LAUSR

There are reports of high rates of viral infections after haploidentical transplant, particularly in the setting of PTCy (HaploCy) but detailed data on incidence are lacking. We describe here the comparative incidence of community respiratory virus (CRV) infections occurring by day 180 post-transplant by donor source and their impact on outcomes including survival, relapse, chronic GVHD, and transplant related mortality (TRM) using CIBMTR registry data. The analysis included 2765 patients, all > 2 years of age, who underwent first allogeneic HCT for AML, ALL or MDS from 100 centers between 2012 and 2017 receiving either HaploCy (n=757), Matched related donor (MRD) transplant with PTCy (SibCy n= 403), and MRD transplant with calcineurin inhibitor and either MTX or MMF (SibCNI n= 1605). The cumulative incidences of CRV in the HaploCy, SibCy and SibCNI were: 3% (99% CI, 1.6-4.8), 3% (1.3-5.5) and 2.4 %(1.5-3.5) respectively at day 30 (P =0.649, NS), but notably higher at 15.5% (12.3-19), 16.2% (11.7-21.2) and 9.4 %(7.6-11.4) at 6 months (P<.001) post-transplant [Figure 1]. Identified CRV included primarily Rhinovirus, Parainfluenza, and RSV accounting for approximately 70% of all CRV reported [Table 1]. Figure 2 shows the multivariable models through 2 years post-transplant for survival, relapse, TRM, and chronic GVHD with a reference group of SibCNI without CRV infection for the main effect variable of donor type and infection. Patients in the HaploCy cohort who developed a CRV by day 180 had a higher risk of TRM [p=0.002] and inferior survival [p = 0.001] compared to the reference group. Older age, more advanced disease, and higher HCT-CI were all associated with increased mortality. The incidence of CRVs is higher for patients receiving PTCy, regardless of donor. This finding justifies further studies to understand long-term antiviral immune recovery in different donor sources and GVHD prophylaxis regimens. The higher overall mortality for HaploCy patients developing CRV infection warrants consideration for patient education and heightened awareness for clinicians, as well as long term follow up studies of such patients.