Assistant Professor University of Illinois at Urbana Champaign Urbana, Illinois, United States
Introduction: Extracellular vesicles (EVs) inherit various cellular contents and play a critical role in intercellular communication. One pivotal role of EVs is to transport molecular signals between cells, for which the processing of EVs by the recipient cell is a critical step. For example, tumor EVs can be endocytosed by antigen presenting cells (e.g., DCs), followed by the processing and presentation of the encased antigens by DCs for subsequent priming of antigen-specific T cells. Regarded as a safer source of tumor antigens than conventionally used dead tumor cells or tumor lysates, tumor EVs have demonstrated the ability to induce antitumor cytotoxic T lymphocyte (CTL) response in clinical trials. However, the resultant CTL response and therapeutic efficacy are still modest, likely due to the low abundance of tumor antigens in EVs and sub-optimal activation of DCs for the processing and presentation of EV-encased antigens. Indeed, tumor EVs alone might impair the maturation of DCs. The incorporation of adjuvants (e.g., alum) that can activate DCs has become standard practice for improving conventional vaccines. However, simple mixing with adjuvants has failed to significantly enhance the antitumor efficacy of tumor EV vaccines. These issues motivate the development of new approaches that can well integrate tumor EVs and adjuvants for optimal modulation of DCs and elicitation of CTL response.
Materials and
Methods: We envision that the ability to quantitatively conjugate and display a high number of molecules on the surface of EVs, via our metabolic tagging and targeting approach, will enable the orchestration of the interaction between EVs and the recipient cells. As EVs are endocytosed by DCs via endosomes where TLR3, TLR7, TLR8, and TLR9 are present, we hypothesize that the display of sufficient TLR3/7/8/9 agonists on EVs can timely stimulate TLRs on the surface of intracellular endosomes, resulting in the improved activation of DCs during the endocytosis of tumor EVs (Fig. 1). As a result, the processing and presentation of EV-encased antigens and the overall CTL response and antitumor efficacy can be enhanced. This ability to fine tune the interaction between EVs and antigen presenting cells holds promise to improve the therapeutic efficacy of tumor EV vaccines.
Results, Conclusions, and Discussions: Here we report a facile and universal metabolic tagging technology that can install unique chemical tags (e.g., azido groups) onto EVs. The surface chemical tags enable conjugation of molecules via efficient click chemistry, for the tracking and targeted modulation of EVs. In the context of tumor EV vaccines, we show that the conjugation of toll-like receptor 9 agonists onto EVs enables timely activation of dendritic cells and generation of superior antitumor CD8+ T cell response. These lead to 80% tumor-free survival against E.G7 lymphoma and 33% tumor-free survival against B16F10 melanoma. Our study yields a universal technology to generate chemically tagged EVs from parent cells, modulate EV-cell interactions, and develop potent EV vaccines.
