Monocyte Reconstitution and Gut Microbiota Composition after Hematopoietic Stem Cell Transplantation

Monocytes are an essential cellular component of the innate immune system that support the host’s effectivenss to combat a range of infectious pathogens. Hemopoietic cell transplantation (HCT) results in transient monocyte depletion, but the factors that regulate recovery of monocyte populations are not fully understood. In this study, we investigated whether the composition of the gastrointestinal microbiota is associated with the recovery of monocyte homeostasis after HCT. Methods We performed a single-center, prospective, pilot study of 18 recipients of either autologous or allogeneic HCT. Serial blood and stool samples were collected from each patient during their HCT hospitalization. Analysis of the gut microbiota was done using 16S rRNA gene sequencing and flow cytometric analysis was used to characterize the phenotypic composition of monocyte populations. Results Dynamic fluctuations in monocyte reconstitution occurred after HCT and large differences were observed in monocyte frequency among patients over time. Recovery of absolute monocyte counts and monocyte subsets showed significant variability across the heterogeneous transplant types and conditioning intensities; no relationship to the microbiota composition was observed in this small cohort. Conclusion A relationship between the microbiota composition and monocyte homeostasis could not be firmly established in this pilot study.