Drug name
Last update: Sep 2026Semzuvolimab (UB-421)
Developer(s)
Drug information
Not provided
Semzuvolimab; UB-421; mAb dB4; mAb dB4C7; CAS 2409099-32-5; dB4; dB4C7C22-6 mAb; mAb B4
Not applicable (investigational; no brand name assigned)
Biotherapeutic
CD4 attachment inhibitor (humanised anti-CD4 IgG1 Fc-aglycosylated monoclonal antibody)
Semzuvolimab (UB-421) is a humanised IgG1 monoclonal antibody, aglycosylated in the Fc region, developed by United BioPharma (Taiwan) with UBP Greater China (Shanghai) running part of the programme. It binds competitively to domain 1 of the human CD4 receptor and blocks HIV-1 attachment and entry. Because it targets a host receptor rather than the viral envelope, it is active in vitro against both CCR5- and CXCR4-tropic strains, and no drug resistance emerged in the phase 2 monotherapy study. It is dosed intravenously, most commonly 10 mg/kg weekly or 25 mg/kg every 2 weeks. Its long-acting character comes from the dosing interval achievable with a monoclonal antibody rather than from a depot formulation. A subcutaneous formulation has been evaluated in two phase 1 studies.
Investigational. Not approved in any jurisdiction as of September 2026. NIH Clinicalinfo records semzuvolimab as being in phase 3 development for HIV treatment. Two US NIAID-sponsored studies (NCT04041362, NCT05582694) were withdrawn with zero enrolment, and several sponsor-run records carry ClinicalTrials.gov status UNKNOWN. Live status of the programme is unclear.
No marketing authorisation application identified. Development has taken place under Taiwan FDA, NMPA (China) and US FDA IND oversight across the programme.
Therapeutic area(s)
- HIV
- Treatment
Administration route
Subcutaneous, Intravenous
Associated long-acting platforms
Monoclonal antibodies and antibody drug conjugates
Use of drug
- Administered by a nurse
- To be determined
- Weekly
- Monthly
- Every 2 weeks
No formal acceptability study published. In the phase 2 NEJM study of 29 participants, the most common possibly or probably related adverse event was grade 1 or 2 skin rash in 48.3%; rash was the only grade 2 or higher adverse event reported and led to discontinuation in one participant. Grade 2 or higher laboratory abnormalities included eosinophilia and raised liver function tests. There were no deaths and no severe drug-related adverse events.
Dosage
Investigational. Doses studied intravenously: 10 mg/kg weekly and 25 mg/kg every 2 weeks (and every 4 weeks in NCT03743376 / NCT04404049). Subcutaneous dose levels not publicly specified.
25 mg/kg per infusion (highest dose level reported in the published programme)
No approved regimen. Regimens evaluated: UB-421 10 mg/kg IV weekly for 8 weeks, or 25 mg/kg IV every 2 weeks for 16 weeks (monotherapy during analytical treatment interruption); 25 mg/kg every 2 or 4 weeks alongside ART for reservoir reduction; and UB-421 plus optimised background regimen in multidrug-resistant HIV-1.
Doses reported in this entry are derived from trial registry records and the published phase 2 study.
Not provided
Associated compounds, formulations and regimens
Not provided
Associated technologies
Not provided
Additional information
Developer(s)
Drug structure
Scale-up and manufacturing prospects
Not reported for this product. Generic monoclonal antibody scale-up considerations apply: formulation stability, maintenance of critical quality attributes, and the higher concentrations needed for a subcutaneous presentation.
Not reported for this product. Standard therapeutic mAb train assumed: production bioreactors, continuous disc-stack centrifugation and depth/membrane filtration for harvest clarification, Protein A and polishing chromatography, viral inactivation and filtration, ultrafiltration/diafiltration, sterile fill-finish.
Recombinant humanised IgG1 produced in mammalian cell culture; aglycosylated Fc. Detailed cell line, process and facility information has not been published.
Not reported for this product. Standard mAb characterisation applies: ion-exchange chromatography and capillary isoelectric focusing for charge variants, size-exclusion chromatography for aggregates, DSC for thermal stability, subvisible particle counting, and binding/potency assays (CD4 receptor occupancy by flow cytometry).
Excipients & delivery device(s)
Not provided
Not provided
Not provided
No delivery device
Safety, Efficacy and Evidence Summary
Not provided
Not provided
Not provided
Not provided
There are either no relevant patents or these were not yet submitted to LAPaL