Early induction of polyfunctional simian immunodeficiency virus (SIV)-specific T lymphocytes and rapid disappearance of SIV from lymph nodes of sooty mangabeys during primary infection.

Although the cellular immune response is essential for controlling SIV replication in Asian macaques, its role in maintaining nonpathogenic SIV infection in natural hosts such as sooty mangabeys (SM) remains to be defined. We have previously shown that similar to rhesus macaques (RM), SM are able to mount a T lymphocyte response against SIV infection. To investigate early control of SIV replication in natural hosts, we performed a detailed characterization of SIV-specific cellular immunity and viral control in the first 6 mo following SIV infection in SM. Detection of the initial SIV-specific IFN-γ ELISPOT response in SIVsmE041-infected SM coincided temporally with a decline in peak plasma viremia and was similar in magnitude, specificity, and breadth to SIVsmE041-infected and SIVmac239-infected RM. Despite these similarities, SM showed a greater reduction in postpeak plasma viremia and a more rapid disappearance of productively SIV-infected cells from the lymph node compared with SIVmac239-infected RM. The early Gag-specific CD8(+) T lymphocyte response was significantly more polyfunctional in SM compared with RM, and granzyme B-positive CD8(+) T lymphocytes were present at significantly higher frequencies in SM even prior to SIV infection. These findings suggest that the early SIV-specific T cell response may be an important determinant of lymphoid tissue viral clearance and absence of lymph node immunopathology in natural hosts of SIV infection.

Tissue-specific reduction in DC-SIGN expression correlates with progression of pathogenic simian immunodeficiency virus infection.

Studies were undertaken to determine whether previously described reductions in splenic DC-SIGN expression in simian acquired immune deficiency syndrome (AIDS) are limited to pathogenic simian immunodeficiency virus (SIV) infection. DC-SIGN expression was evaluated by immunohistochemistry in lymphoid tissues from AIDS-susceptible Asian macaque monkeys as compared with AIDS-resistant sooty mangabey monkeys in the presence and absence of SIV infection. The phenotype of DC-SIGN+ cells in susceptible and resistant species was identical and most consistent with macrophage identity. Significantly lower levels of DC-SIGN expression were identified in spleen, mesenteric lymph node, and bone marrow of macaques with AIDS (P<0.05). Reduced levels of splenic DC-SIGN correlated significantly with CD4T cell depletion in long-term pathogenic infection of macaques (P<0.01), whereas SIV-infected mangabeys retained high levels of DC-SIGN expression in spleen despite persistent infection. Reduced expression of DC-SIGN in spleen specifically characterizes pathogenic forms of SIV infection, correlates with disease progression, and may contribute to SIV pathogenesis.

Dose-response model for Listeria monocytogenes-induced stillbirths in nonhuman primates.

A dose-response model using rhesus monkeys as a surrogate for pregnant women indicates that oral exposure to 10(7) CFU of Listeria monocytogenes results in about 50% stillbirths. Ten of 33 pregnant rhesus monkeys exposed orally to a single dose of 10(2) to 10(10) CFU of L. monocytogenes had stillbirths. A log-logistic model predicts a dose affecting 50% of animals at 10(7) CFU, comparable to an estimated 10(6) CFU based on an outbreak among pregnant women but much less than the extrapolated estimate (10(13) CFU) from the FDA-U.S. Department of Agriculture-CDC risk assessment using an exponential curve based on mouse data. Exposure and etiology of the disease are the same in humans and primates but not in mice. This information will aid in risk assessment, assist policy makers, and provide a model for mechanistic studies of L. monocytogenes-induced stillbirths.

Dynamics of T- and B-lymphocyte turnover in a natural host of simian immunodeficiency virus.

Increased lymphocyte turnover is a hallmark of pathogenic lentiviral infection. To investigate perturbations in lymphocyte dynamics in natural hosts with nonpathogenic simian immunodeficiency virus (SIV) infection, the nucleoside analog bromodeoxyuridine (BrdU) was administered to six naturally SIV-infected and five SIV-negative sooty mangabeys. As a measure of lymphocyte turnover, we estimated the mean death rate by fitting a mathematical model to the fraction of BrdU-labeled cells during a 2-week labeling and a median 10-week delabeling period. Despite significantly lower total T- and B-lymphocyte counts in SIV-infected sooty mangabeys than in SIV-negative mangabeys, the turnover rate of B lymphocytes and CD4(+) and CD8(+) T lymphocytes was not increased in the SIV-infected animals. A small, rapidly proliferating CD45RA(+) memory subset and a large, slower-proliferating CD45RA(-) central memory subset of CD4(+) T lymphocytes identified in the peripheral blood of sooty mangabeys also did not show evidence of increased turnover in the context of SIV infection. Independently of SIV infection, the turnover of CD4(+) T lymphocytes in sooty mangabeys was significantly higher (P < 0.01) than that of CD8(+) T lymphocytes, a finding hitherto not reported in rhesus macaques or humans. The absence of aberrant T-lymphocyte turnover along with an inherently high rate of CD4(+) T-lymphocyte turnover may help to preserve the pool of central memory CD4(+) T lymphocytes in viremic SIV-infected sooty mangabeys and protect against progression to AIDS.

Live attenuated Listeria monocytogenes expressing HIV Gag: immunogenicity in rhesus monkeys.

Induction of strong cellular immunity will be important for AIDS vaccine candidates. Natural infection with wild-type Listeria monocytogenes (Lm), an orally transmitted organism, is known to generate strong cellular immunity, thus raising the possibility that live attenuated Lm could serve as a vaccine vector. We sought to examine the potential of live attenuated Lm to induce cellular immune responses to HIV Gag. Rhesus macaques were immunized with Lmdd-gag that expresses HIV gag and lacks two genes in the D-alanine (D-ala) synthesis pathway. Without this key component of the bacterial cell wall, vaccine vector replication critically depends on exogenous D-ala. Lmdd-gag was given to animals either solely orally or by oral priming followed by intramuscular (i.m.) boosting; D-ala was co-administered with all vaccinations. Lmdd-gag and D-ala were well tolerated. Oral priming/oral boosting induced Gag-specific cellular immune responses, whereas oral priming/i.m. boosting induced systemic as well as mucosal anti-Gag antibodies. These results suggest that the route of vaccination may bias anti-Gag immune responses either towards T-helper type 1 (Th1) or Th2 responses; overall, our data show that live attenuated, recombinant Lmdd-gag is safe and immunogenic in primates.

Depletion of CD8+ cells in sooty mangabey monkeys naturally infected with simian immunodeficiency virus reveals limited role for immune control of virus replication in a natural host species.

SIV infection of sooty mangabeys (SMs), a natural host species, does not cause AIDS despite high-level virus replication. In contrast, SIV infection of nonnatural hosts such as rhesus macaques (RMs) induces an AIDS-like disease. The depletion of CD8+ T cells during SIV infection of RMs results in marked increases in plasma viremia, suggesting a key role for CD8+ T cells in controlling levels of SIV replication. To assess the role that CD8+ T cells play in determining the virologic and immunologic features of nonpathogenic SIV infection in SMs, we transiently depleted CD8+ T cells in SIV-infected and uninfected SMs using a CD8alpha-specific Ab (OKT8F) previously used in studies of SIV-infected RMs. Treatment of SMs with the OKT8F Ab resulted in the prompt and profound depletion of CD8+ T cells. However, in contrast to CD8+ cell depleted, SIV-infected RMs, only minor changes in the levels of plasma viremia were observed in most SIV-infected SMs during the period of CD8+ cell deficiency. Those SMs demonstrating greater increases in SIV replication following CD8+ cell depletion also displayed higher levels of CD4+ T cell activation and/or evidence of CMV reactivation, suggesting that an expanded target cell pool rather than the absence of CD8+ T cell control may have been primarily responsible for transient increases in viremia. These data indicate that CD8+ T cells exert a limited influence in determining the levels of SIV replication in SMs and provide additional evidence demonstrating that the absence of AIDS in SIV-infected SMs is not due to the effective control of viral replication by cellular immune responses.

Pharmacokinetics of the anti-human immunodeficiency virus agent 1-(beta-D-dioxolane)thymine in rhesus monkeys.

Beta-D-dioxolane-thymine (D-DOT) has potent and selective in vitro activity against several clinically important resistant human immunodeficiency virus (HIV) mutants and is in advanced preclinical development. Therefore, the single-dose intravenous and oral pharmacokinetics of D-DOT were studied with three rhesus monkeys. The pharmacokinetic profiles of D-DOT in serum and urine were adequately described by a two-compartment open pharmacokinetic model. D-DOT was rapidly and almost completely absorbed (absorption rate constant = 2.7 h(-1); fraction of oral dose absorbed = 0.82 to 1.06). The average serum beta half-life was 2.16 h. The average central and steady-state volumes of distributions were 0.52 and 1.02 liter/kg of body weight, respectively, and the average systemic and renal clearance values were 0.36 liter/h/kg and 0.18 liter/h/kg. Four or eight percent of administered D-DOT was eliminated in the urine as glucuronide within 8 h after intravenous or oral administration, respectively. D-DOT reached levels in the cerebrospinal fluid in excess of 10 to 20 times the median effective concentration for wild-type HIV and resistant mutants. The potent antiretroviral activity of D-DOT against a lamivudine- and zidovudine-resistant HIV-1 mutant, together with an excellent pharmacokinetic profile for rhesus monkeys, suggest that further development is warranted.

Coinfection with Schistosoma mansoni reactivates viremia in rhesus macaques with chronic simian-human immunodeficiency virus clade C infection.

We tested the hypothesis that helminth parasite coinfection would intensify viremia and accelerate disease progression in monkeys chronically infected with an R5 simian-human immunodeficiency virus (SHIV) encoding a human immunodeficiency virus type 1 (HIV-1) clade C envelope. Fifteen rhesus monkeys with stable SHIV-1157ip infection were enrolled into a prospective, randomized trial. These seropositive animals had undetectable viral RNA and no signs of immunodeficiency. Seven animals served as virus-only controls; eight animals were exposed to Schistosoma mansoni cercariae. From week 5 after parasite exposure onward, coinfected animals shed eggs in their feces, developed eosinophilia, and had significantly higher mRNA expression of the T-helper type 2 cytokine interleukin-4 (P = 0.001) than animals without schistosomiasis. Compared to virus-only controls, viral replication was significantly increased in coinfected monkeys (P = 0.012), and the percentage of their CD4(+) CD29(+) memory cells decreased over time (P = 0.05). Thus, S. mansoni coinfection significantly increased viral replication and induced T-cell subset alterations in monkeys with chronic SHIV clade C infection.

Time dependence of protective post-exposure prophylaxis with human monoclonal antibodies against pathogenic SHIV challenge in newborn macaques.

In a primate model of postnatal virus transmission, we have previously shown that 1 h post-exposure prophylaxis (PEP) with a triple combination of neutralizing monoclonal antibodies (nmAbs) conferred sterilizing protection to neonatal macaques against oral challenge with pathogenic simian-human immunodeficiency virus (SHIV). Here, we show that nmAbs can also partially protect SHIV-exposed newborn macaques against infection or disease, when given as 12 or 24 h PEP, respectively. This work delineates the potential and the limits of passive immunoprophylaxis with nmAbs. Even though 24 h PEP with nmAbs did not provide sterilizing immunity to neonatal monkeys, it contained viremia and protected infants from acute disease. Taken together with our results from other PEP studies, these data show that the success of passive immunization depends on the nmAb potency/dose and the time window between virus exposure and start of immunotherapy.

Studies on GM-CSF DNA as an adjuvant for neutralizing Ab elicited by a DNA/MVA immunodeficiency virus vaccine.

Here, we use a vaccine consisting of DNA priming followed by MVA boosting in rhesus macaques to investigate the ability of GM-CSF DNA to serve as an adjuvant for the elicitation of neutralizing Ab against an HIV-1 Env. The trial used Gag, Pol, and Env sequences from SHIV-89.6 in the immunogens and a neutralization escape variant of SHIV-89.6, SHIV-89.6P, for challenge. Co-delivery of GM-CSF and vaccine DNAs enhanced the temporal appearance of neutralizing Ab and broadened the specificity of the neutralizing activity to include SHIV-89.6P. Two long-term SHIV-89.6 infections elicited neutralizing activity for SHIV-89.6 but not SHIV-89.6P. Studies on the avidity of the anti-Env antisera revealed that the GM-CSF-adjuvanted vaccine had elicited higher avidity Ab than the non-adjuvanted vaccine or the infection. The GM-CSF-adjuvanted group showed a trend towards better control of the challenge infection and had better control of re-emergent virus (P < 0.01) than the non-adjuvanted group.

Isolation and characterization of a new simian rotavirus, YK-1.

BACKGROUND: To effectively analyze the requirements for protection to rotavirus infection, a reliable animal model that reasonably mimics infection and disease in humans is needed. A requirement for an effective animal model is the availability of appropriate rotavirus stocks for challenge. RESULTS: A new simian rotavirus, designated YK-1, was isolated from a 2-year-old immunodeficient pigtailed macaque with chronic diarrhea. YK-1 was distinguishable by electropherotype from the other simian rotavirus strains, SA11 and RRV. One variant of YK-1, clone 311, which was isolated after adaptation and plaque purification in cell cultures, displayed an unusual RNA electropherotype with an abnormally migrating gene 11 segment. Sequence analysis demonstrated a genetic rearrangement that involved a partial duplication of the gene 11 ORF encoding NSP5. YK-1 was identified as a Group A rotavirus belonging to subgroup 1. To further characterize the YK-1 strain, the genes encoding VP4, VP7, and NSP4 were sequenced. Analysis of VP4 and VP7 gene fragments suggests that this strain is a G3P3 rotavirus and is closely related to the simian rotavirus strain RRV. Serotype analysis also identified YK-1 as a G3 rotavirus. The NSP4 genotype of YK-1 is C, the same genotype as RRV. CONCLUSION: This newly isolated rotavirus, YK-1, is being used to establish a nonhuman primate model for studying the infectivity, immunity, and pathogenesis of rotavirus and for evaluating candidate rotavirus vaccines.

The AIDS resistance of naturally SIV-infected sooty mangabeys is independent of cellular immunity to the virus.

In contrast to human immunodeficiency virus (HIV)-infected humans, natural hosts for simian immunodeficiency virus (SIV) very rarely progress to acquired immunodeficiency syndrome (AIDS). While the mechanisms underlying this disease resistance are still poorly understood, a consistent feature of natural SIV infection is the absence of the generalized immune activation associated with HIV infection. To investigate the immunologic mechanisms underlying the absence of AIDS in SIV-infected sooty mangabeys (SMs), a natural host species, we performed a detailed analysis of the SIV-specific cellular immune responses in 110 SIV-infected SMs. We found that while SIV-specific T-cell responses are detectable in the majority of animals, their magnitude and breadth are, in fact, lower than what has been described in HIV-infected humans, both in terms of cytokine production (ie, IFN-gamma, TNF-alpha, and IL-2) and degranulation (ie, CD107a expression). Of importance, SIV-specific T-cell responses were similarly low when either SIVmac239-derived peptides or autologous SIVsmm peptides were used as stimuli. No correlation was found between SIV-specific T-cell responses and either viral load or CD4+ T-cell count, or between these responses and markers of T-cell activation and proliferation. These findings indicate that the absence of AIDS in naturally SIV-infected sooty mangabeys is independent of a strong cellular immune response to the virus.

Widely varying SIV prevalence rates in naturally infected primate species from Cameroon.

Although it is now well established that a substantial proportion of wild-living primates in sub-Saharan Africa harbor SIV, no study to date has examined to what extent the various species are naturally infected. In this study, we first describe the development and validation of sensitive and specific SIV antibody detection assays representing all major known primate lentiviral lineages on a panel of 207 sera from 11 different primate species with known infection status. The newly developed assays were then used to determine SIV prevalence rates in nine primate species native to Cameroon. Analysis of 722 sera revealed widely varying prevalence rates, ranging from an apparent absence of SIV infection in crested mona (0/70), grey cheeked (0/36) and agile mangabeys (0/92), to prevalence rates of 3%, 4%, 11%, 27%, 39% and 52% for mustached (6/203), greater spot-nosed (8/193), northern talapoin (3/26), mantled guereza (14/52), De Brazza's (9/23) and mandrill (14/27) monkeys, respectively. The epidemiology of naturally occurring SIV infections is thus more complex than previously appreciated and the various non-human primate hosts seem to differ in their susceptibility to SIV infection. The newly developed assays should now permit to define with greater accuracy existing SIV reservoirs and associated human zoonotic risk.

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.

Studies using a viral challenge and CD8 T cell depletions on the roles of cellular and humoral immunity in the control of an SHIV-89.6P challenge in DNA/MVA-vaccinated macaques.

Here, we study immune responses in four DNA/MVA-vaccinated macaques following an SHIV-89.6P challenge and a subsequent CD8 cell depletion. Both post-challenge and post-depletion peaks of viremia contracted with the expansion, or re-emergence, of CD8 T cells. Post-depletion, CD8 cells expanded in the presence of higher levels of neutralizing Ab and CD4 help than post-challenge and had superior maturational characteristics as measured by expression of the anti-apoptotic protein Bcl-2, the IL-7 receptor CD127 and co-production of IFN-gamma and IL-2. Pre-challenge and pre-depletion titers of neutralizing Ab correlated inversely with peaks of viremia and directly with peaks for anti-viral CD4 cells. Thus, our results reveal CD8 cells playing a central role, and neutralizing Ab, a supporting role in SHIV-89.6P control. They also suggest a dynamic relationship between neutralizing Ab, antigen load and anti-viral CD4 cells in the maturation of high-quality anti-viral CD8 T cells.

Timely triggering of homeostatic mechanisms involved in the regulation of T-cell levels in SIVsm-infected sooty mangabeys.

Sooty mangabeys, the natural host of simian immunodeficiency virus (SIVsm), generally avoid progressive depletion of CD4+ T cells and opportunistic infections associated with infection of humans (HIV) and macaques (SIVmac). The means by which the SIVsm-infected mangabeys maintain CD4+ T-cell levels despite high rates of viral replication is unknown. One cytokine that has a key role in the regulation of T-cell levels is interleukin-7 (IL-7). Here, the longitudinal assessment of 6 SIVsm-infected mangabeys identified an early increase in plasma IL-7 levels at weeks 1 to 5 after infection. This IL-7 increase correlated with an early decline in CD4+ T-cell levels (decline of 492-1171 cells/microL) accompanying acute viremia. Elevated IL-7 levels were followed by increased T-cell proliferation (Ki67) and maintenance of lower but stable (more than 500 cells/microL) CD4+ T-cell levels in each mangabey through 37 weeks of infection. These data contrast with our earlier studies in SIVmac-infected macaques, in which the IL-7 increase was delayed until 20 to 40 weeks after infection, just before the onset of simian AIDS. Taken together, these data suggest that timely triggering of IL-7 is important for stabilizing healthy T-cell levels in mangabeys and that timely administration of exogenous IL-7 may show benefit during pathogenic SIVmac and HIV infection.

Pharmacology and pharmacokinetics of the antiviral agent beta-D-2',3'-dideoxy-3'-oxa-5-fluorocytidine in cells and rhesus monkeys.

Beta-D-2',3'-dideoxy-3'-oxa-5-fluorocytidine (D-FDOC) is an effective inhibitor of human immunodeficiency virus 1 (HIV-1) and HIV-2, simian immunodeficiency virus, and hepatitis B virus (HBV) in vitro. The purpose of this study was to evaluate the intracellular metabolism of d-FDOC in human hepatoma (HepG2), human T-cell lymphoma (CEM), and primary human peripheral blood mononuclear (PBM) cells by using tritiated compound. By 24 h, the levels of D-FDOC-triphosphate (D-FDOC-TP) were 2.8 +/- 0.4, 6.7 +/- 2.3, and 2.0 +/- 0.1 pmol/10(6) cells in HepG2, CEM, and primary human PBM cells, respectively. Intracellular D-FDOC-TP concentrations remained greater than the 50% inhibitory concentration for HIV-1 reverse transcriptase for up to 24 h after removal of the drug from cell cultures. In addition to d-FDOC-monophosphate (D-FDOC-MP), -diphosphate (D-FDOC-DP), and -TP, D-FDOC-DP-ethanolamine and d-FDOC-DP-choline were detected in all cell extracts as major intracellular metabolites. D-FDOC was not a substrate for Escherichia coli thymidine phosphorylase. No toxicity was observed in mice given D-FDOC intraperitoneally for 6 days up to a dose of 100 mg/kg per day. Pharmacokinetic studies in rhesus monkeys indicated that D-FDOC has a t(1/2) of 2.1 h in plasma and an oral bioavailability of 38%. The nucleoside was excreted unchanged primary in the urine, and no metabolites were detected in plasma or urine. These results suggest that further safety and pharmacological studies are warranted to assess the potential of this nucleoside for the treatment of HIV- and HBV-infected individuals.

Effect of CD8+ lymphocyte depletion on virus containment after simian immunodeficiency virus SIVmac251 challenge of live attenuated SIVmac239delta3-vaccinated rhesus macaques.

Although live attenuated vaccines can provide potent protection against simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus challenges, the specific immune responses that confer this protection have not been determined. To test whether cellular immune responses mediated by CD8+ lymphocytes contribute to this vaccine-induced protection, we depleted rhesus macaques vaccinated with the live attenuated virus SIVmac239Delta3 of CD8+ lymphocytes and then challenged them with SIVmac251 by the intravenous route. While vaccination did not prevent infection with the pathogenic challenge virus, the postchallenge levels of virus in the plasmas of vaccinated control animals were significantly lower than those for unvaccinated animals. The depletion of CD8+ lymphocytes at the time of challenge resulted in virus levels in the plasma that were intermediate between those of the vaccinated and unvaccinated controls, suggesting that CD8+ cell-mediated immune responses contributed to protection. Interestingly, at the time of challenge, animals expressing the Mamu-A*01 major histocompatibility complex class I allele showed significantly higher frequencies of SIV-specific CD8+ T-cell responses and lower neutralizing antibody titers than those in Mamu-A*01- animals. Consistent with these findings, the depletion of CD8+ lymphocytes abrogated vaccine-induced protection, as judged by the peak postchallenge viremia, to a greater extent in Mamu-A*01+ than in Mamu-A*01- animals. The partial control of postchallenge viremia after CD8+ lymphocyte depletion suggests that both humoral and cellular immune responses induced by live attenuated SIV vaccines can contribute to protection against a pathogenic challenge and that the relative contribution of each of these responses to protection may be genetically determined.

Serum IgG mediates mucosal immunity against rotavirus infection.

We evaluated the protective role of passively transferred circulating antibodies in protecting non-human primates against experimental rotavirus infection. Pooled sera with rotavirus-specific IgG titers that were either high (1:10,000), intermediate (1:300), or negative (< 1:25) were infused i.v. into naive pigtailed macaques (ages 3-6 months). Rotavirus-specific IgG could be detected in the sera at 18 h in all animals infused with antibody-containing serum, and fecal IgG titers could be detected only in animals given high-titer pooled sera. When orally challenged with 10(6) fluorescent-forming units of a simian rotavirus strain, YK-1, at 18 h after serum transfer, control animals shed virus starting 1-3 days after challenge and continued to shed virus at high titers for 6-8 days, whereas passively immunized macaques did not shed virus or had delayed shedding at low titers for only a limited time. The observation that passively transferred antibodies can suppress or delay viral infection in rotavirus-challenged pigtailed macaques has important implications for the design and testing of parenteral candidate rotavirus vaccines.

Experimental infection of pigtailed macaques with a simian rotavirus, YK-1.

Experimental rotavirus infection was investigated in pigtailed macaques to study the infectivity, immunity, and pathogenesis of rotavirus. A challenge virus, YK-1, was administered intragastrically to four seronegative macaques (age: 11-16 months). Although none of the monkeys developed diarrhea, an active infection occurred with high titers of rotavirus antigen detected in stools 2-10 days after challenge. These animals developed rotavirus-specific antibody responses similar to those seen following primary exposure to rotavirus. YK-1 was then inoculated in four seropositive macaques (age: 14-16 months). All animals shed viral antigen in their stool, but the titers and duration were significantly less when compared to seronegative macaques. When rechallenged 28 days after initial YK-1 challenge, the macaques demonstrated significant protection against reinfection. All seropositive animals developed a rise in rotavirus-specific serum and fecal antibodies during YK-1 challenge and rechallenge. To independently assess the role of age and preexisting IgG titers to rotavirus, a 4-month-old seronegative and 6-month-old seropositive macaque were inoculated with YK-1. The seronegative macaque shed high titers of virus for 9 days, while the seropositive macaque shed only 3 days and in low titer. These data suggest that a primate model of rotavirus infection using the YK-1 strain may be useful in examining the immune response and protection from infection in pigtailed macaques and indicate that levels and duration of shedding may provide a good measure of protection from natural infection and from that induced by oral or parenteral vaccines.