Dasheng Xu

Tacrolimus (FK506) and sirolimus (rapamycin) in combination are not antagonistic but produce extended graft survival in cardiac transplantation in the rat

Combined use of tacrolimus (FK506) with sirolimus (rapamycin [RAPA]) was examined in a model of vascularized heart allograft in the rat. For prevention of acute rejection, three different combinations of low doses of FK506 and RAPA from day 1 up to day 14 after transplantation produced significantly longer cardiac allograft survival than each agent alone (P<0.05). Identical results were observed in a model of reversal of ongoing acute rejection, where two combinations of low doses of FK506 and RAPA from day 4 up to day 18 after surgery also demonstrated significantly longer graft survival than each immunosuppressant alone (P<0.05). All the low-dose-treated groups in these two models presented significantly longer heart graft survival than naive controls (P<0.05), confirming that both agents are potent immunosuppressants in the models chosen. These results also indicate that, in contrast with in vitro studies, the combined use of FK506 and RAPA in vivo did not produce antagonism, but rather had synergistic effect in prolonging the allograft survival as compared with each agent alone. It appears likely that the abundance of FKBP-12 available for binding in vivo prevents inhibitive competition of the two agents for their receptor.

Effect of tacrolimus (FK506) and sirolimus (rapamycin) mono- and combination therapy in prolongation of renal allograft survival in the monkey

BACKGROUND Our previous studies confirmed that tacrolimus (FK506) and sirolimus [rapamycin (RAPA)], in combination, are not antagonistic but are synergistic in the prolongation of heart and small bowel grafts in the rodent. The aim of this study was to confirm further the synergistic effect of combined FK506 and RAPA in the more clinically relevant model, kidney transplantation in monkeys. METHODS A total of 60 male Vervet monkeys were randomly assigned to 10 groups (n> or =5). Monkeys with renal allografts were treated with different doses of FK506 and/or RAPA orally for 60 days. Graft survival, body weight, clinical biochemistry determinations, oral glucose tolerance test, trough levels of the two drugs, and histopathology were investigated. RESULTS Low doses of FK506 (1 or 4 mg/kg) combined with RAPA (0.5 mg/kg) produced synergistic effect in the prolongation of renal graft survival [combination index (CI) = 0.292, 0.565]. There were no additive or synergistic drug-associated toxicities such as hyperglycemia, nephrotoxicity, and hyperlipidemia. There also was no pharmacological antagonism. CONCLUSION Concomitant therapy of low-dose (drug-optimal) FK506 and RAPA produced a synergistic effect in the prolongation of kidney allograft survival in Vervet monkeys without additive drug-associated toxicities.

Synergistic effects of mycophenolate mofetil and sirolimus in prevention of acute heart, pancreas, and kidney allograft rejection and in reversal of ongoing heart allograft rejection in the rat

BACKGROUND The effect of mycophenolate mofetil (MMF) and sirolimus (rapamycin, RAPA) mono- and combination-therapy was examined in prevention of acute heart, pancreas, and kidney allograft rejection and in reversal of ongoing heart allograft rejection in the rat. METHODS Both drugs were administered orally for up to 30 days. Eleven groups (n=6) were involved in the first part of the heart allografting model. Brown Norway (RT1n) to Lewis (RT1(1)) combination was used in the heart and pancreas transplantation models, whereas Buffalo (RT1b) to Wistar Furth (RT1u) was used in the kidney transplantation model. RESULTS The naive control group showed a mean survival time of 6.5+/-0.6 days. There were graded dose-responses to monotherapy of MMF 10 and 20 mg(kg/ day (12.5+/-2.6 days; 19.3+/-9.0 days) and RAPA 0.2, 0.4, 0.8, and 1.8 mg/kg/day (19.2+/-2.0 days; 30.0+/-7.3 days; 50.8+/-12.5 days; 51.2+/-2.6 days), respectively (P=0.001). Results with the combined use of drugs indicate that a synergistic or very strong synergistic interaction was produced when compared with monotherapy of MMF or RAPA: MMF 10 mg(kg/day+RAPA 0.2 mg/kg(day (52.7+/-5.7 days, combination index [CI] =0.189), MMF 20 mg(kg/day+RAPA 0.2 mg/kg/day (57.7+/-5.7 days, CI=0.084), MMF 10 mg/kg/day+RAPA 0.4 mg(kg/day (50.2+/-13.5 days, CI=0.453), and MMF 20 mg/kg(day+ RAPA 0.4 mg/kg(day (51.5+/-6.8 days, CI=0.439), respectively. These results were repeatable in the prevention of acute pancreas and kidney allograft rejection in the rat. In the second part of the study of reversal of ongoing acute heart allograft rejection model, the combined treatment of MMF 10 mg/kg(day+RAPA 0.2 mg/ kg(day (35.5+/-16.0 days, CI=0.794) and MMF 20 mg/kg day+RAPA 0.2 mg(kg/day (57.2+/-4.7 days, CI=0.310) represented synergistic interaction compared with monotherapy of MMF or RAPA. CONCLUSIONS Concomitant therapy of MMF and RAPA produces a synergistic effect in prevention of heart, pancreas, and kidney allograft rejection and in reversal of ongoing heart allograft rejection in the rat.

Reversal of ongoing heart, kidney, and pancreas allograft rejection and suppression of accelerated heart allograft rejection in the rat by rapamycin.

Rapamycin was examined for its effects on reversal of ongoing rejection of heart, kidney, and pancreas allografts and on suppression of accelerated heart allograft rejection in the rat. A 14-day continuous intravenous infusion of RAPA by an osmotic pump at 0.02, 0.08, and 0.8 mg/kg/day to WFu recipients, starting 4 days postoperation, significantly protected the BUF heart allografts with a mean survival time (MST) +/- 1 SD of 33.2 +/- 19.8 (p < 0.001), 48.2 +/- 14.8 (p < 0.001), and 107.0 +/- 86.3 (p < 0.001) days, respectively, as compared with 7.2 +/- 0.8 days in vehicle-treated controls. Combination of low dose RAPA (0.02 mg/kg or 0.08 mg/kg) and low dose CsA (2 mg/kg) achieved significantly longer cardiac allograft survival than RAPA or CsA alone. RAPAs effect in reversing ongoing rejection of renal and pancreatic allografts was also significant. The BUF kidney and pancreas in WFu recipients treated with a 14-day course of RAPA (0.8 mg/kg/day starting 4 days postoperation) had an MST of 44.7 +/- 15.9 (p < 0.001) and 46.4 +/- 12.5 (p < 0.001), while in vehicle-treated controls, the grafts were rejected within 10 days. RAPA could also suppress accelerated cardiac allograft rejection. Hyperimmunized WFu recipients were treated with two 14-day courses of continuous i.v. RAPA at 0.8 mg/kg/day before and after BUF heart allografting. Significantly longer survival of the grafts (25.5 +/- 3.7 days, p < 0.001) was achieved compared with that of the vehicle-treated controls (3.8 +/- 1.0 days). One-course RAPA treatment before or after heart transplantation was considerably less effective. RAPA was also shown to prevent the increase of serum IgG levels and to inhibit the production of specific cytotoxic Ab in the rat receiving repetitive immunizations. Such effects presumably contribute to the inhibition of the accelerated rejection. The results of this study suggest that RAPA is potentially useful in treatment of ongoing as well as accelerated allograft rejection.

Synergistic effects of malononitrilamides (FK778, FK779) with tacrolimus (FK506) in prevention of acute heart and kidney allograft rejection and reversal of ongoing heart allograft rejection in the rat.

Background. The effects of tacrolimus (FK506) and malononitrilamides (MNA) (FK778 and FK779) monotherapy and combination therapy were examined in prevention of acute heart and kidney allograft rejection and reversal of ongoing acute heart allograft rejection in the rat. Methods. Brown Norway (RT1n)-to-Lewis (RT11) and ACI (RT1a)-to-Lewis (RT11) combinations were used, respectively, for heart and kidney transplantation models. Immunosuppressants were administered orally from day 1 to day 14 for preventing acute rejection and from day 4 to day 34 after transplantation for the reversal of ongoing acute rejection. Results. In the prevention of acute heart rejection model, recipient rats treated with monotherapy of tacrolimus or MNA (FK778, FK779) showed a dose-related prolongation of mean survival time (MST) compared with naive control rats (P <0.01). The mean survival time in combination therapy of tacrolimus (FK506) and FK778 indicated that an additive to synergistic interaction was produced when compared with the respective monotherapies (combination index [CI]=0.631–1.022). These results were reproducible with tacrolimus and FK779 combination therapy (CI=0.572–0.846). Furthermore, similar results were also found in the prevention of acute kidney allograft rejection in the rat (CI=0.137–0.516). In the reversal of ongoing acute heart allograft rejection, combination therapy of tacrolimus and FK778 demonstrated a strong synergistic interaction (CI=0.166–0.970) compared with monotherapy of tacrolimus or FK778. Conclusions. Combination therapy of tacrolimus and MNA (FK778, FK779) produces synergistic effects in prevention of acute heart and kidney rejection and reversal of ongoing heart allograft rejection in the rat.

Significant prolongation of renal allograft survival by delayed combination therapy of FK778 with tacrolimus in nonhuman primates

Background. Malononitrilamide 715 (FK778) is a new class of low-molecular-weight immunosuppressant that is a derivative of the active metabolite of leflunomide, A77 1726. In this study, the authors evaluated the combined effect of FK778 with tacrolimus in prevention of renal allograft rejection in Vervet monkeys. Methods. Male Vervet monkeys were obtained from Caribbean Primates Ltd. Donor and recipient monkeys were from different breeding colonies. Eleven groups (n≥4 per group) were involved in this study. FK778 and tacrolimus were administered orally for 60 days according to protocol. Results. Naive controls rejected renal grafts, with a median survival time (MST) of 8.0 days in group 1. When recipient monkeys were treated with tacrolimus 1.0 mg/kg/day in group 2 or FK778 2.5 mg/kg/day in group 3, the MST was 16.0 days (P =0.001) and 11.0 days (P =0.266), respectively. Combination therapy of these two agents at the same doses immediately after transplantation resulted in an MST of 25.0 days (P =0.016) in group 4. When tacrolimus was initiated immediately after transplantation and FK778 treatment was delayed until day 7 after surgery in group 5, recipient survivals were significantly prolonged to 38.0 days (P =0.02). These results were repeatable when FK778 5.0 mg/kg/day (9.0 days, P =0.544 in group 6) was combined with tacrolimus 1.0 mg/kg/day immediately after transplantation (8.0 days, P =0.339) in group 7, or when FK778 was delayed 7 days (60.0 days, P =0.002) in group 8. Furthermore, it was also repeatable when FK778 10 mg/kg/day was combined with tacrolimus 1.0 mg/kg/day with a 7-day delay. Conclusions. A significant prolongation of renal allograft survival was produced when FK778 administration was delayed by 7 days combined with tacrolimus in Vervet monkeys.

Compromised kidney graft rejection response in Vervet monkeys after withdrawal of immunosuppressants tacrolimus and sirolimus.

BACKGROUND In nonprimates, organ allografts are often not rejected after withdrawal of immunosuppression. In this study, we examined whether such a phenomenon also occurs in primates. METHODS Vervet monkeys were transplanted with renal allografts and treated for 60 days with tacrolimus, or tacrolimus plus sirolimus. The drugs were totally withdrawn on day 61. The survival of the monkeys was monitored, and their response to donor- or third party-derived alloantigens was examined in vivo and in vitro. RESULTS The majority (80-100%) of the grafts survived for at least additional 30 days with no signs of acute rejection. The compromised rejection is donor-specific, because recipient monkeys failed to reject a donor-derived skin graft, but a third-party skin graft was rejected. In vitro mixed lymphocyte reaction and interleukin-2 production in the mixed lymphocyte reaction between the recipients and their donors or between the recipients and a third party had no discernable patterns, and thus did not reflect the in vivo status of the immune system. Although the recipients could not reject the graft acutely after drug withdrawal, the kidney grafts and the donor-derived skin grafts had pathological findings of chronic rejection. CONCLUSIONS The rejection response of the monkeys to an established graft after withdrawal of immunosuppression is compromised. The compromised rejection is specific and is not due to a permanent alteration of the immune system by the initial drug treatment. The allografts are not inert but have low levels of interaction with the recipient immune system.

Long-term in vivo effects of rapamycin on humoral and cellular immune responses in the rat

Rapamycin (RAPA) is a strong immunosuppressant and is able to prevent allograft rejection in animal models. We have demonstrated that RAPA could strongly inhibit in vitro immunoglobulin (Ig) production by human lymphocytes. The present study investigated the long-term in vivo effect of RAPA on humoral and cellular immune responses, and the effect of RAPA on accelerated rejection. It was shown that RAPA strongly inhibited antigen (Ag) specific antibody (AB) production (i.e. cytotoxic Ab to donor lymphocytes and Ab to tetanus toxoid) during the period of drug administration. The accelerated rejection of cardiac allografts in presensitized animals was alleviated by RAPA administration. These results suggest the potential application of RAPA in treatment of presensitized candidates for organ transplantation. A little more than two months after the drug withdrawal, the rats were basically competent in Ab response to further Ag challenges. When tested 4 months after the RAPA-treatment, the rats showed uncompromised cardiac allograft rejection, and the cellular immune response in vitro according to mixed lymphocyte reaction (MLR) and mitogen-stimulated proliferation were not hampered. Such results suggest that the immune system can return to normal status without sequelae after discontinuation of RAPA.

Rapamycin graft pretreatment in small bowel and kidney transplantation in the rat.

The effect of rapamycin (RAPA) as graft pretreatment was evaluated in orthotopic small bowel and kidney allotransplantation (Tx) in the rat. In the small bowel Tx model, six groups were involved, each including three combinations for evaluation of host-ver-sus-graft (HVG) [Lewis (LEW) × Brown Norway (BN) (LBN)-F1 → Lewis], graft-versus-host (GVH) (LEW → F1), and combined HVG and GVH immune responses (BN → LEW). RAPA graft pretreatment alone (16 μg/ml × 3 ml) was able to induce a modest but significant prolongation of survival in all three combination models compared with controls (P<0.05). The same was observed for low dose CsA treatment (2 mg/kg/day × 14 days) of the recipient only (P<0.05). Combination of graft pretreatment with RAPA and CsA recipient treatment produced a marked prolongation of survival especially in HVG response. Recipients treatment with one 48-μg bolus of RAPA i.v. immediately after graft revascularization failed to achieve any prolongation of survival for the GVH or combined HVG and GVH responses. This seems to exclude a “carryover” effect of RAPA from graft to recipient. RAPA efficacy was also clearly confirmed in the kidney graft pretreatment model as compared to recipient treatment with an equivalent RAPA dose. These results demonstrate that graft RAPA pretreatment prolongs SB survival after Tx in the rat for HVG, GVH, and bidirectional immune responses. Intragraft interaction with passenger leukocytes or APC function appears as one of the possible mechanisms. RAPA graft pretreatment potentiates low dose CsA recipient treatment suggesting a possible use in clinical organ Tx.

The immunosuppressive effect of rapamycin on mouse small bowel transplantation

The efficacy of rapamycin (RAPA) was tested on small bowel transplantation in the mouse and compared with cyclosporine (CsA). Four groups were involved, each one included three combinations (n > or = 6) for evaluation of host-versus-graft (HVG, C57BL/6 X BALB/c F1 (CB6F1)-to-BALB/c), graft-versus-host (GVH, BALB/c-to-CB6F1), and combined HVG and GVH responses (C57BL/6-to-BALB/c). Grafts were transplanted to recipients heterotopically. Groups were as follows: group 1: naive controls; groups 2 and 3: recipient mice treated with RAPA 2 mg/kg/day and 4 mg/kg/day orally for 14 days, respectively; group 4: recipient mouse treated with CsA 4 mg/kg/day orally for 14 days. In the HVG model, the mean survival time (MST) of recipients was significantly longer in group 2 (32.9 +/- 17.7 days, P=0.006), group 3 (32.7 +/- 10.4 days, P=0.0001), and group 4 (37.9 +/- 11.8 days, P=0.0001), compared with naive controls in group 1 (8.5 +/- 1.6 days). In the GHV model, the MST of recipients in group 2 (41.8 +/- 19.9 days, P=0.002), group 3 (48.2 +/- 21.4 days, P=0.001) and group 4 (56.5 +/- 30.6 days, P=0.003) were significantly prolonged compared with control group 1 (8.5 +/- 1.6 days). In combined HVG and GVH responses, MST of recipient in group 2 (20.9 +/- 4.9 days, P=0.0001), group 3 (27.0 +/- 4.3 days, P=0.008), and group 4 (35.2 +/- 23.9 days, P=0.0001) were also significantly longer than that in controls (6.9 +/- 1.4 days), but in all three combinations, there were no statistically significant differences between groups 2 and 3, groups 2 and 4, or groups 3 and 4 (P>0.05). RAPA is a potent immunosuppressant able to significantly prolong small bowel allograft survival in mice using a short-term treatment. There is no statistically significant difference in recipient survival between low and high doses of RAPA treatment and the CsA standard dose used in this study.