Introduction: Organ transplantations requires immunosuppressive drugs and islets transplantation made no exception. Most of current immunosuppressive protocols included calcineurin inhibitors (tacrolimus), but this drug is known to induced glucose intolerance. Co-stimulation blockage with CTLA4-Ig (belatacept) is an alternative to tacrolimus to avoid calcineurin inhibitors islet cell toxicity and reduce the risk of post transplantation diabetes. If this effect is driven by tacrolimus withdrawal, the effect of belatacept itself on islet cells is unknown.

Material & Methods: We studied the impact of belatacept (1mg/mL) or tacrolimus (100µg/mL) on INS1 and MIN6 beta cell lines. INS1 were exposed to glucotoxicity (24h of DMEM 5g/L dextrose) and viability was assessed by FACS (annexin/propidium iodide labelling). MIN6 were exposed to cytokines cocktail (24-hour incubation in the presence of IL1-β 600IU/mL, IFN-γ 6000IU/mL and TNF-α 6000IU/mL for both). Viability was checked by FACS, and glucose stimulated insulin secretion (GSIS) was performed (insulin secretion index = [insulin] in 16.7mM dextrose / [insulin] in 2.8mM).

Results: In control condition, insulin secretion index of MIN6 decrease after exposure with tacrolimus (1.14 ± 0.15, n = 4, p > 0.05). With belatacept, no difference on MIN-6 insulin secretion is observed as compared to control (1.82 ± 0.74, vs control 1.56 ± 0.41, p > 0.05). Viability of MIN6 (87.1 ± 3.0, n = 4) did not differed with tacrolimus (86.7 ± 3.0, p > 0.05) or belatacept exposure (86.3 ± 2.2, p > 0.05).
Glucotoxicity test increased INS1 mortality (38.3 ± 12.6% vs. control 22.2 ± 1.90%, n=6, p < 0.05) over. The glucose-induced mortality was not prevented significantly by tacrolimus nor belatacept.
Cytokine stress increased MIN6 mortality (37.5 ± 3.22% vs. control 22.2 ± 3.22%, n=4, p<0.05). This over mortality was prevented by belatacept (20.3 ± 2.73%, vs. control p > 0.05) but not by tacrolimus (25.0 ± 3.17%, vs. control p < 0.05).           

Discussion: Need for immunosuppressive drug without glucose secretion impairment is necessary to prevent post-transplant diabetes. In these experiments both (belatacept and tacrolimus) failed to prevent impact of glucotoxicity on beta cells. However, we shown that tacrolimus has a tendency (not even significant) to disrupt insulin secretion in response to glucose with an insulin secretion index close to 1. This was not observed with belatacept. Moreover, belatacept seems to be able to prevent cytokine-induced toxicity on beta cells. Altogether, these results suggest that belatacept could be of interest for immunosuppressive regiment dedicated to islet transplantation. Further explorations are needed, and it is necessary to consolidate the results already obtained by replicating the experiments on human islets.