Review of the current TB human infection studies for use in accelerating TB vaccine development: A meeting report.

Tools to evaluate and accelerate tuberculosis (TB) vaccine development are needed to advance global TB control strategies. Validated human infection studies for TB have the potential to facilitate breakthroughs in understanding disease pathogenesis, identify correlates of protection, develop diagnostic tools, and accelerate and de-risk vaccine and drug development. However, key challenges remain for realizing the clinical utility of these models, which require further discussion and alignment amongst key stakeholders. In March 2023, the Wellcome Trust and the International AIDS Vaccine Initiative (IAVI) convened international experts involved in developing both TB and Bacillus Calmette-Guerin (BCG) human infection studies (including mucosal and intradermal challenge routes) to discuss the status of each of the models and the key enablers to move the field forward. This report provides a summary of the presentations and discussion from the meeting. Discussions identified key issues, including demonstrating model validity, to provide confidence for vaccine developers, which may be addressed through demonstration of known vaccine effects, e.g. BCG vaccination in specific populations, and by comparing results from field efficacy and human infection studies. The workshop underscored the importance of establishing safe and acceptable studies in high-burden settings, and the need to validate more than one model to allow for different scientific questions to be addressed as well as to provide confidence to vaccine developers and regulators around use of human infection study data in vaccine development and licensure pathways.

Ethical approval for controlled human infectious model clinical trial protocols - A workshop report.

Controlled Human Infectious Model studies (CHIM) involve deliberately exposing volunteers to pathogens. To discuss ethical issues related to CHIM, the European Vaccine Initiative and the International Alliance for Biological Standardization organised the workshop "Ethical Approval for CHIM Clinical Trial Protocols", which took place on May 30-31, 2023, in Brussels, Belgium. The event allowed CHIM researchers, regulators, ethics committee (EC) members, and ethicists to examine the ethical criteria for CHIM and the role(s) of CHIM in pharmaceutical development. The discussions led to several recommendations, including continued assurance that routine ethical requirements are met, assurance that participants are well-informed, and that preparation of study documents must be both ethically and scientifically sound from an early stage. Study applications must clearly state the rationale for the challenge compared to alternative study designs. ECs need to have clear guidance and procedures for evaluating social value and assessing third-party risks. Among other things, public trust in research requires minimisation of harm to healthy volunteers and third-party risk. Other important considerations include appropriate stakeholder engagement, public education, and access to health care for participants after the study.

Fourth Controlled Human Infection Model (CHIM) meeting, CHIM regulatory issues, May 24, 2023.

Many aspects of Controlled Human Infection Models (CHIMs, also known as human challenge studies and human infection studies) have been discussed extensively, including Good Manufacturing Practice (GMP) production of the challenge agent, CHIM ethics, environmental safety in CHIM, recruitment, community engagement, advertising and incentives, pre-existing immunity, and clinical, immunological, and microbiological endpoints. The fourth CHIM meeting focused on regulation of CHIM studies, bringing together scientists and regulators from high-, middle-, and low-income countries, to discuss barriers and hurdles in CHIM regulation. Valuable initiatives for regulation of CHIMs have already been undertaken but further capacity building remains essential. The Wellcome Considerations document is a good starting point for further discussions.

Fourth Controlled Human Infection Model (CHIM) meeting - CHIMs in endemic countries, May 22-23, 2023.

Earlier meetings laid the foundations for Controlled Human Infection Models (CHIMs), also known as human challenge studies and human infection studies, including Good Manufacturing Practice (GMP) production of the challenge agent, CHIM ethics, environmental safety in CHIM, recruitment, community engagement, advertising and incentives, pre-existing immunity, and clinical, immunological, and microbiological endpoints. The fourth CHIM meeting focused on CHIM studies being conducted in endemic countries. Over the last ten years we have seen a vast expansion of the number of countries in Africa performing CHIM studies, as well as a growing number of different challenge organisms being used. Community and public engagement with assiduous ethical and regulatory oversight has been central to successful introductions and should be continued, in more community-led or community-driven models. Valuable initiatives for regulation of CHIMs have been undertaken but further capacity building remains essential.

Practical considerations for a TB controlled human infection model (TB-CHIM); the case for TB-CHIM in Africa, a systematic review of the literature and report of 2 workshop discussions in UK and Malawi.

Background: Tuberculosis (TB) remains a major challenge in many domains including diagnosis, pathogenesis, prevention, treatment, drug resistance and long-term protection of the public health by vaccination. A controlled human infection model (CHIM) could potentially facilitate breakthroughs in each of these domains but has so far been considered impossible owing to technical and safety concerns. Methods: A systematic review of mycobacterial human challenge studies was carried out to evaluate progress to date, best possible ways forward and challenges to be overcome. We searched MEDLINE (1946 to current) and CINAHL (1984 to current) databases; and Google Scholar to search citations in selected manuscripts. The final search was conducted 3 rd February 2022. Inclusion criteria: adults ≥18 years old; administration of live mycobacteria; and interventional trials or cohort studies with immune and/or microbiological endpoints. Exclusion criteria: animal studies; studies with no primary data; no administration of live mycobacteria; retrospective cohort studies; case-series; and case-reports. Relevant tools (Cochrane Collaboration for RCTs and Newcastle-Ottawa Scale for non-randomised studies) were used to assess risk of bias and present a narrative synthesis of our findings. Results: The search identified 1,388 titles for review; of these 90 were reviewed for inclusion; and 27 were included. Of these, 15 were randomised controlled trials and 12 were prospective cohort studies. We focussed on administration route, challenge agent and dose administered for data extraction. Overall, BCG studies including fluorescent BCG show the most immediate utility, and genetically modified Mycobacteria tuberculosis is the most tantalising prospect of discovery breakthrough. Conclusions: The TB-CHIM development group met in 2019 and 2022 to consider the results of the systematic review, to hear presentations from many of the senior authors whose work had been reviewed and to consider best ways forward. This paper reports both the systematic review and the deliberations. Registration: PROSPERO ( CRD42022302785; 21 January 2022).

A Brief History of Human Challenge Studies (1900-2021) Emphasising the Virology, Regulatory and Ethical Requirements, Raison D'etre, Ethnography, Selection of Volunteers and Unit Design.

Venetian quarantine 400 years ago was an important public health measure. Since 1900 this has been refined to include "challenge" or deliberate infection with pathogens be they viruses, bacteria, or parasites. Our focus is virology and ranges from the early experiments in Cuba with Yellow Fever Virus to the most widespread pathogen of our current times, COVID-19. The latter has so far caused over four million deaths worldwide and 190 million cases of the disease. Quarantine and challenge were also used to investigate the Spanish Influenza of 1918 which caused over 100 million deaths. We consider here the merits of the approach, that is the speeding up of knowledge in a practical sense leading to the more rapid licensing of vaccines and antimicrobials. At the core of quarantine and challenge initiatives is the design of the unit to allow safe confinement of the pathogen and protection of the staff. Most important though is the safety of volunteers. We can see now, as in 1900, that members of our society are prepared and willing to engage in these experiments for the public good. Our ethnology study, where the investigator observed the experiment from within the quarantine, gave us the first indication of changing attitudes amongst volunteers whilst in quarantine. These quarantine experiments, referred to as challenge studies, human infection studies, or "controlled human infection models" involve thousands of clinical samples taken over two to three weeks and can provide a wealth of immunological and molecular data on the infection itself and could allow the discovery of new targets for vaccines and therapeutics. The Yellow Fever studies from 121 years ago gave the impetus for development of a successful vaccine still used today whilst also uncovering the nature of the Yellow Fever agent, namely that it was a virus. We outline how carefully these experiments are approached and the necessity to have high quality units with self-contained air-flow along with extensive personal protective equipment for nursing and medical staff. Most important is the employment of highly trained scientific, medical and nursing staff. We face a future of emerging pathogens driven by the increasing global population, deforestation, climate change, antibiotic resistance and increased global travel. These emerging pathogens may be pathogens we currently are not aware of or have not caused outbreaks historically but could also be mutated forms of known pathogens including viruses such as influenza (H7N9, H5N1 etc.) and coronaviruses. This calls for challenge studies to be part of future pandemic preparedness as an additional tool to assist with the rapid development of broad-spectrum antimicrobials, immunomodulators and new vaccines.

Human infection studies: Key considerations for challenge agent development and production.

Human infection (or challenge) studies involve the intentional administration of a pathogen (challenge agent) to volunteers. The selection, isolation, development and production of the challenge agent is one of the first steps in developing a challenge study and critical for minimising the risk to volunteers. Regulatory oversight for this production differs globally. Manufacturing agents within a Good Manufacturing Practice (GMP) facility reduces the risk of the manufacturing process by including processes such as confirming the identity of the challenge agent and ascertaining that it's pure and free from impurities. However, in some cases it's not possible or feasible to manufacture to GMP standards, for example where the challenge agent requires an intermediate vector for growth. There is lack of clear guidance on what the minimum requirements for high-quality safe manufacture outside of GMP facilities should be and here we describe the development of a considerations document for the selection and production of challenge agents to meet this need.

Viewpoint of a WHO Advisory Group Tasked to Consider Establishing a Closely-monitored Challenge Model of Coronavirus Disease 2019 (COVID-19) in Healthy Volunteers.

WHO convened an Advisory Group (AG) to consider the feasibility, potential value, and limitations of establishing a closely-monitored challenge model of experimental severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19) in healthy adult volunteers. The AG included experts in design, establishment, and performance of challenges. This report summarizes issues that render a COVID-19 model daunting to establish (the potential of SARS-CoV-2 to cause severe/fatal illness, its high transmissibility, and lack of a "rescue treatment" to prevent progression from mild/moderate to severe clinical illness) and it proffers prudent strategies for stepwise model development, challenge virus selection, guidelines for manufacturing challenge doses, and ways to contain SARS-CoV-2 and prevent transmission to household/community contacts. A COVID-19 model could demonstrate protection against virus shedding and/or illness induced by prior SARS-CoV-2 challenge or vaccination. A limitation of the model is that vaccine efficacy in experimentally challenged healthy young adults cannot per se be extrapolated to predict efficacy in elderly/high-risk adults.

Randomized controlled trials for influenza drugs and vaccines: a review of controlled human infection studies.

OBJECTIVES: Controlled human infection, the intentional infection of healthy volunteers, allows disease pathogenesis to be studied and vaccines and therapeutic interventions to be evaluated in a controlled setting. A systematic review of randomized controlled trials of countermeasures for influenza that used the experimental human infection platform was performed. The primary objective was to document the scope of trials performed to date and the main efficacy outcome in the trials. The secondary objective was to assess safety and identify serious adverse events. METHODS: The PubMed database was searched for randomized controlled influenza human challenge studies with predetermined search terms. Review papers, papers without outcomes, community-acquired infections, duplicated data, pathogenesis studies, and observational studies were excluded. RESULTS: Twenty-six randomized controlled trials published between 1947 and 2014 fit the study inclusion criteria. Two-thirds of these trials investigated antivirals and one-third investigated influenza vaccines. Among 2462 subjects inoculated with influenza virus, the incidence of serious adverse events was low (0.04%). These challenge studies helped to down-select three antivirals and one vaccine that were subsequently approved by the US Food and Drug Administration (FDA). CONCLUSIONS: Controlled human infection studies are an important research tool in assessing promising influenza vaccines and antivirals. These studies are performed quickly and are cost-effective and safe, with a low incidence of serious adverse events.

Low antibody titers 5 years after vaccination with the CYD-TDV dengue vaccine in both pre-immune and naïve vaccinees.

Globally, dengue virus (DENV) is one of the most widespread vector-borne viruses. Dengue disease affects populations in endemic areas and, increasingly, tourists who travel to these countries, but there is currently no approved vaccine for dengue. A phase 3 efficacy trial with Sanofi-Pasteur's recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) conducted in South East Asia showed an overall efficacy of 56% against virologically confirmed dengue infections of any severity and any of the 4 serotypes, but the long-term protection of the vaccine has yet to be demonstrated. To address longevity of antibody titers and B cell memory, we recalled study participants from an earlier CYD immunogenicity study (Phase 2) conducted in Singapore that enrolled healthy volunteers in the year 2009. Depending on the age group, 57-84% of the participants initially generated a neutralizing antibody titer ≥ 10 to all 4 DENV serotypes 28 d after the third and final dose. We observed very low antibody titers in blood samples collected from 23 vaccinees 5 y after the first dose, particularly titers of antibodies binding to virus particles compared with those binding to recombinant E protein. The in vivo efficacy of plasma antibodies against DENV-2 challenge was also tested in a mouse model, which found that only 2 out of 23 samples were able to reduce viremia. Although the sample size is too small for general conclusions, dengue immune memory after vaccination with CYD-TDV appears relatively low.

The potential for a controlled human infection platform in Singapore.

For over 100 years, controlled human infection (CHI) studies have been performed to advance the understanding of the pathogenesis, treatment and prevention of infectious diseases. This methodology has seen a resurgence, as it offers an efficient model for selecting the most promising agents for further development from available candidates. CHI studies are utilised to bridge safety and immunogenicity testing and phase II/III efficacy studies. However, as this platform is not currently utilised in Asia, opportunities to study therapeutics and vaccines for infections that are important in Asia are missed. This review examines the regulatory differences for CHI studies between countries and summarises other regulatory differences in clinical trials as a whole. We found that the regulations that would apply to CHI studies in Singapore closely mirror those in the United Kingdom, and conclude that the regulatory and ethical guidelines in Singapore are compatible with the conduct of CHI studies.

A new intranasal influenza vaccine based on a novel polycationic lipid-ceramide carbamoyl-spermine (CCS). II. Studies in mice and ferrets and mechanism of adjuvanticity.

We recently showed that lipid assemblies comprised of a novel polycationic sphingolipid (ceramide carbamoyl-spermine, CCS) are an effective adjuvant/carrier when complexed with cholesterol (CCS/C) for influenza and other vaccines administered parenterally and intranasally (i.n.) in mice. Here we expand these studies to ferrets, an established model of influenza infection. We also address the question of why the CCS/C-based liposomal vaccine (also known as VaxiSome™) in mice is superior to vaccines based on liposomes of other lipid compositions (neutral, anionic or cationic). Ferrets immunized i.n. with CCS/C-influenza vaccine produced significantly higher hemagglutination inhibition (HI) antibody titers compared to ferrets immunized intramuscularly with the unadjuvanted influenza vaccine, indicating that the CCS/C-based vaccine is very immunogenic. Furthermore, the i.n. adjuvanted vaccine was shown to significantly reduce the severity of influenza virus infection in ferrets following homologous viral challenge as determined by weight loss, temperature rise and viral titer. No adverse reactions were observed. Pharmacokinetic and biodistribution studies following i.n. administration in mice of CCS/C-based vaccine showed that both the lipids and antigens are retained in the nose and lung for at least 24h, and it appears that this retention correlates with the superior immunogenicity elicited by the adjuvanted vaccine formulation. The CCS lipid also increases production of cytokines (mainly IFN gamma, IL-2 and IL-12) and co-stimulatory molecules' expression, which might further explain the robust adjuvantation of this liposome-based vaccine.

Immunogenicity, protective efficacy and mechanism of novel CCS adjuvanted influenza vaccine.

We optimized the immunogenicity of adjuvanted seasonal influenza vaccine based on commercial split influenza virus as an antigen (hemagglutinin = HA) and on a novel polycationic liposome as a potent adjuvant and efficient antigen carrier (CCS/C-HA vaccine). The vaccine was characterized physicochemically, and the mechanism of action of CCS/C as antigen carrier and adjuvant was studied. The optimized CCS/C-HA split virus vaccine, when administered intramuscularly (i.m.), is significantly more immunogenic in mice, rats and ferrets than split virus HA vaccine alone, and it provides for protective immunity in ferrets and mice against live virus challenge that exceeds the degree of efficacy of the split virus vaccine. Similar adjuvant effects of optimized CCS/C are also observed in mice for H1N1 swine influenza antigen. The CCS/C-HA vaccine enhances immune responses via the Th1 and Th2 pathways, and it increases both the humoral responses and the production of IL-2 and IFN-γ but not of the pro-inflammatory factor TNFα. In mice, levels of CD4(+) and CD8(+) T-cells and of MHC II and CD40 co-stimulatory molecules are also elevated. Structure-function relationship studies of the CCS molecule as an adjuvant/carrier show that replacing the saturated palmitoyl acyl chain with the mono-unsaturated oleoyl (C18:1) chain affects neither size distribution and zeta potential nor immune responses in mice. However, replacing the polyalkylamine head group spermine (having two secondary amines) with spermidine (having only one secondary amine) reduces the enhancement of the immune response by ∼ 50%, while polyalkylamines by themselves are ineffective in improving the immunogenicity over the commercial HA vaccine. This highlights the importance of the particulate nature of the carrier and the polyalkylamine secondary amines in the enhancement of the immune responses against seasonal influenza. Altogether, our results suggest that the CCS/C polycationic liposomes combine the activities of a potent adjuvant and efficient carrier of seasonal and swine flu vaccines and support further development of the CCS/C-HA vaccine.

Preclinical evaluation of a replication-deficient intranasal DeltaNS1 H5N1 influenza vaccine.

BACKGROUND: We developed a novel intranasal influenza vaccine approach that is based on the construction of replication-deficient vaccine viruses that lack the entire NS1 gene (DeltaNS1 virus). We previously showed that these viruses undergo abortive replication in the respiratory tract of animals. The local release of type I interferons and other cytokines and chemokines in the upper respiratory tract may have a "self-adjuvant effect", in turn increasing vaccine immunogenicity. As a result, DeltaNS1 viruses elicit strong B- and T- cell mediated immune responses. METHODOLOGY/PRINCIPAL FINDINGS: We applied this technology to the development of a pandemic H5N1 vaccine candidate. The vaccine virus was constructed by reverse genetics in Vero cells, as a 5:3 reassortant, encoding four proteins HA, NA, M1, and M2 of the A/Vietnam/1203/04 virus while the remaining genes were derived from IVR-116. The HA cleavage site was modified in a trypsin dependent manner, serving as the second attenuation factor in addition to the deleted NS1 gene. The vaccine candidate was able to grow in the Vero cells that were cultivated in a serum free medium to titers exceeding 8 log(10) TCID(50)/ml. The vaccine virus was replication deficient in interferon competent cells and did not lead to viral shedding in the vaccinated animals. The studies performed in three animal models confirmed the safety and immunogenicity of the vaccine. Intranasal immunization protected ferrets and mice from being infected with influenza H5 viruses of different clades. In a primate model (Macaca mulatta), one dose of vaccine delivered intranasally was sufficient for the induction of antibodies against homologous A/Vietnam/1203/04 and heterologous A/Indonesia/5/05 H5N1 strains. CONCLUSION/SIGNIFICANCE: Our findings show that intranasal immunization with the replication deficient H5N1 DeltaNS1 vaccine candidate is sufficient to induce a protective immune response against H5N1 viruses. This approach might be attractive as an alternative to conventional influenza vaccines. Clinical evaluation of DeltaNS1 pandemic and seasonal influenza vaccine candidates are currently in progress.

A throat lozenge containing amyl meta cresol and dichlorobenzyl alcohol has a direct virucidal effect on respiratory syncytial virus, influenza A and SARS-CoV.

A potent virucidal mixture containing amyl metacresol and dichlorobenzyl alcohol at low pH inactivated enveloped respiratory viruses influenza A, respiratory synctial virus (RSV) and severe acute respiratory syndrome coronavirus (SARS-CoV) but not viruses with icosahedral symmetry, such as adenoviruses or rhinoviruses. A titre of approximately 3.5 log10 TCID50 was reduced to below the level of detection within two minutes. Electron microscopy of purified influenza A virus showed extensive clumping and morphological changes in spike configuration after contact with the virucidal mixture, but no overt destruction of the viral membrane. We conclude that, formulated as a lozenge, the mixture could have significant effects in reducing the infectivity of certain infectious viruses in the throat and presumably in cough droplets, thus reducing, theoretically, opportunities for person-to-person transmission.

New antiviral drugs, vaccines and classic public health interventions against SARS coronavirus.

Severe acute respiratory syndrome (SARS) is caused by one of two recently discovered coronaviruses. The virus is emergent from South East (SE) Asian mammals: either the civet cat, a related species or a rat species. The virus has a long incubation period and low reproduction number (R0 value) and hence the first outbreak in 2004 was controlled by hygiene and quarantine. However, the healthcare system was compromised and the economic cost was extremely high. Fortunately, the virus is easily cultivated in Vero E6 cells and therefore the search for new antivirals and vaccines was initiated within weeks of the discovery of the virus using classic techniques of cell culture and electron microscopy. Molecular diagnostics facilitated rapid and accurate diagnosis, a key factor in containing the outbreak. The broad-spectrum molecule ribavirin was used in SE Asia in infected patients alongside corticosteroids. In retrospect, many patients survived due to careful nursing. The only currently accepted intervention is interferon. Coronavirus replicon systems should facilitate rapid screening of new inhibitors and the complex mechanism of viral replication will ensure that drugs are developed against at least five molecular targets, in particular the viral protease.

A new millennium conundrum: how to use a powerful class of influenza anti-neuraminidase drugs (NAIs) in the community.

Influenza A and B viruses cause serious medical problems and social disruption every year in particular countries of the world. The virus is notoriously fickle and may attack citizens in say two adjacent countries but not the third. More rarely a global pandemic virus emerges causing millions of deaths worldwide. The SARS outbreak has illuminated weaknesses in planning for sudden outbreaks of disease in a modern society and in particular how panic can grip and cause intense economic disruption. Many communities in the world are neither prepared for a global pandemic nor a very acute epidemic of influenza. The neuraminidase inhibitors (NAIs) are a new class of antiviral drug targeting a viral influenza enzyme, the neuraminidase, which acts both to facilitate virus infection of cells by clearing a passage through otherwise protective respiratory fluids and also by helping release of the virus by cutting the chemical umbilical cord which links up the virus to the infected cell. Extensive laboratory studies of the two molecules zanamivir and oseltamivir have shown that they block all influenza A and B viruses yet tested and would, in theory, even inhibit the 1918 pandemic virus. Both drugs can be used prophylactically to prevent spread of infection in families and communities where 80-90% protection has been documented. The therapeutic effects are also strong in adults and children abbreviating infection, reducing quantities of excreted virus and reducing antibiotic prescriptions. The drugs have to be taken within 48 h of the onset of symptoms. Drug resistance is not a problem at present because although such mutants occur the mutants are compromised and are less virulent than their drug-sensitive parents and they spread less easily. The two drugs could be stockpiled to prepare for an influenza pandemic but, importantly, clinical and scientific experience need to be gained by using these inhibitors in the yearly conflagrations of epidemic influenza, which unchecked do great harm to our communities.