Dysbiosis-Associated Lysophosphatidic Acid Primes Immune Checkpoint Inhibitor-Induced Intestinal Barrier Dysfunction via the Lysophosphatidic Acid Receptor 2-Myosin Light Chain Kinase Axis.

BACKGROUND & AIMS: Immune checkpoint inhibitor therapy is frequently limited by severe gastrointestinal toxicity. Although the immune mechanisms driving late-stage, overt mucosal inflammation are increasingly recognized, the early microbiota-metabolic events that prime epithelial barrier dysfunction remain poorly defined.

METHODS

We employed an integrated multiomics approach in a murine model of early immune checkpoint inhibitor-induced injury, with validation in a clinical cohort of patients with immune checkpoint inhibitor colitis. Mechanisms were investigated using in vitro receptor screening, genetically engineered mice with altered myosin light chain kinase 1 activity, and pharmacologic intervention with repurposed low-dose tacrolimus. Subcutaneous melanoma models were utilized to evaluate the relationship between barrier modulation and antitumor outcomes.

RESULTS

Early immune checkpoint inhibitor treatment induced a distinct dysbiotic state characterized by Pseudomonadota expansion, which was associated with the accumulation of bioactive lysophosphatidic acid-a metabolic signature also observed in human patients. Mechanistically, we identified lysophosphatidic acid receptor 2 as the key epithelial sensor that transduces this metabolic signal into pathological myosin light chain kinase 1 activation, driving the priming phase of barrier dysfunction. Genetic ablation of myosin light chain kinase 1 prevented this early barrier loss and was associated with improved tumor control and favorable regional immune alterations. Conversely, constitutive activation of myosin light chain kinase 1 exacerbated barrier disruption, which correlated with accelerated tumor progression and a systemic immunosuppressive shift. Furthermore, repurposing low-dose tacrolimus as a selective modulator to disrupt FKBP8-dependent myosin light chain kinase 1 recruitment effectively mitigated barrier injury without dampening antitumor responses.

CONCLUSIONS

The dysbiosis-associated lysophosphatidic acid-lysophosphatidic acid receptor 2-myosin light chain kinase axis acts as an early metabolic trigger for the priming phase of immune checkpoint inhibitor-induced barrier dysfunction. Modulating this upstream initiation step provides a temporal and mechanism-based strategy to uncouple intestinal toxicity from anti-tumor efficacy.