The immunosuppressive protocol pioneered by the University of Alberta and used in most previous studies of clinical islet transplantation was in part successful because the investigators recognized that omission of corticosteroids was beneficial for islet function and survival [10
]. Nonetheless, this and similar protocols that followed all relied on CNIs, particularly tacrolimus, for maintenance immunosuppression, and these agents can be problematic in diabetics not only due to their deleterious effect on renal function, but also due to their direct islet toxicity [13
]. Recently, several biological agents without these side effects have been identified and successfully used in organ transplantation; however, none have been used in islet transplantation [16
]. Efalizumab, an anti-LFA-1 antibody is one such agent that has been used extensively in the treatment of psoriasis and has recently been found to be effective in prolonging renal allograft survival [37
]. We chose this agent for our trial due to its ease of administration (weekly subcutaneous injection), excellent overall tolerability by patients, and few initial reports of significant side effects despite widespread clinical use [39
]. The efficacy of an efalizumab-based protocol was also seen in this trial, with all patients treated with efalizumab and sirolimus or MMF achieving stable insulin independence after 1 or 2 islet transplants, and five of eight patients now being independent for more than 1 year. Moreover, all patients have remained insulin independent after discontinuation of efalizumab, although one patient (patient 6) experienced a brief period of insulin dependence after efalizumab withdrawal and now has worsening glycemic control as evidenced by increasing HbA1c levels. It is possible that she will require an additional islet transplant in the near future. This decrease in function may be related to the withdrawal of efalizumab, but seems less likely given that the other patients have remained stable after drug withdrawal.
Several factors may be responsible for our current results. First, our donor selection, organ procurement, and islet isolation protocols were systematically restructured to improve islet quality and yields [21
]. Second, avoidance of corticosteroids and tacrolimus minimized the toxic effects of these agents on the islet graft. Finally, it is possible that the use of a potent T-cell depleting induction agent combined with co-stimulation/migration blockade may provide better protection against allo - and autoimmune responses directed against the islets. In support of this, the percentage of CD4 T-lymphocytes which are phenotypic T-regulatory lymphocytes was consistently higher in our patients than in patients treated with co ventional immunosuppressive protocols [40
]. In addition, the observation that 4/5 patients had decreased IFN-γ production to donor stimulators suggests that some degree of donor-specific hyporesponsiveness may has occurred. Together, these findings suggest that this immunosuppressive protocol may have some tolerogenic properties, though clearly more extensive studies are required to confirm this finding.
Avoiding CNI’s was an important goal of the study, particularly since these agents have renal toxicity that should be minimized in this patient population already at risk for renal insufficiency due to their diabetes [3
]. Unfortunately, CNI therapy had to be initiated in some of our patients after efalizumab withdrawal, thus making interpretation of long-term renal function difficult. Nonetheless, measurements of renal function with iohexol during the CNI-free period were stable or improved in our patients, suggesting that this regimen, at last in the short term, has little nephrotoxicity. It remains to be seen whether long-term renal function in patients on a CNI-free regimen will remain stable and whether reinstitution of low-dose CNI therapy in some patients after efalizumab discontinuation will have adverse effects.
An important aspect of this study was to determine the safety and efficacy of the immunosuppressive regimen used in these patients. The overall tolerability of the regimen was excellent, and many of the adverse events were attributable to sirolimus. Several patients were unable to tolerate full doses of sirolimus due to development of oral ulcers or leg swelling, and as a result required dose reduction and supplementation with or conversion to mycophenolate (Cellcept® or Myfortic®). Overall tolerability of efalizumab was outstanding, with side effects being limited to localized, transient skin irritation at the injection site in 2 patients. Previous studies with efalizumab have shown that CD11a coating and modulation by the drug can occur at doses significantly lower than those routinely used when treating psoriasis [44
]. In addition, studies in renal transplant recipients found an increased incidence of post-transplant lymphoproliferative disease (PTLD) in patients treated with high doses of the drug (2 mg/kg/week) in conjunction with sirolimus and high dose mycophenolate [37
]. Based on these findings, we selected a low dose of the drug (1 mg/kg/week) for our studies and reduced the dose further (to 0.5 mg/kg/week) when patients were 3 months from their final islet transplant. Using this regimen, we did not observe any cases of PTLD throughout the follow-up period. One patient did develop detectable EBV levels, but these resolved spontaneously without treatment. Pharmacokinetic studies in selected patients showed appropriate coating and modulation of CD11a at the doses used (data not shown).
Recent reports have described the development of progressive multifocal leukoencephalopathy (PML) in 4 patients (3 confirmed, 1 suspected) out of approximately 46,000 who had received efalizumab as treatment for psoriasis [45
] These patients had all received standard doses of the drug and had been treated for >3 years [32
]. Although several other immunosuppressive agents have also been associated with PML yet continue to be used clinically, these reports led to withdrawal of the drug from clinical use and prompted us to discontinue the medication to minimize long-term exposure [46
]. We have weaned all of the patients off efalizumab and are now treating them with a maintenance regimen of mycophenolate and/or sirolimus or low-dose tacrolimus. Serial neurologic examinations in all patients have been normal and we continue to monitor these patients closely for any new developments.
There are several drawbacks to this study. First, the lack of a control group treated with sirolimus and/or MMF makes it difficult to evaluate the additive immunosuppressive effect of efalizumab therapy. Although there is evidence from other studies that maintenance immunosuppression consisting of sirolimus and MMF but without CNI results in early islet failure, a control population in our study would be important to clarify these issues and to address the possibility that other factors such as islet isolation play a role in our outcomes [49
]. Second, efalizumab had to be discontinued in all of the patients at varying times after transplant (and in two instances before the second transplant), so the long-term effects of this protocol on islet survival and renal function cannot be evaluated.
A recent editorial called for a “sober reassessment of the clinical applicability” of islet transplantation as the result of the relatively poor glycemic control following islet transplantation, nephrotoxicity of the immunosuppressive agents, and the sensitization of recipients resulting from multiple infusions and failed islet allografts [50
]. It was these important concerns that prompted the current trial using lymphocyte depletion and co-stimulatory/migration blockade to provide effective immmunosuppression to prevent early islet loss, minimize the number of infusions required to obtain insulin independence, and prevent nephrotoxicity in this vulnerable group of Type I diabetic recipients. This study provides preliminary evidence that clinical pancreatic islet transplantation can be successfully achieved using a novel immunosuppressive regimen based on efalizumab that does not require concomitant corticosteroids and minimizes CNI use. Furthermore, insulin independence was achieved with single donor pancreata in 4/8 patients – an important consideration in light of concerns for sensitization from multiple donors as well as the shortage of donor organs and efficacy of whole organ transplantation. Finally, this regimen minimizes the use of beta cell toxic agents, and in the short-term appears to reduce the risk of renal toxicity associated with CNI therapy. These have been important steps in the right direction, although the long-term consequences of this immunosuppressive protocol and the effects of efalizumab discontinuation on graft function remain to be determined and should be carefully monitored and reported. The strategy of avoiding beta-cell toxic and nephrotoxic immunosuppressive agents to protect beta cells will likely also have a role in future replacement protocols, as the sources of beta cells is expanded from adult islets to stem cell derived beta cells [52