Question 9 of 20 Fundamentals Concept
What does humanizing a mouse antibody involve, and why is it done?
Short answer
Humanization grafts the mouse binding loops onto human framework and constant regions, so most of the molecule is human. It is done because a mouse antibody given to people provokes an anti-mouse antibody response that clears the drug quickly and can cause reactions.
Why
Lu and colleagues set out the history. Patients treated with mouse monoclonal antibodies mount a human anti-mouse antibody response, which speeds clearance of the drug, can cause allergic reactions and limits repeat dosing. Mouse Fc also engages human immune effector mechanisms poorly.
The fix, developed by Winter's group in 1986, is complementarity-determining region grafting: transplant the mouse binding loops into a human framework so that specificity is kept while most of the sequence becomes human. The first humanized antibody approved by the FDA was daclizumab in 1997, against the IL-2 receptor, for preventing transplant rejection. Grafting alone often loses affinity, because some framework residues support the loops.
Those residues are then kept from the mouse sequence, or a human framework most similar to the mouse one is chosen, which is what was done for daclizumab. Humanization is no longer the only route. Phage display and transgenic mice that carry human antibody genes produce fully human antibodies from the start, and both have produced approved drugs.
A strong answer covers
- Mouse antibodies provoke an anti-mouse response in people
- CDR grafting puts mouse loops on a human framework
- Framework residues sometimes have to be kept to preserve affinity
- Daclizumab in 1997 was the first approved humanized antibody
- Phage display and transgenic mice give fully human antibodies instead
Common mistakes
- Assuming a humanized antibody cannot be immunogenic at all
- Expecting grafting alone to keep affinity unchanged
- Confusing chimeric antibodies, which keep whole mouse variable domains, with humanized ones
The interviewer might ask next
How would you troubleshoot a humanized variant that lost tenfold affinity after grafting?