Dendritic cells pulsed with RNA are potent antigen-presenting cells in vitro and in vivo.

TLDR

Immunization with defined tumor antigens is limited to a few cancers where tumor rejection antigens have been identified. The study examined whether pulsing dendritic cells with tumor‑derived RNA can induce CTL responses and tumor immunity. DCs pulsed with tumor‑derived RNA, including in vitro–synthesized OVA RNA and RNA from tumor cells, induced stronger or equivalent CTL responses compared to peptide, protected mice from tumor challenge, reduced lung metastases in a metastatic model, and demonstrated that RNA amplification from small tumor samples can sensitize DCs, supporting RNA‑pulsed DC vaccines for patients with minimal disease.

Abstract

Immunization with defined tumor antigens is currently limited to a small number of cancers where candidates for tumor rejection antigens have been identified. In this study we investigated whether pulsing dendritic cells (DC) with tumor-derived RNA is an effective way to induce CTL and tumor immunity. DC pulsed with in vitro synthesized chicken ovalbumin (OVA) RNA were more effective than OVA peptide-pulsed DC in stimulating primary, OVA-specific CTL responses in vitro. DC pulsed with unfractionated RNA (total or polyA+) from OVA-expressing tumor cells were as effective as DC pulsed with OVA peptide at stimulating CTL responses. Induction of OVA-specific CTL was abrogated when polyA+ RNA from OVA-expressing cells was treated with an OVA-specific antisense oligodeoxynucleotide and RNase H, showing that sensitization of DC was indeed mediated by OVA RNA. Mice vaccinated with DC pulsed with RNA from OVA-expressing tumor cells were protected against a challenge with OVA-expressing tumor cells. In the poorly immunogenic, highly metastatic, B16/F10.9 tumor model a dramatic reduction in lung metastases was observed in mice vaccinated with DC pulsed with tumor-derived RNA (total or polyA+, but not polyA- RNA). The finding that RNA transcribed in vitro from cDNA cloned in a bacterial plasmid was highly effective in sensitizing DC shows that amplification of the antigenic content from a small number of tumor cells is feasible, thus expanding the potential use of RNA-pulsed DC-based vaccines for patients bearing very small, possibly microscopic, tumors.