VAV1 Mutations Contributes to the Development of T-Cell Malignancies in Mice

• Published in: Blood 2019-11, Vol.134 (Supplement_1), p.300-300
• Main Authors: Fukumoto, Kota, Sakata-Yanagimoto, Mamiko, Fujisawa, Manabu, Sakamoto, Tatsuhiro, Nguyen, Tran B., Suma, Sakurako, Miyoshi, Hiroaki, Ohshima, Koichi, Kataoka, Keisuke, Ogawa, Seishi, Chiba, Shigeru
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2019-124591

Background: VAV1 is known as an important mediator of T-cell receptor (TCR) signaling through its guanine exchange factor (GEF)-dependent and independent functions. Recent studies identified activating VAV1 mutations in several types of T-cell malignancies including peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), angioimmunoblastic T-cell lymphoma (AITL), ALK-negative anaplastic large cell lymphoma (ALCL), and adult T-cell lymphoma/leukemia (ATLL). However, the functions of VAV1 mutations in T-cell malignancies have not been clarified. Objective: We aim to identify the oncogenic signaling of VAV1 mutations in T cells using genetically engineered mice. Methods: Human VAV1 mutant (p.165_174del) (VAV1-Del) and VAV1-STAP2 fusion cDNAs, identified in our PTCL cohort (Fujisawa, Leukemia 2018) were cloned into a VA vector under the CD2 promoter. The vectors were injected into eggs to generate VAV1-Del and VAV1-STAP2 transgenic mice. The mice were further crossed with p53-/- mice to generate p53-/- x VAV1-Del or p53-/- x VAV1-STAP2 mice. Cell surface markers of tumor cells were analyzed by flowcytometry. Cell suspension of tumors were cultured, and were intraperitoneally injected into BALBc/nu mice to examine the cell-autonomous proliferative activity in vitro and tumor-initiating capacity in vivo, respectively. RNA sequencing was performed to clarify the downstream signaling of VAV1 mutations. Results: The p53-/- mice expressing VAV1 mutants showed significantly poorer overall survival (OS) compared to p53-/- mice (p53-/- x VAV1-Del, median 16.6 weeks; p53-/- x VAV1-STAP2, median 18.6 weeks; vs p53-/-, median 33.7 weeks: p50 weeks). p53-/- x VAV1-Del and p53-/- x VAV1-STAP2 mice developed either T-cell lymphoblastic leukemias (LBL) infiltrating into thymus, lung, spleen, and liver, or mature T-cell lymphomas (Lym) into lymph nodes, spleen, and liver. In contrast, p53-/- mice developed only T-LBL at thymus. Flow cytometric analysis showed that most of T-LBL cells developed in p53-/- mice with VAV1 mutants were CD8+ single positive (SP), while those in p53-/- mice were either CD4+CD8+ (double positive, DP) or CD8+ SP. Lym cells in p53-/- mice with VAV1 mutants were either CD4+ SP or CD4-CD8- (double negative, DN) (in p53-/- x VAV1-Del mice, 5/9 CD8+ SP T-LBL, 1/9 DP T-LBL , 2/9 CD4+ SP Lym , and 1/9 DN Lym; in p