Comparative Pre-Clinical Analysis of CD20-Specific CAR T Cells Encompassing 1F5-, Leu16-, and 2F2-Based Antigen-Recognition Moieties

Over the past decade, CAR T cell therapy for patients with B cell malignancies has evolved from an experimental technique to a clinically feasible option. To date, four CAR T cell products specific for a B cell surface marker, CD19, have been approved by the FDA. Despite the spectacular rates of complete remission in r/r ALL and NHL patients, a significant proportion of patients still relapse, frequently with the CD19 low/negative tumor phenotype. To address this issue, additional B cell surface molecules such as CD20 were proposed as targets for CAR T cells. Here, we performed a side-by-side comparison of the activity of CD20-specific CAR T cells based on the antigen-recognition modules derived from the murine antibodies, 1F5 and Leu16, and from the human antibody, 2F2. Whereas CD20-specific CAR T cells differed from CD19-specific CAR T cells in terms of subpopulation composition and cytokine secretion, they displayed similar in vitro and in vivo potency.

Development and characterization of domain-specific monoclonal antibodies produced against human SLAMF9

SLAMF9 is a member of the signaling lymphocyte-activating molecule (SLAM) immunoreceptor family. The SLAM family receptors are expressed in a broad range of immune cells and play an important role in immunity. To date, SLAMF9 is the least studied member of this family. Its ligand, signaling properties, and cells on whose surface it is expressed are unknown. We generated hybridoma clones 6E11 and 7G5 secreting monoclonal antibodies specific to human SLAMF9. BALB/c mice were immunized with Escherichia coli-expressed purified SLAMF9 protein; splenocytes from these mice were fused with mouse myeloma cell line NS-1. Based on isotyping of the MAbs, clone 6E11 was referred to the IgG1 subclass, while 7G5 to IgG2b. The specificity of these MAbs was assessed by ELISA, immunoblotting, immunohistochemistry, and flow cytometry. According to the results of epitope analysis, clone 6E11 reacts with the C2-like domain, whereas 7G5 is specific to the V-like domain of the SLAMF9 molecule. The generated MAbs were demonstrated to be applicable in various immunochemical analyses. They may be useful tools in studies clarifying the expression and function of human SLAMF9.

Characterization of human FCRLA isoforms

FCRLA is an ER-resident B-cell specific protein. The exact function of this protein remains unclear although human FCRLA has been recently shown to interact with IgM, IgG and IgA. The retention of FCRLA in ER is mediated by the N-terminal domain. The major human FCRLA isoform is encoded by five exons, of which one encodes a short signal peptide (SSP) and the others code four protein domains. Here we show that human tissues also produce transcripts which contain an additional exon and encode proteins with signal peptide that is six residues longer (LSP). Transfection experiments demonstrated that the extension of the signal peptide had no visible effect on the topology and molecular mass of the processed four-domain FCRLA isoform. However, the length of the signal peptide was found to affect processing of two-domain FCRLA isoforms composed of the third and fourth domains (FCRLAd2). The signal peptide was not cleaved in the SSP-FCRLAd2 and this isoform was found to accumulate in the ER. In contrast, the LSP-containing FCRLAd2 isoform was processed, O-glycosylated and secreted. The secreted FCRLAd2 isoform did not interact with IgG- or IgM-immunosorbents.

FCRLA is an intracellular FcR-related protein that binds IgM, IgG and IgA isotypes in B cells (45.11)

Fc-receptor-like A (FCRLA) is a novel member of the extended Fc receptor (FcR) family. Unlike the classical FcRs and Fc receptor-like (FCRL) molecules, which are typically transmembrane receptors with extracellular ligand binding domains, FCRLA has no predicted transmembrane domain or N-linked glycosylation sites and is positioned intracellularly. We show by confocal microscopy and biochemical assays that FCRLA is a soluble, resident ER protein; however, it lacks a characteristic KDEL retention sequence at its C-terminus. Using a series of deletion mutants, we found that its ER retention is most likely mediated by the amino terminal domain. We have also recently identified ER localized immunoglobulin as an FCRLA ligand. These results indicate that FCRLA is unique among the large FcR family in that can associate with multiple immunoglobulin isotypes, including IgM, IgG, and IgA. To better understand the role of this protein in human disease, B cell chronic lymphocytic leukemia (CLL) samples were assayed for FCRLA expression by flow cytometry. Interestingly, the receptor was more highly expressed by the indolent form of CLL, which is distinguished by somatically hypermutated heavy chain variable region genes, than by the aggressive high-risk form, which features more germline B cell receptor characteristics. These results indicate that FCRLA may thus be a useful diagnostic marker for CLL.