PMPA Immediately After SIV Infection is Protective Against Highly Pathogenic SIV
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Following are excerpts from this Journal Of Virology article.
Postinoculation PMPA Treatment, but Not Preinoculation Immunomodulatory Therapy, Protects against Development of Acute Disease Induced by the Unique Simian Immunodeficiency Virus SIVsmmPBj
Journal of Virology, October 1999, p. 8630-8639, Vol. 73, No. 10
Shekema Hodge,1 Juliette de Rosayro,2 Amanda Glenn,2 Ifeoma C. Ojukwu,3Stephen Dewhurst,1 Harold M. McClure,4,5 Norbert Bischofberger,6 Daniel C. Anderson,4 Sherry A. Klumpp,4 and Francis J. Novembre2,7,* Departments of Microbiology and Immunology1 and Pediatrics,3 University of Rochester Medical Center, Rochester, New York; Divisions of Microbiology and Immunology2 and Research Resources,4 Yerkes Regional Primate Research Center, and Departments of Pathology and Laboratory Medicine5 and Microbiology and Immunology,7 Emory University, Atlanta, Georgia; and Gilead Sciences, Foster City, California6
Received 24 February 1999/Accepted 9 July 1999
Abstract: The fatal disease induced by SIVsmmPBj4 clinically resembles endotoxic shock, with the development of severe gastrointestinal disease. While the exact mechanism of disease induction has not been fully elucidated, aspects of virus biology suggest that immune activation contributes to pathogenesis. These biological characteristics include induction of peripheral blood mononuclear cell (PBMC) proliferation, upregulation of activation markers and Fas ligand expression, and increased levels of apoptosis. To investigate the role of immune activation and viral replication on disease induction, animals infected with SIVsmmPBj14 were treated with one of two drugs: FK-506, a potent immunosuppressive agent, or PMPA, a potent antiretroviral agent. While PBMC proliferation was blocked in vitro with FK-506, pig-tailed macaques treated preinoculation with FK-506 were not protected from acutely lethal disease. However, these animals did show some evidence of modulation of immune activation, including reduced levels of CD25 antigen and FasL expression, as well as lower tissue viral loads. In contrast, macaques treated postinoculation with PMPA were completely protected from the development of acutely lethal disease. Treatment with PMPA beginning as late as 5 days postinfection was able to prevent the PBj syndrome. Plasma and cellular viral loads in PMPA-treated animals were significantly lower than those in untreated controls. Although PMPA-treated animals showed acute lymphopenia due to SIVsmmPBj14 infection, cell subset levels subsequently recovered and returned to normal. Based upon subsequent CD4+ cell counts, the results suggest that very early treatment following retroviral infection can have a significant effect on modifying the subsequent course of disease. These results also suggest that viral replication is an important factor involved in PBJ-induced disease. These studies reinforce the idea that the SIVsmmPBj model system is useful for therapy and vaccine testing.
Since it was first isolated in 1985 and 1986 (1, 5, 10, 26), the simian immunodeficiency viruses (SIV) have become an important tool for investigating numerous aspects of lentivirus-host interactions. These viruses have been instrumental in our understanding of the disease process induced by human immunodeficiency virus type 1 (HIV-1) infection in humans. In addition, the SIV-macaque model has been important for investigating new methods for vaccine and therapy development. The SIV isolates from sooty mangabeys (Cercocebus atys) (SIVsmm) and rhesus macaques (Macaca mulatta) (SIVmac) induce a disease in Asian macaques that is remarkably similar to HIV-1 infection in humans (20, 24). The usefulness of the SIV-macaque model system is that it recapitulates HIV-1 pathogenesis in a shorter time. However, the pathogenic nature of SIV varies between isolates. Some isolates, such as the SIVmac1A11 isolate (23), have not been shown to cause any disease. However, most isolates are at least moderately pathogenic and induce AIDS-like disease within a time frame of 5 to 18 months.
We have been investigating a highly pathogenic variant of SIV, termed SIVsmmPBj14 (PBj). This isolate induces an acutely lethal disease that is characterized by diarrhea, dehydration, and anorexia, culminating in death in 5 to 14 days postinfection (11). A major focus of replicating virus is found in the lymphoid system of the intestinal tract. This is also where significant pathology occurs, including blunted intestinal villi and hyperproliferative tissue (9, 11). While the disease appears to be an exaggerated form of acute retroviral disease, clinical signs of disease are similar to those of animals experiencing endotoxic shock. The highly pathogenic nature of this virus suggested that changes in both the genotype and phenotype of SIV contributed to the new disease syndrome. Initial studies showed that this virus had unique characteristics, including the ability to replicate in unstimulated peripheral blood mononuclear cells (PBMC) and induce PBMC to proliferate (8). The latter characteristic appears to correlate with the observation that animals dying of PBj-induced acute disease have hyperproliferative lymphoid tissue in the gut. Contributing to this hyperproliferative state could be the redirection of lymphocytes from the periphery to the intestinal area through induction of specific integrins (12). We have been evaluating the basis for disease development at the molecular, biological, and pathologic levels. It is now clear that multiple viral genetic elements are required for the acutely lethal nature of PBj (27, 28), including a single amino acid change in Nef (7, 33). Furthermore, we have demonstrated that the in vitro phenomenon of PBMC proliferation induction by this virus is linked to its ability to induce acute disease (27). Inoculation of cells in vitro, or of animals, with PBj has been shown to induce the upregulation of activation markers (CD25 and CD45RO) (33). These results, coupled with the additional finding of significantly increased levels of apoptosis in the hyperplastic gut lymphoid areas, strongly suggest that immune activation is intimately associated with the acute disease syndrome (13, 40).
The results presented here suggest that while immune activation may play a significant role in the pathogenesis of PBj-induced disease, viral replication also appears to contribute importantly to disease development.
Infection of macaques, treatments, and subsequent monitoring. Following anesthetization, juvenile macaques were inoculated intravenously with a high dose (104 50% tissue culture infective doses [TCID50]) or a minimum lethal dose (1 TCID50) of virus derived from the PBj6.6 molecular clone.Animals were monitored on a daily basis for development of disease. On days 3, 7, 10, 14, and 21, and monthly thereafter, animals were anesthetized and blood was collected for use in in vitro assays (complete blood count, lymphocyte subset analysis, viral assays, and serological assays). For treatment with FK-506, animals were pretreated on days 2 and 1 (relative to the virus inoculation day), and every other day thereafter, with a dose of 0.75 mg/kg of body weight given subcutaneously. In our hands, this dose had provided excellent levels of FK-506 in plasma when tested in uninfected animals. Trough levels of FK-506 were determined for infected animals at the indicated times after infection by the clinical laboratories at the Emory University Hospital. For treatment with PMPA, infected animals were treated beginning either on day 3 or on day 5 postinfection. The macaques received a subcutaneous injection of PMPA (dose, 30 mg/kg) once per day until day 14 postinfection, after which the animals were withdrawn from therapy. Control animals for both treatments received inoculations of saline.
PMPA has been shown to prevent infection of macaques when treatment is begun either before infection or up to 24 h after infection (35). Additionally, early therapy with PMPA has been shown to prolong the time to disease development in SIV-infected macaques (38). Because of this potent ability of PMPA, we chose to use postinoculation therapy beginning at two different times after infection, so that we could ensure infection of the animals and thus test the effectiveness of therapy on infected macaques.
Treatment with PMPA was able to prevent the acutely lethal syndrome in SIVsmmPBj-inoculated animals when initiated at either 3 or 5 days postinfection. Virus loads in animals treated starting on day 3 were extremely lowno virus could be isolated from PBMC and no p27 antigen or viral RNA could be detected in plasma until after treatment was withdrawn on day 14. No incidence of acute infection was observed in these animals. In contrast, animals treated beginning on day 5 postinfection showed detectable levels of virus as measured by PBMC coculture isolation and by levels of viral RNA and p27 antigen in plasma. One animal in this group (PEe) even exhibited some clinical signs of sickness, including diarrhea and anorexia. The high viral load (bDNA) in this animal on day 7 postinfection was similar to that of the untreated controls, suggesting that the clinical signs of disease were due to accelerated viral replication compared to that of its treatment partner, PZh. These results suggest that a difference of just 2 days could have a significant effect in dampening virus replication in certain animals. The observation that no IL-6 was detected in the plasmaof PMPA-treated animals supports earlier contentions that this is an important cytokine in the pathogenesis of disease. Additional cytokines may also be involved (34); however, a detailed study will need to be performed on tissue samples to determine the relevance of cytokines to pathogenic events.
35. Prevention of SIV Infection in Macaques by [PMPA](R)-9-(2-Phosphonylmethoxypropyl)adenine Che-Chung Tsai (1), Kathryn E. Follis, Alexander Sabo, Thomas W. Beck, Richard F. Grant, Norbert Bischofberger, Raoul E. Benveniste, Roberta Black
The efficacy of pre- and postexposure treatment with the antiviral compound (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) was tested against simian immunodeficiency virus (SIV) in macaques as a model for human immunodeficiency virus (HIV). PMPA was administered subcutaneously once daily beginning either 48 hours before, 4 hours after, or 24 hours after virus inoculation. Treatment continued for 4 weeks and the virologic, immunologic, and clinical status of the macaques was monitored for up to 56 weeks. PMPA prevented SIV infection in all macaques without toxicity, whereas all control macaques became infected. These results suggest a potential role for PMPA prophylaxis against early HIV infection in cases of known exposure.
38. Early Short-Term [PMPA] 9-[2-(R)-(Phosphonomethoxy)Propyl]Adenine Treatment Favorably Alters the Subsequent Disease Course in Simian Immunodeficiency Virus-Infected Newborn Rhesus Macaques
Koen K. A. van Rompay,1 Peter J. Dailey,2 Ross P. Tarara,1 Don R. Canfield,1 Nancy L. Aguirre,1 Julie M. Cherrington,3 Patrick D. Lamy,3Norbert Bischofberger,3 Niels C. Pedersen,4 and Marta L. Marthas1,*
California Regional Primate Research Center1 and Department of Veterinary Medicine and Epidemiology,4 University of California, Davis, California 95616; Chiron Diagnostics, Emeryville, California 946082; and Gilead Sciences, Foster City, California 944043
Received 16 October 1998/Accepted 6 January 1999
Simian immunodeficiency virus (SIV) infection of newborn macaques is a useful animal model of human pediatric AIDS to study disease pathogenesis and to develop intervention strategies aimed at delaying disease. In the present study, we demonstrate that very early events of infection greatly determine the ultimate disease course, as short-term antiviral drug administration during the initial viremia stage significantly delayed the onset of AIDS. Fourteen newborn macaques were inoculated orally with uncloned, highly virulent SIVmac251. The four untreated control animals showed persistently high virus levels and poor antiviral immune responses; they developed fatal immunodeficiency within 15 weeks. In contrast, SIV-infected newborn macaques which were started on 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) treatment at 5 days of age and continued for either 14 or 60 days showed reduced virus levels and enhanced antiviral immune responses. This short-term PMPA treatment did not induce detectable emergence of SIV mutants with reduced in vitro susceptibility to PMPA. Although viremia increased in most animals after PMPA treatment was withdrawn, all animals remained disease-free for at least 6 months. Our data suggest that short-term treatment with a potent antiviral drug regimen during the initial viremia will significantly prolong AIDS-free survival for HIV-infected infants and adults.