Natural Killer (NK) cells are lymphocytes of the innate immune system that recognize and induce the lysis of a variety of target cells, including virally-infected cells, tumor cells, and allogenic cells without prior specific sensitization.
In addition, NK cells elaborate a variety of regulatory cytokines including IFNg, TGFß1, TNFa, IL-1bß, IL-10, G-CSF, and GM-CSF and CC-chemokines, such as RANTES, MIP-1a and MIP-1bß which are involved in the elimination of intracellular pathogens in vivo, as well as in the generation of antigen-specific immune response.
A feature of NK cell cytolytic activities and cytokine production is that their initiation is dependent upon the integrity of MHC class I expression on target cells. Indeed, NK cells express cell surface receptors such as KIR in humans, Ly49 in the mouse, and CD94/NKG2 heterodimers in both species, that can sense the alteration of MHC class I molecules at the surface of target cells.

The main goal of our group is to contribute to the dissection of the functions of NK cells in vivo by elucidating the receptors that confer to NK cell the capacity to distinguish target from non-target cells. We believe that the results obtained in this aim will contribute to reveal novel mode of immune recognition and to precisely envision the potential indications of NK cell manipulation in novel immunotherapeutic strategies.

Natural Killer (NK) cells can recognize, without any prior sensitization, transformed, microbe-infected or allogeneic cells, while sparing most of autologous healthy cells.  Once NK cells have identified a potential target cell, they can eliminate it by diverse mechanisms and/or they can secrete a variety of cytokines and chemokines. Therefore, NK cells play a unique role in innate immune responses, as well as in the polarization of adaptive immunity. We are focusing our work on two aspects of NK cell physiology: their functions and their anatomical distribution. We believe that a better knowledge of these aspects of NK cell biology is essential for both basic and clinical research. In particular, it should help to design  novel therapeutic strategies aimed at activating specific NK cell functions, at the proper place and in due time, to fight cancer or infectious diseases.

The majority of the receptors known to activate NK cells in both human and mice are associated with one of the three ITAM (Immunoreceptor Tyrosine Based) polypeptides KARAP/DAP12, CD3z or FcRg. In order to dissect ITAM-dependent NK cell activation, we have generated mice simultaneously deficient in these 3 signalling molecules, the ITAM-less mice, and we have analyzed the responses of their NK cells in response to various stimuli, ex vivo and in vivo. This approach has revealed that a multiplicity of ITAM-dependent and -independent pathways are involved in the induction of NK cell effector functions, in contrast to the known pathways for T or B lymphocyte activation. The contribution of these different signalling pathways varies according to the nature of the tumor target cell and to activation status of the NK cell, emphasizing the plasticity of the transduction circuits which lead to NK cell activation. Finally, some ITAM-dependent functions are also affected in mice deficient in the LAT or NTAL signalling transmembrane adaptors. When taken together, these results indicate that, in NK cells, multiplicity and plasticity are general features, which are not only restricted to early events such as the nature of the receptors involved in target cell recognition but which also extend to the downstream transduction pathways (Chiesa et al, Blood, 2006).

Another important aspect regarding NK cell physiology is the anatomical distribution of NK cells in the whole organism. NK cells are mainly generated in the bone marrow and can be isolated in the periphery in the spleen, the liver, the lungs, the uterus, the lymph nodes, the thymus, and the peripheral blood. Interestingly, in both humans and mice, the NK cells that are present in different organs harbor distinct phenotypes and functions. Whether NK cells are present in the majority of epithelial tissues is poorly documented and hotly debated. This aspect is of particular interest, as epithelial tissues constitute the first barrier against most microbial, chemical or physical aggressions. We have recently started a new research program focused on the identification and characterization of NK cells in both mouse and human epithelial tissues. Our first goal is to define whether NK cells reside in these tissues under steady-state conditions and/or migrate there under inflammatory conditions. Subsequently, we intend to dissect the role of “epithelial NK cells” in the homeostasis of healthy epithelial tissue as well as in the development of diverse pathologies affecting these tissues.

Self versus non-self discrimination is a central theme in biology, extending from plants to vertebrates. Natural killer (NK) cells in the mammalian immune system constitute an experimental model system for investigating the molecular and cellular mechanisms involved in these complex biological processes. Indeed, NK cells are tolerant to normal self tissues, but kill and produce cytokines in response to cells in distress (tumors, infected cells…). Studies in humans and mice have shown that self-recognition is required for NK cells to acquire functional competence. However, little is known about this developmental process. We therefore propose to elucidate the mechanisms of NK cell "education" to self versus non-self discrimination.

Understanding such complex system, from the molecular scale to higher level tissue architecture and beyond, to the physiology of whole organisms, requires multiple approaches at various levels. We thus work up from the whole organism to the molecular scale. In particular, new mouse mutants are generated by random germline mutagenesis using ENU (N-ethyl-N-nitrosourea). We also try to understand the system as a whole, using genome-wide transcriptome analysis and NK cell imaging in tissues. Finally, the real-time observation of protein dynamics in living cells using a FCS (Fluorescence Correlation Spectroscopy) method in collaboration with the group of D. Marguet (CIML), will allow to measure parameters, such as the number of molecules, diffusion coefficients, spatial distributions and temporal fluctuations, essential for the generation of quantitative models.

By determining the mechanisms allowing both NK cell self-tolerance and their ability to respond to diseased cells, we should improve our understanding of biological processes that may operate broadly in the vertebrate innate immune system. This inter-disciplinary project should also contribute to define the rationale basis of manipulating NK cells in ongoing and forthcoming innovative anti-cancer clinical trials.