Ectopic NMDAR Expression in Cancer Triggers Autoimmunity Through Antibody Maturation
Research reveals how ectopic NMDA receptor expression in triple-negative breast cancer triggers autoimmune disease through antibody maturation. The study shows NMDAR expression recruits B cells and drives affinity maturation, producing antibodies that can cross the blood-brain barrier and cause neurological symptoms while constraining tumor growth.
Ectopic expression of NMDA receptors in triple-negative breast cancer has been shown to directly trigger autoimmune disease through the affinity maturation of germline-encoded antibodies, revealing a mechanistic trade-off between cancer immunity and neurotoxicity. Research demonstrates that intratumoral NMDAR expression recruits B cells and drives their affinity maturation, producing high-affinity antibodies that can cross the blood-brain barrier and cause neurological symptoms. This connection between tumor biology and autoimmunity provides new insights into paraneoplastic syndromes and cancer immune surveillance.
The study verified ectopic expression of GluN1 and GluN2B NMDAR subunits in triple-negative breast cancer and modeled this using orthotopic TNBC tumours with inducible expression of GluN1–GluN2B NMDARs. NMDAR expression was sufficient to induce the recruitment of B cells and their affinity maturation, consistent with an integrated adaptive immune response. Reconstruction of extended intratumoural B cell phylogenies and cryogenic electron microscopy 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 anti-NMDA receptor encephalitis. Researchers further identified a correlation between intratumoural NMDAR expression and anti-NMDAR antibody titres in patients with TNBC.
These findings establish a direct connection between intratumoural NMDAR expression, antibody maturation and the onset of autoimmunity. The data suggest that germline-encoded anti-NMDAR antibodies contribute to immune surveillance but can also trigger autoimmune disease after maturation. This reveals a mechanistic trade-off between cancer immunity and neurotoxicity, where the same immune response that constrains tumor growth can also cause debilitating neurological symptoms.
Paraneoplastic neurological syndrome ANRE (anti-NMDA receptor encephalitis) serves as a paradigm for this connectivity, given that intratumoural NMDAR expression is correlated with the generation of anti-NMDAR antibodies. NMDARs are voltage-dependent cation channels activated by glycine and glutamate, comprising two GluN1 subunits and two GluN2 subunits and/or GluN3 subunits that mediate synaptic plasticity in the central nervous system. ANRE is correlated with the expression of NMDAR in multiple tumour types, including ovarian, breast and pancreas, and is associated with the production of high-affinity anti-NMDAR IgG antibodies from tertiary lymphoid structures.
The anti-NMDAR humoral response constrains tumour growth but is also associated with a debilitating neuropsychiatric syndrome characterized by psychosis, autonomic dysregulation and epileptic seizures. These observations suggest ectopic onconeural antigen expression recruits germline-configuration B cells, which undergo affinity maturation in tertiary lymphoid structures to generate high-affinity IgG autoantibodies that cross the blood-brain barrier.