The Impact of Bone Marrow Hematogones on Umbilical Cord Blood Transplant Outcomes in Acute Myeloid Leukemia Patients,
Authors: Honebrink Theodore , Dayton Vanessa J. , Larsen Karen , Cao Qing , Brunstein Claudio , Weisdorf Daniel J. , Miller Jeffrey S. , Wagner John E. , Verneris Michael R 
Published: October 2019

Abstract 4148

Hematogones are B-lymphocyte precursors which reside in the marrow and undergo an orderly maturation sequence to give rise to mature B cells. (McKenna, Blood 2001) Recently, the percentage of hematogones detected in the bone marrow (BM) after induction therapy for acute myeloid leukemia (AML) has been associated with improved leukemia-free survival and overall survival. (Chantepie, Blood 2011) Early after umbilical cord blood transplant (UCBT), patients show marked differences in BM hematogone percentages. Little is known about whether such differences are clinically relevant, which may explain why hematogones are not routinely reported in BM differential counts and are, instead, combined with other lymphocytes. We hypothesized that increased hematogones would be associated with superior transplant outcomes.

Two independent reviewers assessed hematogone percentages in BM aspirates performed on day 21 and 100 post-UCBT (i.e. D21 & D100) from 88 patients with AML undergoing myeloablative UCBT at the University of Minnesota between 02/1999 and 07/2008. Patients with evidence of relapse at the time of the marrow analysis were excluded. Because of the morphological similarity between hematogones and leukemic lymphoblasts, only patients with AML were included in this analysis. The reviewers were blinded to clinical outcomes. Correlation coefficients for the morphologic assessment of hematogones at D21 and D100 were each >0.8, confirming good interobserver reproducibility (p<0.01).

Prospective outcome data for patients in the lowest marrow hematogone quartile (0% at D21 after UCBT and ≤0.9% at D100 after UCBT) were compared with those of patients in the upper three quartiles using a multivariate analysis (MVA) model. This model incorporated donor number (single vs. double), recipient age (<21 vs. ≥ 21), recipient CMV status (negative vs. positive), total, post-thaw CD34 (<0.50 vs. ≥0.50), total, post-thaw CFU (<0.042 vs. ≥ 0.042), and total nucleated cell (TNC) (<0.38 vs. ≥0.38). Endpoints studied included time to neutrophil and platelet recovery, overall survival, disease free survival (DFS), transplant related mortality (TRM), risk of relapse, acute GVHD (aGVHD), and chronic GVHD (cGVHD).

At D21 after UCBT, the percentage of marrow hematogones varied from 0 to 10.8% (N = 85). In MVA, a high percentage of hematogones at D21 was associated less aGVHD grade 3–4 (RR=0.3 [0.15–0.59], p=0.01). At D100 after UCBT the percentage of marrow hematogones varied from 0 to 29.8% (N = 69). In MVA, a high percentage of BM hematogones at D100 was associated with improved overall survival (p=0.02) and this was due to a lower treatment related mortality (p=<0.01). (See Table 1)

Table 1: MVA examining the percentage hematogones detected in the BM at D100 after UCBT. Outcome Variable RR (95% CI) p value Overall Survival Hem @ Day 100 <0.9 1.00 >=0.9 0.20 (0.05–0.76) 0.02 Donor number 1 1.00 2 0.19 (0.04–0.84) 0.03 Transplant Age <20.5 1.00 >=20.5 4.89 (1.11–21.51) 0.04 Relapse Hem @ Day 100 <0.9 1.00 >=0.9 2.84 (0.32–24.91) 0.35 TRM Hem @ Day 100 <0.9 1.00 >=0.9 0.03 (0–0.34) <0.01 HLA (engrafting unit) 4/6 1.00 5/6 0.61 (0.05–7.13) 0.69 6/6 0 <0.01 CGVHD Hem @ Day 100 <0.9 1.00 >=0.9 0.44 (0.11–1.69) 0.23 Transplant Age <20.5 1.00 >=20.5 3.61 (1.18–11.06) 0.02 RR = relative risk. Hem = percentage hematogones. TRM = transplant-related mortality. HLA = human leukocyte antigen; values correspond to number of matched allelic loci for HLA-A, HLA-B and HLA-DR between recipient and engrafting donor. CGVHD = chronic graft vs. host disease.

This study shows that BM hematogone percentage may be a useful prognostic indicator in AML patients following UCBT. We propose that hematogones be routinely reported in BM differential counts.

Disclosures:

No relevant conflicts of interest to declare.