Embryonic type 3 innate lymphoid cells sense maternal dietary cholesterol to control local Peyer's patch development

Lymphoid tissue inducer (LTi) cells develop during intrauterine life and rely on developmental programs to initiate the organogenesis of secondary lymphoid organs (SLOs). This evolutionary conserved process endows the fetus with the ability to orchestrate the immune response after birth and to react to the triggers present in the environment. While it is established that LTi function can be shaped by maternal-derived cues and is critical to prepare the neonate with a functional scaffold to mount immune response, the cellular mechanisms that control anatomically distinct SLO organogenesis remain unclear. We discovered that LTi cells forming Peyer's patches, gut-specific SLOs, require the coordinated action of two migratory G protein coupled receptors (GPCR) GPR183 and CCR6. These two GPCRs are uniformly expressed on LTi cells across SLOs, but their deficiency specifically impacts Peyer's patch formation, even when restricted to fetal window. The unique CCR6 ligand is CCL20, while the ligand for GPR183 is the cholesterol metabolite 7α,25-Dihydroxycholesterol (7α,25-HC), whose production is controlled by the enzyme cholesterol 25-hydroxylase (CH25H). We identified a fetal stromal cell subset that expresses CH25H and attracts LTi cells in the nascent Peyer's patch anlagen. GPR183 ligand concentration can be modulated by the cholesterol content in the maternal diet and impacts LTi cell maturation in vitro and in vivo, highlighting a link between maternal nutrients and intestinal SLO organogenesis. Our findings revealed that in the fetal intestine, cholesterol metabolite sensing by GPR183 in LTi cells for Peyer's patch formation is dominant in the duodenum, the site of cholesterol absorption in the adult. This anatomic requirement suggests that embryonic, long-lived non-hematopoietic cells might exploit adult metabolic functions to ensure highly specialized SLO development in utero.

An epithelial cell-derived metabolite tunes immunoglobulin A secretion by gut-resident plasma cells

Immunoglobulin A (IgA) secretion by plasma cells, terminally differentiated B cells residing in the intestinal lamina propria, assures microbiome homeostasis and protects the host against enteric infections. Exposure to diet-derived and commensal-derived signals provides immune cells with organizing cues that instruct their effector function and dynamically shape intestinal immune responses at the mucosal barrier. Recent data have described metabolic and microbial inputs controlling T cell and innate lymphoid cell activation in the gut; however, whether IgA-secreting lamina propria plasma cells are tuned by local stimuli is completely unknown. Although antibody secretion is considered to be imprinted during B cell differentiation and therefore largely unaffected by environmental changes, a rapid modulation of IgA levels in response to intestinal fluctuations might be beneficial to the host. In the present study, we showed that dietary cholesterol absorption and commensal recognition by duodenal intestinal epithelial cells lead to the production of oxysterols, evolutionarily conserved lipids with immunomodulatory functions. Using conditional cholesterol 25-hydroxylase deleter mouse line we demonstrated that 7α,25-dihydroxycholesterol from epithelial cells is critical to restrain IgA secretion against commensal- and pathogen-derived antigens in the gut. Intestinal plasma cells sense oxysterols via the chemoattractant receptor GPR183 and couple their tissue positioning with IgA secretion. Our findings revealed a new mechanism linking dietary cholesterol and humoral immune responses centered around plasma cell localization for efficient mucosal protection.

Epithelial-derived oxysterol production tunes intestinal IgA secretion against commensals and enteric pathogen in tissue

Immunoglobulin A (IgA) secretion by plasma cells (PCs), terminally differentiated B cells residing in the intestinal lamina propria, assures microbiome homeostasis and protects the host against enteric infections. However, whether exposure to diet-derived and commensal-derived signals instruct tissue resident PCs effector function and dynamically shape IgA immune responses at the mucosal barrier remain largely uninvestigated. Here, we demonstrated that intestinal epithelial cells (IECs) integrate luminal input to produce 7α,25-dihydroxycholesterol (7α,25-HC), a cholesterol metabolite (oxysterol) with immunomodulatory functions. In IECs, both cholesterol uptake via NPC1L1 and commensal recognition via MyD88 controlled oxysterol production. Mice lacking the oxysterol enzyme CH25H specifically in IECs abolished 7α,25-HC production and allowed to study oxysterol generation and activity in the small intestine. Inability of IECs to generate 7α,25-HC enhanced IgA secretion by PCs in the gut, suggesting that oxysterol negatively regulate humoral response at the mucosal barriers. Mechanistically, we showed that intestinal PCs sensed 7α,25-HC via the chemoattractant receptor GPR183 to position in the lamina propria tissue. This IEC-PC axis was rapidly modulated by cholesterol dietary content and tuned Salmonella-specific IgA response.

Our finding revealed a new mechanism linking dietary cholesterol and humoral immune responses centered around PC localization for efficient mucosal protection.

Supported by grants from Kenneth Rainin Foundation, Innovator Award, Charles H. Hood Foundation Child Health Research Awards Program, The Leukemia and Lymphoma Society New Idea Award and the Multiple Myeloma Research Fellowship, NIH ( AI40098 ) and The American Association of Immunologists Careers in Immunology Fellowship Program. 

The cholesterol metabolite 25-hydroxycholesterol restrains the transcriptional regulator SREBP2 and limits intestinal IgA plasma cell differentiation

Diets high in cholesterol alter intestinal immunity. Here, we examined how the cholesterol metabolite 25-hydroxycholesterol (25-HC) impacts the intestinal B cell response. Mice lacking cholesterol 25-hydroxylase (CH25H), the enzyme generating 25-HC, had higher frequencies of immunoglobulin A (IgA)-secreting antigen-specific B cells upon immunization or infection. 25-HC did not affect class-switch recombination but rather restrained plasma cell (PC) differentiation. 25-HC was produced by follicular dendritic cells and increased in response to dietary cholesterol. Mechanistically, 25-HC restricted activation of the sterol-sensing transcription factor SREBP2, thereby regulating B cell cholesterol biosynthesis. Ectopic expression of SREBP2 in germinal center B cells induced rapid PC differentiation, whereas SREBP2 deficiency reduced PC output in vitro and in vivo. High-cholesterol diet impaired, whereas Ch25h deficiency enhanced, the IgA response against Salmonella and the resulting protection from systemic bacterial dissemination. Thus, a 25-HC-SREBP2 axis shapes the humoral response at the intestinal barrier, providing insight into the effect of high dietary cholesterol in intestinal immunity.

In-silico based screening system to develop allosteric modulators of Bruton’s tyrosine kinase

Ibrutinib is a covalent inhibitor that binds to the Bruton’s tyrosine kinase (BTK) ATP-dependent active site and it is currently used for treating a variety of B cell tumors. A high rate of drug resistance develops in Ibrutinib-treated patients through mutations at the BTK kinase domain, resulting in more aggressive diseases. Thus, there is significant interest in identifying modulators that inhibit BTK in an active site-independent manner, specifically via allosteric modulation. We used an in-silico system to identify small molecules that bind outside of the BTK active site. Candidate compounds were then tested for direct binding to full length BTK protein using Saturated Transfer Difference Nuclear Magnetic Resonance (STD-NMR) and were subsequently used in primary mouse B cell-based assays to determine their functional relevance. Ex vivo B cells were triggered via the BCR in the presence of compounds and signaling events downstream of the BCR, including Nur77 upregulation and calcium flux, were measured by flow cytometry. A series of candidate allosteric BTK inhibitors were then confirmed to retain suppressive activity in an ABC-DLBC lymphoma line that carries the Ibrutinib resistant mutation. Additionally, primary human CLL, but not healthy B cells, were susceptible to candidate inhibitor-mediated death. These results indicate that a screening approach integrating in silico docking, NMR measurements, and cellular assays with primary B cells can be used to identify BTK inhibitors that act outside of the kinase domain. Allosteric BTK inhibitors will broaden the range of treatment options for B cell cancers, possibly overcoming or preventing the Ibrutinib-induced resistance when used as a combination therapy.

Targeting of ITK-SYK fusion oncogene through in-silico generated and biologically validated ITK-PH domain modulators

A subset of human Peripheral T cell Lymphomas, Not Otherwise Specified (PTCL-NOS), harbors a chromosomal translocation of interleukin-2 (IL-2) inducible T cell kinase (ITK) and spleen tyrosine kinase (SYK), giving rise to the composite ITK-SYK protein. ITK, a TEC family member kinase, plays an essential role in TCR and CD28 signaling. SYK signaling pathway is more broadly linked to activation of diverse lymphoid and myeloid cell types. ITK-SYK fusion protein consists of the PH domain of ITK and the SYK kinase domain allowing localization to the signalosome complex at the membrane via the PH domain and constitutive activity in T cells. Given the ubiquitous activity of SYK, it is predicted that targeting the ITK-PH domain of the fusion protein with small molecules can be a precise and less toxic approach to suppress ITK-SYK+PTCL-NOS in vivo. To this end, we performed a computational screen of small molecule libraries to identify candidate ITK-PH domain interacting compounds. A thermal shift assay was used to verify the specificity of binding of candidates to the target protein domain. Cellular assays tested small molecule activity in human and mouse T cells constitutively expressing the ITK-SYK fusion protein. We showed that the first-pass small molecule candidates specific to ITK-PH domain inhibit cytokine production driven by ITK-SYK fusion protein in human and mouse T cells. Our results demonstrate the efficiency of the virtual screening to identify drug candidates with biological activity in lymphocytes. Development of drugs that target ITK-PH domain is a rationale strategy towards first-in-class therapeutics for this subset of PTCL-NOS with very poor prognoses.