Platelets Recovery and Transfusion Needs after Reduced Intensity Conditioning (RIC) Allogeneic Stem Cell Transplantation (allo-SCT).
Authors: Mohty Mohamad , Ferrando Martin , Ladaique Patrick , Faucher Catherine , Furst Sabine , Vey Norbert , Stoppa Anne-Marie , Coso Diane , Viret Frederic , Gravis Gwenaelle , Gastaut Jean-Albert , Blaise Didier 
Published: April 2020

Abstract
The application of RIC allo-SCT can reduce the frequency of transplant-related toxicities, at least in the early period after allo-SCT, and the use of RIC has rapidly increased over the past few years. In this report, we analyzed the profile of platelets recovery and platelets transfusion requirements in the first 3 months after RIC in a single institution series of 90 consecutive patients receiving allo-SCT from an HLA-identical sibling. Patients and graft characteristics are: age 49 y. (range, 18–63), diagnoses: 30 myeloid malignancies (33%), 34 lymphoid malignancies (38%), and 26 metastatic solid tumors (29%). 75 pts (83%) were considered as high risk. 71 pts (79%) received a fludarabine, busulfan and ATG-based RIC, while 19 pts (21%) received a low dose irradiation-based RIC. All patients received a PBSC graft, with 60 (67%) receiving CSA alone for GVHD prophylaxis and 30 (33%) receiving CSA and MMF. 47 pts (52%) developed grade 2–4 acute GVHD. Platelets recovery (&gt;20.000/μL) was observed at a median of 11 days (range, 0–99) after allo-SCT. The kinetics profile of platelets recovery is shown in the figure below. In the whole study population, the nadir was observed around day +7 after allo-SCT, and a plateau was reached by the end of the first month. In this series, patients needed a median of 1 unit (range, 0–53) of filtered and irradiated donor apheresis platelets. Of note, 35 pts (39%) did not require any platelets transfusion during the follow-up period (median follow-up: 392 days). Among the 55 patients (61%; 95%CI, 51–71%) who received at least one transfusion of platelets, 27 were not transfused beyond day +100 after allo-SCT. When comparing these 55 patients, to the group of 35 patients who were never transfused, platelets count prior to RIC allo-SCT (median count 130.000/μL vs. 161.000/μL; P=0.07) and the occurrence of severe acute GVHD (P=0.0001; 100% of patients with grade 3–4 acute GVHD were transfused) were the parameters significantly associated with platelets transfusion needs. In this cohort, 69 pts could be assessed for platelets recovery at day +100: among them, 58 (84%) had a platelet count &gt;50.000/μL. At day +100 after allo-SCT, a diagnosis of myeloid malignancy (AML, CML or MDS) was the strongest factor associated with a delayed platelet recovery (P=0.03). Overall, these observations show a significantly lower rate of platelets transfusions and a quicker kinetics of platelets recovery after RIC allo-SCT, further supporting the overall benefits of RIC strategies as compared to standard myeloablative allo-SCT. In addition, the low level of myeloablation observed after RIC, may offer a window of opportunity for testing of megakaryocytic growth factors, towards further improving the safety and outcome of RIC or nonmyeloablative allo-SCT.
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