IL7 and progressive multifocal leukoencephalopathy: Systemic IL7 treatment seemed to improve PML in several reports17; however, a subsequent flare of sarcoidosis was observed in a patient with the sarcoidosis/PML combination.18 Novel single-case approaches, including JC virus-specific T cells or immune checkpoint inhibitors, aim at re-establishing immunity to the virus rather than being antivirals in the traditional sense.19,20