Hematogones Contained in CD34+ Apheresis Products for Hematopoietic Progenitor Cell Transplantation Have No Adverse Impact On Engraftment Outcomes.
Authors: Ondrejka Sarah L. , Hsi Eric D. , Rybicki Lisa A. , Katanik Deborah A. , Bolwell Brian J. , Duong Hien K. 
Published: October 2019

Abstract
Abstract 3022
Flow cytometric enumeration of CD34+ stem cells is a critical step in evaluation of graft adequacy prior to harvest for hematopoietic progenitor stem cell transplantation (HPSCT). The International Society of Hematotherapy and Graft Engineering (ISHAGE) established a standardized protocol in 1996 that is widely used for this purpose. Use of the sequential gating strategy routinely identifies a separate population of CD34+ events, with low side scatter and immunophenotype characteristic of hematogones (B-lymphocyte precursors) that are not excluded from the total CD34% according to the guideline. Whether including hematogones, presumably committed to lymphoid development, impacts engraftment is unknown. We investigated the effect of hematogones on engraftment.
Apheresis samples for CD34+ stem cell enumeration were analyzed for the presence (≥0.01%) of the additional CD34+ population by flow cytometry prospectively for 12 months. Patients who underwent HPSCT in that time frame were categorized according to whether their infused product(s) contained hematogones (negative= <0.01%, positive= ≥0.01%, or mixed (combination of collection products, some positive and some negative for hematogones)). Stepwise Cox proportional hazards analysis with a variable entry criterion of P≤0.10 and a variable retention criterion of P≤0.05 was used to identify multivariable prognostic factors for each outcome. Outcomes analyzed were neutrophil engraftment (days to absolute neutrophil count (ANC) >500 K/μL) and platelet (PLT) engraftment (days to platelet count >20 K/μL).
In a 12 month review of 274 apheresis samples, 61% harbored hematogones, comprising a median of 7.1% of total CD34+ cells (range 1.3 – 78.0). Patients (n=147, Table 1) received stem cell infusions that were negative, mixed, or positive for hematogones. The positive group had hematogones ranging from 0.22 – 6.31% of total CD34+ cells; hematogone % in the mixed group could not be quantitated. On multivariable analysis, patients in the mixed and positive groups had a marginally greater likelihood of neutrophil engraftment than those with negative hematogones (Table 2). Hematogones had no impact on platelet engraftment.
Hematogones are frequently included in the ISHAGE gating protocol. Reporting CD34% values that are inclusive of hematogones does not have an adverse effect on engraftment. Preliminary analysis suggests that receiving graft products that contain hematogones may predict for better neutrophil engraftment. Whether this is a direct or indirect effect of hematogones in the sample is unknown.
Table 1. Descriptive Data by Hematogone Group (n=60, n=24, n=63) Negative # (range) % Mixed # (range) % Positive # (range) % Median age at transplant, years 58 (27–76) 54 (38–69) 54 (15–76) Male 40 66.7 16 66.7 34 54.0 Diagnosis type 48 80.0 23 95.8 39 61.9 Lymphoid     Transplant type 47 78.3 23 95.8 27 42.9     Autologous (Auto) 4 6.7 – 31 49.2     Myeloablative allogeneic (MA) 5 8.3 1 4.2 2 3.2     Reduced intensity allogeneic (RIC) 4 6.7 – 3 4.8 Mini allogeneic (Mini)     Cell source 55 91.7 24 100.0 36 57.1     Peripheral stem cells (PSC) 1 1.7 – 24 38.1     Bone marrow (BM) 4 6.7 – 3 4.8     Umbilical cord (UC)     Median CD34+ dose, × 106/kg 5.06 (0.01–27.60) 4.38 (1.81–8.59) 4.00 (0.02–11.91)     Total nucleated cell dose (TNC), × 108/kg 9.00 (0.27–46.88) 18.20 (8.55–37.13) 4.54 (0.27–24.93)
Table 2. Predictors for Neutrophil Engraftment Univariable HR 95% CI P-value Multivariable HR 95% CI P-value Hematogones     Mixed/Negative 1.8 1.1–2.9 0.022 1.9 1.2–3.2 0.012     Positive/Negative 0.6 0.4–0.9 0.012 1.5 0.9–2.2 0.09 Age     Per 10 year increase 1.2 1.0–1.4 0.024 Diagnosis type     Lymphoid/others 2.1 1.4–3.2 <0.001 Transplant type     MA/Auto 0.1 0.1–0.2 <0.001 0.1 0.1–0.2 <0.001     Mini+RIC/Auto 0.3 0.1–0.5 <0.001 0.3 0.1–0.5 <0.001 Cell source     BM/PSC 0.2 0.1–0.3 <0.001     UC/PSC 0.1 0.1–0.3 <0.001 CD34+ dose, × 106/kg     Per 1 × 106/kg increase 1.98 1.61–2.43 <0.001 1.77 1.38–2.26 <0.001 TNC, × 108/kg     Per 1 × 108/kg increase 1.33 1.21–1.47 <0.001

Disclosures:
No relevant conflicts of interest to declare.