Predictors of Relapse after Haploidentical Hematopoietic Progenitor Cell Transplantation (Haplo-HCT); A Single-Institution Experience

Abstract

<h3>Background</h3> Haplo-HCT emerged as a reliable option for patients with high risk hematological malignancies with no HLA-matched related or unrelated donors available. Retrospective registry data suggest comparable outcomes to HLA-matched donors; however, relatively little is known regarding predictors of disease relapse following haplo-HCT. We hypothesize that attainment of full-donor CD3 and CD33 chimerism at day 30 (D30) and 100 (D100) is associated with lower incidence of relapse after haplo-HCT. <h3>Methods</h3> We undertook a retrospective analysis of 78 patients who underwent haplo-HCT at the Ohio State University James Cancer Hospital between January 2013 and December 2017. The associations between patient characteristics including CD3/CD33 donor chimerisms and the cumulative incidence rate (CIR) of relapse were evaluated using proportional sub-distribution hazards model, treating death without relapse as the competing risk. The models were built adopting a landmark analysis approach at D30 and D100. Progression-free survival (PFS) was estimated using the method of Kaplan-Meier. <h3>Results</h3> Median age at haplo-HCT was 56 (20-74) years and 68% were males. 50% had acute myeloid leukemia/myelodysplastic syndrome, and 54% had intermediate disease risk index (DRI). Most patients (85%) received reduced-intensity conditioning and 50% received bone marrow (BM) grafts. Complete (100%) CD3 donor chimerism was observed in 63 (84%) patients at D30, and subsequently 59 (95%) patients at D100. Complete CD33 donor chimerism was observed in 67 (89%) patients at D30, and subsequently 56 (88%) patients at D100. In univariable D30 landmark analysis, the CIR of relapse was significantly lower in patients who achieved complete CD3 (and CD33) chimerism compared with patients with less than complete chimerism (Figure 1A; p<0.01 and p<0.01, respectively). Attainment of complete CD3 chimerism at D30 was also associated with PFS (Figure 1B; p<0.01). However, in multivariable analysis, complete CD3 chimerism at D30 was no longer independently associated with the CIR of relapse due to its high correlation with DRI (p=0.01). Receipt of a BM graft was associated with significantly higher CIR of relapse both in univariable and multivariable analyses (HR 2.43, 3.34; p=0.05, 0.01, respectively). D100 complete CD33 chimerism conferred a significant CIR advantage in both univariable (p<0.01) and multivariable (p<0.01) models, although CD3 chimerism did not retain significance (p=0.35). <h3>Conclusions</h3> Complete CD3 and CD33 donor chimerisms at D30 and D100 predict a patient's risk for relapse following haplo-HCT. We observed a strong association between CD3 chimeric status at D30 with DRI, as well suggestive that high risk disease may be associated with impaired immune reconstitution after transplant and perhaps a less robust graft vs disease effect.