Natural Abs represent the indigenous immune repertoire and are thus present at birth and persist throughout life. Previously, human autoantibodies to the α domain of the high-affinity IgE receptor (FcεRIα) have been isolated from Ab libraries derived from normal donors and patients with chronic urticaria. To investigate whether these anti-FcεRIα Abs are present in the germline repertoire, we constructed a phage Fab display library from human cord blood, which represents the naive immune repertoire before exposure to exogenous Ags. All isolated clones specific to the FcεRIα had the same sequence. This single IgM Ab, named CBMα8, was strictly in germline configuration and had high affinity and functional in vitro anaphylactogenic activity. Inhibition experiments indicated an overlapping epitope on the FcεRIα recognized by both CBMα8 and the previously isolated anti-FcεRIα Abs from autoimmune and healthy donors. This common epitope on FcεRIα coincides with the binding site for IgE. Affinity measurements demonstrated the presence of Abs showing CBMα8-like specificity, but with a significantly lower affinity in i.v. Ig, a therapeutic multidonor IgG preparation. We propose a hypothesis of escape mutants, whereby the resulting lower affinity IgG anti-FcεRIα Abs are rendered less likely to compete with IgE for binding to FcεRIα.

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e19505 Background: Receptor tyrosine kinase-like Orphan Receptor-1 (ROR1) is widely expressed on hematological and solid tumors. NVG-111, a first in class humanized tandem scFv ROR1xCD3 bispecific antibody elicits potent killing of ROR1+ tumor cells in vitro and in vivo. This bispecific T-cell engager (TCE) is being evaluated in a first in human, Phase I trial in patients with relapsed/refractory chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). The predicted therapeutic dose and steady state serum concentrations of NVG-111 were estimated by allometric scaling using relevant doses from a murine PK study. To assess free drug levels in patients following 21 days of continuous infusion of NVG-111, a bespoke, sensitive pharmacokinetics (PK) assay with high levels of specificity and sensitivity was developed. Methods: Anti-idiotype (anti-ID) antibodies directed to anti-ROR1 (αROR1-ID) and anti-CD3 (αCD3-ID) were generated by mouse immunization or by phage display from customized libraries. A proof-of-concept sandwich ELISA assay was developed using αCD3-ID to capture NVG-111 and detection by biotinylated hROR1-streptavidin-HRP. Gyrolab and Quanterix Simoa high sensitivity ELISA platforms were used to detect NVG-111 by αCD3-ID capture and αROR1-ID detection. The mesoscale discovery electrochemiluminescence assay (MSD-ECLA) was developed using a reversed format; NVG-111 capture with αROR1-ID and detection with αCD3-ID. Results: Allometric scaling predicted a theoretically relevant therapeutic dose and steady state serum concentration of 1ng/mL NVG-111 in humans, which was just at the level of sensitivity of a conventional ELISA under non-matrix conditions. Transferring the format to Quanterix Simoa had limited success due to high background levels in all configurations evaluated. The Gyrolab platform increased sensitivity to 75pg/mL, but suboptimal individual human sera matrix selectivity limited assay validity. Assessment of MSD-ECLA provided the best signal/noise, enhanced human disease and healthy sera selectivity, and a dynamic sensitivity range of 250pg/mL to 32ng/mL, which enabled the development of a GCLP qualified PK assay. The MSD-ECLA assay was employed to measure NVG-111 concentrations in CLL or MCL subjects dosed with 0.3-30µg/day NVG-111. MSD-ECLA detected drug in patients receiving NVG-111, with a range of steady-state serum concentrations (Cavg.ss) of 168-610pg/mL. This was in-line with the predicted drug levels from the single species allometric scaling, albeit with observed levels being marginally lower than expected. Conclusions: Development, custom optimization and validation of a highly sensitive MSD-ECLA PK assay has enabled GCLP-compliant measurement of circulating NVG-111 in CLL or MCL patients treated with at least 10µg/day cIV NVG-111.

e14506 Background: Bispecific antibodies provide an opportunity to treat a diverse range of disorders because of their ability to simultaneously attenuate several different pathways precisely and effectively, thus overcoming many of the limitations of monoclonal antibodies. The adaptability of bispecifics has facilitated the generation of compelling preclinical data covering a range of malignant and non-malignant disorders. Proof-of-concept early phase clinical trials with bispecific antibodies, including bispecific T-cell engagers (TCE) have been hindered by manufacturing challenges, including a heavy burden in terms of time, quality and costs associated with generating a stable producer cell line. We took a more agile approach, using transient transfection to manufacture a ROR1×CD3 bispecific TCE drug product (DP [NVG-111]) for a first in human, Phase I/II clinical trial. Methods: A HEK293T cell line was expanded into 10-layer cell factories. The cells were transfected with a ROR1xCD3 scFv bispecific antibody (NVG-111) plasmid and incubated. Post incubation, the supernatant containing NVG-111 was clarified by filtration and subjected to solvent/detergent viral inactivation. This was followed by a concentration/buffer exchange step and subsequent DNA reduction using an endonuclease. NVG-111 was captured using a bind/elute Protein A column and the eluate polished on a multimodal anion exchange column in flow through mode to remove residual impurities. The eluate was formulated and concentrated to the target protein concentration, viral and sterile filtered and QC tested. The bulk drug substance was 0.2 µm filtered into Din 2R vials and the DP stored at ≤-65°C pending release. Results: The transient transfection approach resulted in the rapid tech transfer and GMP manufacture of clinical NVG-111 DP. Two batches of DP were manufactured producing 1,971 vials of NVG-111, sufficient to support the Phase I/II clinical trial in patients with advanced Chronic Lymphocytic Leukaemia and Mantle Cell Lymphoma (Clinical Trial.gov NCT04763083). Both batches met the approved specifications for identity, potency, purity/impurities, strength and safety. The exercise took less than 7 months from contract signature to DP in the freezer and cost ̃50% of the more traditional producer cell line approach. Conclusions: We established a novel GMP process in 7 months, using transient transfection to manufacture NVG-111 for Phase I/II trials. The process costed less than the more conventional manufacturing approach of using a producer cell line. The strategy offers a rapid, and very efficient way of reaching a first in human study without a trade-off between time, quality and cost.