November 12–13, 2008
On November 12–13, 2008, in Bethesda, Maryland, the National Institute of Allergy and Infectious Diseases (NIAID) hosted a workshop on the use of nonhuman primates to study AIDS. A goal of the workshop was to have experts provide guidance on how best to invest resources in nonhuman primate models to advance the development of an effective AIDS vaccine. The workshop featured panel presentations, discussions, and the development of priorities for research topics, resources, and reagents.
James Bradac, Ph.D., Chief of the Preclinical Research and Development Branch in NIAID’s Division of AIDS (DAIDS), welcomed the workshop participants. He noted the summit meeting of HIV vaccine researchers that took place in March 2008 in the aftermath of the STEP trial. That meeting determined a need to establish nonhuman primate research priorities and a need to integrate clinical research and discovery. Nancy Miller, Ph.D., of DAIDS’ Vaccine and Prevention Research Program, also welcomed the participants. She charged them to develop recommendations for priority nonhuman primate research topics, funding mechanisms, and broad research strategies.
Panel: Andrew Lackner Ph.D., D.V.M. (leader); Ashley Haase, M.D.; Brandon Keele, Ph.D.; Daniel Douek, M.D., Ph.D.
The first panel focused on mucosal infection, addressing the following topics:
Dr. Lackner cited current knowledge, such as the variety of target cells and viruses, and variations in trafficking to nodes. Dr. Haase reviewed the early events in sexual mucosal transmission of virus, noting that inhibitory responses can stimulate infection. Expansion of the virus occurs in a matter of days. Dr. Keele reported on studies of nonhuman primates that demonstrated that the founding virus can be identified and genetically sequenced.
Dr. Douek reviewed our understanding of the immunological and structural breakdown of the GI barrier in mucosal surfaces in acute infection. He described events such as the loss of CD4 T-cells, Th17, dendritic cells, macrophages, B-cells, and more. Each of these events offers an opportunity for study. There are many unknowns. In particular, we do not know the sequence of events—what leads to what? Dr. Douek stressed that immune cells in the gut are different from immune cells elsewhere, and the gut usually does not feature inflammation.
In discussion, it was noted that we need to determine the half-life of lymphocytes on the mucosal surface. We need to describe the trafficking patterns of migrating cells, and what determines them. We need to understand the differences between individuals. The amount of virus seems to play a role. Low levels offer an opportunity to control the infection. We do not understand the barrier function (epithelium, lumen, etc.). Furthermore, SIV may not operate in the same way that HIV operates. We need a model that can illuminate transmission. Which viruses are selected for transmission in the mucosa? We need to construct a larger research infrastructure to conduct analyses. We need to understand the massive depletion of CD4 T-cells early in infection. Are there facilitators that we might target? We should decide whether a model aims to prevent acquisition or progression. When studying the loss of dendritic cells (as one example) investigators should consider changes in the functions of the cells. They should study how the mucosal barrier breaks down.
Dr. Lackner summarized the discussion by listing the following priorities for research:
Panel: Guido Silvestri, M.D. (leader); Vanessa Hirsch, D.V.M., Sc.D.; Joern Schmitz, M.D.; Jacob Estes, Ph.D.; Beatrice Hahn, M.D.
The second panel focused on the following questions regarding SIV and natural hosts:
Dr. Silvestri lamented the lack of research on SIV infection in the natural host. For example, there are no consortium-type grants. We do not know why infected hosts do not develop disease and why mother-to-infant transmission does not occur. Dr. Silvestri called for research to learn the host’s “tricks” leading to those results. Such factors might play roles in human vaccine strategies. In particular, we should determine what causes the low immune activation in the nonhuman primate host, how that protects the animal, why low-CCR5 expression occurs, and the role of the adaptive response.
Dr. Hirsch stated that vertical transmission through breastfeeding occurs in some cases. We need to study the immunology in the nonhuman primate infants, and we need to learn the mechanisms of transmission (breastfeeding and otherwise). Dr. Schmitz described studies attempting to elucidate the mechanisms of inductive immune responses in natural hosts. Dr. Estes proposed studies of the different virus/CD4 T-cell relationship in natural hosts, and he suggested that natural host models might point to non-classical approaches. Dr. Hahn noted that a small fraction of SIV-infected chimpanzees will die if infected. Chimpanzees might be an example of a species that is ahead of humans in learning how to co-exist with the infection.
It was noted that most transmission during breastfeeding occurs late. There have been no studies of the breast milk and no studies of maternal antibodies. The low levels of CCR5 are present in various species. Investigators should make comparison studies of free virus and cell-associated virus. Dr. Schmitz emphasized that natural hosts with SIV have persistently high levels of viremia. We could be witnessing either an adaptive immune response or an innate immune response. We need to understand not only the response but the regulation of the response.It was suggested that natural hosts might serve better as models for therapeutic interventions than as models for vaccines. Natural hosts have evolved a strategy for co-existing with the virus. For example, they rapidly develop an anti-inflammatory response. If the most effective vaccine-induced responses were to be invoked during the chronic phase, then studies of natural hosts might be beneficial. If, however, the most effective vaccine-induced responses were to occur at a point before breakout from the gut to the periphery, then studies of natural hosts might not be helpful. The natural host model should be used to help understand pathogenesis, not viral replication. Pathogenesis is multifactorial, as is non-pathogenesis. There may be differences among animals. Hence, many animals should be studied.
Dr. Silvestri summarized the discussion by listing the following research priorities:
Session 3: Generation of Protective Cellular and Humoral Immune Responses
Panel: Louis Picker, M.D. (leader); Nancy Haigwood, Ph.D. (leader); David O’Connor, Ph.D.; Norman Letvin, M.D.; Philip Johnson, M.D.; John Mascola, M.D.
The third panel focused on the following issues for the cellular immune response:
The panel focused on the following issues for protective antibodies:
Dr. Picker stressed that we have only a vague understanding of how T-cells are regulated. We need to learn which T-cell effector mechanisms can interfere with HIV in vivo. We must develop tools for such in vivo research. Dr. O’Connor added that we lack an understanding of T-cell specificities and how T-cells interact, often relying on surrogates. The magnitude of T-cell expansion appears to play a key role in events. We need to determine which alleles restrict epitope-specific responses.
Dr. Haigwood stressed the benefits of neutralizing antibodies in viral control. Yet the mechanisms (and kinetics, etc.) of neutralizing antibodies are poorly understood. Dr. Johnson noted that we have not determined the levels of antibody that are protective. We also do not know how to effectively elicit protective antibodies. A gene-transfer approach in animals has found some success.
It was noted that the behaviors in natural hosts might provide lessons for changing the mucosal microenvironment and affecting the adaptive immune response. A recent study found that T-cells that produce chemokines are resistant to HIV infection. Perhaps we could elicit such self-protective T-cells. We need sophisticated computational tools to determine what a vaccine must do. Perhaps investigators should pursue simple questions or algorithms about infecting CD4 cell lines. We need to develop predictive values about T-cells in the models. We need to recognize epitopes and a hierarchy. We need better assays and better tools for studying CD4 depletion.
Dr. Picker summarized the discussion of T-cells, listing the following research areas:
Cellular Immunity and Protection from HIV/AIDS
Dr. Haigwood summarized the discussion of antibodies, listing the following priorities:
Major areas for future investigation: expansion of B cell findings to date
In vivo studies as part of passive transfer studies:
In vivo studies as part of vaccine studies:
Resource and reagent needs:
Panel: R. Paul Johnson, M.D. (leader); Michael Murphey-Corb, Ph.D.; Daniel Barouch, M.D., Ph.D.; Genoveffa Franchini, M.D.
The fourth panel focused on the following questions/topics:
Dr. Johnson noted that mucosal immunity is important for transmission and AIDS pathogenesis. Compartmentalization of the systemic and mucosal immune system is not clear-cut. Mucosal immunity can differ at different sites. We have yet to understand the responses that occur in these complex environments. An immune response (humoral or cellular) at a mucosal site does not necessarily qualify as mucosal immunity. Mucosal sites are fragile, and measurements may perturb the system. Dr. Barouch spoke of the comparative capacities of systems and the need for mucosal challenge studies. We need to understand the degree of compartmentalization following vaccination and the mechanisms of inducing mucosal immunity. Dr. Franchini stressed a need to study the founder virus in the first 3 or 4 days of exposure. We need to determine which T-cell responses to measure for the founder effector cells.
It was suggested that sampling peripheral blood does not capture enough of what is happening. We must sample the mucosa. We need reliable assays. One research strategy would be to differentiate how one infection takes and how another infection does not take (the latter is more common). We should perform mucosal challenge studies with various viruses. This would require standardization of various challenge stocks.
Many issues remain undetermined: expansion in the gut, longevity of the immune response, and complexity of T-cells in the mucosa. And non-neutralizing antibodies might play a protective role. NK cells certainly are important.
Dr. Johnson summarized the discussion by listing the following research priorities:
Reagents/Enabling Technologies–Mucosal Immunity
Panel: Jeffrey Lifson, M.D. (leader); Shiu-Lok Hu, Ph.D.; Mark Lewis, Ph.D.; Ronald Desrosiers, Ph.D.; Cristian Apetrei, M.D., Ph.D.; Malcolm Martin, M.D.; David Watkins, Ph.D.
The fifth panel focused on the following topics:
Dr. Hu stressed the importance of identifying monkey models that recapitulate the sequelae of infection and are predictive of human disease. Yet we can learn from all models. We need more comparative studies in macaque species. Different species have different susceptibilities to viral infection. Dr. Lewis noted that pig-tailed macaques tend to be unavailable and are not practical for vaccine studies. A majority of studies today use the Indian rhesus macaque. They seem to be the best model for study but are becoming expensive. Chinese rhesus macaques are becoming more available. They have good utility, and while they have peak viral loads lower than those of Indian rhesus macaques following challenge, they are useful for studying immune responses.
Dr. Desrosiers noted minor drawbacks in the use of SIV rhesus monkey models. He concluded that they are good models nevertheless, showing CD4 depletion, a chronic disease course, a good time frame, and more.
The participants agreed that Chinese rhesus macaques seem to be appropriate, with some limitations, as research models for current and new viruses. Acquisition of virus in the Indian and Chinese macaques is similar, although long-term follow-up can differ.
Dr. Lifson summarized the discussion by listing the following research priorities:
Dr. Lifson listed the following research priorities within three challenge system components—macaque types, virus options, dosing/frequency:
Dr. Lifson proposed that persons with appropriate expertise convene to determine what challenge virus should be used in the head-to-head comparison of high-dose and repeated low-dose mucosal challenges. The experiments should include standardization of stock sequence characterization.
Panel: Nancy Miller, Ph.D.; Joern Schmitz, M.D.; Jonathan Warren, Ph.D.; John Harding, Ph.D.; David Watkins, Ph.D.; David Montefiori, Ph.D.; Robert Palermo, Ph.D.; Brandon Keele, Ph.D.; Luis Giavedoni, Ph.D.; Ruth Ruprecht, M.D., Ph.D.
The sixth panel focused on resources and reagents, especially NIH funding resources and assay support for studies.
Dr. Miller described NIAID resource contracts at three sites, each with BSL-2 capabilities with a total cage capacity of 500–600 animals. Dr. Schmitz described the DAIT contract support for nonhuman primate reagents. It provides antibodies for in vitro and in vivo work, cell lines and transforming viruses, immunoglobin reference reagents, and a database of commercial antibodies. Rhesus-specific antibodies currently are being developed.
Dr. Warren reviewed the DAIDS reagent contract for AIDS vaccine development. The contractor is Quality Biological, Inc., and it provides flexible, targeted resources, including large reagent lots. Dr. Harding described the NCRR-supported National Primate Centers program, which has about 17,000 monkeys, mostly Indian rhesus macaques. About 63 percent of them are in breeding colonies, and there is very little reserve. Dr. Harding cited a need to determine the types of animals that will be needed in the future, a need to identify new sources for monkeys, and a need to develop a strategy regarding Chinese macaques.
It was noted that the quality of the animals is important and must be considered. To address the growing problem with numbers, we should develop strategies to use the animal models more efficiently through coordination, reuse, and the application of informatics.
Dr. Watkins described the service of MHC testing. The service offers high-throughput MHC class 1 genotyping
Dr. Montefiori reviewed the program for neutralizing antibody assays at Duke University. Using a contract mechanism, the program has provided assays for about 200 studies (about 16,000 samples) during the past 6 years. The program uses assays that are sensitive, quantitative, and reproducible, with correlative value and high throughput. Its lead assay is TZM-bl, which is widely used and validated. The program currently is studying this assay to determine whether it fails to detect some neutralizing antibodies. It is addressing other issues such as transitioning to SIV and variabilities in PBMC donors.
Dr. Palermo described the system of microarray analysis of expressed RNA and a program to apply systems biology and global gene expression profiling. This can support rational design of therapeutics and vaccines. Dr. Palermo stated that functional analysis tools are improving. Species-specific tools are still a long way off.
Dr. Keele made a recommendation to develop a single genome applications (SGA) program, with a core facility and a contract mechanism. It might also feature a database with annotation. The program could go beyond the identification of viruses to a determination of what happens over time.
Dr. Giavedoni described luminex assays for cytokine detection at the NCRR-supported National Primate Center. The program validates against seven rhesus monkey cytokines. It requires 25–50 microliters of sample for each test and uses a variety of reagents.
Dr. Ruprecht described the R5 SHIV vaccine challenge strains, which model HIV-1 transmission. They can be used as tools to assess anti-HIV-1 neutralizing antibody response. The 5 SHIVs are in clades B and C. It would be helpful to develop a SHIV in clade A.
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Last Updated August 26, 2009