Vitro prediction of in vivo half-life

A method for selecting a variant antibody of a parent antibody, comprising the steps of:

• determining a first retention time of the variant antibody and the parent antibody on an FcRn affinity chromatography column with a positive linear pH gradient elution in the presence of a first salt concentration, and determining a second retention time of the variant antibody on an FcRn affinity chromatography column with the positive linear pH gradient elution in the presence of a second salt concentration, wherein:
• the method is for selecting the variant antibody of the IgG1, IgG3 or IgG4 subclass that has a relative in vivo half-life that is increased compared to the parent antibody of the IgG1, IgG3 or IgG4 subclass, by selecting a variant antibody that has a first retention time that is longer than the first retention time of the parent antibody, and a first retention time that is substantially the same as the second retention time,
• wherein the positive linear pH gradient is from about pH 5.5 to about pH 8.8;
• the salt is sodium chloride;
• and
• wherein the first salt concentration is about 140 mM;
• and wherein the second salt concentration is about 400 mM.