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Peptide-loaded exosomes are promising cancer treatment vehicles; however, moderate T cell responses in human clinical trials indicate a need to further understand exosome-induced immunity. We previously demonstrated that antigen-loaded exosomes carry whole protein antigens and require B cells for inducing antigen-specific T cells. Therefore, we investigated the relative importance of exosomal major histocompatibility complex (MHC) class I for the induction of antigen-specific T cell responses and tumour protection. We show that ovalbumin-loaded dendritic cell-derived exosomes from MHCI-/- mice induce antigen-specific T cells at the same magnitude as wild type exosomes. Furthermore, exosomes lacking MHC class I, as well as exosomes with both MHC class I and II mismatch, induced tumour infiltrating T cells and increased overall survival to the same extent as syngeneic exosomes in B16 melanoma. In conclusion, T cell responses are independent of exosomal MHC/peptide complexes if whole antigen is present. This establishes the prospective of using impersonalised exosomes, and will greatly increase the feasibility of designing exosome-based vaccines or therapeutic approaches in humans., Competing Interests: S.G. has a patent on B-cell exosomes for immune therapy, US patent no. US 8932855 B2.

Exosomes are small 40-120 nm vesicles secreted by nearly all cells and are an important form of intercellular communication. Exosomes are abundant, stable, and highly bioavailable to tissues in vivo. Increasingly, exosomes are being recognized as potential therapeutics as they have the ability to elicit potent cellular responses in vitro and in vivo. Patient-derived exosomes have been employed as a novel cancer immunotherapy in several clinical trials, but at this point lack sufficient efficacy. Still other researchers have focused on modifying the content and function of exosomes in various ways, toward the end-goal of specialized therapeutic exosomes. Here we highlight major advances in the use of exosomes for cancer immunotherapy and exosome bioengineering followed by a discussion of focus areas for future research to generate potent therapeutic exosomes. From the Clinical Editor: Exosomes are small vesicles used by cells for intercellular communication. In this short article, the authors described the current status and the potential use of exosomes in the clinical setting., (Copyright © 2015 Elsevier Inc. All rights reserved.)

In recent years exosomes have emerged as potent stimulators of immune responses and as agents for cancer therapy. Exosomes can carry a broad variety of immunostimulatory molecules depending on the cell of origin and in vitro culture conditions. Dendritic cell-derived exosomes (dexosomes) have been shown to carry NK cell activating ligands and can be loaded with antigen to activate invariant NKT cells and to induce antigen-specific T and B cell responses. Dexosomes have been investigated as therapeutic agents against cancer in two phase I clinical trials, with a phase II clinical trial currently ongoing. Dexosomes were well tolerated but therapeutic success and immune activation were limited. Several reports suggest that multiple factors need to be considered in order to improve exosomal immunogenicity for cancer immunotherapy. These include antigen-loading strategies, exosome composition and exosomal trafficking in vivo. Hence, a better understanding of how to engineer and deliver exosomes to specific cells is crucial to generate strong immune responses and to improve the immunotherapeutic potential of exosomes., (Copyright © 2014 Elsevier Ltd. All rights reserved.)