Molecular Biology of STLV-III and HTLV-IV

The FLB-10 provirus represents a full-length molecular clone derived from SIVmac 251 simian immunodeficiency virus. The molecularly cloned virus is replication-competent in vitro and is cytopathic for CEMX174 lymphocytes and primary macaque peripheral blood lymphocytes. Complete nucleotide sequence reveals that the FLB-10 clone contains mutations compromising expression of the vpr, nef and env genes. Therefore, vpr an nef gene products are not necessary for the in vitro replication or cytopathic effect of SIVmac. Virus stocks were inoculated into several cynomolgus monkeys and one juvenile rhesus macaque. While none of the cynomolgus monkeys have developed an infection over one year post-inoculation, the injected macaque became infected and developed a fatal immunodeficiency syndrome. These results will stimulate further studies with larger numbers of animals to address whether vpr or nef reversions occur to allow in vivo SIV replication.