In recent years, researchers all over the world have been seeking a deeper understanding about the impact of people’s gut bacteria—their so-called microbiome—on their health and risk of developing different diseases.
Researchers from the National Food Institute, Technical University of Denmark (DTU), in cooperation with Rigshospitalet, have investigated the microbiome in 37 Danish children and adolescents, who have received a transplant of stem cells harvested from healthy individuals. The aim of these transplants is to give the patient a new immune system, which can fight the patient’s disease, e.g. leukemia.
The study has uncovered associations between the presence or absence of certain gut bacteria and serious side effects, which occur following the transplantation. These associations fall into three groups.
Firstly, the researchers have observed fewer side effects and lower mortality in patients whose microbiome was rich in common anaerobic gut bacteria such as Ruminococcaceae. These patients’ immune system has also regenerated more quickly following the transplantation.
Secondly, the researchers have observed that patients whose blood contained a large amount of a certain immune marker prior to the transplantation also had more Lactobacillaceae bacteria in their gut later after transplantation—and these patients experienced more severe side effects.
Thirdly, the researchers have observed an association between higher levels of inflammatory markers in the patients’ blood and larger amounts of Enterobacteriaceae bacteria in the patients’ microbiome. These types of bacteria are known to cause infection and inflammation in humans.
Based on the study, the researchers cannot show whether the presence or absence of certain bacteria causes patients to experience more or fewer side effects. They are only able to prove associations. However, if doctors have knowledge of their patients’ microbiome, the researchers' findings can be used to plan the best course of treatment, which will avoid some of the worst side effects.
Patients who receive a stem cell transplantation are very ill and therefore already receive a lot of medication before the transplantation. These medications often include antimicrobials to fight infections. Different types of antimicrobials affect the patient's microbiome in different ways by killing some types of bacteria while giving others more favorable growth conditions.
Doctors can use the study's findings of which gut bacteria are desirable to have or to avoid prior to transplantation when prescribing antibiotics to a patient in order to limit side effects associated with the transplantation.
The National Food Institute has launched a new research project to gain a deeper understanding of the link between the microbiome and the side effects following a transplant. A greater number of patients are included in the study and the researchers will analyze more biomarkers.
In the long term, the researchers expect that the work can be used in connection with personalized medicine, where doctors—based on the patient's unique microbiome—adapt the treatment to obtain the greatest effect.