Induction of Potent Antigen-specific Cytotoxic T Cell Response by PLGA-nanoparticles Containing Antigen and TLR Agonist

Abstract

Previously we showed that biodegradable nanoparticles containing poly-IC or CpG oligodeoxynucleotide (ODN) together with ovalbumin (OVA) were efficient at inducing MHC-restricted presentation of OVA peptides in dendritic cells. The CTL-inducing activities of the nanoparticles were examined in the present study. Nanoparticles containing poly-IC or CpG ODN together with OVA were prepared using biodegradable polymer poly(D,L-lactic acid-co-glycolic acid), and then were opsonized with mouse IgG. The nanoparticles were injected into the tail vein of mice, and 7 days later the OVA-specific CTL activities were measured using an in vivo CTL assay. Immunization of mice with the nanoparticles containing poly-IC or CpG ODN together with OVA elicited potent OVA-specific CTL activity compared to those containing OVA only. In accordance with these results, nanoparticles containing poly-IC or CpG ODN together with OVA exerted potent antitumor activity in mice that were subcutaneously implanted with EG7.OVA tumor cells. These results show that encapsulation of poly-IC or CpG ODN together with antigen in biodegradable nanoparticles is an effective approach for the induction of potent antigen-specific CTL responses in vivo.

Keywords: Antitumor activity; CTL; CpG; Nanoparticle; PLGA; Poly-IC.

Figure 1

The CTL inducing activities of the nanoparticles. The nanoparticles containing OVA only (NP [OVA]), both OVA and poly-IC (NP [OVA+I:C], or both OVA and CpG ODN (NP[OVA+CpG]) were injected intravenously into tail veins of mice. Seven days later, an in vivo CTL assay was performed in the mice using CFSE-labeled syngeneic target cells. (A) Representative histograms of the slpeen cells of individual mice were shown. The percentages of specific killing of OVA[257-264] peptide-pulsed target cells in the spleens (B) and lymph nodes (C) were graphically represented.

Figure 2

The antitumor activities of the nanoparticles. (A) Mice were immunized with the nanoparticles containing bovine serum albumin (BSA) only (NP[BSA]), OVA only (NP[OVA]), both OVA and poly-IC (NP[OVA+I:C], or both OVA and CpG ODN (NP[OVA+CpG]), intravenously into tail veins of the mice. Seven days later, the mice were subcutaneously implanted with EG7.OVA tumor cells (5×10⁵/mouse). Two days later, the mice were again immunized with the same nanoparticles intravenously into tail veins of the mice. The tumor size was measured with a slide caliper and expressed as a tumor index, determined as the square root of (major axis×minor axis). (B) Mice were subcutaneously implanted with the tumor cells, and then mixtures of NP[OVA+I:C] and NP[OVA+CpG] were injected into the tumor mass on 10, 12 and 14 days after the tumor implantation.