Refractory metastatic rhabdomyosarcoma is largely incurable. Here we analyze the response of a child with refractory bone marrow metastatic rhabdomyosarcoma to autologous HER2 CAR T cells. Three cycles of HER2 CAR T cells given after lymphodepleting chemotherapy induces remission which is consolidated with four more CAR T-cell infusions without lymphodepletion. Longitudinal immune-monitoring reveals remodeling of the T-cell receptor repertoire with immunodominant clones and serum autoantibodies reactive to oncogenic signaling pathway proteins. The disease relapses in the bone marrow at six months offtherapy. A second remission is achieved after one cycle of lymphodepletion and HER2 CAR T cells. Response consolidation with additional CAR T-cell infusions includes pembrolizumab to improve their efficacy. The patient described here is a participant in an ongoing phase I trial (NCT00902044; active, not recruiting), and is 20 months off T-cell infusions with no detectable disease at the time of this report.

Background: Patients with advanced sarcoma have limited treatment options and poor survival. In our phase 1 dose-escalation trial, intravenous administration of up to 1x108/m2autologous HER2-CAR T cells in patients with HER2+ sarcoma was safe. The goal of the current study is to evaluate if lymphodepleting chemotherapy can safely improve the expansion of HER2-CAR T cells. Methods: In a phase 1 clinical trial, NCT00902044, we administered 1x108/m2autologous HER2-CAR T cells to patients with recurrent/refractory HER2+ sarcoma following lymphodepletion. Results: Ten patients with refractory/metastatic HER2+ sarcoma (5 osteosarcoma, 3 rhabdomyosarcoma [RMS], 1 Ewing sarcoma, 1 synovial sarcoma) with a median age of 14 (range: 4 to 54) were treated; one RMS patient was re-enrolled and retreated. Each patient received up to 3 infusions of 1x108cells/m2 CAR T cells after lymphodepletion with either fludarabine (Flu; n = 3) or Flu and cyclophosphamide (Flu/Cy; n = 8). Eligible patients were given up to an additional 5 subsequent infusions without lymphodepletion. Flu and Flu/Cy induced lymphopenia with an absolute lymphocyte count of <100/ml on the day of the T-cell infusion. Flu/Cy induced neutropenia (absolute neutrophil count <500/ml) for up to 14 days. 8/11 patients developed grade 1-2 cytokine release syndrome (CRS) within 24 hours of CAR T-cell infusion with complete resolution after supportive care, within 5 days of onset. T cells expanded in 9/11 patients with a median peak expansion on day 7 (range: 5 to 28). CAR T cells could be detected by qPCR in 10/10 patients at 6 weeks post infusion. One patient with RMS metastatic to the bone marrow had a complete response (CR) for 12 months then relapsed after 6 months off therapy. The patient was subsequently re-treated and achieved CR that has been maintained for 15 months. One patient with osteosarcoma metastatic to the lungs has an ongoing CR for 32 months. Three patients had stable disease (SD), and 5 had progressive disease (PD). In the RMS patient who attained CR, remodeling of the TCRβ repertoire was observed with each CAR T-cell infusion and distinct antibody responses to oncogenic pathway proteins were identified. Conclusions: Administration of lymphodepletion chemotherapy followed by autologous HER2-CAR T cells is safely tolerated and is associated with objective clinical benefit in some patients with advanced HER2+ sarcoma. Immune correlative studies suggest that the HER2-CAR T cells given in combination with Flu/Cy lymphodepletion induce endogenous immune reactivity. These findings warrant further evaluation in a phase 2 study as a single agent or in combination with other approaches. Citation Format: Shoba A. Navai, Christopher Derenzo, Sujith Joseph, Khaled Sanber, Tiara Byrd, Huimin Zhang, Melinda Mata, Claudia Gerken, Ankita Shree, Pretty R. Mathew, Olga Dakhova, Vita Salsman, John Hicks, Zhongzhen Yi, Meng-Fen Wu, Tao Wang, Bambi Grilley, Cliona Rooney, Malcom Brenner, Helen Heslop, Adrian Gee, Stephen Gottschalk, Nabil Ahmed, Meenakshi Hegde. Administration of HER2-CAR T cells after lymphodepletion safely improves T cell expansion and induces clinical responses in patients with advanced sarcomas [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 LB-147.