Humoral immunity, which is mediated by B cells that mature in germinal centers (GCs) in lymph nodes (LNs), is essential for adaptive immune responses. However, the involvement of B cell responses in anti-tumor and immunotherapy responses remains largely unexplored. Here, we show that activation of B cells in GCs of tumor-draining deep cervical LNs (dcLNs) is necessary for the efficacy of CTLA-4 immune checkpoint blockade in glioma in vivo. We demonstrate that anti-CTLA-4 therapy enhances B cell–CD4 T cell interactions in dcLNs, leading to the expansion of GC B cells, class switching, and the generation of glioma-specific IgG. Glioma-bearing mice lacking antibody-secreting cells did not benefit from CTLA-4 blockade. Furthermore, using our new in vivo reporter system, we show that distally-secreted glioma-specific IgG infiltrates the tumor microenvironment and triggers glioma cell phagocytosis. Our study uncovers a previously unknown B cell–dependent mechanism underlying anti-CTLA-4 mediated control of glioma, which could be harnessed to treat other tumor types.