Team:Paris Bettencourt/Human Practice/TB France

  TB has taken more lives than any other contagious disease before the antibiotics era. It was thought that the disease would be eradicated by the end of the 20th century. However, people living in precarious situations, migrants, immune depressed people (especially HIV patient) still suffer from TB and keep the number of TB case per year from going too low. Therefore in France, 4991 cases of Tuberculosis were diagnosed in 2011.

2) Some departments and class of people are more affected than others

  TB does not affect French Territory the same way. On 22 regions, Ile de France (Paris region) represents 1768 cases (more than 1/3rd). This epidemiological difference can be explained by the different demographic profile of the French Regions. Ile de France is by far the most urbanized and dense region of France. Promiscuity being a very important factor in the transmission of TB, it is logical to observe those differences.

  Population groups are also affected differently. Infant and young people are quite protected. This is mainly due to a very strong vaccination policy that will be explained a bit later. The most affected age group is adults under 60. Indeed, this corresponds to migrants and a lot of HIV patients.

3) The problem of the rise of MDR forms

  The most interesting factor is the apparition of Multi-drug resistance TB (MDR TB)in the last few years. Even if the incidence rate has decreased, the number of MDR TB has risen and is expected to continue to rise. Those forms come mainly from foreign patients arriving in France (mainly from the former Soviet Union and South Africa). This aspect will be developed a bit later.

  When a patient expresses symptoms or corresponds to categories of when TB latent has to be treated, different diagnostic tests are run to determine if those symptoms are caused by a Mycobacterium or not.

  The first test is to get an inoculum by having the patient spit or by getting this with a tube near the lungs. The sample is then analyzed under the microscope. The unit that is looked at is the number of BAAR (Acid-alcohol resistant bacillus) using Ziehl-Neelsen stain. The test is done at least 3 times on 3 different samples taken at 24 hours intervals. Samples are then cultured and a PCR is ran to confirm the strain and to check the most common resistance. It takes approximately a week to get the results. No treatment is given before getting those results, the worst fear being the selection resistant forms.

   Finally there is a third test which is not used by every hospital because it can be difficult to interpretate : the intra Dermo Reaction. Basically, a droplet of liquid containing TB antigenes is put on the skin of the arm of the patient. If the patient has been exposed to a mycobacterium before (or vaccinated),an inflammatory reaction happens.

   Of course, in extreme cases of pulmonary TB, a lung radio can reveal some elements called “cavern” which directly confirm the TB-disease.

  The treatment consists of 4 first-line drugs in combination during 2 months: isoniazid, rifampicin, ethambutol and pyrazinamide. Within the first 2 months of appropriate chemotherapy, the vast majority of bacilli would be killed. It allows clinicians to virtually eliminate the risk of transmission and the selection of drug-resistant mutants. The patient need to follow the treatment during 4 other months (bitherapy: isoniazid, rifampicin).

4) Pharmacological caracteristics of antituberculosis drugs

Isoniazid: The most active drug for the treatment of tuberculosis.

The mechanism of action is the inhibition of synthesis of mycolic acids, which are the main components of mycobacterial cell wall. As a result of the activity, tubercle bacilli lose their features of acid-resistance, water-resistance and proliferating ability, leading to death.Due to its mechanism of action, it is bactericidal against actively growing tubercle bacilli. For resting tubercle bacilli it is bacteriostatic. It is active both on intracellular and extracellular Mycobacteria. Good distribution, it can also penetrate inside the macrophages. It main problems are hepatotoxicity (20% of patients) and neurotoxicity.The metabolism is hepatic including by acetylation (interindividual pharmacogenetic variability). It is eliminated by the kidney.

Rifampicin: The most colored drug for the treatment of tuberculosis.

A multidrug-resistant tuberculosis (MDR TB) is a tuberculosis resistant to isoniazid and rifampicin

An extensively drug-resistant tuberculosis (XDR TB) is an MDR TB + a resistance to a second line drug treatment (fluoroquinolone and aminosids (kanamycine/amikacine/capreomycine). Mortality rate : 35%.

One of the main concern of the clinicians is the appearance of those resistances. The main cause of apparition of resistances in France, is the patient’s lack of therapeutic compliance.

As everything in French public policy systems, missions to fight tuberculosis are divided between several institutions and types of administrations. In a few words, French policy system has three main types of structures :

- The government represented by the ministries and what is called “services déconcentrés”, services that are responsible at a departmental and regional level of the application of the government policies

- The local powers or “collectivités territoriales” : from the city, to the department or regions, those administration are run by people elected locally and are responsible of making the specific interest of a defined territories known and put in place

- Public or semi-public institutions : Might they be firms like the “SNCF” which is responsible for the train or research institutions or monitoring administrations, they are quite independent but under the general direction of ministry and have one or several specific missions.

In order to see clearly who does what, here is a synthetic table which underlines who deals with what in the general monitoring of TB.

A striking fact when talking to professional people dealing with TB is the social aspect of disease. In France, TB is known among medical personnal as the disease of poor people. Doctors mainly diagnose TB according to “the environmental context” that is to say the appearance and life conditions of the patient.

To illustrate this fact, a story of a patient was told to us. A white female 40 years old women, coughed for months, spit blood and expressed all the symptoms of TB. She was seen by more than 10 doctors but no one could figure out what she had because

she was not living in a precarious situation

she was not HIV positiv or immunodepressed

Basically, she did not fit the profile. She got tuberculosis while working in Hahiti and living in promiscuity with people affected by tuberculosis.

In France, this past few years, patients suffering from TB have been more and more coming from a foreign country. In 2010 , the number of foreign patients treated for TB was higher than the number of native ones.

What scares the medical personnal is the rise of MDR forms. Indeed, it is strongly believed in the French medical community that those bacteria are found on migrants who had TB for a long time but a one that were already treated.

Indeed, most of the migrants, who are treated in Paris come from the foreign Soviet Union and South Africa. This can be surprising at first, becquse it could be expected that because of the strong presence of migrants from north and central Africa in France, TB would mainly be found in those populations.

However, the story is a bit more complicated. South Africa and the former Soviet Union have both in common the fact that they have a funcitonning health care system. However, they are not as efficient as occidental ones, especially because they don’t have the financial means to treat every disease as it should be.

Therefore, most patients suffering of TB were treated with one or maybe two antibiotics. This did not lead to the disease being cured but to the development of resistances.

How does this concern France ? In fact, a lot of migrants coming to France from those countries carry an MDR form of TB leading to a rise of the number of MDR forms treated.

In France, even if there is no emergency, everyone is treated and given medical attention. The health care system is national and people who cannot pay don’t. For TB most of the patients who are treated don’ have the financial means to pay, therefore, it is basically paid by the Infectiology department that treat them and in the end by French taxes.

The treatment of TB as described previously , is a long and costly one. Indeed, it is not only about the antibiotics. When a patient is diagnosed, everyone living with him is also screened for TB and the patient is given an appropriate housing situation at least for the duration of the treatment. Social workers are also paid to dispense preventive measures and to practice “active detection of the disease.

As it was explained before, TB outcome for non resistant form is mostly good, as showed on the graph. However the treatment of MDR and XDR form is really not as good.

Clinicians treat the patients with molecules they know are not really effective just in case they might work. In some countries, barbarian methods are used , methods that were used before the appearance of antibiotics. For example, a patient treated in France, had already been treated in its home country by creating intentionally a pneumothorax, that is to say to make the lung collapse on purpose to crush the mass of bacteria. Lungs can also be filled with liquid for a small period of time to drown the mycobacterium.
The entire medical community is definitely in need of new therapies.

No new anti-tb molecule have been developed for 40 years. Indeed, as the disease was easily cured with existing antibiotics and more present in poor countries, it was not profitable for pharmaceutical companies to work on TB. However, in the last few years, the need of new treatments had led to the development of new drugs. However only a handful are near to be marketed.

Up to now, two drugs have been submitted to marketing authorizations : bedaquiline and delamid. Both drugs have led to huge debate in the scientific community for very different reasons.

Bedaquiline developped by Janssen Pharmaceutica under the name Sirturo, inhibits a mycobacterial ATP synthetase. The FDA granted a “fast-track” approval, which means assessing its efficacy by a surrogate measure rather than an actual clinical outcome. This decision was based on the criterion that the drug in addition to a standard MDR TB regimen could change a patient sputum from positive to negative.

However in clinical studies, it was found that 10 out of 79 patients taking the drug died, vs 2 of 81 in the control group. Different medical explanations have been raised to explain this (50% died of TB, others might have suffered from hepatotoxicity …). The fast track approaval requires proprer clinical studies to be done, but those have to be achieved in 2022. The WHO had the drug evaluated by an expert group which reported “bedaquiline may be added to a WHO-recommended regimen in adult MDR-TB patients under the following conditions (conditional recommendation, very low confidence in estimates of effect, i.e. very low quality of evidence) » and listed actions that should be followed before and when giving the drug.

What could be the role of synthetic biology considering those factors? First, it can be noticed, that the new therapies that are developed right now all consist of new drugs to enrich the regimen. We used synthetic biology to at the same time try to improve existing therapies and develop new ones.

According to Christopher Anderson « there is considerable work to be done on diagnostics that will allow the efficient choice of appropriate therapy for each patient diagnosed with TB”, therefore one part of the team worked on developing a new diagnostic tool which could easily and quickly determine the presence of TB and the resistance that it carries. This would help determine the right treatment for the patient more quickly and more efficiently.

In order to develop new drugs, a second project was to reconstruct in E. Coli a pathway metabolizing sulfur, specific to Mycobacterium. This new type of drug sreening would solve a lot of experimental issues faced when dealing with TB like slow growth as well as targeting specifically new pathways. This could lead to a new drug to enrich existing regimens.

According to current national regulation, two out of our four biosynthetic devices could be readily used: our biosensor-based diagnostic test and our safe drug screen. We can improve the diagnostic test by adding TDMH (which will lyse the Mycobacteria cell wall and improve the sensibility of the test). As Christopher Dye pointed out to us, If you want to develop a diagnostic test, you can follow the well-documented path for Xpert, though diagnostics are not so well served by guidelines as drugs and vaccines. Diagnostic tests do not involve any direct contact between the patient and the genetically engineered organism. They must comply with the European regulation of medical devices and be subject to the EC labeling. Even though therapies based on bacterial vectors could stir doubts regarding their safety, they are no less “natural” than antibiotics : after all, we have 100 times more bacteria in our gut than cells in our organism. Refusing to use bacteria as part of “cellular therapies” would therefore be only a waste for humanity. Guidelines for drugs involving living genetically engineered organisms do not exist yet. Although many of these therapeutic devices have proved to be very promising, authorities do not seem to know how to evaluate them. As we can read on the EMEA website,