Whether the B-cell defect in NFKB1 haploinsufficiency is responsible for these nonbacterial infections is unclear.50, 51 PML is most often discovered in the context of an immune reconstitution inflammatory syndrome, as seen in patients with HIV receiving antiretroviral therapy and in patients with multiple sclerosis after natalizumab discontinuation.52 This evidence concerns the gene NFKB1 and progressive multifocal leukoencephalopathy.