A SUCCESSFUL DESENSITIZATION TO OFATUMUMAB

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<h3>Introduction</h3> For immune thrombocytopenic purpura (ITP) standard adjunctive therapies include corticosteroids, intravenous immune globulin (IVIG), and/or thrombopoietin receptor antagonists (TPO-RA). In cases of refractory ITP, splenectomy, or monoclonal antibodies against the CD20 antigen (anti-CD20) can be considered. Hypersensitivity reactions to anti-CD20 monoclonals have been reported, however there are no prior published protocols for ofatumumab desensitization. We describe a complex patient with refractory ITP with a successful desensitization protocol. <h3>Case Description</h3> A 39-year-old female with history of Neimann Pick Disease type B (NPD-B), multiple sclerosis, and refractory ITP ineligible for splenectomy with failed treatment with IVIG and a TPO-RA. She experienced suspected hypersensitivity reactions to three CD20 antagonists. She had serum sickness after eight infusion cycles of rituximab. She then developed urticaria during her ninth ofatumumab infusion despite a significant pretreatment regimen. Finally, she was given obinutuzumab which was associated with urticarial and angioedema on her first dose. As the patient continued to have significant thrombocytopenia and no other available treatment options, her oncologist referred her to allergy with goal of desensitization to ofatumumab. <h3>Discussion</h3> To our knowledge we describe the first successful desensitization to ofatumumab. Given that there were no established protocols in the literature, we utilized a rituximab-based protocol that required significant adjustments as ofatumumab has complex dosing requirements, including modifications for dose escalation and maximal concentrations based on its pharmacologic properties. This case report adds to the literature by describing a successfully implemented ofatumumab desensitization protocol in a medically complex patient with hypersensitivity to multiple anti-CD20 monoclonal antibodies