A Case Report of Refractory Immune Thrombocytopenia (ITP) Following Reduced Intensity Conditioning (RIC) Hematopoietic Cell Transplantation (HCT) for Myelodysplastic Syndrome (MDS) Successfully Treated with Off-Label Use of Daratumumab
Authors: Migdady Yazan , Gupta Ridhi , Ediriwickrema Asiri , Socola Francisco , Arai Sally , Martin Beth A 
Published: October 2019

Abstract
Background:
A source of treatment refractoriness in immune cytopenias appears to be residual CD138/38 positive lymphocyte populations (Audia S et al, Blood 118:4394-400,2011; Mahevas M et al, J Clin Invest 123:432-442, 2013). Persistence of recipient's plasma cells can lead to prolonged refractory thrombocytopenia following RIC-HCT. (Fasano RM et al, Br J Haematol 166(3):425-34, 2014). Daratumumab was effective in the treatment of a child with refractory autoimmune hemolytic anemia after HCT (Tolbert et al, Blood 128:4819, 2016).
Case Report:
The patient is a 60-year-old man with intermediate-high risk MDS who underwent RIC-HCT with total lymphoid irradiation and antithymocyte globulin with peripheral blood graft from a fully matched unrelated male donor. The patient had mild thrombocytopenia prior to HCT consistent with MDS and had not received platelet transfusions. He had not received any prior therapy for MDS. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine and mycophenolate mofetil. Cytomegalovirus (CMV) serologic testing for exposure was negative for the recipient and positive for the donor. Both the patient and the donor had evidence for prior exposure to Epstein-Barr virus (EBV). He achieved engraftment on day +12. His peripheral blood chimerism on day + 30 showed full donor origin (WB 98%,CD3 96%,CD15 95%, CD19 98%, CD56 95%) and has been maintained to date. Acute skin GVHD responded to corticosteroids. While on corticosteroid therapy, he developed an abrupt decline in platelet count from 156,000/mcl on day +152 to 9, 000/mcl on Day + 166 without evidence for recurrent or active GVHD. While this was initially attributed to simultaneous EBV and CMV reactivations, severe thrombocytopenia persisted after viral clearance. An extensive work up for other etiologies of thrombocytopenia was negative. Repeated bone marrow biopsies were normal, including adequate megakaryocytosis and no MDS recurrence. Platelet associated antibody testing and platelet antigen genotyping were not conclusive for autoimmune versus alloimmune etiology. Testing for platelet HLA antibodies showed calculated Panel Reactive Antibody of 31% and unsatisfactory corrected count increment after transfusion of HLA compatible platelets units. The patient experienced prolonged severe thrombocytopenia for over 26 weeks with platelet count less than 5000/mcl for 22 weeks and only above 10,000 /mcl on 6 occasions. Potentially responsible medications were discontinued serially, but testing for drug inducted ITP was not conducted. Therapy included high dose corticosteroids, high dose immune globulin, rituximab, plasma exchange, splenectomy, romiplostim 10 mcg/kg/week, eltrombopag 100 mg to 150 mg daily for over 24 weeks, and low dose danazol. Fostamatinib was not available. Prednisone dose was tapered over many weeks to 5 mg daily. The patient experienced recurrent life-threatening and vision-threatening bleeding. Cumulative transfusions following Day + 166 were 133 single donor platelet units and 42 red cell units. All products were from CMV negative donors. Eltrombopag and danazol were deemed ineffective and tapered to discontinuation. CD38 positive cells were present in spleen and marrow by immunohistochemistry. Daratumumab 1300 mg was infused weekly x 4. Four weeks after the last dose of daratumumab, his platelet count increased to 91,000/mcl. Platelet count normalized to 150,000/mcl in week 5 or HCT Day + 383. Hypogammaglobulinemia has been the only detectable toxicity. Testing to determine autoimmune versus alloimmune origin is ongoing.
Conclusion: Clinical trials of daratumumab for the treatment of severe refractory ITP are indicated.

Disclosures
No relevant conflicts of interest to declare.