Source of hematopoietic progenitor cells determines their capacity to generate innate lymphoid cells ex vivo.

BACKGROUND AIMS: The success of allogeneic hematopoietic cell transplantation (HCT) as therapy for hematologic conditions is negatively impacted by the occurrence of graft-versus-host disease (GVHD). Tissue damage, caused, for example, by chemotherapy and radiotherapy, is a key factor in GVHD pathogenesis. Innate lymphoid cells (ILCs) are important mediators of tissue repair and homeostasis. The presence of ILCs before, and enhanced ILC reconstitution after, allogeneic HCT is associated with a reduced risk to develop mucositis and GVHD. However, ILC reconstitution after allogeneic HCT is slow and often incomplete. A way to replenish the pool of ILC relies on the differentiation of hematopoietic progenitor cells (HPCs) into ILC. METHODS: We developed an ex vivo stromal cell-containing culture system to study the capacity of HPCs to differentiate into all mature helper ILC subsets. RESULTS: ILC development depended on the source of HPCs. ILCs developed at high frequencies from umbilical cord blood- and fetal liver-derived HPC and at low frequencies when HPCs were obtained from allogeneic or autologous adult HCT grafts or healthy adult bone marrow. Although all helper ILC subsets could be generated from adult HPC sources, development of tissue protective ILC2 and NKp44+ ILC3 was notoriously difficult. CONCLUSIONS: Our data suggest that slow ILC recovery after allogeneic HCT may be related to an intrinsic incapability of adult HPC to develop into ILC.

Generation of human ILC3 from allogeneic and autologous CD34+ hematopoietic progenitors toward adoptive transfer.

Type 3 innate lymphoid cells (ILC3) are important in tissue homeostasis. In the gut, ILC3 repair damaged epithelium and suppress inflammation. In allogeneic hematopoietic cell transplantation (HCT), ILC3 protect against graft-versus-host disease (GvHD), most likely by restoring tissue damage and preventing inflammation. We hypothesize that supplementing HCT grafts with interleukin-22 (IL-22)-producing ILC3 may prevent acute GvHD. We therefore explored ex vivo generation of human IL-22-producing ILC3 from hematopoietic stem and progenitor cells (HSPC) obtained from adult, neonatal and fetal sources. We established a stroma-free system culturing human cord blood-derived CD34+ HSPC with successive cytokine mixes for 5 weeks. We analyzed the presence of phenotypically defined ILC, their viability, proliferation and IL-22 production (after stimulation) by flow cytometry and enzyme-linked immunosorbent assay (ELISA). We found that the addition of recombinant human IL-15 and the enhancer of zeste homolog 1/2 inhibitor UNC1999 promoted ILC3 generation. Similar results were demonstrated when UNC1999 was added to CD34+ HSPC derived from healthy adult granulocyte colony-stimulating factor mobilized peripheral blood and bone marrow, but not fetal liver. UNC1999 did not negatively impact IL-22 production in any of the HSPC sources. Finally, we observed that autologous HSPC mobilized from the blood of adults with hematological malignancies also developed into ILC3, albeit with a significantly lower capacity. Together, we developed a stroma-free protocol to generate large quantities of IL-22-producing ILC3 from healthy adult human HSPC that can be applied for adoptive transfer to prevent GvHD after allogeneic HCT.

HIV-1 Infection Results in Sphingosine-1-Phosphate Receptor 1 Dysregulation in the Human Thymus.

Regeneration of functional naïve T lymphocytes following the onset of human immunodeficiency virus (HIV) infection remains a crucial issue for people living with HIV (PLWH), even when adhering to antiretroviral therapy (ART). Thus far, reports on the impact of HIV-1 infection on the entry of thymic precursors and the egress of functional naïve T lymphocytes to and from the thymus are limited. We examined the impact of HIV-1 on Sphingosine-1-phosphate (S1P) signaling, which governs the egress of functional naïve thymocytes from the thymus to the periphery. Using in vitro experiments with primary human thymocytes and in vivo and ex vivo studies with humanized mice, we show that HIV-1 infection results in upregulation of the expression of S1P receptor 1 (S1PR1) in the human thymus. Intriguingly, this upregulation occurs during intrathymic infection (direct infection of the human thymic implant) as well as systemic infection in humanized mice. Moreover, considering the dysregulation of pro- and anti-inflammatory cytokines in infected thymi, the increased expression of S1PR1 in response to in vitro exposure to Interferon-Beta (IFN-ß) and Tumor Necrosis Factor-Alpha (TNF-α) indicates that cytokine dysregulation following HIV infection may contribute to upregulation of S1PR1. Finally, an increased presence of CD3hiCD69- (fully mature) as well as CD3hiCD69+ (less mature) T cells in the spleen during HIV infection in humanized mice, combined with earlier expression of S1PR1 during thymocyte development, suggests that upregulation of S1PR1 may translate to increased or accelerated egress from the thymus. The egress of thymocytes that are not functionally mature from the thymus to peripheral blood and lymphoid organs may have implications for the immune function of PLWH.

Allogeneic hematopoietic cell transplantation, the microbiome, and graft-versus-host disease.

Many patients with hematological malignancies, such as acute myeloid leukemia, receive an allogeneic hematopoietic cell transplantation (HCT) to cure their underlying condition. Allogeneic HCT recipients are exposed to various elements during the pre-, peri- and post-transplant period that can disrupt intestinal microbiota, including chemo- and radiotherapy, antibiotics, and dietary changes. The dysbiotic post-HCT microbiome is characterized by low fecal microbial diversity, loss of anaerobic commensals, and intestinal domination, particularly by Enterococcus species, and is associated with poor transplant outcomes. Graft-versus-host disease (GvHD) is a frequent complication of allogeneic HCT caused by immunologic disparity between donor and host cells and results in tissue damage and inflammation. Microbiota injury is particularly pronounced in allogeneic HCT recipients who go on to develop GvHD. At present, manipulation of the microbiome for example, via dietary interventions, antibiotic stewardship, prebiotics, probiotics, or fecal microbiota transplantation, is widely being explored to prevent or treat gastrointestinal GvHD. This review discusses current insights into the role of the microbiome in GvHD pathogenesis and summarizes interventions to prevent and treat microbiota injury.

Profiling the Fungal Microbiome after Fecal Microbiota Transplantation for Graft-versus-Host Disease: Insights from a Phase 1 Interventional Study.

Disruption of the intestinal bacterial microbiota is frequently observed in the context of allogeneic hematopoietic cell transplantation (HCT) and is particularly pronounced in patients who develop graft-versus-host disease (GVHD). Donor fecal microbiota transplantation (FMT) restores gut microbial diversity and reduces GVHD in HCT recipients. The composition of the intestinal fungal community in patients with GVHD, and whether fungal taxa are transferred during FMT are currently unknown. We performed a secondary analysis of our clinical trial of FMT in patients with steroid-refractory GVHD with a focus on the mycobiota. We characterized the fecal mycobiota of 17 patients and healthy FMT donors using internal transcribed spacer amplicon sequencing. The donor who provided the majority of FMT material in our study represents an n-of-one study of the intestinal flora over time. In this donor, mycobiota composition fluctuated over time while the bacterial microbiota remained stable over 16 months. Fungal DNA was detected more frequently in baseline stool samples from patients with steroid-refractory GVHD than in patients with steroid-dependent GVHD. We could detect fungal taxa in the majority of samples but did not see evidence of mycobiota transfer from donor to recipient. Our study demonstrates the feasibility of profiling the mycobiota alongside the more traditional bacterial microbiota, establishes the methodology, and provides a first insight into the mycobiota composition of patients with GVHD.

Presence of innate lymphoid cells in allogeneic hematopoietic grafts correlates with reduced graft-versus-host disease.

BACKGROUND: Allogeneic hematopoietic cell transplantation (HCT) can be devastating when graft-versus-host disease (GvHD) develops. GvHD is characterized by mucosal inflammation due to breaching of epithelial barriers. Innate lymphoid cells (ILCs) are immune modulatory cells that are important in the maintenance of epithelial barriers, via their production of interleukin (IL)-22 and their T cell suppressive properties. After chemo- and radiotherapy, ILCs are depleted, and recovery after remission-induction therapy and after allogeneic HCT is slow and incomplete in a significant number of patients, which is associated with an increased risk to develop acute GvHD. OBJECTIVE: To investigate whether the presence of mature ILCs within G-CSF-mobilized HCT grafts is correlated with the development of acute GvHD after allogeneic HCT. STUDY DESIGN: We analyzed ILCs in a cohort of 36 patients who received allogeneic HCT for a hematologic malignancy, by flow-cytometric immune-phenotyping of prospectively collected, cryopreserved peripheral blood mononuclear cells (PBMCs) and donor-derived HCT grafts collected for the same patients. Biased analysis, with ILCs defined as CD3-lineage-CD45+CD127+CD161+ lymphocytes, was performed using FlowJo version 10 software. Unbiased analysis was done using FlowSOM, which uses a self-organizing map (SOM) with a minimal spanning tree (MST) to define and visualize different clusters present in the samples. RESULTS: Remission-induction therapy significantly depleted ILCs from the blood, and patients who had a relatively low percentage of ILCs before allogeneic HCT were significantly more prone to develop acute GvHD, confirming previous findings in a separate cohort. Allogeneic HCT grafts, which were all obtained from the blood of G-CSF-mobilized healthy donors, contained ILCs at a frequency very similar to the peripheral blood of healthy individuals. The ILC subset composition was also comparable to that of the blood of healthy individuals, with the exception of NKp44+ ILC3s, which were significantly more abundant in HCT grafts. The relative ILC content of the graft tended to correlate with ILC reconstitution after allogeneic HCT, suggesting that peripheral expansion of transplanted mature ILCs may contribute to early ILC reconstitution after allogeneic HCT. Patients who received a relatively ILC-poor HCT graft had a significantly increased risk to develop acute GvHD, compared with patients who received relatively ILC-rich allogeneic HCT grafts. Unbiased phenotypic analysis with the FlowSOM algorithm confirmed that allogeneic HCT grafts of patients who developed acute GvHD contained a lower frequency of ILCs that clustered in NKp44+ ILC3 signature groups. CONCLUSION: The presence of ILCs in allogeneic HCT grafts is associated with a reduced risk to develop acute GvHD. These data suggest that enhancement of ILC reconstitution of ILC3s in particular, for example via adoptive transfer of ILCs, may prevent acute GvHD and has the potential to improve outcome of allogeneic HCT recipients.

Single-Cell Transcriptomics Reveals Discrete Steps in Regulatory T Cell Development in the Human Thymus.

CD4+CD25+FOXP3+ regulatory T (Treg) cells control immunological tolerance. Treg cells are generated in the thymus (tTreg) or in the periphery. Their superior lineage fidelity makes tTregs the preferred cell type for adoptive cell therapy (ACT). How human tTreg cells develop is incompletely understood. By combining single-cell transcriptomics and flow cytometry, we in this study delineated three major Treg developmental stages in the human thymus. At the first stage, which we propose to name pre-Treg I, cells still express lineage-inappropriate genes and exhibit signs of TCR signaling, presumably reflecting recognition of self-antigen. The subsequent pre-Treg II stage is marked by the sharp appearance of transcription factor FOXO1 and features induction of KLF2 and CCR7, in apparent preparation for thymic exit. The pre-Treg II stage can further be refined based on the sequential acquisition of surface markers CD31 and GPA33. The expression of CD45RA, finally, completes the phenotype also found on mature recent thymic emigrant Treg cells. Remarkably, the thymus contains a substantial fraction of recirculating mature effector Treg cells, distinguishable by expression of inflammatory chemokine receptors and absence of CCR7. The developmental origin of these cells is unclear and warrants caution when using thymic tissue as a source of stable cells for ACT. We show that cells in the major developmental stages can be distinguished using the surface markers CD1a, CD27, CCR7, and CD39, allowing for their viable isolation. These insights help identify fully mature tTreg cells for ACT and can serve as a basis for further mechanistic studies into tTreg development.

Early Effects of HTLV-1 Infection on the Activation, Exhaustion, and Differentiation of T-Cells in Humanized NSG Mice.

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive malignancy of CD4+ T-cells associated with HTLV-1 infection. In this study, we used the model of immunodeficient NSG mice reconstituted with a functional human immune system (HIS) to investigate early events in HTLV-1 pathogenesis. Upon infection, human T-cells rapidly increased in the blood and lymphoid tissues, particularly CD4+CD25+ T-cells. Proliferation of CD4+ T-cells in the spleen and mesenteric lymph nodes (MLN) correlated with HTLV-1 proviral load and CD25 expression. In addition, splenomegaly, a common feature of ATLL in humans, was also observed. CD4+ and CD8+ T-cells predominantly displayed an effector memory phenotype (CD45RA-CCR7-) and expressed CXCR3 and CCR5 chemokine receptors, suggesting the polarization into a Th1 phenotype. Activated CD8+ T-cells expressed granzyme B and perforin; however, the interferon-γ response by these cells was limited, possibly due to elevated PD-1 expression and increased frequency of CD4+FoxP3+ regulatory T-cells in MLN. Thus, HTLV-1-infected HIS-NSG mice reproduced several characteristics of infection in humans, and it may be helpful to investigate ATLL-related events and to perform preclinical studies. Moreover, aspects of chronic infection were already present at early stages in this experimental model. Collectively, we suggest that HTLV-1 infection modulates host immune responses to favor viral persistence.

Endothelium-derived stromal cells contribute to hematopoietic bone marrow niche formation.

Bone marrow stromal cells (BMSCs) play pivotal roles in tissue maintenance and regeneration. Their origins, however, remain incompletely understood. Here we identify rare LNGFR+ cells in human fetal and regenerative bone marrow that co-express endothelial and stromal markers. This endothelial subpopulation displays transcriptional reprogramming consistent with endothelial-to-mesenchymal transition (EndoMT) and can generate multipotent stromal cells that reconstitute the bone marrow (BM) niche upon transplantation. Single-cell transcriptomics and lineage tracing in mice confirm robust and sustained contributions of EndoMT to bone precursor and hematopoietic niche pools. Interleukin-33 (IL-33) is overexpressed in subsets of EndoMT cells and drives this conversion process through ST2 receptor signaling. These data reveal generation of tissue-forming BMSCs from mouse and human endothelial cells and may be instructive for approaches to human tissue regeneration.

Donor fecal microbiota transplantation ameliorates intestinal graft-versus-host disease in allogeneic hematopoietic cell transplant recipients.

Disruption of the intestinal microbiota occurs frequently in allogeneic hematopoietic cell transplantation (allo-HCT) recipients and predisposes them to development of graft-versus-host disease (GvHD). In a prospective, single-center, single-arm study, we investigated the effect of donor fecal microbiota transplantation (FMT) on symptoms of steroid-refractory or steroid-dependent, acute or late-onset acute intestinal GvHD in 15 individuals who had undergone allo-HCT. Study participants received a fecal suspension from an unrelated healthy donor via nasoduodenal infusion. Donor FMT was well tolerated, and infection-related adverse events did not seem to be related to the FMT procedure. In 10 of 15 study participants, a complete clinical response was observed within 1 month after FMT, without additional interventions to alleviate GvHD symptoms. This response was accompanied by an increase in gut microbial α-diversity, a partial engraftment of donor bacterial species, and increased abundance of butyrate-producing bacteria, including Clostridiales and Blautia species. In 6 of the 10 responding donor FMT recipients, immunosuppressant drug therapy was successfully tapered. Durable remission of steroid-refractory or steroid-dependent GvHD after donor FMT was associated with improved survival at 24 weeks after donor FMT. This study highlights the potential of donor FMT as a treatment for steroid-refractory or steroid-dependent GvHD, but larger clinical trials are needed to confirm the safety and efficacy of this procedure.

Innate lymphoid cells in treatment-induced gastrointestinal pathogenesis.

PURPOSE OF REVIEW: Tissue injury often occurs as collateral damage after chemotherapy and radiotherapy and is associated with significant comorbidity and mortality. The arsenal of options to prevent tissue injury other than dose reduction is limited, and treatment is mostly aimed at symptom relief and prevention of complications, such as bacterial translocation and malnourishment. Novel approaches directed at prevention and early repair of damaged tissues are highly anticipated. RECENT FINDINGS: Innate lymphoid cells (ILC) are important in tissue homeostasis and wound healing. Most knowledge of ILC is based on studies in mice, and the contribution of ILC to repair therapy-induced tissue damage in humans is relatively understudied. A picture is nevertheless emerging, suggesting that ILC have several means to maintain tissue homeostasis. Subsets of ILC produce, for example, interleukin (IL)-22 or amphiregulin (AREG) that induce epithelial tissue repair and the release of microbiome modulating proteins. In addition, ILC have immune-regulatory capacities given that adoptive transfer of ILC in a mouse model of graft versus host disease (GvHD) attenuated tissue inflammation. SUMMARY: ILC are important in tissue maintenance and damage repair and as such have the potential to be developed as (adoptive) therapy to prevent and repair therapy-induced tissue damage.

Human ectoenzyme-expressing ILC3: immunosuppressive innate cells that are depleted in graft-versus-host disease.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is often associated with chemotherapy- and radiotherapy-induced host tissue damage, leading to graft-versus-host disease (GVHD). Innate lymphoid cells (ILC) have an essential role in tissue homeostasis and tissue repair via their production of interleukin (IL)-22, which acts on intestinal stem cells. The tissue healing capacities of ILC via IL-22 in the context of allo-HSCT and GVHD has previously been demonstrated in a mouse model for acute GVHD. We investigated potential other ways of ILC-mediated tissue protection against GVHD. Tissue injury leads to the release of danger-associated molecular patterns (DAMPs). DAMPs interact with purinergic receptors and ectoenzymes on immune cells and induce pleiotropic effects, including activation of proinflammatory antigen-presenting cells and immunosuppressive effects via the generation of adenosine. Here, we report a novel subset of human ILC3 that coexpress the ectoenzymes CD39 and CD73 (ecto+ ILC3). Ecto+ ILC3 express RORγt and were present in the oral-gastrointestinal tract and bone marrow. ILC3 ectoenzyme expression is modulated by the proinflammatory cytokine IL-1ß. Extracellular adenosine triphosphate (eATP) stimulated ecto+ ILC3 to produce IL-22 and adenosine. Activated ecto+ ILC3 suppressed autologous T-cell proliferation in coculture experiments via the production of adenosine. In allo-HSCT recipients, intestinal GVHD was associated with reduced proportions of ecto+ ILC3 and decreased levels of adenosine and its metabolite inosine. Taken together, ecto+ ILC3 have immunosuppressive properties, but in patients with GVHD, ecto+ ILC3 are depleted. A lack of ecto+ ILC3 and subsequent reduced capacity to neutralize DAMPs may contribute to the development of GVHD.

ILCs in hematologic malignancies: Tumor cell killers and tissue healers.

Innate lymphoid cells (ILCs) have attracted considerable attention in the past years. As modulators of epithelial barrier immunology and homeostasis they play important roles in (auto)immunity and inflammation. Here we review the role of ILCs in hematologic malignancies, where ILCs act as efficient killer cells and as tissue healers, in the context of chemotherapy, radiotherapy and after allogeneic hematopoietic stem cell transplantation (HSCT).

Mesenchymal Stromal Cells Stimulate the Proliferation and IL-22 Production of Group 3 Innate Lymphoid Cells.

Infusion of mesenchymal stromal cells (MSCs) is a promising and increasingly applied therapy for patients who suffer from a variety of inflammatory diseases, including graft-versus-host disease (GvHD), a common and life-threatening complication after allogeneic hematopoietic stem cell transplantation. The therapeutic effect of MSCs is mainly ascribed to their ability to suppress T cells and to support tissue repair. However, clinical response rates in patients with GvHD are limited to 50%, and the determinants for MSC responsiveness are unknown. We recently reported that high frequencies of activated group 3 innate lymphoid cells (ILC3s) before and after allogeneic hematopoietic stem cell transplantation were associated with a lower risk of GvHD. This may be related to IL-22 production by ILC3s, a cytokine important for intestinal epithelial cell homeostasis. In this study, we investigated whether ILC3s may contribute to the therapeutic effect of MSCs by studying the interaction between MSCs and ILC3s in vitro. ILC3s isolated from human tonsils were cocultured with human bone marrow-derived MSCs for 5 d in the presence of IL-2. Coculture with MSCs enhanced the proliferation and IL-22 production of ILC3s. Reciprocally, ILC3s promoted ICAM-1 and VCAM-1 expression on MSCs. For both directions, the activation was mainly mediated by cell-cell contact and by MSC-derived IL-7 and likely by aryl hydrocarbon receptor ligands. Thus, in addition to inhibiting the proliferation of alloreactive T cells, MSCs also promote the expansion and IL-22 production of ILC3s, which may contribute to healthy homeostasis and wound repair in the treatment of various inflammatory conditions in the intestine, including GvHD.

Human CD5+ Innate Lymphoid Cells Are Functionally Immature and Their Development from CD34+ Progenitor Cells Is Regulated by Id2.

Innate lymphoid cells (ILCs) have emerged as a key cell type involved in surveillance and maintenance of mucosal tissues. Mouse ILCs rely on the transcriptional regulator Inhibitor of DNA-binding protein 2 (Id2) for their development. Here, we show that Id2 also drives development of human ILC because forced expression of Id2 in human thymic progenitors blocked T cell commitment, upregulated CD161 and promyelocytic leukemia zinc finger (PLZF), and maintained CD127 expression, markers that are characteristic for human ILCs. Surprisingly CD5 was also expressed on these in vitro generated ILCs. This was not an in vitro artifact because CD5 was also found on ex vivo isolated ILCs from thymus and from umbilical cord blood. CD5 was also expressed on small proportions of ILC2 and ILC3. CD5+ ILCs were functionally immature, but could further differentiate into mature CD5- cytokine-secreting ILCs. Our data show that Id2 governs human ILC development from thymic progenitor cells toward immature CD5+ ILCs.

CD31, a Valuable Marker to Identify Early and Late Stages of T Cell Differentiation in the Human Thymus.

Although CD31 expression on human thymocytes has been reported, a detailed analysis of CD31 expression at various stages of T cell development in the human thymus is missing. In this study, we provide a global picture of the evolution of CD31 expression from the CD34+ hematopoietic precursor to the CD45RA+ mature CD4+ and CD8+ single-positive (SP) T cells. Using nine-color flow cytometry, we show that CD31 is highly expressed on CD34+ progenitors and stays high until the early double-positive stage (CD3-CD4+CD8α+ß-). After ß-selection, CD31 expression levels become low to undetectable. CD31 expression then increases and peaks on CD3highCD4+CD8+ double-positive thymocytes. However, following positive selection, CD31 expression differs dramatically between CD4+ and CD8+ lineages: homogeneously high on CD8 SP but lower or negative on CD4 SP cells, including a subset of CD45RA+CD31- mature CD4+ thymocytes. CD31 expression on TCRγδ thymocytes is very similar to that of CD4 SP cells. Remarkably, there is a substantial subset of semimature (CD45RA-) CD4 SP thymocytes that lack CD31 expression. Moreover, FOXP3+ and ICOS+ cells are overrepresented in this CD31- subpopulation. Despite this CD31-CD45RA- subpopulation, most egress-capable mature CD45RA+ CD4 SP thymocytes express CD31. The variations in CD31 expression appear to coincide with three major selection processes occurring during thymopoiesis: ß-selection, positive selection, and negative selection. Considering the ability of CD31 to modulate the TCR's activation threshold via the recruitment of tyrosine phosphatases, our results suggest a significant role for CD31 during T cell development.

Neuropilin-1 Is Expressed on Lymphoid Tissue Residing LTi-like Group 3 Innate Lymphoid Cells and Associated with Ectopic Lymphoid Aggregates.

Here, we characterize a subset of ILC3s that express Neuropilin1 (NRP1) and are present in lymphoid tissues, but not in the peripheral blood or skin. NRP1+ group 3 innate lymphoid cells (ILC3s) display in vitro lymphoid tissue inducer (LTi) activity. In agreement with this, NRP1+ ILC3s are mainly located in proximity to high endothelial venules (HEVs) and express cell surface molecules involved in lymphocyte migration in secondary lymphoid tissues via HEVs. NRP1 was also expressed on mouse fetal LTi cells, indicating that NRP1 is a conserved marker for LTi cells. Human NRP1+ ILC3s are primed cells because they express CD45RO and produce higher amounts of cytokines than NRP1- cells, which express CD45RA. The NRP1 ligand vascular endothelial growth factor A (VEGF-A) served as a chemotactic factor for NRP1+ ILC3s. NRP1+ ILC3s are present in lung tissues from smokers and patients with chronic obstructive pulmonary disease, suggesting a role in angiogenesis and/or the initiation of ectopic pulmonary lymphoid aggregates.

Interleukin-12 and -23 Control Plasticity of CD127(+) Group 1 and Group 3 Innate Lymphoid Cells in the Intestinal Lamina Propria.

Human group 1 ILCs consist of at least three phenotypically distinct subsets, including NK cells, CD127(+) ILC1, and intraepithelial CD103(+) ILC1. In inflamed intestinal tissues from Crohn's disease patients, numbers of CD127(+) ILC1 increased at the cost of ILC3. Here we found that differentiation of ILC3 to CD127(+) ILC1 is reversible in vitro and in vivo. CD127(+) ILC1 differentiated to ILC3 in the presence of interleukin-2 (IL-2), IL-23, and IL-1ß dependent on the transcription factor RORγt, and this process was enhanced in the presence of retinoic acid. Furthermore, we observed in resection specimen from Crohn's disease patients a higher proportion of CD14(+) dendritic cells (DC), which in vitro promoted polarization from ILC3 to CD127(+) ILC1. In contrast, CD14(-) DCs promoted differentiation from CD127(+) ILC1 toward ILC3. These observations suggest that environmental cues determine the composition, function, and phenotype of CD127(+) ILC1 and ILC3 in the gut.

The plasmacytoid dendritic cell as the Swiss army knife of the immune system: molecular regulation of its multifaceted functions.

Plasmacytoid dendritic cells (pDC) have been regarded as the "professional type I IFN-producing cells" of the immune system following viral recognition that relies on the expression of TLR7 and TLR9. Furthermore, pDC link the innate and adaptive immune systems via cytokine production and Ag presentation. More recently, their ability to induce tolerance and cytotoxicity has been added to their "immune skills." Such a broad range of actions, resembling the diverse functional features of a Swiss army knife, requires strong and prompt molecular regulation to prevent detrimental effects, including autoimmune pathogenesis or tumor escape. Over the last decades, we and other investigators have started to unravel some aspects of the signaling pathways that regulate the various functions of human pDC. In this article, we review aspects of the molecular regulatory mechanisms to control pDC function in light of their multifaceted roles during immunity, autoimmunity, and cancer.

Activated innate lymphoid cells are associated with a reduced susceptibility to graft-versus-host disease.

Allogeneic hematopoietic stem cell transplantation (HSCT) is widely used to treat hematopoietic cell disorders but is often complicated by graft-versus-host disease (GVHD), which causes severe epithelial damage. Here we have investigated longitudinally the effects of induction chemotherapy, conditioning radiochemotherapy, and allogeneic HSCT on composition, phenotype, and recovery of circulating innate lymphoid cells (ILCs) in 51 acute leukemia patients. We found that reconstitution of ILC1, ILC2, and NCR(-)ILC3 was slow compared with that of neutrophils and monocytes. NCR(+) ILC3 cells, which are not present in the circulation of healthy persons, appeared both after induction chemotherapy and after allogeneic HSCT. Circulating patient ILCs before transplantation, as well as donor ILCs after transplantation, expressed activation (CD69), proliferation (Ki-67), and tissue homing markers for gut (α4ß7, CCR6) and skin (CCR10 and CLA). The proportion of ILCs expressing these markers was associated with a decreased susceptibility to therapy-induced mucositis and acute GVHD. Taken together, these data suggest that ILC recovery and treatment-related tissue damage are interrelated and affect the development of GVHD.