmunization and transplantation.

T-cell immunodeficiency induced by T-cell mitogens combined with cyclophosphamide injection

In the murine system in vivo administration of several T-cell mitogens (LcA, Con A, anti-Thy 1.2 mAb) followed by cyclophosphamide (CP) inhibited the functional activity of T-cell subsets (Th1, Th2, Ts) but not that of B cells. T-cell counts in the spleen of treated mice proved to be significantly decreased. Conversely, T mitogens or CP alone produced a negligible effect if any. Adoptively transferred thymocytes from intact donors restored T-dependent splenocyte responses in experimental mice. In addition, it did not suppress the normal response to sheep red blood cells (SRBC). Our results indicated that the acquired immune deficiency under study is caused by polyclonal elimination (deletion) of mitogen-stimulated T cells, and could be regarded as a model of CP-induced tolerance.

Failure to prolong pancreatic islet allograft survival in rats with donor-specific blood transfusions and immunosuppression

The effects on pancreatic islet allograft survival of donor-specific blood transfusions (DST) in combination with pre- and posttransplant immunosuppression were studied. A total of 12 groups of rats (n = 105) with chemically induced diabetes underwent islet allotransplantation. Multiple DST or third-party blood transfusions (TPT) were given prior to transplantation. Pretransplant immunosuppression consisted of azathioprine and prednisolone, and low-dose cyclosporin A was used for posttransplant immunosuppression. TPT, as well as separate or combined pre- and posttransplant immunosuppression without blood transfusions, did not prolong islet allograft survival. DST resulted in either primary nonfunction of the islet allografts or a markedly decreased islet allograft survival. These findings contrast with the beneficial effect of DST on whole-organ allograft survival in rats previously described by others.

Pretransplant cytotoxic conditioning produces effects consistent with clonal deletion mechanisms

A rat cardiac allograft model (ACl to Lewis) was used to investigate the clonal deletion theory. Twelve groups of Lewis recipients received various combinations of donor-specific blood transfusions (DSTs), immediate post-DST immunosuppression with azathioprine/prednisone, and low-dose cyclosporine (1 mg/kg/day) posttransplant. DSTs and cyclosporine together gave modest prolongation of graft survival (from 6.0 to 17 days). DSTs plus immediate post-DST immunosuppression followed by low-dose cyclosporine prolonged graft survival to an average of 45 days. Third-party transfusions alone and in combination with immunosuppression did not significantly prolong allograft survival. Postoperative cyclosporine was required for the expression of this effect suggesting that clonal depression rather than clonal deletion had occurred. Combining DSTs with brief but intense preoperative immunosuppression may be a more effective method of pretransplant conditioning than DSTs alone.