EUROPEAN UROLOGY 66 (2014) 692–693
available at www.sciencedirect.com journal homepage: www.europeanurology.com
Platinum Priority – Editorial Referring to the article published on pp. 677–688 of this issue
Variations Between Bacillus Calmette-Gue´rin Strains: Lessons from Tuberculosis Prevention Getahun Abate, Daniel F. Hoft * Departments of Internal Medicine and Molecular Microbiology and Immunology, Saint Louis University, St. Louis, MO, USA
Bacillus Calmette-Gue´rin (BCG) is the only available vaccine against tuberculosis (TB). BCG strains are attenuated mycobacteria derived from virulent Mycobacterium bovis after 230 passages over 13 yr. BCG was first introduced into clinical use for TB prevention in 1921. As BCG use expanded, daughter strains were distributed to different parts of the world where they were propagated and maintained with different methods of cultivation. The original strain and daughter strains underwent unregulated serial passages until a seed-lot system was introduced in the 1950s and 1960s. More than 13 different BCG strains have been reported [1,2]. Based on several genetic studies, it is believed that loss of the genomic region of deletion 1 was the first major change leading to attenuation of the initial M. bovis strain. Multiple passages of the daughter strains led to further genetic differences among BCG strains [1,3]. These genetic differences have been shown in some animal studies to translate into phenotypic differences in both reactogenicity and immunogenicity; however, it is unclear whether these changes affect TBprotective efficacy in humans [2]. Studying the clinical relevance of the genetic and/or immunogenicity differences among BCG strains is important because BCG strains are used to protect infants from the worst forms of TB, all new TB vaccination strategies are designed to boost immunity primed by BCG vaccination, and efficacy of BCG as adjunctive chemotherapy for non–muscle-invasive bladder cancer (NMIBC) could be dependent on the specific strain used. In this month’s issue of European Urology, Rentsch et al. [4] report intriguing findings that Connaught BCG gives significantly better recurrence-free survival than Tice BCG when used as immunotherapy for NMIBC. This report
potentially links genetic differences of BCG strains with clinically measured end points. A clinical trial comparing two BCG strains for treatment of bladder cancer is reported. In addition, the authors study genetic differences and differences in immunogenicity in a murine model. Important confounding factors that could have affected the Connaught and Tice comparisons include the strain of BCG used for prior vaccination, tuberculin skin test variations before bladder instillation of BCG, and differences in doses of BCG used for bladder instillation. In mice, prior vaccination with BCG can induce immunity capable of limiting the effects of subsequent BCG challenge [5]; therefore, differences in preexisting immunity due to priming with different BCG strains in subjects enrolled into this adjunctive chemotherapy trial may have affected the results. It also is known that BCG immunity wanes over time, but significant proportions of adults with a history of BCG vaccination have residual immunity, and the level of persistent immunity may vary depending on the BCG strain used for priming [6]. We also agree with the authors that their results may not be directly relevant for populations not previously vaccinated with BCG prior to intravesical therapy. Comparing preexisting BCG-specific immunity in the two study groups prior to BCG intravesical therapy would have been informative. Another confounding factor is the dose of BCG used in the two groups for bladder instillation. The dose range for Connaught BCG (6.6– 19.2 108 colony-forming units [CFU]) was higher than the dose range for Tice BCG (2–8 108 CFU). Despite data presented by the authors suggesting that dose was not a factor, differences in doses of viable and/or nonviable bacilli could have been responsible for differences in clinical effects.
DOI of original article: http://dx.doi.org/10.1016/j.eururo.2014.02.061. * Corresponding author. Saint Louis University, 1100 South Grand Blvd., 8th Floor, St. Louis, MO 63104, USA. Tel. +1 314 977 5500. E-mail address: [email protected] (D.F. Hoft). http://dx.doi.org/10.1016/j.eururo.2014.06.006 0302-2838/# 2014 Published by Elsevier B.V. on behalf of European Association of Urology.
EUROPEAN UROLOGY 66 (2014) 692–693
Despite some limitations, the study by Rentsch et al. [4] suggests that different BCG strains induce differences in clinical effects. TB efficacy studies are difficult because of the requirements for large numbers of subjects studied for prolonged periods of time, since only 5–10% of infected individuals develop active TB disease over their lifetimes. In addition, correlates of protection are not available for use in TB vaccine studies. Consequently, head-to-head comparisons of BCG strains designed with sufficient statistical power to definitively address relative efficacy have not been done. When used as a TB vaccine, BCG is conventionally administered through the intradermal route, and vaccine take is clinically recognized by the development of papules or pustules followed by scar formation at the site of injection. Clinical comparison of intradermal vaccinations with Connaught and Tice BCG demonstrated similar reactogenicities of the two strains, as measured by indurated papule or pustule at the site of immunization [7]. Furthermore, in a double-blind clinical trial in a low-TBprevalence setting, involving purified protein derivative– negative volunteers and using equivalent doses, our group demonstrated that intradermal Connaught and Tice BCG induced similar systemic Th1 immune responses [8]. It is difficult to compare our studies of clinical reactogenicity and immunogenicity with findings from Rentsch et al. [4] for two major reasons. First, the BCG administration route was mucosal in the study by Rentsch et al. and intradermal in our studies. Second, Rentsch et al. did not study immunogenicity after BCG intravesical therapy. To our knowledge, these vaccines have not been directly compared for TB prevention efficacy; therefore, Rentsch et al. are the first to report clinical differences between these two strains. In mice, Rentsch et al. also demonstrated that intravesical Connaught BCG was more potent than Tice BCG in inducing systemic BCG-specific CD4+ and CD8+ responses [4]. They further demonstrated that the two strains differed in the superoxide dismutase C gene, which may be associated with differences in growth kinetics in vivo and immunogenicity. However, it is not clear whether these genetic differences or differences in immunogenicity seen
693
in the murine system are directly linked to the differences in recurrence-free survival of NMIBC patients. In addition, it is important to note that the experiments in mice were performed without prior BCG vaccination, whereas the patients studied in the clinical trial were from a population with prior BCG vaccination. In conclusion, despite some limitations, the findings of Rentsch et al. provide insight into potential differences between BCG strains that may affect immunogenicity and/ or clinical outcome. Additional studies are required to determine whether genetic or other differences are important for the differences in clinical effects. Conflicts of interest: The authors have nothing to disclose.
References [1] Behr MA, Wilson MA, Gill WP, et al. Comparative genomics of BCG vaccines by whole-genome DNA microarray. Science 1999;284: 1520–3. [2] Ritz N, Hanekom WA, Robins-Browne R, Britton WJ, Curtis N. Influence of BCG vaccine strain on the immune response and protection against tuberculosis. FEMS Microbiol Rev 2008;32:821–41. [3] Brosch R, Gordon SV, Garnier T, et al. Genome plasticity of BCG and impact on vaccine efficacy. Proc Natl Acad Sci U S A 2007;104: 5596–601. [4] Rentsch CA, Birkha¨user FD, Biot C, et al. Bacillus Calmette-Gue´rin strain differences have an impact on clinical outcome in bladder cancer immunotherapy. Eur Urol 2014;66:677–88. [5] Lagranderie MR, Balazuc AM, Deriaud E, Leclerc CD, Gheorghiu M. Comparison of immune responses of mice immunized with five different Mycobacterium bovis BCG vaccine strains. Infect Immun 1996;64:1–9. [6] Tissot F, Zanetti G, Francioli P, Zellweger JP, Zysset F. Influence of bacille Calmette-Gue´rin vaccination on size of tuberculin skin test reaction: to what size? Clin Infect Dis 2005;40:211–7. [7] Hoft DF, Leonardi C, Milligan T, et al. Clinical reactogenicity of intradermal bacille Calmette-Gue´rin vaccination. Clin Infect Dis 1999;28:785–90. [8] Hoft DF, Kemp EB, Marinaro M, et al. A double-blind, placebocontrolled study of Mycobacterium-specific human immune responses induced by intradermal bacille Calmette-Gue´rin vaccination. J Lab Clin Med 1999;134:244–52.
available at www.sciencedirect.com journal homepage: www.europeanurology.com
Platinum Priority – Editorial Referring to the article published on pp. 677–688 of this issue
Variations Between Bacillus Calmette-Gue´rin Strains: Lessons from Tuberculosis Prevention Getahun Abate, Daniel F. Hoft * Departments of Internal Medicine and Molecular Microbiology and Immunology, Saint Louis University, St. Louis, MO, USA
Bacillus Calmette-Gue´rin (BCG) is the only available vaccine against tuberculosis (TB). BCG strains are attenuated mycobacteria derived from virulent Mycobacterium bovis after 230 passages over 13 yr. BCG was first introduced into clinical use for TB prevention in 1921. As BCG use expanded, daughter strains were distributed to different parts of the world where they were propagated and maintained with different methods of cultivation. The original strain and daughter strains underwent unregulated serial passages until a seed-lot system was introduced in the 1950s and 1960s. More than 13 different BCG strains have been reported [1,2]. Based on several genetic studies, it is believed that loss of the genomic region of deletion 1 was the first major change leading to attenuation of the initial M. bovis strain. Multiple passages of the daughter strains led to further genetic differences among BCG strains [1,3]. These genetic differences have been shown in some animal studies to translate into phenotypic differences in both reactogenicity and immunogenicity; however, it is unclear whether these changes affect TBprotective efficacy in humans [2]. Studying the clinical relevance of the genetic and/or immunogenicity differences among BCG strains is important because BCG strains are used to protect infants from the worst forms of TB, all new TB vaccination strategies are designed to boost immunity primed by BCG vaccination, and efficacy of BCG as adjunctive chemotherapy for non–muscle-invasive bladder cancer (NMIBC) could be dependent on the specific strain used. In this month’s issue of European Urology, Rentsch et al. [4] report intriguing findings that Connaught BCG gives significantly better recurrence-free survival than Tice BCG when used as immunotherapy for NMIBC. This report
potentially links genetic differences of BCG strains with clinically measured end points. A clinical trial comparing two BCG strains for treatment of bladder cancer is reported. In addition, the authors study genetic differences and differences in immunogenicity in a murine model. Important confounding factors that could have affected the Connaught and Tice comparisons include the strain of BCG used for prior vaccination, tuberculin skin test variations before bladder instillation of BCG, and differences in doses of BCG used for bladder instillation. In mice, prior vaccination with BCG can induce immunity capable of limiting the effects of subsequent BCG challenge [5]; therefore, differences in preexisting immunity due to priming with different BCG strains in subjects enrolled into this adjunctive chemotherapy trial may have affected the results. It also is known that BCG immunity wanes over time, but significant proportions of adults with a history of BCG vaccination have residual immunity, and the level of persistent immunity may vary depending on the BCG strain used for priming [6]. We also agree with the authors that their results may not be directly relevant for populations not previously vaccinated with BCG prior to intravesical therapy. Comparing preexisting BCG-specific immunity in the two study groups prior to BCG intravesical therapy would have been informative. Another confounding factor is the dose of BCG used in the two groups for bladder instillation. The dose range for Connaught BCG (6.6– 19.2 108 colony-forming units [CFU]) was higher than the dose range for Tice BCG (2–8 108 CFU). Despite data presented by the authors suggesting that dose was not a factor, differences in doses of viable and/or nonviable bacilli could have been responsible for differences in clinical effects.
DOI of original article: http://dx.doi.org/10.1016/j.eururo.2014.02.061. * Corresponding author. Saint Louis University, 1100 South Grand Blvd., 8th Floor, St. Louis, MO 63104, USA. Tel. +1 314 977 5500. E-mail address: [email protected] (D.F. Hoft). http://dx.doi.org/10.1016/j.eururo.2014.06.006 0302-2838/# 2014 Published by Elsevier B.V. on behalf of European Association of Urology.
EUROPEAN UROLOGY 66 (2014) 692–693
Despite some limitations, the study by Rentsch et al. [4] suggests that different BCG strains induce differences in clinical effects. TB efficacy studies are difficult because of the requirements for large numbers of subjects studied for prolonged periods of time, since only 5–10% of infected individuals develop active TB disease over their lifetimes. In addition, correlates of protection are not available for use in TB vaccine studies. Consequently, head-to-head comparisons of BCG strains designed with sufficient statistical power to definitively address relative efficacy have not been done. When used as a TB vaccine, BCG is conventionally administered through the intradermal route, and vaccine take is clinically recognized by the development of papules or pustules followed by scar formation at the site of injection. Clinical comparison of intradermal vaccinations with Connaught and Tice BCG demonstrated similar reactogenicities of the two strains, as measured by indurated papule or pustule at the site of immunization [7]. Furthermore, in a double-blind clinical trial in a low-TBprevalence setting, involving purified protein derivative– negative volunteers and using equivalent doses, our group demonstrated that intradermal Connaught and Tice BCG induced similar systemic Th1 immune responses [8]. It is difficult to compare our studies of clinical reactogenicity and immunogenicity with findings from Rentsch et al. [4] for two major reasons. First, the BCG administration route was mucosal in the study by Rentsch et al. and intradermal in our studies. Second, Rentsch et al. did not study immunogenicity after BCG intravesical therapy. To our knowledge, these vaccines have not been directly compared for TB prevention efficacy; therefore, Rentsch et al. are the first to report clinical differences between these two strains. In mice, Rentsch et al. also demonstrated that intravesical Connaught BCG was more potent than Tice BCG in inducing systemic BCG-specific CD4+ and CD8+ responses [4]. They further demonstrated that the two strains differed in the superoxide dismutase C gene, which may be associated with differences in growth kinetics in vivo and immunogenicity. However, it is not clear whether these genetic differences or differences in immunogenicity seen
693
in the murine system are directly linked to the differences in recurrence-free survival of NMIBC patients. In addition, it is important to note that the experiments in mice were performed without prior BCG vaccination, whereas the patients studied in the clinical trial were from a population with prior BCG vaccination. In conclusion, despite some limitations, the findings of Rentsch et al. provide insight into potential differences between BCG strains that may affect immunogenicity and/ or clinical outcome. Additional studies are required to determine whether genetic or other differences are important for the differences in clinical effects. Conflicts of interest: The authors have nothing to disclose.
References [1] Behr MA, Wilson MA, Gill WP, et al. Comparative genomics of BCG vaccines by whole-genome DNA microarray. Science 1999;284: 1520–3. [2] Ritz N, Hanekom WA, Robins-Browne R, Britton WJ, Curtis N. Influence of BCG vaccine strain on the immune response and protection against tuberculosis. FEMS Microbiol Rev 2008;32:821–41. [3] Brosch R, Gordon SV, Garnier T, et al. Genome plasticity of BCG and impact on vaccine efficacy. Proc Natl Acad Sci U S A 2007;104: 5596–601. [4] Rentsch CA, Birkha¨user FD, Biot C, et al. Bacillus Calmette-Gue´rin strain differences have an impact on clinical outcome in bladder cancer immunotherapy. Eur Urol 2014;66:677–88. [5] Lagranderie MR, Balazuc AM, Deriaud E, Leclerc CD, Gheorghiu M. Comparison of immune responses of mice immunized with five different Mycobacterium bovis BCG vaccine strains. Infect Immun 1996;64:1–9. [6] Tissot F, Zanetti G, Francioli P, Zellweger JP, Zysset F. Influence of bacille Calmette-Gue´rin vaccination on size of tuberculin skin test reaction: to what size? Clin Infect Dis 2005;40:211–7. [7] Hoft DF, Leonardi C, Milligan T, et al. Clinical reactogenicity of intradermal bacille Calmette-Gue´rin vaccination. Clin Infect Dis 1999;28:785–90. [8] Hoft DF, Kemp EB, Marinaro M, et al. A double-blind, placebocontrolled study of Mycobacterium-specific human immune responses induced by intradermal bacille Calmette-Gue´rin vaccination. J Lab Clin Med 1999;134:244–52.
