Infection of macaques with an R5-tropic SHIV bearing a chimeric envelope carrying subtype E V3 loop among subtype B framework.

To establish simian/human immunodeficiency virus (SHIV) clones bearing a chimeric envelope carrying subtype E V3 loop among subtype B envelope, four subtype E V3 sequences were substituted into SHIV(MD14), a SHIV clone bearing an envelope derived from a CXCR4 (X4)/CCR5 (R5)-dual tropic subtype B HIV-1 strain. SHIV-TH09V3, an only V3-chimera clone capable of replicating in human and macaque peripheral blood mononuclear cells (PBMCs), was propagated in pig-tailed macaque PBMCs and in cynomolgus macaque splenic mononuclear cells. The propagated virus stocks were intravenously inoculated into respective macaque species. SHIV-TH09V3 infected both macaque species as shown by plasma RNA viremia, isolated viruses from PBMCs and plasma, and antibody production against viral proteins. To assess how the substituted V3 sequence affected coreceptor usage, SHIV-TH09V3 stocks propagated in vitro and after isolation from macaques were verified for their corecepor usage by GHOST cells assay. SHIV-TH09V3 maintained R5-tropic phenotype both in vitro and after isolation from macaques, in contrast to the X4/R5-dual tropic SHIV(MD14). This indicates the substituted V3 sequence among the backbone of SHIV(MD14) governs coreceptor usage. Future study of infecting macaques with SHIV-TH09V3 and SHIV(MD14) will focus on differences of the outcome caused by the different V3 sequences in connection with coreceptor usage.