There is an urgent need for active immunization strategies that, if administered shortly after birth, could protect infants in developing countries from acquiring human immunodeficiency virus (HIV) infection through breast-feeding. Better knowledge of the immunogenic properties of vaccine candidates in infants and of the effect of maternal antibodies on vaccine efficacy will aid in the development of such a neonatal HIV vaccine. Simian immunodeficiency virus (SIV) infection of infant macaques is a useful animal model of pediatric HIVinfection with which to address these questions. Groups of infant macaques were immunized at birth and 3 weeks of age with either modified vaccinia virus Ankara (MVA) expressing SIV Gag, Pol, and Env (MVASIVgpe) or live-attenuated SIVmac1A11. One MVA-SIVgpe-immunized group had maternally derived anti-SIV antibodies prior to immunization. Animals were challenged orally at 4 weeks of age with a genetically heterogeneous stock of virulent SIVmac251. Although all animals became infected, the immunized animals mounted better antiviral antibody responses, controlled virus levels more effectively, and had a longer diseasefree survival than the unvaccinated infected monkeys. Maternal antibodies did not significantly reduce the efficacy of the MVA-SIVgpe vaccine. In conclusion, although the tested vaccines delayed the onset of AIDS, further studies are warranted to determine whether a vaccine that elicits stronger early immune responses at the time of virus exposure may be able to prevent viral infection or AIDS in infants.

A better understanding of the host and viral factors associated with human immunodeficiency virus (HIV) transmission is essential to developing effective strategies to curb the global HIV epidemic. Here we used the rhesus macaque-simian immunodeficiency virus (SIV) animal model of HIV infection to study the range of viral genotypes that are transmitted by different routes of inoculation and by different types of viral inocula. Analysis of transmitted variants was undertaken in outbred rhesus macaques inoculated intravenously (IV) or intravaginally (IVAG) with a genetically heterogeneous SIVmac251 stock derived from a well-characterized rhesus macaque viral isolate. In addition, we performed serial IV and IVAG passage experiments using plasma from SIV-infected macaques as the inoculum. We analyzed the V1-V2 region of the SIV envelope gene from virion-associated RNA in plasma from infected animals by the heteroduplex mobility assay (HMA) and by DNA sequence analysis. We found that a more diverse population of SIV genetic variants was present in the earliest virus-positive plasma samples from all five IV SIVmac251-inoculated monkeys and from two of five IVAG SIVmac251-inoculated monkeys. In contrast, we found a relatively homogeneous population of SIV envelope variants in three of five monkeys inoculated IVAG with SIVmac251 stock and in two monkeys infected after IVAG inoculation with plasma from an SIV-infected animal. In some IVAG-inoculated animals, the transmitted SIV variant was the most common variant in the inoculum. However, a specific viral variant in the SIVmac251 stock was not consistently transmitted by IVAG inoculation. Thus, it is likely that host factors or stochastic processes determine the specific viral variants that infect an animal after IVAG SIV exposure. In addition, our results clearly demonstrate that the route of inoculation is associated with the extent and breadth of the genetic complexity of the viral variant population in the earliest stages of systemic infection.

Four types of experiential learning approaches used for predoctoral graduate students and postdoctoral scholars in the biomedical sciences are described and associated learning objectives and evaluation strategies are compared. This framework will help other institutions design and deliver experiential learning programs for career training.

We used the rhesus macaque model of heterosexual human immunodeficiency virus (HIV) transmission to test the hypothesis that in vitro measures of macrophage tropism predict the ability of a primate lentivirus to initiate a systemic infection after intravaginal inoculation. A single atraumatic intravaginal inoculation with a T-cell-tropic molecular clone of simian immunodeficiency virus (SIV), SIVmac239, or a dualtropic recombinant molecular clone of SIV, SIVmac239/1A11/239, or uncloned dualtropic SIVmac251 or uncloned dualtropic simian/human immunodeficiency virus (SHIV) 89.6-PD produced systemic infection in all rhesus macaques tested. However, vaginal inoculation with a dualtropic molecular clone of SIV, SIVmac1A11, resulted in transient viremia in one of two rhesus macaques. It has previously been shown that 12 intravaginal inoculations with SIVmac1A11 resulted in infection of one of five rhesus macaques (

The simian immunodeficiency virus (SIV)-newborn rhesus macaque model of AIDS can be used to study directly the virulence of viral mutants which are resistant to antiviral drugs. A viral mutant called SIVmac79A6.1, isolated from an SIV-infected macaque after prolonged zidovudine treatment, was found to have a double-base-pair change at codon 151 of reverse transcriptase, resulting in a glutamine to methionine substitution (Q151M). This mutation was associated with more than 100-fold increased resistance to zidovudine and low-level cross-resistance to other dideoxynucleoside analogs. To determine whether this Q151M mutation affects viral virulence, four newborn macaques were inoculated intravenously with a biological clone of this drug-resistant SIVmac79A6.1 mutant; two of these animals were also treated orally with zidovudine. All four animals showed persistent viremia, and two of the four animals developed fatal immunodeficiency at 3 and 8 months of age, respectively. The remaining two animals had CD4 ؉ T-cell depletion and clinical symptoms of AIDS at 22 months. No phenotypic or genotypic reversion of virus to the wild type could be detected in any of the four animals. These results demonstrate that the Q151M mutation in SIV reverse transcriptase does not reduce viral virulence. MATERIALS AND METHODS Biological cloning of AZT-resistantSIVmac. An AZT-resistant virus isolate, obtained from an SIV-infected infant macaque after prolonged AZT treatment (as described previously [47]), was serially diluted and cultured with CEMϫ174 cells in 96-well plates (at eight replicates per dilution) in the presence of 60 M AZT. After 5 days, cell-free supernatants from individual wells containing the highest dilution that had detectable p27 by an antigen-capture enzyme-linked immunosorbent assay (ELISA) (16) were briefly propagated on CEMϫ174 cells and were serially diluted to infect the next round of CEMϫ174 cells. After three rounds of limiting dilution culture, the biological clone SIVmac79A6.1 with highly reduced susceptibility to AZT was isolated.Animal procedures. Four newborn rhesus macaques (Macaca mulatta) from type D retrovirus-and SIV-seronegative dams at the California Regional Pri-* Corresponding author. Mailing address: California Regional Pri-