Preclinical characterization of an mRNA-encoded anti-Claudin 18.2 antibody

IMAB362/Zolbetuximab, a first-in-class IgG1 antibody directed against the cancer-associated gastric-lineage marker CLDN18.2, has recently been reported to have met its primary endpoint in two phase 3 trials as a first-line treatment in combination with standard of care chemotherapy in CLDN18.2-positive Her2 negative advanced gastric cancer. Here we characterize the preclinical pharmacology of BNT141, a nucleoside-modified RNA therapeutic encoding the sequence of IMAB362/Zolbetuximab, formulated in lipid nanoparticles (LNP) for liver uptake. We show that the mRNA-encoded antibody displays a stable pharmacokinetic profile in preclinical animal models, mediates CLDN18.2-restricted cytotoxicity comparable to IMAB362 recombinant protein and inhibits human tumor xenograft growth in immunocompromised mice. BNT141 administration did not perpetrate mortality, clinical signs of toxicity, or gastric pathology in animal studies. A phase 1/2 clinical trial with BNT141 mRNA-LNP has been initiated in advanced CLDN18.2-expressing solid cancers (NCT04683939).

Elimination of factor VIII-specific B cells by immunotoxins composed of a single factor VIII domain fused to Pseudomonas exotoxin A

Essentials There is still a need for novel therapeutic approaches for hemophilia A patients with inhibitors. A factor VIII domain was used as the targeting moiety for elimination of FVIII-specific B cells. The immunodominant C2 domain was fused to exotoxin A from Pseudomonas aeruginosa (hC2-ETA). Murine C2 domain-specific B cells were selectively and efficiently eliminated by hC2-ETA ex vivo. SUMMARY: Background Today, the most serious complication for patients with hemophilia A undergoing factor VIII (FVIII) replacement therapy is the development of neutralizing antibodies (inhibitors). Although inhibitors can be eradicated by application of high doses of FVIII, the immune tolerance induction therapy fails in up to 30% of patients. Hence, there is still an urgent need for novel therapeutic approaches for patients with persisting inhibitors. Objectives In the present study, the potential use of immunotoxins containing exotoxin A (ETA) from Pseudomonas aeruginosa for selective elimination of FVIII-specific B cells was explored. Methods The immunodominant C2 domain of human FVIII was used as a targeting moiety instead of the full-length FVIII protein and the resulting human C2 domain-ETA fusion protein (hC2-ETA) was produced in Escherichia coli. Results Binding studies with monoclonal C2 domain-specific antibodies confirmed the conformational integrity of the C2 domain in hC2-ETA. The functionality of hC2-ETA was tested ex vivo by incubation of splenocytes from inhibitor-positive FVIII knockout mice with hC2-ETA and controls. FVIII-specific memory B cells from splenocytes were differentiated by FVIII stimulation in antibody-secreting cells (ASC) and detected by an enzyme-linked immunospot assay. Although the controls showed no effect, incubation of splenocytes with hC2-ETA reduced the number of C2-specific ASC in a dose-dependent fashion, indicating specific and efficient elimination of C2-specific memory B cells. Conclusions Overall, the results of the study support the fact that FVIII domain immunotoxins might be a potential new tool for the elimination of FVIII-specific B cells in patients with hemophilia A and persisting inhibitors.

Epitope mapping via selection of anti-FVIII antibody-specific phagepresented peptide ligands that mimic the antibody binding sites

The most serious complication in today’s treatment of congenital haemophilia A is the development of neutralising antibodies (inhibitors) against factor VIII (FVIII). Although FVIII inhibitors can be eliminated by immune tolerance induction (ITI) based on repeated administration of high doses of FVIII, 20–30% of patients fail to become tolerant. Persistence of FVIII inhibitors is associated with increased morbidity and mortality. Data from recent studies provide evidence for a potential association between ITI outcome and epitope specificity of FVIII inhibitors. Nevertheless the determination of epitopes and their clinical relevance has not yet been established. In this study a general strategy for the identification of anti-FVIII antibody epitopes in haemophilia A patient plasma was to be demonstrated. Phage-displayed peptide libraries were screened against anti-FVIII antibodies to isolate specific peptides. Peptide specificity was confirmed by FVIII-sensitive ELISA binding. Peptide residues essential for antibody binding were identified by mutational analysis and epitopes were predicted via FVIII homology search. The proposed mapping strategy was validated for the monoclonal murine antibody (mAb) 2–76. Binding studies with FVIII variants confirmed the location of the predicted epitope at the level of individual amino acids. In addition, anti-FVIII antibody-specific peptide ligands were selected for 10 haemophilia A patients with FVIII inhibitors. Detailed epitope mapping for three of them showed binding sites on the A2, A3 and C2 domains. Precise epitope mapping of anti-FVIII antibodies using antibody-specific peptide ligands can be a useful approach to identify antigenic sites on FVIII.

Neutralisation of factor VIII inhibitors by anti-idiotypes isolated from phage-displayed libraries

Following replacement therapy with coagulation factor VIII (FVIII), up to 30 % of haemophilia A patients develop FVIII-specific inhibitory antibodies (FVIII inhibitors). Immune tolerance induction (ITI) is not always successful, resulting in a need for alternative treatments for FVIII inhibitor-positive patients. As tolerance induction in the course of ITI appears to involve the formation of anti-idiotypes specific for anti-FVIII antibodies, such anti-idiotypes might be used to restore haemostasis in haemophilia A patients with FVIII inhibitors. We isolated anti-idiotypic antibody fragments (scFvs) binding to murine FVIII inhibitors 2-76 and 2-77 from phage-displayed libraries. FVIII inhibitor/anti-idiotype interactions were very specific as no cross-reactivity with other FVIII inhibitors or isotype controls was observed. ScFvs blocked binding of FVIII inhibitors to FVIII and neutralised their cognate inhibitors in vitro and a monoclonal mouse model. In addition, scFv JkH5 specific for FVIII inhibitor 2-76 stained 2-76-producing hybridoma cells. JkH5 residues R52 and Y226, located in complementary determining regions, were identified as crucial for the JkH5/2-76 interaction using JkH5 alanine mutants. SPR spectroscopy revealed that JkH5 interacts with FVIII inhibitor 2-76 with nanomolar affinity. Thus, FVIII inhibitor-specific, high-affinity anti-idiotypes can be isolated from phage-displayed libraries and neutralise their respective inhibitors. Furthermore, we show that anti-idiotypic scFvs might be utilised to specifically target inhibitor-specific B cells. Hence, a pool of anti-idiotypes could enable the reestablishment of haemostasis in the presence of FVIII inhibitors in patients or even allow the depletion of inhibitors by targeting inhibitor-specific B cell populations.