Dysbiosis-associated LPA primes ICI-induced intestinal barrier dysfunction via the LPAR2-MLCK axis

Immune checkpoint inhibitor (ICI) therapy is frequently limited by severe gastrointestinal toxicity. While 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.

We employed an integrated multi-omics approach in a murine model of early ICI-induced injury, with validation in a clinical cohort of patients with ICI-colitis. Mechanisms were investigated using in vitro receptor screening, genetically engineered mice with altered MLCK1 activity, and pharmacological intervention with repurposed low-dose tacrolimus. Subcutaneous melanoma models were utilized to evaluate the relationship between barrier modulation and anti-tumor outcomes.

Early ICI treatment induced a distinct dysbiotic state characterized by Pseudomonadota expansion, which was associated with the accumulation of bioactive lysophosphatidic acid (LPA)-a metabolic signature also observed in human patients. Mechanistically, we identified LPAR2 as the key epithelial sensor that transduces this metabolic signal into pathological MLCK1 activation, driving the priming phase of barrier dysfunction. Genetic ablation of MLCK1 prevented this early barrier loss and was associated with improved tumor control and favorable regional immune alterations. Conversely, constitutive activation of MLCK1 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 MLCK1 recruitment effectively mitigated barrier injury without dampening anti-tumor responses.

The dysbiosis-associated LPA-LPAR2-MLCK axis acts as an early metabolic trigger for the priming phase of ICI-induced barrier dysfunction. Modulating this upstream initiation step provides a temporal and mechanism-based strategy to uncouple intestinal toxicity from anti-tumor efficacy.