Abstract
Introduction: In the scenario of immunomodulation by regulatory T cells (Tregs), studies show that the increase in Bifidobacterium probiotics, in addition to colonizing the intestine, alters the intestinal microbiota, activating Treg cells, which produces anti-tumor effects. Objective: This was to establish, through a systematic review study, the main clinical studies that show the positive effects of probiotics and nutrients in stimulating regulatory T cells in cancer patients, to enable immunotherapy for the control, reduction, or even elimination of cancer cells. Methods: The systematic review rules of the PRISMA Platform were followed. The search was carried out from April to May 2025 in the Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: 141 articles were found. A total of 40 articles were fully assessed and 31 were included and developed in the present systematic review study. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 26 studies with a high risk of bias and 24 studies that did not meet GRADE and AMSTAR-2. Most studies showed homogeneity in their results, with X2=67.8%>50%. It was concluded that probiotics, together with intestinal microbiota, have been increasingly proposed to improve immune checkpoint blockade treatments against cancer by activating Treg cells. Oral administration of butyrate, propionate, and acetate, individually or in combination, led to an increase in the number of Treg cells in the colon. Also, all-trans retinoic acid (atRA), a bioactive form of vitamin A, stimulates Treg cells in the human intestine.