To explore the possibility that the Lyst protein mutated in CHS patients confers a block in cell-to-cell transmission and to provide a second line of evidence that the defect in HIV-1 spread in CHS cells was restricted to Lyst function, we carried out RNAi knockdown of Lyst by transducing T cells with lentivirus expressing lyst-specific shRNA and directly analyzed cell-to-cell spread of virus. This evidence concerns the gene LYST and Chédiak-Higashi syndrome.