Develop a new Activation-Induced Marker (AIM) assay to quantify antigen-specific T cell responses to putative disease-relevant target antigens in children with MS.

Cryopreserved PBMC collected from children with MS and controls with other CNS inflammatory diseases were thawed and either left with no-antigen, or stimulated polyclonally or with previously defined immune-dominant peptide-pools of disease-implicated myelin and viral antigens. After 24 hrs, cells were maintained with IL-2-containing media for 10 days, then re-stimulated with respective antigen for 6 hrs prior to assessment of stimulation-induced surface activation, measured as the frequency of CD69⁺CD154⁺ T cells within total CD4⁺T cells.

While no differences in activation were seen for polyclonal or tetanus stimulation in children with MS compared to children with other CNS inflammatory diseases, we observed variable degrees of abnormally increased activation of CNS-antigen specific and EBV-antigen specific T cells in the children with MS. T cells of children with MS consistently exhibited abnormal T cell activation in absence of exogenous antigen, which we coin abnormal ‘autoactivation’, likely recapitulating the abnormal T cell ‘autoproliferation’ recently reported in adults with MS.

Our AIM assay captures abnormally increased circulating T cell autoactivation in children with MS compared to controls. Abnormally enhanced antigen-specific T cell responses to both EBV and CNS myelin antigens appear superimposed on the abnormal T cell autoactivation in the children with MS. The consistent presence and higher magnitude of autoactivation in face of the more variable presence of abnormal CNS- and EBV-directed reactivities suggest that autoactivation in our AIM assay more sensitively captures a hallmark abnormality of T cell responses, potentially directed at a broader range of MS relevant antigenic specificities that differ across individual children.