Conclusions
Elderly patients were characterized by increased numbers of CD8+ T cells and impaired cytolytic molecule expression. The observed immune signature was also associated with a loss of clonal neoantigens and the accumulation of immunosuppressive elements. These findings show a unique immune microenvironment in senescence and support biomarker-guided candidate identification for anti-PD-1/PD-L1 therapeutic strategies for elderly patients with LUAD.
Methods
Transcriptome profiles and clinical characteristics of patients with LUAD were retrieved from The Cancer Genome Atlas as a discovery cohort. Immune cell infiltration (quantified by a single-sample gene set enrichment analysis), immunoregulatory molecule expression, and mutational patterns (from The Cancer Immunome Atlas) were compared between young and elderly patients. Immune cell infiltration was verified by immunohistochemistry using a validation cohort including 105 treatment-naïve patients with LUAD. A tissue microarray consisting of 120 LUAD patients was used in the immunohistochemistry validation.
Results
Activated CD8+ T cell numbers increased slightly with age, but cytolytic molecules in T cells (granzyme B [GZMB], perforin 1 [PRF1], granzyme A [GZMA], granzyme M [GZMM], and granulysin [GNLY]) gradually declined. PD-L1 expression was not associated with age; however, a number of immunosuppressive elements beyond PD-L1 were upregulated in aging patients, including regulatory T cells and co-inhibitory molecules, for example, TIM-3, TIGIT, and HHLA2. Finally, senescence was accompanied by a loss of clonal neoantigens, which is believed to be correlated with responsiveness to immune checkpoint inhibitors. Conclusions: Elderly patients were characterized by increased numbers of CD8+ T cells and impaired cytolytic molecule expression. The observed immune signature was also associated with a loss of clonal neoantigens and the accumulation of immunosuppressive elements. These findings show a unique immune microenvironment in senescence and support biomarker-guided candidate identification for anti-PD-1/PD-L1 therapeutic strategies for elderly patients with LUAD.