State of oral innate immunity and salivary microbiome with allogeneic hematopoietic stem cell transplant

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) and the use of chemotherapy and antibiotics cause large changes in the gut and oral microbiomes. In patients, these differences in the oral microbiome may be related to the re-establishment of the innate immunity in the oral cavity. Saliva samples were collected from a pilot group of allo-HSCT patients before transplant and at the time of engraftment, when blood neutrophil count had rebounded. As expected, alpha diversity measures of the salivary bacterial community (bacteriome) were low prior to the beginning of the treatment and even lower at the time of engraftment. To examine the local innate immunity, a DNA epigenetic/methylation-based identification of salivary granulocytes was performed post-HSCT on harvested oral DNA samples. At the time of engraftment, salivary granulocyte levels were elevated in allo-HSCT patients vs the level in healthy controls. Salivary and blood neutrophil concentrations both trended to correlate with the Chao1 alpha diversity of the salivary microbiome in patients at the time of engraftment.There was correlation or trends toward correlation between levels of both hematocrit and platelets in blood and the Chao1 and Shannon alpha diversity of the saliva microbiome. In conclusion, the data analysis suggested that during the time of engraftment of the donor stem cells those patients with lowerst diversity of oral bacteria also had the lowest numbers of oral and blood neutrophils. This may contribute to the known higher risk of health complications in patients with dysbiotic microbiomes post-HSCT.