STRAT4PAIS — Immune Endotypes of Paediatric Post-Acute Infection Syndromes (PAIS): Mechanistic Stratification of ME/CFS and Related Post-Infectious Conditions

Children and young people living with post-infectious conditions such as ME/CFS or Long COVID are usually treated as if they were all suffering from the same condition. However, it is reasonable to assume that different biological processes underlie these similar symptoms. STRAT4PAIS is systematically investigating this hidden diversity for the first time. The starting point is four post-infectious clinical presentations: abnormal circulatory and cardiac rhythm responses; a persistent immune response to viral infections; autoimmune processes; and headaches in which, amongst other things, increased intracranial pressure can be detected. The aim is to determine whether these four clinical presentations are underpinned by four distinct biological mechanisms. To clarify this, the immune systems of the affected children and adolescents will be examined using state-of-the-art single-cell analysis methods (single-cell technologies). At the heart of this is single-cell transcriptome analysis (scRNA-seq): following targeted cell sorting, the gene activity of each individual immune cell is analysed, supplemented by the individual immune receptors of the T and B cells (TCR/BCR repertoire) and selected surface proteins. This enables the identification of exhausted antiviral T-cell states and autoreactive B-cell programmes; in parallel, the innate immune system is analysed (NK cells, monocytes, dendritic cells). High-dimensional flow cytometry verifies findings across the entire cohort, whilst a broad protein multiplex analysis (~250 mediators) captures the inflammatory response. Furthermore, the test screens for traces of reactivated herpesviruses (e.g. Epstein-Barr virus) and autoantibodies. Measurements are taken at various stages of the disease course: during periods of stability, during post-exertional malaise (PEM) and during a febrile infection. It is precisely these critical moments, when the body is under stress, that could reveal correlations which remain hidden at rest. And because the same patients are compared with themselves in different states, it may be possible to identify the disease-driving changes with particular clarity. Using all this data, the aim is to determine which patients are biologically similar to one another and can be assigned to common endotypes. The aim is to highlight what distinguishes these children and young people from one another biologically, and to pave the way for future treatments to target the specific underlying cause. STRAT4PAIS is linked, amongst other projects, to the PEDNET-LC project funded by the Federal Ministry of Health (BMG).