TABLE 1.

Ability of serum samples collected from immunized macaques at week 36 to neutralize HIV-1^a

Immunization group	Monkey	Neutralizing antibody titer
		Anti- HIV-1 MN	Anti- HIV-1 IIIB
pCEnv + pCSGag/pol + pCDNA3	1
	2
pCEnv + pCSGag/pol + IL-2	3
	4	1:4
pCEnv + pCSGag/pol + IFN-γ	5
	6
pCEnv + pCSGag/pol + IL-4	7
	8	1:64
Control	9
	10

^aThe ability of sera to neutralize viral infection in vitro was assessed according to described methods (8, 13). All serum samples were heat inactivated at 56°C for 40 min prior to use. T-cell-line-adapted HIV-1 isolates IIIB and MN were obtained from the National Institutes of Health AIDS Research and Reagent Reference Program repository. Dilutions of experimental sera were aliquoted in quadruplicate wells of a 96-well microtiter plate (25 μl per well). Culture media without antibody and preimmune macaque sera served as controls for baseline virus growth. An equal volume of virus stock (25 μl), containing 50 50% tissue culture infective doses of HIV-1 MN or IIIB, was added to each well. After 30 min at 37°C, 3 × 10⁴ MT-2 target cells (100 μl) were added and incubated overnight at 37°C. Cells were then washed extensively to remove p24 antigen and plasma anti-p24 antibody and transferred to a 96-well microtiter plate with culture media. Inhibition of target cell infection was assessed by quantitative p24 measurement of cell supernatants during the early virus growth phase (days 4 to 6 for the viruses in this study) (Coulter [Hialeah, Fla.] enzyme immunoassay). The serum dilution causing a 90% reduction in p24 antigen was calculated by linear regression analysis.