Scientists have added circadian rhythm, also known as the ‘body clock’, amongst the various factors affecting how well the immune system works. The findings of a new Canada-based study shed light on how the adaptive immune system can be more or less efficient during various times of the day and their corresponding circadian rhythm.
The study, which was recently published in the PNAS journal, was supported by grants from the Canadian Institutes of Health Research. It highlights that the CD8 T cells, which play an important role in breaking up infected and tumor cells, respond more or less effectively depending on the time of the day as well as the presence of a ‘clock’ gene. 
“Our study shows that T cells are more prone to be activated at certain times of the day. Identifying the mechanisms through which the biological clock modulates the T cell response will help us better understand the processes that regulate optimal T cell responses. This knowledge will contribute to improving vaccination strategies and cancer immune therapies,” states Nathalie Labrecque, Professor at the Departments of Medicine and Microbiology, Infectious Diseases and Immunology at Université de Montréal. 
Circadian rhythms are responsible for the body to be able to adapt to night and day cycles, as well as the seasons. These are generated by the ‘clock gene’ and are found in sleep, nutrition, and hormonal activity.
This was an animal study which concludes that T cell-based therapies can be based on the time of the day, for them to be more effective.