Tuberculosis (TB) is a disease in which traditional prophylactic approaches
have been largely unsuccessful. A search for new therapeutic interventions is required in order to overcome the low compliance to complex
chemo-antibiotic regimens and to avoid multidrug resistance.
The aim of this project is to produce new knowledge and insight
that bear potential for new therapeutic or prophylactic interventions.
Project partners will be focusing on one of the most critical
immune evasion mechanism of Mycobacterium tuberculosis (Mtb):
the capacity to switch to a dormant status of latency, which
causes its persistence in the host.
The switch implies a reduction/abrogation of the synthesis of antigens required
for activation of T lymphocytes primed in the early phase of infection, while
new products are generated with possible antigenic properties. MILD-TB will
analyse the variations in lipid metabolism and composition associated to
dormancy. This represents advancement beyond the current state of
knowledge, which is limited to proteins synthesized during dormancy. The
immune response against mycobacterial lipid antigens represents an important
mechanism of defence. However, no data are available on the antigenicity of
lipids produced by dormant Mtb. MILD-TB will analyse the immunogenicity of
lipids isolated from non-replicating Mtb produced in vitro, using a culture
method resembling Mtb dormancy in vivo.
Lipids will be analysed in reference strains and clinical isolates from endemic
areas and will be compared to those produced by replicating Mtb. The
immunogenicity of lipids specifically isolated from dormant Mtb will be
determined using pre-existing and newly established lipid-specific T cell clones
and by immunizing CD1b transgenic mice.
Parallel analysis of susceptibility of dormant Mtb to T-dependent mechanisms
of direct or indirect killing will be performed to explore the possibility of new
therapeutic or prophylactic interventions based on vaccination with lipidantigens
or on immune-modulation.
Mycobacterium tuberculosis (Mtb) is one of the most successful human
pathogens and tuberculosis (TB) remains one of the major health
threats to mankind. Key reasons for this are the unavailability of an efficacious
vaccine for adult disease; the rise of multidrug-resistant strains,
and the association of
Combination antiretroviral therapy has resulted in a dramatic decrease in mortality
and HIV-associated morbidity in industrialised countries. Nevertheless,
many serious issues and challenges – namely long term toxicity
and HIV drug resistance - are problematic and important in the
management of HIV infected individuals, even when treated according
to the state-of-the-art. The need for further advances in clinical
governance and management of HIV infection remains a high priority,
both from a public health and from a medical research perspective.
TB with human immunodeficiency virus (HIV) infection. During
the early stages of Mtb infection, the majority of individuals mount an effective
immune response leading to the control of the infection. Consequently,
most of these individuals experience a mild disease (primary TB), often without
However, the immune response that causes such a clinical cure does not clear
the bacilli from infected individuals and after primary TB, Mtb persists causing
a latent infection. In immunocompetent adults TB typically occurs as a
reactivation of pre-existing foci. This suggests the existence of a dynamic
balance between the host immune system and Mtb. In most cases, the host
response is sufficient to forestall activation of the disease for a lifetime.
Occasionally the immune response fails in some way and the infection
reactivates to cause active disease. The immune factors contributing to the
establishment of latent infection and the immunological components that are
required to maintain such an infection and prevent reactivation are still
Regarding the adaptive response of mycobacteria to host antimicrobial
defences, it is unclear how the bacilli survive in the face of a strong immune
response, whereas it is now clear that they profoundly change several
metabolic activities leading to a non replicating status (dormancy).
The main goal of immunointervention is the induction of active immunity that
is capable of eradicating bacilli rather than just controlling Mtb infection. Most
of the current approaches have addressed the control of primary infection.
These vaccination approaches cannot be effective in latent TB, because
dormant bacilli reduce their metabolic activity and to the immune system they
appear very different to replicating bacilli. It is reasonable to hypothesize that
if new antigens are produced during dormancy, the priming of specific T cells
would be inefficient because these antigens would hardly reach secondary
lymphoid organs. In addition, in latent infection there is a reduced
macrophage death. Consequently, cross-presentation of antigen to MHC class
I- and CD1-restricted T cells by dendritic cells (DC) would be greatly reduced.
These phenomena could be responsible for the lack of a T cell response
against dormant Mtb, which would maintain a latent infection. Therefore, it is
of primary importance to identify the metabolic changes that have potential
relevance for immunorecognition and to take advantage of them to design
new immune intervention strategies capable of preventing TB reactivation.
The scientific and technological goals of MILD-TB are:
- The production and characterization of non-replicating (dormant)
Mtb allowing the extraction, purification and identification of
lipids from replicating and non-replicating Mtb cells, and;
- The analysis of immunogenicity of lipids from replicating
and nonreplicating Mtb in vitro in animal models and ex vivo
in patients with different forms of TB infection
Production of non replicating Mtb for lipid extraction and identification;
Identification of dormancy related lipids inducing stimulation
of both the innate and acquired immunity;
Identification and functional evaluation of dormancy related lipid-specific T
cells both in vitro and in vivo.
The main immune evasion mechanism used by Mtb during primary
TB is based on its capacity to switch to a dormancy status in
macrophages or giant cells that are present in the granuloma.
This capacity allows Mtb to survive until the weakened immune
defences of the host do not allow its “resuscitation” to the
replicating and highly invasive form. The lack of eradication
of dormant Mtb is the cause for post-primary reactivation TB.
MILD-TB aims to assess the immunogenic potential of lipids produced
by Mtb during dormancy and to exploit the lipid-specific immune
response to eradicate dormant bacilli. The identification of
immunogenic dormancy-related lipid would be central to the design
of innovative vaccination approaches and novel diagnostic tools
for active vs. latent infection.
Dipartimento di Malattie infettive Parassitarie e Immunomediate
- Istituto Superiore di Sanità
Viale Regina Elena 299
Tel. +39 06 4990 2659
Fax. +39 06 4938 7112
et Glycoconjugués Mycobactériens"
Département des mécanismes
moléculaires des infections
Institut de Pharmacologie
et Biologie Structurale
205 route de Narbonne
|Tel: +33 (0)5 61 17 55 04
Fax: +33 (0)5 61 17 55 05
||Gennaro De Libero
Department of Research
University Hospital Basel
4031 Basel Switzerland.
|Tel: +41 61 265 2327
Fax: +41 61 265 2350
||Istitut Pasteur de Côte d’Ivoire
Abidjan 07 / Abidjan
|Tel: +22 50 554 6761
Fax: +22 52 345 7623