Septic syndromes are a major although largely under-recognized health care problem and represent the first cause of mortality in intensive care units (ICU). While it has long been known that sepsis deeply perturbs immune homeostasis by inducing a tremendous systemic inflammatory response, novel findings indicate that sepsis indeed initiates a more complex immune response that varies over time, with the concomitant occurrence of both pro- and anti-inflammatory mechanisms. As a resultant, after a short pro-inflammatory phase, septic patients enter a stage of protracted immunosuppression. This is illustrated in those patients by reactivation of dormant viruses (cytomegalovirus (CMV) or Herpes Simplex Virus (HSV)) or infections due to pathogens, including fungi, which are normally pathogenic solely in immunocompromised hosts. These alterations might be directly responsible for worsening outcome in patients who survived initial resuscitation as nearly all immune functions are deeply compromised. New promising therapeutic strategies are currently emerging from those recent findings such as adjunctive immunostimulation for the most immunosuppressed patients. The prerequisite for immunostimulation administration (Interferon gama (IFNg), Granulocyte Macrophage Colony Stimulating Factor (GM-CSF), interleukin 7 (IL-7)) however relies on clinicians' capacity to identify patients who could benefit the most from these immunoadjuvant therapies, as there is no clinical sign of immune dysfunctions. In this context, the main objectives of IMMUNOSEPSIS 4 study are: 1. to identify the best biomarkers for sepsis-induced immunosuppression 2. to evaluate ex vivo candidate treatments which could rejuvenate immune functions after septic shock