Prostate Cancer Immunotherapy by Targeting Dendritic Cells In Vivo Using Receptor-Specific Aptamer Conjugated to Prostate Stem Cell Antigen (PSCA)- Encoding RNA

摘要

Dendritic cells (DCs), recognized as major antigen presenting cells, are uniquely equipped to initiate and regulate immune responses, making them a key target for developing new therapies. Although ex vivo DC therapy has shown promise, it is a customized, complex, patient-specific cell therapy that reduces its universal applicability for cancer. Directly targeting antigens to DCs in vivo will facilitate the development of an off-the-shelf tumor vaccine that circumvents the need for ex vivo DC loading. DCs express a number of specialized endocytic receptors of the C-type lectin family enabling capture of antigen by receptor-mediated endocytosis at very low concentrations. To deliver antigens to DCs in vivo, we developed artificial receptor ligands to the macrophage mannose receptor (MMR or CD206), an endocytic C-type lectin receptor expressed on DCs and macrophages. An RNA aptamer library comprised of 40 randomized nucleotides and modified with 2 Fluoro-modified pyrimidines for improved nuclease resistance was selected for affinity binding to MMR. A complex selection scheme with alternating rounds on both, recombinant human and murine MMR, as well as on cells engineered to express human MMR enabled us to identify cross-reactive aptamers that recognize MMR with high affinity. A truncated, minimal version of the identified aptamer with retained receptor- binding properties gets rapidly internalized into human monocyte-derived DCs in vitro.