Patients with Essential Thrombocythemia Have a Gut Microbiota That Differs from Healthy Controls

Background:Essential thrombocythemia (ET), along with polycythemia vera (PV) and primary myelofibrosis (PMF), belongs to the Philadelphia chromosome negative myeloproliferative neoplasms (MPNs). Chronic inflammation is considered a hallmark in the pathogenesis and progression of the MPNs. The human gut microbiota helps regulate and mature the immune system, digest food, protect against pathogens and induce hematopoiesis. As our immune system constantly interacts with our gut microbiota any change to the microbiota could have significant impact on the overall health of the patient. This influence of the gut microbiota on the patient has been described as being involved in the pathogenesis of several diseases, such as obesity and diabetes mellitus. We recently added to this list by showing that the gut microbiota in patients with PV differs significantly from that of healthy controls (HCs), however the composition of the gut microbiota in patients with ET remains unknown. Thus, we hypothesized that patients with ET have a distinct gut microbiota signature compared with that of HCs. This study is the first to explore the gut microbiota in patients with ET specifically and compared with that of HCs. Methods: We included patients with ET, diagnosed according to the 2016 WHO classification. Included patients had not received antibiotics within the last 2 months and no change in cytoreductive treatment had occurred within the last 3 months. Comorbidities were assessed using the Charlson Comorbidity Index score (CCI). The gut microbiota was characterized using amplicon-based next generation sequencing of the V3-V4 region of the 16S ribosomal unit while dada2 was used for taxonomic classification. Alpha diversity, beta diversity and linear discriminant analysis effect size (LEfSe), were used to assess the microbiota between and within the patient groups. Alpha diversity describes the richness and evenness within a sample and beta diversity the difference in composition between the samples, while LEfSe is used for differential abundance analysis. Results: In total, 54 patients with ET (median age 68, range 38-83) and 42 HCs (median age 71, range 66-74), fulfilled the inclusion criteria. Patients with ET had a higher CCI score (p=0.038) compared with the HCs. Thirty-six patients had the JAK2V617F mutation. Seven were positive for calreticulin (CALR), three for myeloproliferative leukemia virus gene (MPL), two for CALR+JAK2V617F mutations, and 6 were triple negative. The treatments were: no cytoreductive treatment (n=15), PEG-interferon-α2 (n=11), anagrelide (ANG)(n=3), hydroxyurea (HU)(n=23) and HU+ANG(n=2). Patients with ET had a significantly higher observed richness (number of different bacteria present) compared with HCs (median, 283.5 vs 191.5; p<0.001), however, no significant difference was found in alpha diversity. The bacterial composition differed significantly between ET and HCs (p=0.004 and R=0.063). Eight taxa, with a relative abundance >1%, differed between ET and HCs. Patients with ET had a lower relative abundance of the phylum Firmicutes (p=0.03), class Clostridia (p=0.001), order Oscillospirales (p<0.01), and family Ruminococcaceae (p<0.001) compared with HCs. On genus level, patients with ET had a lower relative abundance of Faecalibacterium (p <0.001). While all mutations were associated with a significantly different microbiota in ET compared with HCs, ET patients who only had the JAK2V617F differed to a larger degree. Conclusion: The gut microbiota in patients with ET differed significantly from that of HCs, both in regard to richness and bacterial composition. The relative abundance of several taxa within the phylum Firmicutes differed significantly, with ET patients having a lower relative abundance in general. These differences appear to be more pronounced in patients who have the JAK2V617F mutation. Thus, it needs to be elucidated if the change of the microbiota is the cause or the consequence of the disease. Is it the increased inflammatory response which changes the microbiota or is it the change in microbiota which aggravates the inflammatory effects of the JAK2V617F mutation?