Humoral immunity, mediated by B cells that mature in germinal centers in lymph nodes (LNs), is essential for adaptive immune responses, but its role in antitumor immunity and responses to immunotherapy remain unclear. Here, we show that activation of B cells in tumor-draining deep cervical LNs (dcLNs) is necessary for the efficacy of CTLA-4 (cytotoxic T lymphocyte-associated protein 4) immune checkpoint blockade in glioma in vivo. Anti-CTLA-4 therapy enhanced T follicular helper cell (T_FH cell) expansion in dcLNs, leading to germinal center B cell responses, immunoglobulin G (IgG) class switching, and the generation of glioma-reactive antibodies. Glioma-bearing mice lacking antibody-secreting cells did not benefit from CTLA-4 blockade. Distally secreted IgG accumulated in the tumor microenvironment and promoted glioma cell phagocytosis in vivo. These findings define a B cell-dependent mechanism underlying CTLA-4-mediated control of glioma and provide a conceptual framework for future therapeutic strategies in tumor.