To examine the role of IFITMs in restricting HIV-1 replication, we constructed U87 neuroblastoma cells (which do not express detectable IFITMs without IFN induction) encoding CD4 together with one of the two major co-receptors, CXCR4 or CCR5, to express IFITM1, IFITM2, and IFITM3, respectively (Figure S1A, available online). Here, IFNA1 is linked to neuroblastoma.