共表达不同水平的IL-12对于HBV DNA疫苗质粒免疫原性的影响

目的 在HBsAg DNA疫苗质粒中共表达IL-12佐剂分子,研究IL-12的表达水平对于HBV DNA疫苗质粒免疫原性的影响.方法 构建携带来源于中国地区C型HBV参照序列CHN-HBV07-C经密码子优化的preS2-S基因的DNA疫苗质粒pHBV,并将3个不同IL-12表达水平的佐剂分子表达盒序列分别克隆入该疫苗质粒中,通过瞬时转染293T细胞以检测重组质粒IL-12分子及乙肝表面抗原的表达情况.将不同IL-12表达水平的疫苗质粒免疫BALB/c雌性小鼠,IFN-γ的ELISPOT方法检测HBsAg抗原特异性的细胞免疫应答,化学发光定量ELISA法检测HBsAg特异的抗体水平.结果 成功构建3个不同IL-12表达水平的HBV DNA疫苗质粒,293T细胞转染结果显示:不携带IL-12分子表达盒的对照疫苗质粒pHBV的HBsAg表达水平可达70 ng/ml;低表达IL-12的疫苗质粒pHBV-12l的HBsAg表达水平为18 ng/ml;而高表达IL-12的重组疫苗质粒pHBV-12h的HBsAg表达水平仅为6 ng/ml.BALB/c小鼠的免疫结果表明:高表达IL-12分子的疫苗质粒pHBV-12h所诱导的细胞免疫及体液免疫水平相对于对照疫苗质粒pHBV均显著降低了.低表达IL-12分子的疫苗质粒pHBV-12l所诱导的抗体水平也显著降低了,但其细胞免疫应答水平却显著提高了.结论 在同一疫苗质粒中,高表达IL-12分子的质粒可能会影响到抗原蛋白的表达,而低表达IL-12分子的疫苗质粒却能增强细胞免疫应答.因此,平衡好佐剂分子及抗原蛋白的表达水平对于诱导高水平的免疫应答是个重要的因素.

Effects of IL-12 coexpression level on antigen expression and immune responses induced by HBsAg DNA vaccination

Objective To investigate the effects of IL-12 coexpression level on antigen expression and immune responses induced by HBsAg DNA vaccination. Methods DNA vaccine plasmid pHBV carrying codon-optimized preS2-S gene of reference sequence CHN-HBV07-C in China was constructed. Three DNA vaccine plasmids pHBV-12i, pHBV-12l and pHBV-12h were also constructed by subcloning three different IL-12 expression cassettes with various expression strengths to plasmid pHBV, respectively. Expression levels of IL-12 and HBsAg in vaccine plasmid-tranfected 293T cells were measured by quantitative ELISA. DNA vaccines were administered intramuscularly to BALB/c mice and HBsAg-specific cellular immune responses were determined by IFN-γ ELISPOT. HBsAg-specific antibodies were tested by Chemiluminescence Quantitative Immunoassay. Results The HBsAg expression level in 293T cells was 70 ng/ml when transfected by plasmid pHBV without IL-12 expression cassette, and the HBsAg level was 18 ng/ml when transfected by plasmid pHBV-12l carrying low-level IL-12 expression cassette, whereas the HBsAg level was only 6 ng/ml when transfected by plasmid pHBV-12h carrying high-level IL-12 expression cassette.Results of DNA vaccination revealed that HBsAg-specific humoral and cellular immune responses were significantly decreased in mice administering vaccine pHBV-12h carrying high-level IL-12 expression cassette. Although HBsAg-specific antibody responses in mice inoculated with pHBV-12l were also decreased when compared with those in pHBV-vaccinated mice without IL-12 expression, the HBsAg-specific cellular immune responses were significantly increased. Conclusion High-level coexpression of IL-12 may suppress the expression of HBsAg, Whereas modest coexpression of IL-12 significantly enhanced the HBsAg-specific T cell responses induced by DNA vaccination. Therefore, it is so important to balance the expression between adjuvant and antigen to enhance the immune response.