When Maria tried everything for her depression — pills, therapy, more pills — nothing seemed to work. She had what doctors call treatment-resistant depression, meaning the usual treatments just fail. But a new study offers a glimmer of hope: researchers may soon be able to predict which patients like Maria will respond to faster-acting medicines like ketamine, which can lift depression within hours instead of weeks.
Scientists at The University of Texas MD Anderson Cancer Center discovered that rapid-acting antidepressants like ketamine and psilocybin (the active ingredient in magic mushrooms) work by changing how the immune system talks to the brain. Though these medicines act on different parts of the brain, they seem to flip the same biological switches — a finding that could one day help doctors know in advance who will benefit.
"Ketamine and psychedelics affect the brain in different subjective ways, but our findings suggest that they eventually end up in some of the same neuroimmune pathways," said Gregory Jones, M.D., assistant professor of psychiatry who co-led the study published in the journal Molecular Psychiatry.
The team analyzed blood and brain activity in patients with treatment-resistant depression. They found that patients who responded to ketamine had distinct immune markers even before treatment began — specifically, they had lower activity in something called the IL-15 pathway and higher B cell signaling compared to non-responders. After treatment, these patterns flipped back toward normal, suggesting that restoring balance between two immune signals called IL-7 and IL-15 might be key to how these medicines work.
"By studying blood signals and brain activity together, researchers can better understand how the body and brain may work in tandem to respond to antidepressants," Jones said. He added that the team hopes these insights will eventually help patients with depression — a condition that is especially common among people facing cancer diagnoses.
The research is still early. These findings need to be confirmed in larger studies before doctors could use immune markers to guide treatment decisions. But the discovery of shared pathways between different rapid-acting antidepressants is a significant step. If scientists can develop a simple blood test to identify who might respond to these treatments, it could spare many patients months of trial-and-error medication cycles.
Traditional antidepressants can take weeks or months to work and often fail entirely for roughly one in three depressed patients. Ketamine and psilocybin have shown promise for some of these hardest-to-treat cases, but not everyone responds, and there's currently no way to know who will benefit.
Next, the team plans to study whether IL-15, IL-7, and related biomarkers can reliably predict treatment response and whether targeting these immune pathways could make treatments work better or last longer. For the estimated 100 million people worldwide living with treatment-resistant depression, that could be a turning point worth watching.