Overexpression of CTLA-4 and fibronectin, and lower expression of CD137 (4-1BB) is associated with brain metastasis of primary skin melanomas. An analysis of local immune response by digital spatial profiling

Shiva Najjary¹Nur al Amery¹Mengqi Huang¹Disha Vadgama¹Alexander C.J. Akkooi²Jacobus Gilhuis³Zineb Belcaid¹Dana A.M. Mustafa¹Johan M. Kros^1*

• ¹Erasmus Medical Center, Rotterdam, Netherlands
• ²Royal Prince Alfred Hospital, Sydney, New South Wales, Australia
• ³Reinier de Graaf Hospital, Delft, Netherlands

Background: To discover immune response-associated gene expressions related to brain metastases of skin melanomas, we analyzed a group of fifteen primary skin melanomas consisting of five tumors from patients who did not develop systemic metastases (NM); ten from patients with systemic metastasis of which five with (BM), and five without brain involvement (OOM). Regions of interest (ROIs) harboring tumor cells only; immune cells only; or immune cell infiltration in tumor cell regions, were separately analyzed.Methods: we profiled the tumor immune microenvironment (TIME) of primary skin melanomas by using a panel of 77 immune response-related oligo-nucleotide targets in the GeoMx Digital Spatial profiler (Nanostring Technologies).Results: Melanomas from patients who developed brain metastases contained significantly higher levels of (CD45+) immune cells and overexpressed fibronectin and CTLA-4 in all ROIs compared to the melanomas that had metastasized to other sites than the brain (p<0.05). Distant metastases were accompanied by lower expression of CD137 (4-1BB). Downregulation of VISTA, IDO1 and ICOS was associated with melanomas that gave rise to distant metastases including brain. Conclusion: Lower expression of CD137 (4-1BB) is linked with the formation of distant metastases and the expressions of fibronectin and CTLA-4 herald the formation of brain metastasis in particular.