A novel Lactococcus lactis-based antigen-specific platform for the treatment of type 1 diabetes: Essential steps towards successful clinical translation.

In type 1 diabetes (T1D) the insulin-producing beta cell is destroyed by the aberrant immune system leading to blood glucose dysregulation. To date, patients are dependent on external insulin for survival however, limitations such as hypoglycemia unawareness and suboptimal glycemic control leading to micro- and macrovascular complications still exist. Furthermore, although a combination of serum islet autoantibodies, genetic factors, and metabolic features can predict those who will be affected with high accuracy, current pharmacological therapies do not prevent or slow down disease progression. Moreover, interventions in patients with newly diagnosed T1D using clinically acceptable doses of a single systemic immunomodulatory drug, like aCD3, or antigen-specific approaches, like oral insulin, have not lived up to expectations. In addition, their efficacies are not uniform among T1D patients, highlighting on the one hand the complexity of this multifactorial disease and on the other hand the heterogeneity of this patient population. Oral autoAg delivery as a means to induce mucosal tolerance is hindered by practical challenges related to gastric protein degradation. Recombinant biologically contained live L. lactis bacteria have proven to be safe and well tolerated in pre-clinical animal models as well as several clinical trials making these bacteria ideal biofactories to synthesize and deliver autoAgs to the gastrointestinal tract. GM L. lactis secreting proinsulin (PINS) along with the biologically active immunoregulatory cytokine IL-10 (LL-PINS+IL-10) were able to successfully restore glucose homeostasis in newly diagnosed NOD mice when combined with low-dose aCD3. This supports the idea that has been growing for several years now in the field of T1D where preclinical research evidence has encouraged experts to propose combinations of general immunomodulation and Ag-specific approaches as the best strategy to stably cure or prevent T1D. However, clinical translation has failed in the past due to a lack of biomarkers, dosing, ill-suited end points, timing of intervention and a lack of insights in the mechanism of action. Here, we wanted to further explore these potential pitfalls for the CT of low-dose aCD3 combined with LL-PINS+IL-10. First, we generated a clinical-grade recombinant L. lactis strain appropriate for human application secreting human pro-insulin and IL-10. When combined with low-dose aCD3 this combination therapy (CT) was able to reverse diabetes in 66% of newly diagnosed diabetic NOD mice, comparable to plasmid-driven L. lactis. Initial blood glucose concentrations (