Teplizumab

Type 1 diabetes (T1D) is an autoimmune condition in which T cell-mediated destruction of pancreatic β cells leads to loss of insulin production, impaired glycemic control, and reliance on exogenous insulin. T1D is a progressive disease with three recognizable stages and in which only Stage 3 is associated with clinically apparent symptoms. The earliest indication of T1D risk is the presence of at least two autoantibodies against relevant antigens, confirming an important role for B cells in what has traditionally been considered a T cell-dominated condition. Combined with other observations from animal and human studies, it is clear that T and B cells play a role in T1D; treatment has focussed on targeting each of them independently, as well as their interactions.

The T cell receptor (TCR) comprises TCR α and β chains together with six CD3 molecules, including two CD3 ε chains. It is responsible for recognizing antigens displayed on the MHC complex of other cells to elicit a response. Teplizumab, a humanized IgG1κ Fc-nonbinding version of an existing mouse OKT3 antibody (also designated huOKT3γala-ala), is specific for the ε chain of CD3 and inhibits T cell activation through steric inhibition of antigen recognition. Recently, teplizumab has shown efficacy in delaying the time to diagnosis in patients at high risk of developing T1D. However, the exact mechanism underlying this effect remains clear.

One hypothesis is that teplizumab acts as a partial agonist at the TCR, increasing the number of exhausted T cells positive for KLRG1, TIGIT, and CD8. These exhausted T cells persist but cannot perform effector functions and, therefore, would be unlikely to contribute to further β cell destruction. Other studies have noted changes in the T cell populations of clinical responders, including an increase in circulating CD8+ central memory (CD8CM) T cells. It is clear, however, that treatment is most effective in patients who have not yet progressed to Stage 3 and who have an active immune response.