DNA vaccination strategies for anti-tumour effective gene therapy protocols

Abstract

After more than 15 years of experimentation, DNA vaccines have become a promising perspective for tumour diseases, and animal models are widely used to study the biological features of human cancer progression and to test the efficacy of vaccination protocols. In recent years, immunisation with naked plasmid DNA encoding tumour-associated antigens or tumour-specific antigens has revealed a number of advantages: antigen-specific DNA vaccination stimulates both cellular and humoral immune responses; multiple or multi-gene vectors encoding several antigens/determinants and immune-modulatory molecules can be delivered as single administration; DNA vaccination does not induce autoimmune disease in normal animals; DNA vaccines based on plasmid vectors can be produced and tested rapidly and economically. However, DNA vaccines have shown low immunogenicity when tested in human clinical trials, and compared with traditional vaccines, they induce weak immune responses. Therefore, the improvement of vaccine efficacy has become a critical goal in the development of effective DNA vaccination protocols for anti-tumour therapy. Several strategies are taken into account for improving the DNA vaccination efficacy, such as antigen optimisation, use of adjuvants and delivery systems like electroporation, co-expression of cytokines and co-stimulatory molecules in the same vector, different vaccination protocols. In this review we discuss how the combination of these approaches may contribute to the development of more effective DNA vaccination protocols for the therapy of lymphoma in a mouse model.

Fig. 1

Schematic description of DNA vaccines used for therapeutic experiments. pRC110-NTS backbone structure and minigene DNA vaccines used in prime/boost vaccination protocols. pRC115C DNA vaccine encodes V_L and V_H optimised epitopes. pRC114C DNA vaccine encodes a peptide from TTFrC (aa 933–1126) fused to V_L–V_H epitopes. pRC2111 DNA vaccine encodes secreted fusion protein (T-helper-V_L-AAA-V_H optimised) and non secreted V_L-AAA-V_H optimised peptide. pRC2110 DNA vaccine encodes secreted fusion protein (T-helper-V_L-AAA-V_H optimised). pRC2100 DNA vaccine encodes secreted T-helper peptides derived from TTFrC: modified “pGINGKA” (aa 916–932) (pGIN); TT_947–967 (p30); TT_1064–1079 (p21) and TT_1084–1099 (p23)

Fig. 2

Schedule vaccination protocol 1 and therapeutic effects. Protocol 1: Mice (n = 8) received 2 × 10³ 38C13 tumour cells i.p. on day 0. On days 1 ad 11, mice were injected i.m. with 50 μl/30 μl of DNA vaccines in both posterior limbs. All DNA vaccines were administered in combination with EP (175 V/cm, 10 impulses, 20 ms) using a BTX ECM 830 Pulse Generator (Harvard Apparatus). b Mice were vaccinated with empty vector pRC110-NTS, pRC115C and pRC114C DNA vaccines. Un-immunised mice were used as control group. c Tumour-bearing mice were vaccinated with DNA vaccines in a homologous (pRC114C/pRC114C; pRC115C/pRC115C) and heterologous (pRC114C/VL and VH peptides) prime/boost vaccination regimens

Fig. 3

Schedule vaccination protocol 2 and therapeutic effects. a Protocol 2: mice (n = 8) received 2 × 10³ 38C13 tumour cells i.p. on day 0. On days 4 and 10 mice were injected i.m. with 50 μl/30 μl of DNA vaccines in each posterior limbs. Vaccines were administered alone or in combination with EP. b Mice were vaccinated with empty vector pRC110-NTS, pRC115C and pRC114C DNA vaccines. Un-immunised mice were used as control group. c Tumour-bearing mice were injected i.m. with DNA vaccines: pRC2111, pRC2110, pRC2100 and pRC114C