Therapeutic anti-tumor immunity triggered by injections of immunostimulating single-stranded RNA

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• Synthetic RNA oligonucleotides (ORN) and protected messenger RNA (mRNA) activate Toll-like receptors 7 and 8 (TLR7/8), acting as immunostimulatory danger signals.
• The potential of these RNA molecules to induce anti-tumor immunity when delivered directly into tumors was previously unexplored.

Purpose of the Study:

• To investigate whether local injection of RNA can trigger anti-tumor immunity against established tumors.
• To evaluate the safety and efficacy of RNA as a danger signal for active immunotherapy.

Main Methods:

• Utilized the mouse glioma cell line SMA-560 in syngenic VM/Dk mice.
• Administered protamine-stabilized mRNA via intra-tumor injections.
• Assessed tumor regression, long-term anti-tumor immunity, and immune cell infiltration (CD8).
• Compared intra-tumor injections with distant injections and naked mRNA treatments.

Main Results:

• Intra-tumor injections of protamine-stabilized mRNA induced significant tumor regression and long-term anti-tumor immunity.
• CD8 T-cell infiltration was observed in residual RNA-injected tumors.
• Both distant injections of protamine-protected mRNA and intra-tumor injections of naked mRNA also generated anti-tumor immunity.
• RNA molecules, despite being strong danger signals, have short half-lives, preventing adverse effects like splenomegaly seen with CpG DNA.

Conclusions:

• RNA molecules are effective and safe danger signals for active immunotherapy against solid tumors.
• Local RNA administration can overcome tumor defenses and establish durable anti-tumor immunity.
• RNA-based immunotherapy presents a promising strategy for eradicating established tumors with minimal side effects.