This observation was confirmed by subsequent studies reporting that HIV-1 Env clones from the transmitted founder HIV-1 strains are resistant to IFITM3, but the resistance is gradually lost as infection progresses into the acute and chronic stages [104] and that the increased IFITM sensitivity results from the acquisition of mutations in Env and Vpu, which mediate escape from neutralizing antibodies [105]. This evidence concerns the gene IFITM3 and infection.