An Asparagus polysaccharide fraction inhibits MDSCs by inducing apoptosis through toll‐like receptor 4

Despite decades of research, malignant tumors are extremely difficult to eliminate with conventional methods. Although surgical resection potentially eradicates the problem, only a few cases are suitable for operation, and other approaches often involve harmful consequences. Revolutionary methods are desperately needed to improve patient outcomes and diminish harmful side effects. Myeloid-derived suppressor cells (MDSCs), downregulators of the innate and adaptive immune systems, have been widely studied over the past 2 decades. MDSCs inhibit the antitumor immune response by suppressing T cell proliferation, cytokine production, and tumor cell killing. With MDSCs becoming novel targets in cancer therapy, our research has focused on the anti-MDSC function of Asparagus polysaccharide (AP), extracted from asparagus, a traditional Chinese herb. In this study, we have used MDSCs isolated from the spleen of mice with colon cancer as an in vitro model to assess the efficacy of AP. Treatment of MDSCs with AP significantly decreased cell proliferation and induced apoptotic cell death through a toll-like receptor 4 dependent way. Subsequent studies showed that the AP treatment enhanced the expression of Bax and Caspase-9 and inhibited the expression of Bcl-2, suggesting that AP induced apoptosis in the MDSCs via the intrinsic pathway. Altogether, the results showed that AP exhibited a significant anti-MDSC activity and attenuated suppression of the antitumor immune response, thereby indicating its potential use in cancer therapy.