Traditionally known for their role in haemostasis, platelets have also an immune role.

Platelets play a key role in immune mediator secretion, and interact with innate and adaptive immune cells, contributing to the fight against pathogens, as viruses.

Cytomegalovirus (CMV) is responsible of allograft patients' serious infections, because of the induced immune depression. Platelets activation for patients is not determined during the post-graft period, and platelet induced inflammation following a CMV infection is not described.

The descriptive present study will determine if platelet activation is altered during the post-graft follow-up (day 30 to 90).

The activation will be studied spontaneously and after simulation by a CMV (Cytomegalovirus) antigen.

The study will also focus on inflammatory response variation, focusing on the cytokines release during the same post-graft follow-up (spontaneously and after CMV antigen stimulation).

This preliminary study could lead to a better understanding of the immune-modulator role of inflammation, controlled by the platelets, particularly in the initiation of the Graft-versus-host disease in this kind of population.

Inclusion Criteria:

• Patients who received an allogeneic haematopoietic stem cell transplant for less than 2 months for any indication ;
• Platelets > 20 G / L (Giga per Litre) for at least 7 days without transfusion support ;
• Patients affiliated to a social security scheme.

Exclusion Criteria:

• Patients receiving antiplatelet therapy ;
• Major protected or unable to give consent ;
• Pregnant women ;
• Vulnerable persons defined by French legislation.