Pilot study of the safety and effect of intranasal delipidated acid-treated Mycobacterium vaccae in adult asthma

Complete genome sequence of Mycobacterium vaccae type strain ATCC 25954

Mycobacterium vaccae is a rapidly growing, nontuberculous Mycobacterium species that is generally not considered a human pathogen and is of major pharmaceutical interest as an immunotherapeutic agent. We report here the annotated genome sequence of the M. vaccae type strain, ATCC 25954.

DC priming by M. vaccae inhibits Th2 responses in contrast to specific TLR2 priming and is associated with selective activation of the CREB pathway

The environmental mycobacterium, M. vaccae has been used in mouse models to support the contemporary hygiene hypothesis that non-pathogenic microorganisms reduce allergy associated T helper (Th)2 responses and inflammatory diseases by augmenting regulatory T cells. However, data for human models and possible mechanisms are limited. We tested the effect of innate immune interactions between human DC and M. vaccae on DC-dependent T cell responses. M. vaccae activation of DC via Toll like receptor (TLR)2 was compared to a specific TLR2 ligand (Pam(3)CSK4) and alternative stimulation with a TLR4 ligand (LPS). M. vaccae induced DC dependent inhibition of Th2 responses, in contrast to Pam(3)CSK4, which had the opposite effect and LPS, which had no polarizing effect. DC maturation, gene expression and cytokine production, in response to each stimulus did not correlate with the specific functional effects. Comparable DC transcriptional responses to M. vaccae and Pam(3)CSK4 suggested that TLR2 mediated transcriptional regulation was not sufficient for inhibition of Th2 responses. Transcription factor enrichment analysis and assessment of signaling events, implicated a role for selective early activation of the CREB pathway by M. vaccae. Further study of the CREB pathway may provide novel insight into the molecular mechanisms of DC-dependent T cell polarization.

The potential of Mycobacterium to protect against allergy and asthma

The increase in the global incidence of atopic disease and asthma during the past few decades has been ascribed to environmental factors, including the reduction in exposure to serious infections. The hypothetical framework to explain the inverse relationship between infections and atopic disease and asthma has been called the "hygiene hypothesis." Animal and experimental models have identified Mycobacteria as important potential candidates in the hygiene hypothesis by demonstrating that exposure to Mycobacteria or mycobacterial proteins led to subsequent reduction in different atopic manifestations. Although there are epidemiological studies in support, they have not always been consistent. In this review we appraise epidemiologic evidence on the inverse relationship between mycobacterial exposure and atopic disease, explore the immunological mechanisms involved and evidence that this effect may be dose-dependent, and discuss the challenges facing the use of Mycobacteria as vaccine for prevention of atopic disease.

Mycobacteria and allergies

Exposure to mycobacteria was inevitable throughout mammalian evolution. Most mycobacteria are saprophytic environmental organisms that are enormously abundant in soil and untreated water and evoke immune responses in the residents of developing countries. A few species are pathogens. For example Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects approximately 1/3 of the world's population. Many individuals also receive vaccination with the Bacille Calmette Guérin (BCG), which is an attenuated form of the organism causing bovine TB. In order to understand the possible role that mycobacteria might have in the increases in allergic disorders over the last decades, it is necessary to dissect out these different mycobacterial influences. Above all it is essential, when analysing tuberculin test results, to distinguish between individuals who have latent TB and those who do not. Only then can probable effects of diverse types of exposure emerge. There is no doubt that in animal models mycobacteria can both prevent and treat allergic responses either by boosting Th1 or by driving allergen-specific regulatory T cells (RegT). Clinical trials in man remain inconclusive.

Do vaccines modify the prevalence of asthma and allergies?

Epidemiological studies suggest the hypothesis that the increase in asthma and allergies in the industrialized world can be explained by a decline in the number of infectious diseases occurring during childhood. In the context of this 'hygiene hypothesis', is immunization in early life a risk factor for promoting allergic diseases? The majority of studies, especially those conducted with more extensive populations, have not found an increased risk, and although 'not finding an increased risk' is not the same as 'the non-existence of any risk at all', it seems that the evidence is tipped in favor of the absence of risk. Conversely, although some surveys have described a protective effect of vaccination, the majority refuted this result. If there is any effect, it is probably a weak one.

The production of a new extracellular putative long-chain saturated polyester by smooth variants of Mycobacterium vaccae interferes with Th1-cytokine production

Mycobacterium vaccae is of major pharmaceutical interest as an immunotherapeutic agent. Although M. vaccae 15483 ATCC(T) strain displays smooth and rough colonial morphologies on solid culture media, it is not known in which conditions M. vaccae switches from one colonial morphotype to the other or whether there are biological differences, especially immunological, between them. We have found that the change from a smooth to rough stable variant occurs spontaneously at 30 degrees C. The analysis of the composition of the cell wall in both variants showed that the smooth morphotype presents an extracellular material that has never previously been described and was identified as a long-chain saturated polyester that, interestingly, is not produced by the rough morphotype. Our results also indicate that this compound could be implicated in the spreading ability of smooth colonies. Proliferation, IFN-gamma and IL-12(p40) production by splenocyte cultures was significantly higher in mice immunised with the rough variant compared with those immunised with the smooth one. This latter finding suggests that the different colonial morphology of M. vaccae may affect the immunomodulatory effects induced from M. vaccae preparations.

Role of regulatory T cells in human diseases

The discovery of regulatory T lymphocytes (Treg) that are actively involved in maintaining immune tolerance has led to new insights into mechanisms of tolerance breakdown in human diseases, including those resulting from allergic, autoimmune, or infectious causes. Congenital deficiency of CD4(+)CD25(+) Treg cells caused by loss-of-function mutations in the gene encoding Foxp3 triggers a syndrome of lymphoproliferation and myeloproliferation, autoimmunity, and allergic dysregulation, whereas deficient allergen-specific Treg cell responses have been associated with a number of allergic and autoimmune disorders. Tolerization to allergens and autoantigens is associated with augmentation of Treg cell numbers and suppressive function, suggesting the manipulation of Treg cell activity as a potential strategy for future therapeutic interventions in allergic and autoimmune diseases.