Single-Donor, Marginal-Dose Islet Transplantation in Patients With Type 1 Diabetes FREE

Type 1 diabetes remains a therapeutic challenge. The success rate of islet transplants has recently been increased markedly by transplanting a higher mean islet mass (11 547 [SD, 1604] islet equivalents [IEs]/kg) prepared from 2 to 4 donor pancreases and using glucocorticoid-free immunosuppression.^1- 6 However, for islet transplants to become a widespread clinical reality, additional advances are still needed. In particular, restoration of insulin independence must be achieved with a single donor, as is also the case with pancreas transplants, to reduce the risks and costs and increase the availability of islet transplantation. We designed a protocol to limit ischemic injury of islets during pancreas storage, permit initiation of potent immunotherapy prior to transplantation, and minimize calcineurin inhibitor exposure.

Our study was a prospective, single-center, 1-year follow-up pilot trial conducted from July 2001 to August 2003. The primary efficacy end point was the proportion of recipients who achieve insulin independence in the first year after a single-donor islet transplant. We defined recipients as insulin-independent if they maintained fasting blood glucose levels below 126 mg/dL (7.0 mmol/L) and 2-hour postprandial levels below 180 mg/dL (10.0 mmol/L) after discontinuation of insulin.

A total of 8 patients (coincidentally all women) were enrolled. Eligibility criteria are detailed in the Box and detailed recipient characteristics are shown in Table 1. Our study protocol was approved by the local institutional review board, and written informed consent was obtained from all participants.

Inclusion Criteria

Exclusion Criteria

*Defined as C-peptide level <0.2 ng/mL after administration of 5 g of intravenous arginine.

Eighteen consecutive donor pancreases were procured from cadaver donors younger than 50 years with a body mass index (calculated as weight in kilograms divided by square of height in meters) of 27 or greater; the pancreases were preserved for 8 hours or less using the 2-layer method.⁸ ABO compatibility and a negative serum crossmatch for T cells were required, but HLA antigen matching was not. Islets were isolated as previously described.⁹ Briefly, preserved pancreases were perfused with cold Liberase (Roche Diagnostics Corp, Indianapolis, Ind).¹⁰ Islets were isolated by the automated method,¹¹ purified with continuous iodixanol density gradients in a Cobe 2991 cell separator (Gambro BCT, Lakewood, Colo), and cultured free-floating in supplemented CMRL 1066 for 1 day at 37°C and 1 day at 22°C.^9,12- 13 Of the 18 consecutive cadaver donor pancreases processed for this study, preparations from 8 were transplanted (detailed donor and graft characteristics for those 8 are shown in Table 2). Islet preparations from the remaining 10 donor pancreases were not transplanted because of inadequate islet yield for single-donor islet transplantation. The mean islet yield of 7 of those 10 preparations was 301 428 (SD, 59 780) IEs.

After establishing access to the portal vein via minilaparotomy or percutaneous transhepatic portal venous catheterization, we infused 7271 (SD, 1035) IEs/kg of recipient body weight by gravity, along with heparin, 70 U/kg, on day 0 into 8 consecutive participants. Prophylactic anticoagulation was continued with intravenous heparin (target partial thromboplastin time, 50-60 seconds) for 48 hours, followed by enoxaparin (30 mg subcutaneously twice daily) through day 7.

Induction immunosuppression, initiated on day –2, consisted of rabbit antithymocyte globulin (RATG) (0.5 mg/kg of recipient body weight [day –2], 1.0 mg/kg [day –1], 1.5 mg/kg [days 0 through +2]),¹⁴ methylprednisolone (on day –2 only, 2 mg/kg), daclizumab (5 doses of 1 mg/kg every 2 weeks starting on day 0), and etanercept (50 mg intravenously 1 hour pretransplantation, followed by 25 mg subcutaneously on days 3, 7, and 10). Premedication for RATG included acetaminophen and diphenhydramine as well as pentoxifylline, which was extended through day 7 posttransplantation. Maintenance immunosuppression was initiated with sirolimus (0.2 mg/kg starting on day –2, followed by 0.1 mg/kg daily; target whole blood trough levels, 5-15 ng/mL, as tolerated) and reduced-dose tacrolimus (0.015 mg/kg twice daily, starting on day 1; target whole blood trough levels, 3-6 ng/mL). At 1 month posttransplantation, tacrolimus was gradually replaced with mycophenolate mofetil (750-1000 mg, twice daily); tacrolimus was either discontinued or dosed to a target trough level of less than 3 ng/mL. If target levels of sirolimus could not be achieved or maintained, however, tacrolimus (target level, 3-6 ng/mL) was continued.

Antimicrobial and antiviral prophylaxis with imipenem, vancomycin, trimethoprim/sulfamethoxazole, and valganciclovir was administered. Glycemic control was achieved with intravenous insulin from day –2 to day +2 relative to transplant and with subcutaneous insulin for at least 3 additional weeks.

Safety of the transplant protocol was assessed by monitoring the severity and duration of procedural complications, serious infections, or islet- or immunosuppression-related adverse events.

Self-measured blood glucose concentrations (5 or more times daily), hypoglycemic episodes, basal C-peptide levels, and levels of glycosylated hemoglobin (by high-performance liquid chromatography with reference range 4.3%-6.0%; monthly through day 90 posttransplantation, then quarterly) were recorded throughout the study. Recipients also underwent oral glucose tolerance testing (75 g, 2 hours), intravenous glucose tolerance testing, and intravenous arginine stimulation. The acute insulin and C-peptide responses to intravenous arginine (AIR-arginine, ACR-arginine) and to intravenous glucose (AIR-glucose, ACR-glucose) were defined as the mean of the 3 highest poststimulus values between 2 and 5 minutes after the start of the stimulus administration minus the mean of 2 prestimulus values.¹⁵ Human C-peptide levels were measured by double antibody radioimmunoassay (Diagnostic Products Corp, Los Angeles, Calif) (interassay coefficient of variation [CV], 7.9% at a mean C-peptide level of 0.56 ng/mL and 9.1% at a mean of 1.6 ng/mL; intra-assay CV, 9.9% at a mean of 0.08 ng/mL and 2.1% at a mean of 0.73 ng/mL). Human insulin levels were measured by chemiluminescent immunoassay (Immulite; Diagnostic Products Corp) (interassay CV, 6.4% at a mean insulin level of 7.5 mU/L and 7.6% at a mean of 47.7 mU/L; intra-assay CV, 3.3% at a mean of 14.3 mU/L and 6.4% at a mean of 46.5 mU/L). Results were compared with those obtained in control individuals without diabetes, matched for age and body mass index. Islet graft loss was defined by the absence of basal and arginine-stimulated C-peptide levels.

Anti-GAD65 antibody, anti-ICA512 antibody, and anti-insulin antibody titers were measured with radiobinding assays.¹⁶

Data are presented as mean (SD) unless otherwise stated. Comparisons were performed using the 2-tailed t test. Analyses were performed using SAS version 9.1 (SAS Institute Inc, Cary, NC); P<.05 was used to determine statistical significance.

We did not observe procedural complications; serious infections; or serious, unexpected, and islet- or immunosuppression-related adverse events. Expected adverse events included lymphopenia and transient neutropenia requiring short-term (<1 week) administration of granulocyte colony-stimulating factor in 5 recipients. Intermittent oral aphthous ulcers were observed in all participants. No clinically significant changes in creatinine clearance or urinary albumin excretion were observed.

All 8 recipients became insulin-independent, with glycosylated hemoglobin levels within reference range and freedom from hypoglycemia. Of the 8 recipients, 5 have remained insulin-independent for longer than 1 year and 3 were insulin-independent for 121, 76, and 7 days (Table 3). Metabolic tests performed 180 or more days posttransplantation in the 5 recipients with sustained insulin independence showed a mean AIR-glucose level of 16.7 (SD, 5.5) μU/mL (30% [SD, 10%] of controls), an ACR-glucose of 1.23 (SD, 0.46) ng/mL (40% [SD, 15%] of controls), an AIR-arginine of 15.5 (SD, 3.7) μU/mL (53% [SD, 13%] of controls), and an ACR-arginine of 1.07 (SD, 0.15) ng/mL (59 [SD, 8%] of controls). For 4 of these 5 recipients, results of oral glucose tolerance testing at 180 or more days posttransplantation revealed 2-hour plasma glucose levels below 140 mg/dL (7.8 mmol/L). The 2-hour plasma glucose level in the fifth recipient was 208 mg/dL (11.5 mmol/L). These 5 recipients received daily mycophenolate mofetil doses of 1.5 to 2.0 g. They either achieved and maintained sirolimus trough levels greater than 9 ng/mL, with tacrolimus trough levels of 0 to less than 3 ng/mL, or achieved tacrolimus trough levels of 3 to 6 ng/mL in the absence of target sirolimus trough levels. The 3 recipients who resumed exogenous insulin therapy had received 1.5 g/d or more of mycophenolate mofetil but had subtherapeutic sirolimus trough levels (<9 ng/mL) in the absence of measurable tacrolimus trough levels (<3 ng/mL). For additional information, see Table 3 for metabolic monitoring and Table 4 for exposure to immunosuppressive drugs.

Of the 3 participants with graft failure, 2 tested positive for anti-GAD65 and anti-ICA512 in the pretransplantation period. In contrast, none of the 5 who remained insulin-independent tested positive for anti-GAD65 and anti-ICA512.

Graft failure was followed by allosensitization in 2 recipients.

Our results mark a distinct advance in islet transplant efficacy. We not only achieved insulin independence using islets from only 1 donor pancreas (as compared with 2 to 4 in the Edmonton trial¹), we also achieved superior glycemic control (as evidenced by normal results of oral glucose tolerance testing in 4 of 5 recipients with sustained insulin independence) using significantly fewer islets (7271 [SD, 1035] IEs/kg vs 11 547 [SD, 1604] IEs/kg; P<.001). We had previously achieved insulin independence in 4 of 6 participants with type 1 diabetes who received an islet mass of 10 302 (SD, 2594) IEs/kg from 1 donor pancreas.⁹ However, transplantation of such an islet mass is only available from a limited number of donor pancreases and obscures assessment of the ability of a given protocol to permit reversal of diabetes with a lower islet mass retrievable from a larger subgroup of donor pancreases.

Determining the reasons for our high success rates with a lower islet mass from a single donor pancreas will have important ramifications for the advancement of the field. Previous studies by us and others have suggested that excluding pancreases from donors older than 50 years, limiting cold storage to less than 8 hours and using the 2-layer preservation method, avoiding use of Ficoll during islet purification, and culturing islets pretransplantation could conceivably preserve the potency of transplanted islets.^13,17- 22 Since pancreas procurement, preservation, islet processing, and culture protocols in the 2 studies were all identical, we assume that the potency was the same and therefore interpret the high efficacy of single-donor, marginal-dose islet transplants in our current trial as preliminary evidence of improved engraftment. In this study, induction therapy was with RATG, combined with daclizumab and etanercept. The resistance of islet-directed autoimmune responses to conventional immunosuppressive drugs^23- 27 and the immediate exposure of intraportally transplanted islets to primed autoreactive, islet beta cell–directed T cells have also provided a strong rationale for pretransplant initiation of RATG, which is known to cause selective depletion of activated T cells and dose-dependent depletion of resting T cells.²⁸ Many of these effects are shared with the anti-CD3 monoclonal antibody, hOKT3γ1 (Ala-Ala), used in our previous trial.⁹ Thus, they may not sufficiently explain the ability of the protocol used in our current trial to facilitate reversal of diabetes after single-donor, marginal-dose islet transplants. Therefore, the results are possibly related to the peritransplant administration of the soluble tumor necrosis factor receptor etanercept. Tumor necrosis factor α is cytotoxic to human islet beta cells.²⁹ In murine models, selective inhibition of tumor necrosis factor α in the peritransplant period has promoted reversal of diabetes after marginal-mass islet transplants.³⁰ Etanercept administration is a new addition to our protocol and distinguishes this trial from our previous trial,⁹ so it could have been a major factor allowing consistent diabetes reversal with a low islet dose.

Moreover, replacing or minimizing tacrolimus at 1 month posttransplantation, as we did in our current trial, may have enhanced the function of engrafted islets. Low-dose calcineurin inhibitor therapy, with no or minimal doses of steroids, has previously been associated with significantly reduced insulin sensitivity and beta cell secretory reserve,³¹ suggesting that even low-dose tacrolimus therapy may limit the ability of a reduced islet mass to reverse diabetes. Maintenance immunosuppression with mycophenolate mofetil and sirolimus, shown to be synergistic in experimental studies,³² is without diabetogenic or nephrotoxic adverse effects and is sufficiently potent, provided induction immunosuppression is administered and adequate sirolimus levels are achieved and maintained. In light of the results on exposure to immunosuppressive drugs (Table 4), it seems likely that the islet graft failure experienced by 3 recipients was caused by alloimmunity and/or recurrent autoimmunity. The observation that 2 of 3 recipients with graft failure, but none of the 5 who remained insulin-independent, tested positive for both anti-GAD65 and anti-ICA512 in the pretransplant period suggests a possible involvement of autoimmunity in graft failure. More detailed studies in a larger series of recipients will be needed to accurately ascribe islet graft loss to metabolic or immunologic reasons.

In conclusion, potent induction immunotherapy as used in this study may increase the ability of low-dose islet allografts to reverse diabetes and may minimize nephrotoxicity and cardiovascular toxicity by sparing calcineurin inhibitor dosing. While these findings may suggest a distinct advance in islet transplantation, further study in a larger population with longer follow-up will be critical to assess the risk-benefit ratio of this emerging therapeutic option.