Immunotherapy drug shows early promise as depression treatment in UK trial

An early-phase clinical trial conducted at the University of Bristol has shown that the immunotherapy drug tocilizumab produced positive results in depression patients who do not respond to conventional antidepressants. The research is being viewed as a promising finding that may open a new treatment pathway for treatment-resistant depression.

Tocilizumab is a monoclonal antibody normally used for rheumatoid arthritis and other autoimmune conditions. The drug targets a signalling molecule known as IL-6 (interleukin-6); IL-6 is a cytokine known to play a role both in inflammation and in mood regulation.

The study, led by Professor Stafford Lightman at the University of Bristol, was conducted on 120 participants with an average age of 45. All participants had tried at least two different antidepressants without success (clinically classified as 'treatment-resistant depression'). Sixty participants received tocilizumab, while 60 received placebo.

Results of the study were assessed after 12 weeks. In the tocilizumab group, 38 percent of participants experienced a significant reduction in depression symptoms (a drop of five points or more on the PHQ-9 scale). In the placebo group, that figure was 16 percent. The side-effect profile was found to be broadly acceptable.

Professor Lightman emphasised that the results are significant but require 'confirmation in much larger studies'. 'This is the first serious evidence that immunotherapy targeting IL-6 may be genuinely effective in some forms of depression. But we need Phase III trials to turn this into a clinical treatment,' he said.

A hypothesis that there could be a link between depression and inflammation has been put forward for some time. In some patients, depression is thought to be an 'immune-mediated condition', with sustained low-grade inflammation in the body reaching the brain and affecting mood systems. This study offers concrete support for that hypothesis.

One of the study's participants, who spoke to the Bristol research team without giving their name, said: 'I tried antidepressants for years and none of them worked for me. After the tocilizumab trial I started to feel normal for the first time. It's like a miracle.' Others reported mild headache and fatigue as side effects.

The cost of the drug currently sits at around £12,000 to £15,000 (approximately $14,000 to $18,000) per year. NICE (the National Institute for Health and Care Excellence) has not yet considered tocilizumab for approval as a depression treatment. By comparison, conventional antidepressants cost £8 to £30 per month in the UK.

International experts said the results are important but early. Dr Stefan Holiga of Harvard Medical School said: 'This study is a proof of concept. Clinical use will require at least two positive Phase III trials and a regulatory approval process.' The Phase III study is planned to begin in 2027.

Depression is a major public health issue affecting 280 million people worldwide. Up to an estimated 30 percent of patients do not respond adequately to existing antidepressants. Tocilizumab and similar immune-mediated treatments could offer new hope for this large patient group; however, researchers emphasised that until these results are confirmed in larger studies, patients should not switch medications on their own. Treatment decisions must always be taken with a qualified clinician.