Search

A single bolus of soluble complement (C) receptor type 1 (sCR1, TP-10) has been shown to delay hyperacute rejection (HAR) of porcine cardiac xenografts (Xgs) by primate recipients. In these recipients, C activity slowly returned and C deposition was noted in the Xgs at rejection. To evaluate the effect of sustained C inhibition using sCR1 on HAR, two additional cynomolgus monkeys received porcine cardiac Xgs and a continuous infusion of sCR1. In the first recipient, Xgs survival was 5 days (120+ hr), whereas in the second, Xg survival was 7 days (168+ hr). Serial biopsies of the Xgs were remarkable for an increasing cellular infiltrate composed predominantly of neutrophils and macrophages, and the development of edema, hemorrhage, and myocyte necrosis. These findings suggest that once C-mediated HAR has been inhibited, infiltration of the Xg by these cells may lead to accelerated acute rejection, which is an additional barrier to successful longer term Xg survival.

Xenogeneic transplantation (XT) is the transplantation of organs or tissues from a member of one species to a member of another. Mammalian species frequently have circulating antibody which is directed against the foreign organ irrespective of known prior antigen exposure. This antibody may lead to hyperacute rejection. There is no reliable means to avert hyperacute rejection once it ensues so efforts must be directed towards eliminating the pre-existing antibody. In those species in which hyperacute rejection of xenografts does not occur, cell-mediated rejection, similar to allograft rejection, may occur. It is in the prevention of this latter form of rejection that radiation is most likely to be beneficial in XT. Both total lymphoid irradiation (TLI) and selective lymphoid irradiation (SLI) have been investigated for use in conjunction with XT. TLI has contributed to the prolongation of pancreatic islet-cell xenografts from hamsters to rats. TLI has also markedly prolonged the survival of cardiac transplants from hamsters to rats. A more modest prolongation of graft survival has been seen with the use of TLI in rabbit-to-rat exchanges. Therapy with TLI, cyclosporine, and splenectomy has markedly prolonged the survival of liver transplants from hamsters to rats, and preliminary data suggest that TLI may contribute to the prolongation of graft survival in the transplantation of hearts from monkeys to baboons. SLI appears to have prolonged graft survival, when used in conjunction with anti-lymphocyte globulin, in hamster-to-rat cardiac graft exchanges. The current state of knowledge of the use of irradiation in experimental XT is reviewed.

An analysis of data collected during the South Eastern Organ Procurement Foundation (SEOPF) Prospective Study from 1977-1982 was performed to identify the relative effects of different blood products on patient sensitization and graft survival in cadaveric donor renal transplant recipients. More than 2700 primary and 800 regrafted patients from 40 transplant centers were included in this study. A significant increase in actuarial graft survival was seen in primary recipients who had pretransplant transfusions with only frozen blood (P less than 0.003), washed blood (P less than 0.0005), packed blood (P less than 0.0001), or any combination of blood products (P less than 0.002) as compared with those who received no transfusions. No blood product was found to provide a significantly greater increase in graft survival than any other blood product. Likewise, regrafted patients had significant and equivalent increases in graft survival associated with each type of blood product examined. The increased graft survival associated with each blood product was the result of decreased graft rejection, and not apparently related to other differences among patients receiving different types of blood. Furthermore, the type of blood used in pretransplant transfusions did not significantly influence the degree of patient sensitization for first-graft recipients, although regrafted recipients who received packed blood or a combination of blood products showed a slightly greater degree of sensitization than those who received only frozen or washed blood. First-graft recipients given packed or mixed blood had a small, statistically insignificant increase of hepatitis B virus (HBV) antigenemia, compared with those receiving frozen, washed, or no blood. Regrafted patients given any type of transfusion had a 3-4-fold increased incidence of HBV antigenemia as compared with nontransfused patients, but this difference also was statistically not significant. These findings suggest that the benefits of increased graft survival and the risks of sensitization or HBV infection associated with pretransplant transfusions are not significantly affected by the type of blood used.

Total lymphoid irradiation and cyclosporine have profound immunosuppressive properties and permit successful heart allotransplantation. Cyclosporine used alone has not permitted consistently successful transplantation between species in all cases. Total lymphoid irradiation has not been applied to xenotransplantation. The efficacy of total lymphoid irradiation alone and in combination with cyclosporine was examined using an animal model of heart xenotransplantation. Heterotopic heart transplants were performed using inbred Syrian hamsters as donors and Lewis rats as recipients. Total lymphoid irradiation was administered preoperatively over 3 weeks for a total dose of 15 gray. Cyclosporine was started on the day of surgery and was given as a daily intramuscular injection of 2.5, 5, or 10 mg/kg/day until rejection was complete. Neither total lymphoid irradiation nor cyclosporine alone markedly prolonged graft survival. However, combined total lymphoid irradiation and cyclosporine, 5 or 10 mg/kg/day, dramatically prolonged graft survival to greater than 100 days in most recipients. There were no treatment-related deaths. In conclusion, combined total lymphoid irradiation and cyclosporine permit successful long-term survival of heart xenotransplants in this hamster-to-rat model.

A review of more than 3000 cadaver donor renal allograft recipients transplanted between June 1977 and July 1982 as part of the South-Eastern Organ Procurement Foundation (SEOPF) Prospective Study was performed to identify patients who received a transplant following a significant decrease in pretransplant sensitization as measured by the percentage of panel-reactive antibody (PRA). Such patients were identified as having had a most reactive (historical peak sera) PRA level at least 40 percentage points higher than their last sample tested prior to transplant (current sera). Additional data were obtained on 157 of these patients, who also had no history of pretransplant immunosuppression and had a negative pretransplant crossmatch with current sera. Data included the dates of pretransplant sera samples, the specific techniques used for each serum sample that was crossmatched or screened for PRA, and the serological results. The population studied included 17 of 87 first-transplant recipients and 17 of 70 regrafted recipients whose pretransplant crossmatches with peak sera were positive or not done. These subgroups showed no decrease in graft or patient survival compared with cohorts (70/87 first-transplant recipients and 53/70 regrafted recipients) for whom peak sera crossmatching was performed with negative results. Additional stratification for the techniques used in crossmatching and screening, as well as the interval between peak and current PRA levels, showed no significant associations with eventual graft or patient outcome. These results suggest that crossmatch testing using peak sera may not be important in predicting eventual graft or patient outcome for patients with a marked decrease in PRA prior to transplantation and a negative crossmatch with current sera.

In an attempt to investigate the nonspecificity of the effect of administration of donor splenocytes treated with mitomycin C (MMC) 7 days before transplantation in inducing immunological unresponsiveness, the survival rates of liver, heart, small bowel, and skin allografts were compared in the RT1-incompatible ACI(RT1a) to LEW(RT1l) rat combination. ACI donor splenocytes (3 x 10(6)) treated with MMC were administered i.p. or i.v. via the penile vein 7 days before transplantation. Both routes of administration prolonged the survival of hepatic allografts (greater than 87.2 +/- 22.2 days and greater than 78.9 +/- 28.2 days, respectively), compared with controls (10.6 +/- 0.5 days). Cardiac allograft survival in untreated controls was 6.0 +/- 0.4 days. A single i.v. injection of 3 x 10(6) donor splenocytes resulted in significantly prolonged survival (10.0 +/- 4.3 days), whereas i.p. injection showed rejection at a mean of 6.0 +/- 1.2 days. A single i.p. injection of 3 x 10(6) splenocytes did not increase survival of small bowel allografts (10.3 +/- 4.8 days), compared with controls (8.8 +/- 1.8 days). On the other hand, a single i.v. injection of donor splenocytes prior to transplantation significantly prolonged survival of small bowel allografts (13.4 +/- 3.5 days). No signs of graft-versus-host reaction (GVHR) were observed during these experiments. Neither a single i.p. nor a single i.v. injection of donor splenocytes resulted in prolonged survival of ACI-to-LEW skin allografts (6.3 +/- 0.8 days and 6.6 +/- 0.9 days, respectively), compared with controls (5.7 +/- 0.5 days). Interestingly, we confirmed the relative ease with which survival of hepatic allografts can be prolonged in the rat by donor antigen treatment alone, even in a strongly rejecting RT1-incompatible rat strain combination, in contrast to other organ allografts such as heart, small intestine, and skin. The discrepancy in survival of different organ allografts following pretreatment with donor splenocytes treated with MMC may be explained by a difference in the immunogenicity of the organs transplanted or other factors.

The association of inflammatory cell infiltration with orthotopic rat liver transplant rejection was studied by immunopathologic evaluation of allografts at different time points using high- and low-responder strain combinations. PVG(RT-1c) recipients of ACI (RT-1a) liver transplants had prolonged survival (greater than 100 days) without immunosuppression. In contrast, Lewis (RT-1l) recipients of ACI liver transplants had severe acute rejection with mean survival of 10.7 +/- 0.5 days (n = 9). Graft recipients of both strain combinations, as well as control syngeneic PVG-to-PVG and Lewis-to-Lewis graft recipients were sacrificed at various time points posttransplant. Sections of livers were evaluated in a masked fashion for histologic changes as well as the extent and phenotype of cellular infiltrates, as determined by immunoperoxidase labeling using monoclonal antibodies OX1 (pan leukocyte), W3/13 (pan T cell), W3/25 (T helper cell:Th), and OX8 (T cytotoxic-suppressor:Tc-s). The results suggest that: the intensity and relative distribution of rat hepatic allograft T cell infiltrates at a given time point do not necessarily correlate with eventual outcome; the intensities of W3/25 (Th) and OX1 (pan-leukocyte) cell infiltrates parallel each other in both high- and low-responder strain combinations; the relative ratio of T cells (W3/13) to non-T cells increases over time in low-responder strains but remains relatively constant in high-responder strains during active rejection; and the relative ratio of W3/25:OX8 (Th:Tc-s) decreases in high-responder strains but increases in low-responder strains.

Total lymphoid irradiation (TLI) has profound immunosuppressive actions and has been applied successfully to allotransplantation but not xenotransplantation. Cyclosporine (CsA) has not generally permitted successful xenotransplantation of organs but has not been used in combination with TLI. TLI and CsA were given alone and in combination to rats that were recipients of hamster or rabbit cardiac xenografts. Combined TLI and CsA prolonged survival of hamster-to-rat cardiac xenografts from three days in untreated controls to greater than 100 days in most recipients. TLI alone significantly prolonged rabbit to rat xenograft survival with doubling of survival time. However, combined treatment did not significantly prolong rabbit-to-rat cardiac xenograft survival compared with TLI alone. The hamster and rat are phylogenetically closely related. Transplants from hamsters to rat are concordant xenografts since the time course of unmodified rejection is similar to first-set rejection of allografts. Although the rabbit-to-rat transplant is also between concordant species (average survival of untreated controls: 3.2 days) the rabbit and rat are more distantly related. These results suggest that TLI is an effective immunosuppressant when applied to cardiac xenotransplants in these animal models; that the choice of species critically affects xenograft survival when TLI and/or CsA are used for immunosuppression; and that the closely related species combination tested has markedly prolonged (greater than 100 days) survival using combined TLI and CsA.

In an attempt to study the role of class I major histocompatibility complex antigens in inducing immunological unresponsiveness, the survival rates of hepatic allografts were compared in rats pretreated with blood taken from various rat strains. A single intravenous injection of 1 ml fresh heparinized whole blood seven days before transplantation significantly prolonged the survival of subsequent donor-specific hepatic allografts in the fully allogeneic ACI(RT1a)-to-LEW(RT1l) rat combination. However, pretreatment with blood taken from the third-party strain BN(RT1n) did not produce suppression of rejection, attesting to the specificity of the pretransplant transfusion effect. Interestingly, pretransplant transfusion of PVG.r1 blood, sharing only the RT1.A MHC region with ACI, significantly prolonged the survival of ACI-to-LEW hepatic allografts. In addition, no lymphocytotoxic antibodies could be detected at 30 or 100 days after transplantation in animals with long-surviving hepatic allografts pretreated with either PVG.r1 or ACI whole blood. On the other hand, pretreatment with PVG(RT1c) blood increased the survival of ACI-to-LEW hepatic allografts only moderately compared with controls. This finding may be consistent with a partial effect of some third-party blood transfusion. The experimental data suggest that the class I MHC antigens can be immunosuppressive in rat hepatic allografts. Adoptive transfer of 5 x 10(7) splenocytes taken from long-term-surviving hepatic allografts pretreated with donor ACI whole blood or PVG.r1 blood into irradiated (750 rads) LEW rats prolonged the survival of donor-type skin grafts, whereas third-party strain (BN) grafts were rejected. This finding suggests the presence of donor-specific suppressor cells.

Analysis of 2778 primary and 606 regrafted cadaveric donor renal allograft recipients transplanted between June 1977 and July 1982 as part of the South-Eastern Organ Procurement Foundation (SEOPF) Prospective Study was performed to determine the influence of changes in presensitization on graft and patient outcome. Four mutually exclusive groups of patients were identified based on the relative difference in the percentage of panel-reactive antibody (PRA) from highest ever (peak) to most recent (current) pretransplant levels as follows: group 1 (unsensitized): peak = current PRA = 0; group 2 (rising or stable PRA): (peak = current PRA) greater than 0; group 3 (small decrease): (peak - current PRA) = 1-40%;) and group 4 (large decrease): (peak - current PRA) greater than 40%. First-transplant recipients in group 4 had significantly higher mortality when compared with groups 1-3 (P less than 0.002). This decrease in patient survival was evident at 6 months (81% +/- 4 vs 91% +/- 1) and persisted to three years (68% +/- 8 vs 78% +/- 2), and it was associated with a significant (P less than 0.037) increase in death from infectious causes. This finding was even more striking when only transfused recipients were considered: at three years the difference in patient survival was 63% +/- 11 vs. 77% +/- 2. In addition, transfused patients with a decrease in pretransplant PRA of greater than 40% had significantly lower overall graft survival (P less than 0.02) and a higher incidence of irreversible graft rejection (50% +/- 8 vs 33% +/- 1 at two years). For regrafted recipients, there were no differences in patient survival among groups, but those in group 4 had significantly lower graft survival (P less than 0.0033) than groups 1-3. These findings suggest that a substantial decrease in PRA prior to transplant does not necessarily indicate a decrease in potential donor alloreactivity, and in first-graft recipients it may reflect an increased susceptibility to life-threatening infections following transplantation.