**6. Conclusion and perspectives**

Studies conducted so far show that on average one out of two astronauts encounters immunological problems and that stressors encountered during spaceflights can affect all components of the immune system. It is therefore mandatory to understand in details how all immune cell types are affected by space conditions by unraveling the cellular and molecular mechanisms modified within these cells. Indeed, the impact of spatial conditions on certain cells and functions of the immune system have not yet been precisely determined. Furthermore, the impact of long-term missions is largely under-investigated. This is because, up to now, most scientific data are derived from space missions not exceeding 6 months in duration. In addition, the impact of spatial conditions on interconnections between the immune and other systems (such as the musculoskeletal, nervous, respiratory, and cardiovascular systems) should be studied using interdisciplinary approaches. All this knowledge is required (i) to gain a better understanding of the risks incurred during future long-duration space missions (such as planned mission to Mars), where the crew will be left to their own with no possibility of a rapid return to Earth, and (ii) to develop nutritional, psychosocial, and/or pharmacological countermeasures to reduce stress, preserve the immune system, and prevent the development or aggravation of diseases [82]. Another aspect that should be taken into account is in-flight monitoring of astronaut's health and diagnostic data using

miniature and autonomous biosensors to help establish personalized treatments. This corresponds to a new field of research, space biotechnology, which aims to use advanced techniques ("omics" techniques) for the quantitative detection of proteins, nucleic acids, and metabolites in situ [83–86]. Such biosensors capable of analyzing minimum quantities of body fluids and of generating semiquantitative or quantitative results in a few minutes and with minimal resource consumption in terms of weight, volume, reagent storage, and energy will be required to allow deep space exploration. These researches and technological developments could also improve health on Earth as they could led to new therapeutic strategies to treat age- and stress-related immunosuppression and could likely contribute to improve point-of-care diagnostics at a patient's bedside, in a doctor's office, or hospital.
