Immunogenicity when utilizing adenovirus serotype 4 and 5 vaccines expressing circumsporozoite protein in naïve and adenovirus (Ad5) immune mice

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.

Semi-quantification of antibody-dependent enhancement (ADE) in the uptake of Adenovirus serotype 5 into THP-1 cells

Replication defective recombinant Ad5 vectors (rAdV5) are extensively explored for its applications in gene therapy and vaccine delivery. Ad5 enter into monocytes and macrophages through CAR independent route as an immune complex termed as antibody-dependent enhancement (ADE). We developed an effective method for estimating the ADE of rAdV5 encoding GFP (rAdV5-GFP) into THP-1 cells, using fluorimetric semi-quantification of GFP. Initially, twenty numbers of human sera samples were screened in HeLa cells for anti-Ad5 antibody titer using neutralization assay. Uptake of rAdV5-GFP in THP-1 cells was observed only after pre-incubation with the serially diluted human sera which are attributed to ADE. The optimal dilution which showed the maximum GFP expression as per the fluorescence microscopic analysis in THP-1 cells was used for further analysis. Fluorimetric analysis of the THP-1 cell lysate showed a maximum GFP intensity of 17058 RFU, which was equivalent to the 0.397 pmoles of Alexa Fluor 488 under the same experimental condition. Similarly, immunoblot analysis of GFP in THP-1 cell lysate and HeLa cell lysate confirmed the entry of rAdV5-GFP into the cells. The assay can serve as a platform for understanding the molecular events involved in ADE for the uptake of viruses into immune cells.

Comparative Evaluation of the Vaccine Efficacies of Three Adenovirus-Based Vector Types in the Friend Retrovirus Infection Model

Adenovirus (AdV)-based vectors are popular experimental vaccine vectors, but despite their ability to induce strong immune responses, their application is impeded by widespread preexisting immunity against many AdV types that can impair or even abrogate the induction of transgene-specific immune responses. Therefore, the development of vectors based on AdV types with a low seroprevalence is important for effective AdV-based immunization in humans. We investigated the immunization efficacy of vectors based on AdV type 48 (Ad48) and Ad50 in the ovalbumin (ova) model as well as the Friend retrovirus (FV) model, which allows testing of the protective effect of vaccine-induced immunity. Using ova-encoding vectors, we found a significantly lower induction of ova-specific CD8⁺ T cells and antibody responses by Ad48- and Ad50-based vectors than by Ad5-based vectors. Similarly, we found a reduced induction of FV-specific CD8⁺ T cell responses in Ad48- and Ad50.Leader-Gag-immunized mice compared with that in Ad5-immunized mice; however, some of those mice were able to control the FV infection, and protection correlated with the level of neutralizing antibodies 10 days after FV challenge. Analyses of the AdV-specific antibodies and CD8⁺ T cells induced by the individual AdV types revealed a high level of cross-reactivity, and the efficacy of Ad48-based immunization was impaired in Ad5-preimmune mice. Our results show that the immunity induced by Ad48- and Ad50-based vectors is reduced compared to that induced by Ad5 and is sufficient to control FV infection in only some of the immunized mice. A high level of cross-reactivity suggests that AdV preimmunity must be considered even when applying rare AdV-based vectors.IMPORTANCE AdV-based vectors are important tools for the development of vaccines against a wide range of pathogens. While AdV vectors are generally considered safe and highly effective, their application can be severely impaired by preexisting immunity due to the widespread seroprevalence of some AdV types. The characterization of different AdV types with regard to immunogenicity and efficacy in challenge models is of great importance for the development of improved AdV-based vectors that allow for efficient immunization despite anti-AdV immunity. We show that the immunity induced by an Ad48-based vector is inferior to that induced by an Ad5-based vector but can still mediate the control of an FV infection in highly FV-susceptible mice. However, the efficacy of Ad48-based immunization was impaired in Ad5-preimmune mice. Importantly, we found cross-reactivity of both the humoral and cellular immune responses raised by the individual AdV types, suggesting that switching to a different AdV type may not be sufficient to circumvent preexisting anti-AdV immunity.

Characterization of a replication-competent vector encoding DsRed based on a human adenovirus type 4 a-like strain

Human adenovirus type 4 (HAdV4) is an etiological agent of acute respiratory disease (ARD) in pediatric and adult patients. HAdV4 strains can be divided into two major genomic clusters, namely prototype (p)-like viruses and a-like viruses. Here, the complete genome sequence of HAdV4 strain GZ01, isolated from a child with ARD in southern China, is first reported and analyzed. This strain was determined to be of the 4a1 genome-type based on in silico restriction profiles. Then, a replication-competent rAd4DsRed virus, containing the HAdV4 GZ01 infectious genome and expressing the reporter molecule DsRed, was generated and characterized. Recombinant rAd4DsRed can infect AD293, hamster, and mouse cells in which DsRed protein was expressed. No changes in antigenicity and genome replication were detected for rAd4DsRed and wild-type HAdV4. Mice immunized with rAd4DsRed was elicited a marked antibody response to DsRed. A rapid method of testing neutralizing antibodies against HAdV3 and HAdV4 was also established using a mixture of rAd4DsRed and rAd3EGFP. Our results provide the foundation to develop HAdV4 vaccines, potential vector platforms for vaccine and gene therapy, and rapid methods for serological and antiviral screening.

Decreased Vector Gene Expression from E2b Gene-Deleted Adenovirus Serotype 5 Vaccines Intensifies Proinflammatory Immune Responses

Recombinant adenovirus serotype 5 (Ad5) vectors are promising vaccine candidates due to their intrinsic immunogenicity and potent transgene expression; however, widespread preexisting Ad5 immunity has been considered a developmental impediment to the use of traditional, or conventional, E1 and E3 gene-deleted Ad5 (Ad5[E1-]) vaccines. Even in the presence of anti-Ad5 immunity, recent murine and human studies have confirmed E2b gene-deleted Ad5 (Ad5[E1-,E2b-]) vaccines to be highly efficacious inducers of transgene-specific memory responses and significantly less toxic options than Ad5[E1-] vaccines. While these findings have been substantially confirmed, the molecular mechanisms underlying the different reactions to these vaccine platforms are unknown. Using cultures of human peripheral blood mononuclear cells (hPBMCs) derived from multiple human donors, we found that Ad5[E1-,E2b-] vaccines trigger higher levels of hPBMC proinflammatory cytokine secretion than Ad5[E1-] vaccines. Interestingly, these responses were generated regardless of the donors' preexisting anti-Ad5 humoral and cell-mediated immune response status. In vitro hPBMC infection with the Ad5[E1-,E2b-] vaccine also provoked greater Th1-dominant gene responses yet smaller amounts of Ad-derived gene expression than Ad5[E1-] vaccines. These results suggest that Ad5[E1-,E2b-] vaccines, in contrast to Ad5[E1-] vaccines, do not promote activities that suppress innate immune signaling, thereby allowing for improved vaccine efficacy and a superior safety profile independently of previous Ad5 immunity.

Adenoviral vectors as novel vaccines for influenza

OBJECTIVES

Influenza is a viral respiratory disease causing seasonal epidemics, with significant annual illness and mortality. Emerging viruses can pose a major pandemic threat if they acquire the capacity for sustained human-to-human transmission. Vaccination reduces influenza-associated mortality and is critical in minimising the burden on the healthcare system. However, current vaccines are not always effective in at-risk populations and fail to induce long-lasting protective immunity against a range of viruses.

KEY FINDINGS

The development of 'universal' influenza vaccines, which induce heterosubtypic immunity capable of reducing disease severity, limiting viral shedding or protecting against influenza subtypes with pandemic potential, has gained interest in the research community. To date, approaches have focused on inducing immune responses to conserved epitopes within the stem of haemagglutinin, targeting the ectodomain of influenza M2e or by stimulating cellular immunity to conserved internal antigens, nucleoprotein or matrix protein 1.

SUMMARY

Adenoviral vectors are potent inducers of T-cell and antibody responses and have demonstrated safety in clinical applications, making them an excellent choice of vector for delivery of vaccine antigens. In order to circumvent pre-existing immunity in humans, serotypes from non-human primates have recently been investigated. We will discuss the pre-clinical development of these novel vectors and their advancement to clinical trials.

CD46-mediated transduction of a species D adenovirus vaccine improves mucosal vaccine efficacy

The high levels of preexisting immunity against Adenovirus type 5 (Ad5) have deemed Ad5 unusable for translation as a human vaccine vector. Low seroprevalent alternative viral vectors may be less impacted by preexisting immunity, but they may also have significantly different phenotypes from that of Ad5. In this study we compare species D Ads (26, 28, and 48) to the species C Ad5. In vitro transduction studies show striking differences between the species C and D viruses. Most notably, Ad26 transduced human dendritic cells much more effectively than Ad5. In vivo imaging studies showed strikingly different transgene expression profiles. The Ad5 virus was superior to the species D viruses in BALB/c mice when delivered intramuscularly. However, the inverse was true when the viruses were delivered mucosally via the intranasal epithelia. Intramuscular transduction was restored in mice that ubiquitously expressed human CD46, the primary receptor for species D viruses. We analyzed both species C and D Ads for their ability to induce prophylactic immunity against influenza in the CD46 transgenic mouse model. Surprisingly, the species D vaccines again failed to induce greater levels of protective immunity as compared with the species C Ad5 when delivered intramuscularly. However, the species D Ad vaccine vector, Ad48, induced significantly greater protection as compared with Ad5 when delivered mucosally via the intranasal route in CD46 transgenic mice. These data shed light on the complexities between the species and types of Ad. Our findings indicate that more research will be required to identify the mechanisms that play a key role in the induction of protective immunity induced by species D Ad vaccines.

CD8+ T Cell Responses to Plasmodium and Intracellular Parasites

Parasitic protozoa are major threats to human health affecting millions of people around the world. Control of these infections by the host immune system relies on a myriad of immunological mechanisms that includes both humoral and cellular immunity. CD8⁺ T cells contribute to the control of these parasitic infections in both animals and humans. Here, we will focus on the CD8⁺ T cell response against a subset of these protozoa: Plasmodium, Toxoplasma gondii, Leishmania and Trypanosoma cruzi, with an emphasis on experimental rodent systems. It is evident a complex interaction occurs between CD8⁺ T cells and the invading protozoa. A detailed understanding of how CD8⁺ T cells mediate protection should provide the basis for the development of effective vaccines that prevent and control infections by these parasites.

Clinical assessment of a novel recombinant simian adenovirus ChAdOx1 as a vectored vaccine expressing conserved Influenza A antigens

Adenoviruses are potent vectors for inducing and boosting cellular immunity to encoded recombinant antigens. However, the widespread seroprevalence of neutralizing antibodies to common human adenovirus serotypes limits their use. Simian adenoviruses do not suffer from the same drawbacks. We have constructed a replication-deficient chimpanzee adenovirus-vectored vaccine expressing the conserved influenza antigens, nucleoprotein (NP), and matrix protein 1 (M1). Here, we report safety and T-cell immunogenicity following vaccination with this novel recombinant simian adenovirus, ChAdOx1 NP+M1, in a first in human dose-escalation study using a 3+3 study design, followed by boosting with modified vaccinia virus Ankara expressing the same antigens in some volunteers. We demonstrate ChAdOx1 NP+M1 to be safe and immunogenic. ChAdOx1 is a promising vaccine vector that could be used to deliver vaccine antigens where strong cellular immune responses are required for protection.

Randomized, placebo-controlled trial to assess the safety and immunogenicity of an adenovirus type 35-based circumsporozoite malaria vaccine in healthy adults

Malaria results in over 650,000 deaths each year; thus, there is an urgent need for an effective vaccine. Pre-clinical studies and recently reported human trials suggest that pre-erythrocytic stage vaccines can provide protection against infection. A Phase 1, randomized, placebo-controlled, dose-escalation study was conducted with a vaccine composed of a replication-deficient adenovirus-35 backbone with P. falciparum circumsporozoite (CS) surface antigen (Ad35.CS.01). Healthy adult subjects received three doses of 10 (8), 10 (9), 10 (10), or 10 (11) vp/mL Ad35.CS.01 vaccine or saline placebo intramuscularly at 0, 1, and 6-mo intervals. Adverse events were assessed and anti-CS antibody responses were determined by ELISA. Seventy-two individuals were enrolled, with age, gender, and ethnicity similar across each study arm. While the vaccine was generally well tolerated, adverse events were more frequent in the highest dose groups (10 (10) and 10 (11) vp/mL). More robust humoral responses were also noted at the highest doses, with 73% developing a positive ELISA response after the three dose series of 10 (11) vp/mL. The Ad35.CS.01 vaccine was most immunogenic at the highest dosages (10 (10) and 10 (11) vp/mL). Reactogenicity findings were more common after the 10 (11) vp/mL dose, although most were mild or moderate in nature and resolved without therapy.