TABLE 6.

Neutralization of HIV-1_89.6 by MAbs alone or in combination^a

Antibody 2b	ID90 of antibody 1 alone or in combination with antibody 2c
	IgG1 b12	F(ab′)2 b12	2G12	2F5
None	6.25	3.1	100	75
IgG1 b12 (1)			25	50
F(ab′)2 b12 (1)			50	50
2G12 (50)	1.25	NDd		50
2F5 (10)	6.25	ND	50

^aNeutralization synergy of antibody combinations for HIV-1_89.6 was assessed by using an alternative approach to determining synergy in which the neutralization dose-response curve of one MAb (antibody 1) was assessed in the presence or absence of a fixed, weakly neutralizing concentration of a second MAb (antibody 2). 

^bThe fixed concentration of antibody 2 is indicated in micrograms per milliliter in parenthesis. 

^cID₉₀s are shown in micrograms of antibody 1 per milliliter alone or in combination with a weakly neutralizing concentration of antibody 2. A decrease in the ID₉₀ of antibody 1 indicates synergy. 

^dND, not done.