Antituberculous immunity in mice vaccinated with killed tubercle bacilli

Progress in Oral Vaccination against Tuberculosis in Its Main Wildlife Reservoir in Iberia, the Eurasian Wild Boar

Eurasian wild boar (Sus scrofa) is the main wildlife reservoir for tuberculosis (TB) in Iberia. This review summarizes the current knowledge on wild boar vaccination including aspects of bait design, delivery and field deployment success; wild boar response to vaccination with Bacillus Calmette-Guérin (BCG) and inactivated Mycobacterium bovis; and wild boar vaccination biosafety issues as well as prospects on future research. Oral vaccination with BCG in captive wild boar has shown to be safe with significant levels of protection against challenge with virulent M. bovis. An oral vaccination with a new heat-killed M. bovis vaccine conferred a protection similar to BCG. The study of host-pathogen interactions identified biomarkers of resistance/susceptibility to tuberculosis in wild boar such as complement component 3 (C3) and methylmalonyl coenzyme A mutase (MUT) that were used for vaccine development. Finally, specific delivery systems were developed for bait-containing vaccines to target different age groups. Ongoing research includes laboratory experiments combining live and heat-killed vaccines and the first field trial for TB control in wild boar.

A single dose of killed Mycobacterium bovis BCG in a novel class of adjuvant (Novasome™) protects guinea pigs from lethal tuberculosis

The only vaccine currently available for the prevention of tuberculosis in man is a live attenuated vaccine, bacille Calmette-Guerin (BCG), derived from Mycobacterium bovis. Concerns over the lack of the universal efficacy and safety of BCG have resulted in efforts to develop a new generation of TB vaccines. Historically, killed whole-cell preparations of mycobacteria have been ineffective vaccines. We revisited the potential of killed whole-cell vaccines by comparing their efficacy with live BCG Pasteur in a guinea pig challenge model. BCG Pasteur was inactivated with a low concentration of formalin and showed to be non-viable in culture or severe combined immunodeficient mice. Formalin-inactivated BCG was mixed with non-phospholipid liposome adjuvants (Novasomes) and administered to guinea pigs as a single subcutaneous inoculation. All formulations were well tolerated and one conferred a significant survival advantage against lethal aerogenic challenge with M. bovis.

Studies on fractions of methanol extracts of tubercle bacilli. I. Fractions which increase resistance to infection

Fractionation procedures yielding partially purified vaccine preparations from a 60°C. methanol extract of tubercle bacilli have been described. Some of the preparations have the characteristics of lipopolysaccharides. Certain ones have been found capable of increasing resistance to experimental tuberculosis in albino mice of the Rockefeller Swiss strain. The levels of resistance elicited by these preparations are equivalent to those following vaccination with BCG (Phipps) in this strain of mice as reported by other authors. The admixture of two of the crude fractions in amounts as small as 0.05 mg. each per dose per mouse affords an even greater increase in resistance. Neither of these substances alone in larger doses can approach this degree of efficacy in mouse protection experiments. The protective activity appears to involve the stimulation of two supplementary mechanisms, one providing a peak resistance between 1 and 3 weeks post vaccination but falling off to a lower level thereafter, the other not responding fully until approximately 6 weeks but continuing undiminished through a 12 week post-vaccination period. The first of these peaks corresponds to an increase in resistance against staphylococci as well as tubercle bacilli. The possibility that the term "broad specificity," rather than "non-specificity," might best describe this phenomenon permits the implication of classical immune mechanisms.

Immunological behavior after mycobacterial infection in selected lines of mice with high or low antibody responses

Resistance and susceptibility to mycobacterial infection in the Biozzi high and low lines of mice which were genetically selected for their responses to heterologous erythrocytes have been found to be related to the innate ability of nonimmune macrophages to kill or inhibit the growth of the organisms during the first two weeks after infection and to their ability to mount specific and nonspecific immune responses. High antibody-producer mice were more capable of expressing cell-mediated immune parameters than low antibody-producer mice. A direct relationship was observed between the ability of bacteria (BCG vaccine) to multiply inside the reticuloendothelial system and the development of cell-mediated immunity, as measured by the delayed local reaction at the injection site, the lymphoproliferative response in the draining nodes, the tuberculin delayed-type hypersensitivity, the acquired resistance, and the adjuvant effect after BCG inoculation. In high line mice, apart from the inability of their macrophages to inhibit the early growth of bacteria, their lymphocytes in spleen and thymus were more capable of being stimulated in vitro by varying concentrations of living BCG. The data presented in this report are compatible with the hypothesis that a group of genes segregated in each line during the selective breeding controls the innate microbicidal activity.

Antituberculous immunity induced by methanol extracts of tubercle bacilli; its enhancement by adjuvants

It is possible to prepare from tubercle bacilli a fraction soluble in methanol which is capable of eliciting in mice a marked degree of resistance against virulent tuberculous infection. The immunity was evident whether the infective dose was large and caused a disease with a rapid course, or was very small and caused a disease of many months duration. Active material has been obtained by extraction with methanol at 55 degrees C. of bacterial cells killed with 2 per cent phenol, and washed with acetone. The methanol extracts used in the present study have been prepared from the phenol-killed cells of a culture of BCG, and of the avirulent culture H37Ra. Vaccination of mice bas been carried out by the intraperitoneal route, and the challenge infection (with a highly virulent bovine culture), by the intravenous route. Weight for weight, the protective activity of the methanol extract is smaller than that of the bacterial cells from which it is extracted, but its primary toxicity for mice is also considerably lower. The protective activity can be increased, and the immunity prolonged, by using certain adjuvants as vehicle for injection of the vaccine. An oil adjuvant mixture, and small amounts of a highly purified preparation of the somatic antigen of typhoid bacilli, have been found capable of enhancing and prolonging the antituberculous immunity induced by the methanol extract. Under appropriate conditions the resistance resulting from intraperitoneal injection of the methanol extract is of the same order as that which follows vaccination with whole killed tubercle bacilli or with living BCG.

Antituberculous immunity induced in mice by vaccination with killed tubercle bacilli or with a soluble bacillary extract

It proved possible to increase the resistance of mice to tuberculous infection by vaccinating them with a suspension of avirulent tubercle bacilli killed by exposure to 2 per cent phenol. This increase in resistance was demonstrated by two different techniques: (a) observation of survival time of vaccinated animals following challenge infection with a large dose of virulent bacilli, and (b) determination of numbers of virulent bacilli in the spleens of animals 2 weeks after injection of a small infective dose. The minimum protective dose of vaccine corresponded to approximately one-tenth the acutely toxic dose. Addition of an adjuvant to the bacillary suspension markedly increased both the protective effectiveness of the vaccine and the duration of the immunity. It enhanced also the toxicity of the vaccine in approximately the same proportion. However, other lines of evidence suggested that toxicity and protective activity were independent one from the other and were the manifestations of different bacillary constituents. Extraction with absolute methanol released from the bacillary bodies a crude soluble fraction possessing low, if any, toxicity, yet capable of eliciting in mice a state of increased resistance to virulent infection. The protective activity of this methanol-soluble fraction was low; it accounted for only a small part of the total protective activity of the original material.

A fraction of tubercle bacilli possessing primary toxicity

Tubercle bacilli separated from young cultures were thoroughly extracted with monochlorobenzene at temperatures never exceeding 50 degrees C. From the soluble material, a fraction corresponding to approximately 1 per cent of the total bacillary weight was separated by fractional precipitation with petrolic ether at temperatures of 0 degrees or 4 degrees C.-depending upon the strain of bacilli. The monochlorobenzene-soluble-ether-insoluble material (fraction 7) prepared from BCG-P was found to contain 0.14 per cent nitrogen and 0.4 per cent phosphorus. Some of its other chemical characteristics are described. Fraction 7 proved unable to elicit tuberculin allergy in guinea pigs, but injection of 5 microg. of it into the skin produced severe local reactions. In albino mice, a single intraperitoneal injection of 20 microg. caused loss of muscular tone and of weight followed by death within 9 days. The only tissue reaction observed was a slight degree of peritonitis. In mice of the C57 BL strain, a single injection of 40 microg. also caused death in the same time, but with pulmonary hemorrhages-usually massive. Material similar to fraction 7 was obtained from one virulent, two attenuated, and one avirulent strain of mammalian tubercle bacilli (bovine and human). The fractions obtained from the various strains differed somewhat in solubility and toxicity. The more virulent the culture, the more toxic was the fraction obtained from it; but it is possible that this relation was the result of differences in the effectiveness of the extraction procedures, rather than of characteristics inherent to the cultures. Evidence is presented that the toxicity of fraction 7 accounts for much of the primary toxicity of tubercle bacilli.

Experimental studies of vaccination, allergy, and immunity in tuberculosis: 3. Effect of killed BCG vaccine

The antigenic effects of living and killed BCG vaccine have been investigated by comparing the degree of tuberculin allergy, the size of vaccinal lesions, and the survival time after challenge infection in large numbers of guinea-pigs vaccinated with BCG suspensions containing various concentrations of living and killed organisms.The allergizing as well as the immunizing potency of BCG was markedly reduced-though not entirely abolished-when the bacilli were killed, yet the size of the vaccinal lesion was only slightly reduced. Results were about the same regardless of whether heat, light, or phenol had been used to kill the organisms. It would thus appear that viability of the organisms in BCG vaccine is important for immunity as well as for allergy, whereas the size of the vaccinal lesion is determined largely by the total mass of bacterial cells injected.The results of this experiment in laboratory animals are in agreement with results of studies in human beings, so far as allergy and lesions are concerned. Persons vaccinated with heat-killed or irradiated BCG have been shown to have very low degrees of post-vaccination tuberculin allergy compared with persons given a corresponding dose of living BCG, yet the size of the vaccinal lesion differs only slightly. The combination of a large vaccinal lesion and a low degree of post-vaccination allergy should therefore invite suspicion that a vaccine contained mainly killed bacilli and, perhaps, the presumption that it has produced only a low degree of immunity.

Antituberculous immunity induced in mice by vaccination with living cultures of attenuated tubercle bacilli

The immunity induced in mice by vaccination with living attenuated cultures of tubercle bacilli was measured by two criteria. (a) Increase in survival time of the vaccinated animals after infection with a dose of virulent bacilli sufficient to kill all the unvaccinated controls within 10 to 20 days. (b) Difference in the number of living bacilli recovered from the spleen and lungs of vaccinated and normal animals infected with a small dose of virulent bacilli. The level of immunity induced was found to depend upon the extent of multiplication in vivo of the bacilli used for vaccination. This in turn was conditioned by the degree of attenuation characteristic of the bacterial strain used in the preparation of the vaccine, the amount of vaccine injected, the route of vaccination, and the time interval between vaccination and challenge infection. It was possible to prevent or retard the development of immunity by treating the mice in course of immunization with a drug, isoniazid, capable of interrupting the multiplication in vivo of the bacilli used as vaccine. Although immunity regularly developed and lasted for many weeks when the proper conditions of vaccination were used, the immune response was never sufficient to protect the animals against ultimate death from infection with virulent tubercle bacilli. The prolongation of life in the vaccinated mice was not consequent on a direct bactericidal effect but rather on a retarded or interrupted multiplication of the virulent bacilli in vivo. The quantitative bacteriological techniques used in the present study would appear to be of value for the analysis of certain problems of immunity, and for the appraisal of vaccines and techniques of vaccination.