Abstract 5305: Predicting relapse using CD138-independent strategy to detect residual myeloma plasma cells
Authors: Muz Barbara , Azab Feda , de la Puente Pilar , King Justin , Luderer Micah , Vij Ravi , Azab Abdel Kareem 
Published: August 2015

Abstract
Introduction: Despite the introduction of novel therapies, majority of multiple myeloma (MM) patients relapses. The major reason for the relapse in MM is the presence of a minimal residual disease (MRD) population that remains after treatment. MM cells are defined as CD138+; however, the presence of clonogenic CD138-negative MM cells and hypoxia-driven CD138 decrease in expression were previously shown. We propose a novel set of biomarkers (independent of CD138) to detect MRD in MM in order to predict patient relapse.
Procedures: We tested the effect of hypoxia on CD markers expression in MM cell lines. We developed new method to detect MM cells by flow cytometry based on CD38(APC+) gating and negatively selecting other leukocytes including T cells, B cells, monocytes, NK cells, and dendritic cells using CD3, CD19, CD14, CD16, and CD123, respectively (FITC-conjugated), the MM cells were defined as APC+/FITC-. We compared traditional method (CD138-based) with the new set of biomarkers (1) to detect normoxic and hypoxic MM cells, (2) to detect MM cells in the peripheral blood (PB) and the bone marrow (BM) from MM patients, confirming cell clonality by internal staining with Kappa/Lambda light chain antibodies, and (3) to predict relapse in MM patients whose BM was defined a CD138-negative.
Summary of data: We found that hypoxia decreased the expression of CD138 by ∼50%, while CD38 was not altered by hypoxia in MM cells. The use of CD138+ as a marker for MM detected only 60-75% of hypoxic MM cells, whereas APC+/FITC- strategy detected close to a 100% of the hypoxic MM cells in vitro. In patient samples, all patients had a higher number of BM-derived and circulating MM cells as detected by APC+/FITC- strategy compared to CD138+. In addition, the clonality of the APC+/FITC- population in BM negative fractions was the same as the original disease (CD138+ cells). Moreover, studies conducted on 16 patients with BM defined as a CD138-negative, showed that the novel APC+/FITC- strategy was more successful than CD138-based method or histology in predicting recurrence and time to relapse. The median time-to-progression with &lt;2% or ≥2% of MM cells detected by novel strategy was 40 and 20 months, respectively. Moreover, patients who relapsed within 2 years had an average 4.4% of APC+/FITC- cells, while patients who relapse in more than 2 years had an average of 1.6% APC+/FITC- cells in their BM.
Conclusion: CD138 cannot be used as a universal marker to detect MM cells, especially when they are hypoxic. A novel set of biomarkers CD38+/CD3-/CD19-/CD14-/CD16-/CD123- (APC+/FITC-) was designed to detect MM cells independent of CD138 expression and hypoxic status. This strategy was able to detect a clonal CD138-negative MM cell population in the BM and PB from MM patients. Moreover, this strategy predicted tumor recurrence and relapse in MM patients more accurately compared to traditional methods such as CD138-based or histology.
Citation Format: Barbara Muz, Feda Azab, Pilar de la Puente, Justin King, Micah Luderer, Ravi Vij, Abdel Kareem Azab. Predicting relapse using CD138-independent strategy to detect residual myeloma plasma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5305. doi:10.1158/1538-7445.AM2015-5305