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Comparative Pathology Research Programs

Most of the research in the Division of Comparative Pathology is focused on the prevention, pathogenesis, and treatment of infectious diseases using nonhuman primate models with a focus on AIDS, tuberculosis, pediatric immunology, and AIDS-related vaccine programs. We also investigate treatments and preventions for neonatal and adult viral infections including herpesviruses, Zika virus, and other emerging infectious diseases. Our objectives are to develop improved prevention and treatment strategies for current and emerging plagues of humans and animals in highly relevant and directly translateable nonhuman primate models.

Acquired Immune Deficiency Syndrome (AIDS)

Although some progress has been made in treatments, HIV infection remains a major health crisis. According to the National Institute of Allergy and Infectious Diseases (NIAID), There were approximately 36.7 million people worldwide living with HIV/AIDS at the end of 2016. Of these, 2.1 million were children (<15 years old). An estimated 1.8 million individuals worldwide became newly infected per year – about 5,000 new infections per day. This includes 160,000 children per year. In the United States, at least 50,000 new cases of HIV infections occur annually and over 1 million persons are currently infected, with continually higher proportions of new infections in the Southern states. New treatments can prevent or delay the onset of disease, but these treatments are expensive and cannot cure the infection, necessitating daily treatments with expensive and potentially toxic drugs for the lifetime of the infected patient. Thus, HIV infection and AIDS remain a major global health crisis

We now know that human immunodeficiency virus evolved from the evolution and recombination of simian immunodeficiency viruses naturally found in nonhuman primates (NHP), so it is especially relevant to examine the pathogenesis of SIV and SIV/HIV hybrids (SHIVs) in NHP models. Most of the major advances in HIV prevention and treatment were first established in NHP models (reviewed in (1). In combination with recent advances in molecular biology and computational analytics, research in NHPs has the unique potential for future discoveries that will directly lead to new cures for human and animal diseases, including HIV/AIDS.

Investigation of AIDS pathogenesis, prevention and treatment remain the largest research objective of the Division and include; 1) Interactions and effects of SIV/HIV on the mucosal immune system; 2) neuroimmunology and neuropathogenesis of HIV in neonatal and adult hosts; 3) Testing new preventions and vaccines for HIV, and; 4) Testing novel “cure” strategies aimed to eradicate HIV from tissues of infected hosts. Further, as other sexually transmitted diseases (STD) are on the rise in epidemic proportions, the likelihood of this increasing HIV transmission rates is high. Thus, also we have active research programs investigating the prevention of human herpes virus 1 (HSV-1) and HSV-2, and other STD’s using nonhuman primate models.

AIDS pathogenesis: general: The Division of Comparative Pathology has made significant dogma changing discoveries in the immunology and pathogenesis of HIV infection and AIDS using nonhuman primate models (1). The key to each of these discoveries in nonhuman primates was a focus on early events within tissues which could not be examined in humans, and comprehensive examination of the role of cells, adhesion molecules, and inflammatory mediators and receptors in all major tissues such as the intestine, liver, brain, and spleen, which are difficult to impossible to access in humans, especially at early key stages of transmission. Finally, a better understanding of the differences in founder viruses and mucosal transmission have led to the development of molecular clones of SIV and genetic SIV/HIV hybrids (SHIVs) that most closely mimic the transmitted epidemic strains of HIV currently infecting humans.

Advances in Prevention of HIV transmission: In collaboration with several investigators, we have made several key discoveries in the prevention, pathogenesis and treatment of SIV/SHIV in macaques as a model for HIV prevention and treatment strategies. Working with Dr. Tom Hope’s lab and collaborators at Northwestern University, Dr. Ron Veazey’s lab recently confirmed a specific subset of CD4+ T cells (Th17) crucial for maintaining mucosal barrier integrity are the first cells infected and eliminated after vaginal SHIV exposure (2). Within 48 hrs, over 85% of the infected cells in vaginal tissues are CD4+CCR6+ Th17 cells, even though they represent less that 10% of the total CD4+ T cells found in the vagina Th17 cells are important in regulating mucosal barrier function, which may play a role in the early events in vaginal inflammation and transmission. In addition, we have also been examining the cellular and molecular mechanisms of penile, vaginal, and rectal transmission and are testing new methods for prevention of infection through modulating the mucosal immune environment. In collaboration with Dr. Michael Lederman’s lab at the Case Western Reserve University, we showed that topical vaginal treatment with IFN-b could induce innate immune responses sufficient to prevent vaginal transmission (3). We are also examining novel long acting HIV prevention methods, and comparing immune responses of resistant and susceptible macaques to decipher the mechanisms involved in innate resistance to infection.

Novel HIV treatment and cure strategies: Several faculty in the Division are testing new HIV treatment and cure strategies to eliminate residual viral reservoirs in tissues. Drs. Binhua Ling, Andrew MacLean, and Huanbin Xuhave NIH grants to eradicate persistent and latent reservoirs from recessed tissues in nonhuman primates. Since these studies focus on eradicating virus from deep reservoir tissues such as the brain, intestine, bone marrow, etc., such studies simply cannot be performed in humans. We also work with investigators at Harvard Medical School, the University of Pennsylvania and Case Western Reserve University’s Centers for HIV Research (CFARs), as well as with researchers in England, Canada, Denmark, China, and other countries on HIV prevention and cure strategies using NHP models.

Discoveries in HIV Immunology and Pathogenesis: The Division continues to specialize in examining the pathogenesis and immunology of HIV infection using NHP models. We have characterized the early kinetics of T and B cell subsets, innate lymphoid cells (ILC), inflammatory mediators, and various subsets of key regulatory cells in mucosal and systemic lymphoid tissues in macaques, and have made significant progress in understanding the immunologic deficits that occur, and how to treat these with novel therapies. Dr. Mahesh Mohan has focused on research into regulation of microRNAs and epigenetic effects of SIV infection on intestinal epithelial cells and lamina propria cells (4). Dr. Bapi Pahar has shown that TGF-b, a key players in the control of mucosal immune regulation, is highly dysregulated in SIV infection (5). Dr. Pahar is also co-director of the SVEU along with Dr. Pyone Aye (Director of the SVEU) and has expertise in examining B cell and antibody responses in NHP vaccine studies.

Dr. Huanbin Xu’s lab focuses on virus specific and innate immune responses in SIV infection. He showed that T follicular helper cells (TFH) in lymph nodes are rapidly infected and dysregulated in SIV infection. He also demonstrated how TFH cells are infected as “precursors” that express CCR5, yet later lose CCR5 as they migrate into the “immune priviliged” germinal centers where they persist as functionally impaired viral reservoirs out of reach of current therapies (6).

Combined, our studies are leading to a greater understanding of the specific cellular and molecular mechanisms by which HIV infection induces immunosuppression and evades immune responses, which is already leading to new and novel therapeutic targets for HIV treatment and vaccine strategies.

Neuroscience and neuroAIDS: The Division of Comparative Pathology has substantial expertise in the neuropathogenesis of AIDS and neuropathology in general. Several of our faculty have extensive training and experience in neuropathology. Infection of rhesus macaques with SIV results in rapid neuroinvasion and neuropathologic abnormalities that are similar to those observed in HIV-infected humans. We have used this model to examine the role of various inflammatory mediators in specific regions of brains of SIV-infected macaques for decades. We previously demonstrated elevated expression of several chemokines and inflammatory mediators known to affect HIV in perivascular infiltrates in the brain. Dr. Andrew MacLean has published multiple papers on characterizing the type of inflammation in SIV encephalitic lesions, and identified several cellular and soluble inflammatory markers that can predict SIV encephalitis in macaques, that may eventually translate into prognostic indicators of HIV encephalitis. Dr. MacLean has also applied these and other novel techniques to characterize the anatomical defects associated with other infectious and non-infectious diseases as a model for human brain diseases (7). Dr. Binhua Ling has quantified viral reservoirs in the brain of SIV infected macaques (8) and Drs. Veazey, Ling, MacLean, and Xavier Alvarez also work with neuroscientists across the Nation in examining the role of the brain as a reservoir for HIV, as well as the neuropathogenesis of other diseases. We have also made key discoveries in the neuropathology and pathogenesis of several arboviral infections, including Chikungunya, West Nile, Dengue and Zika viruses and other infectious agents designated by the CDC and WHO as being public health emergencies of international concern.

Neonatal Immunology and Pediatric AIDS: Infants and young children are more susceptible than adults to a variety of infectious diseases, particularly those of viral origin. This is particularly evident in children with HIV, who have a more rapid disease course and increased viral loads as compared to adults. Dr. Xiaolei Wang and Veazey have been examining the normal sequential immunologic development of newborn and neonatal primates to determine if vaccination strategies may be improved for infants specifically to decrease the mortality of infectious diseases in children. Dr. Wang has shown that neonatal CD4+ T cells turn over at a markedly higher rate in infants and that the selective infection of the proliferating CD4+ T cells, and Treg cells (which suppress harmful reactions) may explain the higher viral loads and more rapid progression to AIDS in children (9). We are currently working with investigators at Boston Children’s Hospital, Harvard Medical School, and the Tulane University School of Medicine to test new vaccine strategies in infants.

Collaborative research:

The Division of Comparative Pathology works closely with investigators in other Divisions as well as various institutions across the nation. Drs. Pete Didier collaborates with, and play key roles in biodefense and tuberculosis research here at the center . Dr. Didier works with Dr. Chad Roy (Microbiology) on select agent research and with Dr. Deepak Kaushal (Division of Bacteriology) on tuberculosis studies (10). Dr. Robert Blair is an ACVP Board Certified veterinary pathologist, and a co-investigator with Dr. James Hoxie (U Penn CFAR) to examine and compare the pathogenicity of different unique enveloped viruses (11). He also works with Nito Panganiban and Nick Maness on Zika virus, and other infectious diseases. Dr. Xavier Alvarez manages the Molecular Pathology and Confocal Microscopy Core which provides tissue based imaging and analysis to all researchers at the TNPRC and is involved with numerous collaborative research projects with scientists across the nation (9-12).

Dr. Pyone Aye is head of the unit of Collaborative Research and manages financial and regulatory matters and laboratory experiments for multiple research projects (11-12). She is also the PI of the Simian Vaccine Evaluation Units NIH contrract, and coordinates with investigators across the nation in testing new vaccines and vaccine concepts for the NIH. Finally, the Division has strong collaborations with the LSU Health Sciences Center Comprehensive Alcohol Research Center (LSUHSC-CARC) with funding from the National Institute of Alcohol Abuse and Alcoholoism (NIAAA) to examine the roles of alcohol on SIV/HIV transmission and disease progression, and from the National Institute of Drug Abuse (NIDA) to elucidate the role of cannabinoids for their potential role in regulating intestinal inflammation. We also have active collaborations with several investigators at the National Institutes of Health (NIH), Northwestern University in Chicago, Harvard Medical School, The University of Pennsylvania, Case Western Researce University, the Aaron Diamond AIDS Research Institute, and other institutions.

Selected References cited:

1. Veazey RS, Lackner AA. Nonhuman Primate Models and Understanding the Pathogenesis of HIV Infection and AIDS. ILAR journal / National Research Council, Institute of Laboratory Animal Resources. 2017. PubMed PMID: 29228218. (

2. Stieh DJ, Matias E, Xu H, Fought AJ, Blanchard JL, Marx PA, Veazey RS, Hope TJ. Th17 Cells Are Preferentially Infected Very Early after Vaginal Transmission of SIV in Macaques. Cell Host Microbe. 2016;19(4):529-40. PubMed PMID: 27078070; PMCID: PMC4841252. (

3. Veazey RS, Pilch-Cooper HA, Hope TJ, Alter G, Carias AM, Sips M, Wang X, Rodriguez B, Sieg SF, Reich A, Wilkinson P, Cameron MJ, Lederman MM. Prevention of SHIV transmission by topical IFN-beta treatment. Mucosal Immunol. 2016;9(6):1528-36. doi: 10.1038/mi.2015.146. PubMed PMID: 26838048; PMCID: PMC4972705. (

4. Kumar V, Torben W, Kenway CS, Schiro FR, Mohan M. Longitudinal Examination of the Intestinal Lamina Propria Cellular Compartment of Simian Immunodeficiency Virus-Infected Rhesus Macaques Provides Broader and Deeper Insights into the Link between Aberrant MicroRNA Expression and Persistent Immune Activation. J Virol. 2016;90(10):5003-19. doi: 10.1128/JVI.00189-16. PubMed PMID: 26937033; PMCID: PMC4859716. (

5. Pahar B, Pan D, Lala W, Kenway-Lynch CS, Das A. Transforming growth factor-beta1 regulated phosphorylated AKT and interferon gamma expressions are associated with epithelial cell survival in rhesus macaque colon explants. Clin Immunol. 2015;158(1):8-18. Epub 2015/03/15. doi: 10.1016/j.clim.2015.03.001. PubMed PMID: 25769244; PMCID: 4420722. (

6. Xu H, Wang X, Malam N, Lackner AA, Veazey RS. Persistent Simian Immunodeficiency Virus Infection Causes Ultimate Depletion of Follicular Th Cells in AIDS. J Immunol. 2015;195(9):4351-7. doi: 10.4049/jimmunol.1501273. PubMed PMID: 26408660; PMCID: PMC4610871. (

7. Robillard KN, Lee KM, Chiu KB, MacLean AG. Glial cell morphological and density changes through the lifespan of rhesus macaques. Brain, behavior, and immunity. 2016;55:60-9. doi: 10.1016/j.bbi.2016.01.006. PubMed PMID: 26851132; PMCID: PMC4899176. (

8. Perez S, Johnson AM, Xiang SH, Li J, Foley BT, Doyle-Meyers L, Panganiban A, Kaur A, Veazey RS, Wu Y, Ling B. Persistence of SIV in the brain of SIV-infected Chinese rhesus macaques with or without antiretroviral therapy. J Neurovirol. 2018;24(1):62-74. doi: 10.1007/s13365-017-0594-0. PubMed PMID: 29181724; PMCID: PMC5792315. (

9. Wang X, Xu H, Shen C, Alvarez X, Liu D, Pahar B, Ratterree MS, Doyle-Meyers LA, Lackner AA, Veazey RS. Profound loss of intestinal Tregs in acutely SIV-infected neonatal macaques. Journal of leukocyte biology. 2015;97(2):391-400. PMCID: PMC4304427. (

10. Kaushal D, Foreman TW, Gautam US, Alvarez X, Adekambi T, Rangel-Moreno J, Golden NA, Johnson AM, Phillips BL, Ahsan MH, Russell-Lodrigue KE, Doyle LA, Roy CJ, Didier PJ, Blanchard JL, Rengarajan J, Lackner AA, Khader SA, Mehra S. Mucosal vaccination with attenuated Mycobacterium tuberculosis induces strong central memory responses and protects against tuberculosis. Nature communications. 2015;6:8533. PMCID: PMC4608260. (

11. Breed MW, Elser SE, Torben W, Jordan AP, Aye PP, Midkiff C, Schiro F, Sugimoto C, Alvarez-Hernandez X, Blair RV, Somasunderam A, Utay NS, Kuroda MJ, Pahar B, Wiseman RW, O'Connor DH, LaBranche CC, Montefiori DC, Marsh M, Li Y, Piatak M, Jr., Lifson JD, Keele BF, Fultz PN, Lackner AA, Hoxie JA. Elite Control, Gut CD4 T Cell Sparing, and Enhanced Mucosal T Cell Responses in Macaca nemestrina Infected by a Simian Immunodeficiency Virus Lacking a gp41 Trafficking Motif. J Virol. 2015;89(20):10156-75. PMCID: 4580161. (

12. Dowling DJ, van Haren SD, Scheid A, Bergelson I, Kim D, Mancuso CJ, Foppen W, Ozonoff A, Fresh L, Theriot TB, Lackner AA, Fichorova RN, Smirnov D, Vasilakos JP, Beaurline JM, Tomai MA, Midkiff CC, Alvarez X, Blanchard JL, Gilbert MH, Aye PP, Levy O. TLR7/8 adjuvant overcomes newborn hyporesponsiveness to pneumococcal conjugate vaccine at birth. JCI Insight. 2017;2(6):e91020. PMCID: PMC5360187. (