Plant-derived polysaccharides activate dendritic cell-based anti-cancer immunity

Today, cancers pose a major public health burden. Although a myriad of cancer treatments are available, only a few have achieved clinical efficacy. This is partly attributed to cancers capability to evade host immunity by converting dendritic cells (DCs) from potent stimulators to negative modulators of immunity. Dendritic cell-based immunotherapy attempts to resolve this problem by manipulating the functional characteristics of DCs. Plant-derived polysaccharides (PDPs) can stimulate the maturation of DCs conferring on them the capacity to present internalised tumorigenic antigens to naïve T cells and subsequently priming T cells to eliminate tumours. PDPs have been used as immune modulators and later as anti-cancer agents by Traditional Chinese Medicine practitioners for centuries. They are abundant in nature and form a large group of heterogeneous though structurally related macromolecules that exhibit diverse immunological properties. They can induce antigen pulsed DCs to acquire functional characteristics in vitro which can subsequently be re-introduced into cancer patients. They can also be used as adjuvants in DC-based vaccines or independently for their intrinsic anti-tumour activities. Clinically, some in vitro generated DCs have been shown to be both safe and immunogenic although their clinical application is limited in part by unsatisfactory functional maturation as well as impaired migration to draining lymph nodes where T cells reside. We review the relative potencies of individual PDPs to induce both phenotypic and functional maturation in DCs, their relative abilities to activate anti-cancer immunity, the possible mechanisms by which they act and also the challenges surrounding their clinical application.