Background Humoral immune responses have previously been associated with improved outcomes, with B cell infiltrates able to independently predict pathologic complete response to neoadjuvant chemotherapy (NACT). B cells represent a diverse population of cells and the complex interplay between specific 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 tissue samples were dissociated into single cells, stained with two panels of B cell-specific antibodies recognising a total of 24 target proteins, and analysed by flow cytometry. In addition, PMBC before and after NACT were also profiled. B cell subsets were classified as either naïve (CD27—IgD+), class-switched memory (CD27+IgD—), unswitched memory (CD27+IgD+) or double negative (DN)(CD27—IgD—). DN B cells were further characterised into DN1 (CXCR5+CD21+) and DN2 (CXCR5—CD21—) subsets. In vitro co-cultures of breast cancer cell line spheroid and PBMC were carried out.
Results In both treatment naïve and chemotherapy treated samples, we observed a significant expansion in the DN B cell population within the tumour microenvironment (TME) compared to the periphery. DN B cells represented on average 40.96% of B cells in treatment naïve tumours vs 9.48% in PBMC (p<0.0001), and 71.80% vs 6.34% of B cells in post-NACT tumour vs PBMC samples respectively (p<0.05) (figure 1). Interestingly, in treatment naïve PBMC and tumour tissue samples, the largest proportion of the DN subset consisted of DN1 cells, 69.35% and 64.11% respectively. In contrast, following NACT, DN2 cells constituted the majority of the DN population both within the TME (86.30%) and in the periphery (50.44%) (figure 1). Although the specific functions of these B cell subsets remain unclassified, deeper phenotyping suggests DN1 cells more closely resemble the phenotype of class-switched memory cells, whilst DN2 cells are thought to have antibody-secreting properties and more closely resemble the plasmablast phenotype. scRNA sequencing of B cells pre- and post NACT is currently underway.
Conclusions To our knowledge, this work is the first to identify an expanded population of DN B cells in breast tumour tissue and highlights the requirement for further investigation into these cells to decipher their role in the context of chemotherapy treatment and resistance in breast cancer.
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