STUDIES ON THE HETEROLOGOUS IMMUNOGENICITY OF A MENTHANOL-INSOLUBLE FRACTION OF ATTENUATED TUBERCLE BACILLI (BCG). I. ANTIMICROBIAL PROTECTION

BCG's role in strengthening immune responses: Implications for tuberculosis and comorbid diseases

The BCG vaccine represents a significant milestone in the prevention of tuberculosis (TB), particularly in children. Researchers have been developing recombinant BCG (rBCG) variants that can trigger lasting memory responses, thereby enhancing protection against TB in adults. The breakdown of immune surveillance is a key link between TB and other communicable and non-communicable diseases. Notably, TB is more prevalent among people with comorbidities such as HIV, diabetes, cancer, influenza, COVID-19, and autoimmune disorders. rBCG formulations have the potential to address both TB and HIV co-pandemics. TB increases the risk of lung cancer and immunosuppression caused by cancer can reactivate latent TB infections. Moreover, BCG's efficacy extends to bladder cancer treatment and blood glucose regulation in patients with diabetes and TB. Additionally, BCG provides cross-protection against unrelated pathogens, emphasizing the importance of BCG-induced trained immunity in COVID-19 and other respiratory diseases. Furthermore, BCG reduced the severity of pulmonary TB-induced influenza virus infections. Recent studies have proposed innovations in BCG delivery, revaccination, and attenuation techniques. Disease-centered research has highlighted the immunomodulatory effects of BCG on TB, HIV, cancer, diabetes, COVID-19, and autoimmune diseases. The complex relationship between TB and comorbidities requires a nuanced re-evaluation to understand the shared attributes regulated by BCG. This review assessed the interconnected relationships influenced by BCG administration in TB and related disorders, recommending the expanded use of rBCG in healthcare. Collaboration among vaccine research stakeholders is vital to enhance BCG's efficacy against global health challenges.

Functional in-vitro evaluation of the non-specific effects of BCG vaccination in a randomised controlled clinical study

Bacille Calmette-Guérin (BCG), the only currently licenced tuberculosis vaccine, may exert beneficial non-specific effects (NSE) in reducing infant mortality. We conducted a randomised controlled clinical study in healthy UK adults to evaluate potential NSE using functional in-vitro growth inhibition assays (GIAs) as a surrogate of protection from four bacteria implicated in infant mortality. Volunteers were randomised to receive BCG intradermally (n = 27) or to be unvaccinated (n = 8) and were followed up for 84 days; laboratory staff were blinded until completion of the final visit. Using GIAs based on peripheral blood mononuclear cells, we observed a significant reduction in the growth of the Gram-negative bacteria Escherichia coli and Klebsiella pneumonia following BCG vaccination, but no effect for the Gram-positive bacteria Staphylococcus aureus and Streptococcus agalactiae. There was a modest association between S. aureus nasal carriage and growth of S. aureus in the GIA. Our findings support a causal link between BCG vaccination and improved ability to control growth of heterologous bacteria. Unbiased assays such as GIAs are potentially useful tools for the assessment of non-specific as well as specific effects of TB vaccines. This study was funded by the Bill and Melinda Gates Foundation and registered with ClinicalTrials.gov (NCT02380508, 05/03/2015; completed).

Bacillus Calmette-Guerin Vaccine and Nonspecific Immunity

Bacillus Calmette-Guerin (BCG) vaccine is one of the most widely used vaccines in the world. It protects against many non-mycobacterial infections secondary to its nonspecific immune effects. The mechanism for these effects includes modification of innate and adaptive immunity. The alteration in innate immunity is through histone modifications and epigenetic reprogramming of monocytes to develop an inflammatory phenotype, a process called “trained immunity.” The memory T cells of adaptive immunity are also responsible for resistance against secondary infections after administration of BCG vaccine, a process called “heterologous immunity.” Bacillus Calmette-Guerin vaccine is known to not only boosts immune responses to many vaccines when they are co-administered but also decrease severity of these infections when used alone. The BCG vaccine by itself induces a TH1 type response, and its use as a vector has also shown promising results. This review article summarizes the studies showing effects of BCG vaccines on various viral infections, its role in enhancing vaccine responses, the mechanisms for this protective effect, and information on its effect on COVID-19.

Isolation of a Soluble Resistance-Enhancing Factor from Mycobacterium phlei

Fox, Alfred E. (Warner-Lambert Research Institute, Morris Plains, N.J.), Joachim Anschel, George L. Evans, Raam R. Mohan, and Benjamin S. Schwartz. Isolation of a soluble resistance-enhancing factor from Mycobacterium phlei. J. Bacteriol. 92:285-290. 1966.-Extraction of a crude cell wall preparation from Mycobacterium phlei with 20% urea yielded a fraction which induced a state of enhanced resistance to microbial challenge. The resulting soluble extract, after removal of the urea, represented a 15% yield of solids with the separation of the biologically active component(s) and elimination of toxicity. Single oral or subcutaneous submicrogram doses of this material induced a prolonged state of increased resistance to subsequent challenge with Salmonella enteritidis in mice. This effect appeared as early as 2 hr after oral administration and persisted for at least 30 days. Protection against experimental infection with Staphylococcus aureus was also demonstrated. Resistance to viral challenge with influenza type A was observed after intranasal administration of the M. phlei extract to mice. The isolated material was found to contain carbohydrate, protein, nucleic acids, and lipids. The lipids represented 60% of the total solids, and were all short-chain fatty acids. No toxic effects, including pyrogenicity, could be demonstrated after oral or parenteral administration of this preparation.

Stimulation of nonspecific host resistance to infection induced by muramyldipeptides

The effect of muramyldipeptide (MDP), N-acetylmuramyl-L-alanyl-D-isoglutamine [MDP(Ala)], and its analogs on bacterial infection was studied using the experimental model of sepsis infection in mice. Injection of MDP(Ala) gave mice definitive protection against E. coli infection, but only partial protection against P. aeruginosa or K. pneumoniae infection. Several factors influencing the protective activity of MDP(Ala) on E. coli infection were studied, and it was demonstrated that the activity was induced by various routes of administration of MDP(Ala), including the oral route, and was markedly influenced by the bacterial inoculum size. It was also shown that the effective dose of MDP(Ala) was 100 micrograms per mouse for intraperitoneal, intravenous or subcutaneous injections and 1,000 microgram per mouse when administered orally. Furthermore, the optimal interval between MDP-treatment and infection was 24 hr when the treatment was carried out before infection. Clearance of bacterial cells in blood was observed after E. coli infection in mice treated with MDP(Ala). The efficacy of MDP(Ala) and two analogs, N-acetylmuramyl-L-valyl-D-isoglutamine [MDP(Val)] and N-acetylmuramyl-L-seryl-D-isoglutamine [MDP (Ser)], was evaluated for the E. coli infection; MDP(Val) was proven to be slightly less active than MDP(Ala), and MDP(Ser) to be the least effective, although MDP(Val) or MDP(Ser) was reported to have higher adjuvanticity than MDP (Ala) for the development of delayed-type hypersensitivity.

Specific and nonspecific immune resistance enhancing activity of staphage lysate

The immunopotentiating activity of staphage lysate (SPL) was evaluated in terms of its immune protection against lethal bacterial infection and its antitumor activity. Mice were pretreated weekly with 10(8) viable, Staphylococcus aureus, strain 18Z for 3 weeks (Induction), followed by intraperitoneal SPL injections (Elicitation) at various times in relation to infectious challenge or tumor implantation. Induction without elicitation, or elicitation alone failed to provide protection against Klebsiella pneumoniae infection and resulted in only 30-40% survival against homologous infection with pathogenic S. aureus type III, whereas combined induction and elicitation produced enhanced resistance induction and elicitation regimens resulted in 50% and 80-100% survival in mice inoculated with K. pneumoniae and S. aureus, respectively. SPL had no antitumor effect in mice implanted with median survival time resulting from induction and elicitation in animals implanted which Ehrlich's ascites. This enhancement of immune resistance may possibly be related to activation of thymus-modulated lymphocytes and macrophages by SPL.

MER-BCG (NSC-143769): immunogenicity and toxicity of single and repeated intradermal injections in dogs

Intradermal injections of MER-BCG 0.1 mg or 0.2 mg at each of 10 multiple sites, led to local granuloma formation. The nodules reached approximately 10 mm in diameter, ulcerated and were accompanied by granulomatous changes in the regional lymph nodes. Six or twelve successive treatments (each including 10 injections) at 4 week intervals produced the same histopathological lesions but no changes in hematological and blood chemical parameters or general morphology and no changes in general condition with exception of occasional weight loss in a few animals. Injection with 0.01 or 0.001 mg/site produced similar, though less severe, skin lesions but no changes in the draining lymph nodes. The immunogenicity of MER-BCG was characterized by granuloma formation, a positive skin response to old tuberculin, and a positive lymphocyte transformation to PPD tuberculin, thus indicating stimulation of cell-mediated immune responses. However, there was a decreased responsiveness to PHA and PPD with continuing treatment with MER-BCG. The decreased responsiveness and accumulation of numerous depots of antigen would suggest an "immunologic paralysis" contraindicating the administration of excessive amounts of MER-BCG during immunotherapy. A specific humoral response to the administration of MER-BCG was not detected, but an MER-BCG dose independent decrease in albumin associated with a non-specific, dose related elevation in serum IgG was observed.

Enhancement of the neonate's nonspecific immunity to Klebsiella infection by muramyl dipeptide, a synthetic immunoadjuvant

N-acetylmuramyl-L-alanyl-D-isoglutamine (muramyl dipeptide) and certain derivatives that are structural analogs of part of the bacterial peptidoglycan monomer have been shown to be adjuvant active and to enhance the nonspecific immunity of adult mice infected by Klebsiella pneumoniae. In the present study muramyl dipeptide and two other synthetic analogs were found to be active in newborn mice. This activity could be demonstrated after administration by subcutaneous or even by oral route. In contrast to what was observed after treatment by lipopolysaccharide, 8-day-old mice were definitively protected against bacterial challenge by these glycopeptides. Therefore such molecules could have a great value in view of studying and correcting the neonate's unresponsiveness.

Surgical adjuvant immunotherapy for colorectal cancer

One hundred forty-four Wistar-Furth rats in 12 therapeutic groups have been studied in a long-term comparison of the effectiveness of nonspecific immunotherapy with MER (methanol extraction residue) vs active-specific immunotherapy with neuraminidase-modified tumor cells. Six months after surgical adjuvant immunotherapy a 100% improvement in survival was achieved with MER immunotherapy compared to untreated control animals. In addition, the use of MER enhanced the value of active-specific immunotherapy where both modalities were combined in sequence. The predicted value of MER-BCG (Bacillus Calmette-Guerin) for the immunotherapy of solid tumors was borne out by these results suggesting that present ongoing clinical trials of MER as adjuvant therapy for large bowel cancer should prove to be successful if properly controlled. The pattern of survival in these experiments suggests that surgical adjuvant immunotherapy is cytostatic rather than cytocidal, and implies the need for long-term, repeated immunizations.

Enhancement of nonspecific immunity to Klebsiella pneumoniae infection by a synthetic immunoadjuvant (N-acetylmuramyl-L-alanyl-D-isoglutamine) and several analogs

N-Acetylmuramyl-L-alanyl-D-isoglutamine and four other synthetic adjuvants that are structural analogs of part of the mycobacterial peptidoglycan monomer are shown to enhance the nonspecific immunity of mice infected by Klebsiella pneumoniae. These compounds are active by various routes, including oral administration; they are also effective when administered after challenge. Of the seventeen other analogs tested, none is able to increase significantly resistance to infection, although seven of these molecules are adjuvant-active in saline. Previous results have shown that in contrast to lipopolysaccharides, these synthetic adjuvants are devoid of immunogenicity, mitogenicity, and toxicity in normal or adrenalectomized mice.

Effects of BCG, Corynebacterium parvum, and methanol-extration residue in the reduction of mortality from Staphylococcus aureus and Candida albicans infections in immunosuppressed mice

An immunosuppressed mouse model was devised to test the effects of immunopotentiators on the prevention of bacterial and fungal infections. The effects of BCG and Corynebacterium were tested against Staphylococcus aureus and Candida albicans infection. The effect of methanol-extraction residue (MER-BCG) was tested against S. aureus septicemia. CDF mice were given various doses of BCG, 1.0 mg of C. parvum, or 0.5 mg of MER intraperitoneally at varying intervals before injection of an intravenous bacterial challenge. Four days before challenge, 300 mg of cyclophosphamide per ml was given intraperitoneally. BCG (106 colony-forming units) reduced mortality due to S.aureus at pretreatment intervals of 3, 7, 14, and 28 days. Isonicotinic acid hydrazide treatment elimated the protective effect of the live BCG. C. parvum was as effective as BCG against S. aureus septicemia when given 3 days before infection, but lost most of its protective effect after that time. MER protected at doses as small as 0.25 mg when given 25 days prior to challenge. Both BCG and C. parvum exerted a protective effect against Candida albicans infection.

Modulation of the immune response by a methanol-insoluble fraction of attenuated tubercle bacilli (BCG). II. Relationship of antigen dose to heightened primary and secondary immune responses to sheep red blood cells

A methanol extraction residue (MER) of BCG has previously been shown to heighten host resistance to a subsequent challenge with microorganisms or syngeneic tumour grafts and to stimulate the antibody response to sheep red blood cells (SRBC) and phage T₂. Present investigations on the effect of antigen dose on MER stimulation of the primary and secondary response to SRBC indicated that:

(1) Pretreatment by MER stimulates the early primary response most effectively when the immunizing dose of SRBC is less than maximum, and this is due to a greater increase by MER of 19S antibody with low doses of antigen than with high doses of SRBC. Maximum 7S antibody production is higher in MER treated animals at all antigen doses.

(2) MER administered after low doses of SRBC but not high doses stimulates the ongoing primary haemagglutinin response.

(3) Maximum secondary responses of mice treated with MER before priming are considerably elevated above the corresponding controls and the secondary responses in treated mice are not inhibited by high priming doses of antigen.

These results are discussed in relation to the locus of MER activity.

Shared antigens between heterologous bacterial species

Sera from normal rabbits were shown to have antibodies that bound radiolabeled test antigens derived from many taxonomically unrelated bacteria. Sera from rabbits that had been immunized with sonically treated material of 12 different bacteria, including M. bovis strain BCG, had antibodies that bound not only radiolabeled homologous test antigens but also radiolabeled antigens from many unrelated bacteria. Binding by normal and immunized sera to radiolabeled test antigens was inhibited by homologous unlabeled test antigens but not by substances such as bovine serum albumin, polyvinylpyrrolidone, sheep erythrocytes, and endotoxin. The broad range of shared or cross-reactivity among antigens in bacteria may explain the presence of antibodies to many bacteria in sera from normal humans and previously unimmunized experimental animals. The presence of these antibodies raises the question whether resistance to many bacterial infections may be partly due to immune mechanisms, whether cellular or humoral, that have been stimulated by unrelated bacteria.

Shared antigens between Mycobacterium bovis (BCG) and other bacterial species

Antigens from Mycobacterium bovis and Listeria monocytogenes bind to serums from normal rabbits as well as from those immunized with unrelated bacteria, especially intracellular parasites. Binding is to the Fab portion of immunoglobulin G and is immunologically specific.

Modulation of the immune response by a methanol-insoluble fraction of attenuated tubercle bacilli (BCG). I. Primary and secondary responses to sheep red blood cells and T2 phage

Studies were continued on the mode of action of a methanol-insoluble moiety (methanol-extraction residue) of attenuated tubercle bacilli which enhances the immune response. We analysed the effects of treatment with this material on the primary and secondary immune responses of mice to two antigens, sheep red blood cells and T₂ phage.

Pretreatment with methanol-extraction residue enhanced the primary response to sheep red blood cells, accelerating the formation of both 19S and 7S plaqueforming cells and of circulating haemagglutinins, and prolonging high levels of 19S and 7S plaque-forming cells.

Methanol-extraction residue delayed the secondary response to sheep red blood cells when administered between primary and secondary immunization. Methanolextraction residue administration subsequent to immunization did not affect an ongoing primary response to this antigen.

Administration of methanol-extraction residue before primary immunization with T₂ phage, or between primary and secondary immunizations, enhanced both the primary and secondary circulating antibody responses to this antigen.

The findings are discussed in relation to possible sites of action of methanol-extraction residue.

Studies on the mode of action of the heterologous immunogenicity of a methanol-insoluble fraction of attenuated tubercle bacilli (BCG)

Pre-treatment of mice with a methanol-insoluble residue (MER) of phenol-killed BCG tubercle bacilli affected markedly their immunological response to subsequent immunization with sheep red blood cells (SRBC) and allogeneic red blood cells (ARBC), and their ability to clear intravenously injected colloidal carbon from the circulation.

Young adult BALB/c and Swiss albino mice immunized with SRBC usually responded to one or two pre-injections of 0.5 mg each of MER with considerable increments in the total and relative numbers of specifically reactive cells (Jerne plaque-forming cells, PFC) in the spleen. When, however, Swiss albino mice were given MER at ages of 10 weeks or younger and shortly before specific immunization, the splenic content of PFC was depressed. Single preinjection of 0.25–1.0 mg MER stimulated the circulating haemagglutinin response of young adults of the C3H genotype to immunization with Strain A red cells.

The heightened responsiveness of MER-stimulated animals was already evident 1–3 days after red cell immunization, and was seen even when intervals of several weeks or months elapsed between MER treatment and immunization. It was also manifest when there was no increase in the total weight or nucleated cell content of the spleen.

MER enhanced considerably total and functional carbon clearing activity as early as 2 hours after treatment, prior to any change in the ratio of spleen and liver weights to body weight.

These findings point to MER as an active stimulator of antibody formation and phagocytosis in mice, and especially of the early response to antigens and particulate foreign substances.

Specificity of acquired resistance produced by immunization with mycobacterial cells and mycobacterial fractions

Mice were immunized intraperitoneally with 5.0 mg of living and 5.0 mg of heat-killed H37Ra cells of the attenuated strain Mycobacterium tuberculosis and challenged intraperitoneally with Listeria monocytogenes and Klebsiella pneumoniae. The period of protection provided by the living and heat-killed H37Ra cells against both heterologous infections was the same. When mice were immunized intraperitoneally with graded doses of living and heat-killed H37Ra and challenged intraperitoneally with listeria or klebsiella, the lowest immunizing dose providing protection against both klebsiella and listeria challenge was the same for living and heat-killed cells. Living and heat-killed cells also immunized equally effectively when the routes of immunization and challenge were different. Mice also were immunized intraperitoneally with mycobacterial ribosomal fraction, mycobacterial cell walls, and several nonspecific agents (Escherichia coli endotoxin, mineral oil emulsion, and Freund's incomplete adjuvant). The mice were challenged intraperitoneally with listeria or klebsiella at varying times after immunization. The mycobacterial components and all the nonspecific agents provided transitory protection lasting no longer than 4 days after immunization. Only the mycobacterial cell walls and the endotoxin provided protection against listeria challenge. It was concluded that the protection provided by the mycobacterial ribosomal fraction is specific for tuberculosis infection, since this fraction provided no protection against listeria infection and only transitory protection against klebsiella. It was also concluded that the mycobacterial component providing protection against heterologous infections is heat stable and probably is found in the cell wall.

Studies on the heterologous immunogenicity of a methanol-insoluble fraction of attenuated tubercle bacilli (BCG). II. Protection against tumor isografts

A methanol-insoluble residue (MER) of phenol-killed attenuated tubercle bacilli (BCG), which has been reported previously to be capable of evoking heightened resistance to infection with antigenically unrelated microorganisms, was found to affect as well the resistance of highly inbred mice against tumor isografts. In most instances, the MER evoked heightened resistance against the tumor implants, but heightened susceptibility was the effect induced against two of the tumors tested, and no effect was elicited against one neoplasm. It is suggested that the heightened susceptibility occasionally produced by pretreatment with MER may also be of immunological nature, i.e. immunological enhancement. Treatment with MER was more effective when administered some time before tumor challenge than when given simultaneously with, or after, tumor implantation. The protective effects manifested against some tumors were of a high order, a significant number of animals rejecting the neoplastic implants, and were displayed even when several months elapsed between treatment and challenge. Living BCG and intact phenol-killed bacilli also evoked heightened resistance against some of the tumors tested, and in one experiment living BCG proved effective whereas MER did not. On the whole, however, MER was the most active (and least toxic, as shown previously) of the several tubercle bacillus preparations tested. MER elicited heightened reactivity against first transplant generation tumors as well as against tumors maintained for considerable periods of time by repeated animal passage, and against spontaneously arising as well as against induced neoplasms. The experimental parameters necessary to demonstrate maximal effects varied somewhat from tumor to tumor. In general, however, single intraperitoneal injections of small quantities of MER, of the order of 0.25 to 1.0 mg, afforded the best protection.

Stimulation of nonspecific resistance to infection by a crude cell wall preparation from Mycobacterium phlei

Fox, Alfred E. (Warner-Lambert Research Institute, Morris Plains, N.J.), George L. Evans, Frank J. Turner, Benjamin S. Schwartz, and Ansel Blaustein. Stimulation of nonspecific resistance to infection by a crude cell wall preparation from Myocobacterium phlei. J. Bacteriol. 92:1-5. 1966.-Exposure of large quantities of viable Mycobacterium phlei to attrition in a colloid mill resulted in 90 to 95% disruption of the organisms. Isolation of the crude cell wall preparation was accomplished by centrifugation of the broken cells at 10,000 x g, resuspension of the sediment, and repeated centrifugation at 1,000 x g to remove intact cells. Single oral or parenteral doses of the cell wall preparation increased the resistance of mice and guinea pigs to experimental infection with Salmonella enteritidis, and of mice to Staphylococcus aureus, for prolonged periods after administration. Histological examination of the organs of mice treated orally or intraperitoneally revealed a lymphoid hyperplasia of the spleen and a Kupffer cell proliferation of the liver. The preparation was nontoxic to mice by the oral route at doses up to 5,000 mg/kg, and the intraperitoneal ld(50) was approximately 680 mg/kg.

Nonspecific factors in resistance of mice to experimental tuberculosis

Youmans, Guy P. (Northwestern University Medical School, Chicago, Ill.), and Anne S. Youmans. Nonspecific factors in resistance of mice to experimental tuberculosis. J. Bacteriol. 90:1675-1681. 1965.-In contrast to viable attenuated mycobacterial cells, Escherichia coli lipopolysaccharide (LPS) did not produce an acute pulmonary granulomatous response in mice, did not decrease the tolerance of mice to early subsequent intravenous injections of viable attenuated mycobacterial cells, nor did it increase susceptibility to tuberculous infection when injected simultaneously with virulent mycobacterial cells. When the injection of E. coli LPS was followed by the intravenous injection of virulent mycobacterial cells, there was a moderate increase in resistance to tuberculous infection which was maximal 7 to 14 days after the LPS injection. The degree of increased resistance to tuberculous infection was approximately the same as that produced by nearly maximal tolerated doses of heat-killed attenuated mycobacterial cells, and to that produced by a trichloroacetic acid extract of heat-killed attenuated mycobacterial cells. It is suggested that the major, if not entire, immunizing component of heat-killed attenuated mycobacterial cells resides in a heat-stable "nonspecific" component. A "multiple response" theory of immunity to tuberculosis is proposed.

RESISTANCE-ENHANCING ACTIVITY OF CULTURE FILTRATES OF MYCOBACTERIUM TUBERCULOSIS

Hedgecock, Loyd W. (Veterans Administration Hsopital, St. Louis, Mo.). Resistance-enhancing activity of culture filtrates of Mycobacterium tuberculosis . J. Bacteriol. 88: 1349–1355. 1964.—It was demonstrated that filtrates of cultures of Mycobacterium tuberculosis exhibit resistance-enhancing activity against infection with Klebsiella pneumoniae and Diplococcus pneumoniae . Resistance was demonstrable when the culture filtrate was injected 3 hr prior to challenge with K. pneumoniae , and reached the highest level when injected 24 hr before challenge. Protection was maximal when the filtrate and challenging organisms were injected by the same route. After infection with K. pneumoniae , the bacterial titers in the tissues of filtrate-treated animals were significantly lower than those of untreated susceptible controls. Mice injected with the filtrate 24 hr previously demonstrated significantly increased rates of clearance of injected carbon from the blood. In examination of a variety of mycobacteria, resistance-enhancing activity was found only in culture-filtrates of pathogenic mycobacteria, the highest concentration occurring in filtrates of virulent organisms. The injection of a relatively large amount of phenol-killed cells of all of the mycobacteria examined enhanced resistance to infection with K. pneumoniae .