Research progress on the non-specific protective effect of BCG

卡介苗除了用来预防结核病以外,也可以诱导非特异性保护作用。流行病学调查结果显示,卡介苗对其他病原体感染有一定的保护作用,可以有效提高儿童的存活率,并且有些已经通过随机临床试验得到验证。作者将对相关流行病学的研究结果和这种现象形成的机制进行总结。     

卡介苗特异性和非特异性免疫效果研究进展

卡介苗是目前世界上唯一获准使用的用于预防结核病的疫苗, 目标人群为婴幼儿, 但是其保护时效是有限的。有研究证明, 再次接种卡介苗可对成人结核病起保护作用;同时, 通过训练免疫, 卡介苗还可诱导产生非特异性免疫, 对其他呼吸道疾病以及一些慢性病有积极的效果, 尤其是针对新型冠状病毒感染(COVID-19)的免疫效果。目前, COVID-19的流行还未得到有效遏制, 越来越多的研究证明卡介苗对预防COVID-19有积极效果, 是否可以将卡介苗作为预防措施值得思考。世界卫生组织以及中国相关部门并没有提出支持卡介苗复种的相应政策, 随着卡介苗的免疫作用越来越多的发现, 对高危人群的选择性再次接种卡介苗以及是否可以将其更广泛的应用引起了激烈讨论。本文就卡介苗的特异性免疫和非特异性免疫作用对结核及非结核疾病的研究进展作一综述。     

卡介苗在控制结核病中的作用

自从1921年第一个儿童接种卡介苗以来,已经过去了六十多个年头,在此期间,对卡介苗的作用曾几经争议。最近的一次是1979年南印度的研究报告,该报告认为“接种后的头七年半里卡介苗没有任何保护力”。鉴于这项研究是世界卫生组织、美国公共卫生署防病中心和印度医学研究会合作进行的,因此引起了国际防痨界的注意与震动。经五年来国际上的广泛讨论,目前对卡介苗在控制结核病上的作用、概括起来可以从两方面来认识。     

从卡介苗到核酸疫苗谈结核病的预防

目的讨论结核病的最佳预防手段。方法综述传统卡介苗和多种基因工程疫苗对结核病的保护作用和面临的问题。结果卡介苗作为一种传统的预防结核病的疫苗，在学术界其保护作用有争议，研发新的结核病疫苗已经成为趋势。结论基因工程疫苗将是下一个安全、有效、有可能代替卡介苗的结核病疫苗。     

结核病与卡介苗接种

卡介苗免疫接种程序 1977年卡介苗纳入WHO扩大免疫规划(EPI)。在结核感染危险性高的国家和地区，为防止儿童结核病的发生及减少死亡，对新生儿早期接种卡介苗可起到保护作用。     

卡介苗的理论和方法学两个方面的情况综述——从Calmette和Guérin的发现到分子生物学

卡介苗自从1921年以来用于预防结核病,60年代以来又用于肿瘤的免疫刺激。预防性和免疫刺激性两种作用都曾有人对之作出评价并加以报道,但却得出互相矛盾的正反两方面结论。为了客观地评价并解释卡介苗保护作用的功效、有效性和效率,必须考虑以下事实:(1)一些从事生产的实验室业已开发了数种卡介苗次代株,它们的残余毒力各不相同,而后者对免疫原性和反应原性起着决定作用;(2)用了各种液体的和冷冻干燥的卡介苗生产方法,结果使一次剂量所含卡介苗活菌单位各异(3)定量的生物测定方法尚未被用于本疫苗的统计学的质量控制;(4)卡介苗产品被用于各种人口统计的、流行病学的、以及社会经济的情况,其接种制度均不相同;(5)不适当的生物统计学模式常被用于效能、有效性和不良反应的分析。同样的情况也影响对卡介苗在肿瘤形成中免疫刺激作用的准确评价。重组DNA技术将会改进生产方法,并在分子水平上解释卡介苗在结核病中起到的保护作用,和在肿瘤形成中产生免疫刺激的机理。建立在概率逻辑和归纳推理基础上的高水平实验室技术和生物统计学方法,使适当实验设计的制订和实验资料与接种制度所得结果的正确分析得到保证。这些将会导致对卡介苗保护作用的评价,以减少在卡介苗问题上的意见分歧。     

卡介苗免疫小鼠T细胞亚群内穿孔素的表达及意义

卡介苗是目前许多国家批准应用于人体的惟一结核病疫苗[1-2].全世界对于卡介苗对人体抗结核保护性免疫作用各家报道差异甚大.我国是结核病高发国家,我国自卡介苗免疫接种后儿童中结核病的发病牢大幅度下降,特别是小儿结核性脑膜炎、血型播散性结核病发病明显减少,成为我国结核病控制策略中的重要武器.国内外许多学者的研究[3-8]已提示卡介苗对结核患者的免疫保护作用.为进一步明确卡介苗免疫对抗结核保护性免疫作用,进行了该项研究.     

2012年昌平区婴幼儿卡介苗补种原因分析及对策

目的了解昌平区新生儿接种卡介苗现状,探讨卡介苗未接种原因。方法分析2012年在我所卡介苗门诊进行卡介苗补种儿童的未接种原因,并进行分析。结果 2012年新生儿补种卡介苗1038例,卡介苗未接种原因依次为黄疸、早产、心脏疾病、肺炎、低体重、轻度窒息及其他原因,其中黄疸和早产是主要原因,两者占未接种原因的55.97%。结论接种卡介苗对儿童重症结核具有一定的免疫保护作用,黄疸和早产是造成卡介苗未接种的主要原因,应加强围产期保健和新生儿父母宣传教育工作,提高卡介苗接种率。     

卡介苗防痨接种——WHO 1980年651号技术报告中结论和建议部分

一、科学小组认为,印度南部Chingleput地区进行的卡介苗接种预防结核病研究的科学性是较高的。二、科学小组认为,从Chingleput地区所获得的流行资料,以及这些资料对于将来研究卡介苗接种预防结核病方面是有价值的。三、此项研究中所显示的,卡介苗接种对于预防成人开放性肺结核,没有保护作用的结果,不能在世界其他地区机械地搬用。四、这个地区的卡介苗接种缺乏保护作用,可能与当地的流行情况、环境因素以及该地区人民的免疫特性等之间的相互影响有关。     

卡介苗接种政策——WHO 1980年652号技术报告中建议部分

一、根据广泛地回顾了卡介苗接种,包括最近印度南部的研究结果之后,研究小组建议:卡介苗接种作为防痨措施,仍应继续使用。小组赞同目前的卡介苗接种政策。印度南部的研究发现,卡介苗接种对成人开放性肺结核缺乏保护作用,且和当地新近感染者的发病率很低交织在一起。这就提供了一个重要的事实,即存在着不能肯定地预先判定卡介苗接种效果的情况。因此,必须设法弄清楚可能改变卡介苗接种成效的因素。在没有取得这些新的知识之前,由于     

BCG: the challenge continues

It is widely recognized that BCG provides inconsistent and often inadequate protection against tuberculosis; however, simple estimates of efficacy fail to reflect the complexity of protection within, let alone between, populations. A decline in protection with an increase in age at vaccination has been seen in many studies. This may reflect 2 things: (i) that as people age they are exposed to a variety of mycobacterial challenges which may interfere with, or mask, the protection of BCG; and/or (ii) that the vaccine is better at protecting against primary disease than against either reactivation- or reinfection-type disease. These factors need to be taken into consideration when interpreting the results obtained with screening vaccines in animal models, as most of these models mimic acute primary-type disease. In addition, we have no evidence that the protection induced by BCG lasts for > 15 y, in any population. Recent data from South India indicate a complex interaction of age and time effects: BCG imparted consistent protection in children, but no protection for subjects > 15 y old, and may even have imparted negative protection among these older individuals. If true, these findings have important implications for efforts to develop a vaccine against adult pulmonary tuberculosis.     

Optimal models to evaluate the protective efficacy of tuberculosis vaccines.

BCG has been used widely as a vaccine to prevent tuberculosis (TB) for 80 years, yet there is still considerable controversy about its efficacy. Many experimental variables have obscured the true efficacy of BCG. The absence of appropriate animal models for the study of protective efficacy and the lack of in vitro correlates of protective immunity have impeded progress. Laboratory animal studies, which have contributed to understanding the pathogenesis, heritability of resistance and immunology of TB, have failed to identify the immunological pathways necessary for protective immunity. In recent years, cattle and deer, which are naturally susceptible to TB, have been used to study protective immunity in vaccinated animals, challenged with virulent bacteria. A deer TB infection model has been developed that can measure protection against TB infection or the development of disease. Data from this model show that, providing live BCG is administered in a short interval prime-boost protocol, significant protection against infection and disease can be obtained. Single dose vaccine provides suboptimal protection that attenuates pathology but does not prevent infection. Low dose BCG vaccine (10(4)cfu), administered in a prime-boost protocol, sufficient to prevent infection, does not cause conversion to delayed type hypersensitivity or produce unacceptable side-effects. Immune memory for protection against infection persists at optimal levels for at least 12 months post vaccination. Used optimally, BCG produces good levels of protection against TB and improved protocols or its use should be explored, before attempts are made to replace it with new-generation vaccines. It is now possible to integrate the fundamental information obtained from laboratory animals with studies of functional immune protection in target host species. Justification for the use of TB vaccines for domestic livestock under field conditions, must be underpinned by scientific evidence that they provide acceptable levels of protection long term.     

BCG as a game-changer to prevent the infection and severity of COVID-19 pandemic?

The impact of COVID-19 is changing with country wise and depend on universal immunization policies. COVID-19 badly affects countries that did not have universal immunization policies or having them only for the selective population of countries (highly prominent population) like Italy, USA, UK, Netherland, etc. Universal immunization of BCG can provide great protection against the COVID-19 infection because the BCG vaccine gives broad protection against respiratory infections. BCG vaccine induces expressions of the gene that are involved in the antiviral innate immune response against viral infections with long-term maintenance of BCG vaccine-induced cellular immunity. COVID-19 cases are reported very much less in the countries with universal BCG vaccination policies such as India, Afghanistan, Nepal, Bhutan, Bangladesh, Israel, Japan, etc. as compared to without BCG implemented countries such as the USA, Italy, Spain, Canada, UK, etc. BCG vaccine provides protection for 50–60 years of immunization, so the elderly population needs to be revaccinated with BCG. Several countries started clinical trials of the BCG vaccine for health care workers and elderly people. BCG can be uses as a prophylactic treatment until the availability of the COVID-19 vaccine.     

Vaccine protocols to optimise the protective efficacy of BCG.

SETTING: A deer model has been developed to study protection produced with BCG vaccination, against infection and the development of pathology, following experimental intratonsilar infection with virulent Mycobacterium bovis. OBJECTIVE: To determine how the dose of vaccine, the route of vaccination, the viability of the vaccine and exposure to glucocorticoids at the time of vaccination, may affect the protective efficacy of BCG vaccines. DESIGN: Deer were vaccinated with BCG and later challenged with virulent M. bovis via the tonsilar route. Protection against infection and development of disease was evaluated at necropsy six months after challenge with M. bovis, by histological examination and microbial culture. RESULTS: Significant protection against infection and disease were obtained following boosting with two low doses (5 x 10(4) cfu) or moderate doses (5 x 10(7) cfu) of live (freshly cultured and lyophilized) BCG. Inferior levels of protection were obtained with high dose (5 x 10(8) cfu) of live BCG. Similar levels of protection were found with vaccines given subcutaneously or via the tonsilar route. Killed vaccine in a mineral-oil adjuvant did not evoke protective immunity and treatment with dexamethasone prior to vaccination with live BCG ablated its efficacy. Protection against infection did not correlate with skin test delayed type hypersensitivity (DTH) or lymphocyte transformation to tuberculin. CONCLUSIONS: Two doses of live BCG gave significant protection against experimental infection and disease caused by virulent M. bovis. Single dose vaccine protected against disease but not infection. Vaccines administered at a dosage which did not evoke DTH, provided protection against tuberculosis infection and disease.     

Prior BCG vaccination improves survival of Gambian patients treated for pulmonary tuberculosis

The protection provided by BCG against pulmonary tuberculosis ranges from nil to over 90%. While BCG protects against the more serious forms of tuberculosis, it is not known whether or not it protects patients with pulmonary tuberculosis from death. In a study designed to look at the effects of immunotherapy with M. vaccae as an adjunct to chemotherapy in 285 adult Gambian patients treated for proven pulmonary tuberculosis, we examined the association between the presence or absence of a BCG scar and mortality. The data showed that subjects who had a BCG scar were significantly younger than those who did not, and were less likely to have nutritional oedema. During the course of treatment, none of the 85 patients who had a BCG scar died compared to 35 of 200 patients (17.5%) who did not (P < 0.001). In these Gambian patients with pulmonary tuberculosis, prior vaccination with BCG may have provided substantial protection against death. However, there is the possibility that this finding is the result of confounding by other factors or has arisen from bias. Researchers with similar data need to investigate this question as this association, if true, could have major implications for BCG vaccination.     

Neonatal BCG protection against tuberculosis lasts for 20 years in Brazil.

Bacille Calmette-Guérin (BCG) efficacy against pulmonary disease is highly variable; until very recently there was no evidence of protection after 10 years. In the control arm of a trial of efficacy of revaccination of schoolchildren in Brazil we found substantial protection (39%; 95%CI 9-58) of neonatal BCG against all forms of tuberculosis (TB) 15-20 years after vaccination, much longer than previously believed. This confirms recent findings from an earlier trial, and must be considered in the design of trials of new TB vaccines and in policy decisions based on assumed lack of neonatal BCG protection with time.     

Immunoprophylaxis in tuberculosis

In the Chingelput trial of immunoprophylaxis against tuberculosis, BCG vaccination did not protect against pulmonary especially bacillary tuberculosis commonly known 'adult form' of tuberculosis. The study however, did not answer the question whether BCG vaccination offers protection against 'childhood forms of tuberculosis' or not. However, notwithstanding these results, the study has generated some new ideas and has opened vast areas for future research. The results of new projects will be awaited keenly. The current situation is discussed here.     

ag85a-卡介苗重组疫苗的构建、免疫原性及抗结核作用的初步研究

目的构建结核分枝杆菌ag85a-卡介苗重组疫苗,研究其免疫原性及抗结核作用,以期获得结核病预防性或治疗性疫苗。方法通过基因工程重组技术将结核分枝杆菌保护性抗原Ag85A的编码基因与穿梭质粒载体pYUB295重组,采用电穿孔技术导入卡介苗中,应用PCR扩增、PAGE电泳鉴定重组卡介苗。通过ELISA法检测其免疫小鼠血清中特异性抗体,用MTS法分析其脾淋巴细胞增殖指数。通过观察ag85a-卡介苗重组疫苗对结核分枝杆菌感染实验动物半数死亡时间、一定时间内的死亡率、大体病变、T细胞及B细胞免疫功能等指标评价ag85a-卡介苗重组疫苗对结核分枝杆菌感染的预防效果。结果PCR扩增、限制性内切酶酶切、DNA测序鉴定、PAGE电泳表明成功地构建了ag85a基因pYUB295重组质粒,Ag85A蛋白在卡介苗中分泌表达。重组卡介苗免疫原性试验表明：ag85a-卡介苗重组疫苗免疫组小鼠有Ag85A特异性抗体产生,45天时达到最高水平。脾淋巴细胞增殖试验表明刺激指数均达2．0以上,ag85a-卡介苗重组疫苗免疫组小鼠脾淋巴细胞的刺激指数与对照组无明显区别。预防试验表明：ag85a-卡介苗重组疫苗组、卡介苗组与生理盐水对照组比都能延长结核分枝杆菌感染小鼠的半数死亡时间,降低2个月内的死亡率。结核分支杆菌攻击后2个月,处死小鼠时,小鼠脏器大体病变、脏器培养、抗体检测结果及淋巴细胞增殖实验表明：各组间无显著差别。结论正确构建了ag85a-卡介苗重组疫苗,ag85a-卡介苗重组疫苗与卡介苗对结核分枝杆菌感染的预防作用基本相同。