PD-1 suppresses human CD38+ circulating Tfr cells and regulates humoral immunity.

Background: Anti-programmed cell death protein 1 (anti-PD-1) antibodies have achieved revolutionary success in cancer therapy. However, the impact of anti-PD-1 therapy on host humoral immunity in humans during cancer immunotherapy requires further investigation.

Methods: We evaluated immunoglobulin titers by ELISA and screened the immune landscape of immune cells from 25 healthy donors and 50 cases including 25 new-onset hepatocellular carcinoma (HCC) patients prior to systemic treatment and 25 HCC patients undergoing anti-PD-1 therapy by multicolor flow cytometry. Flow or beads sorted cells were cultured ex vivo for proliferation and functional analysis.

Results: Anti-PD-1 therapy significantly increased the levels of IgG and IgA in the periphery of HCC patients. Anti-PD-1 treatment led to an increase in plasmablasts and a notable rise in circulating T follicular regulatory (cTfr) cells, while changes in circulating B cells, T follicular helper cells, or regulatory T cells were not significant. Anti-PD-1 therapy also influenced the proliferation and function of cTfr cells, promoting the differentiation of CD38⁺ cTfr cells. We observed that the CD38⁺ Tfr cell subset in the peripheral blood can promote plasmablast differentiation, associated with altered antibody production.

Conclusions: Together, these data demonstrate the immunomodulatory role of PD-1 in restricting the differentiation and function of human cTfr cells and in regulating humoral immunity.