Gp120-alum boosting of a Gag-Pol-Env DNA/MVA AIDS vaccine: poorer control of a pathogenic viral challenge

HIV/AIDS Vaccines: 2018

Human immunodeficiency virus (HIV) has infected 76 million people and killed an estimated 35 million. During its 40-year history, remarkable progress has been made on antiretroviral drugs. Progress toward a vaccine has also been made, although this has yet to deliver a licensed product. In 2007, I wrote a review, HIV AIDS Vaccines: 2007. This review, HIV AIDS Vaccines: 2018, focuses on the progress in the past 11 years. I begin with key challenges for the development of an AIDS vaccine and the lessons learned from the six completed efficacy trials, only one of which has met with some success.

Monkey Models and HIV Vaccine Research

Since the discovery of acquired immunodeficiency syndrome (AIDS) in 1981, it has been extremely difficult to develop an effective vaccine or a therapeutic cure despite over 36 years of global efforts. One of the major reasons is due to the lack of an immune-competent animal model that supports live human immunodeficiency virus (HIV) infection and disease progression such that vaccine-induced correlates of protection and efficacy can be determined clearly before human trials. Nevertheless, rhesus macaques infected with simian immunodeficiency virus (SIV) and chimeric simian human immunodeficiency virus (SHIV) have served as invaluable models not only for understanding AIDS pathogenesis but also for studying HIV vaccine and cure. In this chapter, therefore, we summarize major scientific evidence generated in these models since the beginning of the AIDS pandemic. Hopefully, the accumulated knowledge and lessons contributed by thousands of scientists will be useful in promoting the search of an ultimate solution to end HIV/AIDS.

HIV-1 gp120 and Modified Vaccinia Virus Ankara (MVA) gp140 Boost Immunogens Increase Immunogenicity of a DNA/MVA HIV-1 Vaccine

An important goal of human immunodeficiency virus (HIV) vaccine design is identification of strategies that elicit effective antiviral humoral immunity. One novel approach comprises priming with DNA and boosting with modified vaccinia virus Ankara (MVA) expressing HIV-1 Env on virus-like particles. In this study, we evaluated whether the addition of a gp120 protein in alum or MVA-expressed secreted gp140 (MVAgp140) could improve immunogenicity of a DNA prime-MVA boost vaccine. Five rhesus macaques per group received two DNA primes at weeks 0 and 8 followed by three MVA boosts (with or without additional protein or MVAgp140) at weeks 18, 26, and 40. Both boost immunogens enhanced the breadth of HIV-1 gp120 and V1V2 responses, antibody-dependent cellular cytotoxicity (ADCC), and low-titer tier 1B and tier 2 neutralizing antibody responses. However, there were differences in antibody kinetics, linear epitope specificity, and CD4 T cell responses between the groups. The gp120 protein boost elicited earlier and higher peak responses, whereas the MVAgp140 boost resulted in improved antibody durability and comparable peak responses after the final immunization. Linear V3 specific IgG responses were particularly enhanced by the gp120 boost, whereas the MVAgp140 boost also enhanced responses to linear C5 and C2.2 epitopes. Interestingly, gp120, but not the MVAgp140 boost, increased peak CD4⁺ T cell responses. Thus, both gp120 and MVAgp140 can augment potential protection of a DNA/MVA vaccine by enhancing gp120 and V1/V2 antibody responses, whereas potential protection by gp120, but not MVAgp140 boosts, may be further impacted by increased CD4⁺ T cell responses.

IMPORTANCE Prior immune correlate analyses with humans and nonhuman primates revealed the importance of antibody responses in preventing HIV-1 infection. A DNA prime-modified vaccinia virus Ankara (MVA) boost vaccine has proven to be potent in eliciting antibody responses. Here we explore the ability of boosts with recombinant gp120 protein or MVA-expressed gp140 to enhance antibody responses elicited by the GOVX-B11 DNA prime-MVA boost vaccine. We found that both types of immunogen boosts enhanced potentially protective antibody responses, whereas the gp120 protein boosts also increased CD4⁺ T cell responses. Our data provide important information for HIV vaccine designs that aim for effective and balanced humoral and T cell responses.

Codelivery of Envelope Protein in Alum with MVA Vaccine Induces CXCR3-Biased CXCR5+ and CXCR5- CD4 T Cell Responses in Rhesus Macaques

The goal of an HIV vaccine is to generate robust and durable protective Ab. Vital to this goal is the induction of CD4(+) T follicular helper (TFH) cells. However, very little is known about the TFH response to HIV vaccination and its relative contribution to magnitude and quality of vaccine-elicited Ab titers. In this study, we investigated these questions in the context of a DNA/modified vaccinia virus Ankara SIV vaccine with and without gp140 boost in aluminum hydroxide in rhesus macaques. In addition, we determined the frequency of vaccine-induced CD4(+) T cells coexpressing chemokine receptor, CXCR5 (facilitates migration to B cell follicles) in blood and whether these responses were representative of lymph node TFH responses. We show that booster modified vaccinia virus Ankara immunization induced a distinct and transient accumulation of proliferating CXCR5(+) and CXCR5(-) CD4 T cells in blood at day 7 postimmunization, and the frequency of the former but not the latter correlated with TFH and B cell responses in germinal centers of the lymph node. Interestingly, gp140 boost induced a skewing toward CXCR3 expression on germinal center TFH cells, which was strongly associated with longevity, avidity, and neutralization potential of vaccine-elicited Ab response. However, CXCR3(+) cells preferentially expressed the HIV coreceptor CCR5, and vaccine-induced CXCR3(+)CXCR5(+) cells showed a moderate positive association with peak viremia following SIV251 infection. Taken together, our findings demonstrate that vaccine regimens that elicit CXCR3-biased TFH cell responses favor Ab persistence and avidity but may predispose to higher acute viremia in the event of breakthrough infections.

Adjuvant-carrying synthetic vaccine particles augment the immune response to encapsulated antigen and exhibit strong local immune activation without inducing systemic cytokine release

Augmentation of immunogenicity can be achieved by particulate delivery of an antigen and by its co-administration with an adjuvant. However, many adjuvants initiate strong systemic inflammatory reactions in vivo, leading to potential adverse events and safety concerns. We have developed a synthetic vaccine particle (SVP) technology that enables co-encapsulation of antigen with potent adjuvants. We demonstrate that co-delivery of an antigen with a TLR7/8 or TLR9 agonist in synthetic polymer nanoparticles results in a strong augmentation of humoral and cellular immune responses with minimal systemic production of inflammatory cytokines. In contrast, antigen encapsulated into nanoparticles and admixed with free TLR7/8 agonist leads to lower immunogenicity and rapid induction of high levels of inflammatory cytokines in the serum (e.g., TNF-α and IL-6 levels are 50- to 200-fold higher upon injection of free resiquimod (R848) than of nanoparticle-encapsulated R848). Conversely, local immune stimulation as evidenced by cellular infiltration of draining lymph nodes and by intranodal cytokine production was more pronounced and persisted longer when SVP-encapsulated TLR agonists were used. The strong local immune activation achieved using a modular self-assembling nanoparticle platform markedly enhanced immunogenicity and was equally effective whether antigen and adjuvant were co-encapsulated in a single nanoparticle formulation or co-delivered in two separate nanoparticles. Moreover, particle encapsulation enabled the utilization of CpG oligonucleotides with the natural phosphodiester backbone, which are otherwise rapidly hydrolyzed by nucleases in vivo. The use of SVP may enable clinical use of potent TLR agonists as vaccine adjuvants for indications where cellular immunity or robust humoral responses are required.

Immunization with multiple vaccine modalities induce strong HIV-specific cellular and humoral immune responses

Heterologous priming and boosting with antigens expressed by DNA, viral vectors, or as proteins, are experimental strategies to induce strong immune responses against infectious diseases and cancer. In a preclinical study we compared the ability of recombinant modified vaccinia Ankara encoding HIV antigens (MVA-CMDR), and/or recombinant gp140C (rgp140C), to boost responses induced by a multigene/multisubtype HIV DNA vaccine delivered by electroporation (EP). Homologous DNA immunizations augmented by EP stimulated strong cellular immune responses. Still stronger cellular immune responses were observed after DNA priming and MVA-CMDR boosting, which was superior to all other immunization schedules tested in terms of antigen-specific IFN-γ, IL-2, and bifunctional IFN-γ and IL-2 responses. For HIV Env-specific antibody responses, mice receiving repeated rgp140C immunizations, and mice boosted with rgp140C, elicited the highest binding titers and the highest numbers of antibody-secreting B cells. When considering both cellular and humoral immune responses, a combination of DNA, MVA-CMDR, and rgp140C immunizations induced the overall most potent immune responses and the highest avidity of HIV Env-specific antibodies. These data emphasize the importance of including multiple vaccine modalities that can stimulate both T and B cells, and thus elicit strong and balanced immune responses. The present HIV vaccine combination holds promise for further evaluation in clinical trials.

T cell chemo-vaccination effects after repeated mucosal SHIV exposures and oral pre-exposure prophylaxis

Pre-exposure prophylaxis (PrEP) with anti-viral drugs is currently in clinical trials for the prevention of HIV infection. Induction of adaptive immune responses to virus exposures during anti-viral drug administration, i.e., a "chemo-vaccination" effect, could contribute to PrEP efficacy. To study possible chemo-vaccination, we monitored humoral and cellular immune responses in nine rhesus macaques undergoing up to 14 weekly, low-dose SHIV(SF162P3) rectal exposures. Six macaques concurrently received PrEP with intermittent, oral Truvada; three were no-PrEP controls. PrEP protected 4 macaques from infection. Two of the four showed evidence of chemo-vaccination, because they developed anti-SHIV CD4(+) and CD8(+) T cells; SHIV-specific antibodies were not detected. Control macaques showed no anti-SHIV immune responses before infection. Chemo-vaccination-induced T cell responses were robust (up to 3,940 SFU/10(6) PBMCs), predominantly central memory cells, short-lived (≤22 weeks), and appeared intermittently and with changing specificities. The two chemo-vaccinated macaques were virus-challenged again after 28 weeks of rest, after T cell responses had waned. One macaque was not protected from infection. The other macaque concurrently received additional PrEP. It remained uninfected and T cell responses were boosted during the additional virus exposures. In summary, we document and characterize PrEP-induced T cell chemo-vaccination. Although not protective after subsiding in one macaque, chemo-vaccination-induced T cells warrant more comprehensive analysis during peak responses for their ability to prevent or to control infections after additional exposures. Our findings highlight the importance of monitoring these responses in clinical PrEP trials and suggest that a combination of vaccines and PrEP potentially might enhance efficacy.

HIV-1 Tat-based vaccines: an overview and perspectives in the field of HIV/AIDS vaccine development

The HIV epidemic continues to represent one of the major problems worldwide, particularly in the Asia and Sub-Saharan regions of the world, with social and economical devastating effects. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals that have access to treatment, it has had a negligible impact on the global epidemic. Hence, the inexorable spreading of the HIV pandemic and the increasing deaths from AIDS, especially in developing countries, underscore the urgency for an effective vaccine against HIV/AIDS. However, the generation of such a vaccine has turned out to be extremely challenging. Here we provide an overview on the rationale for the use of non-structural HIV proteins, such as the Tat protein, alone or in combination with other HIV early and late structural HIV antigens, as novel, promising preventative and therapeutic HIV/AIDS vaccine strategies.

Increased immunogenicity of HIV-1 p24 and gp120 following immunization with gp120/p24 fusion protein vaccine expressing alpha-gal epitopes

Developing an effective HIV-1 vaccine will require strategies to enhance antigen presentation to the immune system. In a previous study we demonstrated a marked increase in immunogenicity of the highly glycosylated HIV-1 gp120 protein following enzymatic addition of alpha-gal epitopes to the carbohydrate chains. In the present study we determined whether gp120(alphagal) can also serve as an effective platform for targeting other HIV-1 proteins to APC and thus increase immunogenicity of both proteins. For this purpose we produced a recombinant fusion protein between gp120 and the HIV-1 matrix p24 protein (gp120/p24). Multiple alpha-gal epitopes were synthesized enzymatically on the gp120 portion of the fusion protein to generate a gp120(alphagal)/p24 vaccine. Immune responses to gp120(alphagal)/p24 compared to gp120/p24 vaccine lacking alpha-gal epitopes were evaluated in alpha1,3galactosyltransferase knockout (KO) mice. These mice lack alpha-gal epitopes and, therefore, are capable of producing the anti-Gal antibody. T cell responses to p24, as assessed by ELISPOT and by CD8+ T cells intracellular staining assays for IFNgamma, was on average 12- and 10-fold higher, respectively, in gp120(alphagal)/p24 immunized mice than in mice immunized with gp120/p24. In addition, cellular and humoral immune responses against gp120 were higher by 10-30-fold in mice immunized with gp120(alphagal)/p24 than in gp120/p24 immunized mice. Our data suggest that the alpha-gal epitopes on the gp120 portion of the fusion protein can significantly augment the immunogenicity of gp120, as well as that of the fused viral protein which lacks alpha-gal epitopes. This strategy of anti-Gal mediated targeting to APC may be used for production of effective HIV-1 vaccines comprised of various viral proteins fused to gp120.

X4 human immunodeficiency virus type 1 gp120 down-modulates expression and immunogenicity of codelivered antigens

In order to increase the immune breadth of human immunodeficiency virus (HIV) vaccines, strategies such as immunization with several HIV antigens or centralized immunogens have been examined. HIV-1 gp120 protein is a major immunogen of HIV and has been routinely considered for inclusion in both present and future AIDS vaccines. However, recent studies proposed that gp120 interferes with the generation of immune response to codelivered antigens. Here, we investigate whether coimmunization with plasmid-encoded gp120 alters the immune response to other coadministered plasmid encoded antigens such as luciferase or ovalbumin in a mouse model. We found that the presence of gp120 leads to a significant reduction in the expression level of the codelivered antigen in vivo. Antigen presentation by antigen-presenting cells was also reduced and resulted in the induction of weak antigen-specific cellular and humoral immune responses. Importantly, gp120-mediated immune interference was observed after administration of the plasmids at the same or at distinct locations. To characterize the region in gp120 mediating these effects, we used plasmid constructs encoding gp120 that lacks the V1V2 loops (DeltaV1V2) or the V3 loop (DeltaV3). After immunization, the DeltaV1V2, but not the DeltaV3 construct, was able to reduce antigen expression, antigen presentation, and subsequently the immunogenicity of the codelivered antigen. The V3 loop dependence of this phenomenon seems to be limited to V3 loops known to interact with the CXCR4 molecule but not with CCR5. Our study presents a novel mechanism by which HIV-1 gp120 interferes with the immune response against coadministered antigen in a polyvalent vaccine preparation.

Blood and seminal plasma HIV-1 RNA levels among HIV-1-infected injecting drug users participating in the AIDSVAX B/E efficacy trial in Bangkok, Thailand

BACKGROUND

We investigated effects of vaccination with AIDSVAX B/E HIV-1 candidate vaccine on blood and seminal plasma HIV-1 RNA viral loads (BVL and SVL, respectively) in vaccine recipients (VRs) and placebo recipients (PRs) who acquired infection.

METHODS

Linear mixed models were fitted for repeated measurements of BVL. Generalized estimating equations were used to assess the difference in SVL detectability between VRs and PRs.

RESULTS

A total of 196 participants became HIV-1 infected during the trial. Thirty-two (16%) became infected with HIV-1 subtype B and 164 (84%) with HIV-1 subtype CRF01_AE. Per protocol-specified analysis, there were no differences in BVL levels between VRs and PRs. When stratified by HIV-1-infecting subtype, vaccination with AIDSVAX B/E was initially associated with higher BVL among HIV-1 CRF01_AE-infected VRs compared with HIV-1 CRF01_AE-infected PRs; however, this difference did not persist over time. HIV-1 subtype B-infected VRs had slightly higher BVL levels and were more likely to have detectable SVL during the follow-up period than HIV-1 subtype B-infected PRs.

CONCLUSIONS

Subtle differences in BVL and SVL were detected between VRs and PRs. These results may help to further understand the dynamics between HIV-1 vaccination, HIV-1-infecting subtypes, and subsequent viral expression in different body compartments.

Viral, HLA and T cell elements in cross-reactive immune responses to HIV-1 subtype A, CRF01_AE and CRF02_AG vaccine sequence in Ivorian blood donors

Comprehensive understanding of the determinants of cross-subtype immune responses in HIV infection is critical to developing efficacious HIV vaccines against multiple viral subtypes. Because HIV-1 subtype A or recombinants comprising subtype A are prevalent in Africa and parts of Asia where HIV is spreading, we assessed the determinants of cross-subtype immune responses in HIV-infected blood donors from Cote d'Ivoire to peptides from a candidate CRF02_AG vaccine sequence, a subtype A sequence from western Kenya and a CRF01_AE sequence from Thailand. We present evidence that immune recognition of multiple viral subtypes is maintained by recognition of multiple epitopes. Our data suggest that complete escape of HIV from immune recognition is uncommon. Evaluation of these frequently generated cross-reactive responses should be included in immunogenicity trials of HIV vaccines.

HIV-1 gp120 mannoses induce immunosuppressive responses from dendritic cells

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is a vaccine immunogen that can signal via several cell surface receptors. To investigate whether receptor biology could influence immune responses to gp120, we studied its interaction with human, monocyte-derived dendritic cells (MDDCs) in vitro. Gp120 from the HIV-1 strain JR-FL induced IL-10 expression in MDDCs from 62% of donors, via a mannose C-type lectin receptor(s) (MCLR). Gp120 from the strain LAI was also an IL-10 inducer, but gp120 from the strain KNH1144 was not. The mannose-binding protein cyanovirin-N, the 2G12 mAb to a mannose-dependent gp120 epitope, and MCLR-specific mAbs inhibited IL-10 expression, as did enzymatic removal of gp120 mannose moieties, whereas inhibitors of signaling via CD4, CCR5, or CXCR4 were ineffective. Gp120-stimulated IL-10 production correlated with DC-SIGN expression on the cells, and involved the ERK signaling pathway. Gp120-treated MDDCs also responded poorly to maturation stimuli by up-regulating activation markers inefficiently and stimulating allogeneic T cell proliferation only weakly. These adverse reactions to gp120 were MCLR-dependent but independent of IL-10 production. Since such mechanisms might suppress immune responses to Env-containing vaccines, demannosylation may be a way to improve the immunogenicity of gp120 or gp140 proteins.

Dendritic cells (DCs) initiate immune responses to pathogens or vaccine antigens. The HIV-1 gp120 envelope glycoprotein is an antigen that is a focus of vaccine design strategies. We have studied how gp120 proteins interact with DCs in cell culture. Certain gp120s stimulate DCs from some, but not all, human donors to produce IL-10, a cytokine that is generally immunosuppressive. In addition, whether or not the DCs produce IL-10, their ability to mature properly when activated is impaired by gp120—the gp120-treated DCs have a reduced ability to stimulate T cell growth when the two cell types are cultured together. These various effects of gp120 are caused by its binding to cell surface receptors of the mannose C-type lectin receptor family, including (but probably not exclusively) one called DC-SIGN. Gp120 binds to these receptors via mannose residues that are present on some of the glycan structures that overlay much of its protein surface. Removing the mannoses by digesting gp120 with a suitable enzyme prevents IL-10 induction and impairment of DC maturation, as does the use of inhibitors of the binding of gp120 to DC-SIGN and similar receptors. This work could help with the design of better HIV-1 vaccines.

Absence of SHIV infection in gut and lymph node tissues in rhesus monkeys after repeated rectal challenges following HIV-1 DNA/MVA immunizations

We reported previously the absence of systemic infection in a subset of macaques vaccinated with an HIV-1 DNA/MVA vaccine after 18 or more rectal challenges with low (physiologically relevant) doses of SHIV162P3. To further study the apparent protection, we looked for sequestered virus in gut tissues, lymph nodes, spleen, and testes obtained at necropsy using virus co-culture and nested PCR for SIV Gag, Pol and LTR. There was no evidence of sequestered virus in tissues obtained from the four protected macaques. In contrast, at least one tissue from each of 11 infected animals scored positive by one of these sensitive procedures. Activated PBMC from the protected macaques were not inherently resistant to in vitro infection by the challenge virus. These findings demonstrate that some vaccinated macaques appeared to be free from the challenge virus. Therefore, such T cell-based vaccines may provide some protection when challenge virus doses approach physiological equivalencies.

HIV-1 prophylactic vaccine comprised of topical DermaVir prime and protein boost elicits cellular immune responses and controls pathogenic R5 SHIV162P3

Topical DNA vaccination (DermaVir) facilitates antigen presentation to naive T cells. DermaVir immunization in mice, using HIV-1 Env and Gag, elicited cellular immune responses. Boosting with HIV-1 gp120 Env and p41 Gag augmented Th1 cytokine levels. Intramuscular DNA administration was less efficient in priming antigen-specific cytokine production and memory T cells. In rhesus macaques, DermaVir immunization induced Gag- and Env-specific Th1 and Th2 cytokines and generation of memory T cells. Boosting of DermaVir-primed serum antibody levels was noted following gp140(SHIV89.6P)/p27(SIV) immunization. Rectal challenge with pathogenic R5-tropic SHIV162P3 resulted in control of plasma viremia (4/5 animals) that was reflected in jejunum, colon and mesenteric lymph nodes. An inverse correlation was found between Gag- and Env-specific central memory T cell responses on the day of challenge and plasma viremia at set point. Overall, the topical DermaVir/protein vaccination yields central memory T cell responses and facilitates control of pathogenic SHIV infection.

Immune response in rhesus macaques after mixed modality immunisations with DNA, recombinant adenovirus and recombinant gp120 from human immunodeficiency virus type 1

The establishment of effective regimens for a vaccine against human immunodeficiency virus type 1 (HIV-1) is urgently needed. In the present study we have produced HIV-1 gp120 from a vaccine-relevant primary R5 isolate in recombinant vaccinia (rVV)-infected Vero cells. We have investigated the effect of boosting with this protein in mixed modality immunisations of rhesus macaques following different immunisation. As reported earlier, animals were primed with codon-optimised HIV-1(BX08)env DNA delivered as plasmid or as replication-deficient recombinant human adenovirus type 5 (rAd5), which both induced specific antibody and cellular immune responses (1). Boosting with rAd5 temporarily had increased the anti-gp120 antibody titres approximately 1 log (rAd5+rAd5) or 3 log (DNA+rAd5) (1). However, secondary rAd5 boosting showed less effect due to the induced vector-specific immunity. To further boost the antibody response, the rgp120(BX08) was injected with Quadri A saponin adjuvant. The protein boosting resulted in a 1-2 log antibody increase and also boosting of the cell-mediated immune response. Neutralising antibodies to the heterologous HIV-1(MN) were detected; however, neutralising antibodies to the primary HIV-1(Bx08) isolate were seen only transiently after rAd5 but not the rgp120 immunisation. It is concluded that the rgp120(Bx08) reagent from rVV-infected Vero cells is functional and immunogenic in macaques, inducing both antibody and cellular immunity. The rgp120(Bx08) is a relevant model antigen that may be used to boost antibody and cellular immunity in mixed modality vaccine regimens against HIV-1 in higher animals.

Increased immunogenicity of human immunodeficiency virus gp120 engineered to express Galalpha1-3Galbeta1-4GlcNAc-R epitopes

The glycan shield comprised of multiple carbohydrate chains on the human immunodeficiency virus (HIV) envelope glycoprotein gp120 helps the virus to evade neutralizing antibodies. The present study describes a novel method for increasing immunogenicity of gp120 vaccine by enzymatic replacement of sialic acid on these carbohydrate chains with Galalpha1-3Galbeta1-4GlcNAc-R (alpha-gal) epitopes. These epitopes are ligands for the natural anti-Gal antibody constituting approximately 1% of immunoglobulin G in humans. We hypothesize that vaccination with gp120 expressing alpha-gal epitopes (gp120(alphagal)) results in in vivo formation of immune complexes with anti-Gal, which targets vaccines for effective uptake by antigen-presenting cells (APC), due to interaction between the Fc portion of the antibody and Fcgamma receptors on APC. This in turn results in effective transport of the vaccine to lymph nodes and effective processing and presentation of gp120 immunogenic peptides by APC for eliciting a strong anti-gp120 immune response. This hypothesis was tested in alpha-1,3-galactosyltransferase knockout mice, which produce anti-Gal. Mice immunized with gp120(alphagal) produced anti-gp120 antibodies in titers that were >100-fold higher than those measured in mice immunized with comparable amounts of gp120 and effectively neutralized HIV. T-cell response, measured by ELISPOT, was much higher in mice immunized with gp120(alphagal) than in mice immunized with gp120. It is suggested that gp120(alphagal) can serve as a platform for anti-Gal-mediated targeting of additional vaccinating HIV proteins fused to gp120(alphagal), thereby creating effective prophylactic vaccines.

Prime-boost vaccination using DNA and whole inactivated virus vaccines provides limited protection against virulent feline immunodeficiency virus

Protection against feline immunodeficiency virus (FIV) has been achieved using a variety of vaccines notably whole inactivated virus (WIV) and DNA. However protection against more virulent isolates, typical of those encountered in natural infections, has been difficult to achieve. In an attempt to improve protection against virulent FIV(GL8), we combined both DNA and WIV vaccines in a "prime-boost" approach. Thirty cats were divided into four groups receiving vaccinations and one unvaccinated control group. Following viral challenge, two vaccinated animals, one receiving DNA alone and one the prime-boost vaccine remained free of viraemia, whilst all controls became viraemic. Animals vaccinated with WIV showed apparent early enhancement of infection at 2 weeks post challenge (pc) with higher plasma viral RNA loads than control animals or cats immunised with DNA alone. Despite this, animals vaccinated with WIV or DNA alone showed significantly lower proviral loads in peripheral blood mononuclear cells and mesenteric lymph node cells, whilst those receiving the DNA-WIV prime-boost vaccine showed significantly lower proviral loads in PBMC, than control animals, at 35 weeks pc. Therefore both DNA and WIV vaccines conferred limited protection against viral challenge but the combination of WIV and DNA in a prime-boost approach appeared to offer no significant advantage over either vaccine alone.

Studies on GM-CSF DNA as an adjuvant for neutralizing Ab elicited by a DNA/MVA immunodeficiency virus vaccine

Here, we use a vaccine consisting of DNA priming followed by MVA boosting in rhesus macaques to investigate the ability of GM-CSF DNA to serve as an adjuvant for the elicitation of neutralizing Ab against an HIV-1 Env. The trial used Gag, Pol, and Env sequences from SHIV-89.6 in the immunogens and a neutralization escape variant of SHIV-89.6, SHIV-89.6P, for challenge. Co-delivery of GM-CSF and vaccine DNAs enhanced the temporal appearance of neutralizing Ab and broadened the specificity of the neutralizing activity to include SHIV-89.6P. Two long-term SHIV-89.6 infections elicited neutralizing activity for SHIV-89.6 but not SHIV-89.6P. Studies on the avidity of the anti-Env antisera revealed that the GM-CSF-adjuvanted vaccine had elicited higher avidity Ab than the non-adjuvanted vaccine or the infection. The GM-CSF-adjuvanted group showed a trend towards better control of the challenge infection and had better control of re-emergent virus (P < 0.01) than the non-adjuvanted group.

Signature for long-term vaccine-mediated control of a Simian and human immunodeficiency virus 89.6P challenge: stable low-breadth and low-frequency T-cell response capable of coproducing gamma interferon and interleukin-2

In 2001, we reported 20 weeks of control of challenge with the virulent 89.6P chimera of simian and human immunodeficiency viruses (SHIV-89.6P) by a Gag-Pol-Env vaccine consisting of DNA priming and modified vaccinia virus Ankara boosting. Here we report that 22 out of 23 of these animals successfully controlled their viremia until their time of euthanasia at 200 weeks postchallenge. At euthanasia, all animals had low to undetectable viral loads and normal CD4 counts. During the long period of viral control, gamma interferon (IFN-gamma)-producing antiviral T cells were present at unexpectedly low breadths and frequencies. Most animals recognized two CD8 and one CD4 epitope and had frequencies of IFN-gamma-responding T cells from 0.01 to 0.3% of total CD8 or CD4 T cells. T-cell responses were remarkably stable over time and, unlike responses in most immunodeficiency virus infections, maintained good functional characteristics, as evidenced by coproduction of IFN-gamma and interleukin-2. Overall, high titers of binding and neutralizing antibody persisted throughout the postchallenge period. Encouragingly, long-term control was effective in macaques of diverse histocompatibility types.

Factors limiting the immunogenicity of HIV-1 gp120 envelope glycoproteins

Efficient immune responses to HIV-1 gene products are essential elements to the development and design of an effective vaccine. Ideally, both humoral and cellular responses will be optimally elicited. It is therefore important to elucidate any factors that might limit the immunogenicity of HIV-1 proteins that are likely to be included in an effective vaccine. Since the HIV-1 exterior envelope glycoprotein gp120 is a major target for neutralizing antibodies, it is a virtual certainty that this gene product will be a component of any vaccine that seeks to elicit neutralizing antibody responses from the host humoral immune system. We report here the testing of several HIV-1 gp120 variants derived from a primary isolate that appears deficient in eliciting immune responses at both the level of CD4+ help and consequently in the generation of high-affinity IgG antibody responses in small animals. Factors limiting an effective immune response include (a) envelope glycoprotein strain variation decreasing functional T-cell help, (b) alteration of the glycosylation patterns of gp120 by expression in different cell types, and (c) the native structure of gp120 itself, which may limit the elicitation of effective T-cell help during natural infection or during parenteral immunization in adjuvant. Such limiting factors and others should be considered in the design and testing of gp120-based immunogens in small animals and possibly in primates as well.

Virus-like particles as HIV-1 vaccines

Traditional successful antiviral vaccines have relied mostly on live-attenuated viruses. Live-attenuated HIV vaccine candidates are not ideal as they pose risks of reversion, recombination or mutations. Other current HIV vaccine candidates have difficulties generating broadly effective neutralising antibodies and cytotoxic T cell immune responses to primary HIV isolates. Virus-like-particles (VLPs) have been demonstrated to be safe to administer to animals and human patients as well as being potent and efficient stimulators of cellular and humoral immune responses. Therefore, VLPs are being considered as possible HIV vaccines. Chimeric HIV-1 VLPs constructed with either HIV or SIV capsid protein plus HIV immune epitopes and immuno-stimulatory molecules have further improved on early VLP designs, leading to enhanced immune stimulation. The administration of VLP vaccines via mucosal surfaces has also emerged as a promising strategy with which to elicit mucosal and systemic humoral and cellular immune responses. Additionally, new information on antigen processing and the presentation of particulate antigens by dendritic cells (DCs) has created new strategies for improved VLP vaccine candidates. This paper reviews the field of HIV-1 VLP vaccine development, focusing on recent studies that will likely uncover promising prospects for new HIV vaccines.

Characterization of a DNA vaccine expressing a human immunodeficiency virus-like particle

An ideal human immunodeficiency virus type-1 (HIV-1) vaccine will most likely need to elicit cross-reactive neutralizing antibodies and a strong cell-mediated immune response against multiple HIV-1 antigens to confer protection against challenge. In this study, DNA vaccines were constructed to express virally regulated human immunodeficiency virus-like particles (VLP) to elicit broad-spectrum immune responses to multiple HIV-1 antigens. VLPs were efficiently produced using sequences encoding gag and pol gene products from an X4 isolate and sequences encoding for tat, rev, vpu, and env from R5 or R5X4 isolates. The integrase, vpr, vif, and nef genes were deleted. In addition, the long terminal repeats (LTRs) were removed and transcription of the VLP insert was driven by the addition of the cytomegalovirus immediate-early (CMV-IE) promoter. A second generation of VLP vaccine plasmids was constructed with mutations engineered into the VLP DNA to produce particles deficient in activities associated with viral reverse transcriptase and protease. Primate cell lines, transiently transfected with DNA, efficiently secreted VLP into the supernatant that banded within a sucrose gradient at densities similar to infectious virions. In addition, these particles incorporated Env on the particle surface that bound soluble human CD4. These VLPs provide a safe and efficient strategy for presenting multiple HIV-1 antigens, expressed from a single insert, to the immune system in a structure that mimics the infectious virion.

Multiprotein HIV type 1 clade B DNA/MVA vaccine: construction, safety, and immunogenicity in Macaques

Recently, a simian/human immunodeficiency virus (SHIV) vaccine consisting of priming with a Gag-Pol-Env-expressing DNA and boosting with a Gag-Pol-Env-expressing recombinant modified vaccinia Ankara (rMVA) has successfully controlled a virulent SHIV challenge in a macaque model. In this, and the accompanying paper, we report on the construction and testing of a Gag-Pol-Env DNA/MVA vaccine for HIV-1/AIDS. The DNA vaccine, pGA2/JS2, expresses aggregates of Gag proteins and includes safety mutations that render it integration, reverse transcription, and packaging defective. The rMVA vaccine, MVA/HIV 48, is integration and reverse transcription defective and has a truncated Env to enhance expression on the plasma membrane. In a study in rhesus macaques, priming with pGA2/JS2 and boosting with MVA/HIV 48 raised high frequencies of T cells for Gag and Env and lower frequencies of T cells for PR, RT, and Tat. Stimulations with five peptide pools for Gag and seven peptide pools for Env revealed epitopes for cellular immune responses throughout Gag and Env. On average, CD4 T cells from the vaccinated animals recognized 7.1 peptide pools and CD8 T cells, 3.2 peptide pools. Both the height and the breadth of the elicited cellular response provide hope that this multiprotein DNA/MVA vaccine will successfully control clade B isolates of HIV-1, as well as contribute to the control of other clades and recombinant forms of HIV-1/AIDS.