Clinical Relevance of CD45+/CD19- Stem-like Tumor Cells in Patients with Mantle Cell Lymphoma: A Single Center Experience
Authors: Kim Sung Min , Lee Seung-Tae , Ryu Kyung Ju , Kim Hee-Jin , Kim Sun-Hee , Yoo Kwai Han , Ko Young Hyeh , Kim Won Seog , Kim Seok Jin 
Published: October 2019

Abstract
Background
Mantle cell lymphoma (MCL) is a rare but unique subtype of B-cell non-Hodgkin lymphoma (NHL) that is molecularly characterized by the chromosomal translocation, t(11;14)(q13:q32) leading to cyclin D1 overexpression. MCL is also characterized by heterogeneous clinical features from indolent to aggressive courses. The majority of patients with MCL initially show slowly progressing nature of disease, however, the treatment outcomes of conventional chemotherapy have been poor. As a result, most patients with MCL have shown repeated relapses ultimately resulting in death. Although upfront use of intensified chemotherapy regimens and active application of autologous stem cell transplantation as a consolidation treatment were introduced, MCL has still remained as one of deadly subtype of NHL because its prognosis is still worse than other NHL. Given this heterogeneity and incurability of MCL, the concept of tumor stem cells has been suggested to explain peculiar characteristics of MCL. Thus, previous in vitro studies reported a small fraction of tumor cells, CD45+/CD19- might reflect the presence of tumor stem cells and showed their resistance to chemotherapeutic agents as well as tumor formation ability. However, the clinical relevance of CD45+/CD19- stem-like cell population in bone marrow or other sites has rarely been studied and demonstrated in patients with MCL.
Methods
Between 2011 and 2013, we analyzed patients who were pathologically diagnosed with MCL. They all received systemic chemotherapy with curative intent including rituximab-containing chemotherapy. The flow cytometry for isolating CD45+/CD19- cell population was done with bone marrow aspirates or malignant effusion from patients at diagnosis and/or at the time of relapse. The follow-up evaluation of CD45+/CD19- cells was also done at the end of primary treatment. The in vitro experiments with B-cell lymphoma cell lines were performed to evaluate the association of CD45+/CD19- cell population with the resistance to chemotherapeutic agents. The percentage of CD45+/CD19- cells from surviving cells after doxorubicin treatment at the dosage of IC90 for 48 hours were compared with control group.
Results
Twenty-one patients were enrolled, and the median age was 67 years (range, 50–78 years). Eighteen patients had stage IV disease including 15 cases of bone marrow involvement. All patients’ sample was from bone marrow aspirates except one patient from malignant pleural effusion. The examination for CD45+/CD19- cells was done in six patients at diagnosis and the end of treatment whereas only single evaluation was done in the other patients at diagnosis or at the time of relapse. The median percentage of CD45+CD19- cells was 0.019% (range 0-1.8%) in all examined patients. The mean percentage of patients who relapsed or progressed (0.41%±0.69) was higher than that of patients at diagnosis (0.09%±0.11) or patients at the state of complete or partial response after the completion of chemotherapy (0.01%±0.01). The serial monitoring of three patients who relapsed or progressed showed the increased level of CD45+/CD19- cell population while patients who responded to primary treatment showed the decreased level of CD45+/CD19- cells at the end of treatment. The in vitro study with B-cell lymphoma cell lines, Toledo, Daudi, Raji and BJAB showed the increased fraction of CD19- cells among lymphoma cells resistant to doxorubicin compared to control cells. This increase of CD19- cells was correlated with the increase of ATP-binding cassette subfamily G2 (ABCG2) that was another marker reflecting the presence of tumor stem cells.
Conclusion
The presence of CD45+/CD19- cell population was demonstrated in bone marrow aspirates of patients with MCL, and its level was correlated with clinical outcome including response to treatment and relapse or progression. Considering the association of CD45+/CD19- cells with resistance to treatment, the presence of this extremely small but significant stem-like fraction might be associated with treatment failure in patients with MCL.

Disclosures
No relevant conflicts of interest to declare.