CpG Oligodeoxynucleotides and Interleukin-12 Improve the Efficacy of Mycobacterium bovis BCG Vaccination in Mice Challenged with M. tuberculosis

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is the only vaccine approved for prevention of tuberculosis. It has been postulated that serial passage of BCG over the years may have resulted in attenuation of its effectiveness. Because interleukin-12 (IL-12) and oligodeoxynucleotides (ODN) containing cytidine phosphate guanosine (CpG) motifs have been shown to enhance Th1 responses in vivo, they were chosen as adjuvants to increase the effectiveness of BCG vaccination. In this report, mice were vaccinated with BCG with or without IL-12 or CpG ODN and then challenged 6 weeks later via the aerosol route with the Erdman strain of M. tuberculosis. Mice vaccinated with BCG alone showed a 1- to 2-log reduction in bacterial load compared with control mice that did not receive any vaccination prior to M. tuberculosis challenge. Moreover, the bacterial loads of mice vaccinated with BCG plus IL-12 or CpG ODN were a further two- to fivefold lower than those of mice vaccinated with BCG alone. As an immune correlate, the antigen-specific production IFN-γ and mRNA expression in spleen cells prior to challenge were evaluated. Mice vaccinated with BCG plus IL-12 or CpG ODN showed enhanced production of IFN-γ compared with mice vaccinated with BCG alone. Finally, granulomas in BCG-vaccinated mice were smaller and more lymphocyte rich than those in unvaccinated mice; however, the addition of IL-12 or CpG ODN to BCG vaccination did not alter granuloma formation or result in added pulmonary damage. These observations support a role for immune adjuvants given with BCG vaccination to enhance its biologic efficacy.

牛分枝杆菌卡介苗（BCG）是目前唯一获批用于预防结核病的疫苗。有研究推测，长期以来的传代培养可能导致其防护效力出现衰减。已有研究表明，携带胞嘧啶-磷酸-鸟嘌呤（CpG）基序的寡脱氧核苷酸（ODN）与白细胞介素12（IL-12）可在体内增强Th1型免疫应答，因此二者被选作佐剂以提升BCG疫苗的防护效果。本研究中，研究者对小鼠接种BCG，同时联合或不联合IL-12或CpG ODN，并于6周后通过气溶胶途径以结核分枝杆菌Erdman菌株进行攻毒。与未接种任何疫苗的结核分枝杆菌攻毒对照组小鼠相比，仅接种BCG的小鼠其肺部细菌载量降低了1~2个对数级。此外，联合IL-12或CpG ODN的BCG免疫组小鼠的细菌载量，较仅接种BCG组进一步降低了2~5倍。作为免疫相关性指标，本研究评估了攻毒前脾细胞中抗原特异性干扰素γ（IFN-γ）的产生水平与信使RNA（mRNA）表达情况。相较于仅接种BCG的小鼠，联合IL-12或CpG ODN的免疫组小鼠的IFN-γ产生水平显著升高。最后，相较于未免疫小鼠，BCG免疫小鼠的肉芽肿体积更小且淋巴细胞浸润更丰富；但在BCG疫苗中添加IL-12或CpG ODN并未改变肉芽肿的形成过程，也未加剧肺部损伤。上述研究结果证实，在BCG疫苗接种中联合免疫佐剂可有效提升其生物学防护效力。