Our biological clock regulates most of our physiological processes on a 24-hour rhythm. And our immune system seems to be no exception.
« By studying the migration of dendritic cells (cells involved in triggering immune responses, editor’s note), in the lymphatic system (…) we have demonstrated the fact that immune activation oscillates throughout the day, with a peak at the end of the usual rest phase, just before resuming activity », explains Christoph Scheiermann*, from the University of Geneva.
Tumor growth influenced by the immune system
To reach this conclusion, the researchers, as often, used an animal model, in this case mice. It is important to know – it is important to fully understand what follows – that mice are nocturnal animals. Thus, their circadian profile is reversed compared to ours.
The scientists therefore injected melanoma cells into groups of mice at six different times of the day, then they followed the tumor development for two weeks.
« By modifying only the time of the injection, we observed very surprising results “, relate the authors. ” Tumors implanted in the afternoon develop little, following the rhythm of activation of the immune system of mice, while those implanted overnight grow much faster ».
Then they administered, at different times, an immunotherapy treatment to these rodents. ” The therapeutic vaccine consisted of a tumor-specific antigen, very similar to what is used to treat the sick. Administered in the afternoon, the beneficial effect was increased. »
And in humans?
To find out if these findings carried over to humans, the scientists looked at data from patients treated with therapeutic melanoma vaccines.
They then observed that specific T lymphocytes against melanoma – essential elements of immune activation – responded better to treatments administered early in the morning, which corresponds to the human circadian profile.
« This is very encouraging, but it is only a retrospective review on a small group of ten people », underlines Christoph Scheiermann. « However, the very idea that a treatment can become more powerful depending on the time of day opens up surprising perspectives.. »
* Professor in the Department of Pathology and Immunology, at the Center for Research on Inflammation (GCIR) and at the Center for Translational Research in Onco-Haematology (CRTOH) of the UNIGE Faculty of Medicine.
