Limitations of IL-2 and Rapamycin in Immunotherapy of Type 1 Diabetes

Administration of low-dose interleukin-2 (IL-2) alone or combined with rapamycin (RAPA) prevents hyperglycemia in NOD mice. Also, low-dose IL-2 cures recent-onset type 1 diabetes (T1D) in NOD mice, partially by boosting pancreatic regulatory T cells (T_reg cells). These approaches are currently being evaluated in humans. Our objective was to study the effect of higher IL-2 doses (250,000–500,000 IU daily) as well as low-dose IL-2 (25,000 IU daily) and RAPA (1 mg/kg daily) (RAPA/IL-2) combination. We show that, despite further boosting of T_reg cells, high doses of IL-2 rapidly precipitated T1D in prediabetic female and male mice and increased myeloid cells in the pancreas. Also, we observed that RAPA counteracted IL-2 effects on T_reg cells, failed to control IL-2–boosted NK cells, and broke IL-2–induced tolerance in a reversible way. Notably, the RAPA/IL-2 combination failure to cure T1D was associated with an unexpected deleterious effect on glucose homeostasis at multiple levels, including β-cell division, glucose tolerance, and liver glucose metabolism. Our data help to understand the therapeutic limitations of IL-2 alone or RAPA/IL-2 combination and could lead to the design of improved therapies for T1D.In type 1 diabetes (T1D), the immune system destroys the pancreatic β-cells (1). At clinical onset, ∼30% of β-cells are still able to produce insulin (2), thus stopping autoimmune destruction, which at this stage is a promising approach (3). Along the same lines, there is a growing list of phase I/II clinical trials based on immunomodulation that are currently being conducted in T1D patients (4).NOD mice, which develop spontaneous T1D, represent an accepted model for testing new therapies (5), the gold standard being that treatments that cure overt hyperglycemia in these mice may be most appropriate for translation into the clinic, as was the case for anti-CD3 antibodies (Abs) (6), which have been tested in patients with promising results (7). In addition, results from our own group showing that low-dose interleukin-2 (IL-2) can prevent (8) and revert disease in NOD mice (9) have led to the translation of this strategy into clinical trials in T1D patients (clinical trial reg. no. {"type":"clinical-trial","attrs":{"text":"NCT01353833","term_id":"NCT01353833"}}NCT01353833, clinicaltrials.gov).We have shown that in NOD mice, administration of low-dose IL-2 for 5 days induced the remission of new-onset T1D by specifically boosting regulatory T cells (T_reg cells) in the pancreas without activating pathogenic effector T cells (T_eff cells). However, remission was obtained in only 60% of treated mice, and half of them became diabetic again during the following months (9). Consequently, improving IL-2 therapy by optimizing dosing or combining IL-2 with other immunomodulatory drugs, such as rapamycin (RAPA), could be of great importance for the goal of translating this therapy to humans.RAPA has been used in clinical transplantation for many years (10), and it has been safely administered to T1D patients during islet transplantation (11,12). In mice, RAPA monotherapy can prevent T1D development (13); however, it is unable to induce disease reversal (14). Moreover, RAPA and IL-2 were found to be synergistic for the prevention of diabetes in NOD mice (13). Consequently, we decided to test whether RAPA could synergize with short-term IL-2 therapy to reverse T1D and reinforce the development of long-term tolerance.In this work, we have further studied the mechanisms of action of IL-2 and RAPA alone or in combination in the NOD model of T1D.