Table 2. Summary of affinity and neutralizing activity for Fab 19 or related Fab mutants possessing reverted unmutated ancestor residues.

Location of reversion to unmutated ancestor	Antibody	Steady-state affinity (KD) (M)	Neutralizing specific activity (μg/mL needed to neutralize)
None	wt Fab 19	2.9 × 10−8	3
CDR1	T134F	1.8 × 10−8	1
	L136F	5.0 × 10−8	4
	G138S	1.5 × 10−7	13
	T140S	7.2 x 10−7	120
CDR2	T159S	5.2 x 10−8	3
	G160S	7.0 × 10−8	4
	G161S	3.3 × 10−8	2
	N163S	1.2 × 10−7	3
	F164Y	1.6 × 10−6	130
CDR3	T205R	1.3 × 10−7	9
	P210A	1.7 × 10−6	>200
	P211H	1.6 × 10−6	>200
	H215Y	2.8 × 10−6	>200