Experimental infections in humans-historical and ethical reflections

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.

Embracing nature's complexity: Immunoparasitology in the wild

A wealth of research is dedicated to understanding how resistance against parasites is conferred and how parasite-driven pathology is regulated. This research is in part driven by the hope to better treatments for parasitic diseases of humans and livestock, and in part by immunologists who use parasitic infections as biomedical tools to evoke physiological immune responses. Much of the current mechanistic knowledge has been discovered in laboratory studies using model organisms, especially the laboratory mouse. However, wildlife are also hosts to a range of parasites. Through the study of host-parasite interactions in these non-laboratory systems we can gain a deeper understanding of parasite immunology in a more natural, complex environment. With a focus on helminth parasites, we here explore the insights gained into parasite-induced immune responses through (for immunologists) non-conventional experimental systems, and how current core findings from laboratory studies are reflected in these more natural conditions. The quality of the immune response is undoubtedly a central player in susceptibility versus resistance, as many laboratory studies have shown. Yet, in the wild, parasite infections tend to be chronic diseases. Whilst reading our review, we encourage the reader to consider the following questions which may (only) be answered by studying naturally occurring parasites in the wild: a) what type of immune responses are mounted against parasites in different hosts in the wild, and how do they vary within an individual over time, between individuals of the same species and between species? b) can we use wild or semi-wild study systems to understand the evolutionary drivers for tolerance versus resistance towards a parasite? c) what determines the ability of the host to cope with an infection and is there a link with the type of immune response mounted? d) can we modulate environmental factors to manipulate a wild animal's immune response to parasitic infections, with translation potential for humans, wildlife, and livestock? and e) in context of this special issue, what lessons for Type 2 immunity can we glean from studying animals in their natural environments? Further, we aim to integrate some of the knowledge gained in semi-wild and wild settings with knowledge gained from traditional laboratory-based research, and to raise awareness for the opportunities (and challenges) that come with integrating a multitude of naturally-occurring variables into immunoparasitological research.

The science and medicine of human immunology

Although the development of effective vaccines has saved countless lives from infectious diseases, the basic workings of the human immune system are complex and have required the development of animal models, such as inbred mice, to define mechanisms of immunity. More recently, new strategies and technologies have been developed to directly explore the human immune system with unprecedented precision. We discuss how these approaches are advancing our mechanistic understanding of human immunology and are facilitating the development of vaccines and therapeutics for infection, autoimmune diseases, and cancer.

Human challenge trial workshop: Focus on quality requirements for challenge agents, Langen, Germany, October 22, 2019

Controlled human infection models can be helpful to study pathogenesis and immune responses as a basis for the development of vaccines. In controlled human infection models, human challenge agents are used to infect healthy volunteers, therefore, ethical considerations include that the exposure studies need to be safe and results should be meaningful, e.g. contribute to a better cure. Both in the US and in Europe, the level of Good Manufacturing Practice required is related to the phase of the study ('sliding scale Good Manufacturing Practice'), and, hence, is much more open to speedy drug development than anticipated. Recommendations included: the development of guidelines for human challenge agents; a focus on strain selection, in particular with regard to strain infectivity, stability and purity; the use of whole genome sequencing; a reference repository of challenge agents, the need for early exchange with regulators to ensure acceptability of strain selection and manufacturing for later drug development; sharing of models and challenge agents.

[Development of malaria vaccines-state of the art]

Weltweit leben 3,1 Mrd. Menschen in Gebieten, in denen Malaria endemisch ist (Tropen, Subtropen). Jährlich erkranken etwa 200 Mio. Menschen, ca. 500.000 sterben daran. Betroffen sind vor allem Kinder. Um die Malaria zu kontrollieren und schlussendlich jegliche Neuinfektion zu verhindern, ist die Entwicklung wirksamer Impfstoffe von großer Bedeutung. In diesem Beitrag werden zunächst Hintergrundinformationen zur Geschichte der Impfstoffentwicklung, zur Malariaerkrankung und zu den Möglichkeiten der Therapie und Ausbreitungskontrolle gegeben. Der Hauptteil widmet sich dem aktuellen Forschungsstand zu Impfstoffen gegen den Erreger Plasmodium falciparum, gefolgt von einer ausführlichen Diskussion.

Malaria ist eine parasitäre Infektionskrankheit, die von Einzellern, sog. Plasmodien, verursacht wird. Es werden 5 humanpathogene Spezies unterschieden, von denen P. falciparum über 99 % der Erkrankungen in Afrika verursacht. Überträger (Vektor) ist die Anophelesmücke. Plasmodium bietet innerhalb seines Lebenszyklus verschiedene Ansatzpunkte für die Wirkung von Impfstoffen. Von den insgesamt ca. 70 Impfstoffkandidaten sind die präerythrozytären Impfstoffe, die in den Leberzyklus des Parasiten eingreifen, aktuell am weitesten entwickelt. Die von der Weltgesundheitsorganisation (WHO) angestrebte Wirksamkeit von mindestens 75 % wurde aber längst nicht erreicht.

Mit RTS,S/AS01 wird derzeit erstmals ein mäßig wirksamer Impfstoff großflächig eingesetzt. Schon jetzt ist offensichtlich, dass die Malaria nur im Zusammenspiel mit anderen Maßnahmen eingedämmt werden kann. Expositionsprophylaxe mit imprägnierten Moskitonetzen, der Einsatz von Insektiziden mit Residualeffekt in Innenräumen (Indoor Residual Spraying), die Vernichtung von Moskitobrutplätzen und schnelle Diagnose und Therapie der Erkrankung sind hier wichtige Elemente ebenso wie eine funktionierende Gesundheitsversorgung, die in den von Armut geprägten Gebieten oft nicht gewährleistet ist.