Background/Purpose:  In adult dermatomyositis, clonal populations of T lymphocytes with shared variable (V) gene usage have been identified, suggesting aberrant T cell responses to a common antigen.  A CD4⁺T cell subset, regulatory T (Treg) cells, has recently been identified as important mediators of muscle tissue repair.  A diverse Treg repertoire is thought to be important in maintaining Treg function and may contribute to the Treg response to muscle damage.  Little is known about the T cell repertoire in juvenile dermatomyositis (JDM); further, the Treg repertoire in human inflammatory myopathies has not been evaluated.  Therefore, we employed next generation sequencing to characterize the Treg and effector T (Teff) cell repertoires in JDM.     

Methods:  Peripheral blood (PB) was obtained from JDM patients (n=6) at disease onset and healthy children (n=3).  Treg (CD4⁺CD25⁺CD127^lo) and Teff (CD4⁺CD25^–) cells were isolated from PB mononuclear cells by fluorescence-activated cell sorting.  The T cell receptor (TCR) β chain was amplified by multiplex PCR with genomic DNA serving as the template (ImmunoSEQ^TM).  Illumina HiSeq platform was used for sequencing.  Wilcoxon sign ranked tests were used to compare the clonality index and normalized Shannon entropy in patients and controls.  2-way ANOVA with Bonferroni correction was used to compare TCRVβ family usage in patients versus controls. 

Results:  Three males and 3 females with JDM, average age 7.0 years (range:  3.3-9.4 years), were studied.  The average disease duration was 7 months, and the average MMT8 score was 69.6.  Five of the patients were evaluated before the initiation of any immunosuppressive therapy.  Treg and Teff repertoire clonality and diversity were similar in JDM patients and controls.  In JDM Treg and Teff subsets, TCRVβ families 7, 19, and 28 were used more and TCRVβ families 2, 3, 5, 6 were used less than in controls (p<0.0001 for both Treg and Teff cells).  In particular, TCRVβ7 skewing was most striking, and this Vβ family was used more than twice as often in JDM PB Treg and Teff cells compared to controls.  

Conclusion:  Skewed TCRVβ family usage was observed in JDM patients at disease onset.  Increased usage of TCRVβ7 was observed in JDM PB Treg and Teff cells, and this Vβ family has been linked with other autoimmune conditions including type I diabetes and anti-phospholipid syndrome.  Our early pilot results suggest that T cell repertoire abnormalities may contribute to disease pathogenesis in JDM.  Further studies are planned to evaluate the T cell repertoire in JDM muscle and skin biopsies, as well as longitudinally over the course of disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-lymphocyte-repertoire-in-juvenile-dermatomyositis/