Treatment of pemphigus vulgaris and foliaceus with efgartigimod, a neonatal Fc receptor inhibitor: a phase II multicentre, open-label feasibility trial

BACKGROUND

Pemphigus vulgaris and pemphigus foliaceus are potentially life-threatening autoimmune disorders triggered by IgG autoantibodies against mucosal and epidermal desmogleins. There is an unmet need for fast-acting drugs that enable patients to achieve early sustained remission with reduced corticosteroid reliance.

OBJECTIVES

To investigate efgartigimod, an engineered Fc fragment that inhibits the activity of the neonatal Fc receptor, thereby reducing serum IgG levels, for treating pemphigus.

METHODS

Thirty-four patients with mild-to-moderate pemphigus vulgaris or foliaceus were enrolled in an open-label phase II adaptive trial. In sequential cohorts, efgartigimod was dosed at 10 or 25 mg kg^-1 intravenously with various dosing frequencies, as monotherapy or as add-on therapy to low-dose oral prednisone. Safety endpoints comprised the primary outcome. The study is registered at ClinicalTrials.gov (identifier NCT03334058).

RESULTS

Adverse events were mostly mild and were reported by 16 of 19 (84%) patients receiving efgartigimod 10 mg kg^-1 and 13 of 15 (87%) patients receiving 25 mg kg^-1 , with similar adverse event profiles between dose groups. A major decrease in serum total IgG and anti-desmoglein autoantibodies was observed and correlated with improved Pemphigus Disease Area Index scores. Efgartigimod, as monotherapy or combined with prednisone, demonstrated early disease control in 28 of 31 (90%) patients after a median of 17 days. Optimized, prolonged treatment with efgartigimod in combination with a median dose of prednisone 0·26 mg kg^-1 per day (range 0·06-0·48) led to complete clinical remission in 14 of 22 (64%) patients within 2-41 weeks.

CONCLUSIONS

Efgartigimod was well tolerated and exhibited an early effect on disease activity and outcome parameters, providing support for further evaluation as a therapy for pemphigus.

Abstract P2-05-17: ARGX-111 depletes MET-expressing circulating tumor cells via enhanced ADCC, resulting in inhibition of metastasis

Several lines of experimental evidence suggest that Hepatocyte Growth Factor (HGF) and its receptor MET play an important role in breast cancer progression and drug resistance. To date, targeted MET inhibitors in clinical development have primarily shown cytostatic rather than cytotoxic effects. Development of a cytotoxic MET inhibitor would serve to complement standard breast cancer therapy, especially when administered in the adjuvant/neo-adjuvant setting.

We have developed ARGX-111, a human antibody antagonist of MET function. ARGX-111 blocks both HGF-dependent and -independent signaling, down-regulates tumor cell surface expression of MET and kills MET-overexpressing cells by enhanced antibody-dependent cellular cytotoxicity (ADCC).

ARGX-111 was shown to be more efficacious than an ADCC-inactive control antibody in both HGF-dependent and -independent tumor xenograft models. ADCC reporter assays confirmed the cytotoxic effects of ARGX-111 in patient-derived primary tumor specimens, including MET-expressing breast cancer stem-like cells. In an orthotopic mouse model of metastatic mammary carcinoma (MDA-MB-231), adjuvant or neo-adjuvant treatment with ARGX-111 was significantly more effective in depleting circulating tumor cells (CTCs) and suppressing the development of bone and lung metastases than the ADCC-inactive control.

Taken together, these results provide a rationale for clinical investigation of ARGX-111 in the early breast cancer setting. An ongoing Phase 1 study (NCT02055066) is examining the effects of ARGX-111 on CTCs, alongside the assessment of its safety and efficacy.

Citation Format: Morello V, Hultberg A, De Jonge N, Huyghe L, Hanssens V, Brouckaert P, Saunders M, Dreier T, Thibault A, Rolfo C, Aftimos P, Awada A, Michieli P, de Haard H. ARGX-111 depletes MET-expressing circulating tumor cells via enhanced ADCC, resulting in inhibition of metastasis. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-05-17.

Llama-derived phage display antibodies in the dissection of the human disease oculopharyngeal muscular dystrophy

Functional analysis of the estimated 30,000 genes of the human genome requires fast and reliable high-throughput methods to study spatio-temporal protein dynamics. To explore the suitability of heavy-chain antibodies (HCAbs) for studying mechanisms underlying human disease, we used oculopharyngeal muscular dystrophy (OPMD) as a paradigm for the expanding group of protein aggregation disorders that is characterized by subcellular dislocalization and aggregation of mutant protein. OPMD is caused by a moderate alanine expansion in the poly-A binding protein nuclear 1 (PABPN1) and is associated with intranuclear PABPN1 deposition exclusively in muscle. An experimental approach was designed in which the primary sequence of the PABPN1 gene was employed for generating a prokaryotic expression construct that permitted its expression in the host Escherichia coli. The purified product was used for immunization of a llama as well as for the selection of an antigen-specific antibody fragment from the derived phage display library. This single-domain antibody was able to recognize the native gene product in mammalian cell lines and in human muscle tissue by immunocytochemical, immunohistochemical and immunoblot analysis. Our results suggest that phage display derived heavy-chain antibodies can be used in proteomics to study the localization and function of hypothetical gene products, relevant to human disease.

Vernier zone residue 4 of mouse subgroup II kappa light chains is a critical determinant for antigen recognition

BACKGROUND

During the conversion of murine monoclonal antibodies directed against the human chorionic gonadotropin (hCG) into bacterially expressed single chain fragments (scFv), we found a major reduction of binding activity upon introduction of a primer encoded mutation.

OBJECTIVES

In this study we tried to determine which mutation was responsible and on what manner this mutation affected antigen binding (structural effect versus direct involvement of the residue in binding).

RESULTS

No binding could be detected, when the wild type residue methionine at position 4 within the Framework region 1 of the Vkappa light chain was substituted by serine in two antibodies with a subgroup II kappa light chain. However, a similar replacement within an anti-hCG antibody with a subgroup IV kappa light chain and thereby having leucine as wild type residue, did not affect the binding characteristics. The mutant scFv's derived from both AB-s sensitive for substitution by serine never reacted with antigen in ELISA. Analysis with surface plasmon resonance revealed a residual binding only on a sensorchip with a high density coating of antigen; however, an increased dissociation, relative to that of the wild type scFv and the absence of reactivity in ELISA suggest a drastically altered affinity.

CONCLUSION

A structural explanation for the changed binding characteristics can be the influence of the position 4 residue, as being a constituent of the Vernier zone, on the position of the CDR1 loop of Vkappa, which might harbour residues that directly bind to antigen, or indirectly positions other variable loops of the binding pocket. An increased sensitivity for trypsin digestion supported the hypothesis of a local conformational change in the serine mutant of the subgroup II kappa containing antibody.

Determination of active single chain antibody concentrations in crude periplasmic fractions

We have measured active single chain antibody (scFv) concentrations under mass transfer limitation conditions using surface plasmon resonance on the BIAcore. For the creation of a standard curve scFv 4Dwt, derived from monoclonal antibody (mAb) 4D, directed against human chorionic gonadotropin (hCG), was purified by positive affinity chromatography. Determination of the active antibody fraction after purification was performed using anti-FLAG, reactive against a tag sequence C-terminally fused to the scFv. Two independent experiments showed that the activity remaining represented over 75% of the total amount of purified protein. Calibration curves on high density antigen surfaces showed a linear relationship between antibody concentration and binding rates. Periplasmic fractions of six mutant scFvs, also derived from mAb 4D, revealed a clear difference in the amount of soluble active scFv expressed in the periplasm of E. coli compared with the total amount of antibody present, indicating the necessity of measuring active antibody concentrations. This rapid concentration determination method will be particularly useful for accurately comparing affinity constants, using antibody concentrations determined with the BIAcore, of the many different scFv fragments routinely isolated from phage display libraries.

Cloning and expression of the Lactococcus lactis subsp. cremoris SK11 gene encoding an extracellular serine proteinase

The Lactococcus lactis subsp. cremoris SK11 plasmid-located prtP gene, encoding a cell-envelope-located proteinase (PrtP) that degrades alpha s1-, beta- and kappa-casein, was identified in a lambda EMBL3 gene library in Escherichia coli using immunological methods. The complete prtP gene could not be cloned in E. coli and L. lactis on high-copy-number plasmid vectors. However, using a low-copy-number vector, the complete prtP gene could be cloned in strains MG1363 and SK1128, proteinase-deficient derivatives of L. lactis subsp. lactis 712 and L. lactis subsp. cremoris SK11, respectively. The proteinase deficiency of these hosts was complemented to wild-type (wt) levels by the cloned SK11 prtP gene. The caseinolytic specificity of the proteinase specified by the cloned prtP gene was identical to that encoded by the wt proteinase plasmid, pSK111. The expression of recombinant plasmids containing 3' and 5' deletions of prtP was analyzed with specific attention directed towards the location of the gene products. In this way the expression signals of prtP were localized and overproduction was obtained in L. lactis subsp. lactis. Furthermore, a region at the C terminus of PrtP was identified which is involved in cell-envelope attachment in lactococci. A deletion derivative of prtP was constructed which specifies a C-terminally truncated proteinase that is well expressed and fully secreted into the medium, and still shows the same capacity to degrade alpha s1-, beta- and kappa-casein.