Induction of delayed-type hypersensitivity in human volunteers immunized with a candidate leprosy vaccine consisting of killed Mycobacterium leprae

Bulletin of the World Health Organization, 64 (1): 121-126 (1986) © World Health Organization 1986 Induction of delayed-type hypersensitivity in human volunteers immunized with a candidate leprosy vaccine consisting of killed Mycobacterium leprae H. K. GILL,' A. S . MUSTAFA,2 & T. GODAL3 A killed armadillo-derived Mycobacterium leprae vaccine was examinedfor its ability to induce a delayed-type hypersensitivity (DTH) response in purified protein derivative (PPD)-positive human volunteers living in a leprosy non-endemic country. Four groups of individuals aged between 23 and 28 years were given 1.5 x107 5 x107 1.5 xJO8and 5 X108 M. leprae intradermally. A marked increase in reactivity to the M. leprae-derived skin test antigen (MLSA) was observed in the vaccinated groups receiving the three highest doses of vaccine while there was very little change observed in their PPD reactivity. No unaccept- able side-effects attributable to the vaccine were observed. The killed armadillo-derived M. leprae vaccine thus appears to be able to induce aDTH response in man at doses which do not cause unacceptable side-effects. One of the major goals of the IMMLEP (im- munology of leprosy) programme of the UNDP/ World Bank/WHO Special Programme for Research and Training in Tropical Diseases is the development of a vaccine against leprosy. A major step towards this goal was made in 1971 when Kirchheimer & Storrs (1) discovered that the nine-banded armadillo was extremely susceptible to infection with Myco- bacterium leprae. This led to the availability of un- precedented amounts of bacilli and the possibility of developing a vaccine consisting of killed M. leprae. Such a vaccine would have to meet two important requirements. Firstly, it would have to be purified to remove contaminating host tissue by a process that would leave its immunogenicity intact. And secondly, the vaccine would have to possess the ability to induce a protective cell-mediated immune (CMI) response in its recipients. M. leprae produced in the armadillo is purified by a two-phase system developed by Draper (2), which has been further modified to ensure that the immunogenicity of the bacilli has been left intact! ' Recipient of a fellowship (for Ph.D research) from the UNDP/ World Bank/WHO Special Programme for Research and Training in Tropical Diseases. 2 Recipient of a post-doctoral grant from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases. 3Chief, Laboratory for Immunology, Department of Pathology, The Norwegian Radium Hospital, Montebello, N-0310 Oslo 3, Norway. Requests for reprints should be addressed to this author. Report of thefifth meeting of the Scientific Working Groupon the Immunology of Leprosy. Protocol 1/79. Unpublished WHO document TDR/SWG/IMMLEP (5) 80.3 (1980). Shepard et al. have shown that the immunogenicity of M. leprae remains unaffected by the purification procedure and the heat treatment that is carried out in the preparation of this vaccine (3, 4). As far as the second requirement is concerned, it was originally envisaged that killed M. leprae would have to be incorporated in an adjuvant in order to be able to elicit a CMI response. However, studies carried out in mice (5, 6) and in guinea pigs (7) showed that an irradiated, heat-killed preparation of M. leprae was extremely effective in inducing the CMI response as assessed by delayed type hypersensitivity (DTH) reactions. Moreover, Shepard et al. (5, 8) have shown that such a vaccine was capable of preventing the multiplication of live bacilli in the mouse footpad. Having met the criteria of immunopotency in animal systems and the additional requirement of biological safety, the killed M. leprae vaccine was essentially ready for trials in man. However, owing to the low incidence and long incubation period of leprosy, field trials for the assessment of protective immunity would require large populations to be monitored over a long period of time. Before the start of such large-scale trials, it was considered necessary to assess the efficacy of the vaccine in small popu- lations using appropriate indicators. One such indicator is the ability of the vaccine to elicit a DTH response. DTH reactions are associated with resis- tance to intracellular bacteria such as M. leprae (9). This is most clearly observed in leprosy patients them- selves where an overall association between DTH and 4645 -121- 122 H. K. GILL ET AL. resistance, as measured by clinical, histological and immunological criteria, is found (10, 11). We report here the results of a study carried out in 1983-84 under the IMMLEP programme which examines the DTH response in human volunteers in Norway immunized with this vaccine.b MATERIALS AND METHODS Skin test antigens A soluble antigen from ultrasonicated M. leprae (MLSA, ref. batch CD19) and purified protein derivative (PPD, RT 23 from Statens Serum Insti- tute, Copenhagen) was used throughout the study. Both skin test antigens were provided as coded samples by the IMMLEP M. leprae bank at the National Institute for Medical Research, Mill Hill, London. In addition, uncoded PPD was used for the initial skin testing of the volunteers (see study design). Skin tests were performed on the volar side of the forearm. The tests were read at 48 and 72 hours by recording the horizontal and vertical diameters of the induration reaction. The skin test reaction was expressed as a mean of these two diameters. The 72- hour reading was used in the results presented here as it gave a better measure of the response with much less interference from flare reactions. Study design Ethical clearance was obtained prior to the start of the trial from the Norwegian Radium Hospital, Oslo, the National Norwegian Drug Agency, and theWHO Secretariat Committee on Research Involving Human Subjects (SCRIHS). Thirty-one vaccinees (12 males and 19 females), aged between 23 and 28 years, were initially skin-tested with PPD and subsequently assigned to four groups (7-9 subjects in each) so that an even distribution of the spectrum of PPD responses among these four groups was achieved. This was necessary to allow assessment of PPD- related side-effects in each of the groups. A month after this initial PPD skin-testing, the first group of volunteers was skin-tested again with coded antigens (PPD and MLSA). Immediately after the 72-hour skin-test reaction had been read, this group was given the lowest dose ofM. leprae vaccine, i.e., 1.5 x 107 M. leprae. This was injected intra- dermally into three sites, using a standard grid (equi- lateral triangle of 3 cm), 0.1 ml being delivered into each site on the left deltoid region of the arm. The study was designed so that the group that was to b The main features of the study design were prepared by the IMMLEP Steering Committee in 1981 and reported in Testing of purified armadillo-derived M. leprae in man (unpublished WHO document TDR/IMMLEP/SC/TEST/81.1). receive the next vaccine dose attended the one-month examination of the vaccination site of the previous group. This enabled an assessment of the reactions to the vaccine and a decision on whether a higher dose was acceptable. A control group (8 subjects), which was only skin-tested, was also included in the study. At the completion of the study, the data were sent to WHO headquarters in Geneva where the code was broken. The results were then analysed by the investigators. RESULTS As shown in Fig. 1, a marked increase in reactivity to the M. leprae-derived skin-test antigen (MLSA) was observed in the vaccinated groups receiving the three highest doses of vaccine. In contrast, very little 25 20 i,'' _ l 0o; 1,,1 ,,'' I I Pre Post Pre Post Pre Post Pre Post Pre Post vaccination 1.5xlO, xt07 l.5x 108 5 x 10° Control Vaccination dose Fig. 1. Comparison of the pre- and post-vaccination DTH responses to MLSA. Four groups of individuals were injected intradermally with graded doses of killed M. Ieprae. These individuals were skin-tested for responses to MLSA 72 hours prior to vaccination and 3 months after vaccination. While the pre- and post- vaccination DTH responses were not significantly different in the control group and in group 1 which received a dose of 1.5 x 107 M. Ieprae (P>0.5, student's t-test), they were significantly different in the other groups (P< 0.00 1). LEPROSY VACCINE TESTS IN HUMAN SUBJECTS o.LI I I I IILPrt Post Pre Post Pre Post Pre Post Control 1.5x 107 5 x 107 1.5 x l0o Vaccination dose Pre Post vaccination 5 x ioe Fig. 2. Comparison of the pre- and post-vaccination DTH responses to PPD. The vaccinated individuals were simultaneously skin-tested for responses to PPD 72 hours prior to vaccination and 3 months after vacci- nation. The pre- and post-DTH responses to PPD were not significantly different in any of the groups (P>0.5). 0/ 0/ / / 0 0 0 0 0 00 0/ 0 ° / 00 -0/ 0 0 0 00 0 0X00080 0 ° ° ° ° 0 change was observed in their PPD reactivity (Fig.2). As expected, their PPD reactivity was strong because they had been vaccinated with BCG during ado- lescence according to standard practice in Norway. The possibility that the PPD responses had influenced the responses to MLSA was considered. Cross-reactivity was assessed by comparing pre- vaccination responses to MLSA and PPD. As shown in Fig. 3, a proportion of the volunteers responded in the pre-vaccination skin test to MLSA in a pattern related to their PPD pre-vaccination responses suggesting cross-reactivity between the two antigens. However, the vaccine-related response to MLSA was not confined to MLSA pre-vaccination MLSA- positive responders. As shown in Fig. 4, the post- vaccination MLSA activity was as strong in pre- vaccination negative as in pre-vaccination positive subjects. The only clearly vaccination-related side-effects were observed locally. The local reactions, as measured by induration, reached a peak 3 weeks after vaccination and were clearly dose-related (Fig.5). Scar formation was observed in all subjects receiving the two highest doses of vaccine. The largest scar observed had a diameter of 9.5 mm. A few temporary petechiae were observed on the trunk of 3 subjects (two in group 1 and one in group 3) at 3 months after the vaccination. In the absence of a dose relationship, 25 r E 20 C3.o c 15 g 1 L a Q.S 1 5 0 0 5 10 15 20 25 30 PPD pre-vaccination (mm) 0 0 0 0 _- 0 0 O o0 0 _- 0 8 0MoOgo I I I 0 5 10 15 20 25 MLSA post-vaccination (mm) Fig. 3. Relationship between the DTH response to MLSA and the DTH response to PPD prior to vaccination in each subject. The broken line marks the 450 angle. Fig. 4. Relationship between the DTH response to MLSA before and after vaccination. 20 E E 20 c 20 .2_ 0 j 104 vJ) 0 .j 5 7 123 I I .1/ % ( 11 §--- % k H. K. GILL ET AL. 25r 20H E E uL) cr 10 5 0 * : T ; 0 0 0 1.5x107 5x 10 1.5x108 5x108 Vaccine dose Fig. 5. Vaccine reaction at 3 weeks. Four groups of indi- viduals were injected intradermally with graded doses of killed M. Ieprae. Three weeks later, the induration at the inoculation site was measured. Each dot represents the 3-week vaccine reaction of one individual. Vertical bars include 1 S.E. of the mean. it seems doubtful that these petechiae were a result of the vaccination. DISCUSSION The development of a vaccine requires a systematic examination of all the criteria necessary for its success. Thus, the criteria of purity, efficacy and safety in animal studies having been met, the next logical step was to examine its performance in human subjects. In order to avoid possible interference from natural exposure to M. leprae, it was decided that the vaccine should first be studied in non-endemic countries. Here it was necessary to make a distinction between a BCG-vaccinated population and a non- vaccinated population for the same reason. The present study was carried out in Norway where the population is vaccinated with BCG. This study shows that purified armadillo-derived M. leprae, killed by irradiation and autoclaving, is able to induce a strong delayed-type hypersensitivity reaction in man. The DTH reactions obtained were as strong as the responses to PPD in this BCG-vacci- nated population. This is in agreement with studies carried out by Smelt et al. (12). They showed that 6 out of 7 normal individuals vaccinated with 2 x 108 killed armadillo-derived M. leprae became positive to a soluble M. leprae skin test with a mean increase in induration of 10.4 mm. BCG and M. leprae have been shown, in sero- logical assays (13), to share a number of antigens. Thus, the possibility of cross-reactivity in DTH reactions has been assessed. The comparison of pre- vaccination reactions to MLSA and PPD revealed a pattern of reactivity which suggests a varying, but considerable cross-reactivity. Consequently, the possibility that the killed M. leprae vaccine merely boosted an existing response to cross-reactive anti- gens has to be considered. While the possibility can- not be excluded entirely, in this study, it seems un- likely since the responses were as good after vaccina- tion of MLSA pre-vaccination negative vaccinees as MLSA pre-vaccination positive vaccinees. Moreover, M. leprae-specific T-cell clones have now been developed from the vaccinees (18). Recent studies by Mehra et al. (14) indicate that the suppressor T-lymphocytes associated with multi- bacillary leprosy respond to phenolic glycolipid, an epitope unique to M. leprae. Henceforth, the deletion of such "suppressor" epitopes may be desirable in the development of a vaccine (15). In this regard, it is noteworthy that the present vaccine does not contain detectable levels of phenolic glycolipid (D. B. Young & T. M. Buchanan, personal communication, 1984). Furthermore, none of the vaccinees developed anti- bodies to phenolic glycolipid as tested by a sensitive ELISA method (16). This finding may be very important as it suggests a means of studying the epidemiology of infection and seroconversions to live M. leprae infection in vaccinated populations. The present study suggests that strong DTH re- activity can be induced by M. leprae in man with doses that do not produce unacceptable side-effects. The next step is to carry out similar studies in leprosy endemic areas. Such studies would record the DTH reactions immediately after vaccination as well as the duration of the sensitization afforded by the vaccine. These studies should also compare the efficacy of M. leprae alone versus the efficacy of a combined M. leprae + BCG vaccine, since Convit et al. (17) 124 LEPROSY VACCINE TESTS IN HUMAN SUBJECTS 125 have found that the combined vaccine is able to restore delayed-type hypersensitivity in unresponsive, indeterminate and lepromatous patients. Thus, leprosy could be one of the few infectious diseases where a vaccine may be both prophylactic and immunotherapeutic. ACKNOWLEDGEMENTS This study received financial support from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases. RESUME INDUCTION D'UNE HYPERSENSIBILITE RETARDEE CHEZ DES VOLONTAIRES IMMUNISES AU MOYEN D'UNE PREPARATION PROPOSEE COMME VACCIN ANTILEPREUX ET CONSTITUEE DE MYCOBACTERIUM LEPRAE TUES Parmi les principaux objectifs du programme IMMLEP (Immunologie de la lepre) du Programme special PNUD/ Banque mondiale/OMS de recherche et de formation concernant les maladies tropicales, figure la mise au point d'un vaccin contre la lepre. Des travaux recents effectues chez des animaux ont montre que Mycobacterium leprae tue possede des proprietes adjuvantes intrinseques et est capable de susciter une forte reponse immunitaire a mediation cellulaire in vivo. Apres la mise au point de m6thodes adapt6es pour l'isolement de M. leprae destines A l'utilisation chez l'homme, 1'essai d'un vaccin tue a e envisage chez des volontaires. La presente etude decrit les resultats de cet essai, entrepris sur des volontaires positifs pour le derive proteinique purifie (PPD), residant dans un pays exempt d'endemie lepreuse (Norvege). 9,uatre groupes de sujets ages de 23 a 28 ans ont requ 1,5 x 10, 5 x 1 1,8 x 108 et 5 x 108 M. leprae par voie intradermique. Une augmentation sensible de la reactivite vis-a-vis de l'antigene de M. leprae lors d'une epreuve cutan&e a e observee dans les groupes ayant requ les trois plus fortes doses de vaccin, alors qu'on n'observait qu'une tres faible modification de leur reactivite au PPD. Aucun effet secondaire indesirable pouvant etre attribue au vaccin n'a e observe. Le vaccin constitue de M. leprae tues obtenus sur le tatou semble donc capable d'induire chez l'homme une reponse de type hypersensibilite retard&e, sans effets secondaires inacceptables. Cette etude ouvre la voie a l'essai d'un tel vaccin dans des regions d'endemie lepreuse. REFERENCES 1. KIRCHHEIMER, W. F. & STORRS, E. E. Attempts to establish the armadillo (Dasypus novemcintus Linn.) as a model for the study of leprosy. International journal of leprosy, 39: 693-702 (1971). 2. DRAPER, P. Cell walls of Mycobacterium leprae. International journal of leprosy, 44: 95-98 (1976). 3. SHEPARD, C. C. ET AL. Effect of purification steps on the immunogenicity of Mycobacterium leprae. British journal ofexperimentalpathology, 61: 375-379 (1980). 4. SHEPARD, C. C. ET AL. Heat stability of Myco- bacterium leprae immunogenicity. Infection and im- munity, 22: 87-93 (1978). 5. SHEPARD, C. C. 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