Characteristics of the immune microenvironment and their clinical significance in lung adenocarcinoma patients with different ALK fusion variants.

Background: The tumor immune microenvironment of anaplastic lymphoma kinase (ALK)-rearranged lung adenocarcinoma (LUAD) stratified by ALK fusion variants is poorly pictured. Hence, in this study, we aim to explore the immune heterogeneity of ALK⁺ LUAD across different ALK fusion variants and further investigate their significance on clinical prognosis.

Methods: A retrospective analysis was conducted on ALK⁺ LUAD patients (N=68). DNA and RNA-based next-generation sequencing (NGS) was performed to clarify the specific ALK fusion variants. Clinical and pathological characteristics were compared between long and short ALK variants. To research the immune heterogeneity, multi-fluorescence was carried out to explore the differences in immune properties, such as tumor-infiltrating lymphocyte (TIL) number, TIL subset, and tertiary lymphoid structures (TLS) development, between long and short ALK variants. Furthermore, the prognostic value of these characteristics was analyzed. Finally, the expression of lymphocyte-activation gene-3 (LAG3), one novel immune therapy target, was assessed across ALK⁺ LUAD.

Results: LUAD patients with short ALK fusion variant-driven tumors exhibited higher American Joint Committee on Cancer (AJCC) stage as well as larger tumor size than those with long ALK fusion variant-driven tumors. Compared to long ALK fusion variants, there were more TILs, especially natural killer (NK) cells, within short ALK variants. However, fewer TLS were established in cancers harboring short ALK variants than those with long ALK variants. In advanced-stage LUAD patients with ALK fusion, short ALK variants, hot immune status, and high-level NK cells were identified to be adverse prognostic factors, while high-level B cells, as well as the development of TLS, served as positive prognostic factors. As for LAG3 expression, LAG3⁺ immune cells were more enriched in short ALK variants than in long ALK variants.

Conclusions: LUAD patients with short ALK fusion variant-driven tumors exhibited worse prognosis than those with long ALK fusion variant-driven tumors. The tumor immune microenvironments are heterogeneous across different ALK fusion variants with short variants characterized by higher levels of TIL, especially NK cells, but by less TLS development than long variants ALK⁺ LUAD, which disfavor disease outcomes.