Extraterrestrial Risk

What biosecurity risks do exo-microorganisms pose? Neil Gow, Deputy Vice-Chancellor for Research and Impact, and a professor of microbiology at the University of Exeter, UK, and Mihai Netea, a professor at Radboud University Medical Center, the Netherlands, mulled the idea while walking on the beach at a scientific meeting in the Caribbean – and devised two potential studies on how to address the risks. The first of those studies was published earlier this year (1): “A Weakened Immune Response to Synthetic Exo-Peptides Predicts a Potential Biosecurity Risk in the Retrieval of Exo-Microorganisms.”

Discussing the work at an astrobiology conference in Seattle in 2019, Katja Schaefer, lead author on the study, discussed the field of exo-immunobiology  (originally introduced by Netea) – where the human immune system encounters either a completely alien microorganism, or Earth organisms that have been adapted to space environments. How would the immune system react? And would it even recognize the organisms to elicit an immune response?

Exo-microorganisms are not just a risk for those exploring space – they could be brought back to Earth during sample retrieval from exoplanets or moons, for example. Schaefer, Gow, Netea, and their co-authors believe that exo-microorganisms with distinct proteomes may present immunological challenges. Their study tested the mammalian immune response towards protein antigens containing two amino acids: isovaline and α-aminoisobutyric acid. Both are extremely rare in earth organisms, but have been identified in abundance in chondrite meteorites.

“My background actually lies in fungal pathogens, but when I started working with Neil Gow, he told me about his provocative ideas involving amino acids on meteorites – and it was interesting! We decided that I would start it as a side project to my main work,” says Schaefer. “Other papers have discussed the characterization of amino acids from meteorites, but to find out how they’d affect the immune response, a peptide was needed. I didn’t have an immunological background, so we brought in other collaborators. Once we had the peptide, we isolated immune cells from mice and measured the effect when they were exposed to the peptide.”

The result? The peptide was recognized by the immune system, which led to an immunological response, but T cell activation and proliferation were both significantly reduced compared with exposure to common peptides on Earth.

What does this mean for humans? It’s very difficult to say, but peptides or organisms made up of different amino acids to those on Earth could pose an immunological risk. “There are many other questions that we can also explore, such as why the immune response was low, what enzymes and processes are involved, and whether it is possible for the mammalian immune system to produce antibodies in response to the peptides,” says Schaefer.

The risk could also be greater for astronauts. Conditions in space can also change how the immune system works. Astronauts are exposed to very extreme environmental stresses, including microgravity, radiation, and poor nutrition – which can result in a weakened immune response, including reduced cytokine release and reduced T cell function (2). “This is already in effect without exposure to a pathogen – and also remains in effect for some time after the astronauts have returned to Earth,” explains Schaefer. “It would be interesting to do experiments with the immune cells of returning astronauts to see how the immune response changes when exposed to these rare amino acids. We also want to look at how the properties of terrestrial microbes could be altered by growing on exo-substrates. I’m also interested in the fact that different sugars have been found on meteorites – and, recently, a peptide. This is a vibrant area of research.”