Daniel C. Anderson

Postnatal Passive Immunization of Neonatal Macaques with a Triple Combination of Human Monoclonal Antibodies against Oral Simian-Human Immunodeficiency Virus Challenge

ABSTRACT To develop prophylaxis against mother-to-child human immunodeficiency virus (HIV) transmission, we established a simian-human immunodeficiency virus (SHIV) infection model in neonatal macaques that mimics intrapartum mucosal virus exposure (T. W. Baba et al., AIDS Res. Hum. Retroviruses 10:351–357, 1994). Using this model, neonates were protected from mucosal SHIV-vpu+challenge by pre- and postnatal treatment with a combination of three human neutralizing monoclonal antibodies (MAbs), F105, 2G12, and 2F5 (Baba et al., Nat. Med. 6:200–206, 2000). In the present study, we used this MAb combination only postnatally, thereby significantly reducing the quantity of antibodies necessary and rendering their potential use in humans more practical. We protected two neonates with this regimen against oral SHIV-vpu+ challenge, while four untreated control animals became persistently infected. Thus, synergistic MAbs protect when used as immunoprophylaxis without the prenatal dose. We then determined in vitro the optimal MAb combination against the more pathogenic SHIV89.6P, a chimeric virus encodingenv of the primary HIV89.6. Remarkably, the most potent combination included IgG1b12, which alone does not neutralize SHIV89.6P. We administered the combination of MAbs IgG1b12, 2F5, and 2G12 postnatally to four neonates. One of the four infants remained uninfected after oral challenge with SHIV89.6P, and two infants had no or a delayed CD4+ T-cell decline. In contrast, all control animals had dramatic drops in their CD4+ T cells by 2 weeks postexposure. We conclude that our triple MAb combination partially protected against mucosal challenge with the highly pathogenic SHIV89.6P. Thus, combination immunoprophylaxis with passively administered synergistic human MAbs may play a role in the clinical prevention of mother-to-infant transmission of HIV type 1.

Complete Protection of Neonatal Rhesus Macaques against Oral Exposure to Pathogenic Simian-Human Immunodeficiency Virus by Human Anti-HIV Monoclonal Antibodies

Because milk-borne transmission of human immunodeficiency virus (HIV) diminishes the benefits of perinatal antiviral drug therapy in developing countries, we have developed a new strategy to prevent postnatal and, possibly, intrapartum virus transmission in a primate model. Eight neonatal rhesus macaques were exposed orally to pathogenic simian-human immunodeficiency virus (SHIV); 4 neonates were then given intramuscular postexposure prophylaxis with 3 anti-HIV human neutralizing monoclonal antibodies (nMAbs) with potent cross-clade and cross-group neutralization activity. Untreated infants experienced high viral RNA levels and CD4(+) T-cell losses and died (median survival time, 5.5 weeks). In contrast, all 4 nMAb-treated neonates were protected from infection (P=.028); their plasma, peripheral blood mononuclear cells, and lymph nodes remained virus negative for >1 year. These data are important for designing clinical trials in human neonates and have general implications for AIDS vaccine development, as the epitopes recognized by the 3 nMAbs are conserved among diverse primary isolates.

Spectrum of disease in macaque monkeys chronically infected with SIV/SMM.

Twelve rhesus and one pig-tailed macaque have been monitored for 28-41 months following experimental infection with 10(4) TCID of SIV/SMM. Twelve of the 13 animals became virus positive and seroconverted within 3 to 6 weeks of exposure; the remaining animal seroconverted at 6 months, but has remained virus negative. Six of the 13 animals (46%) died between 14 and 28 months post-infection, following prolonged clinical disease characterized by chronic diarrhea and weight loss, peripheral lymphadenopathy and hemogram abnormalities. Histologic findings ranged from prominent follicular hyperplasia to severe lymphoid depletion, with lymphoid tissues often showing an infiltrate of syncytial giant cells. One animal had intestinal cryptosporidiosis and two had brain lesions comparable to those seen in AIDS encephalopathy in humans. Three of the remaining seven animals have an ARC-like disease and are showing gradual deterioration of their clinical condition. These animals, as well as animals that died, had progressive decreases in CD4+ cells and CD4+/CD8+ cell ratios. These observations further document the marked clinical, pathologic and immunologic similarities between human AIDS and the SIV-infected macaque model.

Prevalence of natural infection with simian immunodeficiency virus and simian T-cell leukemia virus type I in a breeding colony of sooty mangabey monkeys.

The seroprevalence of antibodies to simian immunodeficiency virus (SIVsmm) and simian T-cell leukemia virus type I (STLV-I) in a captive breeding colony of sooty mangabey monkeys was determined, and infection by SIVsmm was confirmed in all cases by virus isolation. Among 138 animals tested, 57 and 33% were infected with SIVsmm and STLV-I, respectively. While the proportion of female mangabeys (66%) differed significantly (P less than 0.01) from the proportion of male mangabeys (42%) infected with SIVsmm, the proportions of males and females infected with STLV-I were similar, suggesting independent transmission of the two viruses. Among mangabeys less than 1 year old, none were infected with STLV-I and only five of 27 mangabeys, all of which were at least 6 months old when first tested, were infected with SIVsmm. The data document that natural infection of sooty mangabey monkeys with SIVsmm or in association with STLV-I infection does not result in increased disease or mortality, and that transmission of both SIVsmm and STLV-I appears to occur primarily through sexual activity.

Tauopathy with Paired Helical Filaments in an Aged Chimpanzee

An enigmatic feature of age‐related neurodegenerative diseases is that they seldom, if ever, are fully manifested in nonhuman species under natural conditions. The neurodegenerative tauopathies are typified by the intracellular aggregation of hyperphosphorylated microtubule‐associated protein tau (MAPT) and the dysfunction and death of affected neurons. We document the first case of tauopathy with paired helical filaments in an aged chimpanzee (Pan troglodytes). Pathologic forms of tau in neuronal somata, neuropil threads, and plaque‐like clusters of neurites were histologically identified throughout the neocortex and, to a lesser degree, in allocortical and subcortical structures. Ultrastructurally, the neurofibrillary tangles consisted of tau‐immunoreactive paired helical filaments with a diameter and helical periodicity indistinguishable from those seen in Alzheimers disease. A moderate degree of Aβ deposition was present in the cerebral vasculature and, less frequently, in senile plaques. Sequencing of the exons and flanking intronic regions in the genomic MAPT locus disclosed no mutations that are associated with the known human hereditary tauopathies, nor any polymorphisms of obvious functional significance. Although the lesion profile in this chimpanzee differed somewhat from that in Alzheimers disease, the copresence of paired helical filaments and Aβ‐amyloidosis indicates that the molecular mechanisms for the pathogenesis of the two canonical Alzheimer lesions—neurofibrillary tangles and senile plaques—are present in aged chimpanzees. J. Comp. Neurol. 509:259–270, 2008.

Brain weight throughout the life span of the chimpanzee

Studies on human postmortem material report lower brain weights in older than in younger cohorts, whereas there is no apparent change with age in the rhesus monkey. In view of these contrasting results, we examined the pattern of brain weight across the life span in the chimpanzee, one of the closest biological relatives of humans. To place the study in context of the empirical life expectancy of the chimpanzee, we first performed a survival analysis on data from 275 chimpanzees that were maintained in the colony of the Yerkes Primate Center. The survival analysis revealed the maximum life spans of female and male chimpanzees to be about 59 and 45 years, respectively. We examined fresh brain weights from 76 chimpanzees ranging in age from birth to 59.4 years of age. The brains were taken from 9 infants (birth to 1 year of age), 25 juveniles (1–7 years), 13 adolescents (7–15 years), 21 young adults (15–30 years), and 8 old adults (over 30 years). Adult brain weight was achieved by the age of 7 years. The adolescent and young adult chimpanzees had the largest brain weights; in these two age groups combined, the mean brain weight (± standard deviation) was 368.1 g (±37.3) for females (n = 17) and 405.6 g (±39.4) for males (n = 17). This sex difference was statistically significant (P < 0.01). Simple linear regression performed on the combined material from females and males aged 7 years and older revealed a decline in brain weight with advancing age of 1.1g/year (P < 0.05). When the effect of sex on brain weight was statistically controlled for, the loss of brain weight with age was 0.9 g/year (P = 0.07). These results suggest that brain weight declines moderately with age in the chimpanzee as it does in humans. J. Comp. Neurol. 409:567–572, 1999.

Progressive Infection in a Subset of HIV-1—Positive Chimpanzees

Chimpanzees are susceptible to infection with human immunodeficiency virus (HIV)-1; however, infected animals usually maintain normal numbers of CD4(+) T lymphocytes and do not develop immunodeficiency. We have examined 10 chronically infected HIV-1-positive chimpanzees for evidence of progressive infection. In addition to 1 animal that developed AIDS, 3 chimpanzees exhibit evidence of progressive HIV infection. All progressors have low CD4(+) T cell counts (<200 cells/microL), severe CD4:CD8 inversion, and marked reduction in interleukin-2 receptor expression by CD4(+) T cells. In comparison with HIV-positive nonprogressor chimpanzees, progressors have higher plasma and lymphoid virus loads, greater CD38 expression in CD8(+)/HLA-DR(+) T cells, and greater serum concentrations of soluble tumor necrosis factor type II receptors and beta2-microglobulin, all markers of HIV progression in humans. These observations show that progressive HIV-1 infection can occur in chimpanzees and suggest that the pathogenesis of progressive infection in this species resembles that in humans.

Nonhuman Primate Models for Evaluation of AIDS Therapya

Infection of macaque monkeys with simian immunodeficiency virus (SIV) has been established as an excellent animal model system for studying the pathogenesis of an HIV-like virus and for evaluating newly developed antiretroviral drugs and vaccines. Based on their genetic, antigenic, and biologic properties, the simian immunodeficiency viruses are the closest known relatives of the human AIDS viruses, and experimental infection of macaque monkeys results in a disease that is remarkably similar to human AIDS. Infected macaques show diarrhea, weight loss, hematologic abnormalities including lymphopenia and thrombocytopenia, lymphadenopathy/lymphoid hyperplasia that progresses to lymphoid depletion, immunosuppression with marked reduction in CD4+ cells and in the CD4+/CD8+ cell ratio, and opportunistic infections. A majority of such macaques die from an AIDS-like disease within one to three years of infection. An acutely lethal variant of SIV has been identified that results in death in susceptible macaques within 7-12 days of infection. Preliminary prophylactic treatment trials with AZT in macaque monkeys exposed to the acutely lethal SIV variant indicate that some protection is provided when AZT treatment is initiated within 24 hours of virus exposure. Other studies with the more chronic SIV infection model, however, failed to show any prophylactic efficacy of CS-87, AZT, D4T, or FDT.

Relative Transmissibility of an R5 Clade C Simian- Human Immunodeficiency Virus Across Different Mucosae in Macaques Parallels the Relative Risks of Sexual HIV-1 Transmission in Humans via Different Routes

BACKGROUND Worldwide, approximately 90% of all human immunodeficiency virus (HIV) transmissions occur mucosally; almost all involve R5 strains. Risks of sexual HIV acquisition are highest for rectal, then vaginal, and finally oral exposures. METHODS Mucosal lacerations may affect the rank order of susceptibility to HIV but cannot be assessed in humans. We measured relative virus transmissibility across intact mucosae in macaques using a single stock of SHIV-1157ipd3N4, a simian-human immunodeficiency virus encoding a primary R5 HIV clade C env (SHIV-C). RESULTS The penetrability of rhesus macaque mucosae differed significantly, with rectal challenge requiring the least virus, followed by vaginal and then oral routes (P = .031, oral vs vaginal; P < .001 rectal vs vaginal). These findings imply that intrinsic mucosal properties are responsible for the differential mucosal permeability. The latter paralleled the rank order reported for humans, with relative risk estimates within the range of epidemiological human studies. To test whether inflammation facilitates virus transmission--as predicted from human studies--we established a macaque model of localized buccal inflammation. Systemic infection occurred across inflamed but not normal buccal mucosa. CONCLUSION Our primate data recapitulate virus transmission risks observed in humans, thus establishing R5 SHIV-1157ipd3N4 in macaques as a robust model system to study cofactors involved in human mucosal HIV transmission and its prevention.

GVHD after haploidentical transplantation: a novel, MHC-defined rhesus macaque model identifies CD28− CD8+ T cells as a reservoir of breakthrough T-cell proliferation during costimulation blockade and sirolimus-based immunosuppression

We have developed a major histocompatibility complex-defined primate model of graft-versus-host disease (GVHD) and have determined the effect that CD28/CD40-directed costimulation blockade and sirolimus have on this disease. Severe GVHD developed after haploidentical transplantation without prophylaxis, characterized by rapid clinical decline and widespread T-cell infiltration and organ damage. Mechanistic analysis showed activation and possible counter-regulation, with rapid T-cell expansion and accumulation of CD8(+) and CD4(+) granzyme B(+) effector cells and FoxP3(pos)/CD27(high)/CD25(pos)/CD127(low) CD4(+) T cells. CD8(+) cells down-regulated CD127 and BCl-2 and up-regulated Ki-67, consistent with a highly activated, proliferative profile. A cytokine storm also occurred, with GVHD-specific secretion of interleukin-1 receptor antagonist (IL-1Ra), IL-18, and CCL4. Costimulation Blockade and Sirolimus (CoBS) resulted in striking protection against GVHD. At the 30-day primary endpoint, CoBS-treated recipients showed 100% survival compared with no survival in untreated recipients. CoBS treatment resulted in survival, increasing from 11.6 to 62 days (P < .01) with blunting of T-cell expansion and activation. Some CoBS-treated animals did eventually develop GVHD, with both clinical and histopathologic evidence of smoldering disease. The reservoir of CoBS-resistant breakthrough immune activation included secretion of interferon-γ, IL-2, monocyte chemotactic protein-1, and IL-12/IL-23 and proliferation of cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin-resistant CD28(-) CD8(+) T cells, suggesting adjuvant treatments targeting this subpopulation will be needed for full disease control.