CD4+ T Cells Open a Path Toward Curing Hepatitis B

A clinical puzzle that has lingered for 15 years may finally have an answer. European physicians had observed that when some patients with chronic hepatitis B went off their medications, the virus rebounded and then disappeared, as though the immune system had been provoked into action. A UC San Francisco team has now identified the cells behind that response—and what they found could reshape how the disease is treated.

The study, published in Science Translational Medicine, pinpoints a population of CD4+ T cells in the liver that detect the rebounding virus and mobilize an attack. Without them, the infection persists.

"It's taken us many years to explain why some of our patients are able to beat hepatitis B," said Jody Baron, co-senior author of the paper. "We think this could lead to much better treatments based on the liver's natural biology."

Hepatitis B infects hundreds of millions of people globally and kills more than a million each year. It is usually passed from mother to child at birth, and infections acquired that early tend to become chronic because the immune system has not yet mounted an effective response. Adults newly exposed to the virus are far more likely to clear it on their own.

"When treatment stops in a structured way, about a third of patients can mount the right immune response and clear the virus—something we almost never see during treatment," said Stewart Cooper, co-senior author of the paper. "But that observation didn't lead to change for most patients."

To pin down the mechanism, the team engineered mice to produce the hepatitis B virus or its proteins while lacking immune cells from birth, then transplanted fresh immune cells. In adult mice, CD4+ T cells quickly recognized the viral proteins and raised an alarm; in young mice, the same cells stayed silent.

Blood samples from treated patients confirmed the pattern. Those who cleared the virus showed activated CD4+ cells in the liver as the virus replicated, while those who failed to clear it did not. The result challenges the long-standing emphasis on CD8+ killer T cells and suggests therapies could be designed to activate CD4+ cells as patients come off antivirals.

"Seeing the same immune patterns in both the mouse model and in patients gives us confidence we're capturing something real about how this disease works," said Gabriela Fragiadakis, co-senior author.