OBJECTIVE: Ofatumumab presents a potentially promising alternative to current second-line immunotherapy for refractory anti-N-methyl-D-aspartate receptor autoimmune encephalitis (NMDAR-AE). We aimed to evaluate the efficacy and safety of ofatumumab as a novel second-line immunotherapy for NMDAR-AE. METHODS: This prospective, multicenter, nested cohort study compared patients with NMDAR-AE from the CHina Autoimmune encephalitiS outcomE study registry (CHASE) recruited between October 2011 and February 2024, treated with and without ofatumumab. The primary outcome was the proportion reaching a favorable functional outcome (modified Rankin Scale [mRS] score ≤2) at the last follow-up. Secondary outcomes included mRS scores and Clinical Assessment Scale in Autoimmune Encephalitis (CASE) scores over the first 24-month follow-up and the proportion with further mRS score improvement after ofatumumab initiation. A propensity score matching was performed to balance major confounders. RESULTS: A total of 715 patients with AE were screened. Fifty-eight propensity score-matched patients with NMDAR-AE each in the ofatumumab group and non-ofatumumab group were analyzed. Fifty-four patients (93.1%) in the ofatumumab group achieved further mRS score improvement with a median time of 14 days from ofatumumab initiation, and 53 (91.4%) reached a favorable functional outcome at the last follow-up. For those who failed first-line immunotherapy, the ofatumumab group demonstrated a faster mRS score and CASE score improvement and more frequently reached a favorable functional outcome at the last follow-up compared with the non-ofatumumab group (87.9% vs. 64.7%, odds ratio [OR] 3.95
95% confidence interval [CI] 1.12-13.94
p = 0.026). No serious adverse events associated with ofatumumab treatment were reported. INTERPRETATION: Ofatumumab showed substantial efficacy and safety, particularly in patients who failed first-line immunotherapy, warranting its consideration in NMDAR-AE management. ANN NEUROL 2025.