Resistance of neonatal monkeys to live attenuated vaccine strains of simian immunodeficiency virus.

A major safety concern of using live-attenuated vaccine strategies against AIDS is the potential exposure of neonates or fetuses to vaccine virus from the mother. Here we report that high viral loads and disease were observed in only 2 of 18 neonatal monkeys infected with gene-deleted vaccine strains of simian immunodeficiency virus. Pathogenicity was restricted to neonates born to unvaccinated mothers, that is, lacking maternal immunity, and that received extremely high doses of vaccine virus orally. No in utero transmission of vaccine virus was observed in four neonates born to mothers vaccinated during the second trimester. Our results suggest that the live attenuated vaccine approach should remain a viable option for preventing HIV infection and disease in high-risk human populations.

Neutralizing antibody-independent containment of immunodeficiency virus challenges by DNA priming and recombinant pox virus booster immunizations.

Eight different protocols were compared for their ability to raise protection against immunodeficiency virus challenges in rhesus macaques. The most promising containment of challenge infections was achieved by intradermal DNA priming followed by recombinant fowl pox virus booster immunizations. This containment did not require neutralizing antibody and was active for a series of challenges ending with a highly virulent virus with a primary isolate envelope heterologous to the immunizing strain.

Induction of immune responses and safety profiles in rhesus macaques immunized with a DNA vaccine expressing human prostate specific antigen.

Prostate specific antigen (PSA) is a widely used marker for prostate cancer, which is secreted by normal prostate cells at low levels, but is produced more substantially by cancer cells. We have previously reported on the use of a DNA vaccine construct that encodes for human PSA gene to elicit host immune responses against cells producing PSA. DNA immunization strategy delivers DNA constructs encoding for a specific immunogen into the host, who becomes the in vivo protein source for the production of antigen. This antigen then is the focus of the resulting immune response. In this study, we examine the induction of immune responses and safety profiles in rhesus macaques immunized with DNA-based PSA vaccine. We observed induction of PSA-specific humoral response as well as positive PSA-specific lymphoproliferative (LPA) response in the vaccinated macaques. We also observed that the stimulated T cells from the PSA-immunized rhesus macaques produced higher levels of Th1 type cytokine IFN-gamma than the control vector immunized animals. On the other hand, DNA immunization did not result in any adverse effects in the immunized macaques, as indicated by complete blood counts, leukocyte differentials and hepatic and renal chemistries. The macaques appeared healthy, without any physical signs of toxicity throughout the observation period. In addition, we did not observe any adverse effect on the vaccination site. The apparent safety and immunogenecity of DNA immunization in this study suggest that further evaluation of this vaccination strategy is warranted.

Engineering enhancement of immune responses to DNA-based vaccines in a prostate cancer model in rhesus macaques through the use of cytokine gene adjuvants.

DNA immunization is an important vaccination technique that is being explored as an immunotherapeutic strategy against a variety of infectious diseases as well as cancer. We have been investigating the utility of DNA-based vaccine strategy against prostate cancer. We have developed a DNA vaccine construct that encodes for the human prostate specific antigen (PSA) gene. PSA expression is limited to prostate cells, and the level of PSA expression is substantially increased in prostate cancer cells. This tissue specificity makes PSA a potential target for the development of immunotherapies against prostate cancer. A DNA-based PSA vaccine was used to elicit PSA-specific host immune responses in rodent and nonhuman primate models. In an effort to enhance the clinical utility of the DNA-based PSA vaccine, we also examined the use of cytokine gene adjuvants to modulate vaccine-induced immune responses in these animal models. We observed that pCPSA vaccine-induced humoral and cellular immune responses can be modulated through the coimmunization with cytokine genes in mice, and these enhancement effects on the PSA-specific cellular responses were extended in macaques. More specifically, coimmunization with interleukin (IL)-2 cDNA construct resulted in a significant enhancement of PSA-specific antibody responses in both mice and macaque models. In contrast, coinjection of IL-12 resulted in reduction of antibody responses in both models. In mice, the groups coimmunized with IL-2, IL-12, or IL-18 showed a dramatic increase in T helper cell proliferation over the results with pCPSA alone. These results support that further evaluation of this vaccination strategy to treat prostate cancer is warranted.

Effect of a cellulose acetate phthalate topical cream on vaginal transmission of simian immunodeficiency virus in rhesus monkeys.

Human immunodeficiency virus type 1 (HIV-1) infection continues to spread in developing countries, mostly through heterosexual transmission. The development of a safe and cost-effective topical microbicide, effective against a range of STDs including HIV-1, would greatly impact the ongoing epidemic. When formulated in a vehicle, a micronized form of cellulose acetate phthalate (CAP), which is an inactive pharmaceutical excipient, has been shown to inactivate HIV-1, herpes simplex virus types 1 and 2, cytomegalovirus, Neisseria gonorrhoeae, Trichomonas vaginalis, Haemophilus ducreyi, and Chlamydia trachomatis in vitro. Formulated CAP was also shown to be effective against herpes simplex virus type 2 in vivo. Here we show that a formulation of CAP protected four of six rhesus monkeys from vaginal infection with simian immunodeficiency virus. Thus, CAP may be a candidate for use as a topical microbicide for preventing HIV-1 infection in humans.

Modulation of antigen-specific cellular immune responses to DNA vaccination in rhesus macaques through the use of IL-2, IFN-gamma, or IL-4 gene adjuvants.

Extensive experiments have shown DNA vaccines' ability to elicit immune responses in vivo in a safe and well-tolerated manner in several model systems, including rodents and non-human primates. As the DNA-based vaccine and immunotherapy approaches are being explored in humans, significant efforts have also been focused on further improving the immune potency of this technology. One strategy to enhance immune responses for DNA vaccines is the use of molecular or genetic adjuvants. These molecular adjuvant constructs (which encodes for immunologically important molecules such as cytokines) can be co-administered along with DNA vaccine constructs. Once delivered, these adjuvants have shown to modulate the magnitude and direction (humoral or cellular) of the vaccine-induced immune responses in rodent models. To date, however, there has been very little data reported from studies in primates. In this study, we examined the effects of cytokine gene adjuvants to enhance the level of cell-mediated immune responses in rhesus macaques. We co-immunized rhesus macaques with expression plasmids encoding for IL-2, IFN-gamma or IL-4 cytokines along with the DNA vaccine constructs encoding for HIV env/rev (pCEnv) and SIV gag/pol (pCSGag/pol) proteins. We observed that coadministration of IL-2 and IFN-gamma cDNA resulted in enhancement of antigen-specific T cell-mediated immune responses.

Vaccine protection by a triple deletion mutant of simian immunodeficiency virus.

Twelve rhesus monkeys were vaccinated with SIVmac316 delta nef (lacking nef sequences), and 12 were vaccinated with SIVmac239 delta3 (lacking nef, vpr, and upstream sequences in U3). SIVmac316 and SIVmac239 differ by only eight amino acids in the envelope; these changes render SIVmac316 highly competent for replication in macrophages. Seventeen of the animals developed persistent infections with the vaccine viruses. Seven of the 24 vaccinated animals, however, developed infections that were apparently transient in nature. Six of these seven yielded virus from peripheral blood when tested at weeks 2 and/or 3, three of the seven had transient antibody responses, but none of the seven had persisting antibody responses. The 24 monkeys were challenged in groups of four with 10 rhesus monkey infectious doses of wild-type, pathogenic SIVmac251 at weeks 8, 20, and 79 following receipt of vaccine. None of the seven with apparently transient infections with vaccine virus were protected upon subsequent challenge. Analysis of cell-associated viral loads, CD4+ cell counts, and viral gene sequences present in peripheral blood in the remainder of the monkeys following challenge allowed a number of conclusions. (i) There was a trend toward increased protection with length of time of vaccination. (ii) Solid vaccine protection was achieved by 79 weeks with the highly attenuated SIV239 delta3. (iii) Solid long-term protection was achieved in at least two animals in the absence of complete sterilizing immunity. (iv) Genetic backbone appeared to influence protective capacity; animals vaccinated with SIV239 delta3 were better protected than animals receiving SIV316 delta nef. This better protection correlated with increased levels of the replicating vaccine strain. (v) The titer of virus-neutralizing activity in serum on the day of challenge correlated with protection when measured against a primary stock of SIVmac251 but not when measured against a laboratory-passaged stock. The level of binding antibodies to whole virus by enzyme-linked immunosorbent assay also correlated with protection.

Effect of 3-hydroxyphthaloyl-beta-lactoglobulin on vaginal transmission of simian immunodeficiency virus in rhesus monkeys.

Heterosexual transmission of human immunodeficiency virus type 1 (HIV-1) is the major cause of the ongoing AIDS epidemic. Application of chemical barrier methods is expected to contribute to the worldwide control of this epidemic. Bovine beta-lactoglobulin modified by 3-hydroxyphthalic anhydride (3-hydroxyphthalovyl-beta-lactoglobulin [3HP-beta-LG]) was shown to inhibit HIV-1, HIV-2, simian immunodeficiency virus (SIV), herpes simplex virus type 1 and 2, and Chlamydia trachomatis infection in vitro. Here, we show that 3HP-beta-LG not formulated into any vehicle protected three of six rhesus monkeys against vaginal infection by SIV. Incorporation of the compound into an appropriate vehicle is expected to increase the degree of protection. 3HP-beta-LG may be effective as a vaginal inhibitor of HIV-1 infection in humans.

Highly attenuated vaccine strains of simian immunodeficiency virus protect against vaginal challenge: inverse relationship of degree of protection with level of attenuation.

Three different deletion mutants of simian immunodeficiency virus (SIV) that vary in their levels of attenuation were tested for the ability to protect against mucosal challenge with pathogenic SIV. Four female rhesus monkeys were vaccinated by intravenous inoculation with SIVmac239Delta3, four with SIVmac239Delta3X, and four with SIVmac239Delta4. These three vaccine strains exhibit increasing levels of attenuation: Delta3 < Delta3X

Protection from immunodeficiency virus challenges in rhesus macaques by multicomponent DNA immunization.

Multicomponent DNA vaccines were used to elicit immune responses, which can impact viral challenge in three separate rhesus macaque models. Eight rhesus macaques were immunized with DNA vaccines for HIV env/rev and SIV gag/pol and were challenged intravenously with 10 animal infective doses (AID(50)) of cell-free SHIV IIIB. Three of eight immunized rhesus macaques were protected, exhibiting no detectable virus. Animals protected from nonpathogenic SHIVIIIB challenge were rested for extended periods of time and were rechallenged first with pathogenic SIV(mac239) and subsequently with pathogenic SHIV89.6P viruses. Following the pathogenic challenges, all three vaccinated animals were negative for viral coculture and antigenemia and were negative by PCR. In contrast, the control animals exhibited antigenemia by 2 weeks postchallenge and exhibited greater than 10 logs of virus/10(6) cells in limiting dilution coculture. The control animals exhibited CD4 cell loss and developed SIV-related wasting with high viral burden and subsequently failed to thrive. Vaccinated animals remained virus-negative and were protected from the viral load, CD4 loss, disease, and death. We observed strong Th1-type cellular immune responses in the protected macaques throughout the study, suggesting their important roles in protection. These studies support the finding that multicomponent DNA vaccines can directly impact viral replication and disease in a highly pathogenic challenge system, thus potentially broadening our strategies against HIV.

Modulation of antigen-specific humoral responses in rhesus macaques by using cytokine cDNAs as DNA vaccine adjuvants.

An important limitation of DNA immunization in nonhuman primates is the difficulty in generating high levels of antigen-specific antibody responses; strategies to enhance the level of immune responses to DNA immunization may be important in the further development of this vaccine strategy for humans. We approached this issue by testing the ability of molecular adjuvants to enhance the levels of immune responses generated by multicomponent DNA vaccines in rhesus macaques. Rhesus macaques were coimmunized intramuscularly with expression plasmids bearing genes encoding Th1 (interleukin 2 [IL-2] and gamma interferon)- or Th2 (IL-4)-type cytokines and DNA vaccine constructs encoding human immunodeficiency virus Env and Rev and simian immunodeficiency virus Gag and Pol proteins. We observed that the cytokine gene adjuvants (especially IL-2 and IL-4) significantly enhanced antigen-specific humoral immune responses in the rhesus macaque model. These results support the assumption that antigen-specific responses can be engineered to a higher and presumably more desirable level in rhesus macaques by genetic adjuvants.

Antigen-specific humoral and cellular immune responses can be modulated in rhesus macaques through the use of IFN-gamma, IL-12, or IL-18 gene adjuvants.

DNA or nucleic acid immunization has been shown to induce both antigen-specific cellular and humoral immune responses in vivo. Moreover, immune responses induced by DNA immunization can be enhanced and modulated by the use of molecular adjuvants. To engineer the immune response in vivo towards more T-helper (Th)1-type cellular responses, we investigated the co-delivery of inteferon (IFN)-gamma, interleukin (IL)-12, and IL-18 genes along with DNA vaccine constructs. We observed that both antigen-specific humoral and cellular immune responses can be modulated through the use of cytokine adjuvants in mice. Most of this work has been performed in rodent models. There has been little confirmation of this technology in primates. We also evaluated the immunomodulatory effects of this approach in rhesus macaques, since non-human primates represent the most relevant animal models for human immunodeficiency virus (HIV) vaccine studies. As in the murine studies, we also observed that each Th1 cytokine adjuvant distinctively regulated the level of immune responses generated. Co-immunization of IFN-gamma and IL-18 in macaques enhanced the level of antigen-specific antibody responses. Similarly, co-delivery of IL-12 and IL-18 also enhanced the level of antigen-specific Th proliferative responses. These results extend this adjuvant strategy in a more relevant primate model and support the potential utility of these molecular adjuvants in DNA vaccine regimens.

Characterization of primary isolate-like variants of simian-human immunodeficiency virus.

Several different strains of simian-human immunodeficiency virus (SHIV) that contain the envelope glycoproteins of either T-cell-line-adapted (TCLA) strains or primary isolates of human immunodeficiency virus type 1 (HIV-1) are now available. One of the advantages of these chimeric viruses is their application to studies of HIV-1-specific neutralizing antibodies in preclinical AIDS vaccine studies in nonhuman primates. In this regard, an important consideration is the spectrum of antigenic properties exhibited by the different envelope glycoproteins used for SHIV construction. The antigenic properties of six SHIV variants were characterized here in neutralization assays with recombinant soluble CD4 (rsCD4), monoclonal antibodies, and serum samples from SHIV-infected macaques and HIV-1-infected individuals. Neutralization of SHIV variants HXBc2, KU2, 89.6, and 89.6P by autologous and heterologous sera from SHIV-infected macaques was restricted to an extent that these viruses may be considered heterologous to one another in their major neutralization determinants. Little or no variation was seen in the neutralization determinants on SHIV variants 89.6P, 89.6PD, and SHIV-KB9. Neutralization of SHIV HXBc2 by sera from HXBc2-infected macaques could be blocked with autologous V3-loop peptide; this was less true in the case of SHIV 89.6 and sera from SHIV 89.6-infected macaques. The poorly immunogenic but highly conserved epitope for monoclonal antibody IgG1b12 was a target for neutralization on SHIV variants HXBc2, KU2, and 89.6 but not on 89.6P and KB9. The 2G12 epitope was a target for neutralization on all five SHIV variants. SHIV variants KU2, 89.6, 89.6P, 89.6PD, and KB9 exhibited antigenic properties characteristic of primary isolates by being relatively insensitive to neutralization in peripheral blood mononuclear cells with serum samples from HIV-1-infected individuals and 12-fold to 38-fold less sensitive to inhibition with recombinant soluble CD4 than TCLA strains of HIV-1. The utility of nonhuman primate models in AIDS vaccine development is strengthened by the availability of SHIV variants that are heterologous in their neutralization determinants and exhibit antigenic properties shared with primary isolates.