Protection by attenuated simian immunodeficiency virus in macaques against challenge with virus-infected cells

A vaccine against AIDS will probably have to protect against challenge both by viable virus-infected cells and by cell-free virus. Eight cynomolgus macaques infected with attenuated simian immunodeficiency virus (SIV) were challenged (four each) with cell-free and cell-associated SIV. All were protected, whereas eight controls were all infected after challenge. These findings show that live-attenuated vaccine can confer protection against SIV in macaques. Extrapolation to human beings will require extensive evaluation of the safety of attenuated retroviruses. Alternatively, the mechanism of this potent protection must be understood and reproduced by less hazardous means.

Evasion of cytotoxic T lymphocyte (CTL) responses by nef-dependent induction of Fas ligand (CD95L) expression on simian immunodeficiency virus-infected cells

Inoculation of macaques with live attenuated SIV strains has been shown to protect against subsequent challenge with wild-type SIV. The protective mechanism(s) remain obscure. To study the effect in more detail, we have investigated the role of virus-specific CTL responses in macaques infected with an attenuated SIV strain (pC8), which has a four-amino acid deletion in the nef gene, as compared with the wild-type SIVmac32H clone (pJ5). Cynomolgus macaques infected with pC8 were protected against subsequent challenge with pJ5 and did not develop any AIDS-like symptoms in the 12 months after infection. The pC8-induced protection was associated with high levels of virus-specific CTL responses to a variety of viral antigens. In contrast, pJ5-infected macaques had little, if any, detectable CTL response to the viral proteins after three months. The latter group of macaques also showed increased Fas expression and apoptotic cell death in both the CD4(+) and CD8(+) populations. In vitro, pJ5 but not pC8 leads to an increase in FasL expression on infected cells. Thus the expression of FasL may protect infected cells from CTL attack, killing viral-specific CTLs in the process, and providing a route for escaping the immune response, leading to the increased pathogenicity of pJ5. pC8, on the other hand does not induce FasL expression, allowing the development of a protective CTL response. Furthermore, interruption of the Fas-FasL interaction allows the regeneration of viral-specific CTL responses in pJ5-infected animals. This observation suggests an additional therapeutic approach to the treatment of AIDS.

Early suppression of SIV replication by CD8+ nef-specific cytotoxic T cells in vaccinated macaques

In order to develop a successful subunit vaccine against infection with the human immunodeficiency virus (HIV), protective immune effector functions must be identified. Until now, there has been only indirect evidence that HIV-specific cytotoxic T lymphocytes (CTLs) fulfill this role. Using the macaque simian immunodeficiency virus (SIV) model, the protective potential of nef-specific CTLs, stimulated by vaccination, was examined in animals challenged with a high intravenous dose of the pathogenic simian immunodeficiency virus, SIVmac251(32H)(pJ5). An inverse correlation was found between the vaccine-induced nef-specific CTL precursor frequency and virus load measured after challenge. In addition, the early decline in viraemia, observed in both vaccinated and unvaccinated control animals was associated with the development of virus-specific CTL activity and not with the presence of virus-specific neutralizing antibodies. The results imply that vaccines that stimulate strong CTL responses could protect against HIV infection.

Human papillomavirus type 16 cooperates with activated ras and fos oncogenes in the hormone-dependent transformation of primary mouse cells

The effect of human papillomavirus (HPV) and activated oncogenes on the growth and morphology of primary baby mouse kidney (BMK) cells has been studied. Early region DNA from HPV types 16, 18, 31, and 33, but not type 6, under the transcriptional control of a heterologous, retroviral promoter cooperated with EJ-ras to produce cell lines that gave rise to carcinomas in syngeneic immunocompetent animals. The same HPV constructs, when cotransfected with a plasmid containing sequences from the Finkel-Biskis-Jinkins murine sarcoma virus provirus (v-fos), produced cell lines that were tumorigenic in nude mice. None of the other activated oncogenes tested, including activated c-myc, displayed any activity with HPV in this cotransfection assay. When the heterologous promoter was replaced by the homologous HPV16 promoter, the transforming effect of HPV16 with either EJ-ras or v-fos required the presence of either glucocorticoid or progestogen. Cell lines derived from transfection of HPV16 with either EJ-ras or v-fos required the continued presence of hormones for proliferation.

A clinically relevant HIV-1 subunit vaccine protects rhesus macaques from in vivo passaged simian-human immunodeficiency virus infection

OBJECTIVES

To investigate whether immunization with recombinant HIV-1 envelope protein derived from a clinical isolate could protect macaques from infection with an in vivo passaged chimeric simian-human immunodeficiency virus (SHIV).

DESIGN AND METHODS

A total of 16 animals were studied from which three groups of four animals were immunized with vaccine formulations of the CC-chemokine receptor-5-binding recombinant gp120 of HIV-1W6.1D. Four weeks after the last immunization, all 16 animals were intravenously challenged with in vivo passaged SHIV derived from the same HIV-1 group B clinical isolate (W6.1D) as the vaccines.

RESULTS

Vaccine protection from infection was demonstrated in 10 out of 12 macaques immunized with recombinant gp120. Complete protection from infection was achieved with all of the animals that received the SBAS2-W6.1D formulation, a potent inducer of both T-cell and humoral immune responses. Partial protection was achieved with SBAS1-W6.1D, a formulation based on immunomodulators known to induce T-cell responses in humans. In vaccinated animals that were infected, virus load was reduced and infection was delayed.

CONCLUSIONS

In a relatively large number of primates, vaccine efficacy was demonstrated with a clinically relevant HIV-1 vaccine. These results reveal that it is possible to induce sterilizing immunity sufficient to protect from infection with SHIV which was passaged multiple times in vivo. Our findings have implications for current HIV-1 clinical vaccine trials and ongoing efforts to develop safe prophylactic AIDS vaccines.

'Chemical condoms' for the prevention of HIV infection: evaluation of novel agents against SHIV(89.6PD) in vitro and in vivo

BACKGROUND

Vaginal agents which are antiviral and/or inhibit the entry of HIV into the cell could prevent heterosexual transmission of HIV, and protect women who cannot negotiate condom use.

METHODS

Four agents have been investigated for activity in vitro and in vivo against SHIV(89.6PD): two anionic polymers, dextrin-2-sulphate (D2S) and PRO 2000 (P2K), and two virucidal agents; a non-ionic detergent, nonoxynol-9 (N9) and a cyclic peptide ionophore, gramicidin-D (GD). All four agents were investigated in rhesus macaques, using an intra-vaginal challenge of two inoculations of 1 x 104 50% tissue culture infectious doses (TCID)50 of SHIV(89.6PD).

RESULTS

D2S, P2K, GD and N9 all inhibited SHIV(89.6PD) in vitro. In vivo, three out of four control macaques were infected as judged by viral culture, seroconversion, DNA and RNA PCR; infection was confirmed in four out of eight macaques pre-treated with P2K, two out of four pre-treated with D2S, one out of four pre-treated with N9, two out of four pre-treated with GD and four out of four pre-treated with D2S + GD, a combination additive in vitro.

INTERPRETATION

D2S and PRO-2000, novel inhibitors of HIV entry, showed evidence of protection in vivo, comparable to that seen with the virucide, N9. These data, together with the results of phase I and phase II studies in healthy women which have shown minimal toxicity, support plans for a phase III efficacy trial of chemically simple inhibitors of HIV entry with low toxicity, for the prevention of HIV infection in women.

Mechanisms of protection induced by attenuated simian immunodeficiency virus. I. Protection cannot be transferred with immune serum

To evaluate its role in protection, immune serum was collected from four macaques which were chronically infected with live attenuated simian immunodeficiency virus (SIVmacC8) and had resisted challenge with wild-type SIVmacJ5. The immune serum was transferred to two naive cynomolgus macaques by intraperitoneal injection (11 ml/kg). Four control macaques received an intraperitoneal injection of normal saline. One day later, all macaques were challenged with 10 MID50 of the J5M challenge stock of SIV. After challenge, all macaques became infected as determined by virus co-culture and diagnostic PCR. Virus loads in PBMC at 2 weeks post-challenge were indistinguishable between the two groups of macaques. Thus, the failure of passive immunization to transfer protection indicates that serum components alone are not sufficient to mediate the potent protection obtained using live attenuated vaccines. This is the first time that serum has been transferred from animals known to be protected against superinfection.

MhcDRB-sequences from cynomolgus macaques (Macaca fascicularis) of different origin

Cynomolgus macaques are frequently used in biomedical research. However, in contrast to their closest relative, the rhesus macaque, little is known about their Mhc genes except for the DQB1 locus. In this study, 33 DRB-sequences belonging to 17 allelic lineages were detected in a total of 68 macaques, 58 originating from Mauritius and 10 from China. The majority of the sequences were detected in the few macaques from China, confirming the low degree of genetic variation in macaques from Mauritius. In summary, the DRB region in cynomolgus macaques is polymorphic. The sequences belong in general to the same allelic lineages as in their closest relative, the rhesus macaque. Two exon 2 DNA sequences were identical in both species and may represent a trans-species origin. In addition, protein sequences of members of the DRB*W1 lineage seem to be rather conserved in the three macaque species examined so far. Six DRB-haplotypes were detected in the macaques from Mauritius. While single DRB-alleles or some protein sequences seemed to be conserved among macaque species, we could not detect any evidence for a trans-species conservation of a complete DRB region. Overall, the data indicate that reorganization of the DRB region by recombination is a major force in creating diversity in cynomolgus macaques as it is in rhesus macaques.

Population sequence analysis of a simian immunodeficiency virus (32H reisolate of SIVmac251): a virus stock used for international vaccine studies

The virus structural genes gag and env (both gp120 and gp41 regions) of the 32H isolate of SIVmac251 were amplified using the polymerase chain reaction (PCR). The proviral template used in the PCR was DNA isolated from cells used to prepare several experimental SIV vaccines, which have been tested in simians, and a standard challenge stock of virus, which has been used in international collaborative studies. The PCR products were cloned and the nucleotide sequences of several clones were determined for each gene. From a comparison of the sequences obtained the predominant amino acid sequences of gag and env were predicted and the degree of sequence heterogeneity was determined. Conserved and more variable regions of each protein were identified. The gp120 region of env was more heterogeneous than gag or the transmembrane protein of env (gp41). Within gp120, sequence variability was concentrated to specific regions equivalent to the V1, V2, and, to a lesser extent, the C1 regions identified for human immunodeficiency virus type 1 (HIV-1). In contrast the region equivalent to the hypervariable "V3-loop" of HIV-1 was highly conserved. The implications of the data is discussed in relation to the ability of this virus stock to prepare effective vaccines against SIV.

Mutations of the human papillomavirus type 16 E7 gene that affect transformation, transactivation and phosphorylation by the E7 protein

The human papillomavirus type 16 (HPV-16) E7 gene cooperates with an activated ras oncogene to transform primary rodent cells and is important in the immortalization of cervical keratinocytes. We have generated a series of point mutations within the E7 gene and show that mutation of residues serine 31 and serine 71 affect the phosphorylation of the E7 protein, but do not alter its ability to cooperate with ras. Further mutations which alter cysteine residues in a -Cys-X-X-Cys- motif decrease transformation markedly, although they do not abolish it entirely. All the mutations generated displayed a decreased ability to transactivate the adenovirus E2 promoter. These results show that neither phosphorylation of E7 nor its ability to transactivate are required for transformation by E7.

Evaluation of a candidate human immunodeficiency virus type 1 (HIV-1) vaccine in macaques: effect of vaccination with HIV-1 gp120 on subsequent challenge with heterologous simian immunodeficiency virus-HIV-1 chimeric virus

Human immunodeficiency virus type 1 (HIV-1) envelope vaccines can now be evaluated for efficacy in macaques by challenging with chimeric viruses in which the env, tat and rev genes of simian immunodeficiency virus (SIV) have been replaced by those of HIV-1. Most experiments have so far been conducted using gp120 molecules derived from T-cell-adapted LAI or MN strains of HIV-1, which predominantly use the CXCR-4 co-receptor. These vaccines protect against infection by apathogenic chimeric virus carrying the same envelope sequences. In the experiment described here, four macaques were vaccinated with W61D gp120 derived from a low passage Dutch isolate and capable of inhibiting the binding of MIP1beta to the co-receptor CCR-5. This vaccine was potent, inducing high titres of binding and neutralizing antibodies against the homologous HIV-1 and tenfold lower titres against a heterologous challenge virus (SHIV(SF33)) in which the env, tat and rev genes of SIV had been replaced by those of a San Francisco isolate, HIV-1(SF33). Despite strong immune responses to the vaccine there was no evidence that it protected against challenge with this chimeric virus. The antigenic divergence between vaccine and challenge virus or the increased virulence of the challenge virus may be responsible for the inability of this vaccine to protect against infection by SHIV(SF33).

Comparison of early plasma RNA loads in different macaque species and the impact of different routes of exposure on SIV/SHIV infection

Various simian immunodeficiency virus (SIV)sm/mac and simian/human immunodeficiency virus (SHIV) strains are used in different macaque species to study AIDS pathogenesis, as well as to evaluate candidate vaccine and anti-retroviral drugs efficacy. In this study we investigated the effect of route of infection, species of macaques and nature of virus stock on early plasma viral RNA load. We monitored the plasma RNA concentrations of 63 rhesus (Macaca mulatta) and cynomolgus macaques (Macaca fascicularis) infected with well-characterised virus stocks administered either by oral, rectal, vaginal or intravenous (i.v.) routes. In SIV(mac)-infected macaques, no significant difference in plasma RNA loads was observed between the rectal, oral and i.v. routes of infection. Cynomolgus macaques developed lower steady state SIV plasma RNA concentrations compared with rhesus macaques and no significant difference was observed between rectal and i.v. routes of infection. In SHIV(89.6p)-infected macaques, no difference between species or between route of infection was observed with this particular chimeric virus.

Mechanisms of protection induced by attenuated simian immunodeficiency virus. II. Lymphocyte depletion does not abrogate protection

To determine the role that cellular immune responses play in the protection conferred by vaccination with attenuated SIVmac32H (pC8), we have attempted to deplete macaques of their CD8+ cells prior to challenge with wild-type SIVmac32H (pJ5). In two of four pC8-infected macaques, N109 and N112, a transient partial depletion of CD8+ cells by antibody treatment was achieved. On the day of challenge peripheral CD2+CD4-CD8+ cell counts were reduced by 92 and 95%, respectively, in animals N109 and N112 and their lymph nodes revealed a 46 and 58% reduction, respectively, in CD2+CD4-CD8+ cells. Two other pC8-immunized macaques, N110 and N111, treated in the same way, did not show significant depletion of CD8+ cells. None of these four pC8-immunized animals became infected when challenged with 50 MID50 of pJ5. Treatment of a further four pC8-infected and protected macaques and two naive control animals with Campath-1H antibody successfully depleted peripheral CD3+ cell counts by >99% in all treated animals. Campath-1H depletion resulted in enhanced, longer lasting lymphoid depletion. Yet subsequent challenge with 20 MID50 of pJ5 still failed to infect the pC8-immunized animals. All eight of the naive controls, including two Campath-1H-treated animals, became infected following challenge. In summary, partial depletion of circulating CD8+ cells or total lymphocytes prior to challenge failed to abrogate the protection conferred by vaccination with pC8.

Increased antibody responses to human papillomavirus type 16 L1 protein expressed by recombinant vaccinia virus lacking serine protease inhibitor genes

The L1 gene of human papillomavirus type 16 (HPV-16) driven by the vaccinia virus major late 4b gene promoter has been inserted into three different sites of the vaccinia virus genome. Insertion into the thymidine kinase (TK) gene was achieved by selection of TK- mutants in BUdR on TK- cells. Insertion into two vaccinia virus serine protease inhibitor (serpin) genes was achieved by co-insertion of the Escherichia coli xanthine guanine phosphoribosyltransferase gene linked to the vaccinia virus 7.5K promoter and selection of mycophenolic acid-resistant recombinant viruses. Each recombinant virus expressed a 57K L1 protein at similar levels and with similar kinetics. However, immunization of mice with these recombinant viruses induced different levels of antibody to the L1 protein. Viruses lacking serpin genes B13R and B24R induced significantly higher antibody levels than did viruses lacking the TK gene. The presence of functional B13R and B24R gene products is therefore somehow immunosuppressive at least for antibody responses to the L1 protein of HPV-16.

The use of the polymerase chain reaction for the detection of Simian immunodeficiency virus in experimentally infected macaques

A rapid, non-radioactive assay for the detection of proviral Simian immunodeficiency virus (SIV) in tissue-culture cells is described. The assay is based on the co-amplification of the SIV env and gag genes by the polymerase chain reaction (PCR). When the gag PCR product is blotted onto a nylon membrane and hybridised to a radioactive oligonucleotide probe, the assay can also be used to detect the SIV gag gene in DNA isolated directly from experimentally infected cynomolgus macaque lymphocytes. This provides a valuable assay for the presence of proviral SIV during animal trials of AIDS vaccines and chemotherapeutics.

The development of PCR based assays for the detection and differentiation of simian immunodeficiency virus in vivo

Polymerase chain reaction based assays, which amplify a region of the gag gene, have been developed for the direct detection of simian immunodeficiency virus (SIV) DNA sequences in the blood of experimentally infected cynomolgus macaques. In macaques infected with a characterised virus pool (11/88 pool SIVmac 32H), an assay employing a single round of amplification was found to be highly sensitive and specific. However, in animals infected with the SIV molecular clones J5 and C8 (Rud et al., J. Gen. Virol. 75, 529-543), it was necessary to use two rounds of amplification and nested primer pairs in order to achieve sensitivity > 90%. In order to differentiate macaques infected with either of the two genetically distinct SIV clones, J5 or C8, a third PCR based assay has been developed, which amplifies a 492 bp region of the nef gene. Sequence differences between the nef genes of the two molecular clones enabled the PCR product amplified from each virus to be distinguished by restriction analysis. These sensitive and specific assays complement virological detection of SIV and enable superinfection studies to be evaluated; a prerequisite for the testing of live attenuated immunodeficiency virus vaccines.

Sequence variation in the env gene of simian immunodeficiency virus recovered from immunized macaques is predominantly in the V1 region

Three cynomolgus macaques were immunized with recombinant envelope protein preparations derived from simian immunodeficiency virus (SIV). Although humoral and cellular responses were elicited by the immunization regime, all macaques became infected upon challenge with 10 MID50 of the 11/88 virus challenge stock of SIVmac251-32H. The polymerase chain reaction was used to amplify proviral SIV gp120 sequences present in the blood of both immunized and control macaques at 2 months post-infection. A comparison of the predominant sequences found in the region from V2 to V5 of gp120 failed to differentiate provirus recovered from either immunized or control animals. A detailed investigation of sequences obtained from the hypervariable V1 region identified a mixture of sequences in both immunized and control macaques. Some sequences were identical to those previously detected in the virus challenge stock, whereas others had not been detected previously. Phenogram analysis of the new V1 sequences found in immunized animals revealed that they were quite distinct from those from the virus challenge stock and that they included alterations to potential N-linked glycosylation sites. In contrast, new sequence variants recovered from the control animals were closely related to sequences from the virus challenge stock. The difference in diversity of new V1 sequences recovered from immunized and control macaques was highly significant (P < 0.001). Thus, the presence of pre-existing immune responses to SIV envelope protein is associated with greater genetic change in the V1 region of gp120. These data are discussed in relation to the epitopes of SIV gp120 that may confer protection from in vivo challenge.

Absence of lentiviral and human T cell leukemia viral sequences in patients with rheumatoid arthritis

OBJECTIVE

The etiology of rheumatoid arthritis (RA) is unknown, and the possibility that an infectious agent is involved has not been excluded. Lentiviruses can cause chronic arthritis in humans and in animals and have been suggested as candidate agents in RA. We therefore tested for the presence of lentiviruses and also for human T cell leukemia virus type I (HTLV-I)/HTLV-II in cells from patients with RA.

METHODS

We used the polymerase chain reaction with degenerate primers designed to recognize highly conserved nucleotide sequences from 5 different pathogenic lentiviruses. This method allowed the detection of at least 1 infected cell/20,000 uninfected cells in control experiments.

RESULTS

Testing of synovial cells and blood cells from patients with early RA and patients with established RA did not yield any specific viral product.

CONCLUSION

Our results do not support the presence of lentiviruses or HTLV-like sequences in RA.

Live attenuated SIV--a model of a vaccine for AIDS

The experimental infection of macaques with simian immunodeficiency virus (SIV) has provided strong evidence that it may be possible to develop a vaccine against AIDS. Live attenuated SIV vaccines have been found to confer the most potent protection against challenge with a variety of pathogenic viruses. This article summarizes the work performed at NIBSC to characterize the protection conferred by live attenuated SIV and to identify mechanisms of vaccine protection. The results of these experiments are discussed in conjunction with observations from related studies made by other groups.

Comparison of in vitro and in vivo infectivity of different clade B HIV-1 envelope chimeric simian/human immunodeficiency viruses in Macaca mulatta

The use of HIV-1 env/SIVmac chimeric viruses expressing divergent HIV-1 envelopes of clinical isolates, facilitates homologous and heterologous evaluation of various recombinant HIV-1 envelope vaccine candidates in lower primates. In this study we compare the in vitro and in vivo infectivity, via intravenous (IV) and intravaginal (IVAG) routes of infection, of stocks of chimeric viruses expressing env from four different clade B HIV-1 isolates. The TCID50/ml was 7.1 x 10(4), 1.0 x 10(4), 6.3 x 10(4), and 1.2 x 10(3) for SHIVsf13, SHIVHan2, SHIVNM-3rn, and SHIVW6.1D, respectively, with a MID50/ml upon IV inoculation of 3.2 x 10(3), 3.2 x 10(4), 3.2 x 10(4), and 3.2 x 10(3), respectively. The same SHIVsf13 stock was infectious after IVAG administration, requiring a 300-fold higher virus dose. Plasma antigenemia and cell-associated viremia were generally highest at weeks 2 or 4 after infection and decreased to subdetectable levels after 8-12 weeks. All infected animals tested developed anti-HIV-1 gp120 antibodies. Inoculated virus dose showed no (linear) quantitative correlation with cellular virus load, duration of viremia, plasma antigenemia, and anti-gp120 antibody titers. No significant changes in peripheral blood CD4 cell levels were observed and none of the animals has shown evidence of disease progression to date (i.e., 13 months postinfection). Four in vivo passages of cell-associated SHIVW6.1D did not result in increased virulence. Vaccine development studies in macaques monkeys have become feasible with the use of various clade B HIV-1 env SHIV chimeras.

Simian immunodeficiency virus Nef gene regulates the production of 2-LTR circles in vivo

The replication dynamics of simian immunodeficiency virus (SIVmac32H-C8), attenuated through discrete genetic disruption of the nef gene, were compared with the wild-type parental clone (SIVmac32H-J5) using quantitative molecular methods. The primary viraemia of both infections were similar during the first week, but peaked on Day 10 at higher levels for wild-type virus. Viral RNA levels differed most markedly at Day 14. The frequency and levels of viral DNA species, detectable as gag provirus or circular 2-LTR episomes, differed depending on the virus and the lymphoid compartment sampled. 2-LTR circles persisted for prolonged periods in the peripheral blood but were never detected in any SIVmac32H C8-infected tissue, even if positive by gag PCR. Paradoxically, the converse was observed following wild-type infection. 2-LTR circles disappeared from the peripheral blood by Day 42 postinfection but persisted in lymphoid tissues. These findings are discussed in terms of nef and the role and stability of 2-LTR circle forms in vivo.