IgG1+ Plasma Cells Promote Immune Checkpoint Blockade Efficacy

The success of immune checkpoint blockade (ICB), including anti–PD-1 therapy, has transformed cancer treatment. While prior studies largely emphasized T cell–mediated mechanisms, Gonzalez-Kozlova, Sweeney, Figueiredo, Tuballes, and colleagues, led by Dr. Gnjatic, identified a prominent role for B cells and plasma cells (PC) in shaping responses to ICB. Bulk, single-cell, and BCR transcriptomic data from a discovery cohort of 38 patients with early-stage hepatocellular carcinoma were analyzed across tumor, adjacent liver, and draining lymph nodes before and after neoadjuvant anti–PD-1 therapy. Responders, defined by >50% tumor necrosis, exhibited increased PC infiltration, whereas non-responders showed an enrichment of class-unswitched memory B cells. IGHG1 emerged as a top unregulated gene uniquely increased in responders after treatment, supporting a role for IgG1-producing PCs in therapeutic benefit. Spatial analyses further revealed that responders harbored IgG1-enriched PCs colocalized with CD8+ T cells within immunogenic niches, while non-responders displayed regions dominated by dysfunctional B cells within immunosuppressive environments. The predominance of IgG1+ PCs in responders was validated across multiple independent internal and external datasets spanning diverse cancers and ICB regimens, highlighting a broader contribution of humoral immunity to treatment outcomes. IGHG1 expression also correlated with improved overall survival. Proteomic serum analyses demonstrated higher levels of tumor-associated IgG1 antibodies to tumor antigens, in particular cancer-testis antigens, and enhanced T-cell activity in responders compared to non-responders. Cell–cell interaction modeling supported an IgG1+ PC-driven immunogenic milieu characterized by increased immunostimulatory signaling, including IL6 and TNF signaling. These findings were further validated across seven additional clinical trial cohorts. Collectively, this work establishes IgG1-secreting plasma cells as key contributors to favorable clinical responses following ICB and identifies potential avenues to enhance immunotherapy efficacy.Gonzalez-Kozlova E, Sweeney R, Figueiredo I, Tuballes K, Ozbey S, Hamon P, et al. Humoral IgG1 responses to tumor antigens underpin clinical outcomes in immune checkpoint blockade. Nat Med 2026 Jan 27 [Epub ahead of print].Note: Research Watch is written by Cancer Discovery editorial staff. Readers are encouraged to consult the original articles for full details. For more Research Watch, visit Cancer Discovery online at https://aacrjournals.org/cdnews.