Scientific Publications

DNA- and modified virus Ankara (MVA)-vectored candidate vaccines expressing human immunodeficiency virus type 1 (HIV-1) clade A-derived p24/p17 gag fused to a string of HLA class I epitopes, called HIVA, were tested in phase I trials in healthy, HIV-1/2-uninfected adults in Oxford, United Kingdom. Eighteen volunteers were vaccinated with pTHr.HIVA DNA (IAVI-001) alone, 8 volunteers received MVA.HIVA (IAVI-003) alone and 9 volunteers from study IAVI-001 were boosted with MVA.HIVA 9-14 months after DNA priming (IAVI-005). Immunogenicity results observed in these trials was published previously [Mwau M, Cebere I, Sutton J, Chikoti P, Winstone N, Wee EG-T, et al. An HIV-1 clade A vaccine in clinical trials: stimulation of HIV-specific T cell responses by DNA and recombinant modified vaccinia virus Ankara (MVA) vaccines in humans. J Gen Virol 2004;85:911-9]. Here, we report on the safety of the two vaccines and the vaccine regimes. Overall, both candidate vaccines were safe and well tolerated. There were no reported vaccine-related adverse events over the 6-month period of the study and up to 2 years after the last vaccination. There were no moderate or severe local symptoms recorded after the pTHr.HIVA DNA intramuscular administration. Almost all participants experienced local reactogenicity events such as redness and induration after MVA.HIVA intradermal injection. Thus, the results from these initial small phase I trials administering the pTHr.HIVA DNA and MVA.HIVA vaccines either alone or in a prime-boost regime to healthy HIV-1/2-negative adults indicated that the vaccines were safe and warranted further testing of this approach in larger phase I/II studies.

The International AIDS Vaccine Initiative has established a consortium to elucidate mechanisms of protection conferred by live attenuated simian immunodeficiency virus vaccines in monkeys. Here, the strategies defining key components of the protective immune response elicited by these vaccines are discussed.

Adenovirus 5 (Ad5) vectors show promise as human immunodeficiency virus vaccine candidates. Indian rhesus macaques vaccinated with Ad5-gag controlled simian-human immunodeficiency virus SHIV89.6P viral replication in the absence of Env immunogens that might elicit humoral immunity. Here we immunized 15 macaques using either a homologous Ad5-gag/Ad5-gag (Ad5/Ad5) or a heterologous DNA-gag/Ad5-gag (DNA/Ad5) prime-boost regimen and challenged them with a high dose of simian immunodeficiency virus SIVmac239. Macaques vaccinated with the DNA/Ad5 regimen experienced a brief viral load nadir of less than 10,000 viral copies per ml blood plasma that was not seen in Mamu-A*01-negative DNA/Ad5 vaccinees, Mamu-A*01-positive Ad5/Ad5 vaccinees, or vaccine-naive controls. Interestingly, most of these animals were not durably protected from disease progression when challenged with SIVmac239. To investigate the reasons underlying this short-lived vaccine effect, we investigated breadth of the T-cell response, immunogenetic background, and viral escape from CD8+ lymphocytes that recognize immunodominant T-cell epitopes. We show that these animals do not mount unusually broad cellular immune response, nor do they express unusual major histocompatibility complex class I alleles. Viral recrudescence occurred in four of the five Mamu-A*01-positive vaccinated macaques. However, only a single animal in this group demonstrated viral escape in the immunodominant Gag181-189 CM9 response. These results suggest that viral 'breakthrough' in vaccinated animals and viral escape are not inextricably linked and underscore the need for additional research into the mechanisms of vaccine failure.

In the absence of strategies for reliable induction of antibodies broadly neutralizing human immunodeficiency virus type 1 (HIV-1), vaccine efforts have shifted toward the induction of cell-mediated immunity. Here we describe the construction and immunogenicity of novel T-cell vaccine NS1.HIVA, which delivers the HIV-1 clade A consensus-derived immunogen HIVA on the surface of tubular structures spontaneously formed by protein NS1 of bluetongue virus. We demonstrated that NS1 tubules can accommodate a protein as large as 527 amino acids without losing their self-assembly capability. When injected into BALB/c mice by several routes, chimeric NS1.HIVA tubules induced HIV-1-specific major histocompatibility complex class I-restricted T cells. These could be boosted by modified virus Ankara expressing the same immunogen and generate a memory capable of gamma interferon (IFN-gamma) production, proliferation, and lysis of sensitized target cells. Induced memory T cells readily produced IFN-gamma 230 days postimmunization, and upon a surrogate virus challenge, NS1.HIVA vaccine alone decreased the vaccinia virus vv.HIVA load in ovaries by 2 orders of magnitude 280 days after immunization. Thus, because of its T-cell immunogenicity and antigenic simplicity, the NS1 delivery system could serve as a priming agent for heterologous prime-boost vaccination regimens. Its usefulness in primates, including humans, remains to be determined.

T cell receptor-transgenic F5 mice were used to assess primary CD8+ T cell responses to a modified virus Ankara (MVA)-vectored vaccine in the absence of CD4+ T cell help. Naive, CD8-enriched, CFSE-labelled F5 cells were transferred into normal or CD4+ cell-depleted mice and the mice were vaccinated with MVA.HIVA-NP. At different time points during the primary response, F5 cells were re-isolated and analysed on divisional basis for a number of parameters. We demonstrated that the primary CD8+ T cell response in the absence of CD4+ T cell help differed from that in normal CD4+ cell-undepleted mice. While in the absence of CD4+ T cell help, the initial migratory progress from the local response to a systemic one was not grossly affected, the proportion of dying F5 cells during the expansion phase was markedly increased and resulted in an overall smaller expansion and significantly decreased frequency of CD8+ T cell memory after contraction. T cells primed without help displayed accelerated proliferation and activation, while expression of interferon-gamma remained similar. These phenomena were observed in the lymph nodes draining the MVA.HIVA-NP immunization site and were similar, but delayed by 2-3 days in spleen and non-draining lymph nodes.

Analysis of the human immunodeficiency virus type 1 (HIV-1) cytolytic T lymphocyte (CTL) epitopes recognized by the targeted population is critical for HIV-1 vaccine design. Peripheral blood mononuclear cells from 47 Indian subjects at different stages of HIV-1 infection were tested for HIV-1 Gag-, Nef-, and Env-specific T cell responses by interferon (IFN)- gamma enzyme-linked immunospot (ELISPOT) assay, using pools of overlapping peptides. The Gag and Nef antigens were targeted by 83% and 36% of responders. Five immunodominant regions, 4 in Gag and 1 in Nef, were identified in the study; these regions are conserved across clades, including the African subtype C clade. Three antigenic regions were also found to be recognized by CTLs of the study participants. These regions were not identified as immunodominant regions in studies performed in Africa, which highlights the importance of differential clustering of responses within HIV-1 subtype C. Twenty-six putative epitopes--15 Gag (10 in p24 and 5 in p17), 10 Nef, and 1 Env (gp 41)--were predicted using a combination of peptide matrix ELISPOT assay and CTL epitope-prediction software. Ninety percent of the predicted epitopes were clustered in the conserved immunodominant regions of the Gag and Nef antigens. Of 26 predicted epitopes, 8 were promiscuous, 3 of which were highly conserved across clades. Three Gag and 4 Nef epitopes were novel. The identification of conserved epitopes will be important in the planning of an HIV-1 vaccine strategy for subtype C-affected regions.

The dynamics of primary CD8+ T cell responses following administration of modified virus Ankara (MVA)- and DNA-vectored vaccines was investigated in a mouse model. To overcome the low frequency of naive antigen-specific precursors and follow the early expansion events, naive CFSE-labelled T cell receptor-transgenic F5 lymphocytes were transferred into syngeneic non-transgenic recipients prior to vaccination. Using the i.d., i.v. and i.m. routes and increasing recombinant MVA (rMVA) vaccine doses, the primary response was analysed on a divisional basis at local and distant lymphoid organs at various times after vaccination. The results indicated that F5 cell divisions were initiated in the local draining lymph nodes and cells only after five to six divisions appeared at more distant sites. The rMVA dose affected frequencies of cells entering division and at the peak response. When priming induced by rMVA and plasmid DNA was compared, dramatic differences in the cycling patterns were observed with plasmid DNA inducing a response slower and more sustained over the first 2 wk than rMVA. Both rMVA and DNA induced comparable IFN-gamma production, which increased with cell divisions. Taken together, the vaccine type, dose and route have a strong influence on the spatial and temporal patterns of initial T cell responses.

Serial samples from source plasma donors with confirmed new HIV infection were investigated for low-level viremia (LLV) (ie, < 100 genome copies [cp]/mL) at time points preceding the period of steadily rising viremia above 100 cp/mL (ramp-up viremia). Fifteen of 44 plasma donor panels previously studied for the dynamics of HIV viremia during primary infection contained 70 samples with undetectable HIV-1 RNA by quantitative polymerase chain reaction (PCR). On retesting with a sensitive qualitative reverse transcriptase PCR assay (95% detection at 4 cp/mL), we identified LLV in 13 of 15 panels and 23 of 69 retested samples. In 6 panels, a total of 11 samples (1-3 per panel) were consistent with LLV before ramp-up viremia. These samples preceded the first sample with >100 cp/mL HIV by 9 to 25 days (median = 18 days) and were separated from the latter by at least 1 sample with undetectable viremia by the qualitative PCR assay. We conclude that LLV is not uncommon during the very early period of primary HIV infection preceding ramp-up viremia. It is not known if blood is infectious during this period; however, given the low viral concentrations and transient nature of the observed viremic 'blips,' the risk of infectivity can be assumed to be small.

Cytokine flow cytometry (CFC) or intracellular cytokine staining (ICS) can quantitate antigen-specific T cell responses in settings such as experimental vaccination. Standardization of ICS among laboratories performing vaccine studies would provide a common platform by which to compare the immunogenicity of different vaccine candidates across multiple international organizations conducting clinical trials. As such, a study was carried out among several laboratories involved in HIV clinical trials, to define the inter-lab precision of ICS using various sample types, and using a common protocol for each experiment (see additional files online).

The genetic diversity of human immunodeficiency virus type 1 (HIV-1) raises the question of whether vaccines that include a component to elicit antiviral T cell immunity based on a single viral genetic clade could provide cellular immune protection against divergent HIV-1 clades. Therefore, we quantified the cross-clade reactivity, among unvaccinated individuals, of anti-HIV-1 T cell responses to the infecting HIV-1 clade relative to other major circulating clades.