Costimulation Blockade Disrupts CD4⁺ T Cell Memory Pathways and Uncouples Their Link to Decline in β-Cell Function in...

We previously reported that costimulation blockade by abatacept limits the decline of β-cell function and the frequency of circulating CD4⁺ central memory T cells (T_CM) (CD45RO⁺CD62L⁺) in new-onset type 1 diabetes. In human subjects receiving placebo, we found a significant association between an increase in CD4⁺ T_CM cells and the decline of β-cell function. To extend and refine these findings, we examined changes in human CD4⁺ and CD8⁺ naive and memory T cell subsets at greater resolution using polychromatic flow and mass cytometry. In the placebo group, we successfully reproduced the original finding of a significant association between T_CM and β-cell function and extended this to other T cell subsets. Furthermore, we show that abatacept treatment significantly alters the frequencies of a majority of CD4⁺ conventional and regulatory T cell subsets; in general, Ag-naive subsets increase and Ag-experienced subsets decrease, whereas CD8⁺ T cell subsets are relatively resistant to drug effects, indicating a lesser reliance on CD28-mediated costimulation. Importantly, abatacept uncouples the relationship between changes in T cell subsets and β-cell function that is a component of the natural history of the disease. Although these data suggest immunological markers for predicting change in β-cell function in type 1 diabetes, the finding that abatacept blunts this relationship renders the biomarkers nonpredictive for this type of therapy. In sum, our findings point to a novel mechanism of action for this successful immunotherapy that may guide other disease-modifying approaches for type 1 diabetes.