An effective vaccine against sexual transmission of human immunodeficiency virus (HIV) should elicit both systemic and mucosal immune responses. In this study, to examine the possibility of using an attenuated virus for mucosal immunization, four female macaques were intranasally or intravenously administered with a chimeric simian-human immunodeficiency virus with a deleted nef gene (SHIV-dn). Although all the monkeys had anti-HIV-1 antibodies with neutralizing activity in the plasma, the intranasally immunized monkeys had much higher levels of HIV-1 Env-specific IgG and IgA antibodies in mucosal secretions compared with the intravenously immunized monkeys. Moreover, three of four intranasally immunized monkeys were completely protected from intravaginal challenge with a pathogenic virus, SHIV-89.6P, whereas only one intravenously immunized monkey was protected. Thus, intranasal immunization of an attenuated virus can induce the protective efficacy against intravaginal infection.

To evaluate the potential of SHIVs as anti-HIV-1 live vaccines, we constructed two gene-deleted SHIVs, designated SHIV-drn and SHIV-dxrn. The former lacks vpr/nef and the latter lacks vpx/vpr/nef. Four macaques that had been vaccinated with SHIV-drn were challenged with SHIV-NM-3rN, which has an HIV-1 Env that is the same as that of SHIV-drn. No challenge virus was detected by DNA PCR in, or recovered from, two of the macaques. In the other two, challenge virus was detected once and twice, respectively. Plasma viral loads were much lower than those in unvaccinated controls. Another four macaques were vaccinated with SHIV-dxrn. These macaques showed resistance but less than that of SHIV-drn-vaccinated macaques. When the two SHIV-drn-vaccinated macaques were challenged with pathogenic SHIV-89.6P, which has an HIV-1 Env that is antigenically different from that of SHIV-drn, replication of the challenge virus was restricted, and the usual decrease in the number of CD4(+) cells was prevented. In this protection, it is noteworthy that protection involved not only neutralizing antibodies and killer cell activity, but also other unknown specific and nonspecific immunity elicited by the infection.

In this study, we tried a DNA vaccination regime in rhesus macaques using a full genome HIV-1 plasmid. The HIV-1 genome is under the control of its original LTR promoter, but has a mutated zinc finger motif gene in the nucleocapsid region. Due to the lack of genomic RNA packaging, the plasmid produces only noninfectious viral particles. We repeatedly injected four macaque monkeys intramuscularly with the naked DNA over a period of 40 weeks. To evaluate the humoral and cell-mediated immunity provided by this DNA vaccination, no other booster or other recombinant viral vectors were used. Immunological responses against HIV-1 were elicited in all of the vaccinated monkeys: stable anti-HIV-1 Env antibodies were raised in two monkeys and CTL activities were induced in the other monkeys. The macaques were intravenously challenged at 54 weeks with 100 TCID(50) of SHIV-NM-3rN, which possesses an envelope gene homologous to the one in the vaccinated plasmid. In all of the vaccinated macaques, the peak plasma viral loads induced by the challenge virus were two to three orders of magnitude lower than those of the naive controls. These results suggest that a DNA vaccination regime with a full genome plasmid alone is potentially efficacious and provides a new possibility for the development of an AIDS vaccine.

To investigate the role of apoptosis in the early phase of HIV infection, we used macaques infected with simian immunodeficiency virus strain mac (SIVmac) as a primate model and examined sequentially the characteristics of apoptosis of lymphocytes in peripheral blood mononuclear cells (PBMCs) and lymph nodes in the early phase of SIVmac infection. Five macaques infected with a pathogenic strain of SIV, SIVmac239, were analyzed during the first 4 weeks after infection. Peripheral CD4+ and CD8+ cells transiently decreased at 1 week postinfection. The percentage of apoptotic cells in cultured PBMCs increased from about 2 weeks postinfection. The number of apoptotic cells in lymph node sections was higher on days 13 and 28 postinfection than before infection and on day 5 postinfection. Fas antigen expression on peripheral lymphocytes was upregulated from day 8 postinfection. These results indicate that apoptosis is induced about 2 weeks after SIVmac239 infection, following the upregulation of Fas antigen expression on lymphocytes. Since apoptosis was induced about 1 week after the decrease in peripheral CD4+ and CD8+ cell counts, it appears that the apoptosis induction does not play an important role in the transient lymphopenia in the early phase of SIVmac infection. In macaques infected with a nonpathogenic derivative of SIVmac239, SIVmac delta nef, apoptosis of lymphocytes was induced as it was in SIVmac239-infected macaques, but to a lesser degree, suggesting a correlation between the extent of apoptosis induction in lymphocytes in the early phase of SIVmac infection and the pathogenicity of SIVmac.

To investigate the role of apoptosis in the progressive loss of CD4+ lymphocytes in HIV infection, we have used macaques infected with SHIV, a hybrid virus of HIV and simian immunodeficiency virus (SIV). In the present study, we sequentially analyzed apoptosis induction in the acute phase of SHIV infection. Four macaques infected with a pathogenic SHIV, SHIV89.6P, and four macaques infected with a nonpathogenic SHIV, NM-3rN, were analyzed during the first 2 or 4 weeks postinfection. In the 89.6P-infected macaques the number of peripheral CD4+ cells sharply decreased at 2 weeks postinfection and was maintained below 50/microl until 4 weeks postinfection, while in the NM-3rN-infected macques the number of the CD4+ cells did not change significantly. Plasma viral loads peaked at 2 and 2-3 weeks postinfection, and the peak values were about 1 x 10(9) and 10(6)-10(7) copies/ml in the 89.6P- and the NM-3rN-infected macaques, respectively. In the 89.6P-infected macaques, Fas antigen expression and the extent of apoptosis in PBMCs and peripheral lymph nodes increased at 1-2 weeks postinfection. A high number of apoptotic cells was also observed in thymus sections 2 and 4 weeks postinfection. On the other hand, apoptosis was scarcely induced in the NM-3rN-infected macaques. These results suggest that the extent of apoptosis induction is closely correlated with the pathogenicity of SHIV and that the apoptosis induction in peripheral lymphoid tissues and thymus, where T cell maturation occurs, may play an important role in the depletion of CD4+ lymphocytes in 89.6P infection.