Transforming Growth Factor-ß Signaling Guides the Differentiation of Innate Lymphoid Cells in Salivary Glands.

The signals guiding differentiation of innate lymphoid cells (ILCs) within tissues are not well understood. Salivary gland (SG) ILCs as well as liver and intestinal intraepithelial ILC1 have markers that denote tissue residency and transforming growth factor-ß (TGF-ß) imprinting. We deleted Tgfbr2 in cells expressing the ILC and NK marker NKp46 and found that SG ILCs were reduced in number. They lost distinct tissue markers, such as CD49a, and the effector molecules TRAIL and CD73. Expression of the transcription factor Eomes, which promotes NK cell differentiation, was elevated. Conversely, Eomes deletion in NKp46(+) cells enhanced TGF-ß-imprinting of SG ILCs. Thus, TGF-ß induces SG ILC differentiation by suppressing Eomes. TGF-ß acted through a JNK-dependent, Smad4-independent pathway. Transcriptome analysis demonstrated that SG ILCs had characteristic of both NK cells and ILC1. Finally, TGF-ß imprinting of SG ILCs was synchronized with SG development, highlighting the impact of tissue microenvironment on ILC development.

Atg5 Is Essential for the Development and Survival of Innate Lymphocytes.

Autophagy is an essential cellular survival mechanism that is required for adaptive lymphocyte development; however, its role in innate lymphoid cell (ILC) development remains unknown. Furthermore, the conditions that promote lymphocyte autophagy during homeostasis are poorly understood. Here, we demonstrate that Atg5, an essential component of the autophagy machinery, is required for the development of mature natural killer (NK) cells and group 1, 2, and 3 innate ILCs. Although inducible ablation of Atg5 was dispensable for the homeostasis of lymphocyte precursors and mature lymphocytes in lymphoreplete mice, we found that autophagy is induced in both adaptive and innate lymphocytes during homeostatic proliferation in lymphopenic hosts to promote their survival by limiting cell-intrinsic apoptosis. Induction of autophagy through metformin treatment following homeostatic proliferation increased lymphocyte numbers through an Atg5-dependent mechanism. These findings highlight the essential role for autophagy in ILC development and lymphocyte survival during lymphopenia.

Development and maturation of natural killer cells.

Natural killer (NK) cells are innate lymphocytes that are critical for host protection against pathogens and cancer due to their ability to rapidly release inflammatory cytokines and kill infected or transformed cells. In the 40 years since their initial discovery, much has been learned about how this important cellular lineage develops and functions. We now know that NK cells are the founding members of an expanded family of lymphocyte known as innate lymphoid cells (ILC). Furthermore, we have recently discovered that NK cells can possess features of adaptive immunity such as antigen specificity and long-lived memory responses. Here we will review our current understanding of the molecular mechanisms driving development of NK cells from the common lymphoid progenitor (CLP) to mature NK cells, and from activated effectors to long-lived memory NK cells.

Nfil3 is crucial for development of innate lymphoid cells and host protection against intestinal pathogens.

The bZIP transcription factor Nfil3 (also known as E4BP4) is required for the development of natural killer (NK) cells and type 1 innate lymphoid cells (ILC1s). We find that Nfil3 plays a critical role in the development of other mucosal tissue-associated innate lymphocytes. Type 3 ILCs (ILC3s), including lymphoid tissue inducer (LTi)-like cells, are severely diminished in both numbers and function in Nfil3-deficient mice. Using mixed bone marrow chimeric mice, we demonstrate that Nfil3 is critical for normal development of gut-associated ILC3s in a cell-intrinsic manner. Furthermore, Nfil3 deficiency severely compromises intestinal innate immune defense against acute bacterial infection with Citrobacter rodentium and Clostridium difficile. Nfil3 deficiency resulted in a loss of the recently identified ILC precursor, yet conditional ablation of Nfil3 in the NKp46(+) ILC3 subset did not perturb ILC3 numbers, suggesting that Nfil3 is required early during ILC3 development but not for lineage maintenance. Lastly, a marked defect in type 2 ILCs (ILC2s) was also observed in the lungs and visceral adipose tissue of Nfil3-deficient mice, revealing a general requirement for Nfil3 in the development of all ILC lineages.

Systemic 4-1BB activation induces a novel T cell phenotype driven by high expression of Eomesodermin.

4-1BB agonist antibody treatment induces a population of KLRG1(+) T cells that infiltrate melanoma tumors. We investigated the origin and function of these cells, as well as their place within established T cell paradigms. We find that these T cells, particularly the CD4 lineage, represent a novel phenotype characterized by enhanced, multipotent cytotoxicity. Distinct from described polarities, this T cell phenotype is driven by the T-box transcription factor Eomesodermin. Formation of this phenotype requires 4-1BB signaling on both T and antigen-presenting cells and the resulting production of the cytokines IL-27, IL-15, and IL-10. Furthermore, we find CD4(+) T cells bearing the signature features of this phenotype in the livers of mice infected with both bacterial and viral intracellular pathogens, suggesting a role for these cells in infectious immunity. These T cells constitute a novel phenotype that resolves multiple questions associated with 4-1BB activation, including how 4-1BB enhances tumor-specific cytotoxicity and how 4-1BB can promote tumor immunity while repressing autoimmunity.

MicroRNA-34a perturbs B lymphocyte development by repressing the forkhead box transcription factor Foxp1.

MicroRNAs (miRNAs) can influence lineage choice or affect critical developmental checkpoints during hematopoiesis. We examined the role of the p53-induced microRNA miR-34a in hematopoiesis by gain-of-function analysis in murine bone marrow. Constitutive expression of miR-34a led to a block in B cell development at the pro-B-cell-to-pre-B-cell transition, leading to a reduction in mature B cells. This block appeared to be mediated primarily by inhibited expression of the transcription factor Foxp1. Foxp1 was a direct target of miR-34a in a 3'-untranslated region (UTR)-dependent fashion. Knockdown of Foxp1 by siRNA recapitulated the B cell developmental phenotype induced by miR-34a, whereas cotransduction of Foxp1 lacking its 3' UTR with miR-34a rescued B cell maturation. Knockdown of miR-34a resulted in increased amounts of Foxp1 and mature B cells. These findings identify a role for miR-34a in connecting the p53 network with suppression of Foxp1, a known B cell oncogene.