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Foamy Virus Vectors Persistently Express High Levels of HIV-1 gag: Potential for an HIV Vaccine
W. David Hardy*1,2, W. David Hardy*1,2, C Liu1, Y Xi2, T Folks3, and I Chen2
1Cedars-Sinai Med Ctr, Los Angeles, CA, US; 2David Geffen Sch of Med, Univ of California, Los Angeles, US; and 3CDC, Atlanta, GA, US
Background: Foamy virus (FV) is a lesser known retrovirus
endemic in many animal species, including nonhuman primates, but not in humans.
A low prevalence (1 to 4%) of human FV infection is well-documented following
bites by primate with persistent viremia, and anti-FV immune response. FV
infection has not been associated with disease in animals or humans. FV
completes reverse transcription in the virion, thus host factors may not be
limiting, as they are with lentviruses.
Methods: Recombinant FV vectors using full-length
HIV-1 gag (FOVgag) and a CTL gag epitope SL9 (FOVSL9) were
constructed using standard molecular techniques. Titers were determined using
β-galactosidase indicator cells. Host cell tropism and transduction
characteristics were studied using regular and real time polymerase chain
reaction (PCR) on infected epithelial and hematopoietic cells lines and primary
monocyte-derived dendritic cells (MDDC). We measured p24 antigen production by
enzyme immunoassay (EIA) and characterized it by Western blot.
Results: FOVgag- and FOVSL9-infected cells
expressed HIV-1 p24 and p17 mRNA and genomic DNA measured by PCR and p24
antigen by EIA in several infected cells.
FOVgag titer was 5.5 log10
or 316.2 transduction units (TU) /µL; FOVSL9 titer was 5.7 log10 or
501.2 transduction units (TU)/µL. Characteristic cytopathic effects were
detected in BHK, 293T, and HTB-65 cells; none were detected in Raji, Daudi,
THP-1, T1 or MDDC. Efficient transduction of these cells was demonstrated by
p24 and p17 DNA, mRNA, and p24 antigen detection. HIV-1 p24 DNA, mRNA, and
protein production increased proportionately in THP-1 cells (monocyte cell
line); p24 antigen peaked at 130 ng/mL for FOVgag
and 55 ng/mL for FOVSL9 and maintained persistent, non-pathogenic infection
longer than 16 weeks. Western blot patterns of FV vector-expressed proteins
showed high correlation with those from HIV-1-infected cells. Infection of
primary MDDC produced detectable p24 antigen >10 days of culture.
Conclusions: FV vectors can successfully transduce human
epithelial and hematopoietic cell lines with detectable p24 DNA, mRNA, and
protein expression for at least 16 weeks post-infection. Transduction of MDDC
by these FV vectors may be a promising, potential HIV-1 antigen-presenting
vaccine strategy.
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