Early immune cell shifts on checkpoint inhibitors tied to melanoma survival

Clinical takeaway: This work points to early on-treatment immune dynamics, including B cell activity, as a potential candidate worth watching. It points to the potential for blood tests that predict response to checkpoint inhibitors.

Scans set the rhythm of evaluating the efficacy of checkpoint inhibitor therapy. They arrive every two to three months, but until they do a clinician has little to work with beyond tolerability. About half of patients will not benefit, and the drugs cost a great deal in both money and immune-related risk while the question remains open.

What might help close the gap sooner is already being drawn at every visit. Circulating lymphocytes reflect whether the immune system has actually reengaged the tumor. Most of that attention has gone to T cells, the arm checkpoint blockade directly releases, leaving humoral immunity, the antibody-producing B cell side, mostly unexamined. A new profiling study looked at both arms together, before and during treatment, and asked which changes tracked with how patients did.

The first six to eight weeks split patients two ways. In some, the mature B cells that make antibodies grew in number, and those patients went longer without their cancer progressing. In others, immature B cells grew instead, and those patients did worse on both progression and survival. T cells moved with them: when active tumor-killing T cells expanded early, patients lived longer. The two shifted in tandem, which is the study's real claim; that response is the whole adaptive system reengaging rather than T cells acting alone.

Patients who already had large numbers of immature or suppressive immune cells in circulation before their first dose did worse, as though the immune system was too depleted or too dampened to respond once the brakes came off. Side effects tracked something else entirely. PD-1, the very protein these drugs block, was more abundant on T cells before treatment in the 13 patients who went on to develop immune-related side effects, and less so in the 11 who did not.

The study followed 24 patients with stage II-IV cutaneous melanoma at a single UK center, against 25 healthy volunteers. Blood came before the first dose and twice during treatment, at six to eight weeks and 12 weeks, though the sample thinned to 18 and then 12. Most received anti-PD-1 alone. Mass cytometry sorted circulating B and T cells into subsets, so specific populations could be tracked rather than the compartment as a whole. Median follow-up was about 21 months.

The next goal is validation in a larger cohort and extension to other tumors with limited options, triple-negative breast cancer among them. Researchers also plan to look at B and T cells inside tumors rather than only in the blood.

"B cells have emerged as critical contributors to survival and treatment outcomes in melanoma. In-depth studies of these cells may provide important insights to help address the current clinical challenges in melanoma treatment. Studying immune cells from patient blood samples allows for a much less invasive method than biopsies," said Lucy Booth, PhD student at St John's Institute of Dermatology, King's College London.

Source: Booth L, et al. (2026 Aug 7) J Immunother Cancer. Circulating B cell and T cell activation states predict clinical outcomes in melanoma and reveal dynamic immune reinvigoration with checkpoint inhibitor immunotherapy