Immunogenicity evaluation of the HIV-1 Tat containing polyepitope DNA vaccine adjuvanted with CpG-ODNs in mice

Abstract

Objectives: HIV-1 is still considered a serious threat to human health, and accessibility of a suitable and efficient vaccine is urgently needed to address the disease burden. DNA vaccines employ the cells of the vaccinated hosts for in situ production of the vaccines. This strategy is an alternative and effective approach for traditional vaccination against high-risk pathogens, e.g., HIV-1. On the other hand, polyepitope vaccines, containing several immunogenic and conserved epitopes from virus vital regulatory and structural proteins, could more efficiently induce cellular and humoral immune responses against different clades of the virus.

Materials and methods: Herein, we comparatively investigated the immunogenic potency of the HIV-1 polytope DNA vaccine containing CpG oligodeoxynucleotides (CpG-ODNs) in BALB/c mice. To this end, after verifying the expression of the recombinant sequence in the eukaryotic HEK 293 cell line, it was amplified and extracted in the prokaryotic host cells (E. coli DH5α)) and then formulated and administered intramuscularly (IM) to the experimental mice (on days 0, 14, and 28) with and without CpG-ODNs adjuvant.

Results: Taken together, the results demonstrated that CpG-ODNs adjuvanted DNA vaccine could significantly elicit cellular and humoral immune responses in the immunized animals in comparison with the control ones (P<0.05).

Conclusion: Regarding the obtained results and also considering the advantages of polytopic and DNA vaccines, this approach might be considered a new regimen in HIV-1/AIDS vaccination.

Keywords: Cellular immunity; CpG oligodeoxynucleotides; DNA vaccine; HIV-1; Humoral immunity.

Figure 1

(a) Analysis of the extracted pcDNA3.1-HIV-1-polyepitope vector on 1% agarose gel. Lane 1, the pcDNA3.1-HIV-1- polyepitope vector that was digested by BamHI and XhoI. The 600 bp bond shows the HIV-1-polyepitope fragment; lane M, molecular size marker. (b) Western blotting of the pure recombinant protein; lane M, molecular size marker; lane 1, the pure HIV-1-polyepitope recombinant protein expressed in the eukaryotic host cell (HEK 293)

Figure 2

Examination of the humoral immunity of HIV-1 polytopic adjuvanted and non-adjuvanted DNA vaccines in mice. The test was carried out 1 week after the final administration and the titers of (a) IgG1 and (b) IgG2a were measured by an indirect ELISA method

Figure 3

Proliferation of lymphocytes in the vaccinated mice. Administration of the candidate DNA vaccines was intramuscularly performed 3 times at 2-week intervals. Spleen lymphocytes were extracted from individual mice 14 days after the third and final immunization, cultured and stimulated with the HIV-1-polyepitope protein. The subsequent proliferation responses were analyzed and represented as the stimulation index (SI) values. The data are from triplicate experiments and expressed as the mean of SI values±SD of (P<0.05)

Figure 4

Assessment of cellular responses to the candidate DNA vaccines. Production of IFN-γ in the splenocytes isolated from the animals vaccinated with the polyepitopic DNA vaccines (in the presence and absence of CpG-ODNs) was evaluated using the ELISA method (P<0.05)

Figure 5

Induction of cytotoxicity responses against the HIV-1-polyepitope DNA vaccine was evaluated by lactate dehydrogenase assay. Data was indicated by the measurement of the amount of the LDH release as a result of the specific cytolysis of the cells that present the desired epitopes. Triton X-100 cell lysate was used as a positive control (P<0.05)