Lessons learnt from the first controlled human malaria infection study conducted in Nairobi, Kenya

Perceptions and acceptability of the controlled human malaria infection (CHMI) model in The Gambia: a qualitative study

Controlled human malaria infection (CHMI) studies, i.e. the deliberate infection of healthy volunteers with malaria parasites to study immune response and/or test drug or vaccine efficacy, are increasingly being conducted in malaria endemic countries, including in sub-Saharan Africa. However, there have been few studies on the perceptions and acceptability of CHMI by the local communities. This qualitative study assessed the perception and acceptability of such studies in The Gambia following the first CHMI study conducted in the country in March-May 2018. Data were collected through non-participant observation, in-depth interviews and focus group discussions and analyzed using NVivo 12 software with an inductive-deductive approach. Sixty-seven participants were involved, including volunteers enrolled in the CHMI, community stakeholders and members of the Gambian Ethics Committee. Respondents expressed a positive view about CHMI. Key motivating factors for participation were the financial compensation, comprehensive health checks, and willingness to support malaria research. Risks associated with participation were considered low. Concerns raised included the frequency of bleeding and the blood volume collected.

Perceptions about controlled human infection model (CHIM) studies among members of ethics committees of Indian medical institutions: A qualitative exploration

Introduction: Controlled Human Infection Model (CHIM) studies provide a unique platform for studying the pathophysiology of infectious diseases and accelerated testing of vaccines and drugs in controlled settings. However, ethical issues shroud them as the disease-causing pathogen is intentionally inoculated into healthy consenting volunteers, and effective treatment may or may not be available. We explored the perceptions of the members of institutional ethics committees (IECs) in India about CHIM studies. Methods: This qualitative exploratory study, conducted across seven sites in India, included 11 focused group discussions (FGD) and 31 in-depth interviews (IDI). A flexible approach was used with the aid of a topic guide. The data were thematically analyzed using grounded theory and an inductive approach. Emerging themes and sub-themes were analyzed, and major emergent themes were elucidated. Results: Seventy-two IEC members participated in the study including 21 basic medical scientists, 29 clinicians, 9 lay people, 6 legal experts and 7 social scientists. Three major themes emerged from this analysis—apprehensions about conduct of CHIM studies in India, a perceived need for CHIM studies in India and risk mitigation measures needed to protect research participants and minimize the associated risks. Conclusion: Development of a specific regulatory and ethical framework, training of research staff and ethics committee members, and ensuring specialized research infrastructure along with adequate community sensitization were considered essential before initiation of CHIM studies in India.

Sporozoite immunization: innovative translational science to support the fight against malaria

INTRODUCTION

Malaria, a devastating febrile illness caused by protozoan parasites, sickened 247,000,000 people in 2021 and killed 619,000, mostly children and pregnant women in sub-Saharan Africa. A highly effective vaccine is urgently needed, especially for Plasmodium falciparum (Pf), the deadliest human malaria parasite.

AREAS COVERED

Sporozoites (SPZ), the parasite stage transmitted by Anopheles mosquitoes to humans, are the only vaccine immunogen achieving >90% efficacy against Pf infection. This review describes >30 clinical trials of PfSPZ vaccines in the U.S.A., Europe, Africa, and Asia, based on first-hand knowledge of the trials and PubMed searches of 'sporozoites,' 'malaria,' and 'vaccines.'

EXPERT OPINION

First generation (radiation-attenuated) PfSPZ vaccines are safe, well tolerated, 80-100% efficacious against homologous controlled human malaria infection (CHMI) and provide 18-19 months protection without boosting in Africa. Second generation chemo-attenuated PfSPZ are more potent, 100% efficacious against stringent heterologous (variant strain) CHMI, but require a co-administered drug, raising safety concerns. Third generation, late liver stage-arresting, replication competent (LARC), genetically-attenuated PfSPZ are expected to be both safe and highly efficacious. Overall, PfSPZ vaccines meet safety, tolerability, and efficacy requirements for protecting pregnant women and travelers exposed to Pf in Africa, with licensure for these populations possible within 5 years. Protecting children and mass vaccination programs to block transmission and eliminate malaria are long-term objectives.

Efficient infection of non-human primates with purified, cryopreserved Plasmodium knowlesi sporozoites

Background

Plasmodium falciparum (Pf) sporozoite (SPZ) vaccines are the only candidate malaria vaccines that induce > 90% vaccine efficacy (VE) against controlled human malaria infection and the only malaria vaccines to have achieved reproducible VE against malaria in adults in Africa. The goal is to increase the impact and reduce the cost of PfSPZ vaccines by optimizing vaccine potency and manufacturing, which will benefit from identification of immunological responses contributing to protection in humans. Currently, there is no authentic animal challenge model for assessing P. falciparum malaria VE. Alternatively, Plasmodium knowlesi (Pk), which infects humans and non-human primates (NHPs) in nature, can be used to experimentally infect rhesus macaques (Macaca mulatta) to assess VE.

Methods

Sanaria has, therefore, produced purified, vialed, cryopreserved PkSPZ and conducted challenge studies in several naïve NHP cohorts. In the first cohort, groups of three rhesus macaques each received doses of 5 × 10², 2.5 × 10³, 1.25 × 10⁴ and 2.5 × 10⁴ PkSPZ administered by direct venous inoculation. The infectivity of 1.5 × 10³ PkSPZ cryopreserved with an altered method and of 1.5 × 10³ PkSPZ cryopreserved for four years was tested in a second and third cohort of rhesus NHPs. The lastly, three pig-tailed macaques (Macaca nemestrina), a natural P. knowlesi host, were challenged with 2.5 × 10³ PkSPZ cryopreserved six years earlier.

Results

In the first cohort, all 12 animals developed P. knowlesi parasitaemia by thick blood smear, and the time to positivity (prepatent period) followed a non-linear 4-parameter logistic sigmoidal model with a median of 11, 10, 8, and 7 days, respectively (r² = 1). PkSPZ cryopreserved using a modified rapid-scalable method infected rhesus with a pre-patent period of 10 days, as did PkSPZ cryopreserved four years prior to infection, similar to the control group. Cryopreserved PkSPZ infected pig-tailed macaques with median time to positivity by thin smear, of 11 days.

Conclusion

This study establishes the capacity to consistently infect NHPs with purified, vialed, cryopreserved PkSPZ, providing a foundation for future studies to probe protective immunological mechanisms elicited by PfSPZ vaccines that cannot be established in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04261-z.

Perceptions about controlled human infection model (CHIM) studies among members of ethics committees of Indian medical institutions: A qualitative exploration

Introduction: Controlled Human Infection Model (CHIM) studies provide a unique platform for studying the pathophysiology of infectious diseases and accelerated testing of vaccines and drugs in controlled settings. However, ethical issues shroud them as the disease-causing pathogen is intentionally inoculated into healthy consenting volunteers, and effective treatment may or may not be available. We explored the perceptions of the members of institutional ethics committees (IECs) in India about CHIM studies. Methods: This qualitative exploratory study, conducted across seven sites in India, included 11 focused group discussions (FGD) and 31 in-depth interviews (IDI). A flexible approach was used with the aid of a topic guide. The data were thematically analyzed using grounded theory and an inductive approach. Emerging themes and sub-themes were analyzed, and major emergent themes were elucidated. Results: Seventy-two IEC members participated in the study including 21 basic medical scientists, 29 clinicians, 9 lay people, 6 legal experts and 7 social scientists. Three major themes emerged from this analysis—apprehensions about conduct of CHIM studies in India, a perceived need for CHIM studies in India and risk mitigation measures needed to protect research participants and minimize the associated risks. Conclusion: Development of a specific regulatory and ethical framework, training of research staff and ethics committee members, and ensuring specialized research infrastructure along with adequate community sensitization were considered essential before initiation of CHIM studies in India.

Ethical and practical considerations arising from community consultation on implementing controlled human infection studies using Schistosoma mansoni in Uganda

Issues related to controlled human infection studies using Schistosoma mansoni (CHI-S) were explored to ensure the ethical and voluntary participation of potential CHI-S volunteers in an endemic setting in Uganda. We invited volunteers from a fishing community and a tertiary education community to guide the development of informed consent procedures. Consultative group discussions were held to modify educational materials on schistosomiasis, vaccines and the CHI-S model and similar discussions were held with a test group. With both groups, a mock consent process was conducted. Fourteen in-depth key informant interviews and three group discussions were held to explore perceptions towards participating in a CHI-S. Most of the participants had not heard of the CHI-S. Willingness to take part depended on understanding the study procedures and the consenting process. Close social networks were key in deciding to take part. The worry of adverse effects was cited as a possible hindrance to taking part. Volunteer time compensation was unclear for a CHI-S. Potential volunteers in these communities are willing to take part in a CHI-S. Community engagement is needed to build trust and time must be taken to share study procedures and ensure understanding of key messages.

Undertaking Community Engagement for a Controlled Human Malaria Infection Study in Kenya: Approaches and Lessons Learnt

Human infection studies (HIS) involve deliberately infecting healthy volunteers with disease-causing pathogens under controlled conditions. These studies are "controlled" by way of using specific types of pathogens, including dose, and the availability of emergency medical facilities to research volunteers. Most HIS involve diseases whose treatment is known and are done to accelerate the development of novel therapeutics such as vaccines, to address emerging and existing infectious diseases. Traditionally, HIS have been conducted primarily in high-income countries (HICs) but are now increasingly being conducted in low-and-middle income countries (LMICs). In LMICs settings, HIS are likely to raise concerns among various stakeholders including participating populations and regulatory bodies, that are unfamiliar with this type of research. Deliberately infecting a healthy individual with a disease-causing pathogen seems to go against the normal practice of medicine of "do no harm". Such types of studies can give rise to increased rumors and jeopardize research participation in study activities, including non-HIS research. Community engagement can be one approach to address particular issues that HIS studies raise through meaningfully engaging with communities, where views and voices inform the conduct of HIS studies. In addition, engagement can inform the ethical conduct and acceptability of HIS studies in LMICs settings and provide opportunities for sharing information, listening to, and responding to concerns and views from potential participants, and the larger community in which the study would be conducted. Despite community engagement being an important aspect to consider, very few published and gray literature cover the types of approaches that have been used, and lessons learnt in engagement for HIS. This article outlinesthe community engagement approaches that were used to engage stakeholders and communities for malaria HIS-controlled human malaria infection (CHMI), undertaken in Kilifi, Kenya. It outlines the engagement activities across the research cycle, from activities conducted during protocol development, to planning, and implementation of the study. We discuss the challenges experienced, lessons learnt, and provide some recommendations for engagement around HIS.

Ethical considerations around volunteer payments in a malaria human infection study in Kenya: an embedded empirical ethics study

Human Infection Studies (HIS) have emerged as an important research approach with the potential to fast track the global development of vaccines and treatments for infectious diseases, including in low resource settings. Given the high level of burdens involved in many HIS, particularly prolonged residency and biological sampling requirements, it can be challenging to identify levels of study payments that provide adequate compensation but avoid 'undue' levels of inducement to participate. Through this embedded ethics study, involving 97 healthy volunteers and other research stakeholders in a malaria HIS programme in Kenya, and using in-depth interviews, focus group discussions and observations during and after a malaria HIS, we give a grounded account of ethical issues emerging in relation to study payments in this setting. While careful community, national, international scientific and ethics review processes meant that risks of serious harm were highly unlikely, the levels of motivation to join HIS seen could raise concerns about study payments being too high. Particular value was placed on the reliability, rather than level, of study payment in this setting, where subsistence livelihoods are common. Study volunteers were generally clear about the study aims at the point of recruitment, and this knowledge was retained over a year later, although most reported experiencing more burdens than anticipated at enrolment. Strict study screening procedures, regular clinical and laboratory monitoring of volunteers, with prompt treatment with antimalarial at predetermined endpoints suggested that the risks of serious harm were highly unlikely. Ethical concerns emerged in relation to volunteers' attempts to conceal symptoms, hoping to prolong residency periods and increase study payments; and volunteers making decisions that compromised important family relationships and personal values. Our findings support an interpretation that, although study volunteers were keen to join the study to access cash payments, they also paid attention to other features of the study and the general clinical research landscape, including levels of risk associated with study participation. Overall, our analysis shows that the ethical concerns emerging from the study payments can be addressed through practical measures, hinged on reducing burdens and strengthening communication, raising important issues for research policy and planning.

Challenges in Developing a Controlled Human Tuberculosis Challenge Model

Controlled human infection models (CHIMs) have provided pivotal scientific advancements, contributing to the licensure of new vaccines for many pathogens. Despite being one of the world's oldest known pathogens, there are still significant gaps in our knowledge surrounding the immunobiology of Mycobacterium tuberculosis (M. tb). Furthermore, the only licensed vaccine, BCG, is a century old and demonstrates limited efficacy in adults from endemic areas. Despite good global uptake of BCG, tuberculosis (TB) remains a silent epidemic killing 1.4 million in 2019 (WHO, Global tuberculosis report 2020). A mycobacterial CHIM could expedite the development pipeline of novel TB vaccines and provide critical understanding on the immune response to TB. However, developing a CHIM for such a complex organism is a challenging process. The first hurdle to address is which challenge agent to use, as it would not be ethical to use virulent M. tb. This chapter describes the current progress and outstanding issues in the development of a TB CHIM. Previous and current human studies include both aerosol and intradermal models using either BCG or purified protein derivative (PPD) as a surrogate agent. Future work investigating the use of attenuated M. tb is underway.

Critical success factors for conducting human challenge trials for vaccine development in low- and middle-income countries

BACKGROUND

Owing to the globalization of vaccine clinical trials, as well as advances in technologies, improved research accountability, and robust regulatory and ethical scrutiny, the choice to perform human challenge trials has become evident, and one of the most significant applications of human challenge trials is the assessment of vaccine efficacy. While human challenge trials have largely been conducted in high-income countries, the concept is relatively new in many low- and middle-income countries. Thus, the aim of this study was to identify the critical success factors for conducting human challenge trials for vaccine development in low- and middle-income countries.

METHODOLOGY

Using a two-step methodology, we first carried out a systematic literature review that was centered on identifying low- and middle-income countries that are either establishing a framework for, have conducted, or are conducting human challenge trials for vaccine development; secondly, we conducted a descriptive cross-sectional survey using a standardized semi-structured online questionnaire administered to eligible stakeholders, to identify the critical success factors for conducting human challenge trials for vaccine development in low- and middle-income countries. Seventeen low- and middle-income countries were identified and included in the survey.

RESULTS

The most cited critical success factors for conducting human challenge trials for vaccine development in low- and middle-income countries were Informed Consent, Risk Compensation and/or Reimbursement, Participant Safety and/or Public Protection, Community Engagement, Infrastructural Capacity, and Ethical and Regulatory Frameworks.

CONCLUSION

From an empirical perspective, this study provides a list of critical success factors that form the basic structure to guide the design and implementation of further human challenge trials in low- and middle-income countries. Further studies are needed to establish a standardized conceptual framework to aid in the review, approval and overall conduct of human challenge trials in low- and middle-income countries.

Reproducibility of malaria sporozoite challenge model in humans for evaluating efficacy of vaccines and drugs: a systematic review

BACKGROUND

The development of novel malaria vaccines and antimalarial drugs is limited partly by emerging challenges to conduct field trials in malaria endemic areas, including unknown effects of existing immunity and a reported fall in malaria incidence. As a result, Controlled Human Malaria Infection (CHMI) has become an important approach for accelerated development of malarial vaccines and drugs. We conducted a systematic review of the literature to establish aggregate evidence on the reproducibility of a malaria sporozoite challenge model.

METHODS

A systematic review of research articles published between 1990 and 2018 on efficacy testing of malaria vaccines and drugs using sporozoite challenge and sporozoite infectivity studies was conducted using Pubmed, Scopus, Embase and Cochrane Library, ClinicalTrials.gov and Trialtrove. The inclusion criteria were randomized and non-randomized, controlled or open-label trials using P. falciparum or P. vivax sporozoite challenges. The data were extracted from articles using standardized data extraction forms and descriptive analysis was performed for evidence synthesis. The endpoints considered were infectivity, prepatent period, parasitemia and safety of sporozoite challenge.

RESULTS

Seventy CHMI trials conducted with a total of 2329 adult healthy volunteers were used for analysis. CHMI was induced by bites of mosquitoes infected with P. falciparum or P. vivax in 52 trials and by direct venous inoculation of P. falciparum sporozoites (PfSPZ challenge) in 18 trials. Inoculation with P. falciparum-infected mosquitoes produced 100% infectivity in 40 studies and the mean/median prepatent period assessed by thick blood smear (TBS) microscopy was ≤ 12 days in 24 studies. On the other hand, out of 12 infectivity studies conducted using PfSPZ challenge, 100% infection rate was reproduced in 9 studies with a mean or median prepatent period of 11 to 15.3 days as assessed by TBS and 6.8 to 12.6 days by PCR. The safety profile of P. falciparum and P.vivax CHMI was characterized by consistent features of malaria infection.

CONCLUSION

There is ample evidence on consistency of P. falciparum CHMI models in terms of infectivity and safety endpoints, which supports applicability of CHMI in vaccine and drug development. PfSPZ challenge appears more feasible for African trials based on current evidence of safety and efficacy.

Engagement of ethics and regulatory authorities on human infection studies: Proceedings of an engagement workshop in Zambia

Human infection studies (HIS) have generally been used as a tool in the pathway for vaccine development in high income settings. Over the last decade, this model has been implemented in LMICs with the aim of accelerating development of next generation vaccines that would perform better in these settings. However, in most LMICs, the ethics and regulatory framework for the conduct of these studies are not in place. In Zambia, these studies are yet to be conducted and thus we conducted a stakeholder engagement workshop in October 2019. We engaged with bioethicists, regulatory authority officials, and scientists from within Zambia and other African countries to anticipate and address foreseeable ethical and regulatory issues when conducting HIS in Zambia for the first time. The workshop largely focused on sensitizing the stakeholders on the benefits of these studies with the following main points for consideration on the implementation of these studies in Zambia: need for in-country legal framework and guidelines; need for adequate informed consent based on comprehensive understanding of the concept of HIS and study requirements; and requirements for heightened vigilance to assure participant safety including good ethical and clinical practice with regulatory, ethical, data safety, and community oversight. Additionally, the workshop emphasized the need for rigorous health screening prior to enrolment; suitable infrastructure for containment; and personnel to provide appropriate treatment including emergency resuscitation and evacuation if indicated. Specific recommendations included compensation for burden of participation; access to care and provision for study related injury (e.g. no-fault insurance); and withdrawal and exit procedures to preserve individual and community safety. Finally, the meeting concluded that researchers should actively engage key gate keepers including civic leaders such as parliamentarians, universities, researchers, potential participants and laypersons to avoid circulation of misinformation.

Understanding the benefits and burdens associated with a malaria human infection study in Kenya: experiences of study volunteers and other stakeholders

BACKGROUND

Human infection studies (HIS) that involve deliberately infecting healthy volunteers with a pathogen raise important ethical issues, including the need to ensure that benefits and burdens are understood and appropriately accounted for. Building on earlier work, we embedded social science research within an ongoing malaria human infection study in coastal Kenya to understand the study benefits and burdens experienced by study stakeholders in this low-resource setting and assess the wider implications for future research planning and policy.

METHODS

Data were collected using qualitative research methods, including in-depth interviews (44), focus group discussions (10) and non-participation observation. Study participants were purposively selected (key informant or maximal diversity sampling), including volunteers in the human infection study, study staff, community representatives and local administrative authorities. Data were collected during and up to 18 months following study residency, from sites in Coastal and Western Kenya. Voice recordings of interviews and discussions were transcribed, translated, and analysed using framework analysis, combining data- and theory-driven perspectives.

FINDINGS

Physical, psychological, economic and social forms of benefits and burdens were experienced across study stages. Important benefits for volunteers included the study compensation, access to health checks, good residential living conditions, new learning opportunities, developing friendships and satisfaction at contributing towards a new malaria vaccine. Burdens primarily affected study volunteers, including experiences of discomfort and ill health; fear and anxiety around aspects of the trial process, particularly deliberate infection and the implications of prolonged residency; anxieties about early residency exit; and interpersonal conflict. These issues had important implications for volunteers' families, study staff and the research institution's reputation more widely.

CONCLUSION

Developing ethically and scientifically strong HIS relies on grounded accounts of volunteers, study staff and the wider community, understood in the socioeconomic, political and cultural context where studies are implemented. Recognition of the diverse, and sometimes perverse, nature of potential benefits and burdens in a given context, and who this might implicate, is critical to this process. Prior and ongoing stakeholder engagement is core to developing these insights.

Understanding the benefits and burdens associated with a malaria human infection study in Kenya: experiences of study volunteers and other stakeholders

Background

Human infection studies (HIS) that involve deliberately infecting healthy volunteers with a pathogen raise important ethical issues, including the need to ensure that benefits and burdens are understood and appropriately accounted for. Building on earlier work, we embedded social science research within an ongoing malaria human infection study in coastal Kenya to understand the study benefits and burdens experienced by study stakeholders in this low-resource setting and assess the wider implications for future research planning and policy.

Methods

Data were collected using qualitative research methods, including in-depth interviews (44), focus group discussions (10) and non-participation observation. Study participants were purposively selected (key informant or maximal diversity sampling), including volunteers in the human infection study, study staff, community representatives and local administrative authorities. Data were collected during and up to 18 months following study residency, from sites in Coastal and Western Kenya. Voice recordings of interviews and discussions were transcribed, translated, and analysed using framework analysis, combining data- and theory-driven perspectives.

Findings

Physical, psychological, economic and social forms of benefits and burdens were experienced across study stages. Important benefits for volunteers included the study compensation, access to health checks, good residential living conditions, new learning opportunities, developing friendships and satisfaction at contributing towards a new malaria vaccine. Burdens primarily affected study volunteers, including experiences of discomfort and ill health; fear and anxiety around aspects of the trial process, particularly deliberate infection and the implications of prolonged residency; anxieties about early residency exit; and interpersonal conflict. These issues had important implications for volunteers’ families, study staff and the research institution’s reputation more widely.

Conclusion

Developing ethically and scientifically strong HIS relies on grounded accounts of volunteers, study staff and the wider community, understood in the socioeconomic, political and cultural context where studies are implemented. Recognition of the diverse, and sometimes perverse, nature of potential benefits and burdens in a given context, and who this might implicate, is critical to this process. Prior and ongoing stakeholder engagement is core to developing these insights.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05455-7.

Public perceptions on Controlled Human Infection Model (CHIM) studies-a qualitative pilot study from South India

Research using Controlled Human Infection Models is yet to be attempted in India. This study was conducted to understand the perceptions of the lay public and key opinion makers prior to the possible introduction of such studies in the country. 110 respondents from urban and rural Bangalore district were interviewed using qualitative research methods of Focus Group Discussions and In-depth Interviews. The data was analyzed using grounded theory. Safety was a key concern of the lay public, expressed in terms of fear of death. The notion of infecting a healthy volunteer, the possibility of continued effects beyond the study duration and the likelihood of vulnerable populations volunteering solely for monetary benefit, were ethical concerns. Public good outcomes such as effective treatments, targeted vaccines and prevention of diseases was necessary justification for such studies. However, the comprehension of this benefit was not clear among non-medical, non-technical respondents and suggestions to seek alternatives to CHIMs repeatedly arose. There was a great deal of deflection-with each constituency feeling that people other than themselves may be ideally suited as participants. Risk takers, those without dependents, the more health and research literate, financially sound and those with an altruistic bent of mind emerged as possible CHIM volunteers. While widespread awareness and advocacy about CHIM is essential, listening to plural voices is the first step in public engagement in ethically contentious areas. Continued engagement and inclusive deliberative processes are required to redeem the mistrust of the public in research and rebuild faith in regulatory systems.

Transient knockdown of Anopheles stephensi LRIM1 using RNAi increases Plasmodium falciparum sporozoite salivary gland infections

BACKGROUND

Plasmodium falciparum (Pf) sporozoites (PfSPZ) can be administered as a highly protective vaccine conferring the highest protection seen to date. Sanaria® PfSPZ vaccines are produced using aseptically reared Anopheles stephensi mosquitoes. The bionomics of sporogonic development of P. falciparum in A. stephensi to fully mature salivary gland PfSPZ is thought to be modulated by several components of the mosquito innate immune system. In order to increase salivary gland PfSPZ infections in A. stephensi and thereby increase vaccine production efficiency, a gene knock down approach was used to investigate the activity of the immune deficiency (IMD) signaling pathway downstream effector leucine-rich repeat immune molecule 1 (LRIM1), an antagonist to Plasmodium development.

METHODS

Expression of LRIM1 in A. stephensi was reduced following injection of double stranded (ds) RNA into mosquitoes. By combining the Gal4/UAS bipartite system with in vivo expression of short hairpin (sh) RNA coding for LRIM1 reduced expression of LRIM1 was targeted in the midgut, fat body, and salivary glands. RT-qPCR was used to demonstrate fold-changes in gene expression in three transgenic crosses and the effects on P. falciparum infections determined in mosquitoes showing the greatest reduction in LRIM1 expression.

RESULTS

LRIM1 expression could be reduced, but not completely silenced, by expression of LRIM1 dsRNA. Infections of P. falciparum oocysts and PfSPZ were consistently and significantly higher in transgenic mosquitoes than wild type controls, with increases in PfSPZ ranging from 2.5- to tenfold.

CONCLUSIONS

Plasmodium falciparum infections in A. stephensi can be increased following reduced expression of LRIM1. These data provide the springboard for more precise knockout of LRIM1 for the eventual incorporation of immune-compromised A. stephensi into manufacturing of Sanaria's PfSPZ products.

Reduced Ebola vaccine responses in CMV+ young adults is associated with expansion of CD57+KLRG1+ T cells

CMV is associated with immunosenescence and reduced vaccine responses in the elderly (>70 yr). However, the impact of CMV in young adults is less clear. In this study, healthy UK and Senegalese adults aged 18–50 yr (average, 29 yr) were vaccinated with the Ebola vaccine candidate chimpanzee adenovirus type 3–vectored Ebola Zaire vaccine (ChAd3-EBO-Z) and boosted with modified vaccinia Ankara Ebola Zaire–vectored (MVA–EBO-Z) vaccine. CMV carriage was associated with an expansion of phenotypically senescent CD4⁺ and CD8⁺ T cells expressing CD57 and killer cell lectin-like receptor G1 (KLRG1), which was negatively associated with vaccine responses in both cohorts. Ebola-specific T cell responses induced by vaccination also contained significantly increased frequencies of terminally differentiated CD57⁺KLRG1⁺ cells in CMV seropositive (CMV⁺) individuals. This study suggests that CMV can also affect vaccine responses in younger adults and may have a particularly marked impact in many developing countries where CMV seroprevalence is almost universal.

Engagement of ethics and regulatory authorities on human infection studies: Proceedings of an engagement workshop in Zambia

Human infection studies (HIS) have generally been used as a tool in the pathway for vaccine development in high income settings. Over the last decade, this model has been implemented in LMICs with the aim of accelerating development of next generation vaccines that would perform better in these settings. However, in most LMICs, the ethics and regulatory framework for the conduct of these studies are not in place. In Zambia, these studies are yet to be conducted and thus we conducted a stakeholder engagement workshop in October 2019. We engaged with bioethicists, regulatory authority, and scientists from within Zambia and other African countries to anticipate and address foreseeable ethical and regulatory issues when conducting HIS in Zambia for the first time. The workshop largely focused on sensitizing the stakeholders on the benefits of these studies with the following main points for consideration on the implementation of these studies in Zambia: need for in-country legal framework and guidelines; need for adequate informed consent based on comprehensive understanding of the concept of HIS and study requirements; and requirements for heightened vigilance to assure participant safety including good ethical and clinical practice with regulatory, ethical, data safety, and community oversight. Additionally, the workshop emphasized the need for rigorous health screening prior to enrolment; suitable infrastructure for containment; and personnel to provide appropriate treatment including emergency resuscitation and evacuation if indicated. Specific recommendations included compensation for burden of participation; access to care and provision for study related injury (e.g. no-fault insurance); and withdrawal and exit procedures to preserve individual and community safety. Finally, the meeting concluded that researchers should actively engage key gate keepers including civic leaders such as parliamentarians, universities, researchers, potential participants and laypersons to avoid circulation of misinformation.

The Equatoguinean Malaria Vaccine Initiative: From the Launching of a Clinical Research Platform to Malaria Elimination Planning in Central West Africa

Fifteen years of investment in malaria control on Bioko Island, Equatorial Guinea (EG), dramatically reduced malaria-associated morbidity and mortality, but the impact has plateaued. To progress toward elimination, EG is investing in the development of a malaria vaccine. We assessed the unique public–private partnership that has had such a significant impact on malaria on Bioko Island and now added a major effort on malaria vaccine development. As part of a $79M commitment, the EG government (75%) and three American energy companies (25%) have invested since 2012 greater than $55M in the Equatoguinean Malaria Vaccine Initiative (EGMVI) to support clinical development of Sanaria^® PfSPZ vaccines (Sanaria Inc., Rockville, MD). In turn, the vaccine development program is building human capital and physical capacity. The EGMVI established regulatory and ethical oversight to ensure compliance with the International Conference on Harmonization and Good Clinical Practices for the first importation of investigational product, ethical approval, and conduct of a clinical trial in Equatoguinean history. The EGMVI has completed three vaccine trials in EG, two vaccine trials in Tanzania, and a malaria incidence study, and initiated preparations for a 2,100-volunteer clinical trial. Personnel are training for advanced degrees abroad and have been trained in Good Clinical Practices and protocol-specific methods. A new facility has established the foundation for a national research institute. Biomedical research and development within this visionary, ambitious public–private partnership is fostering major improvements in EG. The EGMVI plans to use a PfSPZ Vaccine alongside standard malaria control interventions to eliminate Pf malaria from Bioko, becoming a potential model for elimination campaigns elsewhere.

Key criteria for the ethical acceptability of COVID-19 human challenge studies: Report of a WHO Working Group

This report of the WHO Working Group for Guidance on Human Challenge Studies in COVID-19 outlines ethical standards for COVID-19 challenge studies. It includes eight Key Criteria related to scientific justification, risk-benefit assessment, consultation and engagement, co-ordination of research, site selection, participant selection, expert review, and informed consent. The document aims to provide comprehensive guidance to scientists, research ethics committees, funders, policymakers, and regulators in deliberations regarding SARS-CoV-2 challenge studies by outlining criteria that would need to be satisfied in order for such studies to be ethically acceptable.

Human infection challenge studies in endemic settings and/or low-income and middle-income countries: key points of ethical consensus and controversy

Human infection challenge studies (HCS) involve intentionally infecting research participants with pathogens (or other micro-organisms). There have been recent calls for more HCS to be conducted in low-income and middle-income countries (LMICs), where many relevant diseases are endemic. HCS in general, and HCS in LMICs in particular, raise numerous ethical issues. This paper summarises the findings of a project that explored ethical and regulatory issues related to LMIC HCS via (i) a review of relevant literature and (ii) 45 qualitative interviews with scientists and ethicists. Among other areas of consensus, we found that there was widespread agreement that LMIC HCS can be ethically acceptable, provided that they have a sound scientific rationale, are accepted by local communities and meet usual research ethics requirements. Unresolved issues include those related to (i) acceptable approaches to trade-offs between the scientific aim to produce generalisable results and the protection of participants, (iii) the sharing of benefits with LMIC populations, (iii) the acceptable limits to risks and burdens for participants, (iv) the potential for third-party risk and whether the degree of acceptable third-party risk is different in endemic settings, (v) the conditions under which (if any) it would be appropriate to recruit children for disease-causing HCS, (v) appropriate levels of payment to participants and (vi) appropriate governance of (LMIC) HCS. This paper provides preliminary analyses of these ethical considerations in order to (i) inform scientists and policymakers involved in the planning, conduct and/or governance of LMIC HCS and (ii) highlight areas warranting future research. Insofar as this article focuses on HCS in (endemic) settings where diseases are present and/or widespread, much of the analysis provided is relevant to HCS (in HICs or LMICs) involving pandemic diseases including COVID19.

COVID-19: Africa’s relation with epidemics and some imperative ethics considerations of the moment

COVID-19 is a very complex pandemic. It has affected individuals, different countries and regions of the world equally in some senses and differently in other senses. While sub-Saharan Africa has weathered a range of outbreaks of emerging and re-emerging infectious diseases, the manner in which the COVID-19 pandemic has evolved necessitates some observations, remarks and conclusions from our own situated observation point. Compared to previous epidemics/pandemics, many African countries have displayed a sense of solidarity in the face of COVID-19 that convincingly demonstrates that an Ubuntu ethic is viable and globalizable. The African continent seems, at last, to have realized that ethics dumping must be avoided and has made strides in defining its COVID-19 research agenda and strengthening its epidemic response for both public health and health research. More needs to be done in terms of public engagement, funding and technical support for research on potential therapies/candidate vaccines that are a product of scientific studies on the continent.

Serologic Markers of Previous Malaria Exposure and Functional Antibodies Inhibiting Parasite Growth Are Associated With Parasite Kinetics Following a Plasmodium falciparum Controlled Human Infection

BACKGROUND

We assessed the impact of exposure to Plasmodium falciparum on parasite kinetics, clinical symptoms, and functional immunity after controlled human malaria infection (CHMI) in 2 cohorts with different levels of previous malarial exposure.

METHODS

Nine adult males with high (sero-high) and 10 with low (sero-low) previous exposure received 3200 P. falciparum sporozoites (PfSPZ) of PfSPZ Challenge by direct venous inoculation and were followed for 35 days for parasitemia by thick blood smear (TBS) and quantitative polymerase chain reaction. Endpoints were time to parasitemia, adverse events, and immune responses.

RESULTS

Ten of 10 (100%) volunteers in the sero-low and 7 of 9 (77.8%) in the sero-high group developed parasitemia detected by TBS in the first 28 days (P = .125). The median time to parasitemia was significantly shorter in the sero-low group than the sero-high group (9 days [interquartile range {IQR} 7.5-11.0] vs 11.0 days [IQR 7.5-18.0], respectively; log-rank test, P = .005). Antibody recognition of sporozoites was significantly higher in the sero-high (median, 17.93 [IQR 12.95-24] arbitrary units [AU]) than the sero-low volunteers (median, 10.54 [IQR, 8.36-12.12] AU) (P = .006). Growth inhibitory activity was significantly higher in the sero-high (median, 21.8% [IQR, 8.15%-29.65%]) than in the sero-low group (median, 8.3% [IQR, 5.6%-10.23%]) (P = .025).

CONCLUSIONS

CHMI was safe and well tolerated in this population. Individuals with serological evidence of higher malaria exposure were able to better control infection and had higher parasite growth inhibitory activity.

CLINICAL TRIALS REGISTRATION

NCT03496454.

Third human challenge trial conference, Oxford, United Kingdom, February 6-7, 2020, a meeting report

The third Human Challenge Trial Meeting brought together a broad range of international stakeholders, including academia, regulators, funders and industry, with a considerable delegation from Low- and Middle-Income Countries. Controlled human infection models (CHIMs) can be helpful to study pathogenesis and for the development of vaccines. As challenge agents are used to infect healthy volunteers, ethical considerations include that the challenge studies need to be safe and results should be meaningful. The meeting provided a state-of-the-art overview on a wide range of CHIMs, including viral, bacterial and parasitic challenge agents. Recommendations included globally aligned guidance documents for CHIM studies; further definition of a CHIM, based on the challenge agent used; standardization of methodology and study endpoints; capacity building in Low- and Middle-Income Countries, in performance as well as regulation of CHIM studies; guidance on compensation for participation in CHIM studies; and preparation of CHIM studies, with strong engagement with stakeholders.

Risk assessment for the implementation of controlled human Schistosoma mansoni infection trials in Uganda

Schistosomiasis is a parasitic infection highly prevalent in sub-Saharan Africa, and a significant cause of morbidity; it is a priority for vaccine development. A controlled human infection model for Schistosoma mansoni (CHI-S) with potential to accelerate vaccine development has been developed among naïve volunteers in the Netherlands. Because responses both to infections and candidate vaccines are likely to differ between endemic and non-endemic settings, we propose to establish a CHI-S in Uganda where Schistosoma mansoni is endemic. As part of a “road-map” to this goal, we have undertaken a risk assessment. We identified risks related to importing of laboratory vector snails and schistosome strains from the Netherlands to Uganda; exposure to natural infection in endemic settings concurrently with CHI-S studies, and unfamiliarity of the community with the nature, risks and rationale for CHI. Mitigating strategies are proposed. With careful implementation of the latter, we believe that CHI-S can be implemented safely in Uganda. Our reflections are presented here to promote feedback and discussion.

Safety Considerations for Malaria Volunteer Infection Studies: A Mini-Review

Malaria clinical studies entailing the experimental infection of healthy volunteers with Plasmodium parasites by bites from infected mosquitos, injection of cryopreserved sporozoites, or injection of blood-stage parasites provide valuable information for vaccine and drug development. Success of these studies depends on maintaining safety. In this mini-review, we discuss the safety risks and associated mitigation strategies of these three types of experimental malaria infection. We aimed to inform researchers and regulators who are currently involved in or are planning to establish experimental malaria infection studies in endemic or non-endemic settings.

Human unconventional T cells in Plasmodium falciparum infection

Malaria is an old scourge of humankind and has a large negative impact on the economic development of affected communities. Recent success in malaria control and reduction of mortality seems to have stalled emphasizing that our current intervention tools need to be complemented by malaria vaccines. Different populations of unconventional T cells such as mucosal-associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells and γδ T cells are gaining attention in the field of malaria immunology. Significant advances in our basic understanding of unconventional T cell biology in rodent malaria models have been made, however, their roles in humans during malaria are less clear. Unconventional T cells are abundant in skin, gut and liver tissues, and long-lasting expansions and functional alterations were observed upon malaria infection in malaria naïve and malaria pre-exposed volunteers. Here, we review the current understanding of involvement of unconventional T cells in anti-Plasmodium falciparum immunity and highlight potential future research avenues.

Stakeholder views on the acceptability of human infection studies in Malawi

BACKGROUND

Human infection studies (HIS) are valuable in vaccine development. Deliberate infection, however, creates challenging questions, particularly in low and middle-income countries (LMICs) where HIS are new and ethical challenges may be heightened. Consultation with stakeholders is needed to support contextually appropriate and acceptable study design. We examined stakeholder perceptions about the acceptability and ethics of HIS in Malawi, to inform decisions about planned pneumococcal challenge research and wider understanding of HIS ethics in LMICs.

METHODS

We conducted 6 deliberative focus groups and 15 follow-up interviews with research staff, medical students, and community representatives from rural and urban Blantyre. We also conducted 5 key informant interviews with clinicians, ethics committee members, and district health government officials.

RESULTS

Stakeholders perceived HIS research to have potential population health benefits, but they also had concerns, particularly related to the safety of volunteers and negative community reactions. Acceptability depended on a range of conditions related to procedures for voluntary and informed consent, inclusion criteria, medical care or support, compensation, regulation, and robust community engagement. These conditions largely mirror those in existing guidelines for HIS and biomedical research in LMICs. Stakeholder perceptions pointed to potential tensions, for example, balancing equity, safety, and relevance in inclusion criteria.

CONCLUSIONS

Our findings suggest HIS research could be acceptable in Malawi, provided certain conditions are in place. Ongoing assessment of participant experiences and stakeholder perceptions will be required to strengthen HIS research during development and roll-out.

Ethics of alternative trial designs and methods in low-resource settings

This editorial introduces articles in this Special Issue, which are based on presentations given at the 2017 meeting of the Global Forum of Bioethics in Research meeting. The main themes presented at the meeting were the use of cluster randomized trials, stepped-wedge cluster randomized trials, and controlled human infection models in research conducted in low-resource settings. The editorial sets out which ethical issues may arise in the context of alternative trial designs and describes the articles in this issue that addresses some or more of the ethical issues, such as justification of the research design, risk-benefit evaluations and consent.

Typhoidal Salmonella human challenge studies: ethical and practical challenges and considerations for low-resource settings

Typhoidal Salmonella is a major global problem affecting more than 12 million people annually. Controlled human infection models (CHIMs) in high-resource settings have had an important role in accelerating the development of conjugate vaccines against Salmonella Typhi.

The typhoidal Salmonella model has an established safety profile in over 2000 volunteers in high-income settings, and trial protocols, with modification, could be readily transferred to new study sites. To date, a typhoidal Salmonella CHIM has not been conducted in a low-resource setting, although it is being considered.

Our article describes the challenges posed by a typhoidal Salmonella CHIM in the high-resource setting of Oxford and explores considerations for an endemic setting.

Development of CHIMs in endemic settings is scientifically justifiable as it remains unclear whether findings from challenge studies performed in high-resource non-endemic settings can be extrapolated to endemic settings, where the burden of invasive Salmonella is highest. Volunteers are likely to differ across a range of important variables such as previous Salmonella exposure, diet, intestinal microbiota, and genetic profile. CHIMs in endemic settings arguably are ethically justifiable as affected communities are more likely to gain benefit from the study. Local training and research capacity may be bolstered.

Safety was of primary importance in the Oxford model. Risk of harm to the individual was mitigated by careful inclusion and exclusion criteria; close monitoring with online diary and daily visits; 24/7 on-call staffing; and access to appropriate hospital facilities with capacity for in-patient admission. Risk of harm to the community was mitigated by exclusion of participants with contact with vulnerable persons; stringent hygiene and sanitation precautions; and demonstration of clearance of Salmonella infection from stool following antibiotic treatment.

Safety measures should be more stringent in settings where health systems, transport networks, and sanitation are less robust.

We compare the following issues between high- and low-resource settings: scientific justification, risk of harm to the individual and community, benefits to the individual and community, participant understanding, compensation, and regulatory requirements.

We conclude that, with careful consideration of country-specific ethical and practical issues, a typhoidal Salmonella CHIM in an endemic setting is possible.

Controlled Human Malaria Infection in Semi-Immune Kenyan Adults (CHMI-SIKA): a study protocol to investigate in vivo Plasmodium falciparum malaria parasite growth in the context of pre-existing immunity

Malaria remains a major public health burden despite approval for implementation of a partially effective pre-erythrocytic malaria vaccine. There is an urgent need to accelerate development of a more effective multi-stage vaccine. Adults in malaria endemic areas may have substantial immunity provided by responses to the blood stages of malaria parasites, but field trials conducted on several blood-stage vaccines have not shown high levels of efficacy.  We will use the controlled human malaria infection (CHMI) models with malaria-exposed volunteers to identify correlations between immune responses and parasite growth rates in vivo.  Immune responses more strongly associated with control of parasite growth should be prioritized to accelerate malaria vaccine development. We aim to recruit up to 200 healthy adult volunteers from areas of differing malaria transmission in Kenya, and after confirming their health status through clinical examination and routine haematology and biochemistry, we will comprehensively characterize immunity to malaria using >100 blood-stage antigens. We will administer 3,200 aseptic, purified, cryopreserved Plasmodium falciparum sporozoites (PfSPZ Challenge) by direct venous inoculation. Serial quantitative polymerase chain reaction to measure parasite growth rate in vivo will be undertaken. Clinical and laboratory monitoring will be undertaken to ensure volunteer safety. In addition, we will also explore the perceptions and experiences of volunteers and other stakeholders in participating in a malaria volunteer infection study. Serum, plasma, peripheral blood mononuclear cells and whole blood will be stored to allow a comprehensive assessment of adaptive and innate host immunity. We will use CHMI in semi-immune adult volunteers to relate parasite growth outcomes with antibody responses and other markers of host immunity. Registration: ClinicalTrials.gov identifier NCT02739763.

Deciphering host immunity to malaria using systems immunology

A century of conceptual and technological advances in infectious disease research has changed the face of medicine. However, there remains a lack of effective interventions and a poor understanding of host immunity to the most significant and complex pathogens, including malaria. The development of successful interventions against such intractable diseases requires a comprehensive understanding of host-pathogen immune responses. A major advance of the past decade has been a paradigm switch in thinking from the contemporary reductionist (gene-by-gene or protein-by-protein) view to a more holistic (whole organism) view. Also, a recognition that host-pathogen immunity is composed of complex, dynamic interactions of cellular and molecular components and networks that cannot be represented by any individual component in isolation. Systems immunology integrates the field of immunology with omics technologies and computational sciences to comprehensively interrogate the immune response at a systems level. Herein, we describe the system immunology toolkit and report recent studies deploying systems-level approaches in the context of natural exposure to malaria or controlled human malaria infection. We contribute our perspective on the potential of systems immunity for the rational design and development of effective interventions to improve global public health.

Conducting human challenge studies in LMICs: A survey of researchers and ethics committee members in Thailand

Questions have been raised over the acceptability of conducting human challenge studies in low and middle income countries (LMICs). Most of these concerns are based on theoretical considerations and there exists little data on the attitudes of stakeholders in these countries. This study examines the view of researchers and REC members in Thailand regarding the design and conduct of challenge studies in the country. A questionnaire was developed based on ethical frameworks for human challenge studies. The target respondents included those who had experience with health-related research at universities, non-university hospitals, and research institutes. A total of 240 respondents completed the on-line survey. In general, the respondents felt that the ethical issues raised by human challenge studies in LMICS do not differ significantly from those in high income countries, including: scientific rationale, safety, appropriate risks, and robust informed consent process. In contrast, issues that have been described as important for human challenge studies in LMICs were rated as having lower importance, including: a publicly available rationale, national priority, and community engagement. Responses did not vary significantly between researchers in different fields, nor between researchers and REC members. These findings provide an important perspective for assessing existing frameworks for human challenges studies in LMICs.

Risk assessment for the implementation of controlled human Schistosoma mansoni infection trials in Uganda

Schistosomiasis is a parasitic infection highly prevalent in sub-Saharan Africa, and a significant cause of morbidity; it is a priority for vaccine development. A controlled human infection model for Schistosoma mansoni (CHI-S) with potential to accelerate vaccine development has been developed among naïve volunteers in the Netherlands. Because responses both to infections and candidate vaccines are likely to differ between endemic and non-endemic settings, we propose to establish a CHI-S in Uganda where Schistosoma mansoni is endemic. As part of a "road-map" to this goal, we have undertaken a risk assessment. We identified risks related to importing of laboratory vector snails and schistosome strains from the Netherlands to Uganda; exposure to natural infection in endemic settings concurrently with CHI-S studies, and unfamiliarity of the community with the nature, risks and rationale for CHI. Mitigating strategies are proposed. With careful implementation of the latter, we believe that CHI-S can be implemented safely in Uganda. Our reflections are presented here to promote feedback and discussion.

Pipeline analysis of a vaccine candidate portfolio for diseases of poverty using the Portfolio-To-Impact modelling tool

Background: The Portfolio-To-Impact (P2I) P2I model is a recently developed product portfolio tool that enables users to estimate the funding needs to move a portfolio of candidate health products, such as vaccines and drugs, along the product development path from late stage preclinical to phase III clinical trials, as well as potential product launches over time. In this study we describe the use of this tool for analysing the vaccine portfolio of the European Vaccine Initiative (EVI). This portfolio includes vaccine candidates for various diseases of poverty and emerging infectious diseases at different stages of development.

Methods: Portfolio analyses were conducted using the existing assumptions integrated in the P2I tool, as well as modified assumptions for costs, cycle times, and probabilities of success based on EVI’s own internal data related to vaccine development.

Results: According to the P2I tool, the total estimated cost to move the 18 candidates currently in the EVI portfolio along the pipeline to launch would be about US $470 million, and there would be 0.69 expected launches across all six diseases in EVI’s portfolio combined during the period 2019-2031. Running of the model using EVI-internal parameters resulted in a significant increase in the expected product launches.

Conclusions: Not all the assumptions underlying the P2I tool could be tested in our study due to limited amount of data available. Nevertheless, we expect that the accelerated clinical testing of vaccines (and drugs) based on the use of controlled human infection models that are increasingly available, as well as the accelerated approval by regulatory authorities that exists for example for serious conditions, will speed up product development and result in significant cost reduction. Project findings as well as potential future modifications of the P2I tool are discussed with the aim to improve the underlying methodology of the P2I model.

Vaccination With Sporozoites: Models and Correlates of Protection

Despite continuous efforts, the century-old goal of eradicating malaria still remains. Multiple control interventions need to be in place simultaneously to achieve this goal. In addition to effective control measures, drug therapies and insecticides, vaccines are critical to reduce mortality and morbidity. Hence, there are numerous studies investigating various malaria vaccine candidates. Most of the malaria vaccine candidates are subunit vaccines. However, they have shown limited efficacy in Phase II and III studies. To date, only whole parasite formulations have been shown to induce sterile immunity in human. In this article, we review and discuss the recent developments in vaccination with sporozoites and the mechanisms of protection involved.

Immune effector mechanisms in malaria: An update focusing on human immunity

The past decade has witnessed dramatic decreases in malaria-associated mortality and morbidity around the world. This progress has largely been due to intensified malaria control measures, implementation of rapid diagnostics and establishing a network to anticipate and mitigate antimalarial drug resistance. However, the ultimate tool for malaria prevention is the development and implementation of an effective vaccine. To date, malaria vaccine efforts have focused on determining which of the thousands of antigens expressed by Plasmodium falciparum are instrumental targets of protective immunity. The antigenic variation and antigenic polymorphisms arising in parasite genes under immune selection present a daunting challenge for target antigen selection and prioritization, and is a given caveat when interpreting immune recall responses or results from monovalent vaccine trials. Other immune evasion strategies executed by the parasite highlight the myriad of ways in which it can become a recurrent infection. This review provides an update on immune effector mechanisms in malaria and focuses on our improved ability to interrogate the complexity of human immune system, accelerated by recent methodological advances. Appreciating how the human immune landscape influences the effectiveness and longevity of antimalarial immunity will help explain which conditions are necessary for immune effector mechanisms to prevail.

Human challenge models: tools to accelerate the development of malaria vaccines

INTRODUCTION

Malaria challenge models, where healthy human volunteers are intentionally infected with Plasmodium species parasites under controlled conditions, can be undertaken in several well-defined ways. These challenge models enable evaluation of the kinetics of parasite growth and clearance, host-pathogen interactions and the host immune response. They can facilitate discovery of candidate diagnostic biomarkers and novel vaccine targets. As translational tools they can facilitate testing of candidate vaccines and drugs and evaluation of diagnostic tests.

AREAS COVERED

Until recently, malaria human challenge models have been limited to only a few Plasmodium falciparum strains and used exclusively in malaria-naïve volunteers in non-endemic regions. Several recent advances include the use of alternate P. falciparum strains and other species of Plasmodia, as well as strains attenuated by chemical, radiation or genetic modification, and the conduct of studies in pre-exposed individuals. Herein, we discuss how this diversification is enabling more thorough vaccine efficacy testing and informing rational vaccine development.

EXPERT OPINION

The ability to comprehensively evaluate vaccine efficacy in controlled settings will continue to accelerate the translation of candidate malaria vaccines to the clinic, and inform the development and optimisation of potential vaccines that would be effective against multiple strains in geographically and demographically diverse settings.

Antibody Responses to Antigenic Targets of Recent Exposure Are Associated With Low-Density Parasitemia in Controlled Human Plasmodium falciparum Infections

The majority of malaria infections in low transmission settings remain undetectable by conventional diagnostics. A powerful model to identify antibody responses that allow accurate detection of recent exposure to low-density infections is controlled human malaria infection (CHMI) studies in which healthy volunteers are infected with the Plasmodium parasite. We aimed to evaluate antibody responses in malaria-naïve volunteers exposed to a single CHMI using a custom-made protein microarray. All participants developed a blood-stage infection with peak parasite densities up to 100 parasites/μl in the majority of participants (50/54), while the remaining four participants had peak densities between 100 and 200 parasites/μl. There was a strong correlation between parasite density and antibody responses associated with the most reactive blood-stage targets 1 month after CHMI (Etramp 5, GLURP-R2, MSP4 and MSP1-19; Spearman’s ρ = 0.82, p < 0.001). Most volunteers developed antibodies against a potential marker of recent exposure: Etramp 5 (37/45, 82%). Our findings justify validation in endemic populations to define a minimum set of antigens needed to detect exposure to natural low-density infections.

Bioethics of establishing a CHIM model for dengue vaccine development

INTRODUCTION

Controlled human infection models (CHIM) have been used in vaccine development to up-select and down-select potential vaccine candidates and to provide proof of vaccine efficacy, and have also been used as a basis for licensure of vaccines for cholera and typhoid by regulatory agencies.

CHIM IN DENGUE VACCINES DEVELOPMENT

Dengue fever results in ∼400 million infections a year and is of significant health concern especially in India. There are currently no antivirals for the disease and the only licensed vaccine for dengue is not widely used owing to safety concerns. Controlled dengue human challenge models (DHCM) are currently being used to assess the efficacy of vaccines in development for dengue.

DENGUE CHIM IN INDIA

Conducting CHIM studies in India especially for evaluation of dengue vaccine candidates will be hugely beneficial as the disease is endemic to India and hence the effect of pre-exposure to the virus on vaccine safety and efficacy can be established. However, to date no CHIM studies have been conducted in India and there is a need to educate ethics committee members, policy makers and the public on the importance of such studies and what they entail.

Is Saglin a mosquito salivary gland receptor for Plasmodium falciparum?

BACKGROUND

Saglin, a 100 kDa protein composed of two 50 kDa homodimers, is present in the salivary glands of Anopheles gambiae and has been considered an essential receptor for sporozoites (SPZ) of Plasmodium berghei and Plasmodium falciparum (Pf), allowing SPZ to recognize, bind to, and infect mosquito salivary glands. Spatial and temporal patterns of Saglin expression reported here, however, suggest that this model does not fully describe the Saglin-SPZ interaction.

RESULTS

Saglin protein was detected by indirect immunofluorescence microscopy only in the medial and proximal-lateral lobes, but not in the distal-lateral lobes, of the salivary glands of An. gambiae; the pattern of expression was independent of mosquito age or physiological state. These results were confirmed by steady-state Saglin transcript and protein expression using qRT-PCR and Western-blot analysis, respectively. Saglin was localized to the basal surface of the cells of the medial lobes and was undetectable elsewhere (intracellularly, on the lateral or apical membranes, the cells' secretory vacuoles, or in the salivary duct). In the cells of the proximal lateral lobes of the salivary glands, Saglin was distinctly intracellular and was not localized to any of the cell surfaces. Transgenic Anopheles stephensi were produced that expressed An. gambiae Saglin in the distal lateral lobes of the salivary gland. Additional Saglin expression did not enhance infection by PfSPZ compared to non-transgenic siblings fed on the same gametocyte-containing blood meal.

CONCLUSIONS

The absence of Saglin in the distal lateral lobes of the salivary glands, a primary destination for SPZ, suggests Saglin is not an essential receptor for Plasmodium SPZ. The lack of any correlation between increased Saglin expression in the distal lateral lobes of the salivary glands of transgenic An. stephensi and PfSPZ infection is also consistent with Saglin not being an essential salivary gland receptor for Plasmodium SPZ.

Controlled Human Malaria Infection in Semi-Immune Kenyan Adults (CHMI-SIKA): a study protocol to investigate in vivo Plasmodium falciparum malaria parasite growth in the context of pre-existing immunity

Malaria remains a major public health burden despite approval for implementation of a partially effective pre-erythrocytic malaria vaccine. There is an urgent need to accelerate development of a more effective multi-stage vaccine. Adults in malaria endemic areas may have substantial immunity provided by responses to the blood stages of malaria parasites, but field trials conducted on several blood-stage vaccines have not shown high levels of efficacy.  We will use controlled human malaria infection (CHMI) studies with malaria-exposed volunteers to identify correlations between immune responses and parasite growth rates in vivo.  Immune responses more strongly associated with control of parasite growth should be prioritized to accelerate malaria vaccine development. We aim to recruit up to 200 healthy adult volunteers from areas of differing malaria transmission in Kenya, and after confirming their health status through clinical examination and routine haematology and biochemistry, we will comprehensively characterize immunity to malaria using >100 blood-stage antigens. We will administer 3,200 aseptic, purified, cryopreserved Plasmodium falciparum sporozoites (PfSPZ Challenge) by direct venous inoculation. Serial quantitative polymerase chain reaction to measure parasite growth rate in vivo will be undertaken. Clinical and laboratory monitoring will be undertaken to ensure volunteer safety. In addition, we will also explore the perceptions and experiences of volunteers and other stakeholders in participating in a malaria volunteer infection study. Serum, plasma, peripheral blood mononuclear cells and extracted DNA will be stored to allow a comprehensive assessment of adaptive and innate host immunity. We will use CHMI in semi-immune adult volunteers to relate parasite growth outcomes with antibody responses and other markers of host immunity. Registration: ClinicalTrials.gov identifier NCT02739763.

Ethical considerations in Controlled Human Malaria Infection studies in low resource settings: Experiences and perceptions of study participants in a malaria Challenge study in Kenya

Background: The range and amount of volunteer infection studies, known as Controlled Human Infection Model (CHMI) studies, in Low-Middle Income Countries (LMICs) is increasing with rapid technological advancement, world-class laboratory facilities and increasing capacity development initiatives. However, the ethical issues these studies present in LMICs have not been empirically studied. We present findings of a descriptive social science study nested within a malaria volunteer infection study, on-going at the time of writing, at the KEMRI-Wellcome Trust Research Programme (KWTRP) on the Kenyan Coast. Methods: The study included non-participant observations, five group discussions with more than half of the CHMI study participants, two in-depth interviews with study team members, and an exit questionnaire administered to the participants. Results: Participants understood the key elements of the study, including that they would be deliberately infected with malaria parasites and may get malaria as a result, there would be regular blood draws, and they would spend up to 24 days in a residence facility away from their homes. The greatest motivation for participation was the monetary compensation of 20 USD per overnight stay given as a lump-sum at the end of their residency stay. Also appreciated were the health screening tests prior to enrolment and the positive relations with the study team. Concerns raised included the amount and regularity of blood draws experienced, and concerns that this type of research may feed into on-going rumours about research generally. Conclusion: With the increasing range and number of CHMI studies being conducted in LMICs, current ethical guidance are inadequate.  This study highlights some of the ethical issues that could emerge in these settings, emphasizing the heavy responsibility placed on research review and regulatory systems, researchers and funders, as well as the importance of carefully tailored community engagement and consent processes.

Ethical challenges posed by human infection challenge studies in endemic settings

Human infection challenge studies (HCS) involve intentionally infecting research participants with pathogens, often with the ultimate aim of developing new interventions against infectious diseases. Despite ethical concerns about research involving vulnerable populations, there are both scientific and ethical reasons to consider conducting more HCS in low- and middle-income countries where neglected diseases are often endemic. HCS researchers can reduce the risks to participants (and the risks of transmission from participants to others) by controlling multiple factors (eg those related to the laboratory environment, participant selection, the pathogen, and the timing of treatment); but HCS nonetheless raise important ethical issues, some of which may be particularly pertinent to HCS in endemic settings. This article provides background on HCS in general, as well as recent HCS in low- and middle-income countries, and an overview of the ethical issues associated with HCS in endemic settings.

Ethical and scientific considerations on the establishment of a controlled human infection model for schistosomiasis in Uganda: report of a stakeholders' meeting held in Entebbe, Uganda

Controlled human infection (CHI) models are gaining recognition as an approach to accelerating vaccine development, for use in both non-endemic and endemic populations: they can facilitate identification of the most promising candidate vaccines for further trials and advance understanding of protective immunity. Helminths present a continuing health burden in sub-Saharan Africa. Vaccine development for these complex organisms is particularly challenging, partly because protective responses are akin to mechanisms of allergy. A CHI model for Schistosoma mansoni (CHI-S) has been developed at Leiden University Medical Centre, the Netherlands. However, responses to schistosome infections, and candidate vaccines, are likely to be different among people from endemic settings compared to schistosome-naïve Dutch volunteers. Furthermore, among volunteers from endemic regions who have acquired immune responses through prior exposure, schistosome challenge can be used to define responses associated with clinical protection, and thus to guide vaccine development.  To explore the possibility of establishing the CHI-S in Uganda, a Stakeholders' Meeting was held in Entebbe in 2017. Regulators, community members, researchers and policy-makers discussed implementation challenges and recommended preparatory steps: risk assessment; development of infrastructure and technical capacity to produce the infectious challenge material in Uganda; community engagement from Parliamentary to grass-roots level; pilot studies to establish approaches to assuring fully informed consent and true voluntariness, and strategies for selection of volunteers who can avoid natural infection during the 12-week CHI-S; the building of regulatory capacity; and the development of study protocols and a product dossier in close consultation with ethical and regulatory partners. It was recommended that, on completion, the protocol and product dossier be reviewed for approval in a joint meeting combining ethical, regulatory and environment management authorities. Most importantly, representatives of schistosomiasis-affected communities emphasised the urgent need for an effective vaccine and urged the research community not to delay in the development process.

Ethical and scientific considerations on the establishment of a controlled human infection model for schistosomiasis in Uganda: report of a stakeholders' meeting held in Entebbe, Uganda

Controlled human infection (CHI) models are gaining recognition as an approach to accelerating vaccine development, for use in both non-endemic and endemic populations: they can facilitate identification of the most promising candidate vaccines for further trials and advance understanding of protective immunity. Helminths present a continuing health burden in sub-Saharan Africa. Vaccine development for these complex organisms is particularly challenging, partly because protective responses are akin to mechanisms of allergy. A CHI model for Schistosoma mansoni (CHI-S) has been developed at Leiden University Medical Centre, the Netherlands. However, responses to schistosome infections, and candidate vaccines, are likely to be different among people from endemic settings compared to schistosome-naïve Dutch volunteers. Furthermore, among volunteers from endemic regions who have acquired immune responses through prior exposure, schistosome challenge can be used to define responses associated with clinical protection, and thus to guide vaccine development.  To explore the possibility of establishing the CHI-S in Uganda, a Stakeholders' Meeting was held in Entebbe in 2017. Regulators, community members, researchers and policy-makers discussed implementation challenges and recommended preparatory steps: risk assessment; development of infrastructure and technical capacity to produce the infectious challenge material in Uganda; community engagement from Parliamentary to grass-roots level; pilot studies to establish approaches to assuring fully informed consent and true voluntariness, and strategies for selection of volunteers who can avoid natural infection during the 12-week CHI-S; the building of regulatory capacity; and the development of study protocols and a product dossier in close consultation with ethical and regulatory partners. It was recommended that, on completion, the protocol and product dossier be reviewed for approval in a joint meeting combining ethical, regulatory and environment management authorities. Most importantly, representatives of schistosomiasis-affected communities emphasised the urgent need for an effective vaccine and urged the research community not to delay in the development process.

Ethical considerations in Controlled Human Malaria Infection studies in low resource settings: Experiences and perceptions of study participants in a malaria Challenge study in Kenya

Background: The range and amount of volunteer infection studies, known as Controlled Human Infection Model (CHMI) studies, in Low-Middle Income Countries (LMICs) is increasing with rapid technological advancement, world-class laboratory facilities and increasing capacity development initiatives. However, the ethical issues these studies present in LMICs have not been empirically studied. We present findings of a descriptive social science study nested within a malaria volunteer infection study, on-going at the time of writing, at the KEMRI-Wellcome Trust Research Programme (KWTRP) on the Kenyan Coast. Methods: The study included non-participant observations, five group discussions with more than half of the CHMI study participants, two in-depth interviews with study team members, and an exit questionnaire administered to the participants. Results: Participants understood the key elements of the study, including that they would be deliberately infected with malaria parasites and may get malaria as a result, there would be regular blood draws, and they would spend up to 24 days in a residence facility away from their homes. The greatest motivation for participation was the monetary compensation of 20 USD per overnight stay given as a lump-sum at the end of their residency stay.  Also appreciated were the health screening tests prior to enrolment and the positive relations with the study team. Concerns raised included the amount and regularity of blood draws experienced, and concerns that this type of research may feed into on-going rumours about research generally. Conclusion: With the increasing range and number of CHMI studies being conducted in LMICs, current ethical guidance for more than minimal risk studies is inadequate. This study highlights some of the ethical issues that could emerge in these settings, emphasizing the heavy responsibility placed on research review and regulatory systems, researchers and funders, as well as the importance of carefully tailored community engagement and consent processes.

A framework for Controlled Human Infection Model (CHIM) studies in Malawi: Report of a Wellcome Trust workshop on CHIM in Low Income Countries held in Blantyre, Malawi

Controlled human infection model (CHIM) studies have pivotal importance in vaccine development, being useful for proof of concept, pathogenesis, down-selection and immunogenicity studies.  To date, however, they have seldom been carried out in low and middle income countries (LMIC), which is where the greatest burden of vaccine preventable illness is found.  This workshop discussed the benefits and barriers to CHIM studies in Malawi.  Benefits include improved vaccine effectiveness and host country capacity development in clinical, laboratory and governance domains.  Barriers include acceptability, safety and regulatory issues. The report suggests a framework by which ethical, laboratory, scientific and governance issues may be addressed by investigators considering or planning CHIM in LMIC.

DSM265 for Plasmodium falciparum chemoprophylaxis: a randomised, double blinded, phase 1 trial with controlled human malaria infection

BACKGROUND

A drug for causal (ie, pre-erythrocytic) prophylaxis of Plasmodium falciparum malaria with prolonged activity would substantially advance malaria control. DSM265 is an experimental antimalarial that selectively inhibits the parasite dihydroorotate dehydrogenase. DSM265 shows in vitro activity against liver and blood stages of P falciparum. We assessed the prophylactic activity of DSM265 against controlled human malaria infection (CHMI).

METHODS

At the Institute of Tropical Medicine, Eberhard Karls University (Tübingen, Germany), healthy, malaria-naive adults were allocated to receive 400 mg DSM265 or placebo either 1 day (cohort 1A) or 7 days (cohort 2) before CHMI by direct venous inoculation (DVI) of 3200 aseptic, purified, cryopreserved P falciparum sporozoites (PfSPZ Challenge; Sanaria Inc, Rockville, MD, USA). An additional group received daily atovaquone-proguanil (250-100 mg) for 9 days, starting 1 day before CHMI (cohort 1B). Allocation to DSM265, atovaquone-proguanil, or placebo was randomised by an interactive web response system. Allocation to cohort 1A and 1B was open-label, within cohorts 1A and 2, allocation to DSM265 and placebo was double-blinded. All treatments were given orally. Volunteers were treated with an antimalarial on day 28, or when parasitaemic, as detected by thick blood smear (TBS) microscopy. The primary efficacy endpoint was time-to-parasitaemia, assessed by TBS. All participants receiving at least one dose of chemoprophylaxis or placebo were considered for safety, those receiving PfSPZ Challenge for efficacy analyses. Log-rank test was used to compare time-to-parasitemia between interventions. The trial was registered with ClinicalTrials.gov, number NCT02450578.

FINDINGS

22 participants were enrolled between Oct 23, 2015, and Jan 18, 2016. Five participants received 400 mg DSM265 and two participants received placebo 1 day before CHMI (cohort 1A), six participants received daily atovaquone-proguanil 1 day before CHMI (cohort 1B), and six participants received 400 mg DSM265 and two participants received placebo 7 days before CHMI (cohort 2). Five of five participants receiving DSM265 1 day before CHMI and six of six in the atovaquone-proguanil cohort were protected, whereas placebo recipients (two of two) developed malaria on days 11 and 14. When given 7 days before CHMI, three of six volunteers receiving DSM265 became TBS positive on days 11, 13, and 24. The remaining three DSM265-treated, TBS-negative participants of cohort 2 developed transient submicroscopic parasitaemia. Both participants receiving placebo 7 days before CHMI became TBS positive on day 11. The only possible DSM265-related adverse event was a moderate transient elevation in serum bilirubin in one participant.

INTERPRETATION

A single dose of 400 mg DSM265 was well tolerated and had causal prophylactic activity when given 1 day before CHMI. Future trials are needed to investigate further the use of DSM265 for the prophylaxis of malaria.

FUNDING

Global Health Innovative Technology Fund, Wellcome Trust, Bill & Melinda Gates Foundation through Medicines for Malaria Venture, and the German Center for Infection Research.