Abstract
BACKGROUND: Bacillus Calmette-Guérin (BCG) is capable of enhancing the infiltration of immune cells into the tumour. However the temporal dynamics of immune cell patterns in patients receiving BCG instillation remains unclear. METHODS: Ninety-six patients who underwent intravesical BCG therapy, comprising 46 responders and 50 non-responders, were retrospectively enroled to explore the evolving immune landscape. This study involved a detailed examination of sequential samples collected before, during, and after BCG treatment to assess BCG's influence on the immune microenvironment, employing techniques such as immunohistochemistry, fluorescent multiplex immunohistochemistry, and mass spectrometry techniques. RESULTS: Our study found that initial BCG instillation leads to enhanced immune cell infiltration, correlating with treatment efficacy, with responders exhibiting more pronounced increases. Non-responders experience a rise in immune cell infiltration and PD-L1 expression during the first instillation, which returns to baseline after treatment. In non-responders, BCG re-challenge fail to further increase immune cell infiltration into the tumour or improve patient outcomes. Strikingly, proteomics data revealed that GBP1 expression was induced by BCG treatment in non-responders. CONCLUSIONS: Our findings demonstrated the induction of tumour PD-L1 expression by BCG in non-responders, and therefore provide insights for the combination of BCG and anti-PD1/anti-PD-L1 therapy.