A recent review study published in Frontiers in Immunology showed that oral microbiota composition could affect the outcomes of allogeneic hematopoietic stem cell transplantation (HSCT). Adverse outcomes, such as oral mucositis and graft-versus-host disease (GVHD), were associated with specific imbalances in the oral flora of transplant recipients.
Allogeneic HSCT is a last-line treatment for many blood cancers, and though it has a high success rate, it also carries an increased risk of posttransplant disease. The most severe and life-threatening of these diseases is GVHD, which occurs in 30-60% of transplant recipients. Approximately 50% of people who develop GVHD die from the disease.
In the review study, authors from the Okayama University Hospital in Okayama, Japan, observed results from over 100 studies on oral microbiota, many of which were directly related to allogeneic HSCT recipients.
The authors first noted that the pretreatment and prophylaxis for HSCT caused or exacerbated existing oral dysbiosis—or imbalance in the natural microbiota. Given that many environmental factors, such as diet and smoking status, can cause dysbiosis, and that pretreatment for HSCT commonly includes antibiotic therapy and total-body irradiation, this was perhaps an expected finding. The next thing they noted, however, is a bit more surprising.
The review stated that elevated levels of, or even the presence of, certain organisms predicted the occurrence of certain posttransplant diseases.
“The risk of [acute GVHD] was higher when Streptococcus and Corynebacterium abundance in the supragingival dental biofilm was high during preconditioning,” the authors reported. However, it wasn’t just the occurrence of GVHD that was linked to bacterial levels. Certain organisms were linked to GVHD grade. The authors reported, “the relative increase in the abundance of oral Actinomycetaceae, Prevotellaceae, and Propionibacteriaceae at preconditioning could be a predictor of the development of aGVHD of grade II or higher.”
The good news is that certain bacteria showed the opposite effect. “Conversely, high Veillonella abundance was associated with a low risk of aGVHD. This may be because lactic acid metabolism by Veillonella contributes to the resilience of the oral microbiota against acidification.”
The results of this review suggest that oral microbiota, not just gut flora, play a role in the presence or absence of GVHD. Nurses frequently involved in the care of patients receiving HSCT should be aware of the associations and potential predictive nature of variances in oral flora.
Impact of oral microbiota on pathophysiology of GVHD
Graft-versus-host disease: a complex long-term side effect of hematopoietic stem cell transplant