Cellular islet autoimmunity associates with clinical outcome of islet cell transplantation

Abstract

Background: Islet cell transplantation can cure type 1 diabetes (T1D), but only a minority of recipients remains insulin-independent in the following years. We tested the hypothesis that allograft rejection and recurrent autoimmunity contribute to this progressive loss of islet allograft function.

Methodology/principal findings: Twenty-one T1D patients received cultured islet cell grafts prepared from multiple donors and transplanted under anti-thymocyte globulin (ATG) induction and tacrolimus plus mycophenolate mofetil (MMF) maintenance immunosuppression. Immunity against auto- and alloantigens was measured before and during one year after transplantation. Cellular auto- and alloreactivity was assessed by lymphocyte stimulation tests against autoantigens and cytotoxic T lymphocyte precursor assays, respectively. Humoral reactivity was measured by auto- and alloantibodies. Clinical outcome parameters--including time until insulin independence, insulin independence at one year, and C-peptide levels over one year--remained blinded until their correlation with immunological parameters. All patients showed significant improvement of metabolic control and 13 out of 21 became insulin-independent. Multivariate analyses showed that presence of cellular autoimmunity before and after transplantation is associated with delayed insulin-independence (p = 0.001 and p = 0.01, respectively) and lower circulating C-peptide levels during the first year after transplantation (p = 0.002 and p = 0.02, respectively). Seven out of eight patients without pre-existent T-cell autoreactivity became insulin-independent, versus none of the four patients reactive to both islet autoantigens GAD and IA-2 before transplantation. Autoantibody levels and cellular alloreactivity had no significant association with outcome.

Conclusions/significance: In this cohort study, cellular islet-specific autoimmunity associates with clinical outcome of islet cell transplantation under ATG-tacrolimus-MMF immunosuppression. Tailored immunotherapy targeting cellular islet autoreactivity may be required. Monitoring cellular immune reactivity can be useful to identify factors influencing graft survival and to assess efficacy of immunosuppression.

Trial registration: Clinicaltrials.gov NCT00623610.

Figure 1. CONSORT-style flowchart of 24 consecutive islet cell transplantation recipients.

Figure 2. Kaplan-Meier curves showing cumulative insulin independence after β-cell transplantation, stratified for A) pre-transplant cellular autoimmunity and B) pre-transplant presence of autoantibodies.

Continuous lines represent patients without reactivity to autoantigens, striped lines patients with reactivity to a single antigen, and dotted lines patients with reactivity to two antigens (or three in the case of autoantibodies).

Figure 3

A) C-peptide levels stratified for cellular autoimmune status before and after transplantation. Total C-peptide levels over one year for patients that are not autoreactive pre- nor post-transplant (−/−, n = 3) only pre- (+/−, n = 6) or only post-transplant (−/+, n = 5), and both pre- and post transplant (+/+, n = 4). Areas under the curve differ significantly between groups (p = 0.009, one-way ANOVA). Horizontal lines represent average C-peptide level per group. B) average basal C-peptide levels (black lines)±SD (grey areas) over time for the four different groups. Differences between −/− and +/+ and between −/+ and +/+ remain significant after Bonferroni correction. Pre-transplant autoreactivity significantly reduces total C-peptide production (p = 0.006, unpaired t-test).

Figure 4. Influence of pre-transplant T cell autoreactivity stratified for total injected β-cell mass.

Shown are pre-transplant T cell autoreactivity and achievement of insulin independence for patients receiving more or less than the median total injected β-cell mass (the single patient receiving the median β-cell mass is excluded). Groups are compared by Fischer exact test.