Exploratory Study of PD-1 Neoadjuvant Treatment of Recurrent Meningioma

Inclusion Criteria: * Pathologically diagnosed as a patient with WHO grade III recurrent meningioma * Age ≥ 18 years * Kps≥70 * able to accept second surgery * ECOG Performance Status \< 2 * Glucocorticoid dosage dexamethasone ≤5mg/ day or equivalent dose Exclusion Criteria: * Participants who have had chemotherapy, targeted small molecule therapy or study therapy within 14 days of protocol treatment, or those who have not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to agents administered more than 2 weeks earlier. * Participants who are receiving any other investigational agents. * Participants who have a diagnosis of an immunodeficiency. * Requires treatment with high dose systemic corticosteroids defined as dexamethasone \>2mg/day or bioequivalent within 7 days of initiating therapy. * Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent. Unable to undergo brain MRI.