Vaccine adjuvant AS01 induces trained immunity and slows tumor growth in mice

A vaccine adjuvant best known for boosting the effectiveness of licensed vaccines may do more than sharpen immune memory against pathogens. A new study published in the journal Myeloid Cells reports that AS01, an adjuvant system used in approved vaccines, can induce trained immunity in human monocytes and slow tumor growth in selected mouse cancer models. The findings, described by the authors as preclinical, point to a possible new role for an established immunological tool in cancer research, while stopping well short of any claim of therapeutic benefit for patients.

Trained immunity refers to a form of long-term functional reprogramming of innate immune cells, the body’s first-line defenders such as monocytes and macrophages. In the study, researchers exposed human monocytes to AS01 and then challenged the cells with lipopolysaccharide, a potent bacterial molecule. The AS01-trained cells produced increased amounts of inflammatory cytokines, including IL-6 and TNF, after restimulation, suggesting that the adjuvant had enhanced their innate immune responsiveness.

Encouraged by these cellular results, the researchers turned to animal models. They tested AS01 in mouse models of melanoma, bladder cancer, and lung carcinoma. The treatment reduced tumor growth in the B16-F10 melanoma and MB49 bladder cancer models, but no comparable effect was observed in the Lewis lung carcinoma model. This split outcome is an important detail: it indicates that AS01’s antitumor activity is model-dependent rather than universal, a pattern the authors themselves highlight as a key question for future work.

The experimental design was detailed in the published figures. In the melanoma model, C57BL/6 mice were injected with B16-F10 cells and then treated intramuscularly with either phosphate buffered saline or AS01 at specified days relative to tumor injection. Mice received either two doses of PBS or one or two doses of 10 or 20 micrograms of AS01 at days 0 and 4 after tumor cell injection, with tumor volumes monitored for 16 days. Group sizes ranged from seven to ten mice per treatment arm. In the bladder cancer model, only the double injection schedule at the higher 20-microgram dose was used, with tumor volumes followed for 13 days and excised tumors weighed at the endpoint.

In the responsive models, AS01 treatment was associated with measurable changes in the tumor immune microenvironment. At the same time, the proportion of tumor-associated macrophages declined.

“These findings suggest that AS01 can induce a trained immunity phenotype and may have potential as a strategy to modulate antitumor immune responses,” the authors report. The study also emphasizes the need for further research to clarify the mechanisms involved, to determine why responses differ across tumor models, and to evaluate whether the approach could eventually inform cancer immunotherapy development. The authors are careful to frame the work as hypothesis-generating rather than as a demonstration of a new treatment.

The mechanistic link between trained immunity and the observed antitumor effects remains to be fully established. How this formulation drives the reprogramming seen in human monocytes, and whether that same program underlies the altered tumor microenvironment in mice, are questions the authors flag for future investigation.

The limitations of the work are clearly stated. The authors emphasize that the findings are preclinical and should not be interpreted as evidence of therapeutic efficacy in patients. Further studies will be required before any clinical application can be considered.

The study, titled “AS01 adjuvant is a trained immunity inducer with potent antitumor activity,” was published on 21 August 2026 with DOI 10.70401/mc.2026.0011. The other authors declared no competing interests.

Whether trained immunity can be safely and effectively harnessed against cancer in humans remains an open question, one that will require mechanistic dissection, additional preclinical models, and eventually careful clinical testing before the promise seen in these mouse experiments can be assessed in patients.

Subject of Research: Trained immunity induction by the AS01 vaccine adjuvant and its antitumor effects in preclinical mouse cancer models

Article Title: Study finds AS01 adjuvant can induce trained immunity and slow tumor growth in mouse models

Article References: Study finds AS01 adjuvant can induce trained immunity and slow tumor growth in mouse models. Original publication (Bibliographic details unavailable.)

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Keywords: AS01, trained immunity, vaccine adjuvant, innate immunity, monocytes, tumor microenvironment, melanoma, bladder cancer, CD8 T cells, preclinical study, immunotherapy, cytokines