Generation and immunogenicity of novel HIV/AIDS vaccine candidates targeting HIV-1 Env/Gag-Pol-Nef antigens of clade C

Recombinants based on the attenuated vaccinia virus strains MVA and NYVAC are considered candidate vectors against different human diseases. In this study we have generated and characterized in BALB/c and in transgenic HHD mice the immunogenicity of two attenuated poxvirus vectors expressing in a single locus (TK) the codon optimized HIV-1 genes encoding gp120 and Gag-Pol-Nef (GPN) polyprotein of clade C (referred as MVA-C and NYVAC-C). In HHD mice primed with either MVA-C or NYVAC-C, or primed with DNA-C and boosted with the poxvirus vectors, the splenic T cell responses against clade C peptides spanning gp120/GPN was broad and mainly directed against Gag-1, Env-1 and Env-2 peptide pools. In BALB/c mice immunized with the homologous or the heterologous combination of poxvirus vectors or with Semliki forest virus (SFV) vectors expressing gp120/GPN, the immune response was also broad but the most immunogenic peptides were Env-1, GPN-1 and GPN-2. Differences in the magnitude of the cellular immune responses were observed between the poxvirus vectors depending on the protocol used. The specific cellular immune response triggered by the poxvirus vectors was Th1 type. The cellular response against the vectors was higher for NYVAC than for MVA in both HHD and BALB/c mice, but differences in viral antigen recognition between the vectors was observed in sera from the poxvirus-immunized animals. These results demonstrate the immunogenic potential of MVA-C and NYVAC-C as novel vaccine candidates against clade C of HIV-1.

Evaluation of immunogenicity and efficacy of combined DNA and adjuvanted protein vaccination in a human immunodeficiency virus type 1/murine leukemia virus pseudotype challenge model

A DNA plasmid encoding human immunodeficiency virus type 1 (HIV-1) env, nef and tat genes was used in mice in a prime-boost immunization regimen with the corresponding recombinant proteins. The genetic immunogen was delivered with a gene gun and the proteins were injected intramuscularly together with the adjuvant AS02A. Immunizations were followed by experimental challenge with pseudotyped HIV-1 subtype A or B virus. In an initial experiment in which animals were challenged four weeks after the final immunization, all single modality and prime-boost vaccinations resulted in a significant level of protection as compared to control animals. There was a trend for DNA-alone immunization yielding the highest protection. In a subsequent study, a late challenge was performed 19 weeks after the final immunization. All groups having received the DNA vaccine, either alone or in combination with adjuvanted protein, exhibited strong protection against HIV replication. The subtype-specific protection against the experimental HIV challenge was significantly stronger than the cross-protection. Cellular and humoral immune responses were assessed during immunization and after challenge, but without clear correlation to protection against HIV replication. The data suggest that either DNA or protein antigens alone provide partial protection against an HIV-1/MuLV challenge and that DNA immunization is essential for achieving very high levels of efficacy in this murine HIV-1 challenge model. While prime-boost combinations were more immunogenic than DNA alone, they did not appear to provide any further enhancement over DNA vaccine mediated efficacy. The DNA immunogen might prime low levels of CD8+ T cells responsible for virus clearance or possibly a yet unidentified mechanism of protection.

Design of immunogens that present the crown of the HIV-1 V3 loop in a conformation competent to generate 447-52D-like antibodies

gp120 is a subunit of the envelope glycoprotein of HIV-1. The third variable loop region of gp120 (V3 loop) contains multiple immunodominant epitopes and is also functionally important for deciding cell-tropism of the virus. 447-52D is a monoclonal antibody that recognizes the conserved tip of the V3 loop in a beta-turn conformation. This antibody has previously been shown to neutralize diverse strains of the virus. In an attempt to generate an immunogen competent to generate 447-52D-like antibodies, the known epitope of 447-52D was inserted at three different surface loop locations in the small, stable protein Escherichia coli Trx (thioredoxin). At one of the three locations (between residues 74 and 75), the insertion was tolerated, the resulting protein was stable and soluble, and bound 447-52D with an affinity similar to that of intact gp120. Upon immunization, the V3 peptide-inserted Trx scaffold was able to generate anti-V3 antibodies that could compete out 447-52D binding to gp120. Epitope mapping studies demonstrated that these anti-V3 antibodies recognized the same epitope as 447-52D. Although the 447-52D-type antibodies were estimated to be present at concentrations of 50-400 microg/ml of serum, these were not able to effect neutralization of strains like JRFL and BAL but could neutralize the sensitive MN strain. The data suggest that because of the low accessibility of the V3 loop on primary isolates such as JRFL, it will be difficult to elicit a V3-specific, 447-52D-like antibody response to effectively neutralize such isolates.

Combination DNA plus protein HIV vaccines

A major challenge in developing an HIV vaccine is to identify immunogens and delivery methods that will elicit balanced humoral and cell mediate immunities against primary isolates of HIV with diverse sequence variations. Since the discovery of using protein coding nucleic acids (mainly DNA but also possible RNA) as a means of immunization in the early 1990s, there has been rapid progress in the creative use of this novel approach for the development of HIV vaccines. Although the initial impetus of using DNA immunization was for the induction of strong cell-mediated immunity, recent studies have greatly expanded our understanding on the potential role of DNA immunization to elicit improved quality of antibody responses. This function is particularly important to the development of HIV vaccines due to the inability of almost every previous attempt to develop broadly reactive neutralizing antibodies against primary HIV-1 isolates. Similar to the efforts of developing cell mediated immunity by using a DNA prime plus viral vector boost approach, the best antibody responses with DNA immunization were achieved when a protein boost component was included as part of the immunization schedule. Current experience has suggested that a combination DNA plus protein vaccination strategy is able to utilize the benefits of DNA and protein vaccines to effectively induce both cell-mediated immunity and antibody responses against invading organisms.

Prime-boost strategies in DNA vaccines

Induction of HIV-specific T-cell responses by vaccines may facilitate efficient control of HIV replication. Plasmid DNA vaccines and recombinant fowlpox virus (rFPV) vaccines are promising HIV-1 vaccine candidates, although delivering either vaccine alone may be insufficient to induce sufficient T-cell responses. A consecutive immunization strategy, known as "prime-boost," involving priming with DNA and boosting with rFPV vaccines encoding multiple common HIV antigens, is used to induce broad and high-level T-cell immunity and ameliorate AIDS in macaques. This vaccine strategy is proceeding to clinical trials. This chapter describes the use of prime-boost vaccines to induce T-cell responses against HIV-1 and protective immunity against AIDS in macaques. Methods for the construction of the vaccines, the use of animal models, and the detection of immune responses are described.

Building collaborative networks for HIV/AIDS vaccine development: the AVIP experience

The need for an effective HIV/AIDS vaccine is imperative to halt a pandemic that involves more than 40 million individuals worldwide as of 2005 and is causing enormous socio-economic losses, especially in developing countries (DC). The overall failure of more than two decades of HIV vaccine research justifies the demands for a concerted effort for the rapid development of new and efficacious vaccines against HIV/AIDS. In this context, building international collaborative networks is a must for speeding up scientific research and optimizing the use of funding in a synergistic fashion, as resources for HIV/AIDS are limited and do not involve most of the biggest Pharmas that are more interested in drug discovery. The AIDS Vaccine Integrated Project (AVIP) consortium is an example of synergistic partnership of international European Union and DC experts with a common research goal. AVIP is a European Commission-funded (FP-6), consortium-based, 5-year program directed to the fast development of new HIV/AIDS vaccine candidates to be tested in phase I clinical trials in Europe for future advancement to phase II/III testing in DC. To ensure their rapid development, AVIP novel combined vaccines include both regulatory and structural HIV antigens, which have already been tested, as single components, in phase I clinical trials. In particular, such combination vaccines may be superior to earlier vaccine candidates, the vast majority of which are based only on either structural or regulatory HIV products. In fact, the generation of immune responses to both types of viral antigens expressed either early (regulatory products) or late (structural products) during the viral life cycle can maximize immune targeting of both primary or chronic viral infection. Further, the rational design of combined vaccines allows exploitation of immunomodulatory functions of HIV regulatory proteins, which can improve immunity against structural vaccine components. The building of the AVIP consortium and its scientific strategy will be reviewed in this paper as an example of the establishment of a consortium regulated by a specific intellectual property agreement.

Recombinant vesicular stomatitis virus as an HIV-1 vaccine vector

Recombinant vesicular stomatitis virus (rVSV) is currently under evaluation as a human immunodeficiency virus (HIV)-1 vaccine vector. The most compelling reasons to develop rVSV as a vaccine vector include a very low seroprevalence in humans, the ability to infect and robustly express foreign antigens in a broad range of cells, and vigorous growth in continuous cell lines used for vaccine manufacture. Numerous preclinical studies with rVSV vectors expressing antigens from a variety of human pathogens have demonstrated the versatility, flexibility, and potential efficacy of the rVSV vaccine platform. When administered to nonhuman primates (NHPs), rVSV vectors expressing HIV-1 Gag and Env elicited robust HIV-1-specific cellular and humoral immune responses, and animals immunized with rVSV vectors expressing simian immunodeficiency virus (SIV) Gag and HIV Env were protected from AIDS after challenge with a pathogenic SIV/HIV recombinant. However, results from an exploratory neurovirulence study in NHPs indicated that these prototypic rVSV vectors might not be adequately attenuated for widespread use in human populations. To address this safety concern, a variety of different attenuation strategies, designed to produce a range of further attenuated rVSV vectors, are currently under investigation. Additional modifications of further attenuated rVSV vectors to upregulate expression of HIV-1 antigens and coexpress molecular adjuvants are also being developed in an effort to balance immunogenicity and attenuation.

Ancestral and consensus envelope immunogens for HIV-1 subtype C

Immunogens based on "centralized" (ancestral or consensus) HIV-1 sequences minimize the genetic distance between vaccine strains and contemporary viruses and should thus elicit immune responses that recognize a broader spectrum of viral variants. However, the biologic, antigenic and immunogenic properties of such inferred gene products have to be validated experimentally. Here, we report the construction and characterization of the first full-length ancestral (AncC) and consensus (ConC) env genes of HIV-1 (group M) subtype C. The codon-usage-optimized genes expressed high levels of envelope glycoproteins that were incorporated into HIV-1 virions, mediated infection via the CCR5 co-receptor and retained neutralizing epitopes as recognized by plasma from patients with chronic HIV-1 subtype C infection. Guinea pigs immunized with AncC and ConC env DNA developed high titer binding, but no appreciable homologous or heterologous neutralizing antibodies. When tested by immunoblot analysis, sera from AncC and ConC env immunized guinea pigs recognized a greater number of primary subtype C envelope glycoproteins than sera from guinea pigs immunized with a contemporary subtype C env control. Mice immunized with AncC and ConC env DNA developed gamma interferon T cell responses that recognized overlapping peptides from the cognate ConC and a heterologous subtype C Env control. Thus, both AncC and ConC env genes expressed functional envelope glycoproteins that were immunogenic in laboratory animals and elicited humoral and cellular immune responses of comparable breadth and magnitude. These results establish the utility of centralized HIV-1 subtype C Env immunogens and warrant their continued evaluation as potential components of future AIDS vaccines.

Cross-subtype T-cell immune responses induced by a human immunodeficiency virus type 1 group m consensus env immunogen

The genetic diversity among globally circulating human immunodeficiency virus type 1 (HIV-1) strains is a serious challenge for HIV-1 vaccine design. We have generated a synthetic group M consensus env gene (CON6) for induction of cross-subtype immune responses and report here a comparative study of T-cell responses to this and natural strain env immunogens in a murine model. Three different strains of mice were immunized with CON6 as well as subtype A, B, or C env immunogens, using a DNA prime-recombinant vaccinia virus boost strategy. T-cell epitopes were mapped by gamma interferon enzyme-linked immunospot analysis using five overlapping Env peptide sets from heterologous subtype A, B, and C viruses. The CON6-derived vaccine was immunogenic and induced a greater number of T-cell epitope responses than any single wild-type subtype A, B, and C env immunogen and similar T-cell responses to a polyvalent vaccine. The responses were comparable to within-clade responses but significantly more than between-clade responses. The magnitude of the T-cell responses induced by CON6 (measured by individual epitope peptides) was also greater than the magnitude of responses induced by individual wild-type env immunogens. Though the limited major histocompatibility complex repertoire in inbred mice does not necessarily predict responses in nonhuman primates and humans, these results suggest that synthetic centralized env immunogens represent a promising approach for HIV-1 vaccine design that merits further characterization.

Immunogenicity testing of a novel engineered HIV-1 envelope gp140 DNA vaccine construct

DNA vaccines expressing the envelope (env) of the human immunodeficiency virus type 1 (HIV-1) have been relatively ineffective at generating strong immune responses. In this study, we described the development of a recombinant plasmid DNA (pEK2P-B) expressing an engineered codon-optimized envelope gp140 gene of primary (nonrecombinant) HIV-1 subtype B isolate 6101. Codon usage and RNA optimization of HIV-1 structural genes has been shown to increase protein expression in vitro as well as in the context of DNA vaccines in vivo. To further increase the expression, a synthetic IgE leader with kozak sequences were fused into the env gene. The cytoplasmic tail of the gene was also truncated to prevent recycling. The expression of env by the recombinant pEK2P-B was evaluated using T7 coupled transcription/translation. The construct demonstrated high expression of the HIV-1 env gene in eukaryotic cells as demonstrated in transfected 293-T and RD cells. Immunogenicity of pEK2P-B was evaluated in mice using IFN-gamma ELISpot assay, and the construct was found to be highly immunogenic and crossreactive with HIV-1 clade C env peptides. Three immunodominant peptides were also mapped out. Furthermore, by performing a CFSE flow cytometry-based proliferation assay, 2.4 and 1.5% proliferation was observed in CD4+, CD8+, and CCR+ memory T cells, respectively. Therefore, this engineered synthetic optimized env DNA vaccine may be useful in DNA vaccine and other studies of HIV-1 immunogenicity.

Assembly of human immunodeficiency virus (HIV) antigens on bacteriophage T4: a novel in vitro approach to construct multicomponent HIV vaccines

Bacteriophage T4 capsid is an elongated icosahedron decorated with 155 copies of Hoc, a nonessential highly antigenic outer capsid protein. One Hoc monomer is present in the center of each major capsid protein (gp23*) hexon. We describe an in vitro assembly system which allows display of HIV antigens, p24-gag, Nef, and an engineered gp41 C-peptide trimer, on phage T4 capsid surface through Hoc-capsid interactions. In-frame fusions were constructed by splicing the human immunodeficiency virus (HIV) genes to the 5' or 3' end of the Hoc gene. The Hoc fusion proteins were expressed, purified, and displayed on hoc(-) phage particles in a defined in vitro system. Single or multiple antigens were efficiently displayed, leading to saturation of all available capsid binding sites. The displayed p24 was highly immunogenic in mice in the absence of any external adjuvant, eliciting strong p24-specific antibodies, as well as Th1 and Th2 cellular responses with a bias toward the Th2 response. The phage T4 system offers new direction and insights for HIV vaccine development with the potential to increase the breadth of both cellular and humoral immune responses.

Molecular analysis and phylogenetic characterization of HIV in Iran

The rate of human immunodeficiency virus type 1 (HIV-1) infection in Iran has increased dramatically in the last few years. While the earliest cases were found in hemophiliacs, intravenous drug users are now fueling the outbreak. In this study, both the 122 clones of HIV-1 gag p17 and the 131 clones of env V1-V5 region were obtained from 61 HIV-1 seropositives belonging to these two groups in Iran. HIV-1 subtyping and phylogenetic analysis was done by heteroduplex mobility assays (HMA) and multiple clone sequencing. The result indicated all hemophiliacs are infected with HIV-1 subtype B and all intravenous drug users are infected with HIV-1 subtype A. Since intravenous drug abuse is the major transmission route in Iran, HIV-1 subtype A is likely to be the dominant viral subtype circulating in the country. The analysis of genetic distances showed subtype B viruses in Iran to be twice as heterogeneous as the subtype A viruses. In conclusion, this first molecular study of HIV-1 genotypes in Iran suggests two parallel outbreaks in distinct high-risk populations and may offer clues to the origin and spread of infection in Iran.

Inhibition of viral assembly in murine cells by HIV-1 matrix

In human cells, the N-terminal matrix (MA) domain of the human immunodeficiency virus type 1 (HIV-1) Gag targets assembly to specific membrane compartments. In murine fibroblasts, membrane targeting of Gag and assembly of HIV-1 are inefficient. These deficiencies are relieved by replacement of HIV-1 MA with murine leukemia virus (MLV) MA in chimeric proviruses. In this study, we examined chimeric HIV-1 carrying tandem MLV and HIV-1 MA domains and found that the addition of MLV MA to the N-terminus of HIV-1 Gag enhanced membrane binding in murine cells, but was not sufficient to stimulate virus production. Removal of HIV MA was required to observe more efficient Gag processing and increased virus production in murine cells. Deletion of the globular head of MA also alleviated the blocks to membrane binding and Gag processing in murine cells, yet did not lead to increased virus production. These MA-dependent, cell-type-specific phenotypes suggest that host factors interact with the globular head of MA to regulate membrane binding and additional membrane-independent step(s) required for assembly.

HIV-1 Matrix Protein p17 Modulatesin VivoPreactivated Murine T-Cell Response and Enhances the Induction of Systemic and Mucosal Immunity Against Intranasally Co-administered Antigens

HIV-1 p17 is a viral cytokine that acts on preactivated, but not on resting, human T cells promoting proliferation, proinflammatory cytokines release and HIV-1 replication, after binding to a cellular receptor (p17R). Here, we demonstrate that p17Rs are expressed on activated murine T cells, which respond to p17 stimulation similarly to their human counterpart. We developed a mouse model of abortive HSV-1 infection to induce T cell activation in vivo. Preactivated cells expressed p17Rs and were highly susceptible to p17 stimulation, which triggered proinflammatory cytokines release and promoted CD4+ T cell survival and expansion. Coculture of in vivo activated splenocytes with macrophages in the presence of p17 further increased their ability to produce IFN-gamma. The presence of macrophages and activated T cells at mucosal sites prompted us to investigate the immunomodulatory activities of p17 in vivo. Intranasal coadministration of p17 with beta-galactosidase (beta-gal) resulted in improved beta-gal specific cellular and humoral immune responses at systemic and mucosal levels. It is well established that HIV-1 replication is driven in an autocrine/paracrine manner by endogenously produced proinflammatory cytokines. Our results highlight the role of p17 in sustaining cellular activation and inflammation, thereby promoting a permissive microenvironment for HIV-1 replication. In addition, p17 is a promising candidate antigen, exhibiting immunomodulatory/adjuvant properties, that need to be exploited in the development of HIV/AIDS vaccines.

Motif inference reveals optimal CTL epitopes presented by HLA class I alleles highly prevalent in southern Africa

HIV-specific CTL play a central role in immune control of HIV. The basis for understanding the success or failure of this immune response requires identification of the specific epitopes targeted by CTL. However, in populations most severely affected by the global epidemic, this fundamental knowledge is hindered by the lack of characterization of many of the HLA class I alleles highly prevalent in such populations. Overall, the peptide-binding motif has been determined for a small minority (9%) of HLA class I alleles, with a strong bias toward those alleles prevalent in Caucasoid populations. These studies therefore set out to define, in a South African Zulu/Xhosa population at the epicenter of the epidemic, the epitopes presented by alleles highly prevalent, but for which the peptide-binding motif had not been characterized. Using a method of motif inference, epitopes presented by four such alleles prevalent in the Zulu/Xhosa population of Durban, South Africa, namely, B*3910, B*4201, B*8101, and Cw*1801, are described. Importantly, this approach may additionally facilitate optimization of epitopes in certain instances where conflicting reports in the literature exist regarding the peptide-binding motif, such as for HLA-A*2902, also highly prevalent in southern African populations. These data indicate that the previously anomalous position of HLA-A*2902 among HLA-A alleles, outside any recognized HLA-A supertype, is artifactual, and the true position of the A*2902 motif overlaps those of the A1 and A24 supertypes.

Use of a new dual-antigen enzyme-linked immunosorbent assay to detect and characterize the human antibody response to the human immunodeficiency virus type 2 envelope gp125 and gp36 glycoproteins

A dual-antigen enzyme-linked immunosorbent assay specific for human immunodeficiency virus type 2 (HIV-2) envelope proteins, ELISA-HIV2, was developed with two new recombinant polypeptides, rpC2-C3 and rgp36, derived from the HIV-2 envelope. The diagnostic performance was determined with HIV-2, HIV-1, and HIV-1/2 samples. Both polypeptides showed 100% specificity. Clinical sensitivity was 100% for rgp36 and 93.4% for rpC2-C3. ELISA-HIV2 may be used for the specific diagnosis and confirmation of HIV-2 infection.

Molecular analysis of HIV strains from a cluster of worker infections in the adult film industry, Los Angeles 2004

OBJECTIVES

In April 2004, 13 susceptible women were exposed to a single acutely HIV-1-infected man while employed to perform various sex acts for the production of adult films; three women were subsequently found to have acquired HIV infection (23% attack rate). As part of the investigation of this infection cluster, we evaluated whether viral strains collected from infected individuals were significantly related.

METHODS

We determined nucleotide sequences from the C2V3C3 and gp41 region of env and the p17 region of gag in viruses from the three infected individuals from whom specimens were available. We then compared these sequences phylogenetically to comparable sequences from available reference strains. Genotypic and phenotypic antiretroviral drug resistance was determined for plasma virus from the male index case and one female contact at a separate commercial laboratory.

RESULTS

The env and gag sequences of the HIV strains from the male index case and two of the infected women were 100% similar. Genotyping of the male index case's virus identified 12 mutations, which represented known naturally occurring polymorphisms in the subtype B consensus sequence that are not associated with antiretroviral drug resistance. Genotyping of the virus from the female contact identified 10 mutations, all of which were shared by the virus from the male index case. Phenotyping demonstrated that both viruses were susceptible to all antiretroviral drugs tested.

CONCLUSION

Molecular and virological data strongly support the epidemiological conclusion that these women were infected with an identical strain of HIV through occupational exposure to an individual with an acute HIV infection.

Characterization of antibody responses elicited by human immunodeficiency virus type 1 primary isolate trimeric and monomeric envelope glycoproteins in selected adjuvants

We previously reported that soluble, stable YU2 gp140 trimeric human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein immunogens could elicit improved breadth of neutralization against HIV-1 isolates compared to monomeric YU2 gp120 proteins. In this guinea pig immunization study, we sought to extend these data and determine if adjuvant could quantitatively or qualitatively alter the neutralizing response elicited by trimeric or monomeric immunogens. Consistent with our earlier studies, the YU2 gp140 immunogens elicited higher-titer neutralizing antibodies against homologous and heterologous isolates than those elicited by monomeric YU2 gp120. Additionally, the GlaxoSmithKline family of adjuvants AS01B, AS02A, and AS03 induced higher levels of neutralizing antibodies compared to emulsification of the same immunogens in Ribi adjuvant. Further analysis of vaccine sera indicated that homologous virus neutralization was not mediated by antibodies to the V3 loop, although V3 loop-directed neutralization could be detected for some heterologous isolates. In most gp120-inoculated animals, the homologous YU2 neutralization activity was inhibited by a peptide derived from the YU2 V1 loop, whereas the neutralizing activity elicited by YU2 gp140 trimers was much less sensitive to V1 peptide inhibition. Consistent with a less V1-focused antibody response, sera from the gp140-immunized animals more efficiently neutralized heterologous HIV-1 isolates, as determined by two distinct neutralization formats. Thus, there appear to be qualitative differences in the neutralizing antibody response elicited by YU2 gp140 compared to YU2 monomeric gp120. Further mapping analysis of more conserved regions of gp120/gp41 may be required to determine the neutralizing specificity elicited by the trimeric immunogens.

Fowlpox virus vaccines for HIV and SHIV clinical and pre-clinical trials

DNA prime and recombinant fowlpox virus (rFPV) boost vaccines were designed to express multiple HIV or SIV antigens for use in human clinical trials and in pre-clinical trials in macaques. Three sets of vaccines with matching HIV or SIV antigen sets, modified for vaccine safety considerations, were constructed and shown to express the relevant proteins. The rFPV vaccines with inserts at up to three sites, were stable on passage in chick cell culture, including during GMP manufacture of vaccines for human Phase I clinical trials. Cellular and humoral immunogenicity in mice was demonstrated using a DNA prime/rFPV boost and vaccinia virus challenge model. These data establish a preliminary safety and efficacy profile for these multigenic vaccines suggesting they are suitable for advanced development as candidate HIV vaccines.

Emergence of a three codon deletion in gag p17 in HIV type 1 subtype C long-term survivors, and general population spread

In a population-based study in northern Malawi we investigated HIV-1 subtype C gag and env gene sequences associated with long-term survival. DNA samples were available from 31 individuals surviving between population surveys carried out in the 1980s and 1990s. Most survivors with paired sequences dating from the 1980s and the 1990s had a three codon deletion in the gag p17 region of the sequence retrieved from the sample collected in the 1990s that was not present in the sequence from the same individual dating from the 1980s. This deletion was also not present in any other 1980s sequences from Malawi, but was common in samples collected in Malawi in the 1990s. The deletion is equivalent to the loss of three amino acids in the D helix region of the gag protein, and may be associated with longer survival and onward transmission.

Conflicting selective forces affect T cell receptor contacts in an immunodominant human immunodeficiency virus epitope

Cytotoxic T lymphocytes (CTLs) are critical for the control of human immunodeficiency virus, but containment of virus replication can be undermined by mutations in CTL epitopes that lead to virus escape. We analyzed the evolution in vivo of an immunodominant, HLA-A2-restricted CTL epitope and found two principal, diametrically opposed evolutionary pathways that exclusively affect T cell-receptor contact residues. One pathway was characterized by acquisition of CTL escape mutations and the other by selection for wild-type amino acids. The pattern of CTL responses to epitope variants shaped which variant(s) prevailed in the virus population. The pathways notably influenced the amount of plasma virus, as patients with efficient CTL selection had lower plasma viral loads than did patients without efficient selection. Thus, viral escape from CTL responses does not necessarily correlate with disease progression.

Control of human immunodeficiency virus replication by cytotoxic T lymphocytes targeting subdominant epitopes

Despite limited data supporting the superiority of dominant over subdominant responses, immunodominant epitopes represent the preferred vaccine candidates. To address the function of subdominant responses in human immunodeficiency virus infection, we analyzed cytotoxic T lymphocyte responses restricted by HLA-B*1503, a rare allele in a cohort infected with clade B, although common in one infected with clade C. HLA-B*1503 was associated with reduced viral loads in the clade B cohort but not the clade C cohort, although both shared the immunodominant response. Clade B viral control was associated with responses to several subdominant cytotoxic T lymphocyte epitopes, whereas their clade C variants were less well recognized. These data suggest that subdominant responses can contribute to in vivo viral control and that high HLA allele frequencies may drive the elimination of subdominant yet effective epitopes from circulating viral populations.

Criteria for selection of HIV vaccine candidates—general principles

The generation of a vaccine against HIV/AIDS is extremely challenging, as evidenced by more than 20 years of attempts. Here are highlighted the strategies adopted within the AIDS Vaccine Integrated project (AVIP) to speed up the clinical evaluation of novel vaccine candidates and to increase the chances to get an effective preventive and/or therapeutic vaccine.

Development and validation of an immunoassay for identification of recent human immunodeficiency virus type 1 infections and its use on dried serum spots

The objective was to develop and to validate an immunossay to identify recent human immunodeficiency virus type 1 (HIV-1) infections that can be used on dried serum spots (DSS). A single, indirect enzyme-linked immunosorbent assay was developed to quantify antibodies toward four HIV-1 antigens: consensus peptides of the immunodominant epitope of gp41 (IDE), consensus V3 peptides, recombinant integrase, and recombinant p24. The parameters of the logistic regression used to classify the samples were estimated on a training sample (210 serum samples) using resampling techniques to get stable estimates and then applied to a validation sample (761 serum samples). The IDE and V3 peptides were the best able to discriminate between the antibodies present in serum from recently (< or =6 months) infected individuals and those with long-lasting infection. Combined quantification of antibody binding to these two synthetic antigens allowed us to identify recent infections with an area under the receiver operating characteristic curve of 0.949 and a sensitivity of 88.3%, with a specificity of 97.6% in patients with long-term infection (but not AIDS) and 86.0% in patients suffering from AIDS with a threshold of 0.50 in the validation sample. This simple immunoassay can be used to identify recently HIV-1-infected patients. Its performance is compatible with its use in population-based studies including DSS.