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

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

Viral Vectors for the Induction of Broadly Neutralizing Antibodies against HIV

Extensive research on generating an efficient HIV vaccine is ongoing. A major aim of HIV vaccines is the induction of long-lasting, broadly neutralizing antibodies (bnAbs) that can confer sterile immunity for a prolonged period of time. Several strategies have been explored to reach this goal, i.e. protein immunization, DNA, or viral vectors, or a combination thereof. In this review, we give an overview of approaches using viral vectors for the induction of HIV-specific bnAbs. Many pre-clinical studies were performed using various replication-competent and -incompetent vectors. Amongst them, poxviral and adenoviral vectors were the most prevalent ones. In many studies, viral vectors were combined with a DNA prime or a protein boost. However, neutralizing antibodies were mainly induced against the homologous HIV-1 vaccine strain or tier 1 viruses, and in rare cases, against tier 2 viruses, indicating the need for improved antigens and vaccination strategies. Furthermore, we also review next generation Env antigens that are currently being used in protein vaccination approaches and point out how they could be utilized in viral vectors.

Chlamydial Type III Secretion System Needle Protein Induces Protective Immunity against Chlamydia muridarum Intravaginal Infection

Chlamydia trachomatis imposes serious health problems and causes infertility. Because of asymptomatic onset, it often escapes antibiotic treatment. Therefore, vaccines offer a better option for the prevention of unwanted inflammatory sequelae. The existence of serologically distinct serovars of C. trachomatis suggests that a vaccine will need to provide protection against multiple serovars. Chlamydia spp. use a highly conserved type III secretion system (T3SS) composed of structural and effector proteins which is an essential virulence factor. In this study, we expressed the T3SS needle protein of Chlamydia muridarum, TC_0037, an ortholog of C. trachomatis CdsF, in a replication-defective adenoviral vector (AdTC_0037) and evaluated its protective efficacy in an intravaginal Chlamydia muridarum model. For better immune responses, we employed a heterologous prime-boost immunization protocol in which mice were intranasally primed with AdTC_0037 and subcutaneously boosted with recombinant TC_0037 and Toll-like receptor 4 agonist monophosphoryl lipid A mixed in a squalene nanoscale emulsion. We found that immunization with TC_0037 antigen induced specific humoral and T cell responses, decreased Chlamydia loads in the genital tract, and abrogated pathology of upper genital organs. Together, our results suggest that TC_0037, a highly conserved chlamydial T3SS protein, is a good candidate for inclusion in a Chlamydia vaccine.

Neutralizing Antibody Response and Antibody-Dependent Cellular Cytotoxicity in HIV-1-Infected Individuals from Guinea-Bissau and Denmark

The development of therapeutic and prophylactic HIV vaccines for African countries is urgently needed, but the question of what immunogens to use needs to be answered. One approach is to include HIV envelope immunogens derived from HIV-positive individuals from a geographically concentrated epidemic with more limited viral genetic diversity for a region-based vaccine. To address if there is a basis for a regional selected antibody vaccine, we have screened two regionally separate cohorts from Guinea-Bissau and Denmark for neutralizing antibody activity and antibody-dependent cellular cytotoxicity (ADCC) against local and nonlocal circulating HIV-1 strains. The neutralizing activity did not demonstrate higher potential against local circulating strains according to geography and subtype determination, but the plasma from Danish individuals demonstrated significantly higher inhibitory activity than that from Guinea-Bissau individuals against both local and nonlocal virus strains. Interestingly, an opposite pattern was observed with ADCC activity, where Guinea-Bissau individual plasma demonstrated higher activity than Danish plasma and was specifically against the local circulating subtype. Thus, on basis of samples from these two cohorts, no local-specific neutralizing activity was detected, but a local ADCC response was identified in the Guinea-Bissau samples, suggesting potential use of regional immunogens for an ADCC-inducing vaccine.

Preclinical Assessment of Viral Vectored and Protein Vaccines Targeting the Duffy-Binding Protein Region II of Plasmodium Vivax

Malaria vaccine development has largely focused on Plasmodium falciparum; however, a reawakening to the importance of Plasmodium vivax has spurred efforts to develop vaccines against this difficult to treat and at times severe form of relapsing malaria, which constitutes a significant proportion of human malaria cases worldwide. The almost complete dependence of P. vivax red blood cell invasion on the interaction of the P. vivax Duffy-binding protein region II (PvDBP_RII) with the human Duffy antigen receptor for chemokines (DARC) makes this antigen an attractive vaccine candidate against blood-stage P. vivax. Here, we generated both preclinical and clinically compatible adenoviral and poxviral vectored vaccine candidates expressing the Salvador I allele of PvDBP_RII – including human adenovirus serotype 5 (HAdV5), chimpanzee adenovirus serotype 63 (ChAd63), and modified vaccinia virus Ankara (MVA) vectors. We report on the antibody and T cell immunogenicity of these vaccines in mice or rabbits, either used alone in a viral vectored prime-boost regime or in “mixed-modality” adenovirus prime – protein-in-­adjuvant boost regimes (using a recombinant PvDBP_RII protein antigen formulated in Montanide^®ISA720 or Abisco^®100 adjuvants). Antibodies induced by these regimes were found to bind to native parasite antigen from P. vivax infected Thai patients and were capable of inhibiting the binding of PvDBP_RII to its receptor DARC using an in vitro binding inhibition assay. In recent years, recombinant ChAd63 and MVA vectors have been quickly translated into human clinical trials for numerous antigens from P. falciparum as well as a growing number of other pathogens. The vectors reported here are immunogenic in small animals, elicit antibodies against PvDBP_RII, and have recently entered clinical trials, which will provide the first assessment of the safety and immunogenicity of the PvDBP_RII antigen in humans.

Combining viral vectored and protein-in-adjuvant vaccines against the blood-stage malaria antigen AMA1: report on a phase 1a clinical trial

The development of effective vaccines against difficult disease targets will require the identification of new subunit vaccination strategies that can induce and maintain effective immune responses in humans. Here we report on a phase 1a clinical trial using the AMA1 antigen from the blood-stage Plasmodium falciparum malaria parasite delivered either as recombinant protein formulated with Alhydrogel adjuvant with and without CPG 7909, or using recombinant vectored vaccines—chimpanzee adenovirus ChAd63 and the orthopoxvirus MVA. A variety of promising “mixed-modality” regimens were tested. All volunteers were primed with ChAd63, and then subsequently boosted with MVA and/or protein-in-adjuvant using either an 8- or 16-week prime-boost interval. We report on the safety of these regimens, as well as the T cell, B cell, and serum antibody responses. Notably, IgG antibody responses primed by ChAd63 were comparably boosted by AMA1 protein vaccine, irrespective of whether CPG 7909 was included in the Alhydrogel adjuvant. The ability to improve the potency of a relatively weak aluminium-based adjuvant in humans, by previously priming with an adenoviral vaccine vector encoding the same antigen, thus offers a novel vaccination strategy for difficult or neglected disease targets when access to more potent adjuvants is not possible.

Boosting of HIV-1 neutralizing antibody responses by a distally related retroviral envelope protein

Our knowledge of the binding sites for neutralizing Abs (NAb) that recognize a broad range of HIV-1 strains (bNAb) has substantially increased in recent years. However, gaps remain in our understanding of how to focus B cell responses to vulnerable conserved sites within the HIV-1 envelope glycoprotein (Env). In this article, we report an immunization strategy composed of a trivalent HIV-1 (clade B envs) DNA prime, followed by a SIVmac239 gp140 Env protein boost that aimed to focus the immune response to structurally conserved parts of the HIV-1 and simian immunodeficiency virus (SIV) Envs. Heterologous NAb titers, primarily to tier 1 HIV-1 isolates, elicited during the trivalent HIV-1 env prime, were significantly increased by the SIVmac239 gp140 protein boost in rabbits. Epitope mapping of Ab-binding reactivity revealed preferential recognition of the C1, C2, V2, V3, and V5 regions. These results provide a proof of concept that a distally related retroviral SIV Env protein boost can increase pre-existing NAb responses against HIV-1.

Optimization of HIV-1 Envelope DNA Vaccine Candidates within Three Different Animal Models, Guinea Pigs, Rabbits and Cynomolgus Macaques

HIV-1 DNA vaccines have many advantageous features. Evaluation of HIV-1 vaccine candidates often starts in small animal models before macaque and human trials. Here, we selected and optimized DNA vaccine candidates through systematic testing in rabbits for the induction of broadly neutralizing antibodies (bNAb). We compared three different animal models: guinea pigs, rabbits and cynomolgus macaques. Envelope genes from the prototype isolate HIV-1 Bx08 and two elite neutralizers were included. Codon-optimized genes, encoded secreted gp140 or membrane bound gp150, were modified for expression of stabilized soluble trimer gene products, and delivered individually or mixed. Specific IgG after repeated i.d. inoculations with electroporation confirmed in vivo expression and immunogenicity. Evaluations of rabbits and guinea pigs displayed similar results. The superior DNA construct in rabbits was a trivalent mix of non-modified codon-optimized gp140 envelope genes. Despite NAb responses with some potency and breadth in guinea pigs and rabbits, the DNA vaccinated macaques displayed less bNAb activity. It was concluded that a trivalent mix of non-modified gp140 genes from rationally selected clinical isolates was, in this study, the best option to induce high and broad NAb in the rabbit model, but this optimization does not directly translate into similar responses in cynomolgus macaques.

The requirement for potent adjuvants to enhance the immunogenicity and protective efficacy of protein vaccines can be overcome by prior immunization with a recombinant adenovirus

A central goal in vaccinology is the induction of high and sustained Ab responses. Protein-in-adjuvant formulations are commonly used to achieve such responses. However, their clinical development can be limited by the reactogenicity of some of the most potent preclinical adjuvants and the cost and complexity of licensing new adjuvants for human use. Also, few adjuvants induce strong cellular immunity, which is important for protection against many diseases, such as malaria. We compared classical adjuvants such as aluminum hydroxide to new preclinical adjuvants and adjuvants in clinical development, such as Abisco 100, CoVaccine HT, Montanide ISA720, and stable emulsion-glucopyranosyl lipid A, for their ability to induce high and sustained Ab responses and T cell responses. These adjuvants induced a broad range of Ab responses when used in a three-shot protein-in-adjuvant regimen using the model Ag OVA and leading blood-stage malaria vaccine candidate Ags. Surprisingly, this range of Ab immunogenicity was greatly reduced when a protein-in-adjuvant vaccine was used to boost Ab responses primed by a human adenovirus serotype 5 vaccine recombinant for the same Ag. This human adenovirus serotype 5-protein regimen also induced a more cytophilic Ab response and demonstrated improved efficacy of merozoite surface protein-1 protein vaccines against a Plasmodium yoelii blood-stage challenge. This indicates that the differential immunogenicity of protein vaccine adjuvants may be largely overcome by prior immunization with recombinant adenovirus, especially for adjuvants that are traditionally considered poorly immunogenic in the context of subunit vaccination and may circumvent the need for more potent chemical adjuvants.

Tailoring subunit vaccine immunogenicity: maximizing antibody and T cell responses by using combinations of adenovirus, poxvirus and protein-adjuvant vaccines against Plasmodium falciparum MSP1

Subunit vaccination modalities tend to induce particular immune effector responses. Viral vectors are well known for their ability to induce strong T cell responses, while protein-adjuvant vaccines have been used primarily for induction of antibody responses. Here, we demonstrate in mice using a Plasmodium falciparum merozoite surface protein 1 (PfMSP1) antigen that novel regimes combining adenovirus and poxvirus vectored vaccines with protein antigen in Montanide ISA720 adjuvant can achieve simultaneous antibody and T cell responses which equal, or in some cases surpass, the best immune responses achieved by either the viral vectors or the protein vaccine alone. Such broad responses can be achieved either using three-stage vaccination protocols, or with an equally effective two-stage protocol in which viral vectors are admixed with protein and adjuvant, and were apparent despite the use of a protein antigen that represented only a portion of the viral vector antigen. We describe further possible advantages of viral vectors in achieving consistent antibody priming, enhanced antibody avidity, and cytophilic isotype skew. These data strengthen the evidence that tailored combinations of vaccine platforms can achieve desired combinations of immune responses, and further encourage the co-administration of antibody-inducing recombinant protein vaccines with T cell- and antibody-inducing recombinant viral vectors as one strategy that may achieve protective blood-stage malaria immunity in humans.

Pandemic influenza 1918 H1N1 and 1968 H3N2 DNA vaccines induce cross-reactive immunity in ferrets against infection with viruses drifted for decades

Please cite this paper as: Bragstad et al. (2010) Pandemic influenza 1918 H1N1 and 1968 H3N2 DNA vaccines induce cross‐reactive immunity in ferrets against infection with viruses drifted for decades. Influenza and Other Respiratory Viruses 5(1), 13–23.

Background  Alternative influenza vaccines and vaccine production forms are needed as the conventional protein vaccines do not induce broad cross‐reactivity against drifted strains. Furthermore, fast vaccine production is especially important in a pandemic situation, and broader vaccine reactivity would diminish the need for frequent change in the vaccine formulations.

Objective  In this study, we compared the ability of pandemic influenza DNA vaccines to induce immunity against distantly related strains within a subtype with the immunity induced by conventional trivalent protein vaccines against homologous virus challenge.

Methods  Ferrets were immunised by particle‐mediated epidermal delivery (gene gun) with DNA vaccines based on the haemagglutinin (HA) and neuraminidase (NA) and/or the matrix (M) and nucleoprotein genes of the 1918 H1N1 Spanish influenza pandemic virus or the 1968 H3N2 Hong Kong influenza pandemic virus. The animals were challenged with contemporary H1N1 or H3N2 viruses.

Results  We demonstrated that DNA vaccines encoding proteins of the original 1918 H1N1 pandemic virus induced protective cross‐reactive immune responses in ferrets against infection with a 1947 H1N1 virus and a recent 1999 H1N1 virus. Similarly, a DNA vaccine, based on the HA and NA of the 1968 H3N2 pandemic virus, induced cross‐reactive immune responses against a recent 2005 H3N2 virus challenge.

Conclusions  DNA vaccines based on pandemic or recent seasonal influenza genes induced cross‐reactive immunity against contemporary virus challenge as good as or superior to contemporary conventional trivalent protein vaccines. This suggests a unique ability of influenza DNA to induce cross‐protective immunity against both contemporary and long‐time drifted viruses.

A novel recombinant bacterial vaccine strain expressing dual viral antigens induces multiple immune responses to the Gag and gp120 proteins of HIV-1 in immunized mice

Recombinant Salmonella enterica serovar Typhi can function as a live vector to deliver foreign antigens to the mammalian immune system and induce both mucosal and systemic immunity. In this study, we generated a recombinant Salmonella Typhi strain pilS⁻pilT⁻Gag⁺(pVAX1-gp120) harboring the human immunodeficiency virus (HIV) gag gene integrated into the bacterial chromosome and gp120 gene carried by a plasmid. Mice inoculated with this recombinant bacterium through intranasal route produced high titers of IgG to gp120 in sera and IgA to gp120 in fecal washes. In addition, Gag-specific and gp120-specific cytotoxic T lymphocyte (CTL) responses were observed in sorted spleen lymphocytes of immunized mice. These results demonstrated that this recombinant Salmonella Typhi strain elicits multiple immune responses against both Gag and gp120 antigens of HIV, and thus would be a potential vaccine candidate to the prevention of HIV/AIDS.