A Bispecific Protein Capable of Engaging CTLA-4 and MHCII Protects Non-Obese Diabetic Mice from Autoimmune Diabetes

Crosslinking ligand-engaged cytotoxic T lymphocyte antigen-4 (CTLA-4) to the T cell receptor (TCR) with a bispecific fusion protein (BsB) comprised of a mutant mouse CD80 and lymphocyte activation antigen-3 (LAG-3) has been shown to attenuate TCR signaling and to direct T-cell differentiation toward Foxp3(+) regulatory T cells (Tregs) in an allogenic mixed lymphocyte reaction (MLR). Here, we show that antigen-specific Tregs can also be induced in an antigen-specific setting in vitro. Treatment of non-obese diabetic (NOD) female mice between 9-12 weeks of age with a short course of BsB elicited a transient increase of Tregs in the blood and moderately delayed the onset of autoimmune type 1 diabetes (T1D). However, a longer course of treatment (10 weeks) of 4-13 weeks-old female NOD animals with BsB significantly delayed the onset of disease or protected animals from developing diabetes, with only 13% of treated animals developing diabetes by 35 weeks of age compared to 80% of the animals in the control group. Histopathological analysis of the pancreata of the BsB-treated mice that remained non-diabetic revealed the preservation of insulin-producing β-cells despite the presence of different degrees of insulitis. Thus, a bifunctional protein capable of engaging CTLA-4 and MHCII and indirectly co-ligating CTLA-4 to the TCR protected NOD mice from developing T1D.