Immunological factors are assumed to be determinants for some psychiatric disorders, thus anti-inflammatory drugs may be helpful. However, studies on such treatments are scarce. An inflammatory modulating drug rituximab, cluster of differentiation antigen 20 antibodies (anti-CD20 antibodies), is a standard treatment for e.g. multiple sclerosis.

The investigators aim to test rituximab in a randomised placebo-controlled double-blinded, add-on treatment trial in 120 participants (18-55 years) with schizophrenia spectrum disorder. Sampling from blood for analyses of inflammatory mediators are investigated at gene and protein levels and resting state functional magnetic resonance imaging (rsfMRI) and lumbar puncture are optional. Biomarkers will be investigated in relation to treatment response.

Family member(s) to the patient and the patient (separate) will be asked to participate in a qualitative interview by an independent researcher after 3 months.

Immunological factors are assumed to be determinants for some psychiatric disorders, thus anti-inflammatory drugs may be helpful. However, studies on such treatments are scarce. Rituximab (anti-CD20 antibodies), a standard treatment for multiple sclerosis in Sweden, is an inflammatory modulating drug. In a small open pilot trial, markedly ill, treatment-resistant participants with schizophrenia spectrum disorder were treated with a single- dose rituximab (1000 mg), as add-on treatment to antipsychotics in Örebro, Sweden (2019-2022). Large improvements in all types of psychotic symptoms were evident, with long-lasting effects and few side-effects in most of the participants.

This is a proof-of-concept study based on our earlier findings. The investigators will conduct a multicenter, placebo-controlled, double-blinded, add-on intervention study for 120 participants with schizophrenia spectrum disorder (18-55 years). Sampling from blood for analyses of inflammatory mediators are investigated at gene and protein levels and rsfMRI and lumbar puncture are optional at baseline and endpoints. Biomarkers will be investigated in relation to treatment response.

Participants are assessed at five time-points; week 0, 2, 7, 12 (endpoint I) and 24 (endpoint II).

Research questions:

I Does the addition of rituximab to standard psychiatric treatment improve psychotic symptoms in SSD?

II Does overall disability improve with the addition of rituximab?

III Are clinical or biological markers related to treatment response?

IV Is rituximab safe and well tolerated by participants with SSD?

V Is rituximab effective for treatment resistant SSD?

In addition family member(s) to the patient will be asked to participate in a qualitative interview by a researcher after 3 months on changes in the patient's mood and anxiety level, general functioning, behaviours, energy level, psychotic symptoms, motivation, emotional reciprocity and insight to enable a qualitative analysis. We will also ask them about their general thoughts on the study. In addition we will interview the patient after 3 months using qualitative methods.

We also aim study changes in negative symptoms with the Motivation and pleasure- self report (MAP-SR) in addition to the Positive and Negative Syndrome Scale (PANSS) scale and Self-evaluation of Negative Symptoms (SNS). Childhood onset neuropsychiatric symptoms will be investigated retrospectively by the use of Five-to-Fifteen Brief (FTF-Brief), filled out by a family member.

All PIs are trained in the PANSS interview and interrater agreement will be analysed across the 30 PANSS items. At endpoint all PIs are requested to blindly guess which treatment they believe each patient has received in the study (prior to breaking the codes). In addition, a blinded psychologist who performs qualitative interviews with patients and caregivers assess improvement according to CGI-I by dividing the participants into three groups: Group 1, very much or much improved; Group 2, minimally improved, and Group 3, no change or deteriorated. Correlations between the PI´s CGI-I assessment and the psychologist´s assessments at Endpoint I will be performed. Patients and caregivers are also requested to guess what treatment they have received in the study.

A revision of the original study protocol, version 3.1, was approved by the Ethical committee, Stockholm, Sweden on the 30th of August 2023 and by the Swedish Medical Product Agency on the 8th of August 2023 and published in BMC Psychiatry on October 23, 2023. A revision of the protocol (version 3.2) was approved by the Medical Products Agency (MPA) on February 8, 2024, and by the Swedish Ethical Review Authority on April 3, 2024. The revision included the following changes:

1. The five-part differential hematology analysis was removed from endpoint assessments because lymphocyte counts could potentially compromise study blinding. The erythrocyte sedimentation rate was also removed on clinical grounds, while neutrophil counts, plasma protein fractioning, hemoglobin, and thrombocyte counts were added to endpoint assessments.
2. Additional questions regarding treatment resistance were incorporated into the background interview to investigate potential improvement among therapy-resistant cases.
3. The Positive, Negative, and General Psychopathology subscales of the Positive and Negative Syndrome Scale (PANSS) were analyzed separately, in addition to the total PANSS score at both endpoints, and the subscales were added as secondary outcomes.
4. The voluntary lumbar puncture, the Magnetic Resonance Imaging examination (MRI), and biobank sampling were removed from Endpoint II for practical reasons.
5. The informant-rated Five to Fifteen Brief Assessment Scale was moved from Endpoint I to baseline for practical reasons.
6. Body weight was measured again at 12 weeks to monitor weight changes.
7. Endpoint assessments could be conducted by other qualified clinicians, such as psychologists, in place of physicians.
8. Additional secondary endpoint: Improvement at week 12 and 24, corresponding to the Clinical Global Impression-Improvement scale (CGI-I) of 1 or 2 among participants defined as having treatment resistant SSD.
9. Additional secondary endpoint: Improvement in the three PANSS subscales and in the PANSS Marder negative factor at week 12 and 24.

On August 27, 2024, the sponsor/Principal PI requested approval from the MPA to submit a protocol modification concerning the primary outcome measure. The proposed alteration was to replace the previous secondary outcome, "proportion of responders to treatment", defined as patients rated as much or very much improved on the CGI-I, as the primary outcome. The former primary outcome, change in psychotic symptoms measured by PANSS, was moved to the list of secondary outcomes. The assessment time frame for both measures and the informed consent form remained unchanged. This second request was submitted prior the first interim analysis (i.e. after 32 participants had reached Endpoint I) performed by the independent Data Monitoring Committee.

Protocol version 4.1 was submitted on September 28, 2024, and the proposal was forwarded to the Ethical Review Authority. Additional information requested by the authorities was provided on November 11, 2024, and a formal response was submitted on November 13, 2024. No negative opinion was issued by the Ethical Review Authority. Protocol version 4.1 received final approval by MPA on December 11, 2024.

Inclusion Criteria:

1. ages 18 to 55 years
2. duration of illness exceeding 1 year
3. diagnosed with Schizophrenia spectrum disorder (SSD) according to The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5).
4. if female and with any risk for pregnancy, willing to use contraceptives or abstinence if normal and preferred lifestyle.
5. participants should be judged by the investigator to be lucid and oriented to person, place, time, and situation when giving the informed consent.
6. insufficiently recovered from previous antipsychotic treatments.
7. a minimum score of 4 (moderately ill) in Clinical global impression - severity (CGI-S) at baseline.

Exclusion Criteria:

1. pregnancy or breast-feeding
2. weight below 40 kg
3. clinically relevant ongoing infection at the discretion of the physician
4. chronic infections
5. positive test for hepatitis B, hepatitis C, HIV, or tuberculosis
6. malignancy currently or within 2 years prior to inclusion
7. current severe heart failure (NYHA grade IV) or any other severe heart disease (e.g. or history of cardiac arrhythmia or myocardial infarction)
8. any change of antipsychotic medication within the previous 4 weeks
9. unable to make an informed decision to consent to the trial
10. ongoing clozapine treatment
11. ongoing immunomodulatory treatment
12. treatments with monoclonal antibodies within 1 year before the inclusion

informant, psychologist, laboratory staff