Christoph Ellebrecht

"Engineering chimeric antigen receptor (CAR) T cells for treatment of γδ T cell lymphomas"

Christoph Ellebrecht, MD; Enrico Radaelli, DVM, PhD; Charles-Antoine Assenmacher, DVM, MSc, Aimee S. Payne, MD, PhD
 γδ T cell lymphomas (γδTCLs) have 3 major subtypes, hepatosplenic, mucosal, and cutaneous, reflecting the tissue tropism of γδ T cells. A common feature of γδTCLs is their poor prognosis. Primary cutaneous γδTCLs are highly resistant to treatment, with a median survival of 15 months. Chimeric antigen receptors (CARs) redirect T cells to specifically kill cancer cells if they express the antigen targeted by the CAR. γδ T cells are uniquely identified by expression of a γδ T cell receptor (TCR), and γδ T cell-deficient mice have no baseline phenotypic defects, thus identifying an ideal CAR target for γδTCLs, as well as the 10% of T cell leukemias that express γδ TCRs. Here we show that primary human T cells can be engineered to express CARs that specifically target the TCRδ constant region. In vitro, anti-TCRδ CAR T cells demonstrate robust cytotoxicity toward benign and leukemic γδ T cells while sparing αβ T and B cells. Anti-TCRδ CAR T cells specifically eliminated primary human γδ, but not αβ T cells or B cells, in a human stem cell xenograft model (n=4 per group, p=0.0047). In a tumor xenograft model, a single injection of anti-TCRδ CAR T cells, but not control T cells, eradicated an established human γδ T cell leukemia in a dose-dependent fashion (n=35, p=0.0012) by in vivo imaging, confirmed by flow-cytometric analysis of peripheral blood. Comprehensive histopathological analysis of 19 different tissues from CAR or control treated mice demonstrated absence of acute CAR T cell mediated toxicity (n=16) compared to controls, which additionally reflected in absence of serum chemistry and blood count abnormalities after CAR treatment. In conclusion, we provide evidence of potent in vitro and in vivo efficacy of anti-TCRδ CAR T cells and establish a novel treatment modality for γδTCL that offers the potential for durable remissions of previously incurable cancers.