Antibody drugs are very useful tools for the treatment of many chronic diseases. 
Recently, however, patients and doctors have encountered the problem of drug 
resistance. How to improve the affinity of antibody drugs has therefore become a 
pressing issue. Ibalizumab is a humanized monoclonal antibody that binds human 
CD4, the primary receptor for human immunodeficiency virus type 1. This study 
investigates the mutation residues of the complementarity determining regions of 
Ibalizumab. We propose using the wild and mutations of Ibalizumab-human CD4 
receptor complex structures, molecular dynamics techniques, alanine-scanning 
mutagenesis calculations and solvated interaction energies methods to predict 
the binding free energy of the Ibalizumab-human CD4 receptor complex structures. 
This work found that revealed three key positions (31th, 32th and 33th in 
HCDR-1) of the residues may play an important role in Ibalizumab-human CD4 
receptor complex interactions. Therefore, bioengineering substitutions of the 
three key positions and increasing number of intermolecular interactions (HCDR-1 
of Ibalizumab/human CD4 receptor) might improve the binding affinities of this 
complex structure.