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Background: The cell mediated immune profiles following immunization with a recombinant DNA vaccine was assessed in the simian-human immunodeficiency virus (SHIV) and Macaque model. Earlier work demonstrated increased numbers of antigen specific CD8 and CD4 effector cells able to secrete IFN-gamma., Method: The vaccine strategy included co-immunization of a DNA based vaccine alone or in combination with a macaque IL-12 expressing plasmid (pmacIL12). Antigen activated lymphocytes were studied for activation of a set of immunological molecules., Results: The current study demonstrates lymphocytes isolated and activated from the group that was immunized with DNA and pmacIL12 had a higher level of IFN-gamma producing cells. We also observed a different immunological profile when comparing the cells isolated from macaques immunized with DNA as compared to those animals that also received pmacIL12., Conclusion: The observed immune profiles are reflective of the co-delivery of pmacIL12 and demonstrates that IL-12 can increase the magnitude and polyfunctionality of the cellular immune response.

In vitro infectivity experiments were performed to assess the susceptibility of cells from various monkey species to HIV-1. T lymphocytes from pigtailed macaques, but not those from rhesus or cynomolgus monkeys, were susceptible to infection, but virus expression was limited. The majority of HIV-1 isolates were unable to productively infect pigtailed macaque cells. Inoculation of autologous, HIV-1 expressing cells led to establishment of persistent infection in pigtailed macaques as evidenced by recovery of infectious virus and development of virus-specific antibody responses.

The macaque infectious dose (MID) of a single-cell clone of simian immunodeficiency virus isolated from a pig-tailed macaque (SIV/Mne clone E11S) was determined in rhesus macaques (Macaca mulatta). Twenty-one macaques were inoculated with 10-fold dilutions of the virus stock (three or four animals per dose). The virologic and clinical status of these animals was monitored for 26 weeks. The 25% MID (MID25) occurred at a 10(5)-fold dilution of the viral stock.

The decline in the CD4% and CD4/CD8 ratios have been compared in lymph nodes and blood from SIVMNE/E11S infected rhesus macaques. The results indicate that loss from the LN CD4+ cell pool does not occur until CD4/CD8 ratios of less than 0.5 is reached in blood. These changes also correlate with the ability to isolate virus from the blood and the transition of CD45RAhi to highly activated CD45RAlo CD8+ cells both of which may play a role in eliminating CD4+ cells. In end-stage disease, CD8+ cells also decline in LN and mitogen responsiveness no longer exists in any nodes. Interestingly at this stage, the circulating CD8% increases significantly and represents the only source of functional T cells remaining in the body.

In contrast to pig-tailed and cynomolgus macaques, which die in 6-10 days following infection with the SIV-PBj-14 isolate, only about 50% of rhesus succumbed to rapid disease. Using a CD45RA MAb that delineates memory (CD45RAlo), naive (CD45RAmed) and "activated" (CD45RAhi) T-cell subsets, it was seen that PBMC from pig-tailed and cynomolgus monkeys, unlike rhesus, have reduced CD4/CD8 ratios and a skewing of T cells towards CD45RAhi expression. Such preactivation of CD4+ cells could lead to enhanced viral replication and early death.