Toward experimental assessment of receptor occupancy: TGN1412 revisited

Area of Science:

• Immunology
• Clinical Pharmacology
• Biotechnology

Background:

• Serious adverse events occurred during a first-in-human trial of the anti-CD28 monoclonal antibody TGN1412 in 2006.
• Initial investigations ruled out drug contamination or protocol errors as causes.
• An expert group recommended strategies to mitigate risks in early-phase clinical trials.

Purpose of the Study:

• To develop and validate a flow cytometry method for experimentally determining TGN1412's CD28 receptor occupancy.
• To assess if experimental receptor occupancy data aligns with in silico predictions.
• To establish receptor occupancy as a parameter for defining safe starting doses in clinical trials.

Main Methods:

• Development of a flow cytometric assay to measure CD28 receptor occupancy on T cells.
• Application of the assay to samples from the TGN1412 trial conditions.
• Comparison of experimental results with in silico calculations.

Main Results:

• The developed flow cytometry method experimentally determined CD28 receptor occupancy to be approximately 45% to 80%.
• This experimental range differs from the in silico predicted range of 86.2% to 90.9% at the trial's initial dose.
• The findings underscore the importance of experimental validation over theoretical calculations for risk assessment.

Conclusions:

• Experimental determination of receptor occupancy is essential for establishing the minimal anticipated biological effect level.
• This method can inform the calculation of safer starting doses for novel therapeutics, particularly monoclonal antibodies.
• Implementing such experimental measures can significantly enhance the safety of first-in-human clinical trials.