Hematogones (medullar pro-B Cells) Are Present but Decreased in Active Multiple Myeloma and Are a Prognostic Factor in Treated Myeloma Patients
Authors: Cabrera Quentin , Chantepie Sylvain , Mear Jean-Baptiste , Salaun Véronique , Cornet Edouard , Troussard Xavier , Reman Oumedaly , Macro Margaret 
Published: October 2019

Abstract
BACKGROUND
Hematogones (HG) are normal bone marrow B-cells precursors, characterized on Multiparameter Flow Cytometry (MFC) study by CD19 expression, progressive loss of CD10 and CD34, acquisition of CD45 and CD20. HG level is lowered by age or medullar tumoral infiltration, but is higher (>5%) after chemotherapy, Hematopoietic Stem Cell Transplantation (HSCT) or viral infection. An HG level >0.01% in first complete remission in Acute Myeloid Leukemia (AML) patients is associated with a better Overall Survival (OS) and Progression Free Survival (PFS). Further correlations have been made between HG level and good evolutions in AML patients or HSCT recipients. Although Multiple Myeloma (MM) is a mature B-cell malignancy, no clinical study has focused on HG in MM patients. Furthermore, there is no data on prognostic impact of HG in treated MM patients. However, HG study could be of prime interest for medullar micro-environment evaluation which is not assessed by routine prognostic factors.
AIM
Our primary objective was to establish the presence and level of HG in the bone marrow of patients with Monoclonal Gammopathy of Undetermined Significance (MGUS), Smoldering Myeloma (SM) or active MM (aMM), and to analyze correlations with clinical characteristics. Our secondary objective was to determine a prognostic correlation between HG level at diagnosis and PFS or OS in aMM patients.
METHODS
In this monocentric prospective observational study conducted between March 2011 and January 2014, we analyzed all bone marrow samples sent to the MFC lab in our center of CHU de Caen, France. Samples were routinely obtained by bone marrow aspirations at diagnosis for MGUS or MM patients. Medullar cells were analyzed by 4-color MFC, using a CD20-FITc/CD19-PE/CD45-PerCp/CD10-APC panel for HG detection. HG level was calculated over all nuclear medullar cells, samples with less than 100.000 cells were excluded, and sensitivity was 1/104 cells. All biological data were recorded at diagnosis. The median follow-up was 16 months. All statistical analysis, including multivariate analysis, were performed with two-sided 95% confidence intervals.
RESULTS
A total of 90 patients have been included: 25 MGUS (27%), 12 SM (13%) and 53 aMM (58%). The mean age at diagnosis was respectively 63, 68 and 67 y (35-90), and mean β2-µglobulinemia (β2) was 2.5, 5 and 6.3 mg/l respectively. HG were detected in more than 90% of cases. The mean HG level was significantly higher in MGUS (2.86%, median 2%, p=0.006) or in SM (1.95%, median 1.5%, p=0.019) than in aMM (1.10% median 0.5%) (Figure 1). HG level at diagnosis was inversely correlated with age, plasma cell infiltration, hypoalbuminemia, or β2 (mean HG=2% if β2≤3.5 mg/l, and 0.8% if β2>5 mg/l). HG level was higher in patients with hemoglobin levels ≥10 g/dL (2.8% vs 0.7%, p=0.015). There were no correlations between HG level at diagnosis and white blood cells count, gender, renal insufficiency, plasma cell phenotype nor monoclonal component subtype.
In the subgroup of 53 aMM patients, 22% were ISS1, 29% were ISS2 and 49% ISS3. Mean HG levels were 2.1%, 0.8% and 0.85% respectively (p=0.008 between ISS1 vs ISS2+3). All patients but one received a triple regimen chemotherapy including Bortezomib. Patients with HG level >0.5% at diagnosis (median of the group) had a longer median PFS (29.8 vs 13.5 months, n=26 and 27, p=0.002, cf. Figure 2) and a better OS (85% alive vs 60% at 20 months, median not reached, p=0.02). In multivariate analysis, a cut-off of 0.5% of HG at diagnosis was a prognostic factor for PFS in aMM patients (p=0.03, IC=0.14-0.9), with age (p=0.041, IC=1.0-1.09) but not ISS subgroup (p=0.6). Furthermore, patients who achieved Very Good Partial Response (VGPR) or more had higher HG level at diagnosis than patients who achieved Partial Response or less (IC=1.08-6.07, p=0.015).
CONCLUSION
HG are present in MM patients. The HG level is decreased in MM patients as compared to MGUS, and is inversely correlated with the disease biomarkers or activity. An HG level >0.5% at diagnosis is a good prognostic factor in treated MM patients, and may reflect bone marrow micro-environment condition.
Figure 1. HG level and disease stage at diagnosis. Figure 1. HG level and disease stage at diagnosis.
Figure 2. PFS of aMM patients sort by HG at diagnosis. Figure 2. PFS of aMM patients sort by HG at diagnosis.

Disclosures
No relevant conflicts of interest to declare.