Abstract PO1-13-03: Tumour infiltrating double negative (CD20+CD27- IgD-) B cells in high-risk early breast cancers. Friend or Foe??
Authors: Carpenter Esme , Buckley Paul , Alaguthurai Thanussuyah , Graham Rosalind , Kakkassery Helen , Alhity Gheed , Hossain Farhana , Mukhtar Sadiyah , Irshad Sheeba 
Published: May 2024

Abstract
Background: B cells exhibit diverse phenotypes and function and the complex interplay between different B cell subsets in the context of chemotherapy treated breast cancers remains unclear. Here, we investigate the dynamic changes in the B cell immune landscape before and after NACT treatment across different breast cancer subtypes. Methods: Treatment naïve, mid-treatment and post-NACT breast tumour, matched lymph node, blood and serum samples were profiled for B cell subsets and cytokines by flow cytometry, cytometry by time-of-flight (CyTOF) and Luminex technologies. Ex vivo autologous tumour organoid and immune cells cocultures to functionally assess the B-cell interactions across breast cancer subtypes were performed. Multiplex spatial analysis method was used to explore the dynamics of double negative B cell cellular crosstalk within the tumour and axillary lymph nodes. The results are being associated with treatment outcomes. Expression and activity of purinergic ectoenzymes within B cell subsets were also assessed by flow cytometry and high-performance liquid chromatography. Current work focusses on how these findings may relate to immunotherapy response, a new paradigm shift in the treatment of triple negative breast cancer patients. Results: We observed a significant expansion in the CD20+CD27−IgD− cells, also termed as double-negative (DN) B cells, within the TME of treatment naïve and post-neoadjuvant residual tumours compared to the periphery. Specifically, DN1 (CD20+ CD27−IgD− CD21+CXCR5+) cells represented the majority of DN B cells within the treatment naïve TME and in circulation. However, NACT promotes an expansion of the DN2 (CD20+CD27−IgD−CD21-CXCR5-) subset as well as a relatively uncharacterised DN3 (CD19+IgD−CD27−CXCR5−CD11c−) cell population. Preliminary analyses on how these changes (especially the enrichment of DN2 cells) relate to treatment response show significant expansion of DN2 cells in the periphery of poor responders to NACT, coupled with significantly reduced infiltration of DN2 into resistant residual tumours. Among circulating B, T and NK cells, B cells showed the highest CD73 and CD39 surface expression at baseline, but their expression significantly drops following NACT especially within the DN2 B cell subset. These ecto-5’-nucleotidases are known to play a critical role in B and T cell interactions. Spatial analyses between these cell types is ongoing. Conclusion: We report for the first time an enrichment of DN cells in breast cancer tumour tissue, specifically the expansion of DN2 cells following neoadjuvant chemotherapy. Functional analyses of tumour-infiltrated B-cells suggest that mechanistically, these B-cell subgroups may contribute to immunosurveillance and point to an important role of purinergic signalling in early breast cancers. Our study highlights the requirement for further investigation into the role of DN B cells in the context of chemo/immunotherapy resistance in breast cancers.
Citation Format: Esme Carpenter, Paul Buckley, Thanussuyah Alaguthurai, Rosalind Graham, Helen Kakkassery, Gheed Alhity, Farhana Hossain, Sadiyah Mukhtar, Sheeba Irshad. Tumour infiltrating double negative (CD20+CD27- IgD-) B cells in high-risk early breast cancers. Friend or Foe?? [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-13-03.