03
Feb
2026
Why do viruses make some people sick and others not? Max Kellner seeks answers where infections cause little harm: by examining natural hosts such as bats. A portrait of curiosity, crises, and risk-prone research. By Björn Lohmann.
When Max Kellner boarded the last plane leaving England for Vienna in early March 2020, the doctoral student from Austria had no idea that this moment would have a permanent impact on his academic career. In Cambridge, everything had just been shut down: halls of residence, institutes, public life. ‘It was a weird atmosphere,’ Kellner recalls how he felt the beginning of the COVID-19 pandemic. ‘Everyone had to leave—and no one had any idea when they would be able to return.’
Back in Vienna a few days later, he received a request that called for many of the qualities that distinguish him as a researcher: curiosity, methodological openness—and the desire to make a real contribution to science. Colleagues from a pandemic task force asked him to join in their endeavours to develop a fast, robust alternative to PCR diagnostics. At the beginning of the pandemic, it usually took about a week to evaluate a PCR test because the laboratories were overloaded. Kellner lost no time accepting the opportunity offered by his colleagues. His master’s thesis had introduced him to CRISPR-based virus diagnostics, methods that work even without sophisticated laboratories. ‘At the time, it was clear that if social life was ever to be possible again, it would only be via having access to rapid tests,’ he says.
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More InformationVirus vs. host: Why do humans and animals get sick differently?
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What began as a crisis response became a turning point. Kellner found himself spending his days in an almost empty institute in a Vienna devoid of tourists—developing a rapid RT-LAMP test together with colleagues. First developed in the 2000s, this molecular method detects viral RNA without the need for complex laboratory technology. However, the method only became suddenly popular with the arrival of Covid-19. The test developed in Vienna was later not only used in Austria, but also further developed in collaboration with researchers in Ghana and adapted to different pathogens for use in field conditions. ‘Open-source diagnostics were important to us,’ says Kellner. ‘People should be able to understand how a test works and be able to apply it freely.’
Today, five years later, Max Kellner heads his own junior research group at the Helmholtz Centre for Infection Research (HZI) in Braunschweig. His research focuses on the molecular interactions between viruses and their hosts. He is particularly interested in finding out why some mammals tolerate highly pathogenic viruses—i.e., those that cause serious illness in humans—surprisingly well without becoming ill themselves. It is research at the frontier of ignorance, as he says—and one that is interwoven with his own biography.
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Jahanzaib Ahmad is one of three doctoral students conducting research in the junior research group.
Curiosity as a way of life
Born in Vienna, Kellner is the first in his family to have earned a bachelor’s degree. What shaped him early on was not so much a specific career goal but rather the great deal of freedom he was afforded in his formative years: ‘My parents always supported me without dictating a direction,’ he says. ‘I was able to figure out for myself what kind of future I really wanted.’
Even at a very young age he was full of curiosity, collecting knowledge about birds and dinosaurs, regularly visiting the Natural History Museum with his grandfather, and spending time in nature while camping with his grandparents. Later, a chemistry set was added. ‘My interest in experimenting and creating things came long before the specific desire to become a scientist,’ he says.
Kellner first started playing American football and flag football while still at elementary school. He later became a multiple Austrian champion, played for the national team, and was member of the winning team of the European club championship. He remained loyal to the sport until his mid-twenties. At some point, four training sessions per week and matches on the weekend became incompatible with his desire to give his all to research. ‘Also physically, though, that level would no longer be feasible today,’ he says soberly. But the ambition has remained.
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The research group works with organoids, mini-tissues grown in the laboratory. They mimic the structure and function of real organs and enable biological processes to be studied in a realistic manner.
From plant laboratory to virus research
After graduating from school and completing his community service in a kindergarten, Kellner decided against studying medicine—out of respect for the responsibility involved. ‘At the time, I couldn’t imagine that the lives of patients might depend directly on decisions made by me,’ he says.
Instead, he studied biology, specializing in molecular biology, and gained early laboratory experience as a student assistant to Michael Nodine at the Gregor Mendel Institute in Vienna.
There, he experienced for the first time the everyday life of researchers—and realized that it was more to his liking than he had thought. ‘I realized that they weren’t so very much different from my parents, who didn’t have academic careers—they just had the same passion for experimentation,’ he says.
For his master’s thesis, Kellner went to the Broad Institute of MIT and Harvard—to the lab of Feng Zhang, one of the pioneers of CRISPR technology. ‘That was my first insight into US research,’ he says. ‘Very competitive, highly successful—and at the same time incredibly open.’ The fact that, as a young researcher, he was co-authoring publications there alongside a Nobel Prize candidate encouraged him to continue along the path towards a doctorate. Nodine, Zhang, and his later mentors exercised a great influence on his work, as did the experience that lab hierarchies matter less than curiosity and innovative ideas.
He began his doctorate at the University of Cambridge in Madeline Lancaster‘s laboratory. There, he worked for the first time with stem cells and 3D organoids to investigate questions in the field of evolutionary biology about human brain development. Organoids are mini-tissues grown in the laboratory that mimic the structure and function of real organs and make it possible to study biological processes in a realistic manner. ‘I was fascinated by the fact that the human brain is so much larger than that of chimpanzees,” he says. And in his hands, the technique of organoid research soon became a tool capable of reaching far beyond this question.
The pandemic as a moment of insight
Then came the pandemic—and with it a new perspective. Working on rapid tests took Kellner deep into virology. He learned that viral load and disease severity often do not coincide. ‘Some people had extremely high viral loads—without showing any symptoms at all,’ he says. ‘That really got me thinking.’
Instead of focusing on the question of what goes wrong in sick people, he became increasingly interested in a strikingly different aspect of disease: What is different about those who do not get sick? This consideration led him to natural reservoir hosts—animal species that have evolved to adapt to certain viruses and usually do not become ill when infected. Bats in particular came into focus. In bats, infections with viruses that are life-threatening to humans are often completely asymptomatic.
‘A virus is not pathogenic per se,’ says Kellner. ‘It only becomes pathogenic in interaction with a specific host.’ Ebola, SARS, and MERS are dangerous to humans, but not to other animal species. This insight becomes the core of his current research.
Bat organoids and new perspectives
For his dissertation, Kellner moved permanently to Vienna, to Josef Penninger‘s laboratory at the Institute of Molecular Biotechnology. There, he established novel organoid cell culture systems for researching bats—a methodologically challenging approach for which there are hardly any models. ‘There are almost no established tools for bat research,’ he says. I could just as easily study infections in a mouse model,’ says Kellner, ‘but a mouse is not a bat.’ In the organoid, he studies the bat itself and thus comes closer to reality.
In collaboration with high-security laboratories in Germany and Sweden, he is investigating the immune response of bats to highly pathogenic viruses such as the Marburg virus or SARS-CoV-2. The central hypothesis is that bats have genetically anchored mechanisms that enable a strong innate immune response while at the same time dampening inflammatory reactions and thus preventing severe disease progression. Understanding this resilience could open up new avenues for prevention and therapy in the long term.
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"I want to have helped people find a good path in life, regardless of whether they go on to do research themselves or something completely different," says Kellner.
Responsibility, doubt, and creative freedom
Today, Kellner sits in a 12-square-meter office on the spacious campus of the HZI in Braunschweig. Two screens, a whiteboard for one-on-one meetings, and a short walk to the lab. ‘The institute is a bit like a huge shared apartment,’ he says. ‘You don’t sleep here, but you work, eat, and have lots of opportunities for discussion.’
Since April 2025, he has been leading the VICO (Virus-Host Coevolution) junior research group, which is funded for at least five years. Three doctoral students are currently working with him. ‘It’s an enormous responsibility,’ he says. ‘Not only scientifically, but also for the lives of the people who work here.’ A twelve-hour working day is quite the norm. ‘For me, research is both work and a hobby,’ explains the biologist. That’s why he never takes work home with him.
The long-term funding from zukunft.niedersachsen plays a central role in Kellner’s research. ‘Our research deliberately pushes the boundaries of established knowledge,’ he says. ‘Without sufficient funding and freedom, much of what we do would not be feasible.’ He considers Lower Saxony to be an ideal location: high research density, short distances between universities, medical and veterinary institutions, and a strong Helmholtz network. ‘Here, you can access virtually any expertise within an hour through direct exchange,’ he says.
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In collaboration with high-security laboratories in Germany and Sweden, the research group is investigating the immune response of bats to highly pathogenic viruses such as Marburg virus and SARS-CoV-2.
At the same time, he has no illusions about the structural problems of the scientific system. ‘There are many more talented, motivated people than there are long-term employment prospects,’ he says. He considers it problematic that careers are often decided by chance and individual publications. This makes it all the more important for him to maintain an open culture in his group: communication, transparency, sharing negative results. ‘We work at the frontier of ignorance,’ he says. ‘Failure is part of it.’
Looking ahead
When Kellner looks ten years into the future, he measures success not only in terms of knowledge. ‘I want to have accompanied people on a good path in life,’ he says, ‘regardless of whether they later do research themselves or something completely different.’ He sees science not only as a profession, but as an attitude—driven by curiosity, responsibility, and a willingness to constantly embrace the unknown. Or as Max Kellner puts it: ‘For curious people, science is the most fulfilling profession imaginable.’
