Retifanlimab is a humanized IgG4κ monoclonal antibody directed against programmed death receptor-1 (PD-1). It is a recombinant biological API developed as an immune checkpoint inhibitor for oncology applications. Retifanlimab binds PD-1 and blocks its interaction with PD-L1 and PD-L2, thereby restoring T-cell activity against tumor cells. The FDA describes retifanlimab-dlwr as an approximately 148 kDa antibody produced in Chinese hamster ovary (CHO) cells.
The FDA Global Substance Registration System identifies Retifanlimab CAS No. 2079108-44-2 as the primary CAS identifier and 2226345-85-1 as an additional CAS entry with no structure given. For this page, 2079108-44-2 is used as the primary CAS number.
Retifanlimab is a recombinant protein rather than a conventional small-molecule API. It is a humanized IgG4κ monoclonal antibody with a molecular weight of approximately 148 kDa. Because it is a complex biologic, conventional small-molecule parameters such as molecular formula, melting point, logP and exact mass are not appropriate as primary quality specifications.
The antibody is produced in CHO cells and is designed to recognize human PD-1. FDA nonclinical characterization demonstrated binding to human PD-1 with a reported affinity of approximately 0.6 nM and to cynomolgus monkey PD-1 at approximately 3.6 nM.
Retifanlimab-dlwr is marketed as ZYNYZ. The current FDA-approved indications include:
The current recommended dosage is 500 mg by intravenous infusion over 30 minutes every 4 weeks.
PD-1 is an immune checkpoint receptor expressed on T cells. Binding of PD-L1 or PD-L2 to PD-1 can inhibit T-cell proliferation and cytokine production and contribute to tumor immune evasion.
Retifanlimab binds to PD-1 and prevents its interaction with PD-L1 and PD-L2. This releases PD-1-mediated inhibitory signaling and potentiates T-cell activity against tumor cells.
In FDA nonclinical studies, retifanlimab blocked PD-1/PD-L1 interaction in a cell-based assay with an EC50 of 0.138 μg/mL. It also enhanced T-cell signaling and IFN-γ secretion in appropriate cellular assays.
As a recombinant monoclonal antibody API, Retifanlimab requires biologic-specific analytical characterization, including:
FDA development documentation included binding and cell-based functional assays for characterization of retifanlimab activity.
No universal public numerical bulk-drug-substance release limits were identified for all of these quality attributes. Therefore, unsupported assay, impurity, aggregate or endotoxin limits should not be presented as universal API specifications.
Retifanlimab is produced using recombinant biotechnology in Chinese hamster ovary (CHO) cells. The manufacturing process for a monoclonal antibody API generally incorporates controlled cell culture, harvest, clarification, chromatographic purification, viral clearance and final drug-substance processing.
Critical quality attributes include protein identity, molecular integrity, purity, aggregation, charge heterogeneity, glycosylation, biological potency and process-related impurities.
The manufacturing process must therefore be controlled under appropriate biologics GMP requirements rather than conventional small-molecule API manufacturing specifications.
The affinity and cell-based activity values are from FDA nonclinical characterization, while the 25 mg/mL concentration and pH 5.1 refer to the approved finished product formulation.
The approved ZYNYZ injection is supplied as a 500 mg/20 mL (25 mg/mL) single-dose vial. It is a sterile, preservative-free, clear to slightly opalescent, colorless to pale-yellow solution free from visible particles.
The current FDA labeling specifies storage at 2–8°C (36–46°F) in the original carton to protect from light. The product should not be frozen or shaken.
These conditions apply to the approved finished drug product. Bulk Retifanlimab drug-substance storage should follow validated stability data and the applicable API specification.
Typical documentation for Retifanlimab API or biological drug substance may include:
A qualified Retifanlimab API manufacturer in India should have appropriate recombinant monoclonal antibody manufacturing and characterization capabilities.
Particular attention should be given to control of CHO-cell production, purification, viral safety, aggregation, charge variants, glycosylation, protein integrity and PD-1 binding/potency. Because Retifanlimab is a biologic, comprehensive biologic-specific analytical characterization is essential for establishing consistent quality.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.1% |
| Heavy Metals | NMT 20 ppm |
| pH (1% Solution) | 5.1 |
| Individual Impurity | NMT 0.5% |