Single-cell transcriptomics of non-functioning and functioning PitNET subtypes reveals differences in the tumor microenvironment and tumor-specific gene expression signatures that correlate with aggressive tumor growth

Pituitary neuroendocrine tumors (PitNET) are among the most common intracranial tumors. Despite a frequently benign course, aggressive behavior occurs for unexplained reasons, especially in functional PitNET. Tumor behavior is known to be under the influence of the tumor microenvironment (TME). However, the relationship between TME cells and aggressive tumor behavior has not been adequately explored in PitNET. We used single-cell RNA sequencing and other analyses to comparatively characterize the transcriptome of seven gonadotroph and three lactotroph PitNET and correlate it with clinical behavioral patterns. In our lactotroph PitNET samples, we detect a highly proliferative gene profile with significantly increased expression levels in tumors with aggressive behavioral patterns within a bulk RNA-seq cohort of 134 PitNET samples. We also report high intratumoral heterogeneity in both gonadotroph and lactotroph PitNET and detect gene expression programs belonging to epithelial, endocrine and immunological functional networks in both subtypes. Direct comparison of the lymphoid compartment of both subtypes reveals increased CD4+ T cell abundances in gonadotroph and increased CD4-/CD8- double negative T cell and natural killer T cell abundances in lactotroph PitNET. Also notable is the presence of proliferative lymphocytes, whose occurrence in the bulk RNA-seq cohort positively correlates with more aggressive tumor behavior. Increased CD8+ T cell and natural killer (NK) cell abundancies, however, correlate significantly with reduced aggressiveness indicating anti-tumoral effects. Our study expands the knowledge of the differences in cellular composition of functional and non-functional PitNET subtypes and lays the foundation for further studies on the influence of lymphoid cells on the variable aggressive behavior of PitNET. Regarding the treatment of drug-resistant lactotroph PitNET, proliferative lymphocytes, CD8+ T and NK cells could represent potentially valuable targets for the development of new cancer immunotherapies in the future.