HIF1A⁺ macrophages as key mediators of immune suppression and recurrence in early-stage small cell lung cancer.

e20111 Background: Being the most aggressive pulmonary malignancy, early recurrence remains extremely common even in early-stage small cell lung cancer (SCLC) after radical surgery and adjuvant chemotherapy. It is critical for us to understand the mechanisms of early recurrence and disease progression. Here, we present a myeloid cell landscape of the tumor microenvironment (TME) and point out the key mechanism of early recurrence among early-stage SCLCs using single-nucleus RNA sequencing (snRNA-seq). Methods: Frozen tumor and paired adjacent normal tissue were collected from 24 early-stage SCLC patients admitted to the Shanghai Chest Hospital between 2020 and 2022. All patients received at least one cycle of adjuvant chemotherapy after radical surgery. The median follow-up time was more than two years. 10X snRNA-seq was performed in 24 tumor tissues and 9 adjacent tissues. Results: Among those 24 patients with SCLC, half suffered disease recurrence. An HIF1A⁺ macrophage (Mφ) subpopulation was significantly enriched in tumor tissues of the recurrence group (p=0.04), compared to the non-recurrence group, and was nearly absent in adjacent normal tissues. These Mφs exhibited high expression of hypoxia- and angiogenesis-related genes, including HIF1A , HIF1A-AS2 , VEGF , HK2 , VCAN and SPP1 , which have been reported as immunosuppressive mediators when expressed in tumor-associated Mφs. In line with this, pathway level analyses showed that this population was significantly enriched for the Regulation of Angiogenesis pathway, indicating their pro-angiogenic characteristics. Additionally, the proportion of HIF1A⁺ Mφs positively correlated with CD8⁺Tex cell infiltration (R=0.61, p=0.0014). The increased abundance of HIF1A⁺ Mφs in recurrent tumors, along with its strong correlation with infiltrating exhausted T cells, highlight this myeloid subset as a critical component of the TME. Further cell-cell communication analysis revealed that HIF1A⁺ Mφs engaged in significant ligand-receptor interactions with lymphocytes via SPP1-CD44/(ITGA4+ITGB1) and FN1-CD44/(ITGA4+ITGB1), with stronger interactions in the recurrence group compared to the non-recurrence group. These ligand–receptor pair interactions largely promote immune suppression, pointing to direct cellular contact as a mechanism by which HIF1A⁺Mφs down-regulate T-cell activity leading to T cell exhaustion and an immunosuppressive TME. Conclusions: Collectively, these findings suggest that HIF1A⁺ Mφs play a key role in shaping an immunosuppressive TME that fosters tumor progression in SCLC through interactions with lymphocytes. It may represent a potential therapeutic target for modulating the TME and improving clinical outcomes in SCLC patients.