Mavrilimumab, a Fully Human Granulocyte-Macrophage Colony-Stimulating Factor Receptor α Monoclonal Antibody: Long-Term Safety and Efficacy in Patients With Rheumatoid Arthritis.

OBJECTIVE: Mavrilimumab, a human monoclonal antibody, targets granulocyte-macrophage colony-stimulating factor receptor α. We undertook to determine the long-term safety and efficacy of mavrilimumab in rheumatoid arthritis patients in 2 phase IIb studies (1071 and 1107) and in 1 open-label extension study (ClinicalTrials.gov identifier: NCT01712399). METHODS: In study 1071, patients with an inadequate response to disease-modifying antirheumatic drugs (DMARDs) received mavrilimumab (30, 100, or 150 mg) or placebo every other week plus methotrexate. In study 1107, patients with an inadequate response to anti-tumor necrosis factor agents and/or DMARDs received 100 mg mavrilimumab every other week or 50 mg golimumab every 4 weeks plus methotrexate. Patients entering the open-label extension study received 100 mg mavrilimumab every other week plus methotrexate. Long-term safety and efficacy of mavrilimumab were assessed. RESULTS: A total of 442 patients received mavrilimumab (14 of 245 patients from study 1071, 9 of 70 patients from study 1107, and 52 of 397 patients from the open-label extension study discontinued mavrilimumab treatment throughout the studies). The cumulative safety exposure was 899 patient-years; the median duration of mavrilimumab treatment was 2.5 years (range 0.1-3.3 years). The most common treatment-emergent adverse events (AEs) were nasopharyngitis (n = 69; 7.68 per 100 patient-years) and bronchitis (n = 51; 5.68 per 100 patient-years). At weeks 74 and 104, 3.5% and 6.2% of patients, respectively, demonstrated reduction in forced expiratory volume in 1 second, while 2.9% and 3.4% of patients, respectively, demonstrated reduction in forced vital capacity (>20% reduction from baseline to <80% predicted). Most pulmonary changes were transient and only infrequently associated with AEs. Mavrilimumab at 100 mg every other week demonstrated sustained efficacy; at week 122, 65.0% of patients achieved a Disease Activity Score in 28 joints using the C-reactive protein level (DAS28-CRP) of <3.2, and 40.6% of patients achieved a DAS28-CRP of <2.6. CONCLUSION: Long-term treatment with mavrilimumab maintained response and was well-tolerated with no increased incidence of treatment-emergent AEs. Safety data were comparable with those from both phase IIb qualifying studies.

Gene correction of human induced pluripotent stem cells repairs the cellular phenotype in pulmonary alveolar proteinosis.

RATIONALE: Hereditary pulmonary alveolar proteinosis (hPAP) caused by granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor α-chain (CSF2RA) deficiency is a rare, life-threatening lung disease characterized by accumulation of proteins and phospholipids in the alveolar spaces. The disease is caused by a functional insufficiency of alveolar macrophages, which require GM-CSF signaling for terminal differentiation and effective degradation of alveolar proteins and phospholipids. Therapeutic options are extremely limited, and the pathophysiology underlying the defective protein degradation in hPAP alveolar macrophages remains poorly understood. OBJECTIVES: To further elucidate the cellular mechanisms underlying hPAP and evaluate novel therapeutic strategies, we here investigated the potential of hPAP patient-derived induced pluripotent stem cell (PAP-iPSCs) derived monocytes and macrophages. METHODS: Patient-specific PAP-iPSCs were generated from CD34(+) bone marrow cells of a CSF2RA-deficient patient with PAP. We assessed pluripotency, chromosomal integrity, and genetic correction of established iPSC lines. On hematopoietic differentiation, genetically corrected or noncorrected monocytes and macrophages were investigated in GM-CSF-dependent assays. MEASUREMENTS AND MAIN RESULTS: Although monocytes and macrophages differentiated from noncorrected PAP-iPSCs exhibited distinct defects in GM-CSF-dependent functions, such as perturbed CD11b activation, phagocytic activity, and STAT5 phosphorylation after GM-CSF exposure and lack of GM-CSF uptake, these defects were fully repaired on lentiviral gene transfer of a codon-optimized CSF2RA-cDNA. CONCLUSIONS: These data establish PAP-iPSC-derived monocytes and macrophages as a valid in vitro disease model of CSF2RA-deficient PAP, and introduce gene-corrected iPSC-derived monocytes and macrophages as a potential autologous cell source for innovative therapeutic strategies. Transplantation of such cells to patients with hPAP could serve as a paradigmatic proof for the potential of iPSC-derived cells in clinical gene therapy.

Use of induced pluripotent stem cells to recapitulate pulmonary alveolar proteinosis pathogenesis.

RATIONALE: In patients with pulmonary alveolar proteinosis (PAP) syndrome, disruption of granulocyte/macrophage colony-stimulating factor (GM-CSF) signaling is associated with pathogenic surfactant accumulation from impaired clearance in alveolar macrophages. OBJECTIVES: The aim of this study was to overcome these barriers by using monocyte-derived induced pluripotent stem (iPS) cells to recapitulate disease-specific and normal macrophages. METHODS: We created iPS cells from two children with hereditary PAP (hPAP) caused by recessive CSF2RA(R217X) mutations and three normal people, differentiated them into macrophages (hPAP-iPS-Mφs and NL-iPS-Mφs, respectively), and evaluated macrophage functions with and without gene-correction to restore GM-CSF signaling in hPAP-iPS-Mφs. MEASUREMENTS AND MAIN RESULTS: Both hPAP and normal iPS cells had human embryonic stem cell-like morphology, expressed pluripotency markers, formed teratomas in vivo, had a normal karyotype, retained and expressed mutant or normal CSF2RA genes, respectively, and could be differentiated into macrophages with the typical morphology and phenotypic markers. Compared with normal, hPAP-iPS-Mφs had impaired GM-CSF receptor signaling and reduced GM-CSF-dependent gene expression, GM-CSF- but not M-CSF-dependent cell proliferation, surfactant clearance, and proinflammatory cytokine secretion. Restoration of GM-CSF receptor signaling corrected the surfactant clearance abnormality in hPAP-iPS-Mφs. CONCLUSIONS: We used patient-specific iPS cells to accurately reproduce the molecular and cellular defects of alveolar macrophages that drive the pathogenesis of PAP in more than 90% of patients. These results demonstrate the critical role of GM-CSF signaling in surfactant homeostasis and PAP pathogenesis in humans and have therapeutic implications for hPAP.

Defining the antigenic structure of human GM-CSF and its implications for receptor interaction and therapeutic treatments.

Three epitopes of human Granulocyte-Macrophage Colony-Stimulating Factor (hGM-CSF) recognised by neutralising and non-neutralising monoclonal antibodies (mAbs) were characterised using competitive binding assays, dissociation constant measurements with glycosylated and non-glycosylated rhGM-CSF, bioactivity inhibition studies, and synthetic peptide arrays. Based on the first approach, two different binding sites were identified: an area referred to as A, recognised by mAbs M1B8 and CC5B5, and an area referred to as B, recognised by mAbs CC1H7 and CC3C12. These binding sites on hGM-CSF were accurately delineated using cytokine-derived overlapping peptide scans and combinatorial hexapeptide libraries prepared by SPOT synthesis on cellulose membranes. We assigned the identical linear epitope A1P2A3R4 to both non-neutralising mAbs CC1H7 and CC3C12. The conformational epitopes A18E21R23R24F119 and R23E21N17W13 recognised by mAb CC5B5, and P118F119EW13E14 recognised by mAb M1B8, were delineated by dual-positional scanning and subsequent iterative searches with two interrogating positions. Competitive binding assays with mAbs M1B8 and CC5B5 revealed the overlapping nature of the cytokine recognition. However, peptide library screening confirmed their binding to different epitopes of which the essential amino acids were found very closely located on the native protein surface. Inhibition of hGM-CSF biological activity by these mAbs demonstrated that these epitopes are located within or very near the receptor binding site of hGM-CSF. Finally, this work supports the importance of residues from helix A and residues from the C-terminal region of the cytokine, composing a common area that is indispensable for the cytokine's biological activity.