Immune Checkpoints OX40 and OX40L in Small-Cell Lung Cancer: Predict Prognosis and Modulate Immune Microenvironment

Background: OX40 and OX40 ligand (OX40L), as essential immune checkpoint (IC) modulators, are highly correlated with cancer immunity regulation as well as tumor microenvironment (TME). Immunotherapy showed outstanding advantages in small cell lung cancer (SCLC) therapy. However, functions and clinical significance of OX40 and OX40L in SCLC were not clear yet. Materials and methods: SCLC samples of 143 patients were collected for immunohistochemistry (IHC) and whole exon sequencing (WES). We comprehensively explored the expression and mutation of OX40/OX40L in SCLC, and systematically linked OX40/OX40L with TME. We raised the OX40/OX40L-based classifier through a machine learning-based computing framework, termed immune risk score (IRS), to predict clinical outcome. Results: The expression of OX40/OX40L on tumor cells and tumor-infiltrating lymphocytes (TILs) was found in the IHC cohort, and verified in other cohorts with SCLC tissues and cell lines. The results showed co-expression patterns among OX40/OX40L, other ICs, and T-cell markers. The WES data suggested that OX40/OX40L mutation is rare in SCLC (<5%). Patients with positive OX40 protein expression on TILs showed substantially higher recurrence-free survival (RFS) than those with negative expression (p=0.009). The external dataset also indicated that high OX40/OX40L expression was correlated with better prognosis (overall survival (OS): OX40, p<0.001; OX40, p=0.019). Importantly, activation of immunity and high infiltration of CD4 (+) and CD8 (+) T cells were observed in the high OX40/OX40L expression group. The IRS model that integrated OX40, OX40L, CD3, CD8, and FOXP3 demonstrated superior predictive performance than single marker (AUC 0.914 vs 0.326-0.681). Notably, there were significant differences in both RFS (p=0.012) and OS (p=0.018) between the high and low OX40/OX40L-based IRS groups. High IRS, characterized by decreased abundance of effective immune cells, implied an immune-suppressive TME phenotype with poor survival. Conclusions: Collectively, this work highlighted the significance of OX40 and OX40L in prognosis and TME cell infiltration characterization of SCLC . Evaluating the OX40/OX40L-based IRS of individual patients with SCLC might contribute to quantifying clinical risk and guiding more precise therapy.