THE ORF47 AND ORF66 PUTATIVE PROTEIN-KINASES OF VARICELLA-ZOSTER VIRUS DETERMINE TROPISM FOR HUMAN T-CELLS AND SKIN IN THE SCID-HU MOUSE

The varicella-zoster virus (VZV) genes ORF47 and ORF66 are predicted t o encode serine/threonine protein kinases, which are homologs of herpe s simplex virus 1 (HSV-1) UL13, and US3. When mutants were constructed by inserting stop codons into ORF47 and ORF66, the recombinants ROka4 7S and ROka66S, as well as intact ROka replicated in tissue culture. I n contrast, inoculation of human thymus/liver or skin implants in SCID -hu mice showed that ORF47 protein was required for viral growth in hu man T cells and skin. Eliminating ORF66 expression inhibited VZV infec tivity for T cells partially but did not impair replication in skin co mpared with ROka. Infectivity for T cells and skin was restored when R Oka47S virus was complemented by insertion of ORF47 into a distant, no ncoding site. The ORF47 gene product is the first VZV protein identifi ed as necessary for T cell tropism. It also is essential for skin infe ctivity in vivo, as is glycoprotein C. Expression of ORF66 did not com pensate for the absence of the ORF47 protein. The requirement for ORF4 7 expression in T cells and skin indicates that this gene product, whi ch is dispensable in vitro, has a critical role within differentiated cells that are essential targets for VZV pathogenesis in vivo.