Table 2. Affinities and avidities of R11, R12, and Y31 in Fab and IgG1 formats.¹ .

MAb	Antigen	k on(105) (M−1s−1)	k off(10−4) (s−1)	K d(nM)
Fab R11	Fc-hROR1	20.4	54.7	2.7
	Fc-mROR1	16.9	50.4	3.0
IgG1 R11	Fc-hROR1	19.4	3.6	“0.19”
	Fc-mROR1	9.9	3.0	“0.30”
Fab R12	Fc-hROR1	5.5	3.1	0.56
	Fc-mROR1	no binding	no binding	no binding
IgG1 R12	Fc-hROR1	5.5	0.62	“0.11”
	Fc-mROR1	no binding	no binding	no binding
Fab Y31	Fc-hROR1	8.5	75.2	8.8
	Fc-mROR1	9.1	38.3	4.2
IgG1 Y31	Fc-hROR1	4.9	3.5	“0.71”
	Fc-mROR1	5.4	2.4	“0.44”

¹Fc-hROR1 or Fc-mROR1 were immobilized on the sensor chip. Association (k _on) and dissociation (k _off) rate constants were calculated using Biacore ×100 evaluation software. The equilibrium dissociation constant (K _d), which is shown in quotes for IgG1 to indicate the contribution of the avidity effect, was calculated from k _off/k _on.