ICAM1 and progressive multifocal leukoencephalopathy: It has been shown that psoriasis can be treated with an anti-CD11a mAb (efalizumab) that blocks the ICAM-1/LFA-1 signal (Signal-2).48–50 Unfortunately, the side effect of efalizumab was progressive multifocal leukoencephalopathy (PML), which is often fatal, in a population of patients; in 2009, the use of this drug was terminated.51, 52