Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection, and is characterized by a high mortality of up to 30-40%. Treatment of sepsis was revolutionized by two steps that significantly decreased mortality: antibiotics and the intensive care units. It has been hoped that a third revolution, immunotherapy, would further improve outcome of sepsis, but this hope did not materialize. This was due to the incompletely understood pathophysiology, and the heterogeneity of the immune status in different sepsis patients. We propose that while both overinflammation and immunoparalysis are important, they are present in individual sepsis patients.The mission of the present project is to design and perform a proof-of-concept clinical trial of personalized immunotherapy in sepsis, and within this clinical trial, to develop a next-generation theranostics platform for the design of future personalized immunotherapy trials in sepsis. This theranostics platform would be based on an integrated, multidimensional systems biology analysis of omics-based datasets, to identify biomarkers, clinical endotypes, and therapeutic targets for precision medicine approaches. In order to achieve the mission proposed, several complementary aims will be pursued: Aim 1: To design and perform a large personalized immunotherapy trial in sepsis patients, that can provide a clinical answer towards the usefulness of currently employed immunotherapies for sepsis. Aim 2: To chart host genome, epigenome, transcriptome, metabolome and microbiome in at least 180 sepsis patients enrolled in Aim 1 over a defined time course. Aim 3: To use a theranostics approach based on the data provided by Aim 2 to design novel personalized immunotherapeutic strategies. Aim 4: To integrate the clinical and psychological aspects involved when introducing novel immunotherapies for infections in the health care systems of European countries, building bridges with the patient community.