Listeria -specific proliferative responses in immunized macaques. PBMC from individual monkeys were tested for Listeria-specific proliferative responses at the indicated time points after inoculation with the empty Lmdd vector. Cells were cultured in supplemented RPMI in the presence of HIV IIIB p55 Gag (2 μg/ml) for 4 d. Cells were pulsed with 1 μCi per well of 3H-thymidine (PerkinElmer, Boston, MA) for 18 h prior to harvesting. Thymidine incorporation was assessed using a β-scintillation counter (Beckman Coulter, Inc., Miami, FL). Results are expressed as stimulation index (SI). To test for Lm-specific proliferative responses, whole Lm bacteria (strain 12443) were used as described .