Abstract A003: CD74 as a novel chimeric antigen receptor (CAR)-T cell target for cHL and the TME

Abstract

In Classical Hodgkin lymphoma (cHL), while most patients are cured with front-line chemotherapy, 10-20% of patients will relapse or develop refractory (R/R) disease. Clinical trials investigating CAR-T cells targeting CD30+ Hodgkin Reed-Sternberg cells (HRS) showed a 57% overall response rate, but 1-yr progression free survival was only 39% indicating that a majority of the patients will need additional treatment. The malignant HRS cells represent 1-5% of cells with most of the surrounding tumor-microenvironment (TME) comprised of infiltrating immune cells: T cells, B cells, dendritic cells (DCs), myeloid derived suppressive cells (MDSCs), and tumor associated macrophages (TAMs). Patients with enrichment of immunosuppressive TAMs in the TME have worse outcomes and shorter survival. We hypothesize that engineering CAR-T cell therapy to target the HRS cells and the immunosuppressive TAMs in the TME will result in deeper and more durable responses for R/R cHL. CD74 is a transmembrane protein that facilitates antigen presentation and promotes pro-survival signaling in B cells. We have previously developed and optimized a CAR targeting CD74 with signaling domains of 4-1BB and CD3ζ. Methods: This study utilizes 5 cHL cell lines, patient samples, and a cell line derived xenograft (CDX) of KM-H2. A tissue microarray was used to evaluate CD74 expression by immunohistochemistry and multiplex immunofluorescence (n=45). Spectral flow cytometry was used to confirm CD74 expression in 6 patient tumor biopsies and 4 bone marrow samples, with comparisons to healthy donor peripheral blood and bone marrow. Cytotoxic cytokines were measured by ELISA and specific lysis of target cells was measured by AK release and flow cytometry assays. Results: We show that CD74 is expressed by 4 of 5 cHL cell lines and by HRS cells in 45 patient samples by TMA regardless of the cHL subtype. When co-cultured with CD74-antigen+ cell lines, CD74-CART cells proliferate and release significantly more TNF-α and IFN-γ, correlating to specific lysis of target cells (p<0.0001). Preliminary results from a KM-H2 engrafted CDX, treated with 5 million CD74-CART cells or control cells intravenously, showed significant decrease in tumor volume and bioluminescence of tumor cells (p<0.001 and p<0.05). Flow cytometry confirmed CD74-CART cell expansion in peripheral blood and homing to SQ tumors. Analyzing the cHL TME by spectral flow cytometry confirmed elevated CD74 on HRS cells, TAMs, DCs, B cells, and monocytic-MDSCs; of which expressed significantly more CD74 than matched cell types in patient or healthy bone marrow and peripheral blood (p<0.0001). CD74-CART cells co-cultured with patient samples, show specific lysis of B cells (29%), immunosuppressive TAMs (73%), M-MDSC (58%), and HRS cells (33%) at 24 hrs. Future experiments to model the TME will incorporate cHL engrafted CD34-humanized NSG mice with comparisons made to CD30-CARTs. Conclusion: CD74 is expressed on HRS cells and immunosuppressive TAMs in the TME. CAR-T cells directed at CD74 show therapeutic potential for the treatment of cHL.