Effect of heterozygosity loss of HLA-I on immune evasion and promotion of non-small cell lung cancer brain metastasis and immunotherapy resistance.

209 Background: HLA-I play a crucial role in T cell recognition and killing of tumor cells as well as in PD-1/PD-L1 immunotherapy. Loss of heterozygosity (LOH) of HLA-I alleles has been found to be common in lung cancer patients and influences immune escape during tumor evolution. This study aims to explore the incidence of HLA-I LOH in intracranial metastases of advanced non-small cell lung cancer patients with brain metastasis and its impact on the efficacy of immunotherapy. Methods: A total of 29 patients with non-small cell lung cancer brain metastasis were included in this study. All enrolled patients underwent either percutaneous biopsy or surgical resection of intracranial metastases and had tissue specimens from the primary lung lesions. Whole-exome sequencing was performed on all primary/metastatic lesions to determine HLA-I typing/LOH and calculate tumor mutation burden (TMB). Additionally, we assessed the expression levels of CD8 T cells in the tumor immune microenvironment. Among the enrolled patients, 20 received PD-1/PD-L1 treatment. Results: Among the enrolled patients, 82.8% (24/29) had heterozygous HLA-I typing, with HLA-I LOH present in 25% (6/24) of patients' primary lesions and 58.3% (14/24) in brain metastatic lesions. Analysis of TMB in different lesions revealed a median TMB of 7.8 mut/Mb in lesions with intact HLA-I and 11.4 mut/Mb in lesions with HLA-I LOH. Notably, the median TMB in brain metastatic lesions with HLA-I LOH was 13.2 mut/Mb, higher than that in HLA-I LOH primary lung lesions (10.1 mut/Mb). Immunohistochemistry demonstrated that CD8 T cell expression levels were lowest in brain metastatic lesions with HLA-I LOH and highest in intact HLA-I primary lung lesions. Among patients who received immunotherapy, four cases exhibited inconsistent lesion responses, with stable or regressing primary lesions but progressive intracranial metastases. Survival analysis revealed that patients with HLA-I LOH in brain metastases had significantly lower PFS compared to those without (4.1 months vs. 6.9 months, P < 0.05), with no significant difference in OS. Conclusions: This study indicates that the incidence of HLA-I LOH in brain metastases of lung cancer is higher than that in primary lung lesions, accompanied by higher TMB, possibly due to the ineffective presentation of tumor antigens resulting in the accumulation of mutations in lost HLA-I. Moreover, tumors with HLA-I LOH have reduced levels of CD8 T cell infiltration, suggesting impaired tumor antigen presentation impedes immune cytotoxicity. These phenomena contribute to the poorer efficacy of immunotherapy in such patients. In conclusion, HLA-I LOH may be one of the important mechanisms of immune escape in lung cancer brain metastases.