TABLE 2.

Titers of FIV-neutralizing antibodies in MBM cell-adsorbed day-of-challenge sera from vaccinated cats that had proven protected or unprotected against homologous challenge

Group no.	Vaccine (immunization and challenge history)a	Outcome of challengeb	Serum no.	Titer of NAc
				No adsorption	Cell adsorbed
1	FC (5 vaccine doses; challenge 4 mo after last dose)	Protected from intravenous cell-free virus	733 737 806 3532 3535 3585	<16 <16 256 <16 <16 <16	512 512 512 512 512 512
2	FC (5 vaccine doses; challenge 12 mo after last dose)	Protected from intravenous cell-associated but not from cell-free virus	727 759 824 3558 3587 3607	<16 <16 <16 <16 <16 <16	512 256 512 512 256 512
3	FC (5 vaccine doses + booster after 26 mo; challenge 2 mo after booster)	Not protected from intravenous cell-free virus	733 737 806 3532 3535 3585	<16 <16 <16 <16 <16 <16	<16 <16 16 256 <16 128
4	WIV (5 vaccine doses; challenge 4 mo after last dose)	Not protected from intravenous cell-free virus or from cell-associated mucosal challenge	90 101 234 1166 1169	<16 <16 <16 <16 <16	32 16 16 <16 <16

^aThe vaccine doses, each containing 3 × 10⁷ FC (groups 1, 2, and 3) or 250 μg of WIV (group 4), were administered subcutaneously in Freund's incomplete adjuvant. 

^bCell-free challenge consisted of plasma from infected cats, while cell-associated challenge consisted of PBMC collected directly from infected cats (group 2) or PBMC activated and infected at a multiplicity of infection of 0.0015 in vitro (group 4). 

^cExpressed as in Table 1. The experiment was repeated twice, with comparable results.