ASSURE: Assessing the potential correlation between altered MTB cells and a patient’s risk for relapse
ASSURE aims to assess if TB patients who are considered clinically cured have completely achieved sterilisation at the end of treatment. Dr Caroline Beltran, ASSURE Study Lead, is looking for the presence of metabolically altered TB bacteria in sputum samples from PredictTB patients who have completed anti-TB treatment and the potential association between the presence of these bacteria and reactivation of disease. Diagnostic markers that can accurately provide prognostic information about patients’ risk for relapse would significantly help reduce the global TB burden as doctors could offer extended treatment for high-risk patients before they fall ill again.
In ASSURE, which is an acronym for Assessing Sterilising Cure After Anti-TB Treatment, Dr Caroline Beltran, is looking at a sub-population of MTB that might be a cause for relapse in patients that have gone through complete, seemingly successful, anti-TB treatment. The main goal of ASSURE is to evaluate what percentage of clinically cured patients still retain dormant persistent bacteria and look for potential association between these bacteria and reactivation of disease.
At their final visit, an additional induced sputum is collected from clinically cured PredictTB patients for Dr Caroline Beltran’s study. ASSURE started out as a 28-month PredictTB sub-study, in which Dr Caroline Beltran’s goal was to examine samples from 50 of the project’s patients for live MTB bacteria. The project was extended last year, and Dr Caroline Beltran’s new goal is to look at samples from around 200 patients – both those who have undergone the longer six-month treatment and those who have had the shorter four-month treatment.
Cultivating dormant MTB bacteria can take months
In ASSURE, Dr Caroline Beltran’s hypothesis is that TB patients who relapse after having been declared clinically cured still retain what she refers to as differentiable culturable TB bacteria, bacteria that are not cultured under normal conditions.
This hypothesis is based on hints from previous studies’ that sterilisation is not achieved in a portion of cured patients at the end of anti-TB treatment. This can, in a worst-case scenario, represent a risk for both relapse and subsequent transmission.
Studying dormant TB bacteria is challenging, mainly due to the fact that they are extremely difficult to detect and cultivate and since they are present in very small numbers. To bring them out of their hidden state, Dr Caroline Beltran creates an environment that is favourable for them to replicate by using culture filtrate containing resuscitation promoting factors which is thought to break up the thickened cell wall of dormant MTB, allowing them to resume replication. This process of cultivating the bacteria is extremely labour-intensive and can take several months in a biosafety level 3 (BSL-3) laboratory before a final result is received.
Approximately 200 patients will be included the study
When ASSURE was prolonged, the initial plan was for Dr Caroline Beltran to look at sputum from all PredictTB’s approximate 640 patients. However, that plan was recently reversed, partly due to the current lockdown in South Africa hindering Dr Caroline Beltran from accessing the lab, and partly due to that she has not found live bacteria cells in as many samples as she had expected she would. Her current goal is to include around 200 samples in ASSURE.
Since it takes several months to cultivate these altered bacteria, this method is too time-consuming to be used at a larger scale as a diagnostic marker of relapse. This means that if Dr Caroline Beltran’s study manages to show a correlation between live MTB bacteria and a patient relapsing, the natural next step in her research would be to look for a proxy-marker to the bacteria.