Combined vaccination with BCG and toxoid antigens.

Simultaneous vaccination with different antigens has been widely practised in recent years. A notable example is percutaneous smallpox vaccination together with the intradermal injection of BCG. In contrast, the potentially even more time-saving procedure of combined vaccination (i.e., with vaccines mixed prior to injection) has been tried on only a very limited, experimental scale. Combined vaccination with a mixture of BCG and toxoids has not been suggested before. Such a mixed vaccine, with diphtheria and tetanus toxoids, was used in experiments in vitro and in vivo.No deleterious effect of toxoids on BCG was found in terms of reduction in oxygen uptake, germination rate, or counts of viable particles. The dose-response relationships (delayed hypersensitivity and skin reactivity) for BCG with and without added toxoids were compared in guinea pigs and no differences were found. The antibody response in guinea pigs to toxoids mixed with BCG or with aluminium hydroxide was measured following both primary and booster immunization. The primary response to toxoids was lower with BCG than with aluminium hydroxide. In booster immunization, the response was identical for the two mixtures.It appears that not only is a mixture of toxoids and BCG innocuous (given intradermally) but also BCG may have an adjuvant effect on the production of antibodies to the toxoids. Further experimentation is needed, first in the guinea pig model and later in pilot trials in man, to establish suitable dose levels. Furthermore, since BCG may act as an adjuvant both in producing antibodies and in the cell-mediated response to the toxoids, it would be desirable to clarify the possible interaction of these two immune responses in protection against disease.

Present knowledge of immunization against tuberculosis.

This is a selective review, which, after recalling some immunological aspects, analyses the present knowledge on the protective efficacy of BCG vaccination, the vaccination reactions and complications that may be observed, and current methods of vaccine production and control. As regards the application of BCG vaccination, particular attention is given to dosage and vaccination techniques, direct and simultaneous vaccination, and revaccination. Finally, the evaluation of BCG vaccination programmes is briefly discussed.

Tuberculin sensitivity in guinea-pigs after vaccination with varying doses of BCG of 12 different strains.

In several previously reported studies a number of BCG strains, including those most widely used in vaccine production, were ranked according to their in vivo activity in various experimental models in rodents and to the local and allergic response that they provoked in children. In this report, 12 strains are ranked in terms of tuberculin conversion in guinea-pigs according to the minimum sensitizing dose. For 10 of these strains, this minimum dose is very low, ranging from 5 to 50 culturable particles. Thus the traditional practice of tuberculin-testing guinea-pigs that have been vaccinated with a full human dose of BCG (of the order of one million culturable particles) has such a low discriminating power that it is useless as a routine test for currently used vaccines. The ranking obtained in this model was largely but not completely in accordance with similar rankings in other models. The Tokyo strain and, to some extent, the London strain ranked comparatively lower than they do in children. The pronounced lack of virulence of the Prague strain was confirmed.

Sensitivity to tuberculin and to a nonmammalian sensitin in Mandalay District, Burma.

Delayed hypersensitivity that can be demonstrated with either a strong dose of tuberculin or a conventional dose of a sensitin prepared from certain nonmammalian mycobacteria (mycobacteria of Runyon Groups II and III, e.g., Mycobacterium avium), is known to be highly prevalent in most tropical and many subtropical areas and rare in many temperate zones. Whether such sensitivity interacts significantly with tuberculosis or with leprosy is not known.A study of reactions to tuberculin (PPD-S) and to a sensitin prepared from M. intracellulare (PPD-B) was carried out in villages close to an area in which a clinical trial of the preventive effect of BCG against leprosy was being conducted. The population had not been vaccinated with BCG. Some of the villages were in river valleys that become flooded every year for a long period during the rainy season; others were on slopes above the area subject to floods. The findings showed that sensitivity to the nonmammalian sensitin was prevalent in the area, and thus confirmed previous findings of low-grade tuberculin sensitivity in Burma and neighbouring countries. No difference in this prevalence was found between flooded and nonflooded villages.

Tuberculin sensitivity and skin lesions in children after vaccination with 11 different BCG strains.

In previously published studies, a number of BCG strains used in several production laboratories were compared in animal models. Liquid vaccines from the different strains were prepared in one laboratory with a uniform technique, the aim being to obtain uniform in vitro properties. In the studies reported here, such vaccines were compared by means of vaccinating children in India and Denmark and then measuring their post-vaccination skin lesions and tuberculin sensitivity. One strain induced delayed hypersensitivity strikingly weaker than that induced by any of the others, although the vaccine was in no way inferior in terms of exhaustive in vitro tests. Differences among the other strains were slight, although sometimes statistically significant. The implications of such differences are discussed.

The use of jet-injectors in BCG vaccination.

In mass vaccination programmes, the jet-injection of vaccine may have considerable operational advantages over the classical techniques. The technical performance of two models of jet-injector, the Dermo-Jet and the Ped-O-Jet, in BCG vaccination was assessed in a number of studies which are reviewed by the authors. It is shown that the jet-injectors do not administer the full dose for which they are calibrated and that the size of the vaccination lesion varies more than after vaccination by syringe.By increasing the dosage considerably, the results of vaccination by jet-injection may be improved to a certain extent but the risk of unpleasant reactions is also increased.

The virulence of some strains of BCG for golden hamsters. Further studies.

In principle, a strain of BCG used for the preparation of live vaccine should retain a moderate residual virulence. The inoculation of golden hamsters with large doses of BCG causes progressive, fatal disease but not all strains are equally active. In a previous paper, the present authors gave data from experiments with 9 BCG strains; in this report, 4 additional strains, three of which are in routine use in vaccine-production laboratories, are compared with one of the strains used in the previous experiments. The five strains differ widely in their ability to kill hamsters and were ranked in nearly the same order in two identically designed experiments. The differences in virulence found between strains derived relatively recently from a single mother strain were particularly noticeable. These differences were sometimes accompanied by striking changes in the growth characteristics of the strains with a lower virulence. The hypothesis that the lower virulence in such cases is a sign of genetic mutation is consistent with the general biological experience that virulence is often lost in vitro but that it practically never increases.

The protective effect in bank voles of some strains of BCG.

The bank vole, like the guinea-pig, can be immunized against tuberculosis with very small doses of BCG, presumably because BCG is sufficiently virulent for both these species to multiply freely until the immunization of the animal has reached a maximum. Large doses of BCG induce an earlier, but not an ultimately stronger, immunity. However, the smallest immunizing dose is not the same for all BCG strains and this is a feature that may be used to differentiate strains. In the studies reported by the authors, the smallest immunizing dose for the bank vole was estimated for 11 BCG strains, some of them widely used in man. The results indicate potency ratios of 20: 1 between the strongest and the weakest strains. The ranking of strains in terms of the smallest immunizing dose was found to be correlated in most, but not in all, cases with a previously reported ranking of the lethal effects of the various strains in golden hamsters. The implications of these findings for production requirements and for reference preparations of BCG are discussed.