Innate immune memory is associated with increased disease-free survival in bladder cancer patients treated with bacillus Calmette-Guérin
Introduction: While studies suggest that innate immune memory acquired by circulating monocytes may mediate the benefit of bacillus Calmette-Guérin (BCG) in the treatment of patients with high-risk non-muscle-invasive bladder cancer (NMIBC), prospective studies are lacking. Innate immune memory is defined by enhanced release of pro-inflammatory cytokines by innate immune cells following a secondary challenge with pattern recognition receptor (PRR) ligands.
Methods: Peripheral blood monocytes isolated from 33 patients with intermediate- or high-risk NMIBC before and after two or five induction BCG instillations were stimulated with the PRR ligand lipopolysaccharide (LPS). Inflammatory cytokine levels in the culture medium were measured. Extent of innate immune memory acquisition was determined by dividing the levels of cytokines released after BCG instillation by the levels released prior to BCG therapy.
Results: Monocytes secreted variable levels of TNFα, IL-1β, IL-6, IFNγ, IL-12, and IL-10. Compared with patients with recurrences, the post-BCG:pre-BCG ratio of IL-12 in monocyte cultures from patients without recurrences after five BCG instillations was significantly increased. Patients with no innate immune memory (based on IL-12 ratios) had significantly shorter times-to-recurrence than patients with innate immune memory (p<0.001). Eighty-four percent (16/19) of patients with innate immune memory vs. only 22% (2/9) of patients without memory had disease-free survival of over 500 days.
Conclusion: Results demonstrate a potential link between BCG-induced innate immune memory peripherally and local anti-tumor responses. Further validation will increase our understanding of the mode of action of BCG and, therefore, will be used to enhance its effectiveness.
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