Fucose Sugar Tags Blunt Immune Killing in Anti-RhD Antibodies Used Worldwide
Two widely used anti-D antibodies carry high fucose levels that weaken immune cell killing. Removing fucose boosted activity beyond polyclonal anti-D.
Summary
Haemolytic disease of the fetus and newborn can be prevented by giving RhD-negative mothers anti-D antibodies, but the standard product is made from donor plasma and is costly. Two monoclonal alternatives, Rhoclone and Trinbelimab, are widely used in low- and middle-income countries without FDA/EMA approval. Researchers analyzed both in the lab. They found the antibodies bind the same RhD epitope and share an identical protein sequence. They differ in fucosylation: 96% for Rhoclone versus 86% for Trinbelimab. Both triggered weaker natural killer cell-mediated killing (ADCC) than the polyclonal product Rhophylac. Activity tracked with fucose levels, and engineered low-fucose versions markedly outperformed the polyclonal product. Whether this translates into better clinical prevention remains untested.
Detailed Summary
Haemolytic disease of the fetus and newborn (HDFN) occurs when a mother's immune system makes antibodies against the RhD antigen on her baby's red blood cells. Giving anti-D antibodies prevents this immunization, but the current product comes from hyperimmunized donors, making supply expensive and donor-dependent. Monoclonal antibodies could solve this, yet none has reliably prevented HDFN, and some have even enhanced immunization.
The researchers examined two monoclonal anti-D products, Rhoclone and Trinbelimab (TBL), which are widely used in low- and middle-income countries despite lacking FDA or EMA approval. They used epitope mapping, glycan analysis, and de novo sequencing by LC-MS/MS. They then tested antibody-dependent cellular cytotoxicity (ADCC) and used glycoengineering to alter the antibodies' sugar composition.
Both antibodies recognized RhD epitope 5.5 and had identical amino acid sequences. They differed in fucosylation, with Rhoclone at 96% and TBL at 86%. Both showed lower ADCC than the polyclonal anti-D Rhophylac. ADCC ranked as: afucosylated engineered anti-D > polyclonal > TBL > Rhoclone ≈ fucosylated control. Low-fucose engineered versions markedly enhanced natural killer cell-mediated killing.
The findings suggest that high fucosylation is a key reason these monoclonals are less potent than polyclonal anti-D, and that afucosylation could make monoclonal products mimic or exceed polyclonal function. This offers a rational design path for affordable, scalable HDFN prevention.
The key caveat is that the data are in vitro. The authors explicitly note that clinical efficacy is unproven; ADCC strength may not equal prevention of alloimmunization. Only the abstract was available, so details of assays, sample sizes, and statistics could not be assessed.
Key Findings
- Rhoclone and Trinbelimab bind the same RhD epitope (5.5) and have identical protein sequences.
- Fucosylation differed: Trinbelimab 86% versus Rhoclone 96%.
- Both monoclonals showed weaker ADCC than the polyclonal anti-D product Rhophylac.
- ADCC correlated inversely with fucose levels across all antibodies tested.
- Low-fucose glycoengineered anti-D markedly enhanced NK cell-mediated ADCC beyond polyclonal levels.
Methodology
Laboratory characterization of two clinically used anti-D monoclonals using epitope mapping, glycan profiling, and LC-MS/MS de novo sequencing. ADCC was compared against polyclonal anti-D and controls, and antibodies were glycoengineered to reduce fucose.
Study Limitations
The data are in vitro and do not show that higher ADCC yields better clinical prevention of alloimmunization. Only the abstract was reviewed, so assay details, replication, and statistical rigor could not be evaluated.
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