Preliminary (proof of concept), monocentric, interventional, prospective, non-randomized and analytic trial designed to simultaneously explore intestinal microbiota changes and early post-transplant immune reconstitution, and to correlate biological data with clinical data (antibiotics use, stress level, GVHD).

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the major curative therapeutic approach for hematologic neoplasms. After HSCT, patients have a compromised GI mucosal barrier and an altered microbiota, also called dysbiosis. The later could be due to conditioning or use of broad-spectrum antibiotics, and could be accentuate by stress encountered by patients during their therapy management. Recent data have shown that alterations in the intestinal flora are associated with bad outcome, particularly with graft-versus-host disease (GVHD), bacteremia, and reduced overall survival post-transplantation. How intestinal bacteria can modulate the risk of relapse after HSCT is yet unknown. The scientists hypothesize that the variation of some bacterial taxa may influence post-transplant immune reconstitution, particularly invariant Natural Killer T cells.

Inclusion Criteria:

• Patients > 18 years affiliated to a social security system
• Patients followed at the hospital of Nancy for a allogeneic hematopoietic cell transplantation (HLA matched donor)
• Graft of peripheral blood stem cell
• GVHD prophylaxis by ciclosporin and antilymphocyte serum +/- mycophenolate mofetil or methotrexate.

Exclusion Criteria:

• HIV+ patients
• Patients with active HBV or HCV