Single-cell atlas of ovarian cancer links HLA-DR-high Tregs to platinum resistance in five patients

Researchers have published in the Journal of Ovarian Research a single-cell atlas of T and B lymphocytes in high-grade serous ovarian cancer (HGSOC), the most lethal gynaecological malignancy. They collected paired tumour and peripheral blood samples from five treatment-naïve patients and obtained 35,103 high-quality single cells: 17,667 T cells and 17,436 B cells biomedcentral.comJournal of Ovarian Researchbiomedcentral.comOpen source ↗. The cells were isolated by FACS and profiled by single-cell RNA sequencing and TCR/BCR repertoire sequencing on the 10x Genomics platform, together with flow cytometry.

The authors note that the limited response of HGSOC to immunotherapy is largely attributed to poor T cell infiltration, functional exhaustion and an incompletely characterised immune microenvironment.

Tregs and exhausted CD8 T cells in the tumour

The immune landscape was highly compartmentalised. CD4 regulatory T cells (Tregs) and CD8 exhausted T (Tex) cells were enriched in tumours, whereas naïve and memory lymphocytes predominated in blood. TCR analysis showed clonal expansion of CD8 Tex and CD4 Tregs in the tumour microenvironment; CD8 Tex expanded most and followed a differentiation trajectory from Teff/Tm precursors.

The team identified a tumour-enriched HLA-DR-high Treg subset with elevated MHC class II expression, oxidative phosphorylation and TNFR2 upregulation. This subset was associated with platinum resistance and poor survival biomedcentral.comJournal of Ovarian Researchbiomedcentral.comOpen source ↗. Cell–cell communication analysis with CellChat showed dense TNFR2- and MIF/IL16-mediated crosstalk between these Tregs and CD8 Tex cells, which immunohistochemistry (IHC) and multiplex IHC (mIHC) corroborated in platinum-resistant tumours. Flow cytometry in an independent cohort of 33 patients was also used for validation.

Plasmablasts and B cell maturation

Tumours were infiltrated by plasmablasts and memory B cells. Repertoire analysis showed active somatic hypermutation and class-switch recombination to IgG and IgA, which the authors interpret as antigen-driven activation.

In CIBERSORT deconvolution of the TCGA and ICGC ovarian cancer cohorts, a high plasmablast signature was an independent favourable prognostic factor and was associated with an immunologically active tumour microenvironment. mIHC showed fewer plasmablasts in platinum-resistant tumours.

The authors conclude that an HLA-DR-high Treg–TNFR2 axis drives CD8 T cell exhaustion and platinum resistance, while a plasmablast signature is linked to a favourable prognosis. They state that the findings have implications for patient stratification and for the development of combination immunotherapies in HGSOC biomedcentral.comJournal of Ovarian Researchbiomedcentral.comOpen source ↗. The discovery cohort comprised five patients.