Lung adenocarcinoma (LUAD), a major subtype of lung cancer, presents a significant challenge due to low 5-year survival rates despite advancements in targeted therapy and surgery. Immunotherapy, particularly immune checkpoint inhibitors (ICIs), has revolutionized treatment, but its efficacy is limited to a subset of patients. Identifying predictive biomarkers is crucial to optimize patient selection and improve outcomes. Tumor mutation burden (TMB) and programmed death-ligand 1 (PD-L1) expression are currently used, but their predictive power is imperfect. The tumor immune microenvironment (TIME), a complex interplay of tumor and immune cells and molecules, is increasingly recognized as a key determinant of ICI response. This study focuses on LRP1B, a low-density lipoprotein receptor-related protein, whose mutations have been linked to improved outcomes in various cancers treated with immunotherapy. The researchers hypothesize that LRP1B mutations in LUAD positively influence the TIME, ultimately impacting the efficacy of ICI treatment and patient survival. The study aimed to systematically analyze LRP1B mutation and its association with the TIME and immunotherapy response in LUAD patients.

The introduction section extensively reviewed existing literature on LUAD treatment, the limitations of current predictive biomarkers (TMB and PD-L1), and the importance of TIME in immunotherapy response. Previous studies highlighting the association between LRP1B mutations and improved immunotherapy outcomes in other cancer types are also discussed, setting the stage for the current study's investigation into LUAD. The complexities of TIME, the roles of various immune cells (T cells, macrophages) and immune-related molecules (IFN-γ, PD-L1), and their influence on ICI efficacy are reviewed, underscoring the rationale for exploring LRP1B's role in the context of LUAD's TIME.

The study utilized two cohorts: an ICI-treated LUAD cohort (n=59) and the TCGA-LUAD cohort (n=507). The ICI cohort underwent whole-exome sequencing (WES) to determine LRP1B mutation status, along with clinical data collection including age, sex, treatment response (RECIST 1.1 criteria), neoantigen load (NAL), TMB, and other gene mutations. The TCGA-LUAD cohort provided transcriptomic and somatic mutation data. Statistical analyses compared LRP1B-mutated and wild-type groups for mutation profiles, immunogenicity (TMB, NAL), TIME characteristics (immune gene expression, immune cell infiltration using CIBERSORT), and DNA damage repair (DDR) mutations. Multiplex immunohistochemistry (mIHC) on 20 clinical LUAD specimens (10 LRP1B-mutated, 10 wild-type) was performed to validate bioinformatic findings on immune cell infiltration (CD4+, CD8+, CD68+) and PD-L1 expression. Univariate and multivariate Cox regression analyses and Kaplan-Meier survival curves assessed the association between LRP1B mutation and progression-free survival (PFS). A nomogram was constructed to predict PFS. Statistical significance was set at p<0.05.

The study revealed a high mutation frequency of LRP1B in both cohorts (25% in ICI cohort, 36% in TCGA cohort). LRP1B mutation was strongly associated with multiple immune-related pathways, including T cell activation and differentiation. Analysis of the TIME showed significantly higher expression of genes involved in antigen presentation, cytotoxicity, chemokines, and pro-inflammatory mediators in the LRP1B-mutated group. CIBERSORT analysis indicated increased infiltration of activated immune cells (M1 macrophages, CD8+ T cells, activated CD4+ memory T cells) in LRP1B-mutated tumors. mIHC validation confirmed elevated CD8+ T cell infiltration and PD-L1 expression in LRP1B-mutated LUAD specimens. LRP1B-mutated patients had higher TMB, NAL, and more mutations in DDR pathways. Crucially, LRP1B-mutated LUAD patients in the ICI cohort showed significantly prolonged PFS compared to the wild-type group (p=0.0016). This improved PFS was not observed in the TCGA cohort lacking ICI treatment. A nomogram incorporating LRP1B status, NAL, and TMB demonstrated good predictive power for short-term PFS in ICI-treated patients (AUC values of 0.823 and 0.840 for 1 and 2 years, respectively).

The study's findings demonstrate a strong association between LRP1B mutation and improved response to ICI therapy in LUAD, mediated by alterations in the TIME. The increased immune cell infiltration, enhanced expression of immune-related genes, and higher immunogenicity (TMB, NAL) observed in LRP1B-mutated tumors are consistent with a more favorable immune microenvironment conducive to ICI efficacy. The prolonged PFS in ICI-treated patients with LRP1B mutations strongly supports its role as a potential prognostic biomarker. The nomogram further enhances clinical utility by providing a quantitative tool to predict PFS. The contrasting PFS results between the ICI and TCGA cohorts highlight the importance of the ICI treatment context in the observed benefits linked to LRP1B mutation.

This study establishes LRP1B mutation as a potential prognostic biomarker for LUAD patients receiving ICI therapy. The findings suggest that the detection of LRP1B mutation should be incorporated into the criteria for patient selection for ICI treatment, alongside PD-L1 expression and TMB/NAL assessment. Future research should focus on elucidating the precise molecular mechanisms underlying LRP1B's influence on the TIME and exploring its potential as a therapeutic target.

The study's limitations include the relatively small size of the mIHC cohort and the lack of RNA-seq data in this cohort. While the TCGA-LUAD cohort helped to address the limitations in the size of the mIHC cohort and provided transcriptomic data for comparison of TIME features between LRP1B mutated and wild-type groups, the molecular mechanisms by which LRP1B mutations modulate the TIME require further investigation. The retrospective nature of the study also warrants caution in interpreting the findings.