Table 3. Constant regions used in the cynomolgus monkey PK study.

Constant region	Backbone	FcRn binding	FcγR & C1q binding	pI
SG406	human IgG4	silenced	silenced	low
SG407	human IgG4	enhanced	silenced	low
SG419	human IgG4	enhanced	silenced	high
SG115	human IgG1	enhanced	silenced	high

The constant region of human IgG₄ or IgG₁ was engineered in this study. In SG406, FcRn binding was abrogated to prevent the antibody being salvaged back to plasma from the endosomes by FcRn-mediated recycling. In SG419, human IgG₄ was engineered to increase the pI. The surface-charge engineering was not incorporated in SG115, because the human IgG₁ backbone naturally had high pI.