Saturday Morning Research Review – October 15, 2016

Potential “phenotypic signature” of T cells in pediatric-onset type 1 diabetes

by Adam Burrack, PhD

Predictive markers of T cell responses against beta cells are a highly sought clinical diagnostic. Analysis of a validated, limited, set of cell surface proteins on T cells collected from peripheral blood would facilitate “risk assessment” in people at-risk of developing autoimmunity – before they have developed symptoms. Combining this type of analysis with quantification of autoantibody levels – which is routinely assessed in at-risk individuals – would provide a powerful tool to place at-risk individuals in the “stages” of type 1 diabetes (T1D), as developed by the JDRF, the American Diabetes Association, and Endocrine Society.

A recent report describes just such a set of proteins on the surface of CD8 T cells (ie, “killer T cells”). It was a major goal of this study to compare the broad phenotype – or “activation status” – of CD8 T cells in the blood between pediatric-onset and adult-onset patients with T1D. There were a couple key take-home results from this study.

First, there was a normal distribution of effector, memory, and naïve CD8 T cells in adult-onset T1D patients, but the authors did not observe the normal ratio between these T cell subsets in pediatric-onset patients. Perhaps counter-intuitively, pediatric-onset T1D patients tended to have high percentages of CD8 T cells expressing regulatory molecules (IL-10 and TGF-β) than do adult-onset T1D patients. The authors speculate that the higher expression of regulatory molecules on effector T cells from pediatric patients is a response to the high-inflammation environment in people at-risk of developing autoimmunity – the so-called type 1 IFN signature we have discussed previously. As a corollary to this result, the authors observed an abnormal distribution between naïve, effector, and memory CD8 T cells in pediatric-onset T1D patients, but normal proportions of these populations of CD8 T cells in adult-onset patients. Importantly, this analysis was not investigating autoreactive T cells specifically, but rather was a “global analysis” investigating CD8 T cells in these individuals broadly.

Second, at the single-cell level, the expression several proteins differed between pediatric patients and controls (including regulatory proteins, trafficking proteins, and effector proteins), whereas only a single protein analyzed differed between adult patients and controls (a regulatory protein). This result suggests – along with the above results – a global perturbation in CD8 T cell biology in individuals who develop T1D at a young age.

Third, over time, the abnormal distribution of T cells between naïve, effector, and memory populations persisted in pediatric patients for years after diabetes onset. This is in contrast to some reports, but agrees with the majority of published research describing global differences in the T cell biology of individuals who develop autoimmunity early in life – but the lack of a global perturbation in T cell biology in individuals who develop autoimmunity later in life.

Fourth, the preceding analysis was conducted on RNA, at the level of gene regulation. To translate these findings into a more readily-accessible clinical diagnostic method, the authors investigated expression of the same set of proteins by flow cytometric analysis. Flow cytometry is a common clinical diagnostic tool to investigate protein expression by cells in the peripheral blood, so translating the above results to this method is critical. Virtually all large research hospitals have flow cytometers. These are also the basic tool used in immunology research. Happily, analysis of protein expression confirmed analysis at the RNA level, demonstrating global changes in CD8 T cell proportions and activation status in pediatric-onset T1D patients, but more subtle changes in T cell biology in adult-onset patients.

In conclusion, this method for analyzing T cell activation status and sub-population distribution may be a useful clinical diagnostic for determining “staging” of pre-diabetic individuals at-risk of developing autoimmunity. Combining measures of autoantibody production with direct measurements of T cell activation status allows quantification of the current status of both halves of the adaptive immune system. That is cool stuff, because it would facilitate clinicians to know exactly where in the disease process they are intervening with clinical trials. This would help to “funnel” patients into clinical trials, producing more-informative results than previous clinical trials.

Posted in beta cells, Immunology, Research Review.