Rapamycin, a potent immunosuppressive drug for vascularized heart, kidney, and small bowel transplantation in the rat

The effectiveness of rapamycin (RAPA) was examined for heart, kidney, and small bowel allografts in rats. Untreated or vehicle only-infused Wistar Furth (RT1u) recipients rejected Buffalo (RT1b) heart allografts within a mean survival time (MST) of 6.5 +/- 0.5 and 6.3 +/- 0.5 days, respectively. In contrast, a 14-day continuous intravenous (i.v.) infusion by an osmotic pump of 0.08 mg/kg/day RAPA to WFu recipients prolonged BUF heart allograft survival to an MST of 34.4 +/- 12.1 days (P = 0.0001). There was a graded dose-response to 0.16 mg/kg (39.0 +/- 8.7 days; P = 0.0001), 0.32 mg/kg (55.7 +/- 3.3 days; P = 0.0001) and 0.8 mg/kg (48.0 +/- 3.6; P = 0.0001). Furthermore, intraarterial/intragraft but not i.v. infusion of 0.02 mg/kg/day prolonged BUF heart allografts--namely, an MST of 14.6 +/- 1.4 days versus 8.6 +/- 2.6 days (P = 0.0001), respectively. Local delivery doses of RAPA were about as effective as the same dose delivered i.v.: 0.08 mg/kg MST 37.0 +/- 18.3 days (P = 0.0001); 0.32 mg/kg, 40.0 +/- 3.9 days (P = 0.0001); and 0.8 mg/kg, 54.8 +/- 8.2 days (P = 0.0001). Systemic i.v. RAPA therapy with 0.08 or 0.8 mg/kg/day prolonged the survival of BUF kidney grafts in WFu recipients--namely, an MST of 52.7 +/- 42.7 (NS) and 90.2 +/- 62.4 (P = 0.001) days, respectively, versus an MST of 11.6 +/- 1.5 days in control WFu recipients only infused with vehicle. While normal WFu rats reject heterotopic BUF small bowel allografts within an MST of 10.0 days, a 14-day course of i.v. RAPA treatment significantly (P = 0.0001) prolonged small bowel allograft survival to an MST of 26.8 +/- 3.7 days.     

Inhibition of host-versus-graft and graft-versus-host responses after small bowel transplantation in rats by rapamycin.

The effect of rapamycin (RAPA) on both host-versus-graft (HVG) and graft-versus-host (GVH) immune responses was examined in small bowel transplant models using strongly histoincompatible donor-recipient combinations. Normal Wistar Furth (WFu; RT-1u) recipients rejected Buffalo (BUF; RT-1b) small bowel allografts within a mean survival time (MST) of 10.5 +/- 0.5 days. Administration of RAPA (0.8 mg/kg) by continuous intravenous infusion for 14 days via an osmotic pump prolonged graft survival to 25.0 +/- 4.6 days (P = 0.01). In a second strain combination, the 12.5 +/- 2.2 day survival of Brown Norway (BN; RT-1n) small bowel allografts in Lewis (RT-1l) recipients was prolonged to 21.6 +/- 2.0 and 28.5 +/- 2.8 days by 14 days of i.v. RAPA at doses of 0.8 and 1.6 mg/kg, respectively. In this model RAPA is five times more effective than cyclosporine, which at 4.0 mg/kg prolongs BN small bowel allografts in Lewis recipients to 21.6 +/- 6.3. To isolate HVG and GVH immune responses, (BN x Lewis)F1 hybrid rats served as the graft donor or host, respectively. In the HVG model, (BN x Lewis)F1 small bowel allografts, which were rejected by normal Lewis recipients at 12.2 +/- 3.6 days, were prolonged to 40.8 +/- 5.8 days (P = 0.001) by RAPA (0.8 mg/kg x 14 days). In the GVH model, the ability of Lewis small bowel allografts to produce severe GVH disease in untreated (BN x Lewis)F1 recipients at 12.3 +/- 2.8 days was delayed to 21.3 +/- 5.2 days by 0.8 mg/kg RAPA (P = 0.025). Thus, RAPA protects small bowel allografts more effectively against HVG than GVH immune responses.     

Soluble antigen and cyclosporine-induced specific unresponsiveness in rats. Frequency of alloantigen-specific T cytotoxic cells in normal, sensitized, and unresponsive rats

The cellular mechanisms of unresponsiveness induced with a combined KCl-extracted donor antigen (HAg) and CsA regimen were dissected by limiting-dilution (LD) assay. While untreated Wistar-Furth (WFu, RT1u) rats reject Buffalo (BUF, RT1b) heart allografts within a mean survival time of 6.6 +/- 0.5 days, recipients treated with 3 cycles of CsA alone (-1,0,1; 7,8,9; 15,16,17) maintained BUF heart allografts up to an MST of 22.5 +/- 8.9 days. When CsA was combined with BUF HAg (-1), BUF heart survival was further prolonged up to an MST of 34.2 +/- 6.6 days, while third-party BN HAg was ineffective (MST of 21.5 +/- 2.1 days). On day 10 postgrafting, the frequency of T cytotoxic cells (fTc) within the splenic pan-T-cell population was 1:1437 +/- 301 in CsA and 1:1087 +/- 438 in CsA/HAg treated recipients. In contrast, on day 30 postgrafting, both CsA and CsA/HAg treated WFu rats bearing functional BUF hearts showed within their splenic pan-T-cell populations a profound decrease in fTc to 1:2966 +/- 824 with CsA alone and to 1:4946 +/- 938 with CsA/HAg treatment. In contrast, both untreated WFu rats who rejected BUF heart allografts and CsA-treated WFu recipients who had rejected their BUF heart allografts on day 20 displayed an increased fTc to 696 +/- 243 and to 1:1169, respectively, when examined at day 30 postgrafting. Additionally, both the W3/25+ and OX8+ T cell subsets specifically suppressed the proliferative response of normal WFu T cells against BUF and, to a lesser degree, third-party BN irradiated stimulators. Thus, CsA-treated animals develop a potent specific-suppressor mechanism that is augmented by pretreatment with donor soluble antigen. This suppressor activity may decrease the frequency of alloantigen-specific Tc cells and thereby prolong the survival of BUF heart allografts.     

15AU81, a prostacyclin analog, enhances donor-specific hepatocytes to prolong the survival of rat heart but not small bowel allografts

Prostacyclin analogs have previously been shown to have not only cytoprotective but also independent immunosuppressive effects. The effect of one such analog, 15AU81, to enhance the immunosuppressive effects of liver was investigated. We have previously demonstrated that cyclosporine (CsA) in conjunction with rapamycin (RAPA) potentiates class I+, class II- donor-specific hepatocytes to prolong rat cardiac and small bowel allograft survival. Brown Norway (BN; RT1n) hepatocytes alone (5 x 10(7)/kg, administered intrasplenically) failed to prolong the survival of BN heart allografts in Wistar Furth (WFu; RT1u) recipients, beyond that of untreated controls (MST = 7.2 +/- 0.8 days). Survival of BN hearts was increased to 11.4 +/- 1.7 days in WFu recipients treated with BN hepatocytes and 50 microg/kg/day 15AU81 administered by continuous s.c. infusion for 14 days using osmotic pumps (p < 0.05). The further addition of RAPA 0.0075 mg/kg/day and CsA 0.375 mg/kg/day delivered for 14 days by continuous i.v. infusion (CIVI) using osmotic pumps (a combination that alone prolonged BN heart allografts in WFu hosts to 18.4 +/- 1.3 days and in conjunction with BN hepatocytes prolonged survival to 27.2 +/- 1.9 days) prolonged allograft survival to 35.2 +/- 5.2 days. In contrast, the survival of small bowel allografts was not enhanced by 15AU81 administration. Survival of BN small bowel transplants in LEW recipients treated with hepatocytes alone (MST = 11.6 +/- 1.5 days) or hepatocytes plus 15AU81 (MST = 10.0 +/- 1.0 days) was similar to controls (MST = 10.2 +/- 1.9 days). Treatment with hepatocytes and RAPA/CsA increased survival to 21.2 +/- 1.5 days. The further addition of 15AU81 failed to augment this (MST = 17.0 +/- 1.9 days). In vitro WFu lymphocyte proliferative responses from animals pretreated with BN hepatocytes, 15AU81, or both treatments, for 2 weeks prior to harvesting, exhibited a reduction of at least 50%, compared to untreated controls upon allostimulation with irradiated BN or ACI spleen cells. These findings demonstrate that 15AU81 interacts favorably with hepatocytes either alone or in conjunction with RAPA and CsA to enhance their immunosuppressive effects on rat heart allograft survival. The failure to enhance small bowel allograft survival may be explained by the inability at this low dosage of 15AU81 to influence the intense graft versus host reaction elicited by small bowel transplants.     

Synergistic effect of vincristine with tacrolimus or sirolimus in prevention of acute heart allograft rejection in the rat

The application of multiple immunosuppressive therapy for organ transplantation could enhance therapeutic efficacy, while minimizing the toxicity of individual drugs used in the regimen. In this study, the effect of the combined therapy of vincristine (VCR) with tacrolimus (FK506) or sirolimus (rapamycin, RAPA) was tested in prevention of acute heart allograft rejection in the rat. A Brown Norway (BN, RT 1(n)) to Lewis (LEW, RT 1(1)) rat combination was used in a heart allografting model. VCR was administered intraperitoneally once daily, while FK506 and RAPA were given by gavage once daily for 14 days after transplantation. There were dose-related prolongations of mean survival time (MST) to monotherapy of VCR, FK506, or RAPA. The MST in combination therapy indicated that a synergistic interaction was produced when compared with the respective monotherapies: VCR 0.05 mg/kg/day + FK506 0.5 mg/kg/day (16.00 +/- 1.79 days, P = 0.001; combination index (CI) = 0.557); VCR 0.05 mg/kg/day + FK506 1.0 mg/kg/day (29.00 +/- 10.54 days, P = 0.001; CI = 0.598); VCR 0.05 mg/kg/day + RAPA 0.2 mg/kg/day (17.33 +/- 1.97 days, P = 0.001; CI = 0.500); and VCR 0.05 mg/kg/day + RAPA 0.4 mg/kg/day (21.17 +/- 3.19 days, P = 0.001; CI = 0.838). Combination therapy of VCR and FK506 or RAPA produced synergistic effects in prevention of acute heart allograft rejection in the rat.     

The synergistic effect of total-lymphoid irradiation with extracted donor alloantigen in inducing transplantation unresponsiveness

The synergistic effect of total lymphoid irradiation with KCl-extracted donor type antigen (H-Ag) was examined in the rat cardiac graft model. TLI therapy alone of 10, 16, and 20 Gy achieved by a 2 Gy daily treatment of WFu recipients produced modest prolongation of BUF heart survival to median survival times (MST) of 11, 26, and 30 days, respectively, in comparison with normal control (MST = 6). The TLI immunosuppressive effect was significantly potentiated with donor H-Ag when combined with 16 (greater than 100 days) but not with 10 or 20 Gy TLI therapy. This effect was specific: 16 Gy TLI treated recipients of BUF hearts rejected their grafts in a MST of 27 days when treated with third-party BN H-Ag. The state of unresponsiveness was transferable to 6 Gy total-body-irradiated WFu recipients of BUF hearts with 60 x 10(6) purified T cells isolated from TLI/H-Ag-treated rats (greater than 100) but not from normal controls (MST = 6). In vitro analysis of nontransplanted WFu rats 1-4 weeks after completion of 16 Gy TLI therapy alone demonstrated a nonspecifically reduced MLR proliferative response as well as the presence of potent nonspecific suppressor cells (NSC). By 3 or even 6 months post-TLI, W3/25- NSC displayed persistent suppressive activity and inhibited normal proliferative response to alloantigens. Limiting dilution assay revealed that the frequency of T cytotoxic cells (fTc) was severely decreased to 1:63111 at one day and to 1:16488 at one week postirradiation in comparison with normal control (1:2551). At 3 and 6 months the fTc of 1:2301 and 1:2040, respectively, approximated normal levels. These combined in vivo and in vitro results demonstrate that 16 Gy TLI therapy induces an unresponsiveness mediated by NSC and that the administration of donor type H-Ag facilitates the generation of potent regulatory T cells capable of inducing prolonged heart allograft survival.     

Combination therapy of mycophenolate mofetil and rapamycin in prevention of chronic renal allograft rejection in the rat

BACKGROUND: Chronic rejection is the leading cause of long-term allograft loss. Until now, no therapy has been recognized as being efficient in its prevention. In addition to their immunosuppressive activity, mycophenolate mofetil (MMF) and rapamycin (RAPA) show diverse properties against vascular smooth muscle cell activity, cell-adhesion molecule expression, and ischemia-reperfusion injury. The combination effect of MMF and RAPA was tested to prevent chronic renal allograft rejection in the rat in this study. METHODS: Nephrectomized Lewis recipients underwent orthotopic transplantation with Fisher (F344) kidneys (allograft groups) or Lewis kidneys (isograft control). The initial episode of acute rejection was controlled with a short course of cyclosporine A (CsA) (1.5 mg/kg/day for 10 days). From weeks 4 to 20, animals were thereafter treated every other day either with vehicle, MMF (20 mg/kg), RAPA (0.8 mg/kg), or MMF (20 mg/kg) plus RAPA (0.8 mg/kg) in combination. Animals were sequentially killed at serial intervals over a follow-up of 50 weeks, and histologic study was performed on harvested kidneys according to the Banff working classification for allograft pathology. RESULTS: Animals treated with MMF or RAPA alone showed a Banff sum score similar to the allograft control group (6.31+/-1.01 and 7.27+/-1.14 vs. 7.21+/-1.14, respectively; P>0.05). When the recipient rats were treated with MMF and RAPA in combination, it resulted in a clinically and statistically significant reduction of Banff sum score (4.21+/-0.79, P<0.01), with specific inhibition of vascular fibrous intimal thickening, allograft glomerulopathy, and interstitial fibrosis. CONCLUSION: Over a 50-week study, concomitant therapy of MMF and RAPA prevents chronic renal allograft rejection, probably through reduction of ischemic and cytotoxic degenerative changes. These results warrant further investigation in the combination of MMF and RAPA as anti-chronic rejection therapy in clinical transplantation.     

In vitro correlates of in vivo therapy with cyclosporine to immunosuppress rejection of heterotopic rat cardiac allografts across strong (RT-1) plus weak (non-RT-1) histocompatibility differences.

This study correlated different oral cyclosporine doses with in vivo graft survival, blood and tissue drug levels, and in vitro immune performances. Wistar-Furth (WFu, RT-1u) hosts engrafted with heterotopic cardiac transplants from strongly histoincompatible Buffalo (BUF, RT-1b) rats were treated postoperatively with 14-day courses of different doses of CsA delivered per gavage. There was a graded prolongation of graft survival--namely, no effect at the 1.5 mg/kg dose; a modest effect at 3 mg/kg; a therapeutic effect at 5 mg/kg; and long-term unresponsiveness at 10 mg/kg. Whole blood, serum, and tissue CsA concentrations correlated with drug dose. On day 7 posttransplantation--that is, during the peak of the immune response of untreated recipients and midway during the period of daily CsA therapy--in vitro immune performances were examined in each experimental group. On the one hand, the mixed lymphocyte reaction of WFu host splenic T cells toward donor-type BUF stimulators poorly reflected the administered CsA dose. On the other hand, there was a good correlation between drug dose and both impaired cell-mediated lympholysis and reduced frequency of alloantigen-specific T cytotoxic cell precursors f(CTL)p. Animals treated with therapeutic doses of CsA showed different patterns of T cell-mediated lympholysis: 3 mg/kg did not prevent anti-BUF Tc cell sensitization; 5 mg/kg maintained f(CTL)p levels similar to the normal controls; and 10 mg/kg significantly reduced Tc clones against donor but not third-party targets. These data demonstrate that the fate of alloantigen-specific Tc clones activated in vivo depends upon the local drug concentration. Furthermore, the present studies suggest that CML and f(CTL)p afford useful in vitro indices of in vivo immunosuppression with CsA in rat cardiac allograft recipients.     

Intrasplenic Liver Parenchymal Cells in Conjunction with Low-Dose Rapamycin and Cyclosporine Induce a Unique and Specific Prolongation of Rat Cardiac and Small Bowel Allograft Survival

These experiments investigated the immunosuppressive properties of liver tissue. Brown Norway (BN; RT1ⁿ) rat heart allografts survived in untreated control Wistar Furth (WFu; RTl^u) rat recipients for 6.2 ± 1.5 days, while allografts in animals that received rapamycin (RAPA) 0.0075 mg/kg/day and cyclosporine (CsA) 0.375 mg/kg/day delivered for 14 days by continuous intravenous infusion (civi) using osmotic pumps in conjunction with intrasplenic (i.s.) saline survived to 18.4 ± 1.3 days. i.s. addition of 3 M-KCl extracted BN hepatic antigen or unpurified BN hepatocytes (liver parenchymal cells—5 × 10⁷/kg), which exhibited a 4.8% class II antigen expression, and which alone failed to prolong allograft survival (MST = 6.0 ± 1.4 days), increased heart allograft survival to 25.3 ± 2.3 and 27.2 ± 1.9 days, respectively (p < 0.01). Hepatocyte purification using Dynabeads and Percoll reduced class II expression to 0.9% and increased allograft survival to 32.8 ± 1.6 days (p < 0.01). In contrast, the effect of 5 × 10⁸/kg BN erythrocytes, exhibiting only 0.1% class II expression, was much less (23.8 ± 1.9 days). Administration i.s. of BN splenocytes or nonparenchymal liver cells, demonstrated by flow cytometry to exhibit a 47.3 or 55.1% expression of class II antigen, respectively, failed to induce any significant increase in allograft survival (18.4 ± 4.6 and 19.4 ± 0.5 days, respectively). Survival of BN rat small bowel allografts was increased in Lewis (LEW; RTl¹) rat recipients treated with RAPA, CsA, and unfractionated BN hepatocytes from 10.2 ± 1.9 to 21.2 ± 1.5 days. Pretreatment with i.s. BN hepatocytes, 14 days prior to harvesting, reduced WFu lymphocyte responses to allogeneic stimulation with BN or ACI spleen cells by 75 and 70%, respectively. Addition of 1 × 10⁵ unpurified donor-specific BN or third-party Buffalo (BUF; RTl^b) hepatocytes, but not supernatant, to the responder wells of MLCs resulted in a 61 and 40% suppression, respectively, of the WFu lymphocyte response induced by BN allogeneic stimulation. These findings suggest that while class I MHC expression has a significant role to play in exerting the immunosuppressive effects of hepatocytes, other influences more specific to liver may also prevail.     

In vitro analysis of T cell-mediated cytotoxicity displayed by rat heart allograft recipients rendered unresponsive by total-lymphoid irradiation and extracted donor antigen

The addition of 3M KCl-extracted donor antigen (HAg) to immunosuppressive therapy with 16 Gy total lymphoid irradiation produces a significantly higher fraction of Wistar-Furth (WFu) recipients displaying indefinite survival of heterotopic buffalo (BUF) heart allografts, namely 80 versus 20%. The experiments presented herein analyzed the direct activity as well as estimated the potential precursor numbers at 1 and 3 months in treated recipients. At 1 month post-TLI/HAg therapy, recipients showed reduced proliferative responses in mixed lymphocyte reactions (MLR) in a specific pattern toward donor but not third-party stimulators. Both TLI/Graft and TLI/HAg/Graft groups showed a higher frequency of BUF antigen-directed T-cytotoxic cells (fTc) than TLI-treated, but nontransplanted, WFu hosts. In addition, the TLI/HAg group alone displayed alloantigen-specific suppressor cells that suppressed the MLR proliferative responses of normal spleen T cells against donor, but not third-party, alloantigens. At 3 months postirradition, both TLI/Graft and TLI/HAg/Graft groups displayed variable MLR proliferative responses toward donor and third-party alloantigens. Whereas nontransplanted, TLI-treated WFu rats recovered their fTc to normal levels at 3 months, the TLI and TLI/HAg treated recipients bearing functional heart allografts demonstrated significantly decreased splenic fTc. These results show that reduced numbers of cytotoxic cell precursors may afford more reliable indices of prolonged heart allograft survival than MLR responses. The observations suggest that TLI/HAg transplant hosts display both reduced cytotoxic precursors and activated suppressor elements.     

Prolongation of heterotopic heart allograft survival by local delivery of continuous low-dose cyclosporine therapy

The effectiveness of local versus systemic low-dose CsA (2 mg/kg/day) therapy delivered by osmotic pump for a 14-day continuous infusion was examined in the rat model. Systemic subtherapeutic CsA treatment of WFu recipients either by oral gavage or intravenously using an osmotic pump resulted in quick rejection of BUF heart allografts within a median survival time (MST) of 8 days in comparison with untreated controls (MST = 7 days). In contrast, direct local subtherapeutic CsA delivery to BUF heart allografts produced significantly (P less than 0.01) prolonged heart allograft survivals up to MST of 40 days. Splenic T cells, isolated on days 10 to 12 from locally immunosuppressed WFu recipients, revealed a nonspecifically reduced proliferative response toward alloantigens. Coculture experiments demonstrate that these T cells have the capacity to inhibit normal T cell proliferative responses in a nonspecific fashion either by their suppressor function or more likely by carrying CsA to the culture plate. In contrast, T cells isolated from WFu recipients three weeks after transplantation and tested in vitro demonstrated the presence in alloantigen specific T suppressor cells that coincided with a decreased frequency of alloantigen-specific T cytotoxic cells and may explain the extended heart allograft survival beyond the time of CsA delivery. CsA therapy delivered directly to the graft resulted in high CsA levels within the heart graft (1108 ng/0.1 g) but subtherapeutic levels in other tissues. These results demonstrate that local drug delivery is effective in inhibiting the rejection process within the graft itself, as manifested by prolonged heart allograft survival. Further, subtherapeutic CsA therapy facilitates development of Ts cells that may be responsible for the survival of heart allografts beyond the CsA delivery time.     

The immunosuppressive action of suppressor cells from antigen-cyclosporine-treated hosts on renal allograft survival

Systemic adoptive transfer was employed to assess the immunosuppressive efficacy of antigen-specific suppressor T (Ts) cells purified from recipients treated with 3M KCl-extracted donor histocompatibility antigen (Ag) and cyclosporine (CsA). Suppressor cells were obtained from Wistar-Furth (WFu, RT-1u) hosts treated with a single i.v. injection of 5 mg 3M KCl-extracted donor Buffalo (Buf, RT-1b) antigen combined with a three-day course of CsA, a group that displays prolonged renal allograft survival (MST 23.2 +/- 10.2 days) compared with animals treated with CsA alone (MST 12.2 +/- 2.4 days). These noncytolytic, OX-8 phenotype, 800-rad-resistant/1500-rad-sensitive, nylon-wool-nonadherent and cyclophosphamide-sensitive suppressor T cells (1 X 10(6)) were adoptively transferred ten days after transplantation into virgin, secondary syngeneic hosts-thereby prolonging Buf graft survival from 7.2 to 17.5 days. The suppressor effect was immunologically specific; adoptive transfer did not prolong the survival of third-party Brown-Norway (BN) grafts (MST 10.4 +/- 3.1 days) compared with the nontreated control group (MST 11.0 +/- 2.9 days). The potency of Ts cells purified from Ag-CsA-treated hosts to transfer unresponsiveness into normal secondary WFu hosts (MST 17.5 +/- 8.0 days) was stronger than that of Ts cells from hosts treated with CsA only (MST 10.6 +/- 2.6 days). Moreover, in vitro stimulation of monoclonal-antibody-purified Ts cells by irradiated donor Buf spleen cells potentiated the in vivo induced suppressor activity, leading to an MST of 38.1 +/- 32.6 days; indeed 3 of 12 animals (25%) displayed permanent unresponsiveness. Furthermore, Ts cells from Ag-CsA-treated hosts displayed a synergistic effect with a three-day course of CsA administration into the secondary hosts (MST 24.2 +/- 8.0 days) compared with animals only treated with CsA (MST 12.2 +/- 2.4 days, P less than 0.001). Moreover, the combination of the Ag-CsA regimen with Ts cells administered one day after transplantation caused even greater prolongation of graft survival (MST 34.2 +/- 14.2 days) compared with Ag-CsA-treated hosts (MST 23.2 +/- 10.2 days, P less than 0.025). Thus adoptively transferred antigen-specific suppressor T cells may be explored to intensify the specific immunosuppressive effect of the Ag-CsA regimen to achieve long-term unresponsiveness.     

Pharmacokinetic interactions augment toxicities of sirolimus/cyclosporine combinations

This study correlated the dynamic effects of sirolimus (rapamycin; RAPA) and cyclosporine (CsA) alone versus in combination to produce renal dysfunction, myelosuppression, or hyperlipidemia, with their corresponding blood and tissue concentrations. After salt-depleted rats were treated with RAPA (0.4 to 6.4 mg/kg per d) and/or CsA (2.5 to 20.0 mg/kg per d) for 14 d, the GFR, lipid levels, bone marrow cellularity, and CsA/RAPA concentrations in whole blood versus liver or renal tissues were measured, and the median effect model was used to discern the type of drug interactions. Compared with vehicle controls (1.98 +/- 0.34 ml/min), GFR values were reduced only by large doses of drug monotherapy, namely RAPA (3.2 mg/kg per d = 1.2 +/- 0.02 ml/min or 6.4 mg/kg per d = 1.3 +/- 0.2 ml/min; both P < 0.01) or CsA (10.0 mg/kg per d = 1.2 +/- 0.1 ml/min or 20.0 mg/kg per d = 0.8 +/- 0.4 ml/min; both P < 0.01). In contrast, hosts that were treated with smaller doses of CsA/RAPA combinations showed more pronounced effects in reduction of GFR values: 2.5/0.4 mg/kg per d, modestly (1.5 +/- 0.5 ml/min; P < 0.01); 5.0/0.8 mg/kg per d, moderately (0.23 +/- 0.01 ml/min; P < 0.001); and higher-dose groups, markedly. The exacerbation of renal dysfunction seemed to be due to a pharmacokinetic interaction of RAPA to greatly increase CsA concentrations in whole blood and, particularly, in kidney tissue. In contrast, the pharmacodynamic effects of CsA to potentiate two RAPA-mediated toxicities-myelosuppression and increased serum cholesterol/low-density lipoprotein cholesterol-occurred independently of pharmacokinetic interactions. RAPA aggravates CsA-induced renal dysfunction owing to a pharmacokinetic interaction, whereas CsA produces a pharmacodynamic effect that augments RAPA-induced myelosuppression and hyperlipidemia.     

Synergistic interaction of 3 M KCl-extracted donor antigens (e-HAg) with cyclosporine or cyclosporine/sirolimus for prolongation of rat heart allograft survival

Extracted donor histocompatibility antigens (e-HAg) may potentiate the effects of drugs to protect organ allografts from rejection. We examined the capacity of e-HAg when combined with cyclosporine (CsA) alone, sirolimus (rapamycin, RAPA) alone, or CsA/RAPA combinations to prolong heart allograft survival in rats. Wistar-Furth (WF: RT1^u) rats that received CsA (10 mg/kg/day) by oral gavage for 3 (days 0, 1 and 2) or 7 (days 0, 1, 2, 3, 4, 5 and 6) consecutive days displayed modest prolongation of Brown Norway (BN; RT1ⁿ) heart allograft survival from a mean survival time of 7.2 ± 0.8 days in untreated controls to 12.2 ± 1.1 days and 18.6 ± 2.7 days, respectively (p < 0.01). Although administration on the day of transplantation (day 0) of a single intravenous (i.v.) dose of BN e-HAg (5 mg/kg) failed to affect allograft survival, both three (days 0, 1 and 2) and five (days 0, 1, 2, 3 and 4) injections significantly potentiated the effect of a 3-day course of oral CsA (18.6 ± 1.3 days (p < 0.01) and 20.0 ± 1.4 days (p < 0.01), respectively) and of a 7-day course of oral CsA (25.3 ± 4.4 days (p < 0.05) and 33.5 ± 9.3 days (p < 0.01), respectively). Median-effect analysis confirmed a synergistic interaction between CsA (0.5 mg/kg × 7 days, i.v.) and e-HAg with combination index (CI) values less than 0.7 (CI = 1 shows additive interactions, CI < 1 synergistic, and CI> 1 antagonistic, interactions). In contrast, e-HAg failed to affect the immunosuppressive effect of RAPA. However, e-HAg (5.0 mg/kg × 3 days) significantly potentiated the effects of a 7-day or 14-day course of RAPA (0.01 mg/kg)/CsA (0.5 mg/kg) combination therapy, namely from 26.0 ± 4.8 days with a 7-day treatment of CsA/RAPA alone to 32.6 ± 3.6 days (p < 0.01) and from 28.2 ± 2.7 days with a 14-day course of CsA/RAPA alone to 42.0 ± 4.9 days (p < 0.05), respectively (CI = 0.2–0.5). Thus, e-HAg potentiates the immunosuppressive effects of CsA alone and of the CsA/RAPA combination, but not of sirolimus alone.     

Prolongation of murine skin allografts by prostaglandin E1.

The effects of 16,16-dimethyl prostaglandin E2 methyl ester (di-M-PGE2) and indomethacin (an inhibitor of endogenous prostaglandin biosynthesis) on mouse skin allograft survival were studies in B10.D2 female mice receiving skin allografts from (B10.BR X B10.D2)F1 mice. Control animals with and without i.p. diluent injections had a mean allograft survival of 13.8+/-0.6 and 13.5+/-0.5 days, respectively. Daily administration of di-M-PGE2 (200 microng/kg) prolonged mean allograft survival, both when administered alone, 16.7+/-0.6 days (P less than 0.001), or with indomethacin, 4 mg/kg thrice weekly, 16.0+/0.6 days (P less than 0.005). Increasing concentrations of indomethacin (4, 6, and 8 mg/kg thrice weekly) were inversely corrleated with allograft survival ((12.7+/-0.2, 11.8+/-0.2, and 10.9+/-0.4 days, respectively), coefficient of correlation=-0.6986; P less than 0.001. Mean plasma PGE levels at the time of total allograft rejection were 879+/-80 pg/ml in control, 717+/-59 pg/ml in 100 micron g of indomethacin-treated mice, and 654+/-59 pg/ml in 200 microng of indomethacin-treated mice (P less than 0.05). Exogenous di-M-PGE2 prolonged skin allograft survival in mice. Inhibition of endogenous prostaglandin biosynthesis by indomethacin chortened allograft survival, but this effect was completely abrogated by concurrent injection of di-M-PGE2.     

Ability of 3M KC1-extracted histocompatibility antigen to potentiate the immunosuppressive effect of cyclosporine to prolong the survival of heterotopic rat cardiac allografts

A soluble histocompatibility antigen preparation (HAg) derived by 3M KCl extraction of donor spleen cells has been shown to prolong rat renal allografts in CsA-treated hosts. In the present study, the effect of combined soluble antigen-CsA treatment on cardiac allograft survival was studied in WFu hosts grafted with BUF hearts. Cardiac allograft survival was prolonged in WFu recipients treated with both BUF HAg and CsA compared with survival time in untreated controls or controls treated with HAg or CsA alone. In addition, experiments were performed to test the antigenicity of the HAg extract. BUF extract given sc to WFu hosts before grafting specifically sensitized the hosts to BUF grafts, as shown by the accelerated rejection of BUF grafts but not third-party grafts. Assays to determine the major histocompatibility antigenic determinants present in the extract showed that class I and class II determinants were present.     

Antagonizing leukotriene B4 receptors delays cardiac allograft rejection in mice

BACKGROUND: Allograft rejection is a cellular immunological/inflammatory response that is, in part, directed by potent proinflammatory mediators. This study was designed to test the hypothesis that leukotriene B4 (LTB4) may have a role in graft rejection and that LTB4 receptor antagonists may be clinically useful in the treatment of allograft rejection. METHODS: We evaluated the potent and selective LTB4 receptor antagonist CP-105696 in a murine heterotopic cardiac allograft model with oral dosing daily for 28 days or in an induction protocol (day -1 to day 3). RESULTS: At a dose of 50 mg/kg/day (28 days), B10.BR (H2k) allografts transplanted into C57Bl/6 (H2b) recipients were significantly protected, as reflected by the mean survival time versus control grafts (27+/-20 days [n=10] vs. 12+/-6 days [n=14]; P=0.0146). Using an induction protocol (day -1 to day 3), CP-105696 at 100 mg/kg/day significantly prolonged allograft survival (33+/-23 days [n=9]; P=0.0026), but CP-105696 at 10 mg/kg/day did not (18+/-16 days [n=8]; P=0.1433). Syngeneic grafts survived indefinitely (n=11). Immunohistological evaluation of allografts at rejection revealed a mononuclear cell infiltrate composed primarily of CD3+ and CD11b+ (Mac-1+) cells, which were infrequent in syngeneic grafts. Allografts from mice treated with CP-105696 at 50 or 100 mg/kg/day demonstrated a selective reduction in beta2-integrin (Mac-1) expression on monocytes/macrophages, as demonstrated by CD11b staining density compared with allograft controls. CONCLUSIONS: The results suggest that LTB4 or other potential ligands for LTB4 receptors may be important mediators of allograft rejection and support the clinical evaluation of LTB4 receptor antagonists in human organ transplantation.     

Limb allografts in rats immunosuppressed with FK506. I. Reversal of rejection and indefinite survival

We have tested the effects of FK506 (FK), a new immunosuppressive agent, on a rat limb allograft model. Histoincompatible BN limb allografts were rejected in untreated F344 hosts within 11 +/- 1 days (mean +/- SD) after operation. A single injection of 2 mg/kg, 10 mg/kg, or 50 mg/kg of FK on the day of limb transplantation (day 0) significantly prolonged graft survival in a dose-dependent manner--i.e., mean limb survival times (MST) based on gross signs of skin rejection were 16 +/- 3 days, 51 +/- 6 days, or 104 +/- 17 days, respectively (P less than 0.01). Delayed treatment with a single injection of 10 mg/kg of FK at when early signs of rejection were visible (day 7 or day 10) reversed the ongoing rejection. The MSTs in these groups were comparable to that of those treated with the same dosage of FK on day 0. The FK-induced unresponsiveness toward limb allografts was donor-specific because limb-allografted. FK-protected rats could not accept the skin grafts from a third-party donor. In the next set of experiments, rats were given a single administration of 10 mg/kg of FK on the day of limb allograft, followed by intermittent injections of 3 mg/kg of FK once a week. This regimen produced complete graft survival for more than 200 days, though Pneumocystis carinii pneumonia occurred in most of the recipients. These results represent the unique effects of FK in preventing or reversing the graft rejection and in inducing indefinite survival in this animal model of composite tissue allografts.     

Induction of donor-specific unresponsiveness to rat cardiac allograft by donor leukocytes and cyclosporine

Many recent reports have emphasized the importance of donor antigens in the induction of allograft tolerance. This study examines the effect of pretransplant infusion of 10(8) donor leukocytes (DL) combined with peritransplant cyclosporine (CsA) on W/F cardiac allograft survival in Lewis rats. Peritransplant recipient treatment consisted of CsA 20 mg/kg given i.m. on days 0, +1, and +2 relative to heart transplantation. Lewis recipients, 5-8 per group, were pretreated with 10(8) DL with or without peritransplant CsA. A single DL transfusion on day -3 or day -7 prior to transplantation significantly prolonged the mean survival time (MST) of W/F hearts from 7.0 +/- 0.9 days in controls to 12.2 +/- 4.5 days and 12.4 +/- 1.0 days (P less than 0.01), respectively. Two DL infusions on days -7 and -3 or on days -14 and -7 prolonged the MST to 10.6 +/- 1.3 days (P less than 0.02) and 16.4 +/- 2.8 days (P less than 0.001), respectively. The administration of peritransplant CsA alone significantly prolonged W/F heart allograft survival to 43.1 +/- 2.7 days. When pretransplant DL transfusion on day -3 was combined with CsA treatment, 4/8 animals maintained their grafts indefinitely (greater than 100 days). Similarly, DL infusion on day -7 with peritransplant CsA led to indefinite graft survival in 3/5 animals. Administration of DL on days -7 and -3 combined with CsA resulted in indefinite graft survival (greater than 100 days) in 4/6 animals. Transfusion of DL on day -3 alone or in combination with peritransplant CsA, had no effect on a third-party (ACI) heart allograft survival prolongation compared with appropriate controls. To define the underlying mechanisms responsible for donor-specific unresponsiveness in this model, pooled sera and unseparated spleen cells were passively transferred from recipients of long-term cardiac allografts to syngeneic rats receiving donor-type (W/F) or third-party (ACI) cardiac allografts. Transfer of serum (1 ml on days 0, and 1, 0.5 ml on days +2, +3, and +4) from ungrafted recipients of DL on days -14 and -7 led to significant donor graft survival of 9.8 +/- 0.4 days (P less than 0.02) in unmodified hosts. Similarly, passive transfer of serum obtained at 20 and 100 days after transplantation significantly prolonged the MST of donor-type hearts in syngeneic untreated hosts to 11.3 +/- 0.8 and 10.0 +/- 1.1 days, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)     

Permanent rat cardiac allograft survival induced by ultraviolet B-irradiated donor lymphocytes and peritransplant cyclosporine

This study examines the effect of pretreatment with 10(8) ultraviolet B-irradiated donor leukocytes (UV-DL) with or without peritransplant cyclosporine (CyA) treatment (20 mg/kg on days 0, +1, and +2 relative to transplantation) on rat cardiac allograft survival across major histocompatibility loci. A single UV-DL pretreatment on day -3 or -7 (before transplantation) significantly prolonged survival of heart allografts from Wistar-Furth rats (W/F) in Lewis recipients from 6.8 +/- 0.8 days to 18.4 +/- 2.1 and 17.6 +/- 1.5 days (p less than 0.001), respectively. Multiple UV-DL infusions on days -14 and -7 increased the mean survival time to 20.0 +/- 0.9 days (p less than 0.001). Similarly, UV-DL infusion on day -3 or -7 significantly prolonged the mean survival time of heart allografts from ACI rats in Lewis rats. A single or multiple UV-DL infusions combined with peritransplant CyA led specifically to permanent W/F cardiac allograft survival (more than 200 days) in all recipients. Similarly, UV-DL infusion combined with peritransplant CyA led to indefinite survival of ACI cardiac allografts in two thirds of Lewis recipients. Adoptive transfer of splenocytes from long-term recipients of cardiac allografts, which specifically prolonged donor test grafts in syngeneic hosts, suggests that unresponsiveness to cardiac allografts is, in part, dependent on suppressor cells. This study emphasizes the importance of UV irradiation of DLs in the modulation of alloreactivity and the induction of donor-specific unresponsiveness in adult animals.