ICOS and Friedreich ataxia: Therefore, the expression levels of four commonly tested activation markers (CD69, CD137, HLA-DR, and ICOS)33,34 were assessed in CD4 and CD8 subpopulations at the onset and upon the completion of the manufacturing of CAR-T cells from HDs and from patients with FA (Figure 3A; samples from both transplanted and not transplanted—none of them mosaic patients—were used in these studies).