Immune responses against islet allografts during tapering of immunosuppression - A pilot study in 5 subjects

Abstract

Transplantation of isolated islet of Langerhans cells has great potential as a cure for type 1 diabetes but continuous immune suppressive therapy often causes considerable side effects. Tapering of immunosuppression in successfully transplanted patients would lower patients' health risk. To identify immune biomarkers that may prove informative in monitoring tapering, we studied the effect of tapering on islet auto-and alloimmune reactivity in a pilot study in five transplant recipients in vitro. Cytokine responses to the graft were measured using Luminex technology. Avidity of alloreactive cytotoxic T Lymphocytes (CTL) was determined by CD8 blockade. The influence of immunosuppression was mimicked by in vitro replenishment of tacrolimus and MPA, the active metabolite of mycophenolate mofetil. Tapering of tacrolimus was generally followed by decreased C-peptide production. T-cell autoreactivity increased in four out of five patients during tapering. Overall alloreactive CTL precursor frequencies did not change, but their avidity to donor mismatches increased significantly after tapering (P = 0•035). In vitro addition of tacrolimus but not MPA strongly inhibited CTL alloreactivity during tapering and led to a significant shift to anti-inflammatory graftspecific cytokine production. Tapering of immunosuppression is characterized by diverse immune profiles that appear to relate inversely to plasma C-peptide levels. Highly avid allospecific CTLs that are known to associate with rejection increased during tapering, but could be countered by restoring immune suppression in vitro. Immune monitoring studies may help guiding tapering of immunosuppression after islet cell transplantation, even though we do not have formal prove yet that the observed changes reflect direct effects of immune suppression on immunity.

Low gravity rotational culture and the integration of immunomodulatory stem cells reduce human islet allo‐reactivity

“…The present study indicates that AEC influence both CD4+ and CD8+ T‐cell subsets which are widely implicated in islet immune destruction . CD4+ and CD8+ T cells underwent profound population expansion in response to anti‐CD3/CD28 stimulation, yet concomitant co‐culture with AEC markedly reduced the T‐cell response.…”

“…The underlying cause is multifactorial with poor islet viability post‐isolation, impaired graft revascularization and beta (β)‐cell exhaustion influencing outcome. Further, the islet allo‐graft is vulnerable to the host immune system; the decline in function suggesting that the immunosuppressive regimen fails to adequately restrain the effector response of allo‐specific T cells responsible, in part, for graft rejection . The agents employed also pose attendant risks to the recipient and islet , prompting the search for alternative methods of graft immuno‐protection.…”

“…We have previously characterized a rotational human islet culture system that maintains β‐cell function for up to 10 d , in which islets readily integrate with other cell types to form heterotypic constructs with sustained/improved viability . Here, we employ the conducive environment of this rotational cell culture system (RCCS) for extensive pre‐transplant islet modification, chiefly the intentional dispersal of human islets and their subsequent integration with immunomodulatory amniotic epithelial cells (AEC), with the purpose of suppressing islet‐induced CD4+ and CD8+ T‐cell responses likely to underlie rejection . Such pre‐transplant interventions may be of direct importance to acute and long‐term islet graft survival and therefore the further development of β‐cell replacement therapy.…”

Progress in immune-based therapies for type 1 diabetes

“…With the exception of oral insulin and proinsulin peptide immunotherapy , immunological parameters have not generally been used in selection or randomization of patients in clinical trials. Lessons from the islet transplantation setting, in which baseline immune correlates determine clinical outcome , may be of use here and it is conceivable that incorporating immune correlates into trial design may improve the chance of detecting therapeutic efficacy and indicate subpopulations of patients with particular benefit, lack of efficacy or even adverse responses to certain immune intervention strategies . While common beliefs advocate a combination of drugs for intervention (Table ), it is important to scrutinize potential adverse interference, as may have played a role in the recent trial combining low‐dose interleukin (IL)‐2 and rapamycin, in which each of the separate constituents could have yielded clinical benefit .…”

“…With the exception of oral insulin [15] and proinsulin peptide immunotherapy [16], immunological parameters have not generally been used in selection or randomization of patients in clinical trials. Lessons from the islet transplantation setting, in which baseline immune correlates determine clinical outcome [17][18][19], may be of use here and it is conceivable that incorporating immune correlates into trial design may improve the chance of detecting therapeutic efficacy and indicate subpopulations of patients with particular benefit, lack of efficacy or even adverse responses The primary outcome at 1 year (residual C-peptide after mixedmeal) was significantly higher in the rituximab than in the placebo group; the rituximab group also had significantly lower levels of HbA1c and required less insulin [8] Autologous umbilical cord blood cells…”