CTLA4 and meningioma: Additionally, these studies detected an increased number of CTLA4+/CD3+ lymphocytes in WHO grades II and III tumors with mutations in PIK3CA or SMO. Immunohistochemical analysis of PD-L1 expression in several tumor types associated with NF-1 and NF-2 gene mutations, including meningioma, schwannoma, and neurofibroma showed a variable degree of positivity across these tumors; specifically, they detected PD-L1 expression in 40% of NF2-mutated meningiomas [32].