Deborah L. Birx

Vaccination with ALVAC and AIDSVAX to Prevent HIV-1 Infection in Thailand

BACKGROUND The development of a safe and effective vaccine against the human immunodeficiency virus type 1 (HIV-1) is critical to pandemic control. METHODS In a community-based, randomized, multicenter, double-blind, placebo-controlled efficacy trial, we evaluated four priming injections of a recombinant canarypox vector vaccine (ALVAC-HIV [vCP1521]) plus two booster injections of a recombinant glycoprotein 120 subunit vaccine (AIDSVAX B/E). The vaccine and placebo injections were administered to 16,402 healthy men and women between the ages of 18 and 30 years in Rayong and Chon Buri provinces in Thailand. The volunteers, primarily at heterosexual risk for HIV infection, were monitored for the coprimary end points: HIV-1 infection and early HIV-1 viremia, at the end of the 6-month vaccination series and every 6 months thereafter for 3 years. RESULTS In the intention-to-treat analysis involving 16,402 subjects, there was a trend toward the prevention of HIV-1 infection among the vaccine recipients, with a vaccine efficacy of 26.4% (95% confidence interval [CI], -4.0 to 47.9; P=0.08). In the per-protocol analysis involving 12,542 subjects, the vaccine efficacy was 26.2% (95% CI, -13.3 to 51.9; P=0.16). In the modified intention-to-treat analysis involving 16,395 subjects (with the exclusion of 7 subjects who were found to have had HIV-1 infection at baseline), the vaccine efficacy was 31.2% (95% CI, 1.1 to 52.1; P=0.04). Vaccination did not affect the degree of viremia or the CD4+ T-cell count in subjects in whom HIV-1 infection was subsequently diagnosed. CONCLUSIONS This ALVAC-HIV and AIDSVAX B/E vaccine regimen may reduce the risk of HIV infection in a community-based population with largely heterosexual risk. Vaccination did not affect the viral load or CD4+ count in subjects with HIV infection. Although the results show only a modest benefit, they offer insight for future research. (ClinicalTrials.gov number, NCT00223080.)

Protection of macaques against vaginal transmission of a pathogenic HIV-1/SIV chimeric virus by passive infusion of neutralizing antibodies.

The development of the human immunodeficiency virus-1 (HIV-1)/simian immunodeficiency virus (SIV) chimeric virus macaque model (SHIV) permits the in vivo evaluation of anti-HIV-1 envelope glycoprotein immune responses. Using this model, others, and we have shown that passively infused antibody can protect against an intravenous challenge. However, HIV-1 is most often transmitted across mucosal surfaces and the intravenous challenge model may not accurately predict the role of antibody in protection against mucosal exposure. After controlling the macaque estrous cycle with progesterone, anti-HIV-1 neutralizing monoclonal antibodies 2F5 and 2G12, and HIV immune globulin were tested. Whereas all five control monkeys displayed high plasma viremia and rapid CD4 cell decline, 14 antibody-treated macaques were either completely protected against infection or against pathogenic manifestations of SHIV-infection. Infusion of all three antibodies together provided the greatest amount of protection, but a single monoclonal antibody, with modest virus neutralizing activity, was also protective. Compared with our previous intravenous challenge study with the same virus and antibodies, the data indicated that greater protection was achieved after vaginal challenge. This study demonstrates that antibodies can affect transmission and subsequent disease course after vaginal SHIV-challenge; the data begin to define the type of antibody response that could play a role in protection against mucosal transmission of HIV-1.

DC-SIGN (CD209) Mediates Dengue Virus Infection of Human Dendritic Cells

Dengue virus is a single-stranded, enveloped RNA virus that productively infects human dendritic cells (DCs) primarily at the immature stage of their differentiation. We now find that all four serotypes of dengue use DC-SIGN (CD209), a C-type lectin, to infect dendritic cells. THP-1 cells become susceptible to dengue infection after transfection of DC-specific ICAM-3 grabbing nonintegrin (DC-SIGN), or its homologue L-SIGN, whereas the infection of dendritic cells is blocked by anti–DC-SIGN antibodies and not by antibodies to other molecules on these cells. Viruses produced by dendritic cells are infectious for DC-SIGN– and L-SIGN–bearing THP-1 cells and other permissive cell lines. Therefore, DC-SIGN may be considered as a new target for designing therapies that block dengue infection.

Human skin Langerhans cells are targets of dengue virus infection

Dengue virus (DV), an arthropod-borne flavivirus, causes a febrile illness for which there is no antiviral treatment and no vaccine. Macrophages are important in dengue pathogenesis; however, the initial target cell for DV infection remains unknown. As DV is introduced into human skin by mosquitoes of the genus Aedes, we undertook experiments to determine whether human dendritic cells (DCs) were permissive for the growth of DV. Initial experiments demonstrated that blood-derived DCs were 10-fold more permissive for DV infection than were monocytes or macrophages. We confirmed this with human skin DCs (Langerhans cells and dermal/interstitial DCs). Using cadaveric human skin explants, we exposed skin DCs to DV ex vivo. Of the human leukoctye antigen DR-positive DCs that migrated from the skin, emigrants from both dermis and epidermis, 60–80% expressed DV antigens. These observations were supported by histologic findings from the skin rash of a human subject who received an attenuated tetravalent dengue vaccine. Immunohistochemistry of the skin showed CD1a-positive DCs double-labeled with an antibody against DV envelope glycoprotein. These data demonstrate that human skin DCs are permissive for DV infection, and provide a potential mechanism for the transmission of DV into human skin.

Emergence of unique primate T-lymphotropic viruses among central African bushmeat hunters.

The human T-lymphotropic viruses (HTLVs) types 1 and 2 originated independently and are related to distinct lineages of simian T-lymphotropic viruses (STLV-1 and STLV-2, respectively). These facts, along with the finding that HTLV-1 diversity appears to have resulted from multiple cross-species transmissions of STLV-1, suggest that contact between humans and infected nonhuman primates (NHPs) may result in HTLV emergence. We investigated the diversity of HTLV among central Africans reporting contact with NHP blood and body fluids through hunting, butchering, and keeping primate pets. We show that this population is infected with a wide variety of HTLVs, including two previously unknown retroviruses: HTLV-4 is a member of a phylogenetic lineage that is distinct from all known HTLVs and STLVs; HTLV-3 falls within the phylogenetic diversity of STLV-3, a group not previously seen in humans. We also document human infection with multiple STLV-1-like viruses. These results demonstrate greater HTLV diversity than previously recognized and suggest that NHP exposure contributes to HTLV emergence. Our discovery of unique and divergent HTLVs has implications for HTLV diagnosis, blood screening, and potential disease development in infected persons. The findings also indicate that cross-species transmission is not the rate-limiting step in pandemic retrovirus emergence and suggest that it may be possible to predict and prevent disease emergence by surveillance of populations exposed to animal reservoirs and interventions to decrease risk factors, such as primate hunting.

Naturally acquired simian retrovirus infections in central African hunters

BACKGROUND Hunting and butchering of wild non-human primates infected with simian immunodeficiency virus (SIV) is thought to have sparked the HIV pandemic. Although SIV and other primate retroviruses infect laboratory workers and zoo workers, zoonotic retrovirus transmission has not been documented in natural settings. We investigated zoonotic infection in individuals living in central Africa. METHODS We obtained behavioural data, plasma samples, and peripheral blood lymphocytes from individuals living in rural villages in Cameroon. We did serological testing, PCR, and sequence analysis to obtain evidence of retrovirus infection. FINDINGS Zoonotic infections with simian foamy virus (SFV), a retrovirus endemic in most Old World primates, were identified in people living in central African forests who reported direct contact with blood and body fluids of wild non-human primates. Ten (1%) of 1099 individuals had antibodies to SFV. Sequence analysis from these individuals revealed three geographically-independent human SFV infections, each of which was acquired from a distinct non-human primate lineage: De Brazzas guenon (Cercopithecus neglectus), mandrill (Mandrillus sphinx), and gorilla (Gorilla gorilla), two of which (De Brazzas guenon and mandrill) are naturally infected with SIV. INTERPRETATION Our findings show that retroviruses are actively crossing into human populations, and demonstrate that people in central Africa are currently infected with SFV. Contact with non-human primates, such as happens during hunting and butchering, can play a part in the emergence of human retroviruses and the reduction of primate bushmeat hunting has the potential to decrease the frequency of disease emergence.

A panel of MHC class I restricted viral peptides for use as a quality control for vaccine trial ELISPOT assays.

Vaccines in general and HIV vaccines in particular are focusing ever more on the induction of cellular immunity specifically the generation of cytotoxic T cells (CTL). As progress is made towards developing a safe and effective HIV vaccine, there is a need for a robust, sensitive and reproducible assay to evaluate vaccine-induced cellular immunogenicity in Phase II/III trials. The enzyme-linked immunospot (ELISPOT) assay fits these criteria and is a technology that is readily transferable and amenable to high-through-put screening. There is a need for reagents that can be used as positive controls and for optimizing and standardizing the assay. We selected a panel of 23 8-11 mer Influenza virus (Flu), Cytomegalovirus (CMV) and Epstein Barr virus (EBV) epitopes recognized by CD8 positive T cells and presented by 11 class I HLA-A and HLA-B alleles whose cumulative frequencies represent >100% of Caucasian individuals. We examined interferon-gamma (IFN-gamma) secretion in peripheral blood mononuclear cells (PBMC) incubated with the peptides using a modified ELISPOT assay. IFN-gamma secretion was detected in 15/17 (88%) HIV-1 seronegative and 14/20 (70%) HIV-1 seropositive individuals. Release of IFN-gamma in response to the pool of peptides was CD8+ T cell mediated and HLA restricted. In vitro stimulation of PBMC with individual peptides or the pool of peptides led to the expansion of T cells capable of killing target cells expressing the appropriate viral antigen in a CTL assay. The size, shape and appearance of the spots produced using this peptide panel provided a standard for the establishment of acceptance criteria of spots for the evaluation of ELISPOT plates using an automated reader system.

Effect of Human Immunodeficiency Virus Type 1 (HIV-1) Subtype on Disease Progression in Persons from Rakai, Uganda, with Incident HIV-1 Infection

BACKGROUND Human immunodeficiency virus type 1 (HIV-1) subtypes differ in biological characteristics that may affect pathogenicity. METHODS We determined the HIV-1 subtype-specific rates of disease progression among 350 HIV-1 seroconverters. Subtype, viral load, and CD4(+) cell count were determined. Cox proportional hazards regression modeling was used to estimate adjusted hazard ratios (HRs) of progression to acquired immunodeficiency syndrome (AIDS) (defined as a CD4(+) cell count of < or =250 cells/mm(3)) and to AIDS-associated death. RESULTS A total of 59.1% of study subjects had subtype D strains, 15.1% had subtype A, 21.1% had intersubtype recombinant subtypes, 4.3% had multiple subtypes, and 0.3% had subtype C. Of the 350 subjects, 129 (37%) progressed to AIDS, and 68 (19.5%) died of AIDS. The median time to AIDS onset was shorter for persons with subtype D (6.5 years), recombinant subtypes (5.6 years), or multiple subtypes (5.8 years), compared with persons with subtype A (8.0 years; P = .022). Relative to subtype A, adjusted HRs of progression to AIDS were 2.13 [95% confidence interval {CI}, 1.10-4.11] for subtype D, 2.16 [95% CI, 1.05-4.45] for recombinant subtypes, and 4.40 [95% CI, 1.71-11.3] for multiple subtypes. The risk of progression to death was significantly higher for subtype D (adjusted HR, 5.65; 95% CI, 1.37-23.4), recombinant subtypes (adjusted HR, 6.70; 95% CI, 1.56-28.8), and multiple subtypes (adjusted HR, 7.67; 95% CI, 1.27-46.3), compared with subtype A. CONCLUSIONS HIV disease progression is affected by HIV-1 subtype. This finding may impact decisions on when to initiate antiretroviral therapy and may have implications for future trials of HIV-1 vaccines aimed at slowing disease progression.

A Phase I Evaluation of the Safety and Immunogenicity of Vaccination with Recombinant gp160 in Patients with Early Human Immunodeficiency Virus Infection

BACKGROUND Despite multiple antiviral humoral and cellular immune responses, infection with the human immunodeficiency virus (HIV) results in a progressively debilitating disease. We hypothesized that a more effective immune response could be generated by post-infection vaccination with HIV-specific antigens. METHODS We performed a phase I trial of the safety and immunogenicity of a vaccine prepared from molecularly cloned envelope protein, gp160, in 30 volunteer subjects with HIV infection in Walter Reed stage 1 or 2. The vaccine was administered either on days 0, 30, and 120 or on days 0, 30, 60, 120, 150, and 180. HIV-specific humoral and cellular immune responses were measured; local and systemic reactions to vaccination, including general measures of immune function, were monitored. RESULTS In 19 of the 30 subjects both humoral and cellular immunity to HIV envelope proteins increased in response to vaccination with gp160. Seroconversion to selected envelope epitopes was observed, as were new T-cell proliferative responses to gp160. Response was associated with the CD4 cell count determined before vaccination (13 of 16 subjects [81 percent] with greater than 600 cells per milliliter responded, as compared with 6 of 14 [43 percent] with less than or equal to 600 cells per milliliter; P = 0.07) and with the number of injections administered (87 percent of subjects randomly assigned to receive six injections responded, as compared with 40 percent of those assigned to three injections; P = 0.02). Local reactions at the site of injection were mild. There were no adverse systemic reactions, including diminution of general in vitro or in vivo cellular immune function. After 10 months of follow-up, the mean CD4 count had not decreased in the 19 subjects who responded, but it had decreased by 7.3 percent in the 11 who did not respond. CONCLUSIONS This gp160 vaccine is safe and immunogenic in volunteer patients with early HIV infection. Although it is too early to know whether this approach will be clinically useful, further scientific and therapeutic evaluation of HIV-specific vaccine therapy is warranted. Similar vaccines may prove to be effective for other chronic infections.

Epidemiologic and biologic characterization of a cohort of human immunodeficiency virus type 1 highly exposed, persistently seronegative female sex workers in northern Thailand

Characterization of persons highly exposed to human immunodeficiency virus (HIV)-1 who remain uninfected may help define protective immunity. Seventeen HIV-1-seronegative Thai female sex workers (CSWs) with epidemiologic evidence of exposure to HIV-1 were studied for humoral immune responses and phenotypic and genotypic analyses of HLA class I and CCR5 allelic profiles. Infected CSWs and low-risk HIV-1-seronegative Thai women were controls. Highly exposed, persistently seronegative (HEPS) CSWs did not differ from HIV-infected CSWs in HIV risks, condom use, or sexually transmitted diseases. Significant differences were seen in humoral immune responses: gp160-specific IgA responses were detected in cervicovaginal lavage fluids in 6 of 13 HEPS CSWs but 0 of 21 seronegative subjects. All women had wild-type CCR5. HEPS CSWs were more likely to have the HLA-B18 phenotype and genotype than were matched controls (corrected P=.018). Epidemiologic exposure to HIV-1 without apparent infection, an unusual distribution of HLA class I alleles, and HIV-1 gp160-specific IgA responses suggest a biologic basis for this phenomenon.