A novel mismatch repair deficient lung adenocarcinoma model for immunotherapy research.

Immunotherapy has revolutionised cancer treatment, yet responses vary significantly based on tumour characteristics and microenvironment. Here, we developed and analysed subcutaneous and orthotopic immunocompetent mice models of mismatch repair-deficient (dMMR) lung adenocarcinoma (LUAD) by selectively ablating Mlh1. Subcutaneous tumours demonstrated partial sensitivity to anti-PD-1 therapy, whereas orthotopic tumours exhibited robust responses, with substantial reductions in tumour burden. Although both models displayed to some extent a robust immune microenvironment, they differed in immune cell infiltration patterns following anti-PD-1 treatment, underscoring the critical influence of anatomical site and tumour context in shaping immunotherapy outcomes. Furthermore, the use of clonal cell lines with enriched neoantigen frequency in the orthotopic model highlighted the role of clonal heterogeneity in modulating therapeutic efficacy. Together, our findings emphasise the relevance of orthotopic models for preclinical evaluation and suggest that they more accurately reflect clinical responses to immune checkpoint blockade in dMMR LUAD.