PB2060 THE UTILITY OF VARIABLE LEVELS OF CD39 EXPRESSION BY FLOW CYTOMETRY TO DISTINGUISHING B CELL LYMPHOMA SUBTYPES
Authors: R. Di Gaetano, D. Belvini, B. Callegari, M.A. De Benedetto, E. Pilotto, L. Vassallo, A. Scapinello, R. Sartori
Journal: HemaSphere (2019)

Background: B lymphocytes were considered to be positive regulators of humoral immune responses. Recently B‐cell subsets named “regulatory B cells” (Bregs) have been describe. These subsets negatively regulate immune responses by inhibiting the activity of the effector T lymphocytes (Teff) and favoring that of the regulators T (Treg). The Bregs have been linked to not only inflammatory and autoimmune diseases, but also malignancies via suppressing anti‐tumour immunity. It emerged that B‐cells have regulatory properties having the ability to produce the immunosuppressive adenosine (ADO) via CD39, an ectoenzyme expressed on cells that cooperates to metabolize exogenous ATP to ADO. Studies have experimented that CD39 is upregulated (CD39 high ) in subset of activated immunosuppressive B‐cells. Unlike T and NK, greater than 90% of normal B‐cells express CD39, while the neoplastic B‐cells have an heterogeneous expression of CD39. Aims: The aim of this study was to assess the expression of CD39 in neoplastic B cells of nodal Follicular lymphomas (FL) and Diffuse Large B Cell Lymphomas (DLBCL). Moreover, these were compare with background non‐malignant B cells, when present. Methods We investigated the intensities of CD39 (CD39 all ,CD39 hight ) by flow cytometry (FC) in cell suspensions from dissociated tissues of 17 DLBCL, 22 FL and 10 normal lymph node (N‐LN). According Hans algorithm, among DLBCL 8 case were classified as Germinal Center B (GCB) subtypes and 9 as non‐GCB. The FL are subdivided according to the histological grade: 2 cases G1, 8 G2 and 12 G3. Results: For CD39 all there was no difference in expression between DLBCL and N‐LN ( p = 0,68), while there are significant differences between DLBCL and FL ( p = 0,02) and between FL and N‐LN ( p = 0,019). There were statistical differences for CD39 high expression in DLBCL compared with N‐LN ( p = 0,02) and with FL ( p = 0,002). On the contrary, there were no statistically differences between FL and N‐LN ( p = 0,9). Within the DLBCL the two subgroups were similar for CD39 all ( p = 0,1) but presented different results for CD39 high : non‐GCB subtypes had a stronger expression compared to GCBs (p = 0,01). In FL subgroups CD39 expression showed high heterogeneity with a trend to a greater intensity of the marker as the histological grade increases, although there is not a statistically significant difference Summary/Conclusion: Analysis of CD39 by FC could be an useful tool to distinguishing between FL and DLBCL. In particular, in FLs the intensity of expression could be related to the histological grade. Furthermore, CD39 high seems to differentiate GCB from non‐GCB DLBCL, confirming in the latter the origin from activated B cell. The variable levels of CD39 by FC could contribute to orient in the defining entities that are not always easily and clearly differentiated. In addition, a variation of CD39 expression between neoplastic and normal cells was noted, particularly when clonal elements differ by FC for different sizes according to Side and Forward Scatter. Given that in Breg there is a variable levels of CD39 as a function of their immunosuppressive activity, it could be hypothesized that even in neoplastic B cells the different intensity of expression of the marker could suggest an active role of the B clone in producing immunosuppressive molecules and in characterizing the microenvironment favorable to the same lymphoma. Acknowledgments: This work was supported by Associazione Italiana contro le leucemie‐linfomi e mieloma (AIL) Treviso image