CD34+ Cell Dose, Measurable Residual Disease, and Outcome After Myeloablative HLA-Matched Peripheral Blood Hematopoietic Cell Transplantation for Adults with Acute Myeloid Leukemia

<b>Background</b>: The impact of donor graft cell composition on post-HCT outcomes in AML remains controversial. Furthermore, it is unknown whether this interacts with pre-HCT MRD status. We evaluated the impact of CD34+ and CD3+ cell doses on outcomes of myeloablative conditioning (MAC) HCT in patients with myelodysplastic neoplasm (MDS)/AML or AML with and without detectable MRD in pre-HCT bone marrow specimens. <b>Methods</b>: We utilized an electronic database to identify all adults ≥18 years with MDS/AML or AML who underwent MAC and received 10/10 HLA-matched sibling or unrelated donor mobilized PBSC allografts in first morphologic remission between 2006 and 2023 at the University of Washington/Fred Hutchinson Cancer Center. <b>Results</b>: Among 385 adults, we found a progressive decrease in relapse incidence and improved survival with increasing CD34+ doses up to a threshold of 5.61 × 10⁶/kg, above which the relapse risk no longer decreased. After multivariable adjustment, a low CD34+ dose was associated with increased risk of relapse as well as lower overall and relapse-free survival. Similar results were obtained for patients with and without pre-HCT MRD. Higher CD3+ doses were linearly associated with an increased incidence of moderate-severe chronic GVHD. <b>Conclusions</b>: Our data identify a non-linear relationship between CD34+ cell dose and relapse risk in AML patients undergoing myeloablative allogeneic HCT, with no apparent added benefit beyond a CD34+ dose threshold. Our findings suggest that donor graft composition impacts outcomes in adults with AML undergoing allogeneic HCT after MAC, independent of pre-HCT MRD status; however, additional studies are needed for other donor cell scenarios.