LAUSR

Tumor-derived microparticles activate a lysosomal pathway enabling dendritic cell upregulation of costimulatory molecules and presentation of tumor antigens to CD+ T cells. Elucidation of this molecular pathway has clinical implications for the development of improved cancer vaccines. Tumor cell–derived microparticles (T-MP) contain tumor antigen profiles as well as innate signals, endowing them with vaccine potential; however, the precise mechanism by which DCs present T-MP antigens to T cells remains unclear. Here, we show that T-MPs activate a lysosomal pathway that is required for DCs presenting tumor antigens of T-MPs. DCs endocytose T-MPs to lysosomes, where T-MPs increase lysosomal pH from 5.0 to a peak of 8.5 via NOX2-catalyzed reactive oxygen species (ROS) production. This increased pH, coupled with T-MP–driven lysosomal centripetal migration, promotes the formation of MHC class I–tumor antigen peptide complexes. Concurrently, endocytosis of T-MPs results in the upregulation of CD80 and CD86. T-MP–increased ROS activate lysosomal Ca2+ channel Mcoln2, leading to Ca2+ release. Released Ca2+ activates transcription factor EB (TFEB), a lysosomal master regulator that directly binds to CD80 and CD86 promoters, promoting gene expression. These findings elucidate a pathway through which DCs efficiently present tumor antigen from T-MPs to CD8+ T cells, potentiating T-MPs as a novel tumor cell–free vaccine with clinical applications. Cancer Immunol Res; 6(9); 1057–68. ©2018 AACR.