Factors influencing haematological recovery after allogeneic haemopoietic stem cell transplants: Graft-versus-host disease, donor type, cytomegalovirus infections and cell dose

Platelet recovery after allogeneic haemopoietic stem cell transplant (HSCT) and predictive factors were analysed in 342 patients with haematological malignancies. All patients were prepared with cyclophosphamide plus total body irradiation, and received an unmanipulated HSCT from an HLA-identical sibling (n = 270), a matched unrelated donor (n = 67) or an identical twin (n = 5). The source of stem cells was peripheral blood (n = 15) or bone marrow (n = 327). Graft-vs.-host disease (GvHD) prophylaxis consisted of cyclosporin A with or without methotrexate. The proportion of patients with <50 x 10⁹/1 platelets on d + 50, d + 100, d + 200 and d + 365 after HSCT was 26%, 27%, 14% and 11% respectively. Thrombocytopenia was independent of the degree of complete donor chimaerism. Four variables were predictive of platelet recovery: donor type, acute GvHD, cytomegalovirus (CMV) infection and number of cells infused at transplant. Recipients of an unrelated graft had lower platelet counts (49 x 10⁹/1) on d + 50 than identical sibling grafts (108 x 10⁹/1) (P <0.001) and twin grafts (149 x 10⁹/1) (P <0.001). Patients with GvHD grades 0, I, II, III and IV had significantly different platelet counts on d +50 (153 x 10⁹/1, 102 x 10⁹/1, 85 x 10⁹/1, 32 x 10⁹/1 and 22 x 10⁹/1; P <0.001) and thereafter. Thrombocytopenia was more frequent in patients with high-level CMV antigenaemia (> four positive cells/2 x 10⁵) (P <0.0001) and in patients who received a low cell dose at transplant (≤4.1 x 10⁸/kg) (P = 0.009). Platelet counts predicted transplant-related mortality (TRM) and were higher at all time intervals in patients surviving the transplant. Patients with grade II GvHD and > 50 x 10⁹/1 platelets had a lower TRM than patients with grade II GvHD and ≤50 x 10⁹/1 platelets (14% vs. 40%, P <0.0001). In conclusion, (i) a significant proportion of allogeneic HSCT recipients are thrombocytopenic long-term, irrespective of complete donor chimaerism, (ii) thrombocytopenia identifies patients at greater risk of lethal complications, and (iii) platelet recovery is influenced by GvHD, donor type, CMV infections and cell dose, not by stem cell source or other patient-disease-related variables.