It was further shown that the expanded Tregs in active sarcoidosis patients did not completely inhibit TNF-α and IFN-γ production of CD4+ T cells and thereby were not able to control granuloma formation.12 Although the SAR-PML patients had higher frequencies of Tregs than the SAR-CON, there was a trend for higher frequencies of IFN-γ+ CD4+ T cells and TNF-α+ CD4+ T cells, which could indeed indicate an impaired suppressive capacity of Tregs on IFN-γ and TNF-α secretion resulting in sustained granuloma formation. Here, CD4 is linked to progressive multifocal leukoencephalopathy.