Specific Immune Response Induced by PML-Rarα-hIL-2 Vaccine in BALB/C Mice

Specific active immunotherapy with DNA vaccines offers the hope for a natural nontoxic alternative to eradicate minimal residual disease in cancer patients. However, little data are regarding the DNA vaccines in leukemia. Our previous study has successfully developed a vector containing PML-RARα segment fused to human Interleukin- 2 (hIL-2) gene. In the present study, we analyzed the specific immune response by immunization with the recombinant plasmid in BALB/c mice. The recombinant plasmids were injected into BALB/C mice with a total of 200 μg DNA in normal saline at 14-day intervals for three cycles. The plasmid containing the same sequence of PML-RARα segment or hIL-2 gene alone and blank plasmid served as controls. Two weeks after the final DNA boost, the transcription and expression of PML-RARα and hIL-2 in injection site were detected by RT-PCR and immunohistological methods; the specific cytotoxicity of spleen cells from the vaccinated BALB/C mice was detected by LDH release assay; interferon-γ secretion was measured by ELISA; antibodies against human PML-RARα were detected by indirect immunofluorescene analysis (flow cytometry); and T-cell receptor rearrangement excision circles (TRECs) in DNA from mice thymic cells were detected by real-time quantitative RT-PCR (TaqMan), thereby to evaluate the content of naïve T cells. After immunization, the PML-RARα/hIL-2 mRNA and protein could be identified in the injection site of PML-RARα- hIL-2 vaccinated mice. Time dependent antibody production and an increase in INF–γ could be detected in vaccinated mice serum (p<0.05). Specific cytotoxicity on NB4 cells was significantly higher than that from control groups (p=0.012). TRECs level form PML-RARα-hIL-2 vaccine group was significantly higher than that from PML-RARα, hIL-2 vaccine or control groups (p<0.05). In conclusions, the reconstructed PML-RARα plasmids might display the common feature of DNA vaccine, which can induce specific humoral and cellular immune responses in BALB/c mice in vivo and can induce the increase of naïve T cells in mice thymus, it might relate to stronger cellular immune response, it is to our knowledge, the first description on the change of naïve T cells in response to vaccine.