Ectopic NMDAR expression in breast cancer unmasks germline-encoded autoimmunity: Bulk RNA sequencing data

Autoimmunity and anti-cancer immunity lie on the same biological continuum1,2, but their link remains obscure. The paraneoplastic neurological syndrome anti-NMDA receptor (NMDAR) encephalitis (ANRE) is a paradigm for their connectivity3 given that intratumoral NMDAR expression correlates with the generation of anti-NMDAR antibodies4,5. Here, we verify ectopic expression of GluN1 and GluN2B NMDAR sub-units in triple-negative breast cancer (TNBC)6 and model this using orthotopic TNBC tumors with inducible expression of GluN1-GluN2B NMDARs. We show that NMDAR expression is sufficient to induce B cell recruitment and their affinity maturation, consistent with an integrated adaptive immune response. Reconstruction of extended intratumoral B cell phylogenies and cryo-EM structural analyses demonstrated that affinity-matured hypermutated and class-switched antibodies emerged from pre-existing germline-configuration lower-affinity anti-NMDAR antibodies. Distinct matured antibodies targeted specific epitopes and induced conformational rearrangements within the NMDAR amino-terminal domain, predictive of their functional effects, ranging from inhibition to potentiation. Passive transfer of an NMDAR-potentiating antibody caused autonomic dysregulation and lowered the seizure threshold in healthy female mice, recapitulating key diagnostic criteria of ANRE4,5. We further identify a correlation between intratumoral NMDAR expression and anti-NMDAR antibody titers in TNBC patients. Taken together, our data establish a direct connection between intratumoral NMDAR expression, antibody maturation, and the onset of autoimmunity. These findings suggest that germline-encoded anti-NMDAR antibodies contribute to immune surveillance but can also trigger autoimmune disease upon maturation, revealing a mechanistic tradeoff between cancer immunity and neurotoxicity.

自身免疫与抗肿瘤免疫处于同一生物学连续谱1,2，但二者之间的关联仍不明确。副肿瘤性抗NMDA受体（NMDAR）脑炎（ANRE）是二者关联研究的范式3，因为肿瘤内NMDAR的表达与抗NMDAR抗体的产生相关4,5。本研究验证了三阴性乳腺癌（TNBC）中GluN1与GluN2B这两种NMDAR亚基的异位表达6，并通过构建可诱导表达GluN1-GluN2B型NMDAR的原位TNBC肿瘤模型开展相关研究。结果显示，NMDAR的表达足以诱导B细胞招募及其亲和力成熟，这与整合型适应性免疫应答的特征相符。对扩展的肿瘤内B细胞谱系进行重构，并结合冷冻电镜（cryo-EM）结构分析表明，亲和力成熟的高突变、类别转换抗体起源于预先存在的生殖系构型低亲和力抗NMDAR抗体。不同的成熟抗体靶向特定表位，并可诱导NMDAR氨基末端结构域内发生构象重排，该特征可预测其功能效应，效应范围涵盖从抑制到增强的不同类型。将具有NMDAR增强活性的抗体被动转移至健康雌性小鼠体内后，可引发自主神经功能紊乱并降低癫痫发作阈值，重现了ANRE的关键诊断标准4,5。本研究还在TNBC患者中发现，肿瘤内NMDAR的表达与抗NMDAR抗体滴度存在相关性。综上，本研究数据证实了肿瘤内NMDAR表达、抗体成熟与自身免疫发病之间存在直接关联。上述研究结果表明，生殖系编码的抗NMDAR抗体可参与免疫监视，但在成熟后也可触发自身免疫疾病，揭示了癌症免疫与神经毒性之间存在机制层面的权衡。