An antigen-specific immunotherapeutic, AKS-107, deletes insulin-specific B cells and prevents murine autoimmune diabetes

Evaluation of proinsulin(F25D) as a targeting ligand for insulin-binding B cells in autoimmune diabetes

Insulin-binding B cells are implicated in Type 1 Diabetes (T1D) pathology. Antigen-specific immunotherapy (ASIT) holds promise in T1D. However, ASIT-targeted suppression of insulin-binding B cells is hampered by insulin's hormonal activity and the resulting binding and endocytosis of insulin by insulin receptors (INSR). To evaluate ASIT strategies that target insulin-binding B cells in vivo, non-hormonally active insulin variants are needed. In this work, we aimed to improve upon prior non-hormonal insulin variants by making mutations to the insulin precursor, proinsulin, and including a c-terminal sortase (SrtA) tag (LPETGGHG) to enable facile site-selective bioconjugation to scaffolds or payloads. Of the insulin variants investigated that retained low-nM binding to the murine-derived insulin autoantibody mAb 125, proinsulin(F25D)-SrtA had the lowest INSR binding and activity and the greatest fibrillation resistance. Compared to desoctapeptide insulin, a previously proposed non-hormonal insulin variant, proinsulin(F25D)-SrtA demonstrated 50-fold lower INSR binding and 100-fold greater fibrillation lag time. However, insulin(F25D)-SrtA bound to the anti-insulin antibody 12M4 isolated from a presymptomatic T1D individual, whereas proinsulin(F25D)-SrtA and desoctapeptide insulin did not, highlighting the potential for anti-insulin B cells to develop in human T1D that would escape this ASIT moiety. The characteristics of proinsulin(F25D)-SrtA make it a well-suited non-hormonal insulin variant for insulin-binding B cell targeting and warrants additional study with other anti-insulin B cell specificities derived from T1D individuals.

Dia-B-Ties: B Cells in the Islet-Immune-Cell Interface in T1D

Type 1 diabetes (T1D) is an autoimmune disease that affects an estimated 30 million people worldwide and results in a lifelong dependency of exogenous insulin treatments. While T1D is characterized by T-cell driven-destruction of the insulin-secreting β cells, B lymphocytes play a key role in the islet-immune interface. B cells are an essential intermediary between islet cells and other immune-cell populations. Through antigen presentation, cytokine secretion, and antibody production, B cells play a role in activating autoreactive islet-specific T cells, thus potentiating pancreatic inflammation in the early stages of T1D. Despite this, their role in disease development remains an understudied feature of T1D with significant therapeutic potential. Herein, we will discuss the current knowledge of the islet-immune-cell interface within T1D through the lens of B lymphocytes. We will also consider knowledge gaps that may be limiting further therapeutic opportunities.

Factors Governing B Cell Recognition of Autoantigen and Function in Type 1 Diabetes

Islet autoantibodies predict type 1 diabetes (T1D) but can be transient in murine and human T1D and are not thought to be directly pathogenic. Rather, these autoantibodies signal B cell activity as antigen-presenting cells (APCs) that present islet autoantigen to diabetogenic T cells to promote T1D pathogenesis. Disrupting B cell APC function prevents T1D in mouse models and has shown promise in clinical trials. Autoantigen-specific B cells thus hold potential as sophisticated T1D biomarkers and therapeutic targets. B cell receptor (BCR) somatic hypermutation is a mechanism by which B cells increase affinity for islet autoantigen. High-affinity B and T cell responses are selected in protective immune responses, but immune tolerance mechanisms are known to censor highly autoreactive clones in autoimmunity, including T1D. Thus, different selection rules often apply to autoimmune disease settings (as opposed to protective host immunity), where different autoantigen affinity ceilings are tolerated based on variations in host genetics and environment. This review will explore what is currently known regarding B cell signaling, selection, and interaction with T cells to promote T1D pathogenesis.