Immunological mechanisms may contribute to the causation of mental illness. Autoimmunity is most convincingly shown for anti-NMDA-R encephalitis and Pediatric Acute-Onset Neuropsychiatric Syndrome (PANS); disorders that overlap clinically with schizophrenia and OCD. Altered inflammatory cytokine production, glial activation and auto-antibodies have also been associated with schizophrenia and OCD. In these disorders, however, the treatment results with anti-inflammatory or immunomodulating drugs have hitherto been limited and inconsistent. Yet other targets within the immune system may still be effective and new options are warranted for treatment-resistant patients. Rituximab targets B-lymphocytes and is often used in autoimmune disorders such as rheumatoid arthritis, multiple sclerosis and anti-NMDA-R encephalitis.

We aimed to investigate whether rituximab is clinically effective, safe and tolerable as add-on therapy in markedly ill, treatment-resistant adult psychiatric patients with schizophrenia or OCD. We also wanted to identify putative mediating mechanisms in treatment responders, such as cytokine changes and functional connectivity (FC).

In an open pilot study, adults (18-39 years) with treatment-resistant schizophrenia and/or OCD were included. They received an intravenous infusion of rituximab 1000 mg, once at baseline, in addition to their regular psychiatric medication and were followed for 1 year. The main outcome measures were the Positive and Negative Syndrome Scale (PANSS) or Yale-Brown Obsessive Compulsive Scale (Y-BOCS), the Clinical Global Impression-Improvement scale (CGI-I) and the Personal and Social Performance scale (PSP). Treatment response was defined as ≥ 40 % decrease in PANSS or ≥ 35 % decrease in Y-BOCS, and much improved according to CGI-I. Resting-state fMRI was applied at baseline and after 5 months. Plasma cytokines were measured at 0, 3 and 5 months. Cognitive tests and the recently developed PsychoNeuroinflammatory Related Signs and Symptoms Inventory (PNISSI) were used to identify and measure symptoms related to neuro-inflammation and cognitive function.

Nineteen patients were treated with rituximab. 3-5 months after treatment, 6/9 patients with schizophrenia and 1/10 with OCD responded. One schizophrenia patient continues with rituximab every 6 months and has reportedly done well for almost 3 years. No severe side effects were reported apart from recurrent abdominal pain in a schizophrenia patient and one case of post-COVID-19 syndrome. Significant changes of FC were detected in responders only and correlated with PSP changes.

Aberrant B-cell activities may contribute to treatment-resistant schizophrenia and be amenable to treatment with rituximab. However, the results of this pilot study need confirmation in placebo-controlled trials.

None Declared