Interstitial class II-positive cell depletion by donor pretreatment with gamma irradiation. Evidence of differential immunogenicity between vascularized cardiac allografts and islets

We used an allograft pretreatment regimen involving lethal total-body gamma irradiation of donor rats eight days prior to transplantation to compare directly the immunogenicty of immediately-vascularized heart allografts with isolated, neovascularized pancreatic islet allografts. TBI pretreatment of heart donors (IHT) caused a modest prolongation in cardiac allograft survival compared with controls in a low-responding fully-allogeneic strain combination, Lewis-to-ACI. The addition of 10(5) donor-type dendritic cells (DCs) at the time of transplantation reversed the prolongation of IHT in this strain combination. Donor pretreatment with TBI did not lead to prolonged cardiac allograft survival in either a high-responding combination, ACI-to-Lewis, or in an MHC class II-compatible strain combination, F344-to-Lewis. In contrast, islets from irradiated donors (IIT) showed markedly prolonged survival in both low-responding (Lewis-to-ACI) and high-responding (W/F-to-Lewis) strain combinations. The addition of 10(5) donor-type DCs to the islets at the time of transplantation caused the rejection of only two of six IIT in the Lewis-to-ACI combination. Combined pretreatment regimens involving TBI-pretreated cardiac allografts--such as recipient immunosuppression with peritransplant cyclosporine (10 mg/kg on days 0, 1, and 2) or the combination of TBI (1000 cGy on day -3) and cyclophosphamide (300 mg/kg on day -5) in a pretreatment regimen--did not lead to synergistic graft prolongation in the low-responding Lewis-to-ACI combination. Immunohistologic studies showed that eight days after TBI rat hearts and islet were both greater than 90% depleted of class II (0X6+) interstitial dendritic cells while class I (0X18+) expression was unchanged. IIT are able to increase class II expression when donors are treated with recombinant gamma interferon (4000 U/day on days -3, -2, and -1). MLR data showed that ACI recipients of Lewis IIT reacted normally to donor (Lewis) and third-party (W/F) stimulator cells greater than 100 days after transplantation. The apparent greater immunogenicity of heart allografts as compared with islets in this model could be due to (1) a quantitative difference between the number of residual class II-positive cells in hearts and islets or a greater nnon-MHC antigenic load in the heart grafts given its larger size, or (2) a quanlitative difference between hearts and islets due to the presence of a vascular endothelium in the immediately vascularized heart that can present alloantigen and provide a major stimulus to rejection.

Pancreatic islet transplantation in cynomolgus monkeys. Initial studies and evidence that cyclosporine impairs glucose tolerance in normal monkeys

Using a model of streptozotocin-induced, ketosis-prone, insulin-dependent diabetes mellitus (IDDM) in the cynomolgus monkey, we performed 11 intraportal transplants of collagenase-digested, Ficoll-purified pancreatic islets (9 ABO-compatible allografts and 2 concordant baboon xenografts). Islets were pretreated with ultraviolet-B irradiation and recipients received cyclosporine A immunosuppression. Two grafts never functioned, five grafts showed evidence of partial function, and four grafts (three allografts and one xenograft) showed evidence of good function, with the animals independent of exogenous insulin with morning fasting blood glucose levels less than 200 mg/dl. Because two grafts functioned only after CsA was either tapered or discontinued, we performed a related study that showed that therapeutic doses of CsA (morning trough serum level 150-250 ng/ml) impaired intravenous glucose tolerance tests (IVGTT) of normal monkeys and may contributed to graft dysfunction in our islet transplantation model. The results show that there is a decrease in release of serum insulin during an IVGTT leading to impairment of glucose utilization, while serum glucagon remains unaffected. After cessation of CsA, the IVGTT did not return to normal for 28 days. Oral glucose tolerance tests were unaffected in CsA-treated monkeys. These initial studies show that the streptozotocin-diabetic monkey is a valuable model to study IDDM and islet transplantation in nonhuman primates. We also confirm studies in rodents, dogs, and sheep by showing that CsA partially inhibits beta cell function in normal monkeys.

Humoral immunity in allograft rejection. The role of cytotoxic alloantibody in hyperacute rejection and enhancement of rat cardiac allografts

The role of humoral immunity in graft rejection in the rat model remains controversial. Passive transfer of cytotoxic alloantibody (CAA) has resulted either in hyperacute rejection or in graft enhancement. This study examines the effect of transfer of CAA on cardiac allograft survival in three rat strain combinations that are fully mismatched at the major histocompatibility (MHC) loci. Strain-specific immune responsiveness in donor-recipient pairs varied from low (Lewis-to-ACI) to high (ACI-to-Lewis) as measured by mixed lymphocyte reactions. CAA was obtained from rats sensitized by three successive skin grafts at weekly intervals. Group 1 (high responder recipients), which consisted of Lewis rats presensitized to ACI and had a lymphocytotoxicity titer of 1:512 to 1:2048, rejected ACI cardiac allografts in 10.8 +/- 7.2 hr compared with 6.5 +/- 0.5 days in naive controls (p less than 0.001). Injection of 1 ml of high-titer CAA into naive Lewis rats immediately after ACI cardiac grafting led to hyperacute rejection of ACI hears in 2.1 +/- 0.8 hr while 1 ml of CAA followed by 2 ml of guinea pig complement (GPC) resulted in even faster rejection (mean survival time (MST) of 23.8 +/- 4.7 min). Injection of 2 ml GPC alone or in combination with 1 ml naive Lewis serum had no effect on graft survival. Multiple pretransplant injections of 1 ml of CAA on days -3, -2,-1, and 0 relative to transplantation resulted in significant prolongation of allograft survival (MST of 10.3 +/- 0.3 days; P less than 0.01). In group 2 (intermediate responder recipients), where Lewis rats were presensitized to WF strain and where cytotoxicity titer was 1:16 to 1:256, the recipients rejected WF hearts in 23.8 +/- 5.8 hr compared with 6.8 +/- 0.8 days in unsensitized control recipients (P less than 0.001). Injection of 1 ml of Lewis anti-WF CAA resulted in prolonged graft survival of 9.7 +/- 3.5 days, while injection of 1 ml of CAA followed by 2 ml of GPC caused hyperacute rejection in 104 +/- 61.7 min. Pretransplant injections of CAA on days -3, -2, -1, and 0 resulted in enhancement, with an MST of 16.3 +/- 1.3 days (P less than 0.001). In group 3 (low responder recipients), ACI presensitized to Lewis developed a cytotoxicity titer of 1:2 to 1:32 and rejected Lewis hearts in 5.3 +/- 0.4 days compared with 10.6 +/- 1.0 days in naive recipients.(ABSTRACT TRUNCATED AT 400 WORDS)