FP11 Circulating immunoregulatory B- and T-cell profiles in patients with melanoma modulated with checkpoint inhibitor immunotherapy
Lucy Booth, Zena Willsmore, Katie Stoker, Gabriel Osborn, Rebecca Adams, Silvia Crescioli, Yin Wu, Jenny Geh, Thomas Tull, Sophia Tsoka, Sophia KaragiannisAbstract
Introduction and aims
We conducted deep immunophenotyping of circulating B- and T-cell repertoires of patients with melanoma at baseline and longitudinally during checkpoint inhibitor (CPI) immunotherapy to assess phenotypic changes and to identify predictive biomarkers of response.
Methods
A 45-marker mass cytometry panel was utilized to profile circulating adaptive immune features in patients and healthy participants. Paired pretreatment and on-treatment blood samples assessed CPI-induced shifts in B- and T-cell phenotypes, and baseline signatures were used as predictive biomarkers.
Results
Circulating IL-10+ plasmablasts, double negative (DN), CD21lo B-cell frequencies, and downregulation of key B-cell activation markers (CD21, CXCR5, IL2, CD38) are enriched on B cells from patients with melanoma compared with healthy participants. We observed higher abundance of activated cytotoxic and exhausted (CD8+ PD-1+) and DN (CD4−CD8−) T cells, and higher FoxP3 and transforming growth factor (TGF)β expression by T cells in melanoma. In a patient cohort who received anti-PD1 monotherapy or in combination with anti-LAG3 or anti-CTLA4, we observed a proportional increase in total B-cell frequency, and reduction in memory B cells. We also found expanded activated naïve (CD21hi) B cells and rapidly responding plasmablasts alongside higher expression of B-cell activation markers (CD21, IgD, IgM, CD38, HLA-DR) on the overall B-cell population, suggesting a de novo B-cell response to treatment. Similarly, the T-cell phenotype is altered on treatment favouring activated cytotoxic, immunosuppressive (CD8+ TGFβ+ VEGF+) and exhausted (CD8+ PD-1+) T cells, resting central memory (CD4+) T cells and increased expression of activation markers (CD38, HLA-DR and CD28) by T cells. Baseline enrichment of transitional B cells and plasmablasts, alongside resting CD8+, regulatory (CD4+FoxP3+) and immunosuppressive (VEGF+TGFβ+) T cells were associated with reduced overall survival.
Conclusions
We report distinct immunosuppressive B- and T-cell signatures in the circulation of patients with melanoma that directly correlate with reduced patient prognosis. Alongside enriched levels of stimulated T cells, we report a de novo B-cell response in patients receiving CPI.