Infection of female primary lower genital tract epithelial cells after natural pseudotyping of HIV-1: possible implications for sexual transmission of HIV-1.

The global AIDS pandemic continues to expand and in some regions of the world, such as southern Africa, the prevalence of HIV-1 infection exceeds 20%. The devastating spread of the virus in young women in these countries appears disproportional to overall risk of infection. Regions with high prevalence of HIV-1 are often also highly endemic for other pathogenic viruses including HSV, CMV and HTLV. We propose that acquisition by HIV-1 of the envelope glycoproteins of other viruses, in a process we call "natural pseudotyping," expands the cellular tropism of HIV-1, enabling it to infect female genital epithelial cells directly and thereby dramatically increasing risk of infection during sexual intercourse. In this proof-of-concept study, we demonstrate that when HIV-1 co-infects T cells along with the gammaretrovirus xenotropic murine leukemia virus-related virus (XMRV), progeny HIV-1 particles are produced capable of infecting primary vaginal, ectocervical and endocervical epithelial cells. These cell types are normally resistant to HIV-1 infection. Infection of primary genital cells was neutralized by antisera against the XMRV glycoprotein, confirming that infection was mediated by the XMRV glycoprotein acquired through pseudotyping of HIV. Inhibition by AZT showed that active replication of HIV-1 occurred in these cells and ruled out non-specific endocytic uptake of the virus. These results demonstrate that natural pseudotyping can expand the tropism of HIV-1 to include genital epithelial cells and have potential implications for sexual transmission of the virus

Pseudotyped HIV-1 infects epithelial cells derived from vagina.

<p>Immunofluorescence analysis of HIV-1 infection in VK-2. VK-2 cells were infected with progeny virus from primary CD4+ T cells or CEMX174 and were stained for HIV-1 Gag expression 5 days post-infection. The input virus used to infect producer T cells are as indicated. An enlarged view of epithelial cells exposed to progeny virus from HIV-1/XMRV co-infected CEMX174 cells is shown (second panel). HIV-1 Gag expression is indicated by green fluorescence (FITC); green fluorescence merged to the corresponding bright field image is shown in the bottom panels. B. Target epithelial cells were exposed to progeny viruses in the presence or absence of AZT as indicated on the panels. Data shown are representative of six independent experiments. Bar = 10 µm. <b>C</b> and <b>D</b>, HIV-1 and XMRV viral RNA in the supernatants of the same infected VK-2 cells as in (A) and (B) were quantified by qRT-PCR. The viruses used to infect producer cells are shown on the X axis. The data shown represent the mean ± standard deviation from three independent experiments.</p

LNcap epithelial cell line is susceptible to infection by HIV-1 co-produced with XMRV.

<p><b>A.</b> Visualization of HIV-1 infection in epithelial cells using immunofluorescence staining with anti-HIV Gag monoclonal antibody. LNcap cells were exposed to culture supernatants from CEMX174 cells infected with indicated viruses. Cells were fixed and stained for HIV-1 Gag expression 5 days after exposure to the viral supernatants. Green fluorescence (FITC) indicates HIV-1 Gag expression. Green fluorescence merged with corresponding bright field images are shown in the bottom panels. An enlarged view of cells exposed to HIV-1 co-produced with XMRV is shown in the second panel from the left. <b>B.</b> AZT inhibits HIV-1 infection of epithelial cells. LNcap cells and progeny viruses from HIV-1/XMRV co-infected CEMX174 cells were pretreated with AZT or with medium alone. The virus preparations were then added to the cells and the input virus was removed after 24 hrs. The cells were then cultured for an additional four days in medium alone or medium containing AZT as outlined in Materials and Methods. The cells were then fixed and stained for HIV-1 Gag expression. Cells infected in the absence of AZT are shown on the left. The corresponding bright field image is shown in the bottom panels. Bar = 10 µm. Data are representative of 5 independent experiments. <b>C.</b> HIV-1 RNA in the supernatants of the same LNcap cells from (<b>B.</b>) infected in the presence or absence of AZT was quantified by qRT-PCR. <b>D.</b> XMRV RNA in the supernatants of the infected LNcap cells was quantified by qPCR. The input viruses were supernatants from CEMx174 cells infected as indicated. For (C) and (D) the data shown represent the mean ± standard deviation from five independent experiments. **p<0.001, infection in the absence vs presence of AZT.</p

Pseudotyped HIV-1 infects primary endocervical epithelial cells.

<p>(<b>A, B</b>) Visualization of HIV-1 infection in primary endocervical epithelial cells by dual immunofluorescence staining with FITC-anti-HIV-1 Gag and anti-CK19 MAbs. Primary endocervical epithelial cells were exposed to progeny viruses from infected CEMX174 cells and immunofluorescence staining was performed 5 days post-infection. Epithelial cells exposed to virus in presence of AZT or anti-MLV polyclonal sera diluted 1∶300 are shown as indicated (<b>B</b>, left two panels). HIV-1 Gag fluorescence is shown as green and CK19 as red. The corresponding bright field images are shown on the right (<b>A</b>) or at the bottom (<b>B</b>). HIV-1 Gag staining merged with CK19 staining and enlarged views of HIV-1 infected cells are shown in (A). <b>C and D:</b> XMRV RNA (<b>C</b>) and HIV-1 RNA (<b>D</b>) in supernatants from the same infected primary endocervical epithelial cells from (<b>A</b>) and (B) above were quantified by qRT-PCR. The input virus used to infect producer CEMX174 cells and the treatments are indicated on the X-axis of the graphs (pAb 1∶300 = anti-MLV polyclonal sera at dilution 1∶300; Control serum = normal goat serum diluted 1∶300; No serum = culture medium control). **, p<0.001, control serum vs indicated treatments. The data shown represent the mean ± standard deviation from three independent experiments. <b>^a</b>, HIV-1 and XMRV from CEMX174 cells infected with each virus alone were quantified and mixed at a ratio equal to the ratio of the two viruses in the progeny virus from HIV-1 and XMRV co-infected CEMX174 cells. The virus mixture was then inoculated onto primary endocervical epithelial cells and immunostaining and qPCR was performed exactly as described for progeny virus from co-infected CEMx174 cells.</p

Inhibition of HIV-1 infection of epithelial cells by neutralizing anti-MLV polyclonal antiserum.

<p><b>A.</b> Anti-MLV polyclonal antibody neutralizes XMRV infection in a dose-dependent manner. Progeny viruses from CEMX174 cells infected with HIV-1 and/or XMRV were pre-incubated with the indicated dilutions of anti-MLV polyclonal serum at 37°C for 1 hr before addition to LNcap epithelial cells. XMRV released into the supernatants of infected LNcap cells was quantified by qRT-PCR. pAb = Anti-MLV polyclonal antibody; Con. Serum = normal goat serum diluted 1∶100. The input viruses used to infect producer CEMx174 cells are indicated at the bottom. The data shown represent the mean ± standard deviation from three independent experiments. <b>B.</b> Immunofluorescence analysis of HIV-1 infection in LNcap cells in the presence or absence of anti-MLV neutralizing antibody. The same LNcap cells infected with progeny viruses from HIV-1/XMRV co-infected cells (shown in A) in the presence of indicated dilutions of anti-MLV neutralizing pAb or control serum were stained for HIV-1 Gag (green). The corresponding bright field image for each panel is shown on the right. Bar = 10 µm. Images are representative of three independent experiments. <b>C.</b> HIV-1 viral RNA in supernatants of from the same infected LNcap cells in (B) was quantified by qRT-PCR. The input virus used to infect producer cells and the dilutions of neutralizing or control sera are indicated. The data shown represent the mean ± standard deviation from three independent experiments. *, p<0.05; **, p<0.001, control serum vs anti-MLV pAb.</p

Pseudotyped HIV-1 infects primary vaginal squamous epithelial cells.

<p>(<b>A, B</b>) Dual immunofluorescence staining with FITC-anti-HIV-1 Gag and anti-CK19 MAbs was performed on primary vaginal squamous epithelial cells which were exposed to progeny virus from infected CEMX174 cells. HIV-1 Gag is shown as green and CK19 is shown as red. Corresponding bright field images are also shown as indicated. The input viruses used to infect producer CEMX174 cells is indicated on the panels. Epithelial cells exposed to progeny virus in the presence of AZT or anti-MLV polyclonal sera diluted 1∶300 are shown in the left two columns in <b>B</b>.</p

Pseudotyping of HIV-1 with Human T-Lymphotropic Virus 1 (HTLV-1) Envelope Glycoprotein during HIV-1–HTLV-1 Coinfection Facilitates Direct HIV-1 Infection of Female Genital Epithelial Cells : Implications for Sexual Transmission of HIV-1

Female genital epithelial cells cover the genital tract and provide the first line of protection against infection with sexually transmitted pathogenic viruses. These cells normally are impervious to HIV-1. We report that coinfection of cells by HIV-1 and another sexually transmitted virus, human T-lymphotropic virus 1 (HTLV-1), led to production of HIV-1 that had expanded cell tropism and was able to directly infect primary vaginal and cervical epithelial cells. HIV-1 infection of epithelial cells was blocked by neutralizing antibodies against the HTLV-1 envelope (Env) protein, indicating that the infection was mediated through HTLV-1 Env pseudotyping of HIV-1. Active replication of HIV-1 in epithelial cells was demonstrated by inhibition with anti-HIV-1 drugs. We demonstrated that HIV-1 derived from peripheral blood of HIV-1–HTLV-1-coinfected subjects could infect primary epithelial cells in an HTLV-1 Env-dependent manner. HIV-1 from subjects infected with HIV-1 alone was not able to infect epithelial cells. These results indicate that pseudotyping of HIV-1 with HTLV-1 Env can occur in vivo. Our data further reveal that active replication of both HTLV-1 and HIV-1 is required for production of pseudotyped HIV-1. Our findings indicate that pseudotyping of HIV-1 with HTLV-1 Env in coinfected cells enabled HIV-1 to directly infect nonpermissive female genital epithelial cells. This phenomenon may represent a risk factor for enhanced sexual transmission of HIV-1 in regions where virus coinfection is common