Scientists have identified an important component of the immune response that helps explain why some cancer patients respond well to immunotherapy while others do not.

A study published in Nature Medicine found that antibody-producing immune cells known as IgG1 plasma cells play a key role in how effectively patients respond to PD-1 checkpoint inhibitor immunotherapy — one of the most important modern strategies in cancer treatment.

PD-1 checkpoint inhibitors help the immune system recognize and attack tumors and have become a cornerstone therapy for many types of cancer. However, not all patients experience lasting benefits, and until now the precise mechanisms determining treatment response were not fully understood.

It was previously believed that PD-1 therapy worked mainly through T lymphocytes, but the new research shows that IgG1 plasma cells — cells that produce specific antibodies — also play a significant role by coordinating a more effective and tumor-specific immune response.

In the study, researchers analyzed tumor and blood samples from 38 liver cancer patients who received PD-1 therapy before surgery. Patients were considered responders if more than half of their tumor tissue was destroyed by the treatment. Those who responded well had significantly higher numbers of IgG1 plasma cells in their tumors and lymph nodes, and these cells showed clonal expansion — a sign of an active response to specific tumor targets.

The authors suggest that these antibody-producing plasma cells could serve as biomarkers for predicting response to immunotherapy, and that modulating their activity may help improve treatment effectiveness for a larger number of patients.