The fusion oncogene VAV1-MYO1F triggers aberrant T-cell receptor signaling in vivo and drives peripheral T-cell lymphoma in mice

VAV1-MYO1F is a recently identified gain-of-function fusion protein of the proto-oncogene Vav guanine nucleotide exchange factor 1 (VAV1) that is recurrently detected in T-cell non-Hodgkin's lymphoma (T-NHL) patients. However, the pathophysiological functions of VAV1-MYO1F in lymphomagenesis are insufficiently defined. Therefore, we generated transgenic mouse models to conditionally express VAV1-MYO1F in T-cells in vivo. We demonstrate that VAV1-MYO1F triggers cell autonomous activation of T-cell signaling with an activation of the ERK, JNK, and AKT pathways. VAV1-MYO1F expression induces a T-cell activation phenotype with high surface expression of CD25, ICOS, CD44, PD-1, and decreased CD62L as well as aberrant T-cell differentiation, proliferation, and neoplastic transformation. Consequently, the VAV1-MYO1F expressing T-cells induce a malignant T lymphoproliferative disease with 100% penetrance in vivo that mimics key aspects of human peripheral T-cell lymphoma. These results demonstrate that the human T-cell oncogene VAV1-MYO1F is sufficient to trigger oncogenic T-cell signaling and neoplastic transformation, and moreover, it provides a new clinically relevant mouse model to explore the pathogenesis of and treatment concepts for human T-cell lymphoma.

Oncogenic Vav1-Myo1f induces therapeutically targetable macrophage-rich tumor microenvironment in peripheral T cell lymphoma

Peripheral T cell lymphoma not otherwise specified (PTCL-NOS) comprises heterogeneous lymphoid malignancies characterized by pleomorphic lymphocytes and variable inflammatory cell-rich tumor microenvironment. Genetic drivers in PTCL-NOS include genomic alterations affecting the VAV1 oncogene; however, their specific role and mechanisms in PTCL-NOS remain incompletely understood. Here we show that expression of Vav1-Myo1f, a recurrent PTCL-associated VAV1 fusion, induces oncogenic transformation of CD4⁺ T cells. Notably, mouse Vav1-Myo1f lymphomas show T helper type 2 features analogous to high-risk GATA3⁺ human PTCL. Single-cell transcriptome analysis reveals that Vav1-Myo1f alters T cell differentiation and leads to accumulation of tumor-associated macrophages (TAMs) in the tumor microenvironment, a feature linked with aggressiveness in human PTCL. Importantly, therapeutic targeting of TAMs induces strong anti-lymphoma effects, highlighting the lymphoma cells' dependency on the microenvironment. These results demonstrate an oncogenic role for Vav1-Myo1f in the pathogenesis of PTCL, involving deregulation in T cell polarization, and identify the lymphoma-associated macrophage-tumor microenvironment as a therapeutic target in PTCL.