Design and pre-clinical evaluation of a universal HIV-1 vaccine

An HIV Vaccine for South-East Asia-Opportunities and Challenges

Recent advances in HIV vaccine development along with a better understanding of the immune correlates of risk have emerged from the RV144 efficacy trial conducted in Thailand. Epidemiological data suggest that CRF01_AE is still predominant in South-East Asia and is spreading in China with a growing number of circulating recombinant forms due to increasing human contact, particularly in large urban centers, tourist locations and in sites of common infrastructure. A vaccine countering CRF01_AE is a priority for the region. An Asia HIV vaccine against expanding B/E or BCE recombinant forms should be actively pursued. A major challenge that remains is the conduct of efficacy trials in heterosexual populations in this region. Men who have sex with men represent the main target population for future efficacy trials in Asia. Coupling HIV vaccines with other prevention modalities in efficacy trials might also be envisaged. These new avenues will only be made possible through the conduct of large-scale efficacy trials, interdisciplinary teams, international collaborations, and strong political and community commitments.

HIV vaccine to induce cytotoxic T cells recognizing conserved HIV-1/2-epitopes derived from the most frequent HLA types of the human population

Evaluation of: Pleguezuelos O, Stoloff GA, Caparros-Wanderley W. Synthetic immunotherapy induces HIV virus specific Th1 cytotoxic response and death of an HIV-1 infected human cell line through classic complement activation. Virol. J. 10(1), 107 (2013). AIDS vaccine development represents an unprecedented challenge in both immunogen design and delivery to induce potent and long-lasting HIV-specific immune responses, including neutralizing antibodies and cytotoxic T lymphocytes (CTL). Pleguezuelos and coworkers recognized that immunogen design must address both HIV and HLA diversity to make a global vaccine. The HIV-v synthetic polypeptide vaccine described here sets a new standard in antigen design by selecting conserved regions of global HIV-1 and HIV-2 isolates and epitopes from most frequent HLA types of the human population. The new vaccine induced both antibody and CTL responses. Importantly, the authors demonstrated vaccine-specific HLA restricted CD8(+) CTL responses for one HLA allele that was involved in the antigen design. HIV-v vaccine is a new candidate to be tested in human subjects carrying frequent HLA types.

Development of prophylactic vaccines against HIV-1

The focus of most current HIV-1 vaccine development is on antibody-based approaches. This is because certain antibody responses correlated with protection from HIV-1 acquisition in the RV144 phase III trial, and because a series of potent and broad spectrum neutralizing antibodies have been isolated from infected individuals. Taken together, these two findings suggest ways forward to develop a neutralizing antibody-based vaccine. However, understanding of the correlates of protection from disease in HIV-1 and other infections strongly suggests that we should not ignore CTL-based research. Here we review recent progress in the field and highlight the challenges implicit in HIV-1 vaccine design and some potential solutions.

Absence of systemic toxicity changes following intramuscular administration of novel pSG2.HIVconsv DNA, ChAdV63.HIVconsv and MVA.HIVconsv vaccines to BALB/c mice

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Three novel vaccines were tested in 2 GLP toxicity studies in BALB/c mice.

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Vaccines were vectored by DNA, simian adenovirus and modified vaccinia virus Ankara.

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All 3 vaccines expressed the same conserved regions of HIV-1.

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Intramuscular administration had no systemic toxicity.

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All changes were consistent with i.m. delivery and immune response induction.

Background

The systemic toxicity of three candidate HIV-1 vaccines plasmid pSG2.HIVconsv DNA (D), ChAdV63.HIVconsv (C) and MVA.HIVconsv (M) expressing chimeric immunogen derived from the most conserved regions of the HIV-1 proteome was evaluated in two repeat-dose studies in the male and female BALB/c mice.

Methods

In study UNO011, mice received three doses of 2 × 10⁷ plaque-forming units of MVA.HIVconsv vaccine (MMM). In study UNO012, mice received 3 doses of 50 μg of pSG2.HIVconsv DNA followed by a single dose of 5.95 × 10⁹ virus particles of ChAdV63.HIVconsv vaccine (DDDC). Similarly constituted control groups received the vehicle alone (phosphate buffered saline) at the same volume-dose. All vaccines were administered by intramuscular needle injection into the right hind limb at 14-day intervals and animals were sacrificed 7 days after the last dose. Assessment of local and systemic toxicity was made. Induction of HIV-1-specific responses was confirmed. Parameters assessed included clinical condition, body weight, food consumption, ophthalmoscopy, haematology, blood chemistry, organ weight and macroscopic and microscopic pathology.

Results

In both studies, treatment with the candidate vaccines elicited strong HIV-1-specific T-cell responses. The vaccine treatment was well-tolerated without any adverse systemic toxicological changes. The local toxicity findings observed in these studies were consistent with the predicted response to a vaccine/substance administration by intramuscular injection.

Conclusions

The three novel anti-HIV-1 vaccines were well tolerated when administered by intramuscular injection to BALB/c mice. These results supported an application for authorisation by the Medicines and Healthcare Products Regulatory Agency of the UK to test these vaccines for the first time in phase I clinical trials in healthy both uninfected subjects and HIV-1-infected patients stable on antiretroviral treatment.

Progress in HIV-1 vaccine development

PURPOSE OF REVIEW

In this review, examples of recent progress in HIV-1 vaccine research are discussed.

RECENT FINDINGS

New insights from the immune correlates analyses of the RV144 efficacy trial have accelerated vaccine development with leads to follow in nonhuman primate studies and improved vaccine designs. Several new vaccine vector approaches offer promise in the exquisite control of acute infection and in improving the breadth of T-cell responses. New targets of broadly neutralizing antibodies (BnAbs) have been elucidated, and improved understanding of how the human host controls BnAb development have emerged from BnAb knock-in mice and from analyses of BnAb maturation and virus evolution in individuals followed from the time of HIV-1 transmission to BnAb induction.

SUMMARY

Based on these observations, it is clear that the development of a successful HIV-1 vaccine will require new vaccine approaches and iterative testing of immunogens in well designed animal and human trials.

Acute-phase CD8 T cell responses that select for escape variants are needed to control live attenuated simian immunodeficiency virus

The overall CD8 T cell response to human/simian immunodeficiency virus (HIV/SIV) targets a collection of discrete epitope specificities. Some of these epitope-specific CD8 T cells emerge in the weeks and months following infection and rapidly select for sequence variants, whereas other CD8 T cell responses develop during the chronic infection phase and rarely select for sequence variants. In this study, we tested the hypothesis that acute-phase CD8 T cell responses that do not rapidly select for escape variants are unable to control viral replication in vivo as well as those that do rapidly select for escape variants. We created a derivative of live attenuated SIV (SIVmac239Δnef) in which we ablated five epitopes that elicit early CD8 T cell responses and rapidly accumulate sequence variants in SIVmac239-infected Mauritian cynomolgus macaques (MCMs) that are homozygous for the M3 major histocompatibility complex (MHC) haplotype. This live attenuated SIV variant was called m3KOΔnef. Viremia was significantly higher in M3 homozygous MCMs infected with m3KOΔnef than in either MHC-mismatched MCMs infected with m3KOΔnef or MCMs infected with SIVmac239Δnef. Three CD8 T cell responses, including two that do not rapidly select for escape variants, predominated during early m3KOΔnef infection in the M3 homozygous MCMs, but these animals were unable to control viral replication. These results provide evidence that acute-phase CD8 T cell responses that have the potential to rapidly select for escape variants in the early phase of infection are needed to establish viral control in vivo.

Superior control of HIV-1 replication by CD8+ T cells targeting conserved epitopes: implications for HIV vaccine design

A successful HIV vaccine will likely induce both humoral and cell-mediated immunity, however, the enormous diversity of HIV has hampered the development of a vaccine that effectively elicits both arms of the adaptive immune response. To tackle the problem of viral diversity, T cell-based vaccine approaches have focused on two main strategies (i) increasing the breadth of vaccine-induced responses or (ii) increasing vaccine-induced responses targeting only conserved regions of the virus. The relative extent to which set-point viremia is impacted by epitope-conservation of CD8⁺ T cell responses elicited during early HIV-infection is unknown but has important implications for vaccine design. To address this question, we comprehensively mapped HIV-1 CD8⁺ T cell epitope-specificities in 23 ART-naïve individuals during early infection and computed their conservation score (CS) by three different methods (prevalence, entropy and conseq) on clade-B and group-M sequence alignments. The majority of CD8⁺ T cell responses were directed against variable epitopes (p<0.01). Interestingly, increasing breadth of CD8⁺ T cell responses specifically recognizing conserved epitopes was associated with lower set-point viremia (r = - 0.65, p = 0.009). Moreover, subjects possessing CD8⁺ T cells recognizing at least one conserved epitope had 1.4 log₁₀ lower set-point viremia compared to those recognizing only variable epitopes (p = 0.021). The association between viral control and the breadth of conserved CD8⁺ T cell responses may be influenced by the method of CS definition and sequences used to determine conservation levels. Strikingly, targeting variable versus conserved epitopes was independent of HLA type (p = 0.215). The associations with viral control were independent of functional avidity of CD8⁺ T cell responses elicited during early infection. Taken together, these data suggest that the next-generation of T-cell based HIV-1 vaccines should focus on strategies that can elicit CD8⁺ T cell responses to multiple conserved epitopes of HIV-1.

Translating HIV sequences into quantitative fitness landscapes predicts viral vulnerabilities for rational immunogen design

A prophylactic or therapeutic vaccine offers the best hope to curb the HIV-AIDS epidemic gripping sub-Saharan Africa, but it remains elusive. A major challenge is the extreme viral sequence variability among strains. Systematic means to guide immunogen design for highly variable pathogens like HIV are not available. Using computational models, we have developed an approach to translate available viral sequence data into quantitative landscapes of viral fitness as a function of the amino acid sequences of its constituent proteins. Predictions emerging from our computationally defined landscapes for the proteins of HIV-1 clade B Gag were positively tested against new in vitro fitness measurements and were consistent with previously defined in vitro measurements and clinical observations. These landscapes chart the peaks and valleys of viral fitness as protein sequences change and inform the design of immunogens and therapies that can target regions of the virus most vulnerable to selection pressure.

HIV-1 vaccines: let's get physical

Ferguson et al. (2013) use applied physics to quantitate the fitness of HIV-1 Gag based on sequence variability across the protein. This enables a new approach to vaccine design that focuses CD8+ T cell responses on fitness-constrained parts of Gag.

Immunogenicity of sequences around HIV-1 protease cleavage sites: potential targets and population coverage analysis for a HIV vaccine targeting protease cleavage sites

Developing an effective preventative vaccine against HIV-1 has proved to be a great challenge. The classical and proven vaccine approach has failed so far or produced a modest effect, new approaches are needed. In this study we evaluated the immunogenicity of the sequences around the protease cleavage sites (PCS) and the population coverage of a vaccine targeting HIV-1 PCS. The sequence conservation was evaluated by comparing entropy score of sequences around PCS with Gag and Pol. The immunogenicity of sequences around the 12 PCS (+10/-10 amino acids) was analyzed by identifying epitopes of HLA class I alleles in PCS region using four approaches: (1) identification of previously reported HLA class I allele epitopes around PCS region; (2) screening and validating epitopes of 8 HLA class I alleles common to most world populations using iTopia Epitope Discovery system and IFN-γ ELISpot assays; (3) screening of 151 patients of Pumwani cohort for PBMC IFN-γ ELISPOT responses to the subtype A and D consensus around PCS region; and (4) prediction of HLA alleles with epitopes around the PCS using NetMHCpan. Population coverage was calculated using the web-based analysis tool of the Immune Epitope Database based on HLA class I genotype frequencies from dbMHC database. The results showed that many HLA class I alleles have multiple epitopes in the 12 PCS regions, indicating sequence immunogenicity around PCS. Multiple epitopes of many HLA class I alleles common to >95% world populations have been identified around the 12 PCS region. Targeting these sites is a feasible vaccine approach.

HIV-1 p24(gag) derived conserved element DNA vaccine increases the breadth of immune response in mice

Viral diversity is considered a major impediment to the development of an effective HIV-1 vaccine. Despite this diversity, certain protein segments are nearly invariant across the known HIV-1 Group M sequences. We developed immunogens based on the highly conserved elements from the p24^gag region according to two principles: the immunogen must (i) include strictly conserved elements of the virus that cannot mutate readily, and (ii) exclude both HIV regions capable of mutating without limiting virus viability, and also immunodominant epitopes located in variable regions. We engineered two HIV-1 p24^gag DNA immunogens that express 7 highly Conserved Elements (CE) of 12–24 amino acids in length and differ by only 1 amino acid in each CE (‘toggle site’), together covering >99% of the HIV-1 Group M sequences. Altering intracellular trafficking of the immunogens changed protein localization, stability, and also the nature of elicited immune responses. Immunization of C57BL/6 mice with p55^gag DNA induced poor, CD4⁺ mediated cellular responses, to only 2 of the 7 CE; in contrast, vaccination with p24CE DNA induced cross-clade reactive, robust T cell responses to 4 of the 7 CE. The responses were multifunctional and composed of both CD4⁺ and CD8⁺ T cells with mature cytotoxic phenotype. These findings provide a method to increase immune response to universally conserved Gag epitopes, using the p24CE immunogen. p24CE DNA vaccination induced humoral immune responses similar in magnitude to those induced by p55^gag, which recognize the virus encoded p24^gag protein. The inclusion of DNA immunogens composed of conserved elements is a promising vaccine strategy to induce broader immunity by CD4⁺ and CD8⁺ T cells to additional regions of Gag compared to vaccination with p55^gag DNA, achieving maximal cross-clade reactive cellular and humoral responses.

HIV-1 conserved-element vaccines: relationship between sequence conservation and replicative capacity

To overcome the problem of HIV-1 variability, candidate vaccine antigens have been designed to be composed of conserved elements of the HIV-1 proteome. Such candidate vaccines could be improved with a better understanding of both HIV-1 evolutionary constraints and the fitness cost of specific mutations. We evaluated the in vitro fitness cost of 23 mutations engineered in the HIV-1 subtype B Gag-p24 Center-of-Tree (COT) protein through fitness competition assays. While some mutations at conserved sites exacted a high fitness cost, as expected under the assumption that the most conserved residue confers the highest fitness, there was no overall strong relationship between sequence conservation and replicative capacity. By comparing sites that have evolved since the beginning of the epidemic to those that have remain unchanged, we found that sites that have evolved over time were more likely to correspond to HLA-associated sites and that their mutation had limited fitness costs. Our data showed no transcendent link between high conservation and high fitness cost, indicating that merely focusing on conserved segments of HIV-1 would not be sufficient for a successful vaccine strategy. Nonetheless, a subset of sites exacted a high fitness cost upon mutation--these sites have been under selective pressure to change since the beginning of the epidemic but have proved virtually nonmutable and could constitute preferred targets for vaccine design.

Antigenicity and immunogenicity of transmitted/founder, consensus, and chronic envelope glycoproteins of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) vaccine development requires selection of appropriate envelope (Env) immunogens. Twenty HIV-1 Env glycoproteins were examined for their ability to bind human anti-HIV-1 monoclonal antibodies (MAbs) and then used as immunogens in guinea pigs to identify promising immunogens. These included five Envs derived from chronically infected individuals, each representing one of five common clades and eight consensus Envs based on these five clades, as well as the consensus of the entire HIV-1 M group, and seven transmitted/founder (T/F) Envs from clades B and C. Sera from immunized guinea pigs were tested for neutralizing activity using 36 HIV-1 Env-pseudotyped viruses. All Envs bound to CD4 binding site, membrane-proximal, and V1/V2 MAbs with similar apparent affinities, although the T/F Envs bound with higher affinity to the MAb 17b, a CCR5 coreceptor binding site antibody. However, the various Envs differed in their ability to induce neutralizing antibodies. Consensus Envs elicited the most potent responses, but neutralized only a subset of viruses, including mostly easy-to-neutralize tier 1 and some more-difficult-to-neutralize tier 2 viruses. T/F Envs elicited fewer potent neutralizing antibodies but exhibited greater breadth than chronic or consensus Envs. Finally, chronic Envs elicited the lowest level and most limited breadth of neutralizing antibodies overall. Thus, each group of Env immunogens elicited a different antibody response profile. The complementary benefits of consensus and T/F Env immunogens raise the possibility that vaccines utilizing a combination of consensus and T/F Envs may be able to induce neutralizing responses with greater breadth and potency than single Env immunogens.

Porcine reproductive and respiratory syndrome virus vaccines: current status and strategies to a universal vaccine

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of PRRS, the most significant infectious disease currently affecting swine industry worldwide. In the United States alone, the economic losses caused by PRRS amount to more than 560 million US dollars every year. Due to immune evasion strategies and the antigenic heterogeneity of the virus, current commercial PRRSV vaccines (killed-virus and modified-live vaccines) are of unsatisfactory efficacy, especially against heterologous infection. Continuous efforts have been devoted to develop better PRRSV vaccines. Experimental PRRSV vaccines, including live attenuated vaccines, recombinant vectors expressing PRRSV viral proteins, DNA vaccines and plant-made subunit vaccines, have been developed. However, the genetic and antigenic heterogeneity of the virus limits the value of almost all of the PRRSV vaccines tested. Developing a universal vaccine that can provide broad protection against circulating PRRSV strains has become a major challenge for current vaccine development. This paper reviews current status of PRRSV vaccine development and discusses strategies to develop a universal PRRSV vaccine.

Adjuvanted HLA-supertype restricted subdominant peptides induce new T-cell immunity during untreated HIV-1-infection

We investigated the potential of inducing additional T-cell immunity during chronic HIV-1 infection directed to subdominant HIV-1 epitopes from common HLA-supertypes. Ten treatment-naïve HIV-1-infected individuals were immunized with peptides in the adjuvant CAF01. One individual received placebo. T-cell immunogenicity was examined longitudinally by a flow cytometry (CD107a, IFNγ, TNFα, IL-2 and/or MIP1β expression) as well as IFNγ ELISPOT. Safety was evaluated by clinical follow up combined with monitoring of biochemistry, hematology, CD4 T-cell counts and viral load. New CD4 and CD8 T-cell responses specific for one or more vaccine epitopes were induced in 10/10 vaccinees. The responses were dominated by CD107a and MIP1β expression. There were no significant changes in HIV-1 viral load or CD4 T-cell counts. Our study demonstrates that the peptide/CAF01 vaccine is safe and that it is possible to generate new HIV-1 T-cell responses to defined epitopes in treatment-naïve HIV-1-infected individuals.

HIV-1 Vaccine Trials: Evolving Concepts and Designs

An effective prophylactic HIV-1 vaccine is needed to eradicate the HIV/AIDS pandemic but designing such a vaccine is a challenge. Despite many advances in vaccine technology and approaches to generate both humoral and cellular immune responses, major phase-II and -III vaccine trials against HIV/AIDS have resulted in only moderate successes. The modest achievement of the phase-III RV144 prime-boost trial in Thailand re-emphasized the importance of generating robust humoral and cellular responses against HIV. While antibody-directed approaches are being pursued by some groups, others are attempting to develop vaccines targeting cell-mediated immunity, since evidence show CTLs to be important for the control of HIV replication. Phase-I and -IIa multi-epitope vaccine trials have already been conducted with vaccine immunogens consisting of known CTL epitopes conserved across HIV subtypes, but have so far fallen short of inducing robust and consistent anti-HIV CTL responses. The concepts leading to the development of T-cell epitope-based vaccines, the outcomes of related clinical vaccine trials and efforts to enhance the immunogenicity of cell-mediated approaches are summarized in this review. Moreover, we describe a novel approach based on the identification of SIV and FIV antigens which contain conserved HIV-specific T-cell epitopes and represent an alternative method for developing an effective HIV vaccine against global HIV isolates.

Identification of conserved subdominant HIV Type 1 CD8(+) T Cell epitopes restricted within common HLA Supertypes for therapeutic HIV Type 1 vaccines

The high HIV-1 prevalence, up to 4.6% in Guinea-Bissau, West Africa, makes it a relevant location for testing of therapeutic vaccines. With the aim of performing a clinical study in Guinea-Bissau, after first testing the vaccine for safety in Denmark, Europe, we here describe the design of a universal epitope peptide-based T cell vaccine with relevance for any geographic locations. The two major obstacles when designing such a vaccine are the high diversities of the HIV-1 genome and of the human major histocompatibility complex (MHC) class I. We selected 15 CD8-restricted epitopes predicted from conserved regions of HIV-1 that were subdominant (i.e., infrequently targeted) within natural infections. Moreover, the epitopes were predicted to be restricted to at least one of the five common HLA supertypes (HLA-A01, A02, A03, B07, and B44). Here, we validated the resulting peptide-specific, HLA-restricted T cell specificities using peptide-MHC class I tetramer labeling of CD8(+) T cells from HIV-1-infected individuals. The selected vaccine epitopes are infrequently targeted in HIV-1-infected individuals from both locations. Moreover, we HLA-typed HIV-1-infected individuals and demonstrated that the selected vaccine epitopes, when targeted, are restricted to the five most common HLA supertypes at both locations. Thus, the HLA supertype-directed approach achieved HLA coverage of 95% and 100% of the examined cohorts in Guinea-Bissau and Denmark, respectively. In conclusion, the selected vaccine epitopes match the host populations and HIV-1 strains of these two distant geographic regions, justifying clinical testing in both locations.

Conservation of HIV-1 T cell epitopes across time and clades: validation of immunogenic HLA-A2 epitopes selected for the GAIA HIV vaccine

HIV genomic sequence variability has complicated efforts to generate an effective globally relevant vaccine. Regions of the viral genome conserved in sequence and across time may represent the "Achilles' heel" of HIV. In this study, highly conserved T-cell epitopes were selected using immunoinformatics tools combining HLA-A2 supertype binding predictions with relative global conservation. Analysis performed in 2002 on 10,803 HIV-1 sequences, and again in 2009, on 43,822 sequences, yielded 38 HLA-A2 epitopes. These epitopes were experimentally validated for HLA binding and immunogenicity with PBMCs from HIV-infected patients in Providence, Rhode Island, and/or Bamako, Mali. Thirty-five (92%) stimulated an IFNγ response in PBMCs from at least one subject. Eleven of fourteen peptides (79%) were confirmed as HLA-A2 epitopes in both locations. Validation of these HLA-A2 epitopes conserved across time, clades, and geography supports the hypothesis that such epitopes could provide effective coverage of virus diversity and would be appropriate for inclusion in a globally relevant HIV vaccine.

T cells induced by recombinant chimpanzee adenovirus alone and in prime-boost regimens decrease chimeric EcoHIV/NDK challenge virus load

The popularity of nonreplicating adenoviruses of chimpanzee origin (ChAdVs) as vectors for subunit vaccines is on the rise. This is mainly for their excellent safety and impressive immunogenicity observed in human studies to date. Here, we recloned the chimpanzee adenovirus sero type 68 (ChAdV-68), also designated SAdV-25 and AdC68, genome and demonstrated its straightforward genetic manipulation facilitated by the use of bacterial artificial chromosome recombineering. To generate the ChAdV68.GagB vaccine, the HIV-1 consensus clade B Gag-derived Tg was inserted into the E1 region. In part confirming previous observations, the ChAdV68.GagB vaccine alone and in heterologous prime-boost regimens with plasmid DNA- and modified vaccinia virus Ankara (MVA)-vectored vaccines induced robust polyfunctional HIV-1-specific CD8(+) and CD4(+) T-cell responses with a gut-homing phenotype. Importantly, we showed that when a single epitope is expressed as an immunodominant CD8(+) T-cell determinant, responses elicited by ChAdV68.GagB alone and in combination lowered surrogate challenge EcoHIV/NDK (where EcoHIV is chimeric ecotropic HIV) virus load in mice both at the peak T-cell frequencies 2 weeks after vaccination and 16 weeks later indicating development of protective effector memory. These results parallel the immunogenicity of similar vaccine regimens in macaques and an ongoing phase I/IIa trial in humans, and support further development of vaccines vectored by ChAdVs.

Broad and cross-clade CD4+ T-cell responses elicited by a DNA vaccine encoding highly conserved and promiscuous HIV-1 M-group consensus peptides

T-cell based vaccine approaches have emerged to counteract HIV-1/AIDS. Broad, polyfunctional and cytotoxic CD4⁺ T-cell responses have been associated with control of HIV-1 replication, which supports the inclusion of CD4⁺ T-cell epitopes in vaccines. A successful HIV-1 vaccine should also be designed to overcome viral genetic diversity and be able to confer immunity in a high proportion of immunized individuals from a diverse HLA-bearing population. In this study, we rationally designed a multiepitopic DNA vaccine in order to elicit broad and cross-clade CD4⁺ T-cell responses against highly conserved and promiscuous peptides from the HIV-1 M-group consensus sequence. We identified 27 conserved, multiple HLA-DR-binding peptides in the HIV-1 M-group consensus sequences of Gag, Pol, Nef, Vif, Vpr, Rev and Vpu using the TEPITOPE algorithm. The peptides bound in vitro to an average of 12 out of the 17 tested HLA-DR molecules and also to several molecules such as HLA-DP, -DQ and murine IA^b and IA^d. Sixteen out of the 27 peptides were recognized by PBMC from patients infected with different HIV-1 variants and 72% of such patients recognized at least 1 peptide. Immunization with a DNA vaccine (HIVBr27) encoding the identified peptides elicited IFN-γ secretion against 11 out of the 27 peptides in BALB/c mice; CD4⁺ and CD8⁺ T-cell proliferation was observed against 8 and 6 peptides, respectively. HIVBr27 immunization elicited cross-clade T-cell responses against several HIV-1 peptide variants. Polyfunctional CD4⁺ and CD8⁺ T cells, able to simultaneously proliferate and produce IFN-γ and TNF-α, were also observed. This vaccine concept may cope with HIV-1 genetic diversity as well as provide increased population coverage, which are desirable features for an efficacious strategy against HIV-1/AIDS.

Can immunotherapy be useful as a "functional cure" for infection with Human Immunodeficiency Virus-1?

Immunotherapy aims to assist the natural immune system in achieving control over viral infection. Various immunotherapy formats have been evaluated in either therapy-naive or therapy-experienced HIV-infected patients over the last 20 years. These formats included non-antigen specific strategies such as cytokines that stimulate immunity or suppress the viral replication, as well as antibodies that block negative regulatory pathways. A number of HIV-specific therapeutic vaccinations have also been proposed, using in vivo injection of inactivated virus, plasmid DNA encoding HIV antigens, or recombinant viral vectors containing HIV genes. A specific format of therapeutic vaccines consists of ex vivo loading of autologous dendritic cells with one of the above mentioned antigenic formats or mRNA encoding HIV antigens.This review provides an extensive overview of the background and rationale of these different therapeutic attempts and discusses the results of trials in the SIV macaque model and in patients. To date success has been limited, which could be explained by insufficient quality or strength of the induced immune responses, incomplete coverage of HIV variability and/or inappropriate immune activation, with ensuing increased susceptibility of target cells.Future attempts at therapeutic vaccination should ideally be performed under the protection of highly active antiretroviral drugs in patients with a recovered immune system. Risks for immune escape should be limited by a better coverage of the HIV variability, using either conserved or mosaic sequences. Appropriate molecular adjuvants should be included to enhance the quality and strength of the responses, without inducing inappropriate immune activation. Finally, to achieve a long-lasting effect on viral control (i.e. a "functional cure") it is likely that these immune interventions should be combined with anti-latency drugs and/or gene therapy.

Universal fungal vaccines: could there be light at the end of the tunnel?

The complex nature of fungal pathogens, the intricate host-pathogen relationship and the health status of subjects in need of antifungal vaccination continue to hamper efforts to develop fungal vaccines for clinical use. That said, the rise of the universal vaccine concept is hoped to revive fungal vaccine research by expanding the pool of vaccine candidates worthy of clinical evaluation. It can do so through antigenic commonality-based screening for vaccine candidates from a wide range of pathogens and by reassessing the sizable collection of already available experimental and approved vaccines. Development of experimental vaccines protective against multiple fungal pathogens is evidence of the utility of this concept in fungal vaccine research. However, universal fungal vaccines are not without difficulties; for instance, development of vaccines with differential effectiveness is an issue that should be addressed. Additionally, rationalizing the development of universal fungal vaccines on health or economic basis could be contentious. Herein, universal fungal vaccines are discussed in terms of their potential usefulness and possible drawbacks.

Pre-clinical development of BCG.HIVA(CAT), an antibiotic-free selection strain, for HIV-TB pediatric vaccine vectored by lysine auxotroph of BCG

In the past, we proposed to develop a heterologous recombinant BCG prime-recombinant modified vaccinia virus Ankara (MVA) boost dual pediatric vaccine platform against transmission of breast milk HIV-1 and Mycobacterium tuberculosis (Mtb). In this study, we assembled an E. coli-mycobacterial shuttle plasmid pJH222.HIVA^CAT expressing HIV-1 clade A immunogen HIVA. This shuttle vector employs an antibiotic resistance-free mechanism based on Operator-Repressor Titration (ORT) system for plasmid selection and maintenance in E. coli and lysine complementation in mycobacteria. This shuttle plasmid was electroporated into parental lysine auxotroph (safer) strain of BCG to generate vaccine BCG.HIVA^CAT. All procedures complied with Good Laboratory Practices (GLPs). We demonstrated that the episomal plasmid pJH222.HIVA^CAT was stable in vivo over a 20-week period, and genetically and phenotypically characterized the BCG.HIVA^CAT vaccine strain. The BCG.HIVA^CAT vaccine in combination with MVA.HIVA induced HIV-1- and Mtb-specific interferon γ-producing T-cell responses in newborn and adult BALB/c mice. On the other hand, when adult mice were primed with BCG.HIVA^CAT and boosted with MVA.HIVA.85A, HIV-1-specific CD8⁺ T-cells producing IFN-γ, TNF-α, IL-2 and CD107a were induced. To assess the biosafety profile of BCG.HIVA^CAT-MVA.HIVA regimen, body mass loss of newborn mice was monitored regularly throughout the vaccination experiment and no difference was observed between the vaccinated and naïve groups of animals. Thus, we demonstrated T-cell immunogenicity of a novel, safer, GLP-compatible BCG-vectored vaccine using prototype immunogen HIVA. Second generation immunogens derived from HIV-1 as well as other major pediatric pathogens can be constructed in a similar fashion to prime protective responses soon after birth.

Full-length HIV-1 immunogens induce greater magnitude and comparable breadth of T lymphocyte responses to conserved HIV-1 regions compared with conserved-region-only HIV-1 immunogens in rhesus monkeys

A global HIV-1 vaccine will likely need to induce immune responses against conserved HIV-1 regions to contend with the profound genetic diversity of HIV-1. Here we evaluated the capacity of immunogens consisting of only highly conserved HIV-1 sequences that are aimed at focusing cellular immune responses on these potentially critical regions. We assessed in rhesus monkeys the breadth and magnitude of T lymphocyte responses elicited by adenovirus vectors expressing either full-length HIV-1 Gag/Pol/Env immunogens or concatenated immunogens consisting of only highly conserved HIV-1 sequences. Surprisingly, we found that the full-length immunogens induced comparable breadth (P = 1.0) and greater magnitude (P = 0.01) of CD8(+) T lymphocyte responses against conserved HIV-1 regions compared with the conserved-region-only immunogens. Moreover, the full-length immunogens induced a 5-fold increased total breadth of HIV-1-specific T lymphocyte responses compared with the conserved-region-only immunogens (P = 0.007). These results suggest that full-length HIV-1 immunogens elicit a substantially increased magnitude and breadth of cellular immune responses compared with conserved-region-only HIV-1 immunogens, including greater magnitude and comparable breadth of responses against conserved sequences.

A phase I double blind, placebo-controlled, randomized study of a multigenic HIV-1 adenovirus subtype 35 vector vaccine in healthy uninfected adults

Background

We conducted a phase I, randomized, double-blind, placebo-controlled trial to assess the safety and immunogenicity of escalating doses of two recombinant replication defective adenovirus serotype 35 (Ad35) vectors containing gag, reverse transcriptase, integrase and nef (Ad35-GRIN) and env (Ad35-ENV), both derived from HIV-1 subtype A isolates. The trial enrolled 56 healthy HIV-uninfected adults.

Methods

Ad35-GRIN/ENV (Ad35-GRIN and Ad35-ENV mixed in the same vial in equal proportions) or Ad35-GRIN was administered intramuscularly at 0 and 6 months. Participants were randomized to receive either vaccine or placebo (10/4 per group, respectively) within one of four dosage groups: Ad35-GRIN/ENV 2×10⁹ (A), 2×10¹⁰ (B), 2×10¹¹ (C), or Ad35-GRIN 1×10¹⁰ (D) viral particles.

Results

No vaccine-related serious adverse event was reported. Reactogenicity events reported were dose-dependent, mostly mild or moderate, some severe in Group C volunteers, all transient and resolving spontaneously. IFN-γ ELISPOT responses to any vaccine antigen were detected in 50, 56, 70 and 90% after the first vaccination, and in 75, 100, 88 and 86% of Groups A–D vaccine recipients after the second vaccination, respectively. The median spot forming cells (SFC) per 10⁶ PBMC to any antigen was 78–139 across Groups A–C and 158–174 in Group D, after each of the vaccinations with a maximum of 2991 SFC. Four to five HIV proteins were commonly recognized across all the groups and over multiple timepoints. CD4+ and CD8+ T-cell responses were polyfunctional. Env antibodies were detected in all Group A–C vaccinees and Gag antibodies in most vaccinees after the second immunization. Ad35 neutralizing titers remained low after the second vaccination.

Conclusion/Significance

Ad35-GRIN/ENV reactogenicity was dose-related. HIV-specific cellular and humoral responses were seen in the majority of volunteers immunized with Ad35-GRIN/ENV or Ad35-GRIN and increased after the second vaccination. T-cell responses were broad and polyfunctional.

Trial Registration

ClinicalTrials.gov NCT00851383

A DNA-based candidate HIV vaccine delivered via in vivo electroporation induces CD4 responses toward the α4β7-binding V2 loop of HIV gp120 in healthy volunteers

Administration of a clade C/B' candidate HIV-1 DNA vaccine, ADVAX, by in vivo electroporation (EP) was safe and more immunogenic than intramuscular administration without EP. The breadth and specificity of T-cell responses to full-length Env were mapped. Responses to multiple Env regions were induced, with most focusing on V3/C4 and V2 regions, including the α4β7 integrin-binding domain. The breadth of responses induced by this DNA vaccine regimen was comparable to that of viral-vectored vaccine regimens.

Rational design of HIV vaccines and microbicides: report of the EUROPRISE annual conference 2011

Europrise is a Network of Excellence supported by the European Commission within the 6th Framework programme from 2007 to 2012. The Network has involved over 50 institutions from 13 European countries together with 3 industrial partners and 6 African countries. The Network encompasses an integrated program of research, training, dissemination and advocacy within the field of HIV vaccines and microbicides. A central and timely theme of the Network is the development of the unique concept of co-usage of vaccines and microbicides. Training of PhD students has been a major task, and some of these post-graduate students have here summarized novel ideas emanating from presentations at the last annual Europrise meeting in Prague. The latest data and ideas concerning HIV vaccine and microbicide studies are included in this review; these studies are so recent that the majority have yet to be published. Data were presented and discussed concerning novel immunisation strategies; microbicides and PrEP (alone and in combination with vaccines); mucosal transmission of HIV/SIV; mucosal vaccination; novel adjuvants; neutralizing antibodies; innate immune responses; HIV/SIV pathogenesis and disease progression; new methods and reagents. These – necessarily overlapping topics - are comprehensively summarised by the Europrise students in the context of other recent exciting data.

Further progress on defining highly conserved immunogenic epitopes for a global HIV vaccine: HLA-A3-restricted GAIA vaccine epitopes

Two major obstacles confronting HIV vaccine design have been the extensive viral diversity of HIV-1 globally and viral evolution driven by escape from CD8(+) cytotoxic T-cell lymphocyte (CTL)-mediated immune pressure. Regions of the viral genome that are not able to escape immune response and that are conserved in sequence and across time may represent the "Achilles' heel" of HIV and would be excellent candidates for vaccine development. In this study, T-cell epitopes were selected using immunoinformatics tools, combining HLA-A3 binding predictions with relative sequence conservation in the context of global HIV evolution. Twenty-seven HLA-A3 epitopes were chosen from an analysis performed in 2003 on 10,803 HIV-1 sequences, and additional sequences were selected in 2009 based on an expanded set of 43,822 sequences. These epitopes were tested in vitro for HLA binding and for immunogenicity with PBMCs of HIV-infected donors from Providence, Rhode Island. Validation of these HLA-A3 epitopes conserved across time, clades, and geography supports the hypothesis that epitopes such as these would be candidates for inclusion in our globally relevant GAIA HIV vaccine constructs.

Therapeutic live vaccines as a potential anticancer strategy

The design of efficient cancer treatments is one of the major challenges of medical science. Therapeutic vaccines of cancer have been emerged as an attractive approach for their capacity of breaking the immune tolerance and invoking long-term immune response targeting cancer cells without autoimmunity. An efficient antigen delivery system is the key issue of developing an effective cancer vaccine. In this regard, live vaccination strategies including various live bacterial and viral vectors have attracted a great attention. Several bacterial strains such as Salmonella, Listeria monocytogenes and Lactococcus lactis effectively colonize solid tumors and act as antitumor therapeutics. On the other hand, the use of viruses as vaccine vectors such as Vaccinia, Adenovirus, Herpes simplex virus, Paramyxovirus and Retroviruses utilizes mechanisms that evolved in these microbes for entering cells and capturing the cellular machinery to express viral proteins. Viral/bacterial-vectored vaccines induce systemic T-cell responses including polyfunctional cytokine-secreting CD4+ and CD8+ T-cells. However, there is an urgent need for the development of new safe live vaccine vectors that are capable of enhancing antigen presentation and eliciting potent immune responses without the risk of development of disease in humans. Recently, nonpathogenic parasites including Leishmania tarentolae, Toxoplasma gondii and Trypanosoma cruzi have emerged to be a novel candidate for gene delivery and heterologous genes expression. In this review, recent researches on cancer therapy using genetically modified bacteria and virus are summarized. In addition, live parasite-based vectors will be discussed as a novel anticancer therapeutic approach.

Antiviral inhibitory capacity of CD8+ T cells predicts the rate of CD4+ T-cell decline in HIV-1 infection

BACKGROUND

Rare human immunodeficiency virus type 1 (HIV-1)-infected individuals who maintain control of viremia without therapy show potent CD8+ T-cell-mediated suppression of viral replication in vitro. Whether this is a determinant of the rate of disease progression in viremic individuals is unknown.

METHODS

We measured CD8+ T-cell-mediated inhibition of a heterologous HIV-1 isolate in 50 HIV-1-seropositive adults with diverse progression rates. Linear mixed models were used to determine whether CD8+ T-cell function could explain variation in the rate of CD4+ T-cell decline.

RESULTS

There was a significant interaction between CD8+ T-cell antiviral activity in vitro and the rate of CD4+ T-cell decline in chronically infected individuals (P < .0001). In a second prospective analysis of recently infected subjects followed for up to 3 years, CD8+ T-cell antiviral activity strongly predicted subsequent CD4+ T-cell decline (P < .0001) and explained up to 73% of the interindividual variation in the CD4+ T-cell slope. In addition, it was inversely associated with viral load set point (r = -0.68 and P = .002).

CONCLUSIONS

The antiviral inhibitory capacity of CD8+ T cells is highly predictive of CD4+ T-cell loss in early HIV-1 infection. It has potential as a benchmark of effective immunity in vaccine evaluation.

A 2 amino acid shift in position leads to a substantial difference in the pattern of processing of 2 HIV-1 epitopes

BACKGROUND

The sequence diversity that exists between HIV-1 strains presents a major obstacle to the design of a vaccine that will be effective on a global scale. Focusing on highly conserved cytotoxic T-lymphocyte epitopes as vaccine targets has been called into question by evidence that variation within epitope flanking regions can affect processing and presentation.

METHODS

Using epitope-specific T-cell clones tested for recognition of HLA-matched target cells infected with vaccinia viruses expressing HIV-1 nef genes derived from different HIV-1 clades, we examined the efficiency of presentation of an HLA-B*40 restricted HIV-1 nef epitope compared to that of an HLA-B*08 restricted epitope with which it overlaps by 6 amino acides.

RESULTS

This small shift in epitope position substantially changed the patter or epitope processing and led either to an increase or decrease in antigen generation dependent on the viral sequences present.

CONCLUSIONS

These data demonstrate the complexity of the antigen presentation pathway and the difficulties associated with selecting CTL epitopes as targets for an HIV-1 vaccine that will be effective in many populations and against several viral strains.

Lessons learned from HIV-1 vaccine trials: new priorities and directions

A vaccine against human immunodeficiency virus (HIV) seems to be on the horizon. Correlates of risk of infection for [corrected] the RV144 vaccine trial have been found. There is understanding of what makes HIV envelope-specific antibodies broadly neutralizing and new T cell vaccine approaches can overcome virus variability.

Profile of T cell recognition of HIV type 1 consensus group M Gag and Nef peptides in a clade A1- and D-infected Ugandan population

Reagents for evaluating non-clade B HIV-specific T cell responses are uncommon. Peptides based on highly conserved HIV-1 consensus group M sequences that are phylogenetically closer to most circulating strains may provide potential alternative reagents in populations with diverse infections, and may be relevant for vaccine design. Recognition of such reagents in clade A1-and D-infected populations has not been previously evaluated. Interferon (IFN)-γ ELISpot assay was used to evaluate T cell recognition of Gag and Nef peptides based on consensus group M sequences in 50 treatment-naive adults predominantly infected with HIV-1 clades A1 and D. Gag-induced T cell responses were correlated with gag sequence diversity. Infecting clades were determined from gag sequences for 45 of the 50 subjects as 40% clade A1 (18/45), 45% clade D (20/45), 2% clade C (1/45), 2% A1/C recombinant (1/45), 2% A1/D (1/45), 7% CRF10_CD (3/45), and 2% U (unclassifiable) (1/45). The mean genetic divergence and diversity of clade A and D gag region compared to group M consensus sequences at synonymous and nonsynonymous nucleotide and amino acid levels were not always significant. Gag peptides were targeted at significantly higher frequency [88% (44/50)] than Nef [64% (32/50)]; p=0.014, although their mean IFN-γ magnitudes were comparable ([3703 (95% CI 2567-4839)] vs. [2120 (95% CI 478-3762)]), respectively. Measurable virus-induced IFN-γ responses were detected in 96% (48/50) individuals, primarily targeting the more conserved Gag p24 and Nef central core regions. Use of these reagents to screen for HIV-specific IFN-γ responses may mitigate the challenge of viral diversity; although this targeting is apparently biased toward a few highly conserved epitopes.

Superior induction of T cell responses to conserved HIV-1 regions by electroporated alphavirus replicon DNA compared to that with conventional plasmid DNA vaccine

Vaccination using "naked" DNA is a highly attractive strategy for induction of pathogen-specific immune responses; however, it has been only weakly immunogenic in humans. Previously, we constructed DNA-launched Semliki Forest virus replicons (DREP), which stimulate pattern recognition receptors and induce augmented immune responses. Also, in vivo electroporation was shown to enhance immune responses induced by conventional DNA vaccines. Here, we combine these two approaches and show that in vivo electroporation increases CD8(+) T cell responses induced by DREP and consequently decreases the DNA dose required to induce a response. The vaccines used in this study encode the multiclade HIV-1 T cell immunogen HIVconsv, which is currently being evaluated in clinical trials. Using intradermal delivery followed by electroporation, the DREP.HIVconsv DNA dose could be reduced to as low as 3.2 ng to elicit frequencies of HIV-1-specific CD8(+) T cells comparable to those induced by 1 μg of a conventional pTH.HIVconsv DNA vaccine, representing a 625-fold molar reduction in dose. Responses induced by both DREP.HIVconsv and pTH.HIVconsv were further increased by heterologous vaccine boosts employing modified vaccinia virus Ankara MVA.HIVconsv and attenuated chimpanzee adenovirus ChAdV63.HIVconsv. Using the same HIVconsv vaccines, the mouse observations were supported by an at least 20-fold-lower dose of DNA vaccine in rhesus macaques. These data point toward a strategy for overcoming the low immunogenicity of DNA vaccines in humans and strongly support further development of the DREP vaccine platform for clinical evaluation.

T-cell-inducing vaccines - what's the future

In the twentieth century vaccine development has moved from the use of attenuated or killed micro-organisms to protein sub-unit vaccines, with vaccine immunogenicity assessed by measuring antibodies induced by vaccination. However, for many infectious diseases T cells are an important part of naturally acquired protective immune responses, and inducing these by vaccination has been the aim of much research. The progress that has been made in developing effective T-cell-inducing vaccines against viral and parasitic diseases such as HIV and malaria is discussed, along with recent developments in therapeutic vaccine development for chronic viral infections and cancer. Although many ways of inducing T cells by vaccination have been assessed, the majority result in low level, non-protective responses. Sufficient clinical research has now been conducted to establish that replication-deficient viral vectored vaccines lead the field in inducing strong and broad responses, and efficacy studies of T-cell-inducing vaccines against a number of diseases are finally demonstrating that this is a valid approach to filling the gaps in our defence against not only infectious disease, but some forms of cancer.

Prime-boost regimens with adjuvanted synthetic long peptides elicit T cells and antibodies to conserved regions of HIV-1 in macaques

OBJECTIVES

Administration of synthetic long peptides (SLPs) derived from human papillomavirus to cervical cancer patients resulted in clinical benefit correlated with expansions of tumour-specific T cells. Because vaginal mucosa is an important port of entry for HIV-1, we have explored SLP for HIV-1 vaccination. Using immunogen HIVconsv derived from the conserved regions of HIV-1, we previously showed in rhesus macaques that SLP.HIVconsv delivered as a boost increased the breath of T-cell specificities elicited by single-gene vaccines. Here, we compared and characterized the use of electroporated pSG2.HIVconsv DNA (D) and imiquimod/montanide-adjuvanted SLP.HIVconsv (S) as priming vaccines for boosting with attenuated chimpanzee adenovirus ChAdV63.HIVconsv (C) and modified vaccinia virus Ankara MVA.HIVconsv (M).

DESIGN

Prime-boost regimens of DDDCMS, DSSCMS and SSSCMS in rhesus macaques.

METHODS

Animals' blood was analysed regularly throughout the vaccination for HIV-1-specific T-cell and antibody responses.

RESULTS

We found that electroporation spares DNA dose, both SLP.HIVconsv and pSG2.HIVconsv DNA primed weakly HIVconsv-specific T cells, regimen DDDCM induced the highest frequencies of oligofunctional, proliferating CD4(+) and CD8(+) T cells, and a subsequent SLP.HIVconsv boost expanded primarily CD4(+) cells. DSS was the most efficient regimen inducing antibodies binding to regions of trimeric HIV-1 Env, which are highly conserved among the four major global clades, although no unequivocal neutralizing activity was detected.

CONCLUSION

The present results encourage evaluation of the SLP.HIVconsv vaccine modality in human volunteers along the currently trialled pSG2.HIVconsv DNA, ChAdV63.HIVconsv and MVA.HIVconsv vaccines. These results are discussed in the context of the RV144 trial outcome.

The origin and diversity of the HIV-1 pandemic

This review examines the enormous progress that has been made in the past decade in understanding the origin of HIV, HIV genetic variability, and the impact of global HIV diversity on the pandemic. Multiple zoonotic transmissions of simian immunodeficiency virus (SIV) have resulted in different HIV lineages in humans. In addition, the high mutation and recombination rates during viral replication result in a great genetic variability of HIV within individuals, as well as within populations, upon which evolutionary selection pressures act. The global HIV pandemic is examined in the context of HIV evolution, and the global diversity of HIV subtypes and recombinants is discussed in detail. Finally, the impact of HIV diversity on pathogenesis, transmission, diagnosis, treatment, the immune response, and vaccine development is reviewed.

Delivery of large heterologous polypeptides across the cytoplasmic membrane of antigen-presenting cells by the Bordetella RTX hemolysin moiety lacking the adenylyl cyclase domain

The Bordetella adenylate cyclase toxin-hemolysin (CyaA; also called ACT or AC-Hly) targets CD11b-expressing phagocytes and translocates into their cytosol an adenylyl cyclase (AC) that hijacks cellular signaling by conversion of ATP to cyclic AMP (cAMP). Intriguingly, insertion of large passenger peptides removes the enzymatic activity but not the cell-invasive capacity of the AC domain. This has repeatedly been exploited for delivery of heterologous antigens into the cytosolic pathway of CD11b-expressing dendritic cells by CyaA/AC(-) toxoids, thus enabling their processing and presentation on major histocompatibility complex (MHC) class I molecules to cytotoxic CD8(+) T lymphocytes (CTLs). We produced a set of toxoids with overlapping deletions within the first 371 residues of CyaA and showed that the structure of the AC enzyme does not contain any sequences indispensable for its translocation across target cell membrane. Moreover, replacement of the AC domain (residues 1 to 371) with heterologous polypeptides of 40, 146, or 203 residues yielded CyaAΔAC constructs that delivered passenger CTL epitopes into antigen-presenting cells (APCs) and induced strong antigen-specific CD8(+) CTL responses in vivo in mice and ex vivo in human peripheral blood mononuclear cell cultures. This shows that the RTX (repeats in toxin) hemolysin moiety, consisting of residues 374 to 1706 of CyaA, harbors all structural information involved in translocation of the N-terminal AC domain across target cell membranes. These results decipher the extraordinary capacity of the AC domain of CyaA to transport large heterologous cargo polypeptides into the cytosol of CD11b(+) target cells and pave the way for the construction of CyaAΔAC-based polyvalent immunotherapeutic T cell vaccines.

Experience with synthetic vaccines for cancer and persistent virus infections in nonhuman primates and patients

Synthetic vaccines, in particular long synthetic peptides of approximately 25-50 amino acids in length, are attractive for HIV vaccine development and for induction of therapeutic immune responses in patients with (pre-)malignant disorders. In the case of preventive vaccine development against HIV, no major success has been achieved, but the possibilities are by no means exhausted. A long peptide vaccine consisting of 13 overlapping peptides, which together cover the entire length of the two oncogenic proteins E6 and E7 of high-risk human papilloma virus type 16 (HPV16), caused complete regression of all lesions and eradication of virus in 9 out of 20 women with high-grade vulvar intraepithelial neoplasia, a therapy-resistant preneoplastic disorder. The nature and strength of the vaccine-prompted T cell responses were significantly correlated with the clinical response. Synthetic peptide vaccines are attractive, because they allow rational improvement of vaccine design and detailed pharmacokinetic and pharmacodynamic studies not possible with conventional vaccines. Improvements are possible by addition or conjugation of adjuvants, notably TLR ligands, to the synthetic peptides.

Definition of the viral targets of protective HIV-1-specific T cell responses

Background

The efficacy of the CTL component of a future HIV-1 vaccine will depend on the induction of responses with the most potent antiviral activity and broad HLA class I restriction. However, current HIV vaccine designs are largely based on viral sequence alignments only, not incorporating experimental data on T cell function and specificity.

Methods

Here, 950 untreated HIV-1 clade B or -C infected individuals were tested for responses to sets of 410 overlapping peptides (OLP) spanning the entire HIV-1 proteome. For each OLP, a "protective ratio" (PR) was calculated as the ratio of median viral loads (VL) between OLP non-responders and responders.

Results

For both clades, there was a negative relationship between the PR and the entropy of the OLP sequence. There was also a significant additive effect of multiple responses to beneficial OLP. Responses to beneficial OLP were of significantly higher functional avidity than responses to non-beneficial OLP. They also had superior in-vitro antiviral activities and, importantly, were at least as predictive of individuals' viral loads than their HLA class I genotypes.

Conclusions

The data thus identify immunogen sequence candidates for HIV and provide an approach for T cell immunogen design applicable to other viral infections.

For protection from HIV-1 infection, more might not be better: a systematic analysis of HIV Gag epitopes of two alleles associated with different outcomes of HIV-1 infection

A subset of women in the Pumwani Sex Worker Cohort, established in 1985 in Nairobi, Kenya, remains uninfected despite repeated high-risk exposure (HIV-exposed, seronegative [HESN]) through active sex work. This HESN phenotype is associated with several alleles of human leukocyte antigens (HLAs) and specific CD8(+) and CD4(+) T cell responses to HIV-1. The associations of HLA alleles with differential HIV-1 infection are most likely due to their different abilities to present antigen and the different immune responses they induce. The characteristics of epitopes of HLA alleles associated with different outcomes of HIV-1 infection might therefore point to a vital clue for developing an effective vaccine. In this study, we systematically analyzed HIV-1 clade A and D Gag CD8(+) T cell epitopes of two HLA class I alleles associated with different outcomes of HIV-1 infection. Binding affinity and off-rates of the identified epitopes were determined. Gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) assays with patient peripheral blood mononuclear cells (PBMCs) validated the epitopes. Epitope-specific CD8(+) T cells were further phenotyped for memory markers with tetramer staining. Our study showed that the protective allele A*01:01 recognizes only three Gag epitopes. By contrast, B*07:02, the allele associated with susceptibility, binds 30 epitope variants. These two alleles differ most importantly in the spectrum of Gag epitopes they can present and not in affinity, off-rates, the location of the epitopes, or epitope-specific Tem/Tcm frequencies. The binding of more epitopes and strong IFN-gamma ELISpot responses are associated with susceptibility to HIV-1 infection, while more focused antigen recognition of multiple subtypes is protective. Rational vaccine design should take these observations into account.

Optimizing HIV-1-specific CD8+ T-cell induction by recombinant BCG in prime-boost regimens with heterologous viral vectors

The desire to induce HIV-1-specific responses soon after birth to prevent breast milk transmission of HIV-1 led us to propose a vaccine regimen which primes HIV-1-specific T cells using a recombinant Mycobacterium bovis bacillus Calmette-Guérin (rBCG) vaccine. Because attenuated live bacterial vaccines are typically not sufficiently immunogenic as stand-alone vaccines, rBCG-primed T cells will likely require boost immunization(s). Here, we compared modified Danish (AERAS-401) and Pasteur lysine auxotroph (222) strains of BCG expressing the immunogen HIVA for their potency to prime HIV-1-specific responses in adult BALB/c mice and examined four heterologous boosting HIVA vaccines for their immunogenic synergy. We found that both BCG.HIVA(401) and BCG.HIVA(222) primed HIV-1-specific CD8(+) T-cell-mediated responses. The strongest boosts were delivered by human adenovirus-vectored HAdV5.HIVA and sheep atadenovirus-vectored OAdV7.HIVA vaccines, followed by poxvirus MVA.HIVA; the weakest was plasmid pTH.HIVA DNA. The prime-boost regimens induced T cells capable of efficient in vivo killing of sensitized target cells. We also observed that the BCG.HIVA(401) and BCG.HIVA(222) vaccines have broadly similar immunologic properties, but display a number of differences mainly detected through distinct profiles of soluble intercellular signaling molecules produced by immune splenocytes in response to both HIV-1- and BCG-specific stimuli. These results encourage further development of the rBCG prime-boost regimen.

Intra- and inter-clade cross-reactivity by HIV-1 Gag specific T-cells reveals exclusive and commonly targeted regions: implications for current vaccine trials

The genetic diversity of HIV-1 across the globe is a major challenge for developing an HIV vaccine. To facilitate immunogen design, it is important to characterize clusters of commonly targeted T-cell epitopes across different HIV clades. To address this, we examined 39 HIV-1 clade C infected individuals for IFN-γ Gag-specific T-cell responses using five sets of overlapping peptides, two sets matching clade C vaccine candidates derived from strains from South Africa and China, and three peptide sets corresponding to consensus clades A, B, and D sequences. The magnitude and breadth of T-cell responses against the two clade C peptide sets did not differ, however clade C peptides were preferentially recognized compared to the other peptide sets. A total of 84 peptides were recognized, of which 19 were exclusively from clade C, 8 exclusively from clade B, one peptide each from A and D and 17 were commonly recognized by clade A, B, C and D. The entropy of the exclusively recognized peptides was significantly higher than that of commonly recognized peptides (p = 0.0128) and the median peptide processing scores were significantly higher for the peptide variants recognized versus those not recognized (p = 0.0001). Consistent with these results, the predicted Major Histocompatibility Complex Class I IC₅₀ values were significantly lower for the recognized peptide variants compared to those not recognized in the ELISPOT assay (p<0.0001), suggesting that peptide variation between clades, resulting in lack of cross-clade recognition, has been shaped by host immune selection pressure. Overall, our study shows that clade C infected individuals recognize clade C peptides with greater frequency and higher magnitude than other clades, and that a selection of highly conserved epitope regions within Gag are commonly recognized and give rise to cross-clade reactivities.

Universal vaccines: shifting to one for many or shooting too high too soon!

Switching from conventional strain-specific vaccines to multi-strain or multi-species universal vaccines is both justified and scientifically merited. Long-term cross-protective universal vaccines eliminate the need for repetitive short-term vaccination campaigns and short-notice vaccine redesign during impending epidemics. They also have the potential to be cost-effective, convenient, and amenable to stockpiling. Ongoing advances in genomics and reverse vaccinology along with the perceived ability of vaccines, if properly formulated, to induce cross-protective adaptive immunity and long-term T cell memory are at the heart of this trend. Consequently, the search for universal vaccines against influenza, HIV, and many other viral, bacterial, and fungal pathogens has intensified in recent years. Currently, several universal influenza vaccines are at different phases of clinical evaluation. That said, vaccine-related differential effectiveness, escape mutants, pathogen strain replacement, limited scope of cross-protective immunity, and diminished potential to reach optimal herd immunity thresholds present serious challenges to the concept and applicability of universal vaccines. Herein, the case for and the case against universal vaccines are investigated to realistically appreciate their prospects of success.

Protective efficacy of serially up-ranked subdominant CD8+ T cell epitopes against virus challenges

Immunodominance in T cell responses to complex antigens like viruses is still incompletely understood. Some data indicate that the dominant responses to viruses are not necessarily the most protective, while other data imply that dominant responses are the most important. The issue is of considerable importance to the rational design of vaccines, particularly against variable escaping viruses like human immunodeficiency virus type 1 and hepatitis C virus. Here, we showed that sequential inactivation of dominant epitopes up-ranks the remaining subdominant determinants. Importantly, we demonstrated that subdominant epitopes can induce robust responses and protect against whole viruses if they are allowed at least once in the vaccination regimen to locally or temporally dominate T cell induction. Therefore, refocusing T cell immune responses away from highly variable determinants recognized during natural virus infection towards subdominant, but conserved regions is possible and merits evaluation in humans.