TABLE 2.

Neutralization of HIV-1_JR-CSF by individual antibodies or in combination^a

MAb	ID90 (μg/ml)b	Dm (μg/ml)c	rd	CIe at		Dose reduction indexf at
				ID50	ID90	ID50	ID90
IgG1 b12	20	16	0.99			25	29
2F5	50	20	0.99			1.5	2
2G12	200	72	0.91			11	33
Combination (1:20:10)	1.3, 25, 12.5 g	0.65, 13, 6.5 g	0.99	0.8	0.6

^aNeutralization synergy of antibody combinations for HIV-1_JR-CSF was assessed by using the classical approach to analyzing synergy in which dose-response curves were determined for each of the antibodies alone and for antibody combinations mixed at a constant ratio. The ratio at which the antibodies were mixed was based on their relative neutralization potency (ID₉₀). The presence or absence of synergy was assessed by comparing ID₉₀ values and by using the computer program CalcuSyn. Dm, r, CI, and dose reduction index values were determined using the CalcuSyn computer program (10). 

^bID₉₀s were calculated by estimating the 90% neutralization titer from the neutralization curves. 

^cDm, median effect dose; antibody concentration at half-maximal neutralization. 

^dr, linear correlation coefficient. 

^eAccording to Chou, Talalay, and Hayball, CIs of 0.3 to 0.7 indicate synergism, 0.7 to 0.85 indicate moderate synergism, 0.85 to 0.9 indicate slight synergism, 0.9 to 1.1 indicate additivity, and greater CIs indicate antagonism (10, 11). 

^fDose reduction index, the ratio of doses required for each antibody to reach the indicated degree of neutralization (9, 10). 

^gConcentrations of b12, 2F5, and 2G12 in the mixture, respectively.