Summary: A milestone pilot randomized controlled clinical trial delivered the first targeted clinical evidence that immunotherapy could serve as a powerful new treatment paradigm for treatment-resistant depression. The study investigated whether tocilizumab, an existing anti-inflammatory drug traditionally used to treat autoimmune conditions like rheumatoid arthritis, could alleviate depressive symptoms by blocking a specific inflammatory pathway.
By filtering a 30-patient cohort down to individuals exhibiting persistent, low-grade systemic inflammation, researchers successfully bypassed the brain’s standard neurotransmitter pathways, demonstrating that immunotherapy can trigger profound clinical remission.
Key Facts
- The Serotonin Bottleneck: Standard antidepressants exclusively target brain monoamines like serotonin, norepinephrine, and dopamine. However, approximately one in three depressed individuals fail to respond to these conventional chemical treatments.
- The Inflammatory Undercurrent: About 33% of all depression patients display distinct inflammatory markers in their blood, signaling that an overactive peripheral immune system may actively drive their psychiatric symptoms.
- Targeting the IL-6 Pathway: Genetic tracking via Mendelian randomization and longitudinal cohort data previously identified interleukin 6 (IL-6), a master cytokine driving the body’s inflammatory loop, as a definitive root cause of depression rather than a mere correlation.
- Shattering Conventional Remission Rates: Despite the small proof-of-concept sample size (30 participants), a staggering 54% of patients treated with tocilizumab achieved clinical depression remission, compared to just 31% in the saltwater placebo cohort.
- Superior Treatment Efficiency (NNT): The study revealed a Number Needed to Treat (NNT) of 5 for the immunotherapy group, meaning only five patients need to be treated for one additional person to achieve full remission. This markedly outperforms first-line SSRI antidepressants, which carry an NNT of approximately 7.
- A Precision Medicine Roadmap: This clinical trial marks the first time an IL-6 receptor (IL-6R) has been leveraged as a psychiatric treatment target, using an engineered biological screening approach to select the precise patients most likely to benefit from the drug.
Source: University of Bristol
Immunotherapy could be a promising new treatment option for patients with difficult-to-treat depression.
This is a key finding from a University of Bristol-led pilot randomised controlled clinical trial, published in JAMA Psychiatry today [20 May].
Researchers investigated, for the first time, whether tocilizumab, an existing anti-inflammatory drug commonly used to treat immune conditions such as rheumatoid arthritis, could improve symptoms of depression in people who have not responded to standard antidepressant treatments.
While the pilot trial involved a small number of people (30 participants with moderate-to-severe depression), it provides early evidence that, compared with the saltwater placebo, tocilizumab may reduce depression symptoms, fatigue, anxiety and increase overall quality of life.
Current drug treatments for depression are solely based on targeting chemicals in the brain, such as serotonin, norepinephrine, and dopamine. However, around one in three people with depression do not get better with these treatments.
Recent research shows that about one-in-three people with depression have signs of inflammation in their blood, indicating that, for some, their symptoms may be linked to an overactive immune system.
Other studies point to higher levels of certain inflammatory proteins, called cytokines, in depression, including interleukin 6 (IL-6), a cytokine that plays a key role in body’s inflammatory response.
Earlier work by the team using Mendelian randomisation further supports the idea that inflammation, particularly the cytokine IL-6, may contribute to depression. This genetic technique allows researchers to identify causal factors for disease by teasing apart correlation from causation making use of the underlying genetic differences within large populations.
Studies using Mendelian randomisation, along with other study designs like longitudinal cohort studies, together provide triangulated evidence all pointing towards the IL-6 inflammation pathway as one of the key causes of depression.
Researchers wanted to see whether symptoms could improve in people with inflammation-related depression by blocking the IL-6 pathway, thus lowering inflammation levels.
To test this, they conducted a small four-week pilot randomised controlled trial of thirty people with moderate-to-severe depression who had not responded well to standard antidepressants and who showed signs of low-grade inflammation in two separate blood tests taken two weeks apart.
Participants were randomly assigned to receive either tocilizumab (14 people) or a placebo (16 people) and were followed over four weeks to record any effects.
While the results showed little statistical evidence for significant difference between two group, as expected for a small study, participants who received tocilizumab seemed to experience greater improvements over time across several measures as compared to those given a placebo, including overall depression severity, fatigue, state anxiety, and quality of life.
Furthermore, the tocilizumab group was more likely to achieve depression remission compared to placebo group (54% vs 31%), which equates to a Number Needed to Treat (NNT) of 5, meaning an additional 5 patients will need to be treated to make one patient better. For comparison, the NNT for SSRIs – the most common first-line antidepressant for patients with moderate-to-severe depression – is about 7.
Golam Khandakar, Professor of Psychiatry and Immunology from the MRC Integrative Epidemiology Unit (MRC IEU) at the University of Bristol and NIHR Biomedical Research Centre: Bristol (NIHR BRC: Bristol), and the study’s senior author and chief investigator, said: “This work represents an important milestone in the development of new treatments for depression especially difficult-to-treat depression, which affects millions of people in the UK alone.”
“This is one of the first randomised controlled trials to test immunotherapy for depression, the first to test IL-6R as the treatment target, and the first to use a targeted approach to select patients most likely to benefit, and to show that it works.”
Dr Éimear Foley, Senior Research Associate in Immunopsychiatry at Bristol’s MRC IEU and the NIHR BRC: Bristol, and the study’s lead author, added: “Depression is estimated to affect around 10-20% of people worldwide during their lifetime, yet for many patients current treatments do not work well enough.”
“Our study moves us closer to more tailored depression care, where treatments are chosen to better fit a person’s biology. This will help us to provide the right treatment to the right patients at the right time.”
One participant who took part in this study said: “I was happy to take part. Without research, advancements in medicine cannot be made.”
The next step will be to conduct a large-scale phase III randomised control trial that will provide definitive evidence to enable doctors to prescribe immunotherapy for depression.
Funding: The double-blind proof-of-concept randomised controlled trial involved a group of 30 participants recruited via the University of Cambridge and the Cambridgeshire and Peterborough NHS Foundation Trust. Participants were followed up for four weeks after treatment. The research was funded by Wellcome. The research received additional funding from the NIHR BRC: Bristol, NIHR BRC: Cambridge, and BMA Foundation J Moulton grant.
Key Questions Answered:
A: For decades, psychiatry has operated under the assumption that depression is strictly a chemical imbalance inside the brain involving serotonin or dopamine. However, this study exploits a massive biological revelation: roughly one-third of depressed individuals have an overactive, inflamed immune system. High concentrations of an inflammatory protein called interleukin 6 (IL-6) can travel through the body and actively alter brain chemistry. By using the arthritis drug tocilizumab to block the IL-6 pathway, scientists put a fire extinguisher to that peripheral inflammation, instantly relieving the brain and causing depressive symptoms to lift.
A: In a small pilot “proof-of-concept” study involving only 30 people, mathematical models are expected to fall just short of definitive statistical significance due to the low head-count. What makes this an absolute milestone is the undeniable directional data. Achieving a 54% remission rate compared to 31% for the placebo group, and netting a Number Needed to Treat (NNT) score that physically beats standard SSRIs on the market, proves the biological mechanism is highly functional. It provides the exact green light needed to launch a massive Phase III trial to clear the drug for widespread psychiatric prescription.
A: It is all about biological precision. Instead of blindly giving an anti-inflammatory drug to every depressed patient walking through the door, the Bristol team used a strict targeted approach. They explicitly screened for patients who had failed standard antidepressants and who tested positive for low-grade blood inflammation across two separate blood tests taken weeks apart. By intentionally fitting the treatment to the specific biological signature of the patient, they proved that tailored, immunopsychiatric care is the future of medicine.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this immunotherapy and psychopharmacology research news
Author: Joanne Fryer
Source: University of Bristol
Contact: Joanne Fryer – University of Bristol
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Interleukin 6 as a treatment target for depression: a proof-of-concept randomized clinical trial” by Éimear M. Foley, Nicholas Turner, Ruta Margelyte, Hannah J. Jones, Muzaffer Kaser, Glyn Lewis, Peter B. Jones, and Golam M. Khandaker. JAMA Psychiatry
DOI:10.1001/jamapsychiatry.2026.1053
Abstract
Interleukin 6 as a treatment target for depression: a proof-of-concept randomized clinical trial
Importance
Interleukin 6 (IL-6), a keystone inflammatory cytokine, is a credible mechanistic candidate for causing depression. However, randomized clinical trials testing its treatment potential remain scarce.
Objective
To identify likely treatment-sensitive outcomes and effect size for systemic IL-6 inhibition in patients with difficult-to-treat depression.
Design, Setting, and Participants
This 4-week, proof-of-concept, double-blind, parallel-arm, placebo-controlled randomized clinical trial recruited adults with moderate-to-severe International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) depression, poor antidepressant response, low-grade systemic inflammation (high-sensitivity C-reactive protein [hs-CRP] level ≥0.3 mg/dL on 2 tests), and depression somatic symptoms (Beck Depression Inventory II somatic symptoms score ≥7) from primary and secondary care and self-referral from 2018 to 2022.
Participants were randomized into minimization balanced groups on depression severity and sex. Assessments were conducted at baseline and 7, 14, and 28 days after infusion. Data were analyzed from 2023 to 2025.
Intervention
Single intravenous infusion of IL-6R antagonist tocilizumab (8 mg/kg, maximum 800 mg/patient) or normal saline.
Main Outcomes and Measures
The primary outcome was depression somatic symptoms at 14 days after infusion. The secondary outcome was total depression severity. Exploratory outcomes included fatigue, anxiety, anhedonia, quality of life, and cognition. Outcomes were assessed using validated scales and interpreted against clinically meaningful thresholds.
Results
A total of 30 participants (mean [SD] age, 41.1 [12.3] years; 24 [80.0%] female) were randomized, including 14 in the tocilizumab group and 16 in the placebo group. Of these, 29 participants received the assigned infusion and completed follow-up. As expected for a small proof-of-concept study, no results reached statistical significance, including little improvement in depression somatic symptoms at day 14 (adjusted mean difference: −0.12; 95% CI, −2.51 to 2.28).
However, a pattern of greater stepwise improvement over time was observed with tocilizumab in somatic symptoms, depression severity, fatigue, psychological symptoms, state anxiety, and quality of life, with the largest effects observed at the final follow-up (day 28). Tocilizumab may also improve more individual depressive symptoms.
Treatment effects were within ranges considered clinically meaningful for depression severity, fatigue, anxiety, and quality of life. At the final follow-up, remission (7 participants [53.9%] vs 5 participants [31.3%]; number needed to treat [NNT] = 5) and response (6 participants [46.2%] vs 3 participants [18.8%]; NNT = 4) rates favored tocilizumab compared with placebo.
Baseline hs-CRP level, but not IL-6 level, tracked depression improvement, suggesting hs-CRP may better predict immunotherapy response in depression than drug-specific biomarkers. Tocilizumab was well tolerated, with no serious adverse events or withdrawals.
Conclusions and Relevance
These findings highlight treatment-sensitive outcomes, effect sizes, and patient selection methods for testing systemic IL-6 inhibition in patients with difficult-to-treat depression, and call for a large-scale efficacy trial of anti–IL-6 treatment in depression.
Trial Registration
isrctn.org Identifier: ISRCTN16942542
