A yeast sugar particle “trains” lung immune cells to block cancer spread by flipping a mitochondrial switch.

Objective
Test whether inducing trained immunity with yeast-derived whole β-glucan particles (WGP) reprograms lung interstitial macrophages (IMs) to suppress tumor metastasis and define the dominant molecular pathway(s) involved.

Methods

• Design & models: Single intraperitoneal (i.p.) WGP exposure (training) followed 7–21 days later by tumor challenge across multiple metastasis settings: LLC lung metastasis, B16F10 melanoma lung metastasis, EL4 lymphoma liver metastasis, orthotopic 4T1 breast cancer with surgical resection (adjuvant/therapeutic settings), and spontaneous K-rasLA1 lung tumors.
• Cellular & functional readouts: Lung flow cytometry (CD45+CD11b+F4/80+ IMs), ex vivo restimulation (LPS, tumor supernatant, rMIF), phagocytosis and cytotoxicity assays, serum/tissue tumor burdens, histology, survival. Macrophage/monocyte depletion and CD4/CD8/neutrophil depletions tested effector requirements.
• Mechanism mapping: RNA-seq/GSEA of IMs, LC–MS/MS for sphingosine-1-phosphate (S1P), mtROS (MitoSOX), mitochondrial fission (p-DRP1, TMRM, TEM), Seahorse (mitochondrial respiration). Inhibitors used in vitro/in vivo: fumonisin-B1 (ceramide synthase), Sphk2 inhibitor (Sphk2i), Mdivi-1 (DRP1). Adoptive transfers: bone marrow (BM) and WGP-trained BMDMs. Human relevance: WGP-trained human CD14+ monocytes tested in vitro and in NSG mice.

Results

• Antimetastatic efficacy: WGP-trained mice had lower metastatic burden and prolonged survival in LLC and B16F10 models. Benefits also observed in EL4 liver metastases, post-resection 4T1 (adjuvant benefit), and reduced spontaneous K-rasLA1 lung nodules.
• Effector identification: Macrophage depletion abrogated benefit; neutrophil or CD4/CD8 depletion did not. BM chimeras and CCR2 dependence indicate BM-origin IMs mediate control.
• Functional enhancement: WGP-trained IMs showed higher phagocytosis and tumor cytotoxicity, with fewer LLC cells detectable in lungs within 24 h post-challenge.

Human translation: WGP-trained human monocytes exhibited increased cytokine responses, mtROS, DRP1 phosphorylation, and cytotoxicity against A549 lung cancer cells; co-transfer reduced tumor burden in NSG mice.

Interpretation
A single WGP exposure reprograms lung Ims (without requiring adaptive lymphocytes or neutrophils) into a transient, antitumor state that intercepts circulating tumor cells and limits metastatic outgrowth. The effect generalizes across tumor types and therapeutic contexts (adjuvant, therapeutic, spontaneous).

Mechanisms and pathways

• Trigger & sensing: Particulate WGP engages Dectin-1 and is phagocytosed; tumor-secreted factors (e.g., MIF) can serve as secondary stimuli that elicit trained responses from WGP-trained macrophages.
• Metabolic–organelle axis: WGP upregulates sphingolipid biosynthesis (notably Cers6, Sphk2), leading to S1P accumulation, DRP1 phosphorylation, mitochondrial fission, and mtROS increase, which augments phagocytosis and tumoricidal activity.
• Pathways dispensable for in vivo benefit: IL-1β–IL-1R and mTORC1/2 are not required; HIF-1α contributes partially in vitro but is not essential for metastasis control in vivo.

Dosages and adverse reactions

• In vivo training: WGP 1 mg i.p. (day 0). In K-rasLA1 mice, repeated 1 mg i.p. at weeks 6, 9, 12, 15.
• In vitro training/restimulation (for mechanism): WGP 25 μg/mL ×24 h, rest 6 d; LPS 10–100 ng/mL; tumor supernatant 40%; rMIF 100 ng/mL; S1P 200–300 nM; Mdivi-1 10 μM; Sphk2i 25–50 μM; fumonisin-B1 25 μM.
• Adverse reactions: No systemic lung inflammation at baseline after WGP. The study does not include formal toxicity, hematology, or organ-system safety evaluations; clinical tolerability remains unknown.

Quality of study

• Strengths
  • Convergent efficacy across five metastasis/tumor models including post-resection adjuvant and spontaneous disease.
  • Clear causality: macrophage depletion, BM chimeras, adoptive transfer of trained BMDMs, pathway blockade (Sphk2i, Mdivi-1).
  • Multi-omic/mechanistic depth (RNA-seq, LC–MS/MS, mitochondrial imaging/respiration).
  • Human monocyte validation with in vivo xenograft readout.
• Limitations
  • Mouse-centric; durability windows (~1–2 weeks) and dosing frequency not clinically optimized.
  • Investigators not blinded; sample size not pre-powered; normality assumptions not tested (per Statistics).
  • Composition-specific: particulate WGP may behave differently from other β-glucans; manufacturing variability not addressed.
  • Safety/PK/PD and interactions with standard therapies not assessed.

Implications

• β-glucan–based training could be explored as perioperative/adjuvant immunoprophylaxis against metastasis and as a trained macrophage cell therapy platform.
• The S1P-DRP1/mitochondrial fission-mtROS axis provides actionable PD markers and druggable nodes; efficacy appears macrophage-centric and adaptive-independent, suggesting combinability with checkpoint blockade without lymphocyte priming requirements.
• Next steps include conducting early-phase trials to define dose, window of susceptibility, safety, and pharmacodynamics; comparative studies of particulate vs soluble β-glucans; standardized WGP characterization and release testing.