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160 Molecular Construction and in Vivo Transmission of a Simian-Human Immunodeficiency Virus (SHIV) Encoding Envelope Gene of CCR5 Tropic HIV-1 Ba-L
R. Pal*1, J. S. Foulke2, M. Merges2, A. Gibson1, R. Woodward1, P. Markham1, and M. Reitz2
1Advanced BioSci. Labs, Kensington, MD, USA and 2Inst. of Human Virology, Baltimore, MD, USA
Background: Mucosal transmission of HIV-1 accounts for the majority of HIV-1 infection globally. CCR5 coreceptor-tropic HIV-1 isolates transmit via mucosal routes. Thus, CCR5 tropic SHIV isolates would serve as relevant models to test the efficacy of vaccine and therapy in nonhuman primates against mucosal challenge.
Methods: SHIV isolate encoding CCR5 tropic envelope was constructed by substituting the tat, rev, vpu, and env of SIV with that of HIV-1 Ba-L. In vitro transmission was examined by coculturing SHIV Ba-L-transfected HeLa-Tat with PM1 cells. SHIV Ba-L was passaged in vivo in pigtail macaque by blood and bone marrow transfer. Mucosal transmission of SHIV Ba-L was examined by rectal and vaginal inoculation of pigtail and rhesus macaques. Plasma viral RNA load, virus isolation from PBMC, and the presence of SIV anti-gag and HIV anti-env antibody in the serum of challenged animals were used as virological markers to assess transmission in vivo.
Results: HeLa-Tat cells transfected with the SHIV Ba-L plasmid expressed an infectious CCR5 tropic virus, which could be expanded by coculturing with PM1 cells. To enhance infectivity, SHIV Ba-L was passaged in pigtail macaques by blood and bone marrow transfer. Molecular analysis of the envelope sequence of SHIV during this in vivo passage revealed a very low level of genetic heterogeneity compared with the original isolate. Animals infected with SHIV Ba-L via rectal and vaginal routes had a high level of plasma viral load during the first 4 weeks of infection. However, viremia was eventually controlled with no significant drop in CD4 counts. Pretreatment of animals with progesterone enhanced the rate of vaginal transmission of SHIV Ba-L.
Conclusions: A CCR5 tropic SHIV Ba-L isolate transmits efficiently through mucosal routes, has a low degree of genetic heterogeneity, and may serve as a useful model to study efficacy of vaccines and chemokine-based therapy.
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