AS01 adjuvant is a trained immunity inducer with potent antitumor activity

Aims: Trained immunity, defined as long-term functional reprogramming of innate immune cells, has been implicated in the heterologous protective effects of certain vaccines against infection and cancer. AS01-adjuvanted vaccines have been suggested to provide such heterologous protective effects. We therefore aimed to investigate the capacity of AS01 to induce trained immunity and evaluated its potential as an antitumoral therapeutic.Methods: Acute cytokine production was assessed in human monocytes after AS01 stimulation. Trained immunity was subsequently evaluated by interleukin-6 (IL-6) and tumor necrosis factor (TNF) quantification following heterologous restimulation. Antitumor efficacy of AS01 was assessed in mice bearing B16-F10 melanoma, MB49 bladder cancer, or Lewis lung carcinoma by monitoring tumor growth. Immune phenotyping of B16-F10 and MB49 tumor microenvironments was determined with flow cytometry.Results: Although AS01 did not stimulate acute inflammation, it induced trained immunity, marked by increased responsiveness upon secondary stimulation in human monocytes. Treatment of mice bearing B16-F10 melanoma or MB49 bladder cancer with AS01 strongly diminished tumor growth, whereas no effect was observed in the Lewis lung carcinoma model. In these responsive models, the antitumor effects of AS01 were associated with an altered tumor microenvironment, characterized by increased infiltration of CD8+ T cells, regulatory T cells, neutrophils, and monocytes, along with a decrease in tumor-associated macrophages. AS01 also decreased expression of immune checkpoint protein PD-L1 in monocytes and neutrophils, suggesting enhanced antitumor immune responsiveness.Conclusion: Our findings show the capacity of AS01 to induce trained immunity and support its potential to be repurposed as an immunotherapeutic approach for cancer.