Adding to the viral-induced immunosuppressive effects, higher PD-L1 levels are associated with HCMV in tumour specimens, and HCMV infection in vitro induces PD-L1 expression through toll-like receptor 3 (TLR3) regulation in glioblastoma, and this may promote a more malignant phenotype [162]. This evidence concerns the gene TLR3 and cytomegalovirus infection.