Nicole Chenciner

The infiltration kinetics of simian immunodeficiency virus-specific T cells drawn to sites of high antigenic stimulation determines local in vivo viral escape

Despite vigorous cell-mediated immune responses to human and simian immunodeficiency viruses (HIV/SIV) the immune system is unable to clear latently infected resting T cells. These infected cells are reactivated by antigenic stimulation, leading to viral replication. By using the SIV/macaque model of HIV pathogenesis, the dynamics of T cell infiltration into delayed type hypersensitivity sites specific for the purified protein derivative of bacillus Calmette–Guérin have been studied. Early viral mRNA synthesis coincided with the infiltration of antigen-specific T cells. When the infiltration of anti-SIV-specific T cells was rapid compared with the kinetics of viral assembly, the sites were sterilized before the transition to late viral mRNA synthesis occurred. When their infiltration was slow, ephemeral foci of replication were identified. These findings were paralleled by plasma viremia; low viremia coincided with rapid sterilization of the delayed type hypersensitivity sites, whereas high load was found in association with local replication and delayed sterilization. These data suggest that although effective local control of SIV is possible once antiviral T lymphocytes have arrived on site, the slower deployment of these T cells may allow the virus to escape and thus to reseed the pool of memory T cells.

Simian immunodeficiency virus promoter exchange results in a highly attenuated strain that protects against uncloned challenge virus.

ABSTRACT Among the many simian immunodeficiency virus (SIV) immunogens, only live attenuated viral vaccines have afforded strong protection to a natural pathogenic isolate. Since the promoter is crucial to the tempo of viral replication in general, it was reasoned that promoter exchange might confer a novel means of attenuating SIV. The core enhancer and promoter sequences of the SIV macaque 239nefstop strain (NF-κB/Sp1 region from −114 bp to mRNA start) have been exchanged for those of the human cytomegalovirus immediate-early promoter (CMV-IE; from −525 bp to mRNA start). During culture of the resulting virus, referred to as SIVmegalo, on CEMx174 or rhesus macaque peripheral blood mononuclear cells, deletions arose in distal regions of the CMV-IE sequences that stabilized after 1 or 2 months of culture. However, when the undeleted form of SIVmegalo was inoculated into rhesus macaques, animals showed highly controlled viremia during primary and persistent infection. Compared to parental virus infection in macaques, primary viremia was reduced by >1,000-fold to undetectable levels, with little sign of an increase of cycling cells in lymph nodes, CD4+ depletion, or altered T-cell activation markers in peripheral blood. Moreover, in contrast to wild-type infection in most infected animals, the nef stop mutation did not revert to the wild-type codon, indicating yet again that replication was dramatically curtailed. Despite such drastic attenuation, antibody titers and enzyme-linked immunospot reactivity to SIV peptides, although slower to appear, were comparable to those seen in a parental virus infection. When animals were challenged intravenously at 4 or 6 months with the uncloned pathogenic SIVmac251 strain, viremia was curtailed by ∼1,000-fold at peak height without any sign of hyperactivation in CD4+- or CD8+-T-cell compartment or increase in lymph node cell cycling. To date, there has been a general inverse correlation between attenuation and protection; however, these findings show that promoter exchange constitutes a novel means to highly attenuate SIV while retaining the capacity to protect against challenge virus.

Epithelial stem cells as mucosal antigen-delivering cells: A novel AIDS vaccine approach.

A key obstacle limiting development of an effective AIDS vaccine is the inability to deliver antigen for a sufficient period of time resulting in weak and transient protection. HIV transmission occurs predominantly across mucosal surfaces; therefore, an ideal vaccine strategy would be to target HIV at mucosal entry sites to prevent infection. Such a novel strategy relies on the activation of mucosal immune response via presentation of viral antigens by the mucosal epithelial cells. The use of a terminally differentiated epithelial cell promoter to drive expression of antigens leading to viral protein production in the upper layers of the epithelium is central to the success of this approach. Our results show that when administered intradermally to mice, a GFP-reporter gene under the transcriptional control of the involucrin promoter is expressed in the upper layers of the epidermis and, although transduced cells were very low in number, high and sustained anti-GFP antibody production is observed in vivo. A subsequent experiment investigates the effectiveness of GFP-tagged replication-competent SIVdeltaNef and GFP-tagged replication-deficient SIVdeltaVifdeltaNef constructs under the transcriptional control of the involucrin promoter. Optimal conditions for production of pseudotyped VSV-G viral particles destined to transduce basal epithelial stem cells at the mucosal sites of entry of SIV in our animal model were determined. Altogether, the data demonstrate the feasibility of an epithelium-based vaccine containing involucrin-driven viral antigen encoding sequences that integrate into epithelial stem cells and show long-term expression in the upper layer of the epithelium even after multiple cycle of epithelia renewal. Such epithelium-based vaccine should elicit a long-term immunity against HIV/SIV infection at the site of entry of the virus.