PS1315 CHANGES IN THE SECRETOME COMPOSITION OF MULTIPOTENT MESENCHYMAL STROMAL CELLS PATIENTS WITH DIFFUSE LARGE B‐CELL LYMPHOMA WITHOUT BONE MARROW INVOLVEMENT

Abstract

Background:Bone marrow (BM) is not affected in most patients with Diffuse Large B‐cell Lymphoma (DLBCL). However, it has been shown that multipotent mesenchymal stromal cells (MSCs) in DLBCL patients differ from those in healthy donors. MSCs are involved in the formation of a niche for hematopoietic stem cells and secrete many regulatory proteins. Total cellular MSC production from DLBCL patients before and one month after treatment was 1.5 times higher than in healthy donors. At the same time, the relative expression level of BMP4, MMP2, FGFR1, ICAM1 genes was reduced in MSCs from primary patients.Aims:The aim of the study was to investigate the changes in proteome profiles of secretomes from MSCs, isolated from the BM of DLBCL patients and from healthy donors.Methods:The study included 28 DLBCL patients before and one month after treatment and 31 MSC control samples from the BM of healthy donors. MSCs were isolated from the BM by the standard method and secretomes were generated for 24 h. We performed LC‐MS/MS analysis of secretomes of MSCs for 5 patients before and after chemotherapy and 5 donors using Q Exactive HF.Results:We identified 599 up‐regulated proteins and 122 down‐regulated proteins in MSC secretomes from primary patients compared to donors. Among the up‐regulated proteins the molecules of the major HLA 1 class were observed. This may be due to the increased formation of microvesicles. Moreover, functional analysis of up‐regulated proteins demonstrated that the MSC secretomes from primary patients were enriched with proteins involved in vesicle transport (133); regulating of exocytosis (78); immune response (71); proteasome (14). 18 proteins have known functions for tumors; 10 are indicators of rheumatoid arthritis; 10 are associated with signaling pathways of IL‐17 and TNF; 80 proteins are associated with both intracellular and external transport and 30 proteins are associated with transport through the Golgi apparatus, which explains significant difference between the secretomes of MSCs from healthy donors and patients before treatment. 83 elevated proteins are associated with adhesion and its regulation. Patients’ MSCs have elevated proteins associated with signal transmission PDGFR, IL‐12, FGFR.Down‐regulated proteins were involved in the regulation of the immune response, wound healing and inflammation.Of these, 7 proteins are components of PI3K‐Akt signaling pathway; 5 were Rap1 signaling pathway proteins and 5 proteins were associated with Ras signaling pathway. Comparison of proteins before treatment with proteins after treatment revealed a decrease of 366 proteins and an increase of 270.Summary/Conclusion:We show for the first time, that the secretomes from DLBCL patient's MSCs were dramatically altered in comparison with donor's ones. We can conclude that the existence of a lymphoid tumor in an organism, even without BM involvement, leads to very strong changes in the stromal cells.Supported by grant from the Russian Foundation for Basic Research, Project № 17–00‐00170