Abstract 2326: Allo CAR T TM targeting CD70 for the treatment of renal cell carcinoma
Authors: Panowski Siler , Srinivasan Surabhi , Tacheva-Grigorova Silvia , Tan Nguyen , Blarcom Thomas Van , Sai Tao , Heyen Jonathan , Nagarajan Niranjana , Dusseaux Mathilde , Galetto Roman , Sasu Barbra 
Published: August 2019

Abstract
Renal Cell Carcinoma (RCC) represents a substantial patient population, with 65,340 new cases estimated in the US in 2018. Patients with localized tumors undergo nephrectomy, however 30-40% of patients develop metastasis, with a 5-year median survival rate of only 11.6%. Current treatment for advanced disease improves overall survival, but disease relapse is common and additional treatments are needed. RCC is a highly T-cell infiltrated tumor type with responsiveness to Immuno-Oncology (IO) agents and thus it may be amenable to a T-cell based therapy. T cells can be genetically modified to express chimeric antigen receptors (CARs), and adoptive transfer of CAR T cells is showing great promise in hematologic malignancies. To translate this approach for RCC treatment, expression data were mined and CD70 was identified as an antigen expressed in a high proportion of patients with RCC, with limited normal tissue expression on a fraction of activated lymphocytes and subsets of dendritic cells. Since CD70 expression is present on activated T cells, targeting it with a CAR could lead to fratricide and T cell exhaustion. For this reason, screens were specifically designed to identify CARs that were less impacted by these issues and used to triage a large panel of CD70 CARs. Optimal CARs were successfully manufactured and demonstrated robust in vitro and in vivo anti-tumor activity against target cells expressing relevant levels of CD70. A large panel of single chain fragment variables (scFvs) that bind to CD70 were generated and formatted into second-generation 41BB-CD3zeta CARs. CARs were first screened in a Jurkat cell CD70-knockout assay and clones showing tonic signaling were eliminated. CD70 CAR T cells were generated with various scFvs and ranked based on transduction efficiency, phenotype, activation status and expansion. A subset of CD70 CAR T cells were moved into in vitro short and long-term cytotoxicity assays. Target cells expressing high, medium, and low levels of CD70 were utilized. Ability to kill cell lines with CD70 expression similar to that seen in primary tumors was used as criteria for candidate selection. CAR T were evaluated in multiple in vivo xenograft models and robust anti-tumor activity was observed. Some candidates performed better with CD70 knockout and some worked irrespective of knockout. To profile potential toxicity, a cyno toxicity study was conducted with one clone formatted as a CD70-CD3 bispecific antibody. No unexpected findings were observed. In the event of unexpected toxicity, CAR T cells were further engineered to contain an off-switch, by which CAR T are eliminated upon administration of Rituximab. Multiple off-switch CAR formats were evaluated, and optimal formats determined independently for each CAR. One CD70 CAR T was also successfully manufactured in a large-scale process. In summary, multiple CD70 CAR T have been profiled and a subset selected for further investigation as potential clinical candidates.
Citation Format: Siler Panowski, Surabhi Srinivasan, Silvia Tacheva-Grigorova, Nguyen Tan, Thomas Van Blarcom, Tao Sai, Jonathan Heyen, Niranjana Nagarajan, Mathilde Dusseaux, Roman Galetto, Barbra Sasu. Allo CAR T TM targeting CD70 for the treatment of renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2326.