Diffuse Large B-Cell Lymphoma (DLBCL) Tumor Cells Reprogram Lymphatic Fibroblasts into Cancer-Associated Fibroblasts (CAFs) That Contribute to Tumor Microenvironment (TME)-Driven Immune Privilege

There is a clinical need to identify novel treatments for relapsed/refractory DLBCL. Cancer cells engage in novel associations with stromal and immune cells in the TME that provide crucial contributions to disease progression, immune evasion and therapeutic response. However, these hallmark capabilities have been understudied in DLBCL. Given tumor cell genetic complexity, targeting the TME has become a compelling therapeutic strategy. Immune checkpoint blockade therapy (ICB) (e.g. anti-PD-1), which can activate anti-tumor immunity, has provided a new weapon against cancer and serves as an illustrative example of therapeutically re-educating the TME. Clinical results indicate that only a fraction of DLBCL patients currently respond to ICB. Understanding ill-defined TME-driven immune suppression should help optimise ICB and identify novel therapeutic opportunities. Gene expression studies of DLBCL have identified molecular signatures present in both GCB and ABC subtypes related to the TME that correlated with outcome. The prognostically favorable stromal-1 signature reflects reprogrammed stromal cells, extracellular matrix (ECM) and an active immune response. The less favorable stromal-2 signature indicates elevated angiogenesis and blood vessel density. CAFs promote ECM remodelling and angiogenesis in solid cancers. We hypothesized that CAFs play an important role in the pathogenesis of DLBCL including the regulation of subverted host anti-tumor immunity. To assess whether DLBCL tumor cells induce a CAF phenotype in previously healthy stromal cells, we established a co-culture system with subsequent imaging of conditioned cells. Primary human lymphatic fibroblasts (HLFs) were co-cultured for 5 days in direct contact with a panel of GCB (SU-DHL4, SU-DHL6, DOHH2) and ABC (OCI-LY10, RIVA, U2932) DLBCL cell lines or healthy control B-cells. Quantitative analysis revealed a strong induction of CAF molecular marker expression including FAPα and α-SMA in all DLBCL-educated stromal cells compared to healthy B-cell exposed fibroblasts (P In conclusion, our results establish the ability of DLBCL tumor cells to reprogram HLFs into CAFs that acquire functional capabilities to modulate the TME. Notably, activated CAFs show a compensatory inhibitory response by up-regulating PD-L1 expression that may represent an important TME-driven immunosuppressive mechanism. We believe this data contributes to the understanding of the biology that underlies stromal signatures in the DLBCL TME, in particular the contribution of CAFs to immune privilege. Disclosures Ramsay: Celgene: Research Funding; MedImmune: Research Funding.