Single-cell RNA sequencing identifies precise tolerogenic cellular and molecular pathways induced by depigmented-polymerized grass pollen allergen extract.

BACKGROUND: Immunologic mechanism of action of allergoids remains poorly understood. Previous models of allergenicity and immunogenicity have yielded suboptimal knowledge of these immunotherapeutic vaccine products. Novel single-cell RNA sequencing technology offers a bridge to this gap in knowledge. OBJECTIVE: We sought to identify the underpinning tolerogenic molecular and cellular mechanisms of depigmented-polymerized Phleum pratense (Phl p) extract. METHODS: The molecular mechanisms underlying native Phl p, depigmented Phl p (DPG-Phl p), and depigmented-polymerized (DPG-POL-Phl p) allergoid were investigated by single-cell RNA sequencing. Allergen-specific TH2A, T follicular helper (Tfh), and IL-10+ regulatory B cells were quantified by flow cytometry in peripheral blood mononuclear cells from 16 grass pollen-allergic and 8 nonatopic control subjects. The ability of Phl p, DPG-Phl p, and DPG-POL-Phl p to elicit FcεRI- and FcεRII-mediated IgE responses was measured by basophil activation test and IgE-facilitated allergen binding assay. RESULTS: Analysis revealed that DPG-POL-Phl p downregulated genes associated with TH2 signaling, induced functional regulatory T cells exhibiting immunosuppressive roles through CD52 and Siglec-10, modulated genes encoding immunoproteasome that dysregulate the processing and presentation of antigens to T cells and promoted a shift from IgE toward an IgA1 and IgG responses. In grass pollen-allergic subjects, DPG-POL-Phl p exhibited reduced capacity to elicit proliferation of TH2A, IL-4+ Tfh and IL-21+ Tfh cells while being the most prominent at inducing IL-10+CD19+CD5hi and IL-10+CD19+CD5hiCD38intCD24int regulatory B-cell subsets compared to Phl p (all P < .05). Furthermore, DPG-POL-Phl p demonstrated a hypoallergenic profile through basophil activation and histamine release compared to Phl p (31.54-fold, P < .001). CONCLUSIONS: Single-cell RNA sequencing provides an in-depth resolution of the mechanisms underlying the tolerogenic profile of DPG-POL-Phl p.

Differential induction of allergen-specific IgA responses following timothy grass subcutaneous and sublingual immunotherapy.

INTRODUCTION: There is no detailed comparison of allergen-specific immunoglobulin responses following sublingual immunotherapy (SLIT) and subcutaneous immunotherapy (SCIT). OBJECTIVE: We sought to compare nasal and systemic timothy grass pollen (TGP)-specific antibody responses during 2 years of SCIT and SLIT and 1 year after treatment discontinuation in a double-blind, double-dummy, placebo-controlled trial. METHODS: Nasal fluid and serum were obtained yearly (per-protocol population, n = 84). TGP-specific IgA1, IgA2, IgG4, IgG, and IgE were measured in nasal fluids by ELISA. TGP-specific IgA1, IgA2, and Phleum pratense (Phl p)1, 2, 4, 5b, 6, 7, 11, and 12 IgE and IgG4 were measured in sera by ELISA and ImmunoCAP, respectively. RESULTS: At years 2 and 3, TGP-IgA1/2 levels in nasal fluid were elevated in SLIT compared with SCIT (4.2- and 3.0-fold for IgA1, 2.0- and 1.8-fold for IgA2, respectively; all P < .01). TGP-IgA1 level in serum was elevated in SLIT compared with SCIT at years 1, 2, and 3 (4.6-, 5.1-, and 4.7-fold, respectively; all P < .001). Serum TGP-IgG level was higher in SCIT compared with SLIT (2.8-fold) at year 2. Serum TGP-IgG4 level was higher in SCIT compared with SLIT at years 1, 2, and 3 (10.4-, 27.4-, and 5.1-fold, respectively; all P < .01). Serum IgG4 levels to Phl p1, 2, 5b, and 6 were increased at years 1, 2, and 3 in SCIT and SLIT compared with placebo (Phl p1: 11.8- and 3.9-fold; Phl p2: 31.6- and 4.4-fold; Phl p5b: 135.5- and 5.3-fold; Phl p6: 145.4- and 14.7-fold, respectively, all at year 2 when levels peaked; P < .05). IgE to TGP in nasal fluid increased in the SLIT group at year 2 but not at year 3 compared with SCIT (2.8-fold; P = .04) and placebo (3.1-fold; P = .02). IgA to TGP and IgE and IgG4 to TGP components stratified participants according to treatment group and clinical response. CONCLUSIONS: The observed induction of IgA1/2 in SLIT and IgG4 in SCIT suggest key differences in the mechanisms of action.

Induction of IL-10-producing type 2 innate lymphoid cells by allergen immunotherapy is associated with clinical response.

The role of innate immune cells in allergen immunotherapy that confers immune tolerance to the sensitizing allergen is unclear. Here, we report a role of interleukin-10-producing type 2 innate lymphoid cells (IL-10+ ILC2s) in modulating grass-pollen allergy. We demonstrate that KLRG1+ but not KLRG1- ILC2 produced IL-10 upon activation with IL-33 and retinoic acid. These cells attenuated Th responses and maintained epithelial cell integrity. IL-10+ KLRG1+ ILC2s were lower in patients with grass-pollen allergy when compared to healthy subjects. In a prospective, double-blind, placebo-controlled trial, we demonstrated that the competence of ILC2 to produce IL-10 was restored in patients who received grass-pollen sublingual immunotherapy. The underpinning mechanisms were associated with the modification of retinol metabolic pathway, cytokine-cytokine receptor interaction, and JAK-STAT signaling pathways in the ILCs. Altogether, our findings underscore the contribution of IL-10+ ILC2s in the disease-modifying effect by allergen immunotherapy.

EAACI Allergen Immunotherapy User's Guide.

Allergen immunotherapy is a cornerstone in the treatment of allergic children. The clinical efficiency relies on a well-defined immunologic mechanism promoting regulatory T cells and downplaying the immune response induced by allergens. Clinical indications have been well documented for respiratory allergy in the presence of rhinitis and/or allergic asthma, to pollens and dust mites. Patients who have had an anaphylactic reaction to hymenoptera venom are also good candidates for allergen immunotherapy. Administration of allergen is currently mostly either by subcutaneous injections or by sublingual administration. Both methods have been extensively studied and have pros and cons. Specifically in children, the choice of the method of administration according to the patient's profile is important. Although allergen immunotherapy is widely used, there is a need for improvement. More particularly, biomarkers for prediction of the success of the treatments are needed. The strength and efficiency of the immune response may also be boosted by the use of better adjuvants. Finally, novel formulations might be more efficient and might improve the patient's adherence to the treatment. This user's guide reviews current knowledge and aims to provide clinical guidance to healthcare professionals taking care of children undergoing allergen immunotherapy.

Allergen-specific IgG+ memory B cells are temporally linked to IgE memory responses.

BACKGROUND: IgE is the least abundant immunoglobulin and tightly regulated, and IgE-producing B cells are rare. The cellular origin and evolution of IgE responses are poorly understood. OBJECTIVE: The cellular and clonal origin of IgE memory responses following mucosal allergen exposure by sublingual immunotherapy (SLIT) were investigated. METHODS: In a randomized double-blind, placebo-controlled, time course SLIT study, PBMCs and nasal biopsy samples were collected from 40 adults with seasonal allergic rhinitis at baseline and at 4, 8, 16, 28, and 52 weeks. RNA was extracted from PBMCs, sorted B cells, and nasal biopsy samples for heavy chain variable gene repertoire sequencing. Moreover, mAbs were derived from single B-cell transcriptomes. RESULTS: Combining heavy chain variable gene repertoire sequencing and single-cell transcriptomics yielded direct evidence of a parallel boost of 2 clonally and functionally related B-cell subsets of short-lived IgE+ plasmablasts and IgG+ memory B cells. Mucosal grass pollen allergen exposure by SLIT resulted in highly diverse IgE and IgGE repertoires. These were extensively mutated and appeared relatively stable as per heavy chain isotype, somatic hypermutations, and clonal composition. Single IgGE+ memory B-cell and IgE+ preplasmablast transcriptomes encoded antibodies that were specific for major grass pollen allergens and able to elicit basophil activation at very low allergen concentrations. CONCLUSION: For the first time, we have shown that on mucosal allergen exposure, human IgE memory resides in allergen-specific IgG+ memory B cells. These cells rapidly switch isotype, expand into short-lived IgE+ plasmablasts, and serve as a potential target for therapeutic intervention.

Role of IL-35 in sublingual allergen immunotherapy.

BACKGROUND: Grass pollen-specific immunotherapy involves immunomodulation of allergen-specific TH2 responses and induction of IL-10+ and/or TGF-ß+CD4+CD25+ regulatory T cells (induced Treg cells). IL-35+CD4+CD25+ forkhead box protein 3-negative T (IL-35-inducible regulatory T [iTR35]) cells have been reported as a novel subset of induced Treg cells with modulatory characteristics. OBJECTIVE: We sought to investigate mechanisms underlying the induction and maintenance of immunologic tolerance induced by IL-35 and iTR35 cells. METHODS: The biological effects of IL-35 were assessed on group 2 innate lymphoid cells (ILC2s); dendritic cells primed with thymic stromal lymphopoietin, IL-25, and IL-33; and B and TH2 cells by using flow cytometry and quantitative RT-PCR. Grass pollen-driven TH2 cell proliferation and cytokine production were measured by using tritiated thymidine and Luminex MagPix, respectively. iTR35 cells were quantified in patients with grass pollen allergy (seasonal allergic rhinitis [SAR] group, n = 16), sublingual immunotherapy (SLIT)-treated patients (SLIT group, n = 16), and nonatopic control subjects (NACs; NAC group, n = 16). RESULTS: The SAR group had increased proportions of ILC2s (P = .002) and IL-5+ cells (P = .042), IL-13+ cells (P = .042), and IL-5+IL-13+ ILC2s (P = .003) compared with NACs. IL-35 inhibited IL-5 and IL-13 production by ILC2s in the presence of IL-25 or IL-33 (P = .031) and allergen-driven TH2 cytokines by effector T cells. IL-35 inhibited CD40 ligand-, IL-4-, and IL-21-mediated IgE production by B cells (P = .015), allergen-driven T-cell proliferation (P = .001), and TH2 cytokine production mediated by primed dendritic cells. iTR35 cells suppressed TH2 cell proliferation and cytokine production. In addition, allergen-driven IL-35 levels and iTR35 cell counts were increased in patients receiving SLIT (all, P < .001) and NACs (all, P < .001) compared with patients with SAR. CONCLUSION: IL-35 and iTR35 cells are potential novel immune regulators induced by SLIT. The clinical relevance of SLIT can be underscored by restoration of protective iTR35 cells.

A Recombinant Fragment of Human Surfactant Protein D Suppresses Basophil Activation and T-Helper Type 2 and B-Cell Responses in Grass Pollen-induced Allergic Inflammation.

RATIONALE: Recombinant fragment of human surfactant protein D (rfhSP-D) has been shown to suppress house dust mite- and Aspergillus fumigatus-induced allergic inflammation in murine models. OBJECTIVES: We sought to elucidate the effect of rfhSP-D on high-affinity IgE receptor- and CD23-mediated, grass pollen-induced allergic inflammatory responses. METHODS: rfhSP-D, containing homotrimeric neck and lectin domains, was expressed in Escherichia coli BL21(λDE3)pLysS cells. Peripheral blood mononuclear cells and sera were obtained from individuals with grass pollen allergy (n = 27). The effect of rfhSP-D on basophil activation and histamine release was measured by flow cytometry. IgE-facilitated allergen binding and presentation were assessed by flow cytometry. T-helper cell type 2 (Th2) cytokines were measured in cell culture supernatants. The effect of rfhSP-D on IgE production by B cells when stimulated with CD40L, IL-4, and IL-21 was also determined. MEASUREMENTS AND MAIN RESULTS: rfhSP-D bound to Phleum pratense in a dose- and calcium-dependent manner. Allergen-induced basophil responsiveness and histamine release were inhibited in the presence of rfhSP-D, as measured by CD63, CD203c (P = 0.0086, P = 0.04205), and intracellularly labeled diamine oxidase (P = 0.0003, P = 0.0148). The binding of allergen-IgE complexes to B cells was reduced by 51% (P = 0.002) in the presence of rfhSP-D. This decrease was concomitant with reduction in CD23 expression on B cells (P < 0.001). rfhSP-D suppressed allergen-driven CD27-CD4+CRTh2+ T-cell proliferation (P < 0.01), IL-4, and IL-5 levels (all P < 0.01). Moreover, rfhSP-D inhibited CD40L/IL-4- and IL-21-mediated IgE production (77.12%; P = 0.02) by B cells. CONCLUSIONS: For the first time, to our knowledge, we show that rfhSP-D inhibited allergen-induced basophil responses at a single-cell level and suppressed CD23-mediated facilitated allergen presentation and Th2 cytokine production. In addition, rfhSP-D inhibited IgE synthesis by B cells, which is also a novel observation.