Biological considerations in the development of a human immunodeficiency virus vaccine.

Over the last 12 years, many human immunodeficiency virus (HIV) vaccine candidates have been tried in humans, with disappointing results. In particular, recombinant envelope proteins have failed to elicit strong cellular immune responses or neutralizing antibody against many wild-type isolates of HIV-1. Attenuated strains of simian immunodeficiency virus (SIV), although capable of protecting against virulent strains of SIV, often retain residual pathogenicity. These difficulties suggest that it will be necessary to address a number of biological questions that underpin the rational development of an AIDS vaccine: (1) Will natural infection with HIV protect against superinfection? (2) Is partial protection induced by an HIV vaccine adequate to prevent AIDS? (3) What are the immune correlates of protection for an AIDS vaccine? (4) Will a monotypic HIV-1 vaccine confer cross-clade immunity? (5) Is mucosal immunity important for an effective AIDS vaccine? (6) Is there a rationale for therapeutic immunization? Ongoing research that is addressing these questions should lead to the formulation of a safe and effective AIDS vaccine.

Towards an AIDS vaccine: the role of nonhuman primates.

Over the last 10 years, about 20 human immunodeficiency virus (HIV) vaccine candidates have been tried in humans, with disappointing results as gauged by limited immune responses or protection against infection. These difficulties suggest that a new strategy is needed to test systematically new vaccine candidates. That opportunity is now afforded by nonhuman primate models with SIV, which have been shown to provide an excellent mirror of HIV infection in humans. The recent introduction of SHIVs, chimeric viruses that carry the HIV envelope and are able to infect and cause AIDS in monkeys, also has added an important additional research tool. These models can be used to address a series of questions, including the following: (1) Can protection be provided by partial immunity or is sterilizing immunity required? (2) What are the immune parameters that best predict protection against a potentially pathogenic challenge? (3) What role does mucosal immunity play and can it be induced by practical modes of immunization? (4) Can an attenuated virus be selected that is both protective and safe? An orderly strategy for the evaluation of vaccine candidates could be adopted that would involve several phases: (a) the selection of a limited set of challenge models, ranging from very severe to mild and requiring consideration of primate species, age, route of infection, and challenge viruses; (b) the assessment of candidate vaccines using comparable virus challenges; and (c) accelerated testing in humans of any candidate vaccines that have met a 'proof of efficacy' in primates.

Risk factors for perinatal transmission of human immunodeficiency virus type 1 in women treated with zidovudine. Pediatric AIDS Clinical Trials Group Study 185 Team.

BACKGROUND: Maternal, obstetrical, and infant-related factors associated with the risk of perinatal transmission of human immunodeficiency virus type 1 (HIV-1) were identified before the widespread use of zidovudine therapy in pregnant women. The risk factors for transmission when women and infants receive zidovudine are not well characterized. METHODS: We examined the effects of maternal, obstetrical, and infant-related characteristics and maternal virologic and immunologic variables on the risk of perinatal transmission of HIV-1 among 480 women and their infants, all of whom received zidovudine. The women and infants were participating in a phase 3 trial of passive immunoprophylaxis for the prevention of perinatal transmission. RESULTS: In univariate analyses, the risk of perinatal transmission was associated with each of the following: decreased maternal CD4+ lymphocyte counts at base line; decreased maternal HIV p24 antibody levels at base line and delivery; increased maternal HIV-1 titer at base line and delivery; increased maternal HIV-1 RNA levels at base line and delivery; and the presence of chorioamnionitis at delivery. In multivariate analyses, the only independent risk factor was the maternal HIV-1 RNA level at base line (odds ratio for transmission, 2.4 per log increase in the number of copies; 95 percent confidence interval, 1.2 to 4.7; P=0.02) and at delivery (odds ratio, 3.4; 95 percent confidence interval, 1.7 to 6.8; P=0.001). There was no perinatal transmission of HIV-1 among the 84 women who had HIV-1 levels below the limit of detection (500 copies per milliliter) at base line or the 107 women who had undetectable levels at delivery. CONCLUSIONS: Among pregnant women and their infants, all treated with zidovudine, the maternal plasma HIV-1 RNA level was the best predictor of the risk of perinatal transmission of HIV-1. Antiretroviral therapy that reduces the HIV-1 RNA level to below 500 copies per milliliter appears to minimize the risk of perinatal transmission as well as improve the health of the women.

Efficacy of zidovudine and human immunodeficiency virus (HIV) hyperimmune immunoglobulin for reducing perinatal HIV transmission from HIV-infected women with advanced disease: results of Pediatric AIDS Clinical Trials Group protocol 185.

Pediatric AIDS Clinical Trials Group protocol 185 evaluated whether zidovudine combined with human immunodeficiency virus (HIV) hyperimmune immunoglobulin (HIVIG) infusions administered monthly during pregnancy and to the neonate at birth would significantly lower perinatal HIV transmission compared with treatment with zidovudine and intravenous immunoglobulin (IVIG) without HIV antibody. Subjects had baseline CD4 cell counts /=200/microL) but not with time of zidovudine initiation (5.6% vs. 4.8% if started before vs. during pregnancy; P=. 75). The Kaplan-Meier transmission rate for HIVIG recipients was 4. 1% (95% confidence interval, 1.5%-6.7%) and for IVIG recipients was 6.0% (2.8%-9.1%) (P=.36). The unexpectedly low transmission confirmed that zidovudine prophylaxis is highly effective, even for women with advanced HIV disease and prior zidovudine therapy, although it limited the study's ability to address whether passive immunization diminishes perinatal transmission.

The role of nonhuman primates in the development of an AIDS vaccine.

Over the past decade, a substantial research investment has generated a vast body of knowledge relevant to the development of an effective AIDS vaccine. Furthermore, studies in nonhuman primates have demonstrated that a number of candidate immunogens can confer a significant degree of protection against a potentially pathogenic SIV or SHIV. Currently, there exists a robust program that supports discovery of new HIV immunogens and a proven successful program for collaborative human trials of promising vaccine candidates. However, we believe that there is a gap between discovery and clinical trials. An orderly process for screening of candidate immunogens prior to human trials would facilitate the vaccine development program. We suggest that nonhuman primates can fill this strategic gap and could accelerate vaccine development. Recognizing that there is considerable controversy about the potential usefulness of the primate models, we have attempted to set forth the relevant practical and biological issues as a series of questions for discussion. The most important biological problem is the absence of a single immune response correlate that will predict vaccine efficacy. Data from primate models indicate that such a single predictive correlate may not exist. In turn, this argues for a vaccine screening protocol that includes a pathogenic virus challenge, an approach only available in the nonhuman primate model. The further assumption is that nonprimate models can be used to predict the relative protective efficacy of diverse immunization protocols, a hypothesis that can only be tested by comparative studies yet to be conducted. A 'standard' set of virus challenges must be selected for comparison of different immunization protocols, and this effort has been initiated. At the practical level, it appears that the large number of candidate immunogens now being developed requires a screening process of the kind proposed, since it would not be practical to test all new immunogens and protocols in humans. In conclusion, it appears timely to crystallize an orderly process for the discovery, screening, and human testing of candidate AIDS vaccines, understanding that a vaccine development program should not be conducted at the expense of investigator-initiated research in the diverse disciplines that support rational vaccine design and development. The components of a rational process of vaccine development are well established and only remain to be welded into one coherent program.

Safety and pharmacokinetics of hyperimmune anti-human immunodeficiency virus (HIV) immunoglobulin administered to HIV-infected pregnant women and their newborns. Pediatric AIDS Clinical Trials Group Protocol 185 Pharmacokinetic Study Group.

The pharmacokinetics and safety of hyperimmune anti-human immunodeficiency virus (HIV) intravenous immunoglobulin (HIVIG) were evaluated in the first 28 maternal-infant pairs enrolled in a randomized, intravenous immunoglobulin (IVIG)-controlled trial of HIVIG maternal-infant HIV transmission prophylaxis. Using 200 mg/kg, mean half-life and volume of distribution (Vd) in women were 15 days and 72 mL/kg, respectively, after one and 32 days and 154 mL/kg after three monthly infusions, with stable 4 mL/kg/day clearance. Transplacental passage occurred. Newborn single-dose half-life, Vd, and clearance were 30 days, 143 mL/kg, and 4 mL/kg/day, respectively. HIVIG rapidly cleared maternal serum immune complex-dissociated p24 antigen, and plasma HIV-1 RNA levels were stable. Mild to moderate adverse clinical effects occurred in 2 of 103 maternal and 2 of 25 infant infusions. No adverse hematologic, blood chemistry, or immunologic effects were seen. HIVIG is well-tolerated in HIV-infected pregnant women and their newborns, clears antigenemia, crosses the placenta, and exhibits pharmacokinetics similar to those of other immunoglobulin preparations.

Women and HIV. Epidemiology and global overview.

The global HIV-1 epidemic in women continues to expand at an alarming rate. More than 11 million women are currently estimated to be HIV-infected, with the majority living in sub-Saharan Africa. The primary risk factor for HIV infection in women is unprotected heterosexual intercourse. Several cofactors may influence a woman's risk for HIV acquisition. These include the presence of other STDs, the prevalence of HIV in the population, engagement in high-risk sexual behaviors at a young age, an increased number of sexual partners, HIV illness severity in an infected partner, host immunogenetic responses, hormonal and other local effects in the female genital tract, and viral characteristics. The general clinical findings in women with HIV disease are similar to those in HIV-infected men. Some studies have noted higher rates of esophageal candidiasis and decreased rates of Kaposi's sarcoma in women when compared with men. Overall disease progression and survival in women and men are similar once an adjustment is made for other important risk factors such as the time of seroconversion, the receipt of antiretrovirals, and baseline CD4 cell counts. Women with HIV have a high frequency of a number of diseases of the reproductive tract, including low-grade cervical dysplasia and vulvovaginal candidiasis. Despite progress in understanding the risk factors for HIV transmission to women and the variables related to disease progression, major research questions remain. These include the role of hormonal contraceptives in the risk for HIV acquisition, the primary mechanism of infection, and host systemic as well as local hormonal and immune responses in the female reproductive tract that may alter the risk of HIV infection. Over the next decade, it is anticipated that the quality of life and length of survival will improve dramatically for both HIV-infected women and men in settings in which new highly active combination antiretroviral therapy is available and affordable. Unfortunately, in most of the world, these antiretroviral drugs are not available for the treatment of the vast numbers of individuals infected by HIV. Therefore, development of successful strategies for primary prevention of HIV infection in women must be a top public health priority.

PIP: The global HIV epidemic in women continues to expand, primarily as a result of unprotected heterosexual intercourse. Women's risk of HIV acquisition is affected by cofactors such as the presence of other sexually transmitted diseases, the prevalence of HIV in the population, the practice of high-risk sexual behaviors at a young age, an increased number of sexual partners, HIV illness severity in an infected partner, host immunogenetic responses, hormonal and other local effects in the female genital tract, and viral characteristics. Although the general clinical findings in HIV-infected men and women are similar, women also have a high frequency of reproductive tract diseases such as low-grade cervical dysplasia and vulvovaginal candidiasis. Further research is needed to assess the role of hormonal contraception in the risk for HIV acquisition, the primary mechanism of infection, and host systemic as well as local hormonal and immune responses in the female reproductive tract that may alter HIV risk. Although combination antiretroviral therapy has demonstrated the ability to improve the quality of life and survival time of HIV-infected men and women, the high cost of such treatment renders it inaccessible to the majority of HIV-infected patients. Thus, the development of successful strategies for primary prevention of HIV infection--especially among women--remains a top public health priority.

Early phases of HIV type 1 infection.

A workshop entitled "Early Phases of HIV-1 Infection" was held to review current research on the immunological and virological aspects of early phases of HIV infection in humans and in animal models, to identify studies for future research, and to foster collaborations among investigators in the biomedical community. In infections of adults, the appearance of cytotoxic T lymphocyte activity, when present, coincides with a decrease in viral load as measured by plasma viremia. In neonatal infections, however, an initial decrease in viral load has been observed months before cytotoxic T lymphocytes are detected. Immunological data, from a limited number of patients, indicated that CD8+ cytotoxic T lymphocytes detected early after HIV-1 infection may recognize epitopes in any of several HIV-1 proteins: Env, Gag, Pol, Tat, and Nef. With regard to the humoral antibody response, anti-Env binding antibodies appear before neutralizing antibodies and do not predict the appearance of neutralizing activity. The time at which neutralizing antibody appears is variable and unpredictable. Preliminary data indicate that early viral peak load does not predict disease progression in many cases, and the phenotype or virulence of the virus appears to be a critical variable. However, the quantity of HIV-1 RNA in plasma is a strong CD4+ T cell-independent predictor of outcome following HIV-1 seroconversion in homosexual men. Early, high virus load with sustained viremia is often accompanied, in both adults and infants, by the inability to mount an effective immune response, resulting in rapid disease progression.

Summary report: workshop on the potential risks of antibody-dependent enhancement in human HIV vaccine trials.

Concern that ADE of HIV infection could occur in vivo, as a result of HIV immunization, has arisen for several reasons. Immune-mediated disease enhancement occurs in several human and animal viral diseases, including lentiviral diseases. Tropism for host M/M cells is a common characteristic in these diseases. Sera from naturally infected, and possibly HIV-immunized, individuals have been shown to contain infection enhancing antibodies in vitro. Finally, there is considerable genetic, and potentially antigenic, diversity among HIV-1 isolates. This workshop was convened to evaluate these concerns regarding ADE of HIV infection in human HIV vaccine trials and to propose studies that would address this potential risk. Although there is currently no evidence that immune-mediated enhancement of disease occurs in HIV, there is clearly a need for carefully designed experiments to further evaluate this issue. As there are several notable diseases for which in vitro ADE does not correlate with ADE in vivo, in vitro data are insufficient to deter development of current HIV-1 vaccine candidates. In vivo correlates of protection/enhancement are necessary to evaluate the ADE risk accurately. The development of an HIV animal model that would allow testing of vaccine candidates is of primary importance.

Two antigens detected on human ocular melanomas with the mouse monoclonal antibodies 2/10SN and 10/12SN.

Seven human ocular melanoma cell lines were established in vitro and 3 of these, GU-4, LLN-40 and its subline C17-11, were characterized. Mice were immunized with these ocular melanoma cell lines, and 2 hybridomas producing monoclonal IgG1 antibodies (MAb) were produced. MAb 2/10SN recognizes a 44-kDa monomeric protein, whereas MAb 10/12SN reacts with an 83/65-kDa heterodimeric protein. These melanoma-associated antigens (MAA) are detected at high concentrations in the cytoplasm of ocular melanoma cells. However, cell-surface labelling techniques suggest that these MAA are also associated with the cell-surface membrane. These 2 ocular MAA are also expressed by several skin melanoma cell lines. Immunohistochemical studies have localized these antigens to ocular and skin melanomas, to sweat ducts and basal squamous cells in normal skin, with limited expression in several other normal tissues and some carcinomas. Biodistribution studies in nude mice with human ocular melanomas have demonstrated good localization of 125I-labeled MAb 2/10SN at the tumor sites. Therefore, these 2 MAbs, 2/10SN and 10/12SN, recognize MAA which appear to be unique and may prove useful for imaging purposes.

In vivo modulation of the distribution of thymocyte subsets: effects of estrogen on the expression of different T cell receptor V beta gene families in CD4-, CD8- thymocytes.

Estrogen treatment of mice has been shown to deplete CD4+, CD8+ double-positive (DP) thymocytes and to alter the relative proportion of CD4+ and CD8+ single-positive (SP) thymocytes. In this work, we have studied the effect of the steroid hormone 17 beta-estradiol (E2) on the different subsets of CD4-/CD8- double-negative (DN) thymocytes by analyzing the expression of CD5, CD3-epsilon and of several V beta gene family products of the T cell antigen receptor (TCR). After in vivo administration of E2 a significant decrease in the number and proportion of dull CD5+, CD3-, beta-TCR- DN thymocytes was observed. In contrast E2 treatment significantly increased the proportion of bright CD5+, CD3+, beta-TCR+ DN cells. The E2-induced increase in DN/TCR+ cells was observed for subsets expressing V beta 6, V beta 8, and V beta 11, but not V beta 3 gene products of the TCR. Thus, estrogen administration results in a selective inbalance of the DN thymocyte subsets by depleting an immature, dull CD5+, CD3-, TCR beta- DN subset, while enriching a mature, bright CD5+, CD3+, TCR beta+ DN subset of cells. In addition to TCR beta+ DN thymocytes, an increased proportion of CD4+ and CD8+ SP thymocytes expressing V beta 8, V beta 6, and V beta 11, but not V beta 3, TCR proteins was also observed after E2 administration. An involvement of intrathymic cytokine production in mediating the hormone action is suggested by the ability of estrogen to increase the levels of IL-1 alpha mRNA of intact thymus. Our data suggest that estrogen exerts its effects on a broad range of immature cells, including dull CD5+, CD3-, beta-TCR- DN and DP thymocytes.

Selective stimulation of thymocyte precursors mediated by specific cytokines. Different CD3+ subsets are generated by IL-1 versus IL-2.

The sequence of activation signals that stimulate proliferation, differentiation, and selection of mature T cell subsets from immature, dull-CD5+/CD4-, CD8- double negative (bCD5), (dCD5/DN) thymocytes are still unclear. However, it is likely that cytokines play integral roles in these events. Here we report that IL-1, in the presence of Con A, supports the proliferation and differentiation of highly purified dCD5/DN precursors into bright-CD5+ DN, CD2- lymphocytes with an apparently mature phenotype. These cells express CD3 and preferentially express the products of two TCR gene families, V beta 8 and V beta 6, whose expression is dependent on the allelic expression of the Mls-1 locus. Experiments, using DN thymocytes mixed with purified dCD5 subset of DN cells from a congenic strain of mice (i.e., expressing two different alleles of CD5) have shown that the cells that are stimulated by IL-1 and comitogen are derived from the immature dCD5 subset and not from the mature bCD5 cells contained within the DN subset. In contrast, IL-2 with the co-mitogen stimulates three- to fourfold higher levels of proliferation, from the same purified immature precursor population, and nearly a twofold increase in cell yield. However, the cells that were generated from precursor thymic cells stimulated with IL-2 represent a completely different T cell subset compared to IL-1-generated cells; these IL-2-stimulated cells express comparable levels of CD3, but also express substantial levels of CD2 and the TCR-gamma/delta, and a subset expresses CD8. These data suggest that these two TCR-alpha/beta and TCR-gamma/delta subsets of mature thymocytes use different cytokines and therefore possibly different stromal interactions to initiate differentiation.

Characterization of IL-2 receptor expression and function on murine macrophages.

This study was designed to examine the expression and function of IL-2R on murine macrophages. We used a model system of murine macrophage cell lines (ANA-1 and GG2EE) that was established by infecting normal murine bone marrow-derived cells with the J2 (v-raf/v-myc) recombinant murine retrovirus. ANA-1 macrophages did not constitutively express detectable levels of mRNA for the p55, IL-2R alpha. However, a brief exposure to IFN-gamma was sufficient to induce IL-2R alpha mRNA in ANA-1 macrophages. Flow cytometric analysis indicated that ANA-1 macrophages expressed low constitutive levels of IL-2R alpha on their cell surface that were augmented after treatment of the cells with IFN-gamma. Affinity binding and cross-linking of [125I]IL-2 to ANA-1 macrophages demonstrated that IL-2R alpha and the p70-75, IL-2R beta were both present on ANA-1 macrophages constitutively. IFN-gamma increased the expression of IL-2R alpha on ANA-1 macrophages but did not increase the expression of IL-2R beta on these macrophages. Although IL-2 alone did not induce the tumoricidal activity of ANA-1 macrophages, IL-2 acted synergistically with IFN-gamma to induce macrophage tumoricidal activity. These data demonstrate the expression of IL-2R on murine macrophage cell lines and establish the role of IL-2 as a costimulator of macrophage-mediated tumoricidal activity.