The interaction of
lymphoma cells with their microenvironment has an important role in disease pathogenesis and is being actively pursued therapeutically using
immunomodulatory drugs, including
immune checkpoint inhibitors.
Diffuse large B-cell lymphoma (DLBCL) is an aggressive high-grade disease that remains incurable in ~40% of patients treated with R-CHOP immunochemotherapy. The FOXP1
transcription factor is abundantly expressed in such high-risk DLBCL and we recently identified its regulation of immune response signatures, in particular, its suppression of the cell surface expression of major histocompatibility class II (MHC-II), which has a critical role in antigen presentation to T cells. Using CRISPR/Cas9 genome editing we have depleted Foxp1 expression in the aggressive murine A20
lymphoma cell line. When grown in BALB/c mice, this cell line provides a high-fidelity immunocompetent disseminated
lymphoma model that displays many characteristics of human DLBCL. Transient Foxp1-depletion using
siRNA, and stable depletion using CRISPR (generated by independently targeting Foxp1 exon six or seven) upregulated cell surface I-Ab (MHC-II) expression without impairing cell viability in vitro.
RNA sequencing of Foxp1-depleted A20 clones identified commonly deregulated genes, such as the B-cell marker Cd19, and hallmark DLBCL signatures such as MYC-targets and oxidative phosphorylation. Immunocompetent animals bearing Foxp1-depleted A20
lymphomas showed significantly-improved survival, and 20% did not develop
tumors; consistent with modulating immune surveillance, this was not observed in immunodeficient NOD SCIDĪ³ mice. The A20 Foxp1 CRISPR model will help to further characterize the contribution of Foxp1 to
lymphoma immune evasion and the potential for Foxp1 targeting to synergize with other
immunotherapies.