Les cellules lymphoïdes innées (ILC) représentent une famille de cellules hématopoïétiques récemment identifiée, qui joue un rôle essentiel dans la réponse immunitaire précoce via la production rapide de cytokines. Trois groupes - ou types - d’ILC ont été définis selon l’expression de certaines molécules membranaires ou intracellulaires, ainsi que la production différentielle de cytokines. Les ILC du groupe 1 (ILC1) expriment le facteur de transcription(FT) T-BET et sécrètent des cytokines inflammatoires de la réponse immune de type 1, l’IFN-? et le TNF-?. Les ILC2 sécrètent des cytokines associées à la réponse immune de type 2,notamment l’IL-5 et l’IL-13, et ce de façon dépendante du FT GATA-3. Enfin, les ILC3 se caractérisent par la production de cytokines telles que l’IL-17 et l’IL-22, et expriment le FTROR?t. J’ai étudié en utilisant des techniques de biologie moléculaire et cellulaire, et à partir d’échantillons sanguins et tissulaire de donneurs sains ou de patients atteints de maladies inflammatoires chroniques, la fonction de ces trois groupes d’ILC chez l’homme. Ces travaux ont permis la construction d’un nouveau modèle de développement de ces cellules à partir de précurseurs. / Innate lymphoid cells (ILC) represent a novel family of hematopoietic effectors that serve essential roles in early immune response by rapid cytokines production. Three distinct groups of ILC subsets have been described. Group 1 ILC include cytotoxic natural killer (NK) cells and other type-1 cytokines (IFN-? and TNF-?) producing cells that regulated by T-BET. Group 2 ILC (ILC2) express GATA-3 and ROR?, secrete type-2 cytokines, IL-5 and IL-13. Group 3 ILC (ILC3) utilize ROR?t to drive production of the TH17-associated cytokines, IL-17 and/or IL-22. In this thesis, I have performed series of experiments to uncover the developmental pathway and function of human ILC that may allow us to harness ILC in diverse clinical settings. First, I analyzed the phenotypic and functional heterogeneity of human peripheral blood ILC2. I found human IL-13+ ILC2 can acquire the capacity to produce IFN-?, thereby generating ÔplasticÕ ILC2. ILC2 cultures demonstrated that IFN-?+ ILC2 clones could be derived and were stably associated with increased T-BET expression. The inductive mechanism for ILC2 plasticity was mapped to the IL-12/IL-12R signaling pathway and was confirmed through analysis of patients with Mendelian susceptibility to mycobacterial disease (MSMD) due to IL-12R?1 deficiencies that failed to generate plastic ILC2. This IL-13+IFN-?+ ILC2 are detected ex vivo in gut tissues from CrohnÕs patients. Second, I identified and isolated ILC precursors (ILCP) in peripheral blood of healthy donors. This circulating ILCP can give rise to four lineages of mature ILC including cytotoxic NK cells and helper ILC1, 2 and 3 in vitro and in vivo. Transcirptomic and epigenetic analysis showed ILCP have ILC-committed transcription factor profiles but have mature ILC signature locus at the epigenetics poised states. We further identified ILCP in various tissues including fetal liver, cord blood, postnatal lung and tonsil. Our result proposed a new model of ÒILC-poiesisÓ where circulating ILCP serve as cellular substrates to generate mature ILC subsets in tissues. Understanding the role of IL-12 on driving ILC2 to ILC1 plasticity may allow us to target plastic ILC2 in various diseases. The identification and isolation of ILCP from circulating blood allow further transfer into clinical setting for cellular therapy, especially for various diseases that ILC has been shown to be importance including infection, allergy, cancer and metabolic diseases.