Alterations in the Properties of MSCs in Patients with Diffuse Large B-Cell Lymphoma (DLBCL) without Bone Marrow Involvement

The stromal microenvironment regulating hematopoiesis in patients with hematologic malignancies undergoes significant alterations. The changes in the concentration of colony-forming fibroblast units (CFU-F) in the bone marrow (BM) and disruption in the functioning of multipotent mesenchymal stromal cells (MSCs) are shown in many studies for patients with acute leukemia. Often it is not possible to distinguish the cause of changes in stromal progenitor cells after treatment: interaction with tumor cells or the effects of therapy. Most of the patients with diffuse large B-cell lymphoma (DLBCL) do not have BM involvement. It was assumed that the properties of MSCs in these patients were not changed, and so this could be an attractive model for investigation the effect of antitumor drugs on human BM stromal microenvironment. The aim of the study was to compare the properties of MSCs in patients with DLBCL in the onset of the disease and a month after the end of therapy.

Methods

The study included 20 patients with DLBCL (11 male, 9 female) aged 42-60 years in the onset of the disease and a month after the end of treatment. 3-5 ml of BM were collected during diagnostic punctures after informed consent. MSCs and CFU-F were cultured by standard methods. The total MSCs production, the doubling-population level per day, the concentration of CFU-F, the relative gene expression level (REL) in MSC by real-time PCR and the mean fluorescence intensity (MFI) by flow cytometry were analyzed. The control group included 31 donors of the corresponding age. The analysis of MSCs secretome was carried out using the LC-MS/MS analysis TripleTOF 5600+ mass spectrometer with a NanoSpray III ion source coupled to a NanoLC Ultra 2D+ nano-HPLC System.

Results

The total cell production for 4 passages in primary patients' MSCs was significantly higher than in donors (11.4 ± 2 x 10⁶ per flask versus 6.9 ± 1.1, p = 0.04). It remained elevated after therapy (10.2 ± 1.5). At the same time, the MSCs population-doubling level per day was significantly decreased in patients in comparison with donors (0.6 ± 0.03 vs. 0.4 ± 0.04, p <0.05) and was not restored after treatment. This effect could be explained by the heterogeneity of MSCs population and in particular by the fact that the dividing cells in patients' MSCs population could have the shorter doubling time than donor MSCs population. CFU-F concentration in the patients' BM did not change significantly compared to donors in the onset of the disease and after the end of treatment. There was no change in the REL of genes responsible for MSCs differentiation.

MFI analysis of antigens typical for MSCs revealed significant differences in the patients MSCs. CD54 (ICAM1) was 1.5 times higher in the onset of the disease compared to donors. It increased 6.3 times (456 ± 124 versus 72 ± 16, p <0.05) after treatment. Patients MSCs had increased secretion of this protein, which is involved in the regulation of hematopoietic stem cells quiescence and repopulating capacity. However, the REL of ICAM1 was reduced 2-fold, both in the onset of the disease and after treatment. The MFI of another adhesion molecule - CD146 (MCAM) also was 3.4 times higher (1007 ± 245 vs. 291 ± 69, p <0.05) after treatment, but REL of this gene did not change. MFI of CD73 and CD105 tended to increase in MSCs in the onset of the disease. CD73 increased 1.6 times after treatment (1433 ± 433 vs. 632 ± 57, p <0.05), while the secretion of this protein was increased in the onset of the disease and decreased after treatment. CD105 MFI also increased 4 times (4578 ± 1159 vs. 610 ± 139, p <0.05) after treatment compared with donors. In the onset of the disease, IL6 REL was reduced, and then significantly increased after treatment, but the secretion of this cytokine on the contrary in the onset of the disease was increased and reduced after treatment. The REL of FGF2 receptors changed upward in FGFR2 and decreased in FGFR1, remaining altered after treatment, whereas FGFR1 secretion increased in the onset of the disease and decreased with treatment. All these seemingly contradictory changes clearly indicate aberrations in the regulation of MSCs functioning in DLBCL patients.

Conclusion

Despite the absence of proven BM damage in DLBCL patients, the properties of MSCs - niche components in the stromal microenvironment that regulates hematopoiesis, had been changed.

The materials were supported by the Russian Foundation for Basic Research grants, Projects No. 17-00-00170, 17-00-00172.