Harris, SA; Meyer, J; Satti, I; Marsay, L; Poulton, ID; Tanner, R;Minassian, AM; Fletcher, HA; McShane, H (2013) Evaluation of ahuman BCG challenge model to assess anti-mycobacterial immunityinduced by BCG and a candidate TB vaccine, MVA85A, alone andin combination. The Journal of infectious diseases. ISSN 0022-1899DOI: 10.1093/infdis/jit647

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M A J O R A R T I C L E

Evaluation of a Human BCG Challenge Model toAssess Antimycobacterial Immunity Induced byBCG and a Candidate Tuberculosis Vaccine,MVA85A, Alone and in Combination

Stephanie A. Harris,a Joel Meyer,a Iman Satti, Leanne Marsay, Ian D. Poulton, Rachel Tanner, Angela M. Minassian,Helen A. Fletcher, and Helen McShane

Jenner Institute, University of Oxford, Oxford, United Kingdom

Background. A new vaccine is urgently needed to combat tuberculosis. However, without a correlate of protection,selection of the vaccines to take forward into large-scale efficacy trials is difficult. Use of bacille Calmette-Gurin (BCG)as a surrogate for humanMycobacterium tuberculosis challenge is a novel model that could aid selection.

Methods. Healthy adults were assigned to groups A and B (BCG-naive) or groups C and D (BCG-vaccinated).Groups B and D received candidate tuberculosis vaccine MVA85A. Participants were challenged with intradermal BCG4 weeks after those who received MVA85A. Skin biopsies of the challenge site were taken 2 weeks post challenge andBCG load quantified by culture and quantitative polymerase chain reaction (qPCR).

Results. Volunteers with a history of BCG showed some degree of protective immunity to challenge, having lowerBCG loads compared with volunteers without prior BCG, regardless of MVA85A status. There was a significant inversecorrelation between antimycobacterial immunity at peak response after MVA85A and BCG load detected by qPCR.

Conclusion. Our results support previous findings that this BCG challenge model is able to detect differencesin antimycobacterial immunity induced by vaccination and could aid in the selection of candidate tuberculosis vaccinesfor field efficacy testing.

Clinical Trials Registration. NCT01194180.

Keywords. tuberculosis; human BCG challenge; vaccine; MVA85A.

Disease caused by Mycobacterium tuberculosis contin-ues to be a major global health problem. In 2011, 8.7million new cases of tuberculosis were diagnosedworldwide and 1.4 million people died from the disease[1].With tuberculosis causing a quarter of the deaths in

people living with human immunodeficiency virus(HIV) [1] and with the emergence of increasinglydrug-resistant strains of M. tuberculosis, an effectivevaccine is urgently needed now in order to reduce theburden of this disease.

Since 2002, more than a dozen candidate vaccineshave been entered into clinical testing [2]. However, itis difficult to determine which of these candidates willprogress from relatively small-scale safety and immu-nogenicity studies through to large-scale, expensiveefficacy trials because an immune correlate of vaccine-induced protection against infection or disease doesnot exist. Preclinical animal challenge models of M. tu-berculosis infection [36] and in vitro mycobacterialkilling assays [79] are used to assess vaccine efficacy.However, it is not clear whether either of these reliablypredict what occurs in vivo in humans. Thus, the evalu-ation of vaccine efficacy currently relies on large,

Received 19 August 2013; accepted 30 October 2013; electronically published 23November 2013.

aS. A. H. and J. M. share joint first authorship.Presented in part: Tuberculosis Vaccines Third Global Forum, 2527 March 2013,

Cape Town, South Africa. No.4 in Breakout Session I (Biomarkers) on Tues 26thMarch 2013.

Correspondence: Helen McShane, The Jenner Institute, Old Road Campus Re-search Building, Roosevelt Drive, Oxford, OX3 7DQ, UK (helen.mcshane@ndm.ox.ac.uk).

The Journal of Infectious Diseases 2014;209:125968 The Author 2013. Published by Oxford University Press on behalf of the InfectiousDiseases Society of America. This is an Open Access article distributed under theterms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction inany medium, provided the original work is properly cited.DOI: 10.1093/infdis/jit647

BCG Challenge Post BCG and/or MVA85A JID 2014:209 (15 April) 1259

mailto:helen.mcshane@ndm.ox.ac.ukmailto:helen.mcshane@ndm.ox.ac.ukhttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/

expensive, and time-consuming efficacy trials. A human myco-bacterial challenge model that could be used to assess the effica-cy of candidate tuberculosis vaccines at an early stage wouldbe a great advancement to the field. Human challenge modelsare routinely used in vaccine development for pathogens suchas malaria, influenza, dengue fever, and typhoid [1013]; how-ever, the deliberate infection of humans with M. tuberculosiswould not be ethically acceptable. Previously, we demonstratedthat a novel human challenge model that uses bacille Calmette-Gurin (BCG) as a surrogate for M. tuberculosis infection candetect differences in antimycobacterial immunity induced byprevious BCG vaccination [14]. In this earlier trial, healthy vol-unteers were challenged with intradermal BCG. The BCG loadwas then quantified from a skin biopsy at the challenge site at 1,2, and 4 weeks post challenge by culture on solid agar andquantitative polymerase chain reaction (qPCR). It was foundthat optimum recovery of BCG was achieved in 2 weeks; thistime period was chosen for future challenge studies. Here weuse this BCG challenge model to evaluate the reduction in my-cobacterial load induced by BCG alone; a candidate tuberculo-sis vaccine, MVA85A; and a BCG primeMVA85A boostvaccine regimen.

METHODS

Trial Design

This phase 1 trial (ClinicalTrial.gov registry NCT01194180)was approved by the Medicines and Healthcare ProductsRegulatory Agency (EudraCT 2010-018425-19) and the Ox-fordshire Research Ethics Committee A (reference 10/H0505/31). Twenty-six BCG-vaccinated and 23 BCG-naive healthyvolunteers aged 1855 years were enrolled between March 2011and November 2011 at the Centre for Clinical Vaccinology &Tropical Medicine, Churchill Hospital, Oxford, United King-dom (see Figure 1). All participants gave written informed con-sent, and the trial was conducted according to the principles ofthe Declaration of Helsinki and Good Clinical Practice.

Those enrolled were in good health, had normal baselinehematology and biochemistry, and were serologically negativefor hepatitis B, hepatitis C, and HIV. Latent infection withM. tuberculosis was excluded by a negative ex vivo enzyme-linked immunosorbent spot (ELISpot) assay response toESAT-6 and CFP-10 peptides. The reasons for exclusion of 9participants are shown in Figure 1. One individual in group Bhad to withdraw from follow-up for personal reasons after

Figure 1. Consort diagram showing participant recruitment and follow-up. *One volunteer withdrew from group B for personal reasons after MVA85Avaccination but before bacille Calmette-Gurin challenge.

1260 JID 2014:209 (15 April) Harris et al

receiving MVA85A but before BCG challenge and was thereforereplaced.

Treatment GroupsParticipants were assigned to group A (BCG-naive; no vaccinereceived), group B (BCG-naive at baseline; received intradermalMVA85A, dose 1 108 pfu), group C (BCG-vaccinated at base-line; median time since vaccination 10 years), or group D(BCG-vaccinated at baseline; median time since vaccination10.5 years; received intradermal MVA85A, dose 1 108 pfu)based on their prior BCG vaccination status and meeting inclu-sion criteria. One volunteer who was enrolled into group A onthe basis of negative BCG status was later reassigned to group Cafter discovering that he/she had, in fact, received BCG as aninfant (Figure 1).

VaccineClinical-grade MVA85A was constructed as previously de-scribed [15] and produced following good manufacturing prac-tices by IDT Biologika GmbH (Dessau-Rosslau, Germany).

ChallengeAll participants were challenged with a standard vaccine doseof intradermal BCG (SSI (Statens Serum Institut); 0.1 mLcontaining 2 to 8 105 CFU). Those in groups B and D werechallenged 4 weeks after MVA85A vaccination. To minimizevariation between BCG vials, as many volunteers as possiblewere challenged from the same vial of BCG within 2 hours ofreconstitution (15 different BCG vaccine vials were used overthe course of the trial to challenge 48 volunteers). The chal-lenge dose was verified by plating serial dilutions of a 100-Laliquot onto solid Middlebrook 7H10 agar (Sigma).

Skin BiopsiesSkin biopsies were performed on the BCG challenge site of all48 volunteers by a single operator 2 weeks post challenge aspreviously described [14]. The 4-mm punch biopsy specimenwas taken from the center of the BCG vaccination site, trans-ferred to a sterile Cryovial, snap frozen on dry ice, and stored inliquid nitrogen until the day of processing.

Biopsy Homogenization and CultureAll 48 biopsies were processed on the same day. Samples werethawed in a 37C water bath and transferred to a Dispomixtube (Miltenyl Biotech) that contained 1