Periodic Reporting for period 4 - ILC_REACTIVITY (Biological Determinants of ILC Reactivity for Immune Responses in Health and Disease)
Période du rapport: 2021-02-01 au 2022-07-31
Innate lymphoid cells (ILC) are a newly described family of blood cells that contribute to the first-line immune defense against viral, bacterial, and parasitic infections. Several distinct ILC subsets (ILC1, ILC2, ILC3) have been described that are active during both fetal and adult life and play important roles in tissue homeostasis. ILCs resemble previously described natural killer (NK) cells; both cell types possess a 'natural' effector function which is immediately available during immune responses. In contrast, T cells and B cells that provide immune ‘memory’ after infection or vaccination (‘adaptive’ immunity) require days or weeks in order to respond. This dichotomy in the timing of ‘innate’ and ‘adaptive’ immunity has important implications as it allows the organism to maintain immune defense rapidly and for long periods of time. Still, how NK cells and ILCs acquire the capacity for rapid responses and how these diverse cell types are integrated into the complex coordination of immunity remains unclear.
The ILC_REACTIVITY proposal investigates the critical control points that can regulate ILC and NK cell function during immune responses. Using a combination of cutting-edge technologies, the signals that control various aspects of ILC and NK cell ‘lifestyle’ (their generation, survival, proliferation, activation and death) will be uncovered and deciphered. Together, these complementary studies have already shed new light on the biological determinants which regulate ILC reactivity. For example, the growth factors that are important for generation of ILCs in bone marrow have been identified, that may help to design ways to grow human ILCs for cellular therapies. Understanding how ILC responsiveness is controlled prior to and during immune responses may have important implications for disease intervention, for example in the context of infection or cancer.
The ILC_REACTIVITY proposal investigates the critical control points that can regulate ILC and NK cell function during immune responses. Using a combination of cutting-edge technologies, the signals that control various aspects of ILC and NK cell ‘lifestyle’ (their generation, survival, proliferation, activation and death) will be uncovered and deciphered. Together, these complementary studies have already shed new light on the biological determinants which regulate ILC reactivity. For example, the growth factors that are important for generation of ILCs in bone marrow have been identified, that may help to design ways to grow human ILCs for cellular therapies. Understanding how ILC responsiveness is controlled prior to and during immune responses may have important implications for disease intervention, for example in the context of infection or cancer.
We were able to better characterize ILC precursors (ILCP) and NK cell precursors (NKP) in both mouse and man. Previous studies had suggested that these precursors develop independently, however, using a novel mouse strain with highly sensitive fluorescent reporter that was specifically expressed in ILCP and NKP, we found that these precursor cells were linked in their development and a large fraction of precursor cells in the bone marrow were capable of giving rise to both NK cells and ILCs (Immunity 2019). This work allowed us to redefine the current model for ILC and NK cell development. Moreover, the identification of ILCP/NKP in mice provides the means to better understand the molecular mechanisms that promote functional competence in 'innate' lymphocytes.
The identification of ILCP/NKP in mice also allowed us to compare the process of murine ILC and NK cell development with that operating in humans. In part based on knowledge gleaned by the ILC_REACTIVITY program, we made the first identification and characterization of circulating human ILC precursors (ILCP) that can give rise to human NK cells and ILC subsets in vitro and in vivo (Cell 2017). Remarkably the mouse and human ILCP harbored a similar RNA 'signature' and showed analogous functional properties. This suggests that the process of ILC and NK cell development may be strongly conserved between these two species (Immunity 2018). As such, knowledge derived from mouse studies may have important implications for future human studies aimed at using ILCs in the context of disease.
In another series of experiments, we were able to better understand how ILC function was regulated in the intestine (a critical mucosal barrier) in response to pathogens. In general terms, ILC activation alters several metabolic pathways, that provide 'primed' ILCs with novel functional and migratory attributes. This allows these activated ILCs to contribute more efficiently to immune defense within the tissue (Science 2022).
Using novel imaging approaches and intra-vital microscopy, we have been able to monitor, for the first time, the behavior and dynamics of ILC3 subsets in distinct regions of the intestine, under steady-state as well as inflammatory/infectious conditions (Nature Immunology, 2022). We show that gut ILC3 are immotile under healthy conditions but are shift to patrol barrier sites upon inflammation. We uncovered a role for chemokine in regulating T cell versus ILC3 patrolling. As knowledge in this arena is very limited, these ground-breaking studies help define a working model for the field.
In addition, several important additional studies on human NK cells and ILCs were performed that benefitted from knowledge gleaned by the ILC_REACTIVITY program. These included studies on metabolic changes associated with human NK cell (Blood Adv 2021) and ILC2 (Nature Immunology 2021) homeostasis, growth and activation. Finally, we were able to further delineate signals involved in human ILCP differentiation, especially those involved in the generation of human group 3 ILCs (Nature Communications 2022).
Overall, the main objectives of the ILC_REACTIVITY program were achieved with publication of several high-impact papers that moreover provided novel ways to think about the biology of human and mouse ILC subsets in the context of healthy tissue homeostasis as well as under conditions of inflammation and infection.
The identification of ILCP/NKP in mice also allowed us to compare the process of murine ILC and NK cell development with that operating in humans. In part based on knowledge gleaned by the ILC_REACTIVITY program, we made the first identification and characterization of circulating human ILC precursors (ILCP) that can give rise to human NK cells and ILC subsets in vitro and in vivo (Cell 2017). Remarkably the mouse and human ILCP harbored a similar RNA 'signature' and showed analogous functional properties. This suggests that the process of ILC and NK cell development may be strongly conserved between these two species (Immunity 2018). As such, knowledge derived from mouse studies may have important implications for future human studies aimed at using ILCs in the context of disease.
In another series of experiments, we were able to better understand how ILC function was regulated in the intestine (a critical mucosal barrier) in response to pathogens. In general terms, ILC activation alters several metabolic pathways, that provide 'primed' ILCs with novel functional and migratory attributes. This allows these activated ILCs to contribute more efficiently to immune defense within the tissue (Science 2022).
Using novel imaging approaches and intra-vital microscopy, we have been able to monitor, for the first time, the behavior and dynamics of ILC3 subsets in distinct regions of the intestine, under steady-state as well as inflammatory/infectious conditions (Nature Immunology, 2022). We show that gut ILC3 are immotile under healthy conditions but are shift to patrol barrier sites upon inflammation. We uncovered a role for chemokine in regulating T cell versus ILC3 patrolling. As knowledge in this arena is very limited, these ground-breaking studies help define a working model for the field.
In addition, several important additional studies on human NK cells and ILCs were performed that benefitted from knowledge gleaned by the ILC_REACTIVITY program. These included studies on metabolic changes associated with human NK cell (Blood Adv 2021) and ILC2 (Nature Immunology 2021) homeostasis, growth and activation. Finally, we were able to further delineate signals involved in human ILCP differentiation, especially those involved in the generation of human group 3 ILCs (Nature Communications 2022).
Overall, the main objectives of the ILC_REACTIVITY program were achieved with publication of several high-impact papers that moreover provided novel ways to think about the biology of human and mouse ILC subsets in the context of healthy tissue homeostasis as well as under conditions of inflammation and infection.
We described 'memory' attributes of mouse intestinal ILC3. These cells play important roles in intestinal homeostasis and protection against infection. The fact that exposure to pathogens in the gut result in long-lived attributes in intestinal ILC3 suggest that innate lymphoid cell 'training' or 'memory' can accumulate with immune experience during the lifetime of an individual. This has major implications for protection against disease.
We developed novel approaches to image innate lymphoid cells within the small intestine of living animals (Serafini et al. 2022) which has not been previously. This advance should help others interested in developing approaches to study cellular dynamics within this organ and to characterize effects of inflammation and infection upon immune responses. While ILC3 were expected to be motile cells that help protect the intestine through immunosurveillence, we found that ILC3 are mostly immobile under steady-state conditions. This changes our thinking about T cells versus ILC3 in normal healthy conditions. In contrast, under inflammatory conditions, ILC3 adopt a patrolling behaviour and become active players in immune defense at barrier surfaces.
Our discovery of human ILC precursors (Lim et al. Cell 2017) was a significant finding that changed our appreciation of the was in which ILCs may be generated over the lifetime of an individual. The mechanisms that allow ILC differentiation from ILC precursors are unknown but the discovery of circulating blood ILCP in humans provides an important opportunity to study this process. This is the subject of an 2022 ERC Advanced grant (HU_ILCPOIESIS) that I have submitted and is currently under evaluation (step 2). Finally, this represents a possible first step in a path towards human ILC therapy which have the potential to impact on diverse human diseases that implicate human innate lymphoid cells.
We developed novel approaches to image innate lymphoid cells within the small intestine of living animals (Serafini et al. 2022) which has not been previously. This advance should help others interested in developing approaches to study cellular dynamics within this organ and to characterize effects of inflammation and infection upon immune responses. While ILC3 were expected to be motile cells that help protect the intestine through immunosurveillence, we found that ILC3 are mostly immobile under steady-state conditions. This changes our thinking about T cells versus ILC3 in normal healthy conditions. In contrast, under inflammatory conditions, ILC3 adopt a patrolling behaviour and become active players in immune defense at barrier surfaces.
Our discovery of human ILC precursors (Lim et al. Cell 2017) was a significant finding that changed our appreciation of the was in which ILCs may be generated over the lifetime of an individual. The mechanisms that allow ILC differentiation from ILC precursors are unknown but the discovery of circulating blood ILCP in humans provides an important opportunity to study this process. This is the subject of an 2022 ERC Advanced grant (HU_ILCPOIESIS) that I have submitted and is currently under evaluation (step 2). Finally, this represents a possible first step in a path towards human ILC therapy which have the potential to impact on diverse human diseases that implicate human innate lymphoid cells.