Innate lymphoid cell recovery and occurrence of GvHD after hematopoietic stem cell transplantation.

Lymphocytes are essential for microbial immunity, tumor surveillance, and tissue homeostasis. However, the in vivo development and function of helper-like innate lymphoid cells (ILCs) in humans remain much less well understood than those of T, B, and NK cells. We monitored hematopoietic stem cell transplantation (HSCT) to determine the kinetics of ILC development in both children and adults. It was found that, unlike NK cells, helper-like ILCs recovered slowly, mirroring the pattern observed for T cells, with normalization achieved at 1 year. The type of graft and the proportion of CD34+ cells in the graft did not significantly affect ILC reconstitution. As HSCT is often complicated by acute or chronic graft-versus-host disease (GVHD), the potential role of ILC subsets in maintaining tissue integrity in these conditions was also analyzed. It was found that GVHD was associated with lower levels of activated and gut-homing NKp44+ ILCP, consistent with a non-redundant role of this ILC subset in preventing this life-threatening disorder in lymphopenic conditions.

Single-cell transcriptomic landscape reveals tumor specific innate lymphoid cells associated with colorectal cancer progression.

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes differing from conventional T lymphocytes in having no antigen-specific receptors. ILCs include natural killer (NK) cells, helper-like ILC1s, ILC2s, and ILC3s, and lymphoid tissue-inducer (LTi) cells. Tumor ILCs are frequently found in various cancers, but their roles in cancer immunity and immunotherapy remain largely unclear. We report here the single-cell characterization of blood and gut helper-like ILC subsets in healthy conditions and in colorectal cancer (CRC). The healthy gut contains ILC1s, ILC3s, and ILC3/NKs, but no ILC2s. Additional tumor-specific ILC1-like and ILC2 subsets were identified in CRC patients. Signaling lymphocytic activation molecule family member 1 (SLAMF1) was found to be selectively expressed on tumor-specific ILCs, and higher levels of SLAMF1+ ILCs were observed in the blood of CRC patients. The SLAMF1-high group of CRC patients had a significantly higher survival rate than the SLAMF1-low group, suggesting that SLAMF1 is an anti-tumor biomarker in CRC.

Single-cell profiling reveals the trajectories of natural killer cell differentiation in bone marrow and a stress signature induced by acute myeloid leukemia.

Natural killer (NK) cells are innate cytotoxic lymphoid cells (ILCs) involved in the killing of infected and tumor cells. Among human and mouse NK cells from the spleen and blood, we previously identified by single-cell RNA sequencing (scRNAseq) two similar major subsets, NK1 and NK2. Using the same technology, we report here the identification, by single-cell RNA sequencing (scRNAseq), of three NK cell subpopulations in human bone marrow. Pseudotime analysis identified a subset of resident CD56bright NK cells, NK0 cells, as the precursor of both circulating CD56dim NK1-like NK cells and CD56bright NK2-like NK cells in human bone marrow and spleen under physiological conditions. Transcriptomic profiles of bone marrow NK cells from patients with acute myeloid leukemia (AML) exhibited stress-induced repression of NK cell effector functions, highlighting the profound impact of this disease on NK cell heterogeneity. Bone marrow NK cells from AML patients exhibited reduced levels of CD160, but the CD160high group had a significantly higher survival rate.

Multidimensional molecular controls defining NK/ILC1 identity in cancers.

Innate Lymphoid Cells (ILCs) are a recently described heterogeneous population of non-T, non-B lymphocytes. They are highly abundant at mucosal interfaces and, unlike T and B cells, they do not express somatically rearranged antigen-specific receptors. ILCs may be seen as the innate counterparts of T cells, but, major ILC deficiencies in humans appear to be clinically silent in modern conditions of hygiene and medicine, provided that T and B functions are preserved. NK cells are the founder members of this family and were originally classified in group 1 ILCs with ILC1s, due to similarities in cytokine production and development between these two types of cell. The classification of the ILC subsets was subsequently reviewed and five groups were defined on the basis of cytokine production and the discovery of specific transcription factors determining the different lineages. ILCs include NK cells, lymphoid tissue-inducer (LTi) cells and three other main subsets: ILC1s, ILC2s and ILC3s. The nature of distinct ILC1 population in mice and human is not consensual due to the high degree of similarity between ILCs and NK cells and their plastic relationships in some context. In this review, we will discuss the characteristics currently used for the phenotyping of NK cells and ILC1s in mice and humans, in the context of cancers especially, in which inappropriate discrimination between these two cell types can lead to erroneous conclusions regarding the specific impact of their targeting on tumors. Here, we suggest that multidimensional molecular controls, with the co-ordination of ontogeny-related signals, tissue-specific and tumor microenvironment-derived signals, determine the identity of NK cells and ILC1s. All these molecular stratifications contribute to the construction of cell fate for NK cells and ILC1s and account for the difficulties distinguishing between these two groups of cells.

SnapShot: Natural Killer Cells.

NK cells are broadly distributed innate lymphoid cells (ILCs) encompassing distinct populations based on CD11b and CD27 expression in mice or CD56 intensity in humans. Involved in anti-viral and anti-tumor immunity thanks to their cytokines and chemokines secretion as well as their cytotoxic capabilities, NK cells have emerged as a promising therapeutic target in several solid tumors and hematological malignancies. To view this Snapshot, open or download the PDF.

Helper-like innate lymphoid cells and cancer immunotherapy.

Immunotherapies have revolutionized cancer treatment over the last 20 years. They aim either to boost immune cell activation or decrease immune cell inhibition, to improve control over cancer development. Various strategies for improving tumor immunity have been tested. Some have been approved and others are currently in clinical trials. They target the immune system itself, the tumor cells or the microenvironment. Most focus on enhancing T-cell responses, notably through infusions of activating cytokines, the adoptive transfer of activated or engineered T cells, or immune checkpoint inhibitors. ILCs have also emerged as an interesting target for immunotherapy, initially due to the anti-tumor activities of cytotoxic NK cells. However, the other helper-like ILCs can also infiltrate the tumor microenvironment, having either pro- or anti-tumor effects, depending on their phenotype and the type of cancer. Moreover, given the similarities between helper ILCs and T cells in terms of their cytokine profiles and the surface markers they express, immunotherapies targeting T cells may also target helper-like ILCs. We provide here an overview of the field, summarizing the evidence for a role of helper-like ILCs and ways of targeting these cells in solid tumors and hematological malignancies.

Targeting natural killer cells in solid tumors.

Natural killer (NK) cells are innate lymphoid cells endowed with cytolytic activity and a capacity to secrete cytokines and chemokines. Several lines of evidence suggest that NK cells play an important role in anti-tumor immunity. Some therapies against hematological malignacies make use of the immune properties of NK cells, such as their ability to kill residual leukemic blasts efficiently after conditioning during haploidentical hematopoietic stem cell transplantation. However, knowledge on NK cell infiltration and the status of NK cell responsiveness in solid tumors is limited so far. The pro-angiogenic role of the recently described NK cell-like type 1 innate lymphoid cells (ILC1s) and their phenotypic resemblance to NK cells are confounding factors that add a level of complexity, at least in mice. Here, we review the current knowledge on the presence and function of NK cells in solid tumors as well as the immunotherapeutic approaches designed to harness NK cell functions in these conditions, including those that aim to reinforce conventional anti-tumor therapies to increase the chances of successful treatment.

High-Dimensional Single-Cell Analysis Identifies Organ-Specific Signatures and Conserved NK Cell Subsets in Humans and Mice.

Natural killer (NK) cells are innate lymphoid cells (ILCs) involved in antimicrobial and antitumoral responses. Several NK cell subsets have been reported in humans and mice, but their heterogeneity across organs and species remains poorly characterized. We assessed the diversity of human and mouse NK cells by single-cell RNA sequencing on thousands of individual cells isolated from spleen and blood. Unbiased transcriptional clustering revealed two distinct signatures differentiating between splenic and blood NK cells. This analysis at single-cell resolution identified three subpopulations in mouse spleen and four in human spleen, and two subsets each in mouse and human blood. A comparison of transcriptomic profiles within and between species highlighted the similarity of the two major subsets, NK1 and NK2, across organs and species. This unbiased approach provides insight into the biology of NK cells and establishes a rationale for the translation of mouse studies to human physiology and disease.

Innate lymphoid cells: major players in inflammatory diseases.

Recent years have seen a marked increase in our understanding of innate lymphoid cells (ILCs). ILCs can be classified into different groups based on their similarity to T cell subsets in terms of their expression of key transcription factors and cytokine production. Various immunological functions of ILCs have been described, and increasing numbers of studies have implicated these cells in inflammatory disorders. Here, we detail the roles of ILCs in inflammatory diseases; we cover type 2 inflammatory diseases (such as asthma, chronic rhinosinusitis and atopic dermatitis), as well as inflammatory bowel diseases, psoriasis and other systemic or organ-specific inflammatory and autoimmune diseases. Future directions in the field are discussed, together with potential avenues of treatment.

[Innate lymphoid cells]. / Les cellules lymphoïdes innées.

Innate Lymphoid Cells (ILC) are tissue-resident effector lymphocytes that differ from the B and T lymphocytes subsets since they lack specific antigen receptors derived from gene rearrangements. They can be divided into two groups, cytotoxic ILC (NK cells) which are dependent on the transcription factors Eomes and T-bet and produce IFN-γ, and helper-like ILC (ILC1, ILC2, ILC3) which are dependent on T-bet, GATA-3 or RORγT and produce IFN-γ, IL-5/IL-13 or IL-17/IL-22 respectively. Although they were described recently, ILC are the subject of a large number of studies that characterize their role as one of the first effectors of the innate immune response as well as in the development of a wide number of inflammatory disorders.