Elissa J. Schwartz

Highly Active Antiretroviral Therapy and the Epidemic of HIV+ End-Stage Renal Disease

The rise in the number of patients with HIV-associated nephropathy and HIV-infection with end-stage renal disease (HIV+ ESRD) continues to be a substantial concern for the ESRD program. In order to assess the impact of highly active antiretroviral therapy (HAART) on the progression of patients with AIDS to the development of ESRD and to project the prevalence of HIV+ ESRD through 2020, a mathematical model of the dynamics of HIV+ infection in the ESRD population was developed. Epidemiologic data on AIDS and HIV+ ESRD among black individuals in the United States were obtained since 1991 from the Centers for Disease Control and Prevention and US Renal Data System, respectively. The model was constructed to predict the prevalence of HIV+ ESRD incorporating the current rate of growth in AIDS prevalence. Two possible trends were considered: linear AIDS growth and exponential AIDS growth. The likely effectiveness of HAART in slowing progression to HIV+ ESRD was estimated from the best fit of the model to the data after 1995, when HAART was introduced. The model was then used to evaluate recent data and to project the prevalence of HIV+ ESRD through 2020. The model suggested that HAART has reduced the rate of progression from AIDS to HIV+ ESRD by 38%. The model projected an increase in HIV+ ESRD prevalence in the future as a result of the increase in the AIDS population among black individuals. This increase was predicted even assuming a 95% reduction in the progression from AIDS to HIV+ ESRD. Despite the potential benefit of HAART, the prevalence of HIV+ ESRD in the United States is expected to rise in the future as a result of the expansion of the AIDS population among black individuals. It is concluded that prevention of progression to ESRD should focus on early antiretroviral treatment of HIV-infected patients who have evidence of HIV-associated nephropathy.

HIV-1 Nef Induces Proliferation and Anchorage-Independent Growth in Podocytes

HIV-associated nephropathy (HIVAN) is now the third leading cause of end-stage renal disease in the African American population. HIV-1 infects renal tubular and glomerular epithelial cells or podocytes, cells that are a critical part of the filtration barrier. HIV-1 infection induces the loss of podocyte differentiation markers and increases podocyte proliferation. It has been previously shown that HIV-infection induces loss of contact inhibition. Here, the HIV-1 gene responsible for proliferative changes is identified by using cultured podocytes in vitro. The HIV-1 proviral construct, pNL4-3 was rendered noninfectious by replacing the HIV-1 gag/pol sequences with an EGFP reporter gene (pNL4-3: DeltaG/P-EGFP). This construct was then pseudotyped with VSV.G envelope to infect podocytes that were conditionally immortalized with SV-40 T antigen. In addition, mutated constructs were engineered with premature stop codons in the HIV-1 env, vif, vpr, vpu, nef, or rev genes. The parental construct and all the other mutated constructs, with the exception of nef, induced proliferation under nonpermissive conditions and anchorage-independent growth (colony formation in soft agar) under permissive conditions. In contrast, deletion of nef markedly reduced proliferation and colony formation. Although tat alone, or tat plus rev induced marginal levels of anchorage-independent growth, coexpression with nef significantly increased colony formation. Finally, stable expression of Nef in a retroviral vector, pBabe-puro, was sufficient to induce increased proliferation and colony formation. Moreover, nef induced saturation density and loss of contact inhibition. These data indicate that Nef induces multiple proliferative effects in podocytes in culture and that nef may therefore be an important gene in the pathogenesis of HIVAN in vivo.

32 bp CCR-5 gene deletion and resistance to fast progression in HIV-1 infected heterozygotes

there are known racial differences in the frequencies of the PM phenotype: about 3% of whites and in 13–23% of orientals. 3 Poor metabolism results from a defect in the gene associated with the cytochrome P450 isoenzyme, CYP2C19. Two genetic defects, m1 and m2, have been identified: the former accounts for 75–83% of the defective alleles in both white and Japanese PMs, while the latter was found only in Japanese. 4 We determined the distribution of the two CYP2C19 mutations in two Vanuatu islands. In March, 1996, malariometric surveys were conducted on Tanna and Malakula islands. The survey included finger prick sampling of blood for PCR from a capillary tube (75 µL) on to a filter paper. Dried filter-paper samples were collected from 493 people. DNA was extracted from a quarter of a dried blood spot. PCR was conducted as described by de Morais et al, 4 with PCR amplification of exon 5 followed by Sma1 digestion (CYP2C19m1) and amplification of exon 4 followed by BamH1 digestion (CYP2C19m2). The genotypes of the 493 villagers are shown in the table. Remarkably high frequencies of the two mutations were found. The overall frequency of the m1 alleles was 0·708 (698/986), and that of the m2 alleles was 0·133 (131/986). Only 145 individuals had at least one wild-type allele (wt). The observed genotype distribution corresponded well with those estimated from the allele frequencies of CYP2C19m1 and m2 in the study group, in accordance with a Hardy-Weinberg equilibrium (␹ 2-test, p>0·5, power >99%). The population of Tanna Island showed higher frequency of m1 and lower frequency of m2 than that of Malakula Island (p<0·05). In a separate study we correlated proguanil and cycloguanil concentration profiles in whole blood with genotypes in patients with malaria from the same area (unpublished). The results confirm that the genotyping predicted the phenotypes in all 20 patients tested. Thus, the data in the table suggest that 348 (70·6%) individuals have PM phenotype, which may have major implications for the efficacy of proguanil in this population. CYP2C19 is also involved in the metabolism of other drugs such as imipramine, omeprazole, and diazepam. 3 Anthropological evidences suggest that Melanesians are of Mongoloid origin, and the ancestors of the people in Vanuatu may have migrated from Papua New Guinea about 4000 years ago. 5 Therefore, the finding of m2 mutation in Vanuatu is not surprising. However the reasons for the high frequency …

Predicting the Potential Individual- and Population-Level Effects of Imperfect Herpes Simplex Virus Type 2 Vaccines

BACKGROUND The seroprevalence of herpes simplex virus (HSV) type 2 in the United States has increased dramatically since the 1970s. Vaccines are being developed to control the epidemic. We determined the potential public health impact that imperfect, preexposure HSV-2 vaccines could have on reducing the incidence of infection. METHODS We modeled the future impact of preexposure vaccines with both prophylactic and therapeutic properties. We predicted the individual-level (cumulative number of new infections prevented per 1000 vaccinated individuals) and population-level (cumulative percentage reduction in new infections) impact. RESULTS We show that the percentage reduction in incidence of infection would be relatively modest. However, HSV-2 incidence rates are extremely high; thus, we calculate that even imperfect vaccines would prevent >1 million infections in the United States within a decade after introduction. We found that vaccines would prevent 3 times as many infections per vaccinated person in a high-prevalence epidemic than in a moderate-prevalence epidemic. We also identified the vaccine characteristics that have the greatest impact on reducing the incidence of infection. We determined that vaccine take and degree of protection against infection are equally important, whereas therapeutic characteristics are unimportant. CONCLUSIONS Designing preexposure HSV-2 vaccines with therapeutic characteristics will have little impact on reducing the incidence of infection. HSV-2 vaccines will have a substantially greater public health impact in developing than in developed countries.

Predicting the potential impact of a cytotoxic T-lymphocyte HIV vaccine: How often should you vaccinate and how strong should the vaccine be?

To stimulate the immune systems natural defenses, a post-infection HIV vaccination program to regularly boost cytotoxic T-lymphocytes has been proposed. We develop a mathematical model to describe such a vaccination program, where the strength of the vaccine and the vaccination intervals are constant. We apply the theory of impulsive differential equations to show that the model has an orbitally asymptotically stable periodic orbit, with the property of asymptotic phase. We show that, on this orbit, the vaccination frequency can be chosen so that the average number of infected CD4(+) T cells can be made arbitrarily low. We illustrate the results with numerical simulations and show that the model is robust with respect to both the parameter choices and the formulation of the model as a system of impulsive differential equations.

Transmission-dynamic model to capture the indirect effects of infant vaccination with Prevnar (7-valent pneumococcal conjugate vaccine (PCV7)) in older populations

We developed an age-structured, transmission-dynamic, mathematical model to quantify the direct and indirect benefits of infant PCV7 vaccination. The model simulates the acquisition of asymptomatic carriage of Streptococcus pneumoniae and the development of fatal and non-fatal invasive pneumococcal disease (IPD) among vaccinated and unvaccinated individuals aged <2, 2-4, 5-17, 18-49, 50-64, and >or=65 years old. The model was parameterized using published US surveillance data, supplemented with data from published literature. The model predicts the observed incidence of IPD with good agreement and may be used to predict the impact of various vaccination strategies in the US or other populations yet to introduce PCV7.

Differential immunogenicity of vaccinia and HIV-1 components of a human recombinant vaccine in mucosal and blood compartments

Mucosal immune responses induced by HIV-1 vaccines are likely critical for prevention. We report a Phase 1 safety and immunogenicity trial in eight participants using the vaccinia-based TBC-3B vaccine given subcutaneously to determine the relationship between HIV-1 specific systemic and gastrointestinal mucosal responses. Across all subjects, detectable levels of blood vaccinia- and HIV-1-specific antibodies were elicited but none were seen mucosally. While the vaccinia component was immunogenic for CD8(+) T lymphocyte (CTL) responses in both blood and mucosa, it was greater in blood. The HIV-1 component of the vaccine was poorly immunogenic in both blood and mucosa. Although only eight volunteers were studied intensively, the discordance between mucosal and blood responses may highlight mechanisms contributing to recent vaccine failures.

Effect of target cell availability on HIV-1 production in vitro

Objective The recovery of CD4 target cells following antiretroviral therapy may facilitate virus production and escape from antiretroviral suppression. To address this hypothesis, we directly examined whether the CD4 target cell number increases viral production in the presence of suboptimal therapy. Design The effect of the CD4 T cell number on HIV-1 replication with a suboptimal dose of zidovudine was studied in vitro. Methods Varying numbers of CD4 T cells were infected with HIV-1 and treated with 1 nM zidovudine. Virus production was measured by p24 antigen capture enzyme-linked immunosorbent assay. Partial sequencing of HIV-1 pol was performed to assess zidovudine-resistant mutations. Results Wild type virus production was found to increase eightfold in cultures with 100 × 104 cells compared with cultures with 10 × 104 cells. The IC90 of zidovudine was 4 logs higher in cultures with 16 × 104 cells compared with cultures with 1 × 104 cells. No zidovudine-resistant mutations were found. Conclusion Target cell availability may play a direct role in wild type HIV-1 resurgence following therapy.

Effectiveness and Efficiency of Imperfect Therapeutic HSV-2 Vaccines

BACKGROUND: Efforts are currently underway to develop therapeutic vaccines for Herpes Simplex Virus type 2 (HSV-2). Methods: We use a mathematical model to predict the potential public health impact of imperfect, therapeutic HSV-2 vaccines. We evaluate vaccine effectiveness and efficiency for the general population in the United States where HSV-2 prevalence is currently 22%. We assume that therapeutic vaccines will produce two therapeutic benefits in vaccinated infected-individuals: (i) the rate of viral reactivation will decrease (hence infected-individuals will experience fewer viral shedding episodes), and (ii) the average length of the viral shedding episodes will be shortened. In addition, we assume that therapeutic vaccines will benefit uninfected individuals by reducing viral shedding in (and hence transmission from) vaccinated infected-individuals. RESULTS: Our predictions show that therapeutic vaccines could substantially reduce HSV-2 epidemics by reducing new infections by 77% and preventing 0.84 new infections for each vaccinated individual. These vaccines could prevent 212,600 (median; IQR, 156,064-288,558) new infections after only one year. We show that increased effectiveness and efficiency are more strongly correlated with a vaccine-induced reduction in transmission probability than with either of the two therapeutic benefits that accrue directly to the infected individuals (specifically, the reduction in episode length and number of episodes). CONCLUSIONS: We suggest that current vaccine development efforts target mechanisms that reduce viral shedding (thereby reducing transmission) thus providing both a beneficial therapeutic and a beneficial epidemic-level impact. Our results also demonstrate that therapeutic vaccines would be substantially more useful than prophylactic vaccines for epidemic control.

Identifying the Conditions Under Which Antibodies Protect Against Infection by Equine Infectious Anemia Virus

The ability to predict the conditions under which antibodies protect against viral infection would transform our approach to vaccine development. A more complete understanding is needed of antibody protection against lentivirus infection, as well as the role of mutation in resistance to an antibody vaccine. Recently, an example of antibody-mediated vaccine protection has been shown via passive transfer of neutralizing antibodies before equine infectious anemia virus (EIAV) infection of horses with severe combined immunodeficiency (SCID). Viral dynamic modeling of antibody protection from EIAV infection in SCID horses may lead to insights into the mechanisms of control of infection by antibody vaccination. In this work, such a model is constructed in conjunction with data from EIAV infection of SCID horses to gain insights into multiple strain competition in the presence of antibody control. Conditions are determined under which wild-type infection is eradicated with the antibody vaccine. In addition, a three-strain competition model is considered in which a second mutant strain may coexist with the first mutant strain. The conditions that permit viral escape by the mutant strains are determined, as are the effects of variation in the model parameters. This work extends the current understanding of competition and antibody control in lentiviral infection, which may provide insights into the development of vaccines that stimulate the immune system to control infection effectively.