In-vivo assessment of T cell kinetics in individuals at risk for type 1 diabetes

We previously assessed the kinetics of T cell turnover in vivo by labeling cells with ² H-H₂ O over 42 days in individuals with type 1 diabetes (T1D) and demonstrated an increased turnover of CD4 memory T cells. We have now tested T cell turnover in individuals at risk for T1D using a 3-4-day labeling protocol with ² H-glucose. We studied 30 relatives with T1D with and without autoantibodies, and 10 healthy controls. Peripheral blood mononuclear cells (PBMC) were flow-sorted into T cell subsets of interest; ² H-DNA enrichment was measured by mass spectrometry and in-vivo turnover was calculated as maximum fractional enrichment of deuterated adenosine (F_max ). Among CD4⁺ cells, F_max was highest in regulatory T cells (T_reg ), followed by effector and central memory T cells and lowest in naive cells. Similarly, CD8⁺ central and effector memory T cells had a higher turnover than CD8⁺ terminally differentiated effector memory T cells (TEMRA) and CD8⁺ -naive T cells. Relatives as a group showed significantly increased T_reg turnover by F_max compared to controls (1·733 ± 0·6784% versus 1·062 ± 0·3787%, P = 0·004), suggesting pre-existing immune dysfunction within families with T1D. However, there was no significant difference in F_max between groups according to autoantibody or glucose tolerance status. Repeat testing in 20 subjects 1 year later demonstrated relatively higher within-subject compared to between-subject variability for the measurement of F_max in various T cell subsets. The short labeling protocol with ² H-glucose should be applied in the context of a clinical trial in which the therapy is expected to have large effects on T cell turnover.