Mesenchymal Stem Cells Induce an Immunosuppressive Microenvironment in Pituitary Tumors

The tumor microenvironment (TME) includes diverse cellular components such as mesenchymal stem cells (MSCs) and immune cells, among others. MSC have been isolated from different tumors and they favor tumor cell growth; however, their role in pituitary tumors (PTs) remains unknown.

Herein we report the presence of MSCs in 2 adrenocorticotropin (ACTH)-secreting PTs causing Cushing disease (MCU), 2 nonfunctioning adenomas of gonadotrope differentiation (MNF), and 2 nontumoral pituitary glands (MS).

We have analyzed the transcriptomic profiles by RNA sequencing and compared MSCs in terms of their immunosuppressive effects against lymphoid T-cell and macrophage populations by means of cocultures and flow cytometry.

Our transcriptomic analysis revealed molecular differences between MSCs derived from nontumoral pituitaries and MSCs derived from PTs. Two distinct subpopulations of MSC emerged: one displaying immunosuppressive properties and the other with increased proproliferative capabilities, regardless of their origin. MSCs derived from ACTH- and nonfunctioning PTs, but not those derived from nontumoral glands, significantly inhibited the proliferation of activated T cells, favored the generation of regulatory T cells, and promoted M2 macrophage polarization. Such immunosuppressive effects were correlated with an upregulation of programmed death ligand 1 and intracellular expression of macrophage colony-stimulating factor (M-CSF) and interleukin-10. Importantly, MSC derived from ACTH-PTs showed a higher immunosuppressive potential than MSC isolated from nonfunctioning tumors.

This study demonstrates the presence of at least 2 MSC subpopulations in the pituitary gland and suggests that immunosuppressive effects of MSCs may have important implications in PT growth.