Sequential immunization of macaques with two differentially attenuated vaccines induced long-term virus-specific immune responses and conferred protection against AIDS caused by heterologous simian human immunodeficiency Virus (SHIV(89.6)P)

Induction of cross-neutralizing antibodies by sequential immunization with heterologous papillomavirus L1VLPs and its implications for HPV prophylactic vaccines

Sequential immunization with antigens from different strains of HIV-1, influenza viruses or dengue viruses induced cross-neutralizing antibodies and enhanced the antibody responses against previous antigens. The characteristics of neutralizing antibodies induced by sequential immunization with different types of human papillomavirus (HPV) L1 virus-like particles (L1VLPs) are unclear. In this study, mice were primed with one or two types (HPV-16 or HPV16/18) of L1VLPs, then boosted sequentially with HPV6/18/45/11/31/58 or HPV6/45/11/31/58 L1VLPs, and sera were analyzed with HPV pseudovirus-based neutralization assay. The results showed that neutralizing activities against earlier immunized vaccine types were enhanced gradually by subsequent immunizations, and low levels of neutralizing activities against nonvaccine types (HPV33/35/52/59/68) were also observed. After absorbing the immune sera with vaccine-type (HPV16/18/45) L1VLPs, neutralizing activities against tested priming and boosting types (HPV16/18/58) decreased significantly, and that against nonvaccine type (HPV-33) was also partially eliminated. Moreover, neutralizing activities against vaccine types (HPV16/58) were significantly reduced after absorbing with nonvaccine-type VLPs (HPV33/52). These data suggest that cross-neutralizing epitopes exist among different HPV L1VLPs. The cross-neutralizing activities against nonvaccine types and the enhanced neutralizing activities against earlier immunized vaccine types may result from sequential boosting with these cross-neutralizing epitopes. These observations support early vaccination with more types of L1VLPs derived from HPVs that cause a serious threat to the population.

No acquisition: a new ambition for HIV vaccine development?

Development of a safe and effective prophylactic HIV-1 vaccine presents unique challenges. The pessimism following the failure of two HIV-1 vaccine concepts in clinical trials, HIV-1 gp120 and an adenovirus-based approach to induce only cellular immune responses, has been replaced by cautious optimism engendered by the RV144 trial outcome, the isolation of several new broadly reactive neutralizing monoclonal antibodies, and recent primate model data indicating prevention of viral acquisition by active or passive immunization. Intense efforts are underway to optimize immunogen design, adjuvants, and the tools for preclinical evaluation of candidate vaccines in primates, where correlates of protection can be examined in detail - as proof-of-concept for clinical trials.

Morphine and rapid disease progression in nonhuman primate model of AIDS: inverse correlation between disease progression and virus evolution

HIV and simian immunodeficiency virus (SIV) have a formidable capacity for mutation and adaptation, a characteristic that has contributed to the extensive genetic variability. Evolutionary pressures imposed within the host and the viral capacity to mutate lead to the generation of such variants. To date, very little information is available regarding the evolution of HIV with drug abuse as a cofounding factor. Using our macaque model of drug dependency and AIDS, we have investigated the dynamics of SIV mutations in the genes tat, vpr, envelope, and nef. The results presented in this review, from our laboratory and others, contribute to the overall understanding of how drugs of abuse might influence immune selective pressure contribution to variation in different SIV genes. Additionally, the studies presented could help enlighten the development of HIV vaccines that take into consideration viral diversity.

Protection of macaques against AIDS with a live attenuated SHIV vaccine is of finite duration

Using background data that live vaccines against several viral pathogens are effective in inducing life-long protection against disease, we undertook studies in macaques to determine the duration of protection that two live SHIV vaccines could induce against AIDS. Earlier studies had established that macaques immunized once with a live vaccine and challenged 6 months later were protected, and that other macaques given two sequential inoculations of live vaccines were protected for at least 1 year. Protection was associated with persistence of the vaccine viruses. In this study, we sought to determine whether the duration of protection in macaques given a single inoculation of replication competent live vaccines would extend beyond 3 years. Two groups of four rhesus macaques were inoculated with two live SHIV vaccines, respectively. The viruses replicated transiently in all animals but at the 3-year time point, PCR analysis of PBMC did not detect DNA of either virus in any of the animals, and all were negative for CMI responses in the blood. All 8 animals succumbed to disease when challenged with pathogenic viruses.

Chronic morphine exposure causes pronounced virus replication in cerebral compartment and accelerated onset of AIDS in SIV/SHIV-infected Indian rhesus macaques

Six morphine-exposed and 3 control male Indian rhesus macaques were intravenously inoculated with mixture of SHIV(KU), SHIV(89.6)P and SIV/17E-Fr. These animals were followed for a period of 56 weeks in order to determine CD4 and CD8 profile, viral loads in plasma and cerebrospinal fluid (CSF), relative distribution of 3 pathogenic viruses in blood and brain, binding as well neutralizing antibody levels and cellular immune responses. Both morphine-exposed and control macaques showed a precipitous loss of CD4+ T cells; control animals, however, showed a greater tendency to recover these cells than did their morphine-exposed counterparts. The plasma and CSF viral loads were significantly higher in morphine-exposed group than those in the control group. Four morphine-exposed animals succumbed to SIV/SHIV-induced AIDS at week 18, 19, 20 and 51; post-infection with neurological disorders was found in 3 of the 4 animals. At the end of the 56-week observation period, 2 morphine-exposed and 3 control animals were still alive. All 3 viruses replicated in the blood of both morphine-exposed and control macaques, but the cerebral compartment showed a selection phenomenon; only SIV/17E-Fr and SHIV(KU) successfully crossed the blood brain barrier (BBB). The morphine-exposed macaques further favored viral migration through the blood brain barrier (BBB). SIV/17E-Fr crossed the BBB within 2 weeks in both morphine-exposed and control macaques, whereas SHIV(KU) crossed the BBB more rapidly in morphine-exposed than in control macaques. Three morphine-exposed macaques (euthanized at weeks 18, 19 and 20) did not develop cellular or humoral immune responses, whereas the other 3 morphine-exposed and 3 control macaques developed both cellular and humoral immune responses.

Therapy of "SHIV" infected macaques with liposomes delivering antisense interleukin-4 DNA

BACKGROUND/OBJECTIVES

To explore the effects of antisense (AS) interleukin (IL)-4 on virus replication and CD8+ T-cell responses in lymph nodes and blood of macaques infected with simian human immunodeficiency virus, SHIV(89.6)P.

METHODS

Six macaques were inoculated with simian human immunodeficiency virus (SHIV(89.6)P). Seven days later, four of the animals were given 1 mg AS IL-4 plasmid complexed with Megafectin liposome, intravenously, and two of these received a second injection of the same material on day 9. All six macaques were killed at 2 weeks post infection (pi) and monitored for viral RNA and CD8+ T cells in blood and lymph nodes by real-time reverse transcriptase-polymerase chain reaction, flow cytometry and immunohistochemistry.

RESULTS

In contrast to the lymph nodes from virus control animals, the lymph nodes of AS IL-4-treated animals had a significant reduction in viral loads and reduced depletion of cells from the nodes. There was an increase in CD8+ T cells in the nodes, and many of the cells expressed granzyme B, suggesting functional activation. This trend of virus reduction and increased CD8+ T cell numbers was also reflected in blood.

CONCLUSIONS

The therapeutic effect of the AS IL-4 suggests indirectly that the acute immunosuppressive disease caused by SHIVs is mediated, in part, by IL-4 that causes enhanced virus replication by suppressing anti-viral CD8+ T-cell responses, and that this effect was reduced by treatment of the animals with AS IL-4.

Correlation between SIV Tat evolution and AIDS progression in cerebrospinal fluid of morphine-dependent and control macaques infected with SIV and SHIV

Morphine abuse has been associated with higher virus replication and accelerated disease progression in a non-human primate model of AIDS. In our previous report, we have shown that 50% of morphine-addicted macaques progress rapidly and that 2/3 of the rapid progressors exhibit severe neuropathogenesis. In this report, we examined the sequence evolution of the SIV Tat protein, known to participate in AIDS neuropathology, in the cerebrospinal fluid (CSF) of morphine-dependent and control macaques over the first 20 weeks of infection. The CSF SIV Tat evolution was found to be inversely related with disease progression, and the highly neuropathogenic inoculum clone sequence was the prevalent CSF form in rapid progressors. Divergence from the inoculum clone was significantly greater in both morphine-dependent normal progressors and control macaques than in the morphine-dependent rapid progressors. Furthermore, we also found evidence of a trend that morphine alters the type of mutation, resulting in an enhanced ratio of transitions to transversions (Ts:Tv). Rapid disease exacerbates this trend and appears to influence the distribution of nonsynonymous changes in the first exon of SIV tat, with a clear majority of mutations occurring in the C-terminal half of the protein where the known functionally important domains reside. Thus, morphine abuse may change the nature and extent of mutations that drive viral evolution.

A combination DNA and attenuated simian immunodeficiency virus vaccine strategy provides enhanced protection from simian/human immunodeficiency virus-induced disease

Among the most effective vaccine candidates tested in the simian immunodeficiency virus (SIV)/macaque system, live attenuated viruses have been shown to provide the best protection from challenge. To investigate if preimmunization would increase the level of protection afforded by live attenuated SIVmac239Deltanef (Deltanef), macaques were given two priming immunizations of DNA encoding SIV Gag and Pol proteins, with control macaques receiving vector DNA immunizations. In macaques receiving the SIV DNA inoculation, SIV-specific cellular but not humoral responses were readily detectable 2 weeks after the second DNA inoculation. Following boosting with live attenuated virus, control of Deltanef replication was superior in SIV-DNA-primed macaques versus vector-DNA-primed macaques and was correlated with higher levels of CD8+/gamma-interferon-positive and/or interleukin-2-positive cells. Challenge with an intravenous inoculation of simian/human immunodeficiency virus (SHIV) strain SHIV89.6p resulted in infection of all animals. However, macaques receiving SIV DNA as the priming immunizations had statistically lower viral loads than control animals and did not develop signs of disease, whereas three of seven macaques receiving vector DNA showed severe CD4+ T-cell decline, with development of AIDS in one of these animals. No correlation of immune responses to protection from disease could be derived from our analyses. These results demonstrate that addition of a DNA prime to a live attenuated virus provided better protection from disease following challenge than live attenuated virus alone.

Virus replication and disease progression inversely correlate with SIV tat evolution in morphine-dependent and SIV/SHIV-infected Indian rhesus macaques

We analyzed the association between evolution of the 5' exon of tat and disease progression in an SIV/SHIV macaque model of opiate dependence and AIDS. Cloned tat sequences were obtained by RT-PCR amplification of 3 plasma viruses (recovered at different times) from 6 morphine-dependent and 2 control Indian rhesus macaques inoculated with SHIV(KU-1B) SHIV(89.6P) and SIV/17E-Fr. Approximately ten clones were sequenced for each animal per time point for use in phylogenetic analyses. We found a strong, significant inverse correlation between disease progression and tat diversity in plasma by 20 weeks post-infection. The morphine-dependent macaques developed 2 distinct disease patterns - rapid progressor (Group A) and slow progressor (Group B) - whereas control animals developed into slow progressor only (Group C). The three animals in Group A exhibited approximately 40% (P = 0.01) and approximately 50% (P = 0.028) less diversity than Group B and C animals, respectively, over the 20 weeks. Furthermore, the Group A macaques showed a prominent reemergence of the wild-type SV17E tat sequence used in the inoculum that coincided with disease progression. This suggests that the virus from the original infection represented the most pathogenic form among all animals in these cohorts throughout the first 20 weeks of infection. We were unable to support or rule out a role for immune pressure on tat evolution based on the spectrum of sequence changes in the data set. Thus, in the short duration of this study, the Tat-specific immune pressure cannot explain the different disease outcomes of the six morphine animals nor of the two controls. Our results also suggest that in vivo morphine dependence can contribute to the pathogenesis of SIV/SHIV infection and that it may do so in conjunction with the evolution of viral proteins, such as Tat.

Increased viral replication in simian immunodeficiency virus/simian-HIV-infected macaques with self-administering model of chronic alcohol consumption

Alcohol abuse constitutes a major cohort among HIV-infected individuals. The precise effect of alcohol addiction on HIV pathogenesis remains inconclusive, however. This study was designed to determine the effect of alcohol dependence on virus replication and CD4 profiles in simian immunodeficiency virus/simian-HIV-infected rhesus macaques. A group of 3 male Indian rhesus macaques was adapted to a self-drinking model of alcohol consumption, whereas another group of 3 macaques was provided a Nutrasweet solution. After 7 weeks of alcohol consumption, the alcohol-dependent animals along with controls were intravenously inoculated with a mixture of SHIV(KU), SHIV(89.6)P, and SIV/17E-Fr. These animals were followed for a period of 24 weeks for complete blood cell counts, CD4 cell profiles, and viral loads in the blood and cerebral compartments. The alcohol and control groups showed comparable peak viral loads in the blood. The plasma viral load in the alcohol group was 31- to 85-fold higher than that in the control group at weeks 18 through 24 after infection, however. The pattern of cerebrospinal fluid viral replication was also comparable during the acute phase; however, the virus continued to replicate in the brain of alcohol-dependent animals, whereas it became undetectable in the controls. The extent of CD4 cell loss in the alcohol group was significantly higher than that in the control animals at week 1 after infection.

Construction and characterization of chimeric BHIV (BIV/HIV-1) viruses carrying the bovine immunodeficiency virus gag gene

AIM: To explore the possibility of the replacement of the gag gene between human immunodeficiency virus and bovine immunodeficiency virus, to achieve chimeric virions, and thereby gain a new kind of AIDS vaccine based on BHIV chimeric viruses.

METHODS: A series of chimeric BHIV proviral DNAs differing in the replacement regions in gag gene were constructed, and then were transfected into 293T cells. The expression of chimeric viral genes was detected at the RNA and protein level. The supernatant of 293T cell was ultra centrifuged to detect the probable chimeric virion. Once the chimeric virion was detected, its biological activities were also assayed by infecting HIV-sensitive MT4 cells.

RESULTS: Four chimeric BHIV proviral DNAs were constructed. Genes in chimeric viruses expressed correctly in transfected 293T cells. All four constructs assembled chimeric virions with different degrees of efficiency. These virions had complete structures common to retroviruses and packaged genomic RNAs, but the cleavages of the precursor Gag proteins were abnormal to some extent. Three of these virions tested could attach and enter into MT4 cells, and one of them could complete the course of reverse transcription. Yet none of them could replicate in MT4 cells.

CONCLUSION: The replacement of partial gag gene of HIV with BIV gag gene is feasible. Genes in chimeric BHIVs are accurately expressed, and virions are assembled. These chimeric BHIVs (proviral DNA together with virus particles) have the potential to become a new kind of HIV/AIDS vaccine.

A noninfectious simian/human immunodeficiency virus DNA vaccine that protects macaques against AIDS

Simian/human immunodeficiency virus SHIV(KU2) replicates with extremely high titers in macaques. In order to determine whether the DNA of the viral genome could be used as a vaccine if the DNA were rendered noninfectious, we deleted the reverse transcriptase gene from SHIVKU2 and inserted this DNA (DeltartSHIVKU2) into a plasmid that was then used to test gene expression and immunogenicity. Transfection of Jurkat and human embryonic kidney epithelial (HEK 293) cells with the DNA resulted in production of all of the major viral proteins and their precursors and transient export of a large quantity of the Gag p27 into the supernatant fluid. As expected, no infectious virus was produced in these cultures. Four macaques were injected intradermally with 2 mg of the DNA at 0, 8, and 18 weeks. The animals developed neutralizing antibodies and low enzyme-linked immunospot assay (E-SPOT) titers against SHIVKU2. These four animals and two unvaccinated control animals were then challenged with heterologous SHIV89.6P administered into their rectums. The two control animals developed viral RNA titers exceeding 10(6) copies/ml of plasma, and these titers were accompanied by the loss of CD4+ T cells by 2 weeks after challenge. The two control animals died at weeks 8 and 16, respectively. All four of the immunized animals became infected with the challenge virus but developed lower titers of viral RNA in plasma than the control animals, and the titers decreased over time in three of the four macaques. The fourth animal remained viremic and died at week 47. Whereas the control animals failed to develop E-SPOT responses, all four of the immunized animals developed anamnestic E-SPOT responses after challenge. The animal that died developed the highest E-SPOT response and was the only one that produced neutralizing antibodies against the challenge virus. These results established that noninfectious DNA of pathogenic SHIV could be used as a vaccine to prevent AIDS, even though the immunological assays used did not predict the manner in which the challenge virus would replicate in the vaccinated animals.

Modulation by morphine of viral set point in rhesus macaques infected with simian immunodeficiency virus and simian-human immunodeficiency virus

Six rhesus macaques were adapted to morphine dependence by injecting three doses of morphine (5 mg/kg of body weight) for a total of 20 weeks. These animals along with six control macaques were infected intravenously with mixture of simian-human immunodeficiency virus KU-1B (SHIV(KU-1B)), SHIV(89.6P), and simian immunodeficiency virus 17E-Fr. Levels of circulating CD4(+) T cells and viral loads in the plasma and the cerebrospinal fluid were monitored in these macaques for a period of 12 weeks. Both morphine and control groups showed precipitous loss of CD4(+) T cells. However this loss was more prominent in the morphine group at week 2 (P = 0.04). Again both morphine and control groups showed comparable peak plasma viral load at week 2, but the viral set points were higher in the morphine group than that in the control group. Likewise, the extent of virus replication in the cerebral compartment was more pronounced in the morphine group. These results provide a definitive evidence for a positive correlation between morphine and levels of viral replication.

Protection Against Late-Onset AIDS in Macaques Prophylactically Immunized with a Live Simian HIV Vaccine Was Dependent on Persistence of the Vaccine Virus

This is a 5-year follow-up study on 12 macaques that were immunized orally with two live SHIV vaccines, six with V1 and six with V2. All 12 macaques became persistently infected after transient replication of the vaccine viruses; all were challenged vaginally 6 mo later with homologous pathogenic SHIV(KU-1). Two of the V1 group developed full-blown AIDS without evidence of vaccine virus DNA in tissues. The data on the 10 vaccinated survivors showed that all 10 became infected with SHIV(KU-1) and that DNA of both vaccine and SHIV(KU-1) viruses were present 6 mo postchallenge, with minimal replication of SHIV(KU-1). During the following 5 years, these animals remained persistently infected, but with only one of the two viruses. Six animals eliminated their vaccine virus after variable periods of time and four of these succumbed to reactivation of the challenge virus and AIDS. Five years after challenge, four latently infected animals, two with V2 and two with SHIV(KU-1), were reinoculated with SHIV(KU-1.) This resulted in transient superinfection and the animals promptly returned to their prechallenge status. Immunosuppression of the four animals 1 year later with Abs to CD8+ lymphocytes resulted in transiently productive replication of their respective latent viruses, and upon recovery of CD8+ lymphocytes, they reverted to their latent virus status. The major finding was that of eight animals that eliminated the vaccine virus, six developed AIDS. The two others harboring SHIV(KU-1) remain at risk for developing late-onset disease. The primary correlate against AIDS was persistence of the vaccine virus.

Highly effective control of an AIDS virus challenge in macaques by using vesicular stomatitis virus and modified vaccinia virus Ankara vaccine vectors in a single-boost protocol

Previous studies have shown that vaccination and boosting of rhesus macaques with attenuated vesicular stomatitis virus (VSV) vectors encoding Env and Gag proteins of simian immunodeficiency virus-human immunodeficiency virus (SHIV) hybrid viruses protect rhesus macaques from AIDS after challenge with the highly pathogenic SHIV 89.6P (23). In the present study, we compared the effectiveness of a single prime-boost protocol consisting of VSV vectors expressing SHIV Env, Gag, and Pol proteins to that of a protocol consisting of a VSV vector prime followed with a single boost with modified vaccinia virus Ankara (MVA) expressing the same SHIV proteins. After challenge with SHIV 89.6P, MVA-boosted animals controlled peak challenge viral loads to less than 2 x 10(6) copies/ml (a level significantly lower than that seen with VSV-boosted animals and lower than those reported for other vaccine studies employing the same challenge). MVA-boosted animals have shown excellent preservation of CD4(+) T cells, while two of four VSV-boosted animals have shown significant loss of CD4(+) T cells. The improved protection in MVA-boosted animals correlates with trends toward stronger prechallenge CD8(+)-T-cell responses to SHIV antigens and stronger postchallenge SHIV-neutralizing antibody production.

Immunogenicity in pig-tailed macaques of poliovirus replicons expressing HIV-1 and SIV antigens and protection against SHIV-89.6P disease

In the search for an effective vaccine against the human immunodeficiency virus (HIV), novel ways to deliver viral antigens are being evaluated. One such approach is the use of nonreplicating viral vectors encoding HIV and/or SIV genes that are expressed after infection of host cells. Nonreplicating poliovirus vectors, termed replicons, that expressed HIV-1/HXB2 and SIVmac239 gag and various HIV-1 env genes from different clades were tested for immunogenicity and protective efficacy against intravenous challenge of pig-tailed macaques with SHIV-89.6P. To maximize both cellular and humoral immune responses, a prime-boost regimen was used. Initially, macaques were immunized four times over 35 weeks by either the intranasal and intrarectal or the intramuscular (im) route with mixtures of poliovirus replicons expressing HIV-1 gag and multiple env genes. Immunization with replicons alone induced both serum antibodies and lymphocyte proliferative responses. After boosting with purified Env protein, neutralizing antibodies to SHIV-89.6P were induced in four of five immunized animals. In a second experiment, four macaques were immunized im three times over 27 weeks with replicons expressing the SIVmac239 gag and HIV-1/HXB2 env genes. All immunized animals were then boosted twice with purified HIV-1-89.6 rgp140-Env and SIVmac239 p55-Gag proteins. Four control animals received only the two protein inoculations. Immunized and control animals were then challenged intravenously with the pathogenic SHIV-89.6P. After challenge the animals were monitored for virus isolation from peripheral blood mononuclear cells and plasma viremia and for changes in virus-specific antibody titers. Naïve pig-tailed macaques experienced rapid loss of CD4(+) T cells and died between 38 and 62 weeks after infection. In contrast, macaques immunized with replicons and proteins rapidly cleared plasma virus and did not experience sustained loss of CD4(+) lymphocytes. Furthermore, two of the four macaques that were immunized only with purified proteins maintained high viral burdens and lost greater than 95% of their CD4(+) lymphocytes within 2 to 4 weeks after challenge. Thus, poliovirus replicons expressing HIV-1 and SIV antigens were immunogenic in pig-tailed macaques and appeared to enhance the protective effects observed after administration of purified proteins alone.

Live attenuated, nef-deleted SIV is pathogenic in most adult macaques after prolonged observation

OBJECTIVE

A live attenuated SIV vaccine strain, termed SIVmac239Delta3 and containing large deletions in, and the negative regulatory element, was previously shown to cause AIDS mostly in monkeys vaccinated as infants. In the present study, we demonstrate that SIVmac239Delta3 is pathogenic in most vaccinated adult monkeys, given enough time.

METHODS

Eleven rhesus macaques vaccinated as adults with SIVmac239Delta3 were followed for extended periods (up to 6.8 years).

RESULTS

We found signs of immune dysregulation in all 11 adult vaccinees. All animals developed persistently inverted CD4 : CD8 T-cell ratios, seven (64%) had persistent recurrent viremia, and six (55%) had decreased CD4 T-cell counts (< 500 x 10 cells/l). Further signs included low CD4CD29 lymphocyte subsets, loss of anti-Gag antibodies, anemia, thrombocytopenia, wasting, and opportunistic infections. Two adult vaccinees (18%) subsequently developed AIDS. Development of chronic, recurrent viremia with plasma viral RNA loads > or = 10 copies/ml and cytoviremia was a poor prognostic sign.

CONCLUSION

Our data demonstrate that with time, a live attenuated, multiply deleted SIV vaccine can cause immune dysregulation in most vaccine recipients, even in initially immune competent, healthy adults. Immune dysfunction can progress to full AIDS. However, pathogenic effects became evident only several years after vaccination. Thus, mass vaccination of humans with similarly constructed live attenuated HIV vaccines, recently suggested for countries with high HIV-1 transmission rates, seems contraindicated.

Immunization of macaques with live simian human immunodeficiency virus (SHIV) vaccines conferred protection against AIDS induced by homologous and heterologous SHIVs and simian immunodeficiency virus

To evaluate the vaccine potential of SHIVs attenuated by deletion of viral accessory genes, seven rhesus macaques were sequentially immunized with Delta vpu Delta nefSHIV-4 (vaccine-I) followed by Delta vpuSHIV(PPC) (vaccine-II). Despite the absence of virological evidence of productive infection with the vaccine strains, based on analysis of infectivity among peripheral blood mononuclear cells (PBMC) of the vaccinated animals, all seven animals developed binding as well as neutralizing antibodies against both vaccine-I and -II. The animals also developed vaccine virus-specific CTLs that recognized homologous as well as heterologous pathogenic SHIVs and SIV, and also soluble inhibitory factors that blocked the in vitro replication of the vaccine strains and different challenge viruses. Virus-specific cellular and humoral responses were sustained throughout a 58-week prechallenge period. To model aspects of natural transmission, the animals received a mucosal (rectal) challenge, with a mixture of three challenge viruses, SHIV(KU), SHIV(89.6)P, and SIV(mac)R71/17E. Two mock-vaccinated control animals inoculated with the same mixture of challenge viruses developed large numbers of infectious PBMC, high plasma viremia, and precipitous loss of CD4(+) T cells. The control animals did not develop any immune responses and succumbed to AIDS between 6 and 7 weeks postchallenge. All seven vaccinated animals became infected with challenge viruses as indicated by the presence of infectious cells in the PBMC and/or viral RNA in plasma. However, peak plasma viremia in vaccinates was two to nearly five logs lower than in the control animals and later plasma viral RNA became undetectable in all vaccinates. Vaccinated animals maintained normal CD4(+) T cell levels throughout the study. Challenge with pathogenic viruses caused massive anamnestic responses as determined by quantitation of virus-specific CD4(+) and CD8(+) T cells by intracellular IFN-gamma staining, and these cells persisted for at least 74 weeks. The study is still in progress and at this time DNA of SIV has become undetectable in lymph nodes of six of the seven vaccinates, SHIV(89.6)P in five of the seven, and SHIV(KU) in three of the seven animals.

Systemic infection and limited replication of SHIV vaccine virus in brains of macaques inoculated intracerebrally with infectious viral DNA

SHIV deleted in two accessory genes, DeltavpuDeltanef SHIV(PPC), functioned well as a vaccine against later challenge with highly pathogenic SHIV(KU), and it was able to reach the brain after oral inoculation of live virus. In this study, the proviral genome cloned into a plasmid was inoculated as DNA intracerebrally and spread systemically. Few regions of the brain had detectable proviral DNA by real-time PCR. Two measures of virus replication, detection of viral mRNA expression and circular proviral DNA, were negative for those brain regions, with the exception of the infection site in the right parietal lobe, whereas lymphoid tissues were positive by both measures. Histopathological analyses of all the sampled brain and spinal cord regions did not reveal any abnormalities. Despite intracerebral inoculation of the viral DNA, the brain was not targeted for high levels of virus replication.

CD8+ T-cell immunity to HIV infection

Fifteen years after the first, definitive reports of HIV-1-specific, CD8+ T cells [147,148], there is ample evidence for the importance of these cells in control of HIV-1 infection. As much is known of their role in the natural history of HIV-1 infection and their cellular and molecular mechanisms of reactivity than of T-cell responses to any other human virus. Indeed, HIV-1-related research has led the scientific field in revealing many new, fundamental principles of cellular immunity in the last 15 years. From these data, there are multiple, posited mechanisms for loss of CD8+ T-cell control of HIV-1 infection. These include both intrinsic defects in T-cell function and loss of T-cell recognition of HIV-1 because of its extraordinary genetic diversity and disruption of antigen presentation. Efforts have begun on devising approaches to reverse these immune defects in infected individuals and develop vaccines that induce T-cell immunity for protection from infection. Combination antiretroviral drug regimens now provide exceptional, long-lasting control of HIV-1 infection, even though they do not restore anti-HIV-1 T-cell immunity fully in persons with chronic HIV-1 infection. Very encouraging results show that such treatment can maintain normal T-cell reactivity specific for this virus in some persons with early HIV-1 infection. Unfortunately, the antiviral treatment does not cure the host of this persistent, latent virus. This has led to new strategies for immunotherapeutic intervention to enhance the level and breadth of the T-cell repertoire specific for the host's residual virus in persons with chronic HIV-1 infection. Although the principles of immunotherapy stem from early in the last century, modern era approaches are integrating highly sophisticated, molecular and cell biology reagents and methods for control of HIV-1 infection. The most promising immunotherapies are autologous virus activated in vivo by STI or administered in autologous DC that have been engineered ex vivo. There are also compelling rationales supported by animal models and early clinical trials for use of cytokines and chemokines as recombinant proteins or DNA to augment anti-HIV-1 T-cell reactivity and trafficking of T cells and APC to tissue sites of infection. For prevention of HIV-1 infection, the discouragingly poor results of vaccine development in the late 1980s and early 1990s have led to very encouraging, recent studies in monkeys that show partially protective and possibly sterilizing immunity. Finally, clinical trials of new-generation DNA and live vector vaccines already have indications of improved induction of HIV-1-specific T-cell responses. Knowledge of HIV-1-specific T-cell immunity and its role in protection from HIV-1 infection and disease must continue to expand until the goal of complete control of HIV-1 infection is accomplished.

Preclinical AIDS vaccine research: survey of SIV, SHIV, and HIV challenge studies in vaccinated nonhuman primates

This current supplementary and systematic survey of 237 preclinical AIDS vaccine challenge/protection studies in nonhuman primates enumerates and broadly describes the recent status of different vaccine strategies in macaque and chimpanzee experimental models. Published studies since the previous survey were compiled and categorized by their vaccine types, challenge parameters, and challenge results. These models have supportively verified that some prophylactic vaccine approaches, though rarely preventing infection (which is observed in these models with some passively administered antibody-based vaccines), can control to some degree primate lentivirus replication and disease development, and this is encouraging because it places more potentially effective immunogens on the precipice for early clinical studies. Many of these promising approaches may benefit from more testing in mucosal challenge models, and resources will be needed to follow more of these partially protected vaccinees for longer periods.