Successful use of recombinant factor VIIa in a patient with acquired Glanzmann thrombasthenia

Acquired Glanzmann thrombasthenia associated with platelet desialylation

BACKGROUND

The notable discrepancy between platelet count and bleeding manifestations in immune thrombocytopenia (ITP) patients with acquired Glanzmann thrombasthenia (GT) has been described.

OBJECTIVES

We aimed to examine the mechanisms responsible for thrombocytopenia and the bleeding phenotype in a patient with acquired GT.

PATIENT, METHODS, AND RESULTS

A patient with primary ITP underwent splenectomy due to steroid intolerance. Despite platelet count normalization, bleeding continued. Platelet aggregometry was abnormal with all agonists except for ristocetin. Flow cytometry demonstrated the presence of antiplatelet antibody, which caused dose-dependent inhibition of fibrinogen and PAC-1 binding, induction of neuraminidase-1 expression as well as platelet desialylation in donor platelets. Indirect monoclonal antibody immobilization of platelet specific antigen assay (MAIPA) confirmed specificity to αIIb β3 only, corroborated by binding on Chinese hamster ovary (CHO) cells expressing human glycoprotein αIIb β3 but not GP Ib/IX. Both desialylation and neuraminidase expression were observed with plasma adsorbed on Ib/IX CHO cells and with the immunoglobulin G (IgG) fraction. Desialylation was inhibited in the presence of anti-Fc-gamma receptor IIa (FcγRIIa) antibody. A nonobese diabetic/severe combined immunodeficient ITP murine model was established, which showed rapid hepatic donor platelet clearance in the presence of patient IgG. Treatment of mice with the neuraminidase inhibitor oseltamivir significantly reduced antibody-induced platelet destruction.

CONCLUSIONS

We report the first case of a patient with acquired GT due to ITP with FcγRIIa mediated platelet desialylation, independent of platelet activation. Treatment with neuraminidase inhibitor may prevent platelet clearance by anti-αIIb β3 antibodies.

Acquired platelet function disorders

The possibility of an acquired platelet function disorder should be considered in patients who present with recent onset muco-cutaneous bleeding. Despite the availability of newer and faster platelet function assays, light transmission aggregometry (LTA) remains the preferred diagnostic test. This review examines and discusses the causes of acquired platelet dysfunction; most commonly drugs, dietary factors, medical disorders and procedures. In addition to well-known antiplatelet therapies, clinicians should be alert for newer drugs which can affect platelets, such as ibrutinib. There is little clinical trial evidence to guide the management of acquired platelet function defects, but we summarise commonly employed strategies, which include addressing the underlying cause, antifibrinolytic agents, desmopressin infusions, and in selected patients, platelet transfusions.

First description of an IgM monoclonal antibody causing αIIb β3 integrin activation and acquired Glanzmann thrombasthenia associated with macrothrombocytopenia

Essentials Acquired Glanzmann thrombasthenia (GT) is generally caused by anti-αIIb β3 autoantibodies. We report the case of a man with an acquired GT phenotype associated with macrothrombocytopenia. Perturbed platelet function were associated with an activating anti-αIIb β3 IgM autoantibody. This novel clinical entity raises interesting questions about the αIIb β3 integrin signaling. SUMMARY: Background Acquired Glanzmann thrombasthenia (GT) is a bleeding disorder generally caused by anti-αIIb β3 autoantibodies. Objectives We aimed to characterize the molecular mechanism leading to a progressive GT-like phenotype in a patient with chronic immune thrombocytopenia. Patient, Methods, and Results The patient suffered from repeated episodes of gastrointestinal bleeding; further studies indicated a moderate platelet aggregation defect. A few months later, platelet function showed abolished aggregation using all agonists, but normal agglutination with ristocetin. No platelet-bound antibodies were detected, but the presence of large amounts of an IgM type antibody detected together with αIIb β3 in the patient permeabilized platelets suggested that this IgM was an autoantibody causing the internalization of the complex. This was confirmed by the fact that the patient IgM bound to normal platelets but not to platelets from GT type I patients. Moreover, patient's plasma activated αIIb β3 on controls' platelets as evidenced by increased PAC-1 binding. We also demonstrated that the patient plasma triggered αIIb β3 outside-in signaling, as β3 Tyr773 and FAK were phosphorylated, and increased the rate of actin polymerization in resting platelets reflecting an impairment of cytoskeletal reorganization. Because different signs of dysmegakaryopoiesis were also observed in our patient, we evaluated the ability of its serum to impair proplatelets formation and showed that it significantly decreased the number of proplatelet-bearing megakaryocytes in controls' bone marrow stem cells culture compared with normal serum. Conclusions We present the case of a patient with a progressive and severely perturbed platelet function associated with the presence of an IgM activating autoantibody directed against αIIb β3 .

Acquired Glanzmann thrombasthenia: From antibodies to anti-platelet drugs

In contrast to the inherited platelet disorder given by mutations in the ITGA2B and ITGB3 genes, mucocutaneous bleeding from a spontaneous inhibition of normally expressed αIIbβ3 characterizes acquired Glanzmann thrombasthenia (GT). Classically, it is associated with autoantibodies or paraproteins that block platelet aggregation without causing a fall in platelet count. However, inhibitory antibodies to αIIbβ3 are widely associated with primary immune thrombocytopenia (ITP), occur in secondary ITP associated with leukemia and related disorders, solid cancers and myeloma, other autoimmune diseases, following organ transplantation while cytoplasmic dysregulation of αIIbβ3 function features in myeloproliferative and myelodysplastic syndromes. Antibodies to αIIbβ3 occur during viral and bacterial infections, while drug-dependent antibodies reacting with αIIbβ3 are a special case. Direct induction of acquired GT is a feature of therapies that block platelets in coronary artery disease. This review looks at these conditions, emphasizing molecular mechanisms, therapy, patient management and future directions for research.

A unique phenotype of acquired Glanzmann thrombasthenia due to non-function-blocking anti-αIIbβ3 autoantibodies

Essentials Acquired Glanzmann thrombasthenia (aGT) is generally caused by function-blocking antibodies (Abs). We demonstrated a unique aGT case due to marked reduction of αIIbβ3 with anti-αIIbβ3 Abs. The anti-αIIbβ3 Abs of the patient did not inhibit platelet function but reduced surface αIIbβ3. Internalization of αIIbβ3 induced by the Abs binding may be responsible for the phenotype. SUMMARY: Background Acquired Glanzmann thrombasthenia (aGT) is a bleeding disorder generally caused by function-blocking anti-αIIbβ3 autoantibodies. Aim We characterize an unusual case of aGT caused by marked reduction of surface αIIbβ3 with non-function-blocking anti-αIIbβ3 antibodies (Abs). Methods A 72-year-old male suffering from immune thrombocytopenia since his 50s showed exacerbation of bleeding symptom despite mild thrombocytopenia. Platelet aggregation was absent with all agonists but ristocetin. Analysis of αIIbβ3 expression and genetic analysis were performed. We also analyzed effects of anti-αIIbβ3 Abs of the patient on platelet function and αIIbβ3 expression. Results Surface αIIbβ3 expression was markedly reduced to around 5% of normal, whereas his platelets contained αIIbβ3 to the amount of 40-50% of normal. A substantial amount of fibrinogen was also detected in his platelets. There were no abnormalities in ITGA2B and ITGB3 cDNA. These results indicated that reduced surface αIIbβ3 expression caused a GT phenotype, and active internalization of αIIbβ3 was suggested. Anti-αIIbβ3 IgG Abs were detected in platelet eluate and plasma. These Abs did not inhibit PAC-1 binding, indicating that the Abs were non-function-blocking. Surface αIIbβ3 expression of a megakaryocytic cell line and cultured megakaryocytes tended to be impaired by incubation with the patient's Abs. After 2 years of aGT diagnosis, his bleeding symptom improved and surface αIIbβ3 expression was recovered to 20% of normal with reduction of anti-αIIbβ3 Abs. Conclusion We demonstrated a unique aGT phenotype due to marked reduction of surface αIIbβ3. Internalization induced by anti-αIIbβ3 Abs may be responsible in part for the phenotype.