Abstract 2135: Selectivity and specificity of engineered T cells expressing KITE-585, a chimeric antigen receptor targeting B-cell maturation antigen (BCMA)

Abstract

Background: Immunotherapy has provided treatment options for cancers that are otherwise refractory to standard approaches. One such technique is to use adoptive transfer of engineered autologous T cells expressing a chimeric antigen receptor (CAR) directed against a tumor antigen. The efficacy of CAR T cells directed against hematological malignancies, particularly CD19-expressing B cell leukemia and lymphomas, has been demonstrated in multiple clinical studies. The success of this approach has prompted development of CAR T cells directed to different tumor antigens for other tumor types. To ensure the selectivity and specificity of the CAR T cells against their intended target, screening methods need to be employed. Multiple myeloma is an incurable malignancy of plasma cells. B-cell maturation antigen (BCMA), also known as tumor necrosis factor superfamily member 17 (TNFRSF17) is nearly ubiquitously expressed on multiple myeloma cells, plasma cells and subsets of mature B cells. Methods: In order to screen for the specificity of novel CAR T cells directed against BCMA, we utilized a cell microarray platform developed by Retrogenix. In this screen, approximately 4500 human plasma membrane proteins (representing up to 75% of the human plasma membrane proteome) are individually expressed in human HEK293 cells. Fluorescently labeled CAR T cells, which showed cytolytic activity against MM cell lines expressing BCMA, were applied to the cell microarray and specific binding of the CAR T cells to target cells was determined. Results: Primary hits were sequenced to confirm identity and secondary specificity screens were performed on the identified hits. Specific binding of both mock transduced and BCMA CAR transduced T cells were confirmed for different plasma membrane proteins expressed from the HEK293 cells. These included known T cell interactors, such as ICOSLG, CD244 and CD86, where binding is proposed to be independent of CAR expression. Subtracting the hits of the mock transduced T cells from the BCMA CAR T cells demonstrated specific binding of the CAR T cells to BCMA. Utilizing the fully human IgGs directed against BCMA from which the single-chain variable fragments (scFvs) of the CARs were derived, we further confirmed specific binding to BCMA in additional secondary screens. Additionally, a lack of off-target binding of the fully human IgGs to normal tissue was demonstrated in a tissue cross reactivity screen. Conclusions: These studies highlight the tractability of this cell microarray approach for determining the specificity of novel CAR constructs expressed in T cell. Demonstrating the selectivity and specificity of anti-BMCA CAR T cells further supports the progression of KITE-585 towards Phase 1 clinical studies in MM patients. Citation Format: Gregor B. Adams, Jun Feng, Atefeh Ghogha, Armen Mardiros, Ruben Rodriguez, Tassja J. Spindler, Jed Wiltzius, Tony Polverino. Selectivity and specificity of engineered T cells expressing KITE-585, a chimeric antigen receptor targeting B-cell maturation antigen (BCMA) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2135. doi:10.1158/1538-7445.AM2017-2135

BCMA-targeted immunotherapy for multiple myeloma

“…KITE-585 is a second-generation lentiviral-transduced CAR-T cell product which has a fully human anti-BCMA scFv, a CD28 co-stimulatory domain, and a CD3ζ activation domain. KITE-585 demonstrated potent in vitro and in vivo activity against MM cell lines even in the presence of soluble BCMA and also eradicated xenografted MM tumors in mice [141,142]. A first-inhuman, open-label, multicenter phase 1 study (NCT03318861) has been planned to evaluate the safety and feasibility of KITE-585 in R/R MM patients [143].…”

New Advances in Cell Microarray Technology to Expand Applications in Target Deconvolution and Off-Target Screening

“…As such, it has become integral to off-target safety screening of chimeric antigen receptor (CAR) T cells. 12,13 Minimizing the risk of triggering an inappropriate immune response through unanticipated off-target binding of engineered CAR T cells is essential in ensuring patient safety. Precursor antibodies or ScFvs, as well as the final engineered CAR T cells, can all be screened for off-targets, and data from these studies are being used in regulatory submissions, including the biologics license application (BLA) for Novartis’s tisagenlecleucel (Kymriah) in the United States, 14 Europe, 15 and Japan.…”

Time to evolve: predicting engineered T cell-associated toxicity with next-generation models

“…Furthermore, if off-targets are identified, cell lines or primary cell types endogenously expressing the off-target protein can be used as target cells to assess potential off-target cytotoxicity and CAR T-cell activation. This platform is increasingly being used for CAR T-cell development, 65 and data from these studies have been included in regulatory submissions, including the biologics license application for Novartis's Kymriah. 66 Graft-versus-host disease (GVHD) and rejection associated with allogeneic engineered T cells The use of allogeneic CAR T-cell products generated using cells from healthy donors has the potential to overcome many limitations associated with autologous products but come with their own challenges, including the potential to induce GVHD (figure 1), as well as the risk of immune-mediated rejection by the host.…”