ࡱ > ) , $ % & ' ( l bjbjAA >n + + : : : : : N N N 8 \ \ N vJ > " " # # # # $ $ !H #H #H #H #H #H #H $ 2L N ~ GH : $ # # $ $ GH : : # # 0J i/ i/ i/ $ : # : # =7 i/ $ !H i/ i/ i/ # Z ) i/ )7 FJ 0 vJ i/ bO * bO i/ bO : i/ i/ $ $ $ GH GH - J $ $ $ vJ $ $ $ $ bO $ $ $ $ $ $ $ $ $ : Developing Whole Mycobacteria Cell Vaccines for Tuberculosis: Workshop Proceedings
Max Planck Institute for Infection Biology
Berlin, Germany
July 9, 2014
AUTHOR:
Whole Mycobacteria Cell Vaccines for Tuberculosis Summary Group*
ABSTRACT
On July 9, 2014, Aeras and the Max Planck Institute for Infection Biology convened a workshop entitled Whole Mycobacteria Cell TB Vaccines at the Max Planck Institute for Infection Biology on the grounds of the Charit Hospital in Berlin, Germany, close to the laboratory where, in 1882, Robert Koch first identified Mycobacterium tuberculosis (Mtb) as the pathogen responsible for tuberculosis (TB). The purpose of the meeting was to discuss progress in the development of TB vaccines based on whole mycobacteria cells. Live whole cell TB vaccines discussed at this meeting were derived from Mtb itself, from Bacille Calmette-Gurin (BCG), the only licensed vaccine against TB, which was genetically modified to reduce pathogenicity and increase immunogenicity, or from commensal nontuberculous mycobacteria. Inactivated whole cell TB and non-tuberculous mycobacterial vaccines, intended as immunotherapy or as safer immunization alternatives for HIV+ individuals, also were discussed. Workshop participants agreed that TB vaccine development is significantly hampered by imperfect animal models, unknown immune correlates of protection and the absence of a human challenge model. Although a more effective TB vaccine is needed to replace or enhance the limited effectiveness of BCG in all age groups, members of the workshop concurred that an effective vaccine would have the greatest impact on TB control when administered to adolescents and adults, and that use of whole mycobacteria cells as TB vaccine candidates merits greater support, particularly given the limited understanding of the specific Mtb antigens necessary to generate an immune response capable of preventing Mtb infection and/or disease.
KEYWORDS
Tuberculosis vaccine; Mycobacterium tuberculosis; BCG; live, attenuated vaccine; whole cell killed vaccine
INTRODUCTION
Dr. Stefan H.E. Kaufmann, Managing Director, Max Planck Institute for Infection Biology and Professor of Immunology and Microbiology, Charit Clinics, Berlin, Germany.
The development of an effective vaccination to prevent the spread of tuberculosis (TB) represents an important global health priority. It is estimated that one third of the worlds population is infected with Mycobacterium tuberculosis (Mtb). In 2013, approximately 9 million persons developed active TB, and approximately 1.5 million died of the disease ADDIN EN.CITE WHO201419241[1]192411924127WHOGlobal Tuberculosis Report 20142014WHO[1]. In 2014, the WHO set a goal of reducing incidence of active TB from the current level of greater than 100 cases per 100,000 persons to 10 cases per 100,000 persons by 2035, and reducing mortality by 95% ADDIN EN.CITE WHO201419241[1]192411924127WHOGlobal Tuberculosis Report 20142014WHO[1]. Models of disease reduction strategies suggest that current TB control strategies will not be sufficient to reach this goal unless a vaccine capable of preventing TB infection and/or disease becomes available ADDIN EN.CITE ADDIN EN.CITE.DATA [2-4].
Sixteen different TB vaccine candidates are currently in clinical trials, with more in the preclinical pipeline. Most of these vaccine candidates are subunit vaccines, where selected Mtb antigens are expressed in recombinant viral vectors or are administered as protein/adjuvant combinations ADDIN EN.CITE Anderson201418671[5]186711867117Anderson, Suzanne T.Kaforou, MyrsiniBrent, Andrew J.Wright, Victoria J.Banwell, Claire M.Chagaluka, GeorgeCrampin, Amelia C.Dockrell, Hazel M.French, NeilHamilton, Melissa S.Hibberd, Martin L.Kern, FlorianLangford, Paul R.Ling, LingMlotha, RachelOttenhoff, Tom H.M.Pienaar, SandyPillay, VashiniScott, J. Anthony G.Twahir, HemedWilkinson, Robert J.Coin, Lachlan J.Heyderman, Robert S.Levin, MichaelEley, BrianDiagnosis of Childhood Tuberculosis and Host RNA Expression in AfricaNew England Journal of MedicineNew England Journal of Medicine1712-172337018201424785206http://www.nejm.org/doi/full/10.1056/NEJMoa1303657doi:10.1056/NEJMoa1303657[5]. Approximately 12 different antigens are expressed in the subunit vaccines currently in clinical trials. A major challenge to TB vaccine development, however, is the lack of an immune correlate of protection against Mtb infection or TB disease ADDIN EN.CITE Weiner201419239[6]192391923917Weiner, JKaufmann, SHERecent advances towards tuberculosis control: vaccines and biomarkersJournal of internal medicineJ Intern MedJournal of internal medicine467-480275520141365-2796[6]. Accordingly, there is little certainty about the actual protective effect that may be provided by at least some of the antigens currently under investigation in subunit vaccine candidates ADDIN EN.CITE Comas201016764[7]167641676417Comas, I.Chakravartti, J.Small, P. M.Galagan, J.Niemann, S.Kremer, K.Ernst, J. D.Gagneux, S.Medical Research Council, National Institute for Medical Research, London, UK.Human T cell epitopes of Mycobacterium tuberculosis are evolutionarily hyperconservedNat Genet498-5034262010/05/25Antigens, Bacterial/geneticsConserved SequenceEpitopes, T-LymphocyteEvolution, MolecularGenome, BacterialHumansMycobacterium tuberculosis/ geneticsPhylogenySequence Analysis, DNAT-Lymphocytes/immunology2010Jun1546-1718 (Electronic)
1061-4036 (Linking)20495566http://www.ncbi.nlm.nih.gov/pubmed/204955662883744ng.590 [pii]
10.1038/ng.590 [doi]Nlmeng[7].
Given these concerns, whole mycobacteria cell vaccines are receiving a fresh look as an attractive TB vaccine development strategy ADDIN EN.CITE Kaufmann201219205[8]192051920517Kaufmann, Stefan HEGengenbacher, MartinRecombinant live vaccine candidates against tuberculosisCurrent opinion in biotechnologyCurrent opinion in biotechnology900-90723620120958-1669[8]. The most familiar whole cell vaccine for TB is Bacille CalmetteGurin (BCG). Working in the Institute Pasteur in Lille, France, Albert Calmette and Camille Gurin passaged a Mycobacterium bovis isolate over a period of 16 years, from 19061921, eventually developing a strain sufficiently attenuated to administer safely to humans ADDIN EN.CITE Kaufmann200519203[9, 10]192031920317Kaufmann, Stefan HEWinau, FlorianFrom bacteriology to immunology: the dualism of specificityNature immunologyNature immunology1063-10666112005Calmette19271917919179191796Calmette, AlbertGurin, CamilleBoquet, AugusteNgre, LeopoldLa vaccination prventive contre la tuberculose par le" BCG,"1927Masson et cie[9, 10]. Since its first use in 1921, BCG has become the most widely used vaccine in history, with approximately 4 billion doses administered worldwide ADDIN EN.CITE Anderson201418671[5]186711867117Anderson, Suzanne T.Kaforou, MyrsiniBrent, Andrew J.Wright, Victoria J.Banwell, Claire M.Chagaluka, GeorgeCrampin, Amelia C.Dockrell, Hazel M.French, NeilHamilton, Melissa S.Hibberd, Martin L.Kern, FlorianLangford, Paul R.Ling, LingMlotha, RachelOttenhoff, Tom H.M.Pienaar, SandyPillay, VashiniScott, J. Anthony G.Twahir, HemedWilkinson, Robert J.Coin, Lachlan J.Heyderman, Robert S.Levin, MichaelEley, BrianDiagnosis of Childhood Tuberculosis and Host RNA Expression in AfricaNew England Journal of MedicineNew England Journal of Medicine1712-172337018201424785206http://www.nejm.org/doi/full/10.1056/NEJMoa1303657doi:10.1056/NEJMoa1303657[5]. The full effectiveness of BCG vaccination, however, has yet to be accurately determined. There is consensus that BCG administered to infants shortly after birth reduces the risk of severe childhood TB, particularly TB meningitis and disseminated TB. A meta-analysis of the global effect of BCG vaccination on childhood tuberculous meningitis and military TB estimated that in 2002, about 30,000 cases of tuberculous meningitis and 11,500 cases of military TB were prevented by the 100.5 million BCG vaccinations given to infants in that year ADDIN EN.CITE Trunz200613964[11]139641396417Trunz, B. B.Fine, P.Dye, C.Infectious Disease Epidemiology Unit, London School of Hygiene and Tropical Medicine, London, UK.Effect of BCG vaccination on childhood tuberculous meningitis and miliary tuberculosis worldwide: a meta-analysis and assessment of cost-effectivenessLancetLancetLancet1173-8036795172006/04/18BCG Vaccine/*economicsChild, Preschool*Cost-Benefit AnalysisFemaleHumansInfantMaleRisk FactorsTuberculosis, Meningeal/epidemiology/mortality/*prevention & controlTuberculosis, Miliary/epidemiology/mortality/*prevention & controlWorld Health2006Apr 81474-547X (Electronic)16616560http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16616560S0140-6736(06)68507-3 [pii]
10.1016/S0140-6736(06)68507-3eng[11]. Accordingly, the WHO recommends neonatal BCG immunization in countries endemic for TB ADDIN EN.CITE ADDIN EN.CITE.DATA [11, 12]. BCG also may provide children a degree of protection against Mtb infection for a limited number of years after vaccination, although observational studies suggest that this effect is variable and likely is impacted by the latitude in which the child lives, with children in tropical latitudes exhibiting less protection from subsequent childhood infection, possibly due to a higher rate of exposure to other non-tuberculous mycobacteria ADDIN EN.CITE ADDIN EN.CITE.DATA [13, 14].
Despite its widespread use, BCG vaccination has important limitations. Recent studies in BCG-immunized pediatric populations estimates total incident childhood cases of all forms of TB in 2011 to be almost 1 million, twice that estimated by WHO, and provides an initial assessment of multidrug-resistant (MDR) TB cases at over 30,000 ADDIN EN.CITE ADDIN EN.CITE.DATA [15]. In addition, BCG is not recommended for use in HIV-infected infants because of the risk of disseminated BCG disease ADDIN EN.CITE Hesseling200719197[16]191971919717Hesseling, Anneke CMarais, Ben JGie, Robert PSchaaf, H SimonFine, Paul EMGodfrey-Faussett, PeterBeyers, NuldaThe risk of disseminated Bacille Calmette-Guerin (BCG) disease in HIV-infected childrenVaccineVaccine14-1825120070264-410X[16]. Most importantly, the ongoing global epidemic of TB infection, disease and death among adolescents and adults is occurring in populations in which infant BCG vaccination is nearly universal. Accordingly, developing a more effective whole cell vaccine than BCG represents an important goal of global TB control efforts.
The July 9, 2014 whole mycobacteria cell TB vaccine workshop, convened in the shadow of the laboratory of Robert Koch, discoverer of the Mtb bacillus more than 130 years previously, specifically examined the potential role of whole mycobacterial cells as vaccines to prevent infection and/or disease due to Mtb. The workshop was divided into three sessions: (1) the research and development status of seven whole cell TB vaccines; (2) development pathways for whole mycobacteria cell vaccines, focusing on the rationale for and public health implications of developing replacement BCG vaccines for infants and for using whole cell vaccines to prevent Mtb infection and disease in adolescents and adults; and (3) resource needs for developing whole cell TB vaccines, with a focus on the identification of standardized assays for vaccine immunogenicity and efficacy to permit reliable vaccine candidate comparisons. A summary of the whole mycobacteria cell vaccines for TB discussed in this workshop can be found in Table 1.
SESSION 1: STATUS OF ONGOING WHOLE MYCOBACTERIA CELL VACCINE RESEARCH AND DEVELOPMENT
BCG + ESAT-6 Recombinants. Dr. Roland Brosch, Institut Pasteur, Unit for Integrated Mycobacterial Pathogenomics, Paris, France
Dr. Roland Brosch described efforts by his laboratory to improve the BCG vaccine. Theorizing that BCG may be lacking some important genetic features to provide effective protection against Mtb, Dr. Brosch proposed that vaccine immunogenicity and efficacy may be improved by adding back a gene cluster to BCG that was lost during the BCG passaging and attenuation process. All BCG vaccines lack the RD1 locus, the region of difference 1 ADDIN EN.CITE ADDIN EN.CITE.DATA [17, 18]. The RD1 locus encodes at least 11 genes, including the immunodominant T-cell antigens ESAT-6 (6-kD early secretory antigenic target) and CFP-10 (10-kD culture filtrate protein), both representing important mycobacterial antigens secreted by the ESX-1 type VII secretion system, representing potential Mtb virulence factors. Restoration of the entire RD-1 locus to BCG is required for ESAT-6 secretion and partially restores virulence ADDIN EN.CITE ADDIN EN.CITE.DATA [18]. When the recombinant BCG, BCG::ESX-1, was compared to the parental BCG for immunogenicity and protection against an Mtb challenge ADDIN EN.CITE ADDIN EN.CITE.DATA [19], it was shown to be more virulent in immune deficient mice, more persistent in immune competent mice, but also more effective in protecting against disseminated TB in both mice and guinea pigs ADDIN EN.CITE ADDIN EN.CITE.DATA [18, 19]).
As a possible explanation for the increased virulence in severe combined immune deficient (SCID) mice and the improved protective vaccine efficacy of the recombinant strain, it was found that ESAT-6 may disrupt lipid bilayers ADDIN EN.CITE ADDIN EN.CITE.DATA [20, 21], thereby providing a mechanism for ESX-1 proficient tubercle bacilli to egress from the macrophage phagosome to the cytoplasm ADDIN EN.CITE ADDIN EN.CITE.DATA [22, 23]. The effect of ESAT-6 on the fate of macrophage-phagocytized BCG also was studied with the fluorescent substrate, CCF-4. BCG is unable to progress from the phagosome to the cytoplasm, while BCG::ESX-1 moves to the cytoplasm with Mtb kinetics. Phagosomal rupture is followed by necrotic cell death of infected macrophages, resulting in BCG::ESX-1spread to new host cells. Access to the cytosol by the recombinant BCG::ESX-1 allows additional immunological responses and higher amounts of antigen, in part also explaining the stronger CD8+ T-cell responses observed for Mtb relative to BCG ADDIN EN.CITE Ryan200917124[24]171241712417Ryan, A. A.Nambiar, J. K.Wozniak, T. M.Roediger, B.Shklovskaya, E.Britton, W. J.Fazekas de St Groth, B.Triccas, J. A.Microbial Pathogenesis and Immunity Group, Discipline of Infectious Diseases.Antigen load governs the differential priming of CD8 T cells in response to the bacille Calmette Guerin vaccine or Mycobacterium tuberculosis infectionJ ImmunolJ Immunol7172-7182112009/05/21AnimalsAntigen PresentationAntigens, Bacterial/immunologyBCG Vaccine/ immunologyCD8-Positive T-Lymphocytes/ immunologyLymph Nodes/microbiologyLymphocyte ActivationMiceMycobacterium tuberculosis/ immunology2009Jun 11550-6606 (Electronic)
0022-1767 (Linking)19454714http://www.ncbi.nlm.nih.gov/pubmed/19454714182/11/7172 [pii]
10.4049/jimmunol.0801694 [doi]Nlmeng[24].
A series of recombinant, ESX-1 proficient BCG constructs were developed that retain ESX-1 function but reduce the virulence. Mutation of ESAT-6 leads to less virulent recombinant BCG vaccines that express and secrete modified ESAT-6 antigens which proved to provide better protection in mouse models and to be somewhat more protective in a guinea pig model than the parental BCG Pasteur strain (Bottai and Brosch, unpublished results). The use of different BCG strains as a template for ESX-1 complementation, such as BCG Moreau, also is being explored. Finally, attempts also are being made to use the recombinant BCG::ESX-1 Mar, created using the ESX-1 system from Mycobacterium marinum, a biosafety class 2 organism, to complement BCG strains. Preliminary results for this approach are promising (Groschel and Brosch, unpublished results). Dr. Brosch concluded his presentation by emphasizing that the ESX-1 locus encodes genes critical for mycobacterial host pathogen interaction, and that inclusion of this locus in recombinant BCG vaccines is expected to enhance the immune response to the vaccine on multiple levels which seem all to be impacted by the ability of the vaccine to gain access to the host cytosol ADDIN EN.CITE Majlessi201519212[25]192121921217Majlessi, L.Prados-Rosales, R.Casadevall, A.Brosch, R.Institut Pasteur, Unit for Integrated Mycobacterial Pathogenomics, Paris, France.Release of mycobacterial antigensImmunol RevImmunological reviewsImmunological reviews25-4526412015/02/24EsxMycobacterium tuberculosisPe/ppeantigenssecretionvesicles2015Mar0105-28962570355010.1111/imr.12251NLMeng[25].
VPM1002. Dr. Leander Grode, Vakzine Projekt Management GmbH, Hannover, Germany. Dr. Umesh Shaligram, Serum Institute of India Ltd., Pune , India
Dr. Leander Grode and Dr. Umesh Shaligram jointly discussed progress in scaling up production of the vaccine candidate VPM1002, and shared the results of Phase 1 and Phase 2 clinical trials. VPM1002 employs the pore-forming protein listeriolysin O (Hly) from the facultative anaerobic bacterium Listeria monocytogenes, coupled with a urease C gene deletion in a BCG Prague genetic background, to allow antigen to escape from the phagosome into the cytoplasm of the infected cell ADDIN EN.CITE Grode200519192[26]191921919217Grode, LeanderSeiler, PeterBaumann, SvenHess, JrgenBrinkmann, VolkerEddine, Ali NasserMann, PeggyGoosmann, ChristianBandermann, SilkeSmith, DebbieIncreased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis bacille Calmette-Guerin mutants that secrete listeriolysinJournal of Clinical InvestigationJournal of Clinical Investigation247211592005[26]. The BCG bacteria, however, remain in the phagosome ADDIN EN.CITE Grode200519192[26]191921919217Grode, LeanderSeiler, PeterBaumann, SvenHess, JrgenBrinkmann, VolkerEddine, Ali NasserMann, PeggyGoosmann, ChristianBandermann, SilkeSmith, DebbieIncreased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis bacille Calmette-Guerin mutants that secrete listeriolysinJournal of Clinical InvestigationJournal of Clinical Investigation247211592005[26]. Acidic pH is optimal for Hly activity; deletion of the urease C gene prevents BCG neutralization of the naturally acidic phagosome environment ADDIN EN.CITE Kaufmann201419206[27]192061920617Kaufmann, S. H.Cotton, M. F.Eisele, B.Gengenbacher, M.Grode, L.Hesseling, A. C.Walzl, G.Department of Immunology, Max Planck Institute for Infection Biology, Berlin, Germany.The BCG replacement vaccine VPM1002: from drawing board to clinical trialExpert Rev VaccinesExpert review of vaccinesExpert Rev VaccinesExpert review of vaccinesExpert Rev VaccinesExpert review of vaccines619-301352014/04/08AnimalsBCG Vaccine/*administration & dosageClinical Trials as Topic/*trendsHumansMycobacterium tuberculosis/*drug effects/physiologyTuberculosis/epidemiology/*prevention & control2014May1476-05842470248610.1586/14760584.2014.905746NLMeng[27]. A safety feature of this vaccine is the four amino acid PEST sequence (P, proline; E, glutamic acid; S, serine; T, threonine) which targets the Hly protein for rapid degradation in the cytosol ADDIN EN.CITE Rechsteiner199619224[28, 29]192241922417Rechsteiner, MartinRogers, Scott WPEST sequences and regulation by proteolysisTrends in biochemical sciencesTrends in biochemical sciences267-27121719960968-0004Decatur200019183191831918317Decatur, Amy LPortnoy, Daniel AA PEST-like sequence in listeriolysin O essential for Listeria monocytogenes pathogenicityScienceScience992-995290549320000036-8075[28, 29]. Following entry into the cytosol, the Hly protein is rapidly inactivated, thereby reducing the possibility of adverse events due to the pore-forming bioactivity of this protein. Antigen access to the cytosol is presumed to allow for a broader activation of immune mechanisms and improved vaccine efficacy ADDIN EN.CITE ADDIN EN.CITE.DATA [30-33].
VPM1002 initially was created in the laboratory of Dr. Stefan H.E. Kaufmann ADDIN EN.CITE Hess199819196[34, 35]191961919617Hess, JrgenMiko, DianaCatic, AndrLehmensiek, VeraRussell, David GKaufmann, Stefan HEMycobacterium bovis Bacille CalmetteGurin strains secreting listeriolysin of Listeria monocytogenesProceedings of the National Academy of SciencesProceedings of the National Academy of Sciences5299-530495919980027-8424Kaufmann201019204192041920417Kaufmann, Stefan HELearning from natural infection for rational tuberculosis vaccine design: from basic science to translational researchHuman vaccinesHuman vaccines614-6186820101554-8600[34, 35] and was further developed by VPM. In 2013, the rights to the vaccine were acquired by SII, which has developed a new large-scale production process for the vaccine. VPM1002 is being developed primarily as a BCG replacement vaccine for prevention of serious TB disease in infants. It also is being evaluated as a replacement for BCG immunotherapy of bladder cancer.
Preclinical studies in mice showed that, in contrast to BCG, VPM1002 reproducibly protected against an aerosol challenge model to a clinical isolate of Mtb of the Beijing/W lineage ADDIN EN.CITE Grode200519192[26]191921919217Grode, LeanderSeiler, PeterBaumann, SvenHess, JrgenBrinkmann, VolkerEddine, Ali NasserMann, PeggyGoosmann, ChristianBandermann, SilkeSmith, DebbieIncreased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis bacille Calmette-Guerin mutants that secrete listeriolysinJournal of Clinical InvestigationJournal of Clinical Investigation247211592005[26]. Safety assessment of bacilli persistence in wild type mice found that VPM1002 fell below the level of detection 40 days after immunization while BCG was detectable 90 days after immunization,
The first Phase 1 clinical trial of VPM1002 was completed in Germany in 2012 ADDIN EN.CITE Grode201319193[36]191931919317Grode, LeanderGanoza, Christian ABrohm, ChristianeWeiner, JanuaryEisele, BerndKaufmann, Stefan HESafety and immunogenicity of the recombinant BCG vaccine VPM1002 in a phase 1 open-label randomized clinical trialVaccineVaccine1340-134831920130264-410X[36]. The study consisted of adult male Caucasian volunteers with and without prior exposure to BCG. It was shown to be safe and similar in immunogenicity to BCG ADDIN EN.CITE Grode201318229[37]182291822917Grode, L.Ganoza, C. A.Brohm, C.Weiner, J., 3rdEisele, B.Kaufmann, S. H.Vakzine Projekt Management GmbH, Hannover, Germany.Safety and immunogenicity of the recombinant BCG vaccine VPM1002 in a phase 1 open-label randomized clinical trialVaccineVaccine2013/01/082013Jan 21873-2518 (Electronic)
0264-410X (Linking)23290835S0264-410X(12)01840-3 [pii]
10.1016/j.vaccine.2012.12.053 [doi]Eng[37]. A subsequent Phase 1B trial in South Africa tested VPM1002 in BCG immunized adults. VPM1002 again was found to be safe and immunogenic as a boost to pre-existing immunity from a BCG prime ADDIN EN.CITE ADDIN EN.CITE.DATA [37, 38]. A Phase 2, head-to-head comparison of BCG to VPM1002 in HIV-unexposed neonates recently was completed in South Africa. VPM1002 was at least as well tolerated as BCG in this trial; immunogenicity results are pending. A second Phase 2 clinical trial is planned to begin in January 2015 in South Africa in HIV-exposed and -unexposed populations of BCG-nave neonates.
MTBVAC. Dr. Carlos Martn, Department of Microbiology, Faculty of Medicine, University of Zaragoza, Zaragoza, Spain
Dr. Carlos Martin reported on the development of MTBVAC, the only live-attenuated Mtb-based vaccine currently in clinical trials ADDIN EN.CITE Arbues201319175[39]191751917517Arbues, AinhoaAguilo, Juan IGonzalo-Asensio, JesusMarinova, DessislavaUranga, SantiagoPuentes, EugeniaFernandez, ConchitaParra, AlbertoCardona, Pere JoanVilaplana, CristinaConstruction, characterization and preclinical evaluation of MTBVAC, the first live-attenuated M. tuberculosis-based vaccine to enter clinical trialsVaccineVaccine4867-4873314220130264-410X[39]. The rationale behind the development of an attenuated Mtb vaccine is to immunize with a candidate that manifests as close an antigenic picture to Mtb as possible while minimizing the virulence.
The Geneva Consensus on new live mycobacterial vaccines requires two non-reverting independent mutations to live, Mtb-based vaccines to insure the stability of the attenuation, without the inclusion of antibiotic resistance markers ADDIN EN.CITE ADDIN EN.CITE.DATA [40, 41]. MTBVAC meets these requirements as it contains deletions in the genes encoding fadD26 and phoP and does not contain an antibiotic resistant marker. The fadD26 gene product is involved in the synthesis of the lipid phthiocerol dipimycocerosate (PDIM), a major mycobacterial virulence factor. The phoP gene encodes a transcriptional regulator that controls the expression of two percent of the coding capacity of Mtb genome, including gene families involved in respiration, the hypoxic response, lipid metabolism, stress proteins and the RD1 region, which includes ESAT-6 ADDIN EN.CITE Gonzalo-Asensio200819191[42]191911919117Gonzalo-Asensio, JessMostowy, SergeHarders-Westerveen, JoseHuygen, KrisHernndez-Pando, RogelioThole, JelleBehr, MarcelGicquel, BrigitteMartn, CarlosPhoP: a missing piece in the intricate puzzle of Mycobacterium tuberculosis virulencePLoS OnePLoS Onee349631020081932-6203[42]. The deletion in phoP reduces the virulence mainly from abrogation of the ESX-1 secretion system. As a result of this deletion, MTBVAC maintains the ability to produce ESAT-6 but cannot secrete this, therefore losing the ability to spread from cell to cell ADDIN EN.CITE Aguilo201319173[43]191731917317Aguilo, JIAlonso, H <