Prope tolerance: a step in the search for tolerance in the clinic

Following the demonstration by Knechtle and colleagues that profound T cell depletion in rhesus monkeys treated with a CD3 diphtheria immunotoxin resulted in tolerance to renal allografting, we have used a similarly depleting protocol that, in addition, depletes B cells in recipients of a cadaveric renal transplant. The humanized antiCD52 monoclonal antibody had a rapid depleting effect when given intravenously, 20 mg on days 0 and 1 after-renal transplantation, to 31 patients. At 48 hours after the second dose of low dose monotherapy cyclosporine (Neoral) was given to maintain blood levels averaging 100 ng/ml. Initially no other immunosuppression was given. With an average follow-up of 24 months all but one of the patients are alive, 29 with intact functioning grafts. There have been five rejection episodes, which responded to pulsed steroid treatment. One patient had a recurrence of her original disease. Two patients developed opportunistic infections, which responded to therapy; and one patient with severe heart failure at the time of surgery died from this condition after 11 months. Currently 29 patients are still on the original low dose cyclosporine monotherapy. The outcome in this cohort of patients has been encouraging, with efficacy that compares favorably to our conventional triple therapy but in most cases allows the patients to be steroid-free on low dose immunosuppressive monotherapy. The maintenance treatment is inexpensive and should be beneficial in the context of tight budgetary constraints worldwide. The patients who avoided steroids are pleased with this aspect of the protocol. A randomized trial comparing this treatment with standard therapy is planned.

Immunological tolerance--the liver effect

The developing immune system in the embryo is programmed to accept all its own tissues as self-products and not react against them. It has been the aim of transplantation research for the past 40 years to try and manipulate the developed immune system temporarily to a similar status to that in the embryo at the time of an organ graft, so that the organ graft is accepted but immunity generally is not interfered with. Such a state is known as immunological tolerance and can be produced in the laboratory by a number of special techniques, none of which is appropriate for clinical use in organ grafting. In pigs and rats, an allografted liver can sometimes survive permanently without any immunosuppressive treatment in immunologically mature animals.

Prope tolerance with induction using Campath 1H and low-dose cyclosporin monotherapy in 31 cadaveric renal allograft recipients

The last 40 years has been a period of remarkable evolution of organ transplantation from nothing to a well-established form of treatment with good short-term and tolerable long-term results. Nevertheless by ten years approximately 50% of grafts will have been lost due, mainly, to chronic rejection or the side-effects of immunosuppressive therapy. We now have a number of extremely powerful immunosuppressive drugs and antibodies with different mechanisms of action and the stage is set for a move from current continuous high dose immunosuppressive maintenance therapy to low dose or no maintenance immunosuppression. True tolerance can occur in man, examples being successful bone marrow transplantation and patients with liver grafts who have stopped immunosuppression after years of good function. The antibody Campath 1H with a unique target CH52 on T & B lymphocytes and monocytes has been used to eliminate lymphocytes from the blood for a month in patients with renal allografts who have then been maintained on half dose Cyclosporin without any other maintenance drug. The results with a mean two year follow-up have been encouraging, 29 patients having good function without receiving maintenance steroids. It is likely that this protocol could be improved since dosage timing and various minimal maintenance immunosuppressive protocols have not been fully investigated. This almost or "Prope" tolerance could be a major step forward providing a better quality of life for patients and inexpensive maintenance immunosuppression.

[Isogenic islet transplantation on the rat liver (method for isolation and purification of the Langerhans islets)]

The major indication for pancreas or islet transplantation is diabetes mellitus type I. This process has to supply the insulin necessity keeping glucose under control. We have studied isogenic islet transplantation on the rat (WAG-RT1u) liver. The method of isolation and purification of the islets obtained 2.834 +/- 551.64 islets with purity of 83 +/- 2.45%. Diabetes was induced by streptozotocin and seric glucose prior transplantation was 35 mmol/L. The islet transplantation of 2.834 +/- 551.64 islets in the rat liver has normalized glucose test from 9.62 +/- 2.65 mmol/L 10 days after transplantation to 7.43 +/- 0.27 mmol/L later in the follow-up (P < 0.05). The median survival time of the islets was 73 days. In conclusion both the method of isolation and purification of the islets and islet transplantation was effective in the control of the diabetes induced by streptozotocin with median survival time of both islet and rat more than 73 days when rats were sacrified.

Campath IH allows low-dose cyclosporine monotherapy in 31 cadaveric renal allograft recipients

BACKGROUND

Campath 1H is a depleting, humanized anti-CD52 monoclonal antibody that has now been used in 31 renal allograft recipients. The results have been very encouraging and are presented herein.

METHODS

Campath 1H was administered, intravenously, in a dose of 20 mg, on day 0 and day 1 after renal transplant. Low-dose cyclosporine (Neoral) was then initiated at 72 hr after transplant. These patients were maintained on low-dose monotherapy with cyclosporine.

RESULTS

At present, the mean follow-up is 21 months (range: 15-28 months). All but one patient are alive and 29 have intact functioning grafts. There have been six separate episodes of steroid-responsive rejection. One patient has had a recurrence of her original disease. Two patients have suffered from opportunistic infections, which responded to therapy. One patient has died secondary to ischemic cardiac failure.

CONCLUSIONS

Campath 1H has resulted in acceptable outcomes in this group of renal allograft recipients. This novel therapy is of equal efficacy compared to conventional triple therapy, but allows the patient to be steroid-free and to be maintained on very-low-dose immunosuppressive monotherapy.

Potential for improved therapeutic index of FK506 in liposomal formulation demonstrated in a mouse cardiac allograft model

BACKGROUND

FK506 is a potent immunosuppressant that has improved clinical outcomes in kidney and liver transplantation both as a primary and as a rescue immunosuppressive agent. Despite these benefits, the potential value of FK506 is limited by toxic side effects that result in a narrow therapeutic index. By encapsulating the active drug within liposomes (LipoFK506), a new formulation has been developed that might improve this therapeutic index.

METHODS

The biodistribution of tritiated-FK506 administered i.v. showed that the drug remained associated with the liposomal carrier in vivo, and that its tissue distribution was increased in heart and spleen compared to nonliposomal FK506. The immunosuppressive efficacy of lipoFK506 compared with conventional FK506 formulation was tested in vivo. CBA (H2k) mice were engrafted with BALB/c (H2d) mouse hearts with daily immunosuppression using either 1 mg/kg FK506, or 1 mg/kg LipoFK506, from day 0 to 14.

RESULTS

At day 7 the blood trough level of FK506 in the FK506 group was 10-fold higher (25 microg/L) than that in the LipoFK506 group. In both groups the median heart allograft survival was similar at around 26 days. The possibility that FK506, or LipoFK506, might influence antibody-mediated tolerogenesis was addressed in the same model: neither formulation prevented tolerance induction by CD4 and CD8 blockade.

CONCLUSION

LipoFK506 is a novel formulation of FK506 that is efficacious at low blood trough FK506 levels. This property has a direct potential benefit for clinical organ transplantation.

Sirolimus (rapamycin)-based therapy in human renal transplantation: similar efficacy and different toxicity compared with cyclosporine. Sirolimus European Renal Transplant Study Group

BACKGROUND

Sirolimus (rapamycin) is a potent immunosuppressant with a mechanism of action different from cyclosporine (CsA) or tacrolimus.

METHODS

In 11 European centers, first cadaveric renal allograft recipients were randomized to CsA (n=42) or sirolimus (n=41). Dosing of these agents was concentration-controlled and open-labeled. All patients received corticosteroids and azathioprine.

RESULTS

At 12 months, graft survival (98% sirolimus vs. 90% CsA), patient survival (100% vs. 98%), and incidence of biopsy-confirmed acute rejection (41% vs. 38%) were similar. Serum creatinine was lower with sirolimus, significantly (P< or =0.05) so at 3 and 4 months, and serum uric acid and magnesium were normal. Laboratory abnormalities reported significantly more often with sirolimus included hypertriglyceridemia (51% vs. 12%), hypercholesterolemia (44% vs. 14%), thrombocytopenia (37% vs. 0%), leukopenia (39% vs. 14%), and, of lesser importance, increased liver enzymes and hypokalemia. These abnormalities improved 2 months after transplantation when the sirolimus target trough level was lowered from 30 to 15 ng/ml. Occurrence of cytomegalovirus was comparable (14% vs. 12%); incidences of herpes simplex (24% vs. 10%, P=0.08) and pneumonia (17% vs. 2%, P=0.03) were higher with sirolimus. No gingival hyperplasia was seen with sirolimus, tremor was rare, and hypertension was less frequent (17% vs. 33%). Two malignancies were observed with CsA and none with sirolimus.

CONCLUSIONS

Results at 12 months suggest that sirolimus can be used as base therapy in the prophylaxis of acute renal transplant rejection, and has a safety profile that differs from CsA.

Sirolimus: a potent new immunosuppressant for liver transplantation

BACKGROUND

Sirolimus (rapamycin) is a new immunosuppressant that appears to be synergistic with cyclosporine in kidney transplantation, but with a different side-effect profile. This pilot study evaluated sirolimus in liver transplantation.

METHODS

Patients undergoing orthotopic liver transplantation for primary tumors (8), and later for nonmalignant disease (7), received one of three sirolimus-based immunosuppressive regimens. Protocol A comprised sirolimus, microemulsion cyclosporine (target whole blood concentration: 100 ng/ml), and prednisolone; protocol B omitted prednisolone; and protocol C was sirolimus alone. By 3 months after transplantation, all patients were receiving sirolimus as monotherapy.

RESULTS

Fifteen patients were treated with a follow-up of 117-806 days. Rejection was more common on monotherapy than double therapy, and absent on triple therapy. The drug was generally well tolerated, with only three patients discontinuing sirolimus: one for hyperlipidemia, one for pneumocystis pneumonia, and one for inability to tolerate the taste of the drug. Two patients discontinued cyclosporine early, both as a result of neurological complications; they continued on sirolimus monotherapy. Five patients died; one suffered a cardiac arrest, and four died from sepsis in association with graft-versus-host disease, recurrent tumor, a paralyzed right hemidiaphragm, and primary nonfunction.

CONCLUSIONS

Sirolimus combined with cyclosporine provided potent immunosuppression of liver allografts, and sirolimus monotherapy was adequate and well tolerated as maintenance therapy. Side effects of sirolimus over the short period of follow-up were uncommon and reversible with dose reduction or cessation of therapy.

Graft loss and the antiphospholipid syndrome following liver transplantation

BACKGROUND/AIMS

The antiphospholipid syndrome is characterised by arterial and venous thromboses affecting small and large vessels, together with the presence of lupus anticoagulant and anticardiolipin antibodies.

METHODS

We report two cases of the antiphospholipid syndrome following liver transplantation which resulted in hepatic vessel thrombosis and subsequent graft loss, and we discuss the value of anticoagulation in prevention of further thrombotic episodes. Identification of these cases prompted a retrospective analysis for the presence of IgG anticardiolipin antibody, the most useful laboratory marker of vascular thrombosis in the antiphospholipid syndrome. Serum taken at 2 to 4 weeks following transplantation (when thrombotic events might be anticipated) was analysed further in 132 patients undergoing liver transplantation.

RESULTS

Hepatic vessel thrombosis occurred in 21/132 (16%) post transplantation. Anticardiolipin IgG was present in 2/21 (8.8%) recipients who developed a hepatic vessel thrombosis following liver transplantation, compared to 7/111 (6.3%) (p=0.59) in whom transplantation was not complicated by hepatic vessel thrombosis.

CONCLUSIONS

The presence of IgG anticardiolipin antibody was uncommon in recipients following liver transplantation and was not associated with an increased risk of hepatic vessel thrombosis. In contrast, the antiphospholipid syndrome which is rare may result in hepatic artery occlusion and graft loss, and so prompt recognition of the clinical syndrome is critical. Although screening for the antibody is not warranted in liver transplant recipients, it is important to be aware of the syndrome as optimal management of such cases may prevent graft loss.

Thrombocytopenia following liver transplantation is associated with platelet consumption and thrombin generation

Thrombocytopenia frequently occurs immediately after orthotopic liver transplantation. We have investigated the cause of this phenomenon in a cohort of 45 consecutive liver transplant recipients. The median preoperative platelet count (range) of 129 x 10(9)/l (14-719) fell to 56 x 10(9)/l (23-334) by the fourth postoperative day. The median preoperative reticulated platelet percentage (range) of 6.7% (2.2-23.9) increased to 16.4% (4.6-40.8) on day 7. There was a significant rise in prothrombin fragment F1.2 by the first postoperative day which was followed by rises in fibrinogen and fibrin degradation products. There was no increase in platelet-associated immunoglobulin or markers of endothelial activation. We conclude that there is an increased rate of platelet consumption associated with thrombin generation that reflects the magnitude of liver transplant surgery.