Platelet engraftment after allogenic stem cell transplantation is monitored by digital polymerase chain reaction without interference by platelet support.

Platelet engraftment after allogeneic hematopoietic stem cell transplantation is conventionally monitored by daily platelet counts. Platelet transfusions are frequently required and obscure the detection of platelet engraftment. Digital polymerase chain reaction (ddPCR) of mitochondrial DNA isolated from platelets reliably quantifies circulating platelets derived from the stem cell graft and allows us to distinguish them from transfused single-donor apheresis platelets. In a feasibility study, consecutive daily peripheral blood samples from day 7 to day 20 after transplantation were analyzed by ddPCR in 22 patients after allogeneic transplantation. Platelet engraftment according to ddPCR was defined as the third of at least 3 consecutive days of increasing levels exceeding 1000/µL endogenous platelets. Platelet counts were also assessed according to the engraftment cri`teria of the Center for International Blood & Marrow Transplant Research (CIBMTR) and the European Society for Blood and Marrow Transplantation (EBMT). Out of the 22 patients, five did not achieve platelet engraftment within 20 days by any of the predefined criteria. A subgroup of nine patients did show platelet engraftment by all three definitions. In five patients, engraftment was detectable according to ddPCR and EBMT, whereas in three patients, platelet engraftment within 20 days was only confirmed by ddPCR. The detailed findings suggest that the day of platelet engraftment according to the EBMT criteria closely reflected the ddPCR detection of transplantation-derived platelets. The results from this feasibility study demonstrate that ddPCR offers a sensitive approach to detect platelet engraftment reliably and without interference from the individual noise of platelet counts due to platelet transfusions.