History of bcg vaccine

History of BCG vaccine and its immune mechanism

1. History of BCG vaccine Presented by Chandana Dinakaran Ph.D AAH-PB0-01

2. INTRODUCTION Even in the time of SARS-CoV-2, tuberculosis (TB) is to date the leading global infectious killer due to a single pathogen (i.e., the bacterium, Mycobacterium tuberculosis ( Mtb )) One of the world’s top ten causes of death. According to the World Health Organization (WHO,2020 ), there were an estimated 10 million new cases and 1.4 million deaths due to TB in 2019. Substantial improvement in TB mortality rates, but only minimal global progress in decreasing TB incidence, have been achieved over the past 20 years . COVID-19-related disruptions in TB services are predicted to cause a significant increase in global TB morbidity and mortality in coming years

3. M. tuberculosis ( Mtb ), the intracellular pathogen that causes TB, was discovered in 1882 by Robert Koch ( Kaufmann SH et al., 2010 ). Early last century, hopes were that TB could be conquered by vaccination with the newly developed M. bovis BCG vaccine, isolated by and named after Calmette and Guerin in Lille,France . T he development of the first anti- tuberculous drugs during WWII(world war) by Selman Waksman, who discovered streptomycin bacteriostatic activity towards Mtb ( Waksman SA, 1965 ). Initially, treatment with streptomycin appeared highly efficacious, but the tide turned when drug resistance rapidly developed, an early testimony of Mtb’s ability to acquire drug resistance when treated by single antibiotics . I n the early 1990s, the World Health Organization (WHO ) declared TB a global emergency ( WHO, 1994 ). From that time onwards TB scientists, who had been focusing much of their efforts on other areas of research and development due to a lack of interest in and funding for TB, were able to reorient efforts and initiate significant activities in the study of TB ( Kaufmann SHE et al, 2007 ). The advent of Multidrug- resistant TB (MDR-TB), fueled by the HIV epidemic , were responsible for this shift of interest.

4. 2021- 100 years of BCG Vaccine In 1900 Albert Calmette and Camille Guérin began their research for an antituberculosis vaccine at the Pasteur Institute in Lille. In 1908, starting with a virulent bovine strain of tubercle bacillus supplied by Nocard originally isolated by him in 1902 from the udder of a tuberculous cow), they cultured it on their bile, glycerine and potato medium and then proceeded to subculture at roughly three weekly intervals . By 1913 they were prepared to initiate a vaccination trial in cattle which was interrupted by outbreak of World War I. By 1919, they had a tubercle bacillus which failed to produce progressive tuberculosis when injected into guinea pigs, rabbits, cattle, or horses. T hey named it Bacille Bilie Calmette -Guerin; later they omitted “ Bilie ” and so BCG was born. In 1921, the first human administration of BCG was by Benjamin Weill-Halle (1875-1958) assisted by Raymond Turpin (1895-1988) at the Charité Hospital, Paris . On 18 July 1921, Weill-Halle and Turpin gave a dose of BCG by the oral route to the infant. The oral route was chosen since Calmette considered the gastrointestinal tract to be the usual route of natural infection by the tubercle bacillus The Pasteur Institute at Lille began the mass production of BCG vaccine for use by the medical profession. From 1924 to 1928, 114 000 infants were vaccinated without serious Complications .

5. In the United States, Petroff and his colleagues at Trudeau Sanatorium reported in 1929 that in a specimen of BCG supplied by Calmette they had isolated virulent tubercle bacilli Despite these disturbing reports, Calmette and Guerin remained confident that BCG was safe, until “the Lübeck disaster” happened . The Lübeck disaster (1930 ) In this Northern German city , a scheme to vaccinate newborn babies was undertaken by Professor Deycke , director of the Lübeck General Hospital, and Dr. Alstädt , chief medical officer of the Lübeck Health Department. BCG was supplied from the Pasteur Institute, Paris, but prepared for administration in the tuberculosis laboratory in Lübeck and the oral route was used. After four to six weeks a large number of the infants developed tuberculosis. Of 250 vaccinated, there were 73 deaths in the first year and another 135 were infected but recovered. T he cause of the disaster, which they attributed to negligent contamination of the vaccine by virulent tubercle bacilli in the Lübeck laboratories.

6. The first studies on BCG By the late 1940s, several studies had appeared providing evidence for the utility of BCG in protection against tuberculosis. Tuberculosis had emerged as a major concern in the aftermath of World War II, and BCG use was encouraged, stimulated in particular by UNICEF, by the fledgling World Health Organization (WHO), and by Scandinavian Red Cross Societies. 1950s , major trials were set up by the Medical Research Council in the United Kingdom and by the Public Health Service in the United States. Soon it became evident that the procedure employed in the United Kingdom (a Copenhagen strain BCG, given to tuberculin negative 13-year-olds) was highly eficacious against tuberculosis whereas that in the United States (Tice strain, given to tuberculin negatives of various ages) provided little or no protection.

7. BCG, THE CURRENT VACCINE- AGAINST TB Phenotypic differences between these BCG vaccine strains were first recognized in the 1920s. The genetic background for the attenuation of BCG was unknown until advances in molecular biology allowed direct comparisons between the genomes of M. bovis and the various strains of BCG . It became clear that the long-term in vitro propagation had resulted in the loss of several gene segments clustered in different regions of difference (RDs) ( Behr et al. 1999 ). The efficacy of BCG was studied extensively in clinical trials during the 1930s and the vaccine was widely deployed after World War II. BCG is one of the most widely administered vaccines worldwide and has been part of the EPI since the early 1970s. However, the fact that BCG provides protection against extrapulmonary TB in childhood but not against pulmonary TB in adults suggests that the major problem with BCG is not only its efficacy per se but also waning or changed immune responses in adolescence . The existence of abundant atypical mycobacteria in environmental samples in high-endemic regions adds to the complexity by providing their own level of anti-TB immunity to the population that may mask the effect of BCG or prevent the necessary vaccine replication (the so-called blocking hypothesis)

8. The majority of the world’s population is supplied with BCG vaccine procured by UNICEF (The United Nations Children’s Fund) on behalf of the Global Alliance for Vaccines and Immunization . UNICEF uses only four BCG vaccine suppliers who produce only three different BCG vaccine strains: BCG-Denmark produced by the Statens Serum Institute in Denmark, BCG-Russia (genetically identical to BCG-Bulgaria) produced by Bulbio (BBNCIPD) in Bulgaria and by the Serum Institute in India, and BCG-Japan produced by the Japan BCG Laboratory. In 1993, the WHO declared tuberculosis a global emergency1 because of the re-emergence of the disease, and there was recognition that existing control measures, including the standard antibiotic regimens and BCG vaccination were insufficient to overcome factors such as drug resistance and HIV/AIDs which were driving the TB epidemic. Since the 1993 WHO declaration there has been progress in halting and even reversing the trend for an increase in cases and deaths, but in order to meet new WHO targets to end TB by 2035,

9. Efficacy of BCG BCG reduces the risk of disseminated tuberculosis in childhood, its efficacy in preventing pulmonary tuberculosis in adults varies widely ( Mangtani et al., 2014 ). The variation is attributed to multiple factors, including the BCG strain , dose, and route of administration; prevalence of nontuberculous mycobacteria (NTM); host genetics, microbiota , and coinfections ; and prevalence of specific M. tuberculosis lineages. Variations in outcomes notwithstanding, BCG has not been sufficiently effective to prevent the growth of global TB. One mechanism that may limit BCG efficacy is that its antigenic composition is insufficiently related to M. tuberculosis . Palmer and colleagues, that exposure to various environmental mycobacteria could itself provide some protection against tuberculosis and affect the immune system in various ways and that BCG could not improve greatly upon that background (In an effort to decide between these views, a large trial was organized in the Chingleput area of South India, starting in 1968, with assistance of the Indian Council of Medical Research, the WHO, and the U.S. Public Health Service. The plan was to compare two different BCG strains (Paris/Pasteur versus Danish), he results of the Chingleput trial were made public in 1979, and they revealed that neither vaccine imparted any protection against pulmonary tuberculosis . The most important obstacle with the current vaccine, BCG, is the lack of protection in adults, which may be related to insufficient immunological memory resulting in waning of immunity during childhood.

10. IMMUNE EFFECTOR CELLS AND MECHANISMS : WHAT SHOULD A TB VACCINE DO? Immunity against TB is cell-mediated with T lymphocytes serving as mediators and mononuclear phagocytes as effectors of protection and pathology ( Kaufmann , 2010 ). Immunity against TB is a local event focused on granulomatous lesions with solid granulomas reflecting protection and caseous granulomas mirroring disease ( Reece and Kaufmann 2012 ). Immune mechanisms involve CD4 T lymphocytes of Th1 type. These cells produce interferon g (IFN-g), which activates increased antimycobacterial activities in macrophages. Other T lymphocytes, notably CD8 T lymphocytes, and CD4 T cells producing interleukin (IL)-17 ( Cruz et al. 2010 ), are likely involved in protective immunity ( Ottenhoff , 2012). The Th17 cells seem to participate in the initiation of protective immunity . CD8 T cells can contribute to protection by secreting killer molecules ( comprising perforin and granulysin , which directly attack macrophages and M. tuberculosis [ Mtb ], respectively ) and by secreting IFN-g ( Stenger et al. 1998 ). Aside from IFN-g, other cytokines thought to participate in protection include tumor necrosis factor (TNF), granulocyte– monocyte colony-stimulating factor (GM-CSF), IL-1b, and the small molecule, vitamin D ( Fabri et al. 2011 ).

11. Protection and pathology are focused to granulomatous lesions, which are primarily composed of T lymphocytes, mononuclear phagocytes , dendritic cells (DCs), and B lymphocytes ( Reece and Kaufmann 2012). As long as the cellular components control each other, the lesion remains well-structured and contains Mtb successfully, even though the pathogen is not eradicated. Disturbances in the granuloma result in exaggerated cell death causing necrosis leading to liquefaction ( Reece and Kaufmann 2012 ). Activated macrophages primarily inhibit Mtb growth and rarely eradicate the pathogen fully . Growth control is achieved by a combination of reactive oxygen and nitrogen intermediates supported by lysosomal enzyme attack ( MacMicking et al. 1997 ). On the other hand, Mtb is capable of interfering with phagosome maturation ( Rohde et al. 2007 ). It arrests the phagosome at an early stage, thus prohibiting fusion with lysosomes containing antibacterial enzymes. Aside from mononuclear phagocytes, neutrophils possess potent antibacterial effector functions ( Amulic et al. 2012 ). Yet, these short-lived phagocytes also have a high intrinsic risk of causing tissue damage ( Kaufmann and Dorhoi 2013). Mtb persisting in macrophages within solid granulomas enter a stage of dormancy in which they shut down their replicative and metabolic activity. These dormant Mtb express a different gene profile and therefore different antigens that may have a role in vaccines targeting LTBI ( Andersen 2007).

12. Moreover, dormant Mtb are highly resistant to immune attack ( Gengenbacher and Kaufmann 2012 ). The dormant Mtb does not harm the host but resists its elimination. Before TB disease reactivation, Mtb undergoes resuscitation, resulting in a highly replicative and metabolically active stage, which is characteristic for active TB disease. It is clear that defined immunosuppressive mechanisms tip the balance in favor of the pathogen. Thus , HIV infection, affecting CD4 T lymphocytes, is the driving force for the current TB pandemic ( UNAIDS and WHO 2013 ); treatment of patients with chronic inflammation such as rheumatoid arthritis with LTBI causes TB reactivation( Dixon et al. 2010 ), and individuals with genetic deficiency in the IFN-g signaling pathways have a heightened risk of TB ( Bustamante et al. 2011 ). Current vaccine candidates try to mimic the immune response that prevails in LTBI (i.e., stimulation of IFN-g-producing CD4 T cells) combined with some activation of Th17 cells, and of CD8 T cells. This strategy anticipates that vaccination can induce a protective immune response in susceptible individuals prone to risk of active TB in a similar way as natural Mtb infection does in individuals with lifelong LTBI

13. HOW CAN WE TARGET TB WITH VACCINES (PRE/POST AND THERAPEUTIC ) TB vaccines can be administered at three different stages of infection/disease. ∆ Pre exposure vaccines are administered prior to infection with Mtb . The current vaccine BCG, the recombinant (r) viable vaccine candidates, and most subunit vaccines that will be used to boost BCG have been designed as pre exposure vaccines ( Frick 2013 ). The target population is infants, vaccinated soon after birth. BCG is given during the first weeks of life ∆ Post exposure vaccines target adolescents and adults with LTBI. More recent subunit vaccine candidates have been tailored for this strategy as so-called multistage vaccines by integrating latency antigens of Mtb ( Andersen 2007 ). ∆ Therapeutic vaccines target patients with active TB in adjunct to (and to shorten) chemotherapy or patients suffering from extensively or totally drug-resistant (XDR and TDR, respectively) TB ( Frick 2013 ). Killed Mycobacterium indicus pranii was originally designed as vaccine against leprosy but found to have potential effects against TB. This vaccine has been licensed in India and is currently undergoing clinical phase III testing for TB treatment ( Gupta et al. 2012a,b ).

14. Mechanisms of T Cell Evasion in TB M . tuberculosis possesses multiple mechanisms to perturb innate immunity ( Cambier et al., 2014 ). By disrupting innate responses, such as phagosome maturation ( Mehra et al., 2013 ), apoptosis ( Velmurugan et al., 2007 ), and autophagy ( Ouimet et al., 2016 ), or by inducing detrimental type I interferon secretion ( Mayer- Barber et al., 2011 ) or excessive TNF ( Roca and Ramakrishnan , 2013 ). M . tuberculosis optimizes its early survival and modulates adaptive immunity to its own advantage. Other mechanisms that act early in infection, including impaired or misregulated dendritic cell maturation ( Hanekom et al., 2003 ) and delayed priming of CD4 T cells. ( Wolf et al., 2008 ) should be bypassed by vaccination, although their characterization may shed light on mechanisms that limit T cell containment of infection early after exposure

15. Mechanisms Directed at Antigen-Presenting Cells M . tuberculosis infects professional antigen-presenting cells, the bacteria are ideally located to perturb the functions of these cells. One target is the MHC class II antigen presentation pathway (hereafter termed the MHC II pathway), which is essential for antigen activation of CD4 T cells. Initially described as sequestration of antigens produced by intramacrophage mycobacteria from human CD4 T cells ( Pancholi et al., 1993 ), multiple mechanisms contribute to reduced recognition of M. tuberculosis-infected cells by antigen-specific CD4 T cells. M . tuberculosis inhibits MHC II expression by blocking IFNg mediated induction of class II transactivator (CIITA) ( Pai et al., 2003 ), which controls genes in the MHC II pathway in mice and humans. M . tuberculosis interference with antigen presentation to CD4 T cells contributes to its persistence and imply that interference with antigen presentation contributes to evasion of vaccine-induced T cells. M. tuberculosis also modulates its gene expression to limit T cell efficacy.

16. However, recent studies provide evidence that some types of vaccines, especially live attenuated ones, also induce a long-term improvement in the anti-microbial function of innate immune cells, and this effect can also contribute to protection from reinfection. The reprogramming of the innate immune cells (e.g. myeloid and NK-cells) has been termed ‘ trained immunity’, and represents a de facto innate immune memory Induction of trained immunity has been reported to be an important component of the biological effects of BCG vaccination, which induces epigenetic and metabolic rewiring of myeloid cells though an NOD2- dependent mechanism. Moreover, recent studies have also demonstrated long-term functional and transcriptional reprogramming of myeloid cell progenitors in the bone marrow, which explains the long-term effect of BCG on circulating myeloid cells . The increase in the anti-mycobacterial function of the myeloid cells such as monocytes and macrophages has been suggested to contribute to the beneficial effects of BCG against TB . Not only myeloid cells, but also other innate immune cell populations such as NK cells undergo an increase in their function after BCG vaccination and NK-memory responses have been correlated with BCG effects in humans . It would thus be tempting to speculate that vaccines able to induce both innate and adaptive memory responses would be more efficient against TB.

17. CONCLUSION The single most valuable intervention would be a Vaccine that is effective In preventing M . Tuberculosis infection as well as disease and in aborting progression from infection to disease. Identifying the optimal vaccine and schedule, validating immunologic surrogates as trial end points, and conducting a trial to demonstrate superior efficacy relative to BCG vaccine separately and together pose a formidable challenge

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19. Scriba , T.J., Netea , M.G. and Ginsberg, A.M., 2020, December. Key recent advances in TB vaccine development and understanding of protective immune responses against Mycobacterium tuberculosis. In  Seminars in Immunology  (p. 101431). Academic Press . Andersen, P. and Kaufmann, S.H., 2014. Novel vaccination strategies against tuberculosis.  Cold Spring Harbor perspectives in medicine ,  4 (6), p.a018523 .

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