Development of pancytopenia with neutralizing antibodies to thrombopoietin after multicycle chemotherapy supported by megakaryocyte growth and development factor

Abstract

Clinical trials of thrombopoietin (TPO), the central regulator of megakaryocytopoiesis, have revealed few side effects associated with its use. We here report a case of pancytopenia associated with the development of neutralizing antibodies to TPO that occurred in a patient who had undergone multicycle chemotherapy with multiple cycles of subcutaneous administration of pegylated recombinant human megakaryocyte growth and development factor. Samples of the patient's bone marrow showed trilineage hypoplasia with absence of myeloid, erythroid, and megakaryocyte progenitor cells but with elevated endogenous levels of erythropoietin, granulocyte colony-stimulating factor, and stem-cell factor. To our knowledge, this is the first report of an aplastic anemia-like syndrome associated with neutralizing antibodies to TPO. IntroductionTwo different forms of thrombopoietin (TPO) have entered clinical trials. 1 One is a recombinant form of the native molecule (rhTPO) and the other a pegylated, truncated version (pegylated recombinant human megakaryocyte growth and development factor [PEG-rHuMGDF]) with biologic activity similar to that of the native molecule. Early studies showed that both rhTPO 2 and PEG-rHuMGDF 3 are potent stimulators of thrombopoiesis and enhance platelet recovery when given after chemotherapy. 4,5 Both agents were reported to have minimal toxic effects; in particular, platelets produced after their administration function normally and have no evidence of activation. 2,5,6 Although antibodies to TPO were observed in the initial study of rhTPO, they were nonneutralizing and transient. 2 Here, we describe a case in which prolonged pancytopenia with neutralizing antibodies to TPO developed in a woman with ovarian cancer who had undergone 6 cycles of chemotherapy associated with administration of PEG-rHuMGDF. Study designGranulocyte-macrophage colony-forming cells, erythroid burst-forming units, and megakaryocyte colony-forming cells were assayed as described previously 7-9 by using freshly obtained bone marrow cells. Serum from the patient (stored at Ϫ20°C) was incubated with growth factors for in vitro cultures at 37°C for 60 minutes and examined for its activity on normal bone marrow cells. The highest concentration of patient's serum used was 10% of the final culture volume.Standard solid-phase sandwich enzyme immunoassays were used to measure serum levels of TPO, 10 granulocyte colony-stimulating factor (G-CSF), and erythropoietin (EPO) (R&D Systems, Minneapolis, MN). Cytokine levels were calculated from a standard curve generated by analysis of recombinant cytokines. Stem-cell factor (SCF) was assayed as described previously. 11 More than 200 samples of normal human serum were used to establish the SCF standard of 0.78 Ϯ 0.25 ng/mL (range, 0.29-1.62 ng/mL).Two established assays were used to detect neutralizing antibodies. The first was a solid-phase radioimmunoassay (RIA). 12 Reactivity was determined on the basis of the ratio of counts per minute in the posttreatment sample to the counts per mi...

The biology of thrombopoietin and thrombopoietin receptor agonists

“…Indeed, patients who develop a neutralizing antibody to thrombopoietin eventually develop pancytopenia [10,34,35].…”

Improving stem cell mobilization strategies: future directions

“…145 AEs associated with the use of rhTPO plus G-CSF appear to be similar to those seen with the use of G-CSF alone; 144,145 however, cytopenias owing to neutralizing antibodies to TPO have been reported in a small number of patients who were given rhTPO to treat chemotherapy-induced thrombocytopenia. 146,147 Currently, no TPOs have been approved by the FDA for mobilization. 148 Parathyroid hormone Parathyroid hormone (PTH) activates osteoblasts, which produce hematopoietic growth factors in the stem cell niche, thereby increasing the numbers of circulating stem cells.…”

Pegfilgrastim successfully mobilizes megakaryocyte progenitors into the peripheral blood in subjects with solid tumours

“…[41][42][43] Thrombopoietin, in addition to G-CSF during mobilization has been shown to increase the CD34 þ and CD34/ CD41a þ yields plus results in small but statistically significant improvements in platelet recovery after transplantation. 12,15,44,45 Clinical trials with thrombopoietin have been hampered, however, due to the development of neutralizing Ab and thrombocytopenia, 46,47 risk of thrombocytosis and thrombosis and need for co-administration with G-CSF. 12,15 This study has shown that pegfilgrastim increases CD34/CD41a þ cells in the peripheral blood, producing similar responses to filgrastim and that it is well tolerated.…”