Evaluation of tumor antigen-specific antibody responses in patients with metastatic triple negative breast cancer treated with cyclophosphamide and pembrolizumab

Abstract

The role of B cells in antitumor immunity is becoming increasingly appreciated, as B cell populations have been associated with response to immune checkpoint blockade (ICB) in patients with breast cancer and murine models of breast cancer. Deeper understanding of antibody responses to tumor antigens is needed to clarify the function of B cells in determining response to immunotherapy. We evaluated tumor antigen-specific antibody responses in patients with metastatic triple negative breast cancer treated with pembrolizumab following low-dose cyclophosphamide therapy using computational linear epitope prediction and custom peptide microarrays. We found that a minority of predicted linear epitopes were associated with antibody signal, and signal was associated with both neoepitopes and self-peptides. No association was observed between signal presence and subcellular localization or RNA expression of parent proteins. Patient-specific patterns of antibody signal boostability were observed that were independent of clinical response. Intriguingly, measures of cumulative antibody signal intensity relative to immunotherapy treatment showed that the one complete responder in the trial had the greatest increase in total antibody signal, which supports a potential association between ICB-dependent antibody boosting and clinical response. The antibody boost in the complete responder was largely driven by increased levels of IgG specific to a sequence of N-terminal residues in native Epidermal Growth Factor Receptor Pathway Substrate 8 (EPS8) protein, a known oncogene in several cancer types including breast cancer. Structural protein prediction showed that the targeted epitope of EPS8 was in a region of the protein with mixed linear/helical structure, and that this region was solvent-exposed and not predicted to bind to interacting macromolecules. This study highlights the potential importance of the humoral immune response targeting neoepitopes as well as self epitopes in shaping clinical response to immunotherapy.

B cells and the coordination of immune checkpoint inhibitor response in patients with solid tumors

“…Antibodies secreted by B cells may recognize and bind neoantigens that emerge from mutations or aberrant post-transcriptional modifications. 35 Those can be found on the surface of tumor cells, in the tumor microenvironment on immunogenic cell death, or may even be targeted intracellularly by IgA. 36 Other self-peptides may also be recognized, including normal peptides overexpressed in specific cancer settings such as metalloproteinases, viral epitopes in virusassociated tumors, or peptides that underwent aberrant post-translational modifications.…”

PD-1 and PD-L1: architects of immune symphony and immunotherapy breakthroughs in cancer treatment

“…Detailed high-resolution structural analysis has shown an intricate interaction between the pembrolizumab Fv fragment and the extracellular domain of human PD-1 (71). Furthermore, while the pembrolizumab epitope aligns more with the PD-L1 binding site than with nivolumab, their respective binding sites on PD-1 exhibit minimal overlap (72). By inhibiting the PD-1 pathway, pembrolizumab enhances the immune response against cancer cells (73).…”