The fibroblasts in the tumor microenvironment of mycosis fungoides promote immunosuppression

Mycosis fungoides (MF) is the most common type of the non-Hodgkin cutaneous T cell lymphoma. Cancer associated fibroblasts (CAFs) are a major component in the stroma of the tumor-microenvironment (TME). Exosomes are nano-size extra cellular vesicles secreted by all cells for intercellular communications. We previously demonstrated the presence of CAFs in the TME of MF.

Our aims were to study the effect of MF cancer exosomes on fibroblasts, and the effect of MF fibroblast (MF-F) vs normal fibroblast (N-F) exosomes on the immune system.

Primary fibroblasts were established from MF-patient biopsies and normal skin. Exosomes were isolated from the supernatant of MF-F, N-F and MyLa cells (MF cell-line) by ultracentrifugation, and were confirmed by electron microscope and Nanosight. The internalization of exosomes into normal PBMCs (from healthy donors) and primary fibroblasts was confirmed by microscope analysis of labeled exosomes in the recipient cell cytoplasm.

We found that MyLa-exosomes induced the proliferation and migration of normal fibroblast, presumably to promote CAF phenotype. By applying cyTOF with 41 antibodies on normal PBMCs, we found that N-F-exosomes increase Th1 and CD8+ Tcytotoxic, while MF-F-exosomes reduce Th1, M1 macrophages, Th17 and increase M2 macrophages. Both exosomes increase PDL1 in monocytes with higher increase for MF-F-exosomes. We further confirmed our cyTOF results on primary monocytes and FACS with specific markers for M1, M2 and PDL1 proteins.

We suggest a novel mechanism of MF-fibroblast exosomes in creating immunosuppressive microenvironment through polarization of M2-like macrophages with high PDL1, highlighting a new approach to improve immunotherapy in MF.