FLT3 Ligand Enhances the Cancer Therapeutic Potency of Naked RNA Vaccines

Abstract

Intranodal immunization with antigen-encoding naked RNA may offer a simple and safe approach to induce antitumor immunity. RNA taken up by nodal dendritic cells (DC) coactivates toll-like receptor (TLR) signaling that will prime and expand antigen-specific T cells. In this study, we show that RNA vaccination can be optimized by coadministration of the DC-activating Fms-like tyrosine kinase 3 (FLT3) ligand as an effective adjuvant. Systemic administration of FLT3 ligand prior to immunization enhanced priming and expansion of antigen-specific CD8 þ T cells in lymphoid organs, T-cell homing into melanoma tumors, and therapeutic activity of the intranodal RNA. Unexpectedly, plasmacytoid DCs (pDC) were found to be essential for the adjuvant effect of FLT3 ligand and they were systemically expanded together with conventional DCs after treatment. In response to FLT3 ligand, pDCs maintained an immature phenotype, internalized RNA, and presented the RNAencoded antigen for efficient induction of antigen-specific CD8 þ T-cell responses. Coadministration of FLT3ligand with RNA vaccination achieved remarkable cure rates and survival of mice with advanced melanoma. Our findings show how to improve the simple and safe strategy offered by RNA vaccines for cancer immunotherapy.

Preclinical Evaluation of TriMix and Antigen mRNA-Based Antitumor Therapy

“…To increase the number of DCs that can be recovered from the injected lymph node for analysis, we pretreated the mice with a hydrodynamic injection of a plasmid encoding Flt3 ligand. In analogy with the data described by Kreiter and colleagues (30), FLuc mRNA injected into these mice resulted in increased luminescence reflecting the specific uptake by the DCs (data not shown). Flow cytometry showed that DCs (CD11c þ ) from lymph nodes coinjected with TriMix displayed the highest expression of CD40, CD80, and CD86 than DCs isolated from lymph nodes injected with FLuc mRNA alone or combined with LPS (Fig.…”

“…It was recently implied that an adjuvant should be chosen on the basis of complementarity of its mode of action with that of the vaccine format it will be combined with (30). In that regard, the efficacy of mRNA administered into lymph nodes depends on its uptake and its ability to create a CTL inducing milieu.…”

mTOR Inhibition Improves Antitumor Effects of Vaccination with Antigen-Encoding RNA

“…When tumor-bearing mice were immunized with this RNA vaccine, potent antitumor immunity was elicited, resulting in significant survival benefit (5). We improved the potency of this vaccine platform several logs by molecularly modifying the RNA backbone; our current strategy is to identify synergistic immunomodulatory compounds for combination therapy (10). As CD8 þ T memory cells are critical for efficient and sustained immunity against cancer, compounds capable of tuning vaccine-induced memory response are of particular interest.…”

Parenteral Vaccine Administration: Tried and True

“…The arrows indicate were the injection was made: directly into the right lymph node or subcutaneously 10 cm above the contralateral left lymph node. This fi gure is reprinted, with minor modifi cations, with kind permission from Springer (Kündig et al 2012 ) enhanced the effi cacy of plasmid DNA (pDNA) vaccination in mice (Heinzerling et al 2006 ;Maloy et al 2001 ) as well as RNA vaccination (Kreiter et al 2010(Kreiter et al , 2011. By changing the route of pDNA delivery from subcutaneous, intradermal or the most abundantly used intramuscularly route of administration to the intralymphatic route, the dose of pDNA necessary to stimulate cytotoxic T-cell responses could be reduced by several orders of magnitude, e.g.…”