Data from CD24<sup>hi</sup>CD27<sup>+</sup> Bregs within Metastatic Lymph Nodes Promote Multidrug Resistance in Breast Cancer

<div>AbstractPurpose:<p>Axillary lymph nodes (LN) are the primary and dominant metastatic sites in breast cancer. However, the interaction between tumor cells and immune cells within metastatic LNs (mLN) remains poorly understood. In our study, we explored the effect of CD24^hiCD27⁺ regulatory B cells (Breg) within mLNs on orchestrating drug resistance of breast cancer cells.</p>Experimental Design:<p>We collected mLN samples from patients with breast cancer who had received standard neoadjuvant therapy (NAT) and analyzed the spatial features of CD24^hiCD27⁺ Bregs through multicolor immunofluorescence staining. The effect of CD24^hiCD27⁺ Bregs on drug resistance of breast cancer cells was evaluated via <i>in vitro</i> experiments. A mouse model with mLNs was used to evaluate the strategies with blocking the interactions between Bregs and breast cancer for improving tumor regression within mLNs.</p>Results:<p>In patients with breast cancer who had received NAT, there is a close spatial correlation between activated CD24^hiCD27⁺ Bregs and residual tumor cells within mLNs. Mechanistically, CD24^hiCD27⁺ Bregs greatly enhance the acquisition of multidrug resistance and stem-like features of breast cancer cells by secreting IL6 and TNFα. More importantly, breast cancer cells further promote the activation of CD24^hiCD27⁺ Bregs via CD40L-dependent and PD-L1–dependent proximal signals, forming a positive feedback pattern. PD-L1 blockade significantly attenuates the drug resistance of breast cancer cells induced by CD24^hiCD27⁺ Bregs, and addition of anti-PD-L1 antibody to chemotherapy improves tumor cell remission in mLNs.</p>Conclusions:<p>Our study reveals the pivotal role of CD24^hiCD27⁺ Bregs in promoting drug resistance by interacting with breast cancer cells in mLNs, providing novel evidence for an improved strategy of chemoimmunotherapy combination for patients with breast cancer with mLNs.</p></div>