Non-clinical evaluation of local and systemic immunity induced by different vaccination strategies of the candidate tuberculosis vaccine M72/AS01

A new efficacious tuberculosis vaccine targeting adolescents/adults represents an urgent medical need. The M72/AS01E vaccine candidate protected half of the latently-infected adults against progression to pulmonary tuberculosis in a Phase IIb trial (NCT01755598). We report that three immunizations of mice, two weeks apart, with AS01-adjuvanted M72 induced polyfunctional, Th1-cytokine-expressing M72-specific CD4+/CD8+ T cells in blood and lungs, with the highest frequencies in lungs. Antigen-dose reductions across the three vaccinations skewed pulmonary CD4+ T-cell profiles towards IL-17 expression. In blood, reducing antigen and adjuvant doses of only the third injection (to 1/5th or 1/25th of those of the first injections) did not significantly alter CD4+ T-cell/antibody responses; applying a 10-week delay for the fractional third dose enhanced antibody titers. Delaying a full-dose booster enhanced systemic CD4+ T-cell and antibody responses. Cross-reactivity with PPE and non-PPE proteins was assessed, as Mycobacterium tuberculosis (Mtb) virulence factors and evasion mechanisms are often associated with PE/PPE proteins, to which Mtb39a (contained in M72) belongs. In silico/in vivo analyses revealed that M72/AS01 induced cross-reactive systemic CD4+ T-cell responses to epitopes in a non-vaccine antigen (putative latency-associated Mtb protein PPE24/Rv1753c). These preclinical data describing novel mechanisms of M72/AS01-induced immunity could guide future clinical development of the vaccine.

The RSVPreF3-AS01 vaccine elicits broad neutralization of contemporary and antigenically distant respiratory syncytial virus strains

The RSVPreF3-AS01 vaccine, containing the respiratory syncytial virus (RSV) prefusion F protein and the AS01 adjuvant, was previously shown to boost neutralization responses against historical RSV strains and to be efficacious in preventing RSV-associated lower respiratory tract diseases in older adults. Although RSV F is highly conserved, variation does exist between strains. Here, we characterized variations in the major viral antigenic sites among contemporary RSV sequences when compared with RSVPreF3 and showed that, in older adults, RSVPreF3-AS01 broadly boosts neutralization responses against currently dominant and antigenically distant RSV strains. RSV-neutralizing responses are thought to play a central role in preventing RSV infection. Therefore, the breadth of RSVPreF3-AS01-elicited neutralization responses may contribute to vaccine efficacy against contemporary RSV strains and those that may emerge in the future.

Detection of post-vaccination enhanced dengue virus infection in macaques: An improved model for early assessment of dengue vaccines

The need for improved dengue vaccines remains since the only licensed vaccine, Dengvaxia, shows variable efficacy depending on the infecting dengue virus (DENV) type, and increases the risk of hospitalization for severe dengue in children not exposed to DENV before vaccination. Here, we developed a tetravalent dengue purified and inactivated vaccine (DPIV) candidate and characterized, in rhesus macaques, its immunogenicity and efficacy to control DENV infection by analyzing, after challenge, both viral replication and changes in biological markers associated with dengue in humans. Although DPIV elicited cross-type and long-lasting DENV-neutralizing antibody responses, it failed to control DENV infection. Increased levels of viremia/RNAemia (correlating with serum capacity at enhancing DENV infection in vitro), AST, IL-10, IL-18 and IFN-γ, and decreased levels of IL-12 were detected in some vaccinated compared to non-vaccinated monkeys, indicating the vaccination may have triggered antibody-dependent enhancement of DENV infection. The dengue macaque model has been considered imperfect due to the lack of DENV-associated clinical signs. However, here we show that post-vaccination enhanced DENV infection can be detected in this model when integrating several parameters, including characterization of DENV-enhancing antibodies, viremia/RNAemia, and biomarkers relevant to dengue in humans. This improved dengue macaque model may be crucial for early assessment of efficacy and safety of future dengue vaccines.

Dengue virus (DENV) is responsible for the most widespread arboviral disease affecting humans. A pre-existing suboptimal immunity to DENV is accepted as being the major risk factor for severe dengue. Thus, if vaccination does not elicit optimal DENV-specific immunity, a vaccine might, instead, increase the risk of severe dengue in vaccinated individuals, as seen with the only licensed vaccine (Dengvaxia) in children naïve to DENV at vaccination. It is thus crucial to assess dengue vaccine safety at the earliest development stages, ideally in the preclinical stage. The dengue macaque model has been used to assess preclinical efficacy of dengue vaccines, with post-challenge DENV replication as the sole efficacy endpoint. However, this model had not predicted the Dengvaxia-associated safety signals. Here we characterized, in macaques, a dengue purified and inactivated vaccine (DPIV) candidate for its immunogenicity and efficacy/safety. Using a multiparameter approach, including characterization of viral replication and biomarkers relevant to dengue/severe dengue in humans, we were able to detect vaccine-associated safety signals in this model. While these results enabled us to discontinue at an early stage the DPIV development, this improved dengue macaque model may also be instrumental for early assessment of efficacy/safety of future dengue vaccines.

Characterization of recent and minimally passaged Brazilian dengue viruses inducing robust infection in rhesus macaques

The macaque is widely accepted as a suitable model for preclinical characterization of dengue vaccine candidates. However, the only vaccine for which both preclinical and clinical efficacy results were reported so far showed efficacy levels that were substantially different between macaques and humans. We hypothesized that this model’s predictive capacity may be improved using recent and minimally passaged dengue virus isolates, and by assessing vaccine efficacy by characterizing not only the post-dengue virus challenge viremia/RNAemia but also the associated-cytokine profile. Ten recent and minimally passaged Brazilian clinical isolates from the four dengue virus serotypes were tested for their infectivity in rhesus macaques. For the strains showing robust replication capacity, the associated-changes in soluble mediator levels, and the elicited dengue virus-neutralizing antibody responses, were also characterized. Three isolates from dengue virus serotypes 1, 2 and 4 induced viremia of high magnitude and longer duration relative to previously reported viremia kinetics in this model, and robust dengue virus-neutralizing antibody responses. Consistent with observations in humans, increased MCP-1, IFN-γ and VEGF-A levels, and transiently decreased IL-8 levels were detected after infection with the selected isolates. These results may contribute to establishing a dengue macaque model showing a higher predictability for vaccine efficacy in humans.

Ad35.CS.01-RTS,S/AS01 Heterologous Prime Boost Vaccine Efficacy against Sporozoite Challenge in Healthy Malaria-Naïve Adults

Methods

In an observer blind, phase 2 trial, 55 adults were randomized to receive one dose of Ad35.CS.01 vaccine followed by two doses of RTS,S/AS01 (ARR-group) or three doses of RTS,S/AS01 (RRR-group) at months 0, 1, 2 followed by controlled human malaria infection.

Results

ARR and RRR vaccine regimens were well tolerated. Efficacy of ARR and RRR groups after controlled human malaria infection was 44% (95% confidence interval 21%-60%) and 52% (25%-70%), respectively. The RRR-group had greater anti-CS specific IgG titers than did the ARR-group. There were higher numbers of CS-specific CD4 T-cells expressing > 2 cytokine/activation markers and more ex vivo IFN-γ enzyme-linked immunospots in the ARR-group than the RRR-group. Protected subjects had higher CS-specific IgG titers than non-protected subjects (geometric mean titer, 120.8 vs 51.8 EU/ml, respectively; P = .001).

Conclusions

An increase in vaccine efficacy of ARR-group over RRR-group was not achieved. Future strategies to improve upon RTS,S-induced protection may need to utilize alternative highly immunogenic prime-boost regimens and/or additional target antigens.

Trial Registration

ClinicalTrials.gov NCT01366534

Heterologous prime-boost regimens with a recombinant chimpanzee adenoviral vector and adjuvanted F4 protein elicit polyfunctional HIV-1-specific T-Cell responses in macaques

HIV-1-specific CD4+ and CD8+ T lymphocytes are important for HIV-1 replication control. F4/AS01 consists of F4 recombinant fusion protein (containing clade B Gag/p24, Pol/RT, Nef and Gag/p17) formulated in AS01 Adjuvant System, and was shown to induce F4-specific polyfunctional CD4+ T-cell responses in humans. While replication-incompetent recombinant HIV-1/SIV antigen-expressing human adenoviral vectors can elicit high-frequency antigen-specific CD8+ T-cell responses, their use is hampered by widespread pre-existing immunity to human serotypes. Non-human adenovirus serotypes associated with lower prevalence may offer an alternative strategy. We evaluated the immunogenicity of AdC7-GRN ('A'), a recombinant chimpanzee adenovirus type 7 vector expressing clade B Gag, RT and Nef, and F4/AS01 ('P'), when delivered intramuscularly in homologous (PP or AA) and heterologous (AAPP or PPAA) prime-boost regimens, in macaques and mice. Vaccine-induced HIV-1-antigen-specific T cells in peripheral blood (macaques), liver, spleen, and intestinal and genital mucosa (mice) were characterized by intracellular cytokine staining. Vaccine-specific IgG antibodies (macaques) were detected using ELISA. In macaques, only the heterologous prime-boost regimens induced polyfunctional, persistent and balanced CD4+ and CD8+ T-cell responses specific to each HIV-1 vaccine antigen. AdC7-GRN priming increased the polyfunctionality of F4/AS01-induced CD4+ T cells. Approximately 50% of AdC7-GRN-induced memory CD8+ T cells exhibited an effector-memory phenotype. HIV-1-specific antibodies were detected with each regimen. In mice, antigen-specific CD4+ and CD8+ T-cell responses were detected in the mucosal and systemic anatomical compartments assessed. When administered in heterologous prime-boost regimens, AdC7-GRN and F4/AS01 candidate vaccines acted complementarily in inducing potent and persistent peripheral blood HIV-1-specific CD4+ and CD8+ T-cell responses and antibodies in macaques. Besides, adenoviral vector priming modulated the cytokine-expression profile of the protein-induced CD4+ T cells. Each regimen induced HIV-1-specific T-cell responses in systemic/local tissues in mice. This suggests that prime-boost regimens combining adjuvanted protein and low-seroprevalent chimpanzee adenoviral vectors represent an attractive vaccination strategy for clinical evaluation.

Identification of non-CSP antigens bearing CD8 epitopes in mice immunized with irradiated sporozoites

Immunization of BALB/c mice with irradiated sporozoites (IrSp) of Plasmodium yoelii can lead to sterile immunity. The circumsporozoite protein (CSP) plays a dominant role in protection. Nevertheless after hyper-immunization with IrSp, complete protection is obtained in CSP-transgenic BALB/c mice that are T-cell tolerant to the CSP and cannot produce antibodies [CSP-Tg/JhT(-/-)]. This protection is mediated exclusively by CD8(+) T cells [1]. To identify the non-CSP protective T cell antigens, we studied the properties of 34 P. yoelii sporozoite antigens that are predicted to be secreted and to contain strong Kd-restricted CD8(+) T cell epitopes. The synthetic peptides corresponding to the epitopes were used to screen for the presence of peptide-specific CD8(+) T cells secreting interferon-γ (IFN-γ) in splenocytes from CSP-Tg/JhT(-/-) BALB/c mice hyper immunized with IrSp. However, the numbers of IFN-γ-secreting splenocytes specific for the non-CSP antigen-derived peptides were 20-100 times lower than those specific for the CSP-specific peptide. When mice were immunized with recombinant adenoviruses expressing selected non-CSP antigens, the animals were not protected against challenge with P. yoelii sporozoites although large numbers of CD8(+) specific T cells were generated.

Interplay between CD8α+ dendritic cells and monocytes in response to Listeria monocytogenes infection attenuates T cell responses

During the course of a microbial infection, different antigen presenting cells (APCs) are exposed and contribute to the ensuing immune response. CD8α(+) dendritic cells (DCs) are an important coordinator of early immune responses to the intracellular bacteria Listeria monocytogenes (Lm) and are crucial for CD8(+) T cell immunity. In this study, we examine the contribution of different primary APCs to inducing immune responses against Lm. We find that CD8α(+) DCs are the most susceptible to infection while plasmacytoid DCs are not infected. Moreover, CD8α(+) DCs are the only DC subset capable of priming an immune response to Lm in vitro and are also the only APC studied that do so when transferred into β2 microglobulin deficient mice which lack endogenous cross-presentation. Upon infection, CD11b(+) DCs primarily secrete low levels of TNFα while CD8α(+) DCs secrete IL-12 p70. Infected monocytes secrete high levels of TNFα and IL-12p70, cytokines associated with activated inflammatory macrophages. Furthermore, co-culture of infected CD8α(+) DCs and CD11b+ DCs with monocytes enhances production of IL-12 p70 and TNFα. However, the presence of monocytes in DC/T cell co-cultures attenuates T cell priming against Lm-derived antigens in vitro and in vivo. This suppressive activity of spleen-derived monocytes is mediated in part by both TNFα and inducible nitric oxide synthase (iNOS). Thus these monocytes enhance IL-12 production to Lm infection, but concurrently abrogate DC-mediated T cell priming.

The immunology of Leishmania infection and the implications for vaccine development

Leishmania parasites are vector-borne protozoal pathogens found in tropical and subtropical regions of both the Old and New World. These parasites can cause visceral or cutaneous disease, and the pathology of the infection is determined by both host immune factors and species/strain differences of the parasite. Dogs are an important reservoir for maintaining the population of Leishmania parasites that can lead to visceral leishmaniasis in humans, and a vaccination approach may be an effective method for reducing the numbers of infected dogs. Resistance to leishmaniasis has been consistently associated with a T helper 1 immune response, characterized by the production of IFN-gamma by the antigen-specific lymphocyte population. The development of this Th1 response has been shown to be dependent upon both cytokines and dendritic cells during T cell activation. However, the development of a Leishmania vaccine effective in preventing these chronic diseases has proven to be a challenge. Vaccine trials have focused on whole-killed or subunit vaccines with adjuvants. Newer experimental strategies involve the attenuation of the Leishmania parasite via gene deletion technologies or the expression of specific Leishmania peptides within attenuated organisms, such as Bacillus Calmette Guérin. DNA vaccines and dendritic cell potentiators, such as CpG oligodeoxynucleotides and Flt-3 ligand, are also in the early stage of development. In addition, as part of blocking the transmission cycle of leishmaniasis, several laboratories are also exploring the possibility of immunomodulating the host toward the bite of the sand fly.

Late Cutaneous Metastases in C3H SCID Mice Infected with Leishmania amazonensis

The biological behavior of Leishmania amazonensis in the mammalian host is highly variable, resulting in local to diffuse cutaneous lesions that sometimes metastasize. Inflammation and, more specifically, CD4+ T cells have been shown to enhance metastases in mice infected with L. amazonensis, suggesting that the process may be lymphocyte mediated. However, we document, in this study, the development of multiple cutaneous metastases in C3H SCID mice infected with L. amazonensis. This shows that functional T and B cells are not required for metastases to occur.

Protection of C3HeB/FeJ mice against Leishmania amazonensis challenge after previous Leishmania major infection

The Th1 response elicited in mice infected with Leishmania major has been used as a model to characterize cellular immune defects associated with L. amazonensis infection. However, it is not known if the immune response associated with the infection by virulent L. major parasites can promote resistance to a subsequent L. amazonensis infection. Our data demonstrate that C3HeB/FeJ mice infected subcutaneously with virulent L. major are resistant to an L. amazonensis challenge. The healing phenotype is characterized by a Th1 response as measured by increased production of interferon-gamma and low levels of interleukin-4 in the draining lymph node. Together, this indicates that the Th1 response associated with L. major infection can promote resistance to L. amazonensis infection and that it can be used as a tool to study the immune defects associated with L. amazonensis infection.

The biology of dendritic cells and their potential use in veterinary medicine

Dendritic cells have been shown to be the main antigen-presenting cells in vitro and in vivo, playing a pivotal role in the induction of both tolerance and immunity. Dendritic cells from humans and mice have been extensively studied and dendritic cell-based vaccines have been shown to be effective in the prevention and treatment of infectious, allergic and neoplastic diseases. Studies of dendritic cells of domestic animal origin are becoming available and confirm a role for these cells in the pathogenesis of a variety of animal diseases, suggesting that dendritic cells could be used as adjuvants for prophylactic and therapeutic strategies in veterinary medicine.

Intracellular trafficking of Mycobacterium avium ss. paratuberculosis in macrophages

The granulomatous enteric lesions of cattle with Johne's disease are composed of infected macrophages, and grow by accumulation, re-infection, and expansion of macrophage populations in the intestinal wall. We have examined the growth of bacteria in macrophages to define characteristics of intracellular trafficking for exocytosis, replication, and antigen presentation. Using immunocytochemical markers for light, confocal and electron microscopy, we have examined potential pathway tropisms using data for bacterial attachment, phagosomal acidification, phagolysosomal degradation and apoptosis. Our hypotheses are that pathogenic/wild-type strains block phagosomal acidification so that the phagosome fails to obtain markers of the late phagosome and phagolysosome, and this leads to the replication pathway within bacteriophorous vacuoles. Non-pathogenic strains appear to be processed to exocytosis, and avirulent mutant strains may be degraded and have preference of antigen processing pathways that involve transport vesicles bearing MHC II antigens. Pathogenicity in a nude mouse model of intestinal infection reveals lesion development and confirms pathway preferences of virulent strains for bacteriophorous vacuole formation.