Session 2: Microenvironment and resistance

Fibrinogen-like protein 2 (FGL2) is a multifaceted immune checkpoint with potential therapeutic application in B-cell non-Hodgkin Lymphomas

Juan GARCIA VALERO^1,2, Dolors COLOMER^1,2,5,6, Sergio ROA^2,4,7,8, Patricia PÉREZ-GALÁN^1,2, Noelia SANDOVAL-HELLÍN¹, Anna VIDAL-CRESPO^1,2, Blanca BERROZPE^3,8, Fabián ARENAS^1,2, Javier MELCHOR^3,4, Sara Contreras GRIJALBA^3,8, Marcos GARCIA LACARTE^3,4,8, Heribert PLAYA-ALBINYANA^1,2

¹Fundació de Recerca Clínic Barcelona, Barcelona, Spain
²Centro de Investigación Biomédica en Red-Oncología, Madrid, Spain
³Department of Biochemistry and Genetics, Universidad de Navarra, Pamplona, Spain
⁴Hemato-Oncology Program, Center for Applied Medical Research (CIMA), Pamplona, Spain
⁵Hospital Clínic, Barcelona, Spain
⁶University of Barcelona, Medical School, Barcelona, Spain
⁷Department of Biochemistry and Genetics, Universidad de Navarra, Pamplona, Spain
⁸Navarra Institute for Health Research (IdiSNA), Pamplona, Spain

Purpose

Follicular Lymphoma (FL) and Diffuse Large B-Cell Lymphoma (DLBCL) represent, respectively, the most common indolent and aggressive B-cell non-Hodgkin lymphoma (B-NHL). These malignancies are characterized by a close cooperation between genetic aberrations and an immunosuppressive tumor microenvironment (TME). Here, we have, explored the role of fibrinogen-like protein 2 (FGL2) as a non-canonical immune checkpoint in B-NHL, given its established immunosuppressive functions in other cancers like glioblastoma. FGL2, which exists in both membrane-bound (mFGL2) and secreted (sFGL2) forms, is implicated in immune suppression and may present a novel therapeutic target in B-NHL.

Experimental Design

We conducted an extensive meta-analysis from public databases to assess FGL2 expression in FL and DLBCL biopsies compared to normal tonsils, and measured sFGL2 levels in patient serum samples versus healthy controls. The therapeutic potential of FGL2 blockade was evaluated through antibody-mediated inhibition in vitro using Patient Derived Lymphoma Spheroids (PDLS). In vivo studies were performed using two immunocompetent lymphoma mouse models: the A20 syngeneic murine B lymphoma model and the pBIC multitransgenic model for DLBCL, to assess tumor regression, survival outcomes and TME remodeling, focusing on key immune cell populations infiltrating the lymphomas.

Results

Our analysis revealed elevated mRNA FGL2 expression in both tumor cells and the TME of FL and DLBCL biopsies, with increased sFGL2 levels in patient serums compared to healthy controls. Moreover, flow cytometry and immunofluorescence in lymphoma patient samples confirmed the expression of mFGL2 in tumoral B cells. FGL2 blockade in PDLS (n=8) showed a mean depletion of 34%.

In vivo, FGL2 blockade led to complete tumor regression in the A20 lymphoma model and significantly extended survival in pBIC mice. The anti-FGL2 treatment reprogrammed the immune microenvironment by reducing M2 macrophages, CD39+ Tregs, and MDSCs while increasing CD44high CD8 T cells. These changes resulted in a sustained therapeutic response, with 30% of treated mice remaining in remission two months post-treatment.

Conclusion

The therapeutic blockade of FGL2 shows promising potential by reshaping the TME, enhancing anti-tumor immunity, and leading to sustained tumor regression and increased survival in preclinical models. These results support the further exploration of FGL2 as a novel immunotherapeutic target in B-NHL.