Phase I experience with first in class TnMUC1 targeted chimeric antigen receptor T-cells in patients with advanced TnMUC1 positive solid tumors.
Authors: Gutierrez Rodolfo , Shah Payal D , Hamid Omid , Garfall Alfred L. , Posey Avery , Bishop Michael Russell , Blumenschein George R. , Johnson Melissa Lynne , Lee Sylvia , Luke Jason J. , Morgensztern Daniel , Fountaine Thomas J. , Dryer-Minnerly Rebecca , Najmi Saltanat , Hufner Pam , Chagin Karen 
Published: June 2021

e14513 Background: MUC1 is a glycoprotein that is expressed in healthy tissues on the luminal surface of simple and glandular epithelium. In tumors that arise from these cells, an alternate form with aberrant glycosylation is frequently over expressed and distinguishes tumor associated TnMUC1 from normal MUC1. We have generated a novel chimeric antigen receptor (CAR) targeting the TnMUC antigen comprised of a mouse anti-human scFv derived from the monoclonal antibody 5E5 which recognizes the epitope comprising Tn glycan of MUC1, a CD8a transmembrane region and dual CD2 and CD3z intracellular signaling domains. CD2 signaling in T-cells has been demonstrated to result in delayed exhaustion. The novel incorporation of this co-stimulatory domain may lead to enhanced persistence of the CART cells which is believed to be critical for efficacy in solid-tumors. Methods: This is a multi-center first in human Phase I study to evaluate the safety and preliminary efficacy of CART-TnMUC1-Cells for the treatment of solid-tumors. Solid-tumors included in the dose-escalation phase include metastatic treatment-resistant ovarian cancer (OC), pancreatic adenocarcinoma (PC), triple-negative breast cancer (TNBC) or non-small lung cancer (NSCLC). All patients must have TnMUC1 expression as determined by immunohistochemistry. Results: As of January 2021, a total of six patients were treated. Three in Cohort 1 (no lymphodepletion; dose = 1-2 x 107 TDN CART cells; tumors = 1 OC, 1 TNBC and 1 PC) and 3 in Cohort 2 (flu/cy lymphodepletion; dose = 1-2 x 107 TDN CART cells; tumors = 1 NSCLC and 2 OC). None of the patients treated experienced DLT’s. The trial is currently enrolling to Cohort 3 (flu/cy lymphodepletion, 5-6 x 107 TDN). No CRS, neurotoxicity, serious adverse reactions and no on-target/off-tumor toxicity was observed at these dose levels. The most common AE’s were low-grade GI symptoms (e.g., nausea, abdominal pain) in 5/6 patients (83.3%), generalized disorders (e.g., chills, fatigue) in 5/6 (83.3%) and hematologic disorders (e.g., anemia, neutropenia) in 3/6 (50%) of patients. CAR expansion was demonstrated in all patients and was improved in Cohort 2 following LD chemotherapy. Preliminary efficacy assessed by RECIST v1.1 at Day +28 demonstrate SD in all patients in Cohort 2. Conclusions: This is the first report of a novel CART-TnMUC1 construct containing a CD2 co-stimulatory domain that has been used in clinical trials for the treatment of refractory solid-tumor malignancies. While the study is still early in dose-escalation having completed only 2 of 6 planned dose levels there is no evidence of safety concerns or on-target/off-tumor toxicity. Additional safety, efficacy and biomarker data is currently being reviewed and will be presented. Clinical trial information: NCT04025216.