Molecularly cloned SHIV-1157ipd3N4: a highly replication- competent, mucosally transmissible R5 simian-human immunodeficiency virus encoding HIV clade C Env.

Human immunodeficiency virus type 1 (HIV-1) clade C causes >50% of all HIV infections worldwide, and an estimated 90% of all transmissions occur mucosally with R5 strains. A pathogenic R5 simian-human immunodeficiency virus (SHIV) encoding HIV clade C env is highly desirable to evaluate candidate AIDS vaccines in nonhuman primates. To this end, we generated SHIV-1157i, a molecular clone from a Zambian infant isolate that carries HIV clade C env. SHIV-1157i was adapted by serial passage in five monkeys, three of which developed peripheral CD4(+) T-cell depletion. After the first inoculated monkey developed AIDS at week 137 postinoculation, transfer of its infected blood to a naïve animal induced memory T-cell depletion and thrombocytopenia within 3 months in the recipient. In parallel, genomic DNA from the blood donor was amplified to generate the late proviral clone SHIV-1157ipd3. To increase the replicative capacity of SHIV-1157ipd3, an extra NF-kappaB binding site was engineered into its 3' long terminal repeat, giving rise to SHIV-1157ipd3N4. This virus was exclusively R5 tropic and replicated more potently in rhesus peripheral blood mononuclear cells than SHIV-1157ipd3 in the presence of tumor necrosis factor alpha. Rhesus macaques of Indian and Chinese origin were next inoculated intrarectally with SHIV-1157ipd3N4; this virus replicated vigorously in both sets of monkeys. We conclude that SHIV-1157ipd3N4 is a highly replication-competent, mucosally transmissible R5 SHIV that represents a valuable tool to test candidate AIDS vaccines targeting HIV-1 clade C Env.

Extensively deleted simian immunodeficiency virus (SIV) DNA in macaques inoculated with supercoiled plasmid DNA encoding full-length SIVmac239.

Using long-distance DNA PCR, we prospectively followed rhesus monkeys that had been inoculated intramuscularly with supercoiled plasmid DNA encoding intact simian immunodeficiency virus (SIV). From 4 to 10 weeks postinoculation onward, we detected extensively deleted proviral genomes along with full-length viral genomes in peripheral blood mononuclear cells (PBMC) in adult macaques. During their chronic asymptomatic phase of infection, the frequency of deleted proviral genomes was similar in PBMC and lymph nodes. The latter, however, harbored significantly more full-length proviral DNA than PBMC, consistent with the lack of effective antiviral cytotoxic T-cell activity in lymph nodes described by others during human immunodeficiency virus infection. After the macaques progressed to AIDS, full-length proviral DNA became equally abundant in lymph nodes and in PBMC. We have demonstrated that although a single molecular species of proviral DNA was inoculated, genomic diversity was detected within a short time, thus confirming the genetic instability of the SIV genome in vivo.

Protection of neonatal macaques against experimental SHIV infection by human neutralizing monoclonal antibodies.

Neonatal macaques were completely protected against oral challenge with SHIV-vpu+, a simian-human immunodeficiency virus that encodes the envelope gene of a laboratory-adapted HIV strain, by pre- and post-natal treatment with a triple combination of human neutralizing monoclonal antibodies (mAbs). The mAbs were directed either against the CD4 binding site, a glycosylation-dependent gp120 epitope, or against a linear epitope on gp41. This triple combination was highly synergistic in vitro and neutralized primary HIV completely. Subsequently, oral challenge was performed with pathogenic SHIV89.6P, an animal-passaged variant of a chimeric virus that encodes the envelope gene of the primary, dual-tropic HIV89.6. Only post-natal treatment with a similar triple mAb combination was used. One out of 4 mAb-treated infants was completely protected from infection. In the other 3 treated animals, there was a tendency towards lower peak viral RNA loads compared with untreated controls. Two out of 4 mAb-treated infants maintained normal CD4+ T-cell numbers, in contrast to all controls that had steep declines at 2 weeks post-challenge. We conclude that the triple mAb combination significantly protected the neonates, even against mucosal challenge with pathogenic SHIV89.6P. Passively administered synergistic human mAbs may play a role in preventing mother-infant transmission of HIV, both against intrapartum transmission as well as against infection through breast milk. As passive immunization is a tool to assess correlates of immune protection, we conclude that the epitopes recognized by the mAbs in our combinations are important for AIDS vaccine development. Future passive immunization studies may reveal other important conserved epitopes.

Production of HIV-1 by resting memory T lymphocytes.

BACKGROUND: The persistence of HIV-1 within resting memory CD4 T cells constitutes a major obstacle in the control of HIV-1 infection. OBJECTIVE: To examine the expression of HIV-1 in resting memory CD4 T cells, using an in-vitro model. DESIGN AND METHODS: Phytohaemagglutinin-activated peripheral blood mononuclear cells were challenged with T cell-tropic and macrophage-tropic HIV-1 clones, and with a replication-incompetent and non-cytotoxic HIV-1-derived vector (HDV) pseudotyped by the vesicular stomatitis virus glycoprotein G. To obtain resting memory CD4 T cells containing HIV-1 provirus, residual CD25(+), CD69(+) and HLA-DR(+) cells were immunodepleted after a 3 week cultivation period. RESULTS: In spite of the resting phenotype, the majority of provirus-harbouring T cells expressed HIV-1 genomes and produced infectious virus into cell-free supernatant. The expression of HDV dropped by only 30% during the return of activated HDV-challenged cells into the quiescent phase. Although resting memory T cells generated in vitro expressed HIV-1 and HDV genome when infected during the course of the preceding T cell activation, they were resistant to HIV-1 and HDV challenge de novo. The infected culture of resting memory T cells showed a higher resistance to the cytotoxic effects of HIV-1 in comparison with the same cultures after reactivation by phytohaemagglutinin. CONCLUSION: The majority of resting memory T cells infected during the course of a preceding cell activation produces virus persistently, without establishing a true HIV-1 latency. The described system could be used as a model for testing new drugs able to control residual HIV-1 replication in resting memory T cells.

Selective HIV-1-induced downmodulation of CD4 and coreceptors.

CD4 and members of the chemokine receptor family are required for infection of host cells, in vitro and in vivo, by the human immunodeficiency virus type-1. Although it is established that HIV-1 gp 120 interacts with CD4 and the coreceptors CCR5 or CXCR4 at the plasma membrane during HIV entry, longer-term interactions taking place between these molecules and HIV Env are less well understood. We have measured the cell surface expression of CD4, CCR5 and CXCR4 on a CD4+/CXCR4+CCR5+ T cell line following infection by cell line-adapted X4 and primary X4, X4R5 and R5 viruses. We report a selective downmodulation of CD4 by X4 and R5X4 viruses, but not by R5 viruses. None of the viruses tested significantly reduced CXCR4 expression at any time after infection. CCR5 protein and mRNA expression was eliminated by chronic infection with R5 viruses. These results indicate that chronic HIV-1 infection has distinct effects on CD4 and coreceptor membrane expression that depends on viral origin and coreceptor usage.

Primary intestinal epithelial cells can be infected with laboratory-adapted strain HIV type 1 NDK but not with clinical primary isolates.

Infectivities of HIV-1 primary isolates and laboratory-adapted strains were compared in primary fetal enterocytes and the colonic epithelial cell line HT29. Infection by two laboratory strains, HIV-1 NDK and HIV-1 NDK(A4), which were adapted on CEM and HT29 cells, respectively, produced significant amounts of virus in both target cell systems. Intestinal cells were resistant to infection with HIV-1 primary isolates regardless of their genetic subtype or SI/NSI phenotype. Biological properties of analyzed viruses rather than differences in cultivation system seem to be responsible for differences between these in vitro and ex vivo results.