Early viral reactivation despite excellent immune reconstitution following haploidentical Bone marrow transplant with post‐transplant cytoxan for sickle cell disease.

Background: Haploidentical bone marrow transplant (haplo‐BMT) offers near universal donor availability as a curative modality for individuals with severe sickle cell disease (SCD). However, the required intense immunodepletion is associated with increased infectious complications. A paucity of data exists on immune reconstitution following haplo‐BMT for SCD. Methods: A multi‐institution learning collaborative was developed in the context of a phase II clinical trial of a non‐myeloablative, related haplo‐BMT with post‐transplant cyclophosphamide for SCD. We report results from a cohort of 23 patients for whom immune reconstitution data up to one year were available. Results: Median age was 14.8 years. Out of 23, 18 participants received pre‐conditioning with azathioprine, hydroxyurea, and hypertransfusions. 70% (16/23) of participants had multiple indications for haplo‐BMT. We observed excellent immune reconstitution of CD4, CD8, CD19, and CD56 cellular subsets by 6 months post transplant. Engraftment rate and event‐free survival in this cohort were 100% and 96%, respectively. 70% (16/23) of patients had at least one viral reactivation or infection, including CMV 35% (8/23), HHV‐6 22% (5/23), and polyoma virus 17% (4/23), with no cases of post‐transplant lymphoproliferative disease. Conclusion: Further prospective studies are needed to better characterize immune reconstitution and the immunologic basis for increased viral reactivation following haplo‐BMT with post‐transplant cyclophosphamide for SCD. [ABSTRACT FROM AUTHOR]