Recent published data suggest that specific alterations in intestinal metabolome signature of hematopoietic stem cell transplant (allo-SCT) recipients might influence incidence and severity of acute graft versus host disease (aGVHD). Nevertheless, this possible relationship has not been undoubtedly established, pathophysiologic mechanisms have not been elucidated and possible clinical implications have not been studied. We hypothesized that in the early phase of allo-SCT, specific alterations in faecal metabolome occurred related to loss of intestinal microbiota diversity and disbalance of specific bacterial taxa, and that both alterations determine reduced survival of patients through increased incidence and severity of aGVHD. To test this hypothesis, a prospective multi-center cohort of allo-SCT recipients will had faecal and plasmatic samples collected at predetermined time-points pre&post-allo-SCT, and clinical relevant variables will be prospectively recorded throughout two years posttransplant follow-up. Metabolomic and microbiome analysis will be done to answer objectives of the study. To additionally explore if differential evolving characteristics in the intestinal metabolome and microbiome of donor/recipient sibling pairs influence the incidence and severity of aGVHD, probability of malignancy relapse and early and late mortality an additional cohort of family donors of enrolled patients will also have faecal and plasmatic samples collected and analysed.

Patients Patients receiving an allotransplant at participating hospitals during the study period before initiating conditioning period.

Inclusion Criteria:

• Patients of any age who will receive allogeneic hematopoietic transplantation of any modality with any diagnosis.
• Agreement of the patient to participate by signing the informed consent or his/her legal representatives/assent (if applicable).

Exclusion Criteria

- Allotransplant recipients in stages after the initial pre-conditioning.

Donors

Family donors from patients included in the study:

Inclusion criteria:

• Agreement of the donor to participate by signing the informed consent or his/her legal representatives/assent (if applicable).
• Donor relatives with any degree of identity in the Human Leukocyte Antigens (HLA).

Exclusion Criteria:

• Unrelated donors
• Transplants from umbilical cord blood source.

Patients receiving an allotransplant and family donors of the included patients.