Thirteen is the charm in anaphylaxis: Immunoglobulin E (IgE) is a type of antibody associated with allergies and response to parasites such as worms. When high-affinity, allergen-specific IgE binds its target, it can cross-link receptors on mast cells that induce anaphylaxis. It remains unclear, however, how B cells are instructed to generate high-affinity IgE. Gowthaman et al. discovered a subset of T follicular helper cells (T _FH 13) that direct B cells to do just that. T _FH 13 cells are induced by allergens but not during parasite infection. Transgenic mice lacking these cells show impaired production of high-affinity, anaphylactic IgE. T _FH 13 cells, which are elevated in patients with food and aeroallergies, may be targeted in future antianaphylaxis therapies. Science , this issue p. eaaw6433

Background/Objectives: Osteosarcoma is the most common malignant bone tumor in children, characterized by a high degree of genomic instability, resulting in copy number alterations and genomic rearrangements without disease-defining recurrent mutations. Clinical trials based on molecular characterization have failed to find new effective therapies or improve outcomes over the last 40 years. Methods: To better understand the immune microenvironment of osteosarcoma, we performed single-cell RNA sequencing on six tumor biopsy samples, combined with a previously published cohort of six samples. Additional osteosarcoma samples were profiled using spatial transcriptomics for the validation of discovered subtypes and to add spatial context. Results: Analysis revealed immunosuppressive cells, including myeloid-derived suppressor cells (MDSCs), regulatory and exhausted T cells, and LAMP3+ dendritic cells. Conclusions: Using cell–cell communication modeling, we identified robust interactions between MDSCs and other cells, leading to NF-κB upregulation and an immunosuppressive microenvironment, as well as interactions involving regulatory T cells and osteosarcoma cells that promoted tumor progression and a proangiogenic niche.

Dedicator of cytokinesis 8 (DOCK8) mutations lead to a primary immunodeficiency associated with recurrent gastrointestinal infections and poor antibody responses but, paradoxically, heightened IgE to food antigens, suggesting that DOCK8 is central to immune homeostasis in the gut. Using Dock8-deficient mice, we found that DOCK8 was necessary for mucosal IgA production to multiple T cell-dependent antigens, including peanut and cholera toxin. Yet DOCK8 was not necessary in T cells for this phenotype. Instead, B cell-intrinsic DOCK8 was required for maintenance of antigen-specific IgA-secreting plasma cells (PCs) in the gut lamina propria. Unexpectedly, DOCK8 was not required for early B cell activation, migration, or IgA class switching. An unbiased interactome screen revealed novel protein partners involved in metabolism and apoptosis. Dock8-deficient IgA⁺ B cells had impaired cellular respiration and failed to engage glycolysis appropriately. These results demonstrate that maintenance of the IgA⁺ PC compartment requires DOCK8 and suggest that gut IgA⁺ PCs have unique metabolic requirements for long-term survival in the lamina propria.

Patients with loss-of-function DOCK8 or dominant-negative STAT3 variants have hyper-IgE syndrome, although only DOCK8 deficiency consistently presents with elevated food-specific IgE and symptomatic allergy. We previously found in mice that DOCK8 restricts the differentiation of IL-13+ T follicular helper (Tfh13) cells that drive anaphylactic IgE, although the mechanisms were unclear. Here, we show that DOCK8 promotes STAT3 activity, which inhibits GATA3 in T cells. However, only patients with DOCK8, but not STAT3, deficiency had elevated Tfh13 cells. Cell-specific deletion of either Dock8 (T-Dock8−/−) or Stat3 (T-Stat3−/−) augmented peanut-specific IgE and Tfh13s when oral sensitization was promoted by adjuvants. However, the phenotypes diverged during adjuvant-free oral peanut exposure: only T-Dock8−/− mice developed Tfh13 cells and peanut-specific IgE, accompanied by reduced Foxp3+ Tregs. Treg depletion in T-Stat3−/− mice unmasked Tfh13 induction to oral antigen alone. Thus, DOCK8 and STAT3 cooperate to restrain Tfh13 differentiation to food allergens, and additional Treg impairment in DOCK8 deficiency allows for Tfh13 cell induction and allergy.

Osteosarcoma is the most common malignant bone tumor in children, characterized by a high degree of genomic instability, resulting in copy-number alterations and genomic rearrangements without disease-defining recurrent mutations. Clinical trials based on molecular characterization have failed to find new effective therapies or improve outcomes over the last 40 years. To better understand the immune microenvironment of osteosarcoma, we performed single-cell RNA sequencing on six tumor biopsy samples, combined with a previously-published cohort of six samples. Additional osteosarcoma samples were profiled using spatial transcriptomics for validation of discovered subtypes and to add spatial context. Analysis revealed immunosuppressive cells, including myeloid-derived suppressor cells (MDSCs), regulatory and exhausted T-cells, and LAMP3+ dendritic cells. Using cell-cell communication modeling, we identified robust interactions between MDSCs and other cells, leading to NF-κB upregulation and an immunosuppressive microenvironment, as well as interactions involving regulatory T-cells and osteosarcoma cells that promoted tumor progression and a proangiogenic niche. Statement of Significance: Osteosarcoma patient survival has remained stagnant for several decades due to lack of successful therapy for high-risk patients, including those with metastatic disease. Identifying novel therapeutics including immunotherapies is of great clinical importance. Our study highlights several important immunosuppressive mechanisms within osteosarcoma that should be considered when developing future immunotherapies.