Simian immunodeficiency virus SIVrcm, a unique CCR2-tropic virus, selectively depletes memory CD4+ T cells in pigtailed macaques through expanded coreceptor usage in vivo

Journal of Virology

Volumn 83, Issue 16, 2009, Pages 7894-7908

  Gautam, Rajeev ^a   Gaufin, Thaidra ^a   Butler, Isolde ^a   Gautam, Aarti ^a   Barnes, Mary ^a   Mandell, Daniel ^a   Pattison, Melissa ^a   Tatum, Coty ^a   Macfarland, Jeanne ^a   Monjure, Christopher ^a   Marx, Preston A ^a,b   Pandrea, Ivona ^a,c   Apetrei, Cristian ^a,b  

^a TULANE NATIONAL PRIMATE RESEARCH CENTER   (United States)

^b TULANE UNIVERSITY   (United States)

^c TULANE UNIVERSITY SCHOOL OF MEDICINE   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CHEMOKINE RECEPTOR CCR2; MESSENGER RNA; RNA;

ANIMAL CELL; ANIMAL EXPERIMENT; ANIMAL TISSUE; ARTICLE; CD4 LYMPHOCYTE COUNT; CONTROLLED STUDY; FOLLOW UP; HUMAN; HUMAN CELL; IMMUNOCOMPETENT CELL; IN VIVO STUDY; INOCULATION; MACACA; MEMORY CELL; NONHUMAN; NUCLEOTIDE SEQUENCE; PATHOGENESIS; PRIORITY JOURNAL; PROTEIN EXPRESSION; SIMIAN IMMUNODEFICIENCY VIRUS; VIRUS LOAD; VIRUS REPLICATION;

ANIMALS; CD4-POSITIVE T-LYMPHOCYTES; CELLS, CULTURED; DISEASE MODELS, ANIMAL; GENE EXPRESSION; HIV; HIV INFECTIONS; HUMANS; LEUKOCYTES, MONONUCLEAR; MACACA NEMESTRINA; MOLECULAR SEQUENCE DATA; RECEPTORS, CCR2; RECEPTORS, CCR4; RECEPTORS, HIV; SIMIAN ACQUIRED IMMUNODEFICIENCY SYNDROME; SIMIAN IMMUNODEFICIENCY VIRUS; VIRAL LOAD; VIRUS INTERNALIZATION; VIRUS REPLICATION;

MACACA; SIMIAN IMMUNODEFICIENCY VIRUS;

EID: 67749095197     PISSN: 0022538X     EISSN: None     Source Type: Journal    
DOI: 10.1128/JVI.00444-09     Document Type: Article

References (76)

1. Agy, M. B., L. R. Frumkin, L. Corey, R. W. Coombs, S. M. Wolinsky, J. Koehler, W. R. Morton, and M. G. Katze. 1992. Infection of Macaca nemestrina by human immunodeficiency virus type-1. Science 257:103-106.
2. Ambrose, Z., V. Boltz, S. Palmer, J. M. Coffin, S. H. Hughes, and V. N. Kewalramani. 2004. In vitro characterization of a simian immunodeficiency virus-human immunodeficiency virus (HIV) chimera expressing HIV type 1 reverse transcriptase to study antiviral resistance in pigtail macaques. J. Virol. 78:13553-13561.
3. + monocyte-derived macrophages activate resting T cells for HIV infection by producing CCR3 and CCR4 ligands. J. Immunol. 176:5760-5771.
4. Apetrei, C., A. Kaur, N. W. Lerche, M. Metzger, I. Pandrea, J. Hardcastle, S. Fakelstein, R. Bohm, J. Kohler, V. Traina-Dorge, T. Williams, S. Staprans, G. Plauche, R. S. Veazey, H. McClure, A. A. Lackner, B. Gormus, D. L. Robertson, and P. A. Marx. 2005. Molecular epidemiology of SIVsm in U.S. primate centers unravels the origin of SIVmac and SIVstm. J. Virol. 79:8991-9005.
5. Apetrei, C., N. W. Lerche, I. Pandrea, B. Gormus, M. Metzger, G. Silvestri, A. Kaur, R. Bohm, D. L. Robertson, J. Hardcastle, A. A. Lackner, and P. A. Marx. 2006. Kuru experiments triggered the emergence of pathogenic SIVmac. AIDS 20:317-321.
6. Beer, B. E., C. R. Brown, S. Whitted, S. Goldstein, R. Goeken, R. Plishka, A. Buckler-White, and V. M. Hirsch. 2005. Immunodeficiency in the absence of high viral load in pig-tailed macaques infected with simian immunodeficiency virus SIVsun or SIVlhoest. J. Virol. 79:14044-14056.
7. Beer, B. E., B. T. Foley, C. L. Kuiken, Z. Tooze, R. M. Goeken, C. R. Brown, J. Hu, M. St. Claire, B. T. Korber, and V. M. Hirsch. 2001. Characterization of novel simian immunodeficiency viruses from red-capped mangabeys from Nigeria (SIVrcmNG409 and -NG411). J. Virol. 75:12014- 12027.
8. Bibollet-Ruche, F., A. Galat-Luong, G. Cuny, P. Sarni-Manchado, G. Galat, J. P. Durand, X. Pourrut, and F. Veas. 1996. Simian immunodeficiency virus infection in a patas monkey (Erythrocebus patas): evidence for cross-species transmission from African green monkeys (Cercopithecus aethiops sabaeus) in the wild. J. Gen. Virol. 77:773-781.
9. Blois-Heulin, C., and B. Girona. 1999. Patterns of social visual attention in the red-capped mangabey (Cercocebus torquatus torquatus) in the context of food competition. Folia Primatol. (Basel) 70:180-184.
10. Borda, J. T., X. Alvarez, I. Kondova, P. Aye, M. A. Simon, R. C. Desrosiers, and A. A. Lackner. 2004. Cell tropism of simian immunodeficiency virus in culture is not predictive of in vivo tropism or pathogenesis. Am. J. Pathol. 165:2111-2122.
11. Brennan, G., Y. Kozyrev, T. Kodama, and S. L. Hu. 2007. Novel TRIM5 isoforms expressed by Macaca nemestrina. J. Virol. 81:12210-12217.
12. Carruth, L. M., M. C. Zink, P. M. Tarwater, M. D. Miller, M. Li, L. A. Queen, J. L. Mankowski, A. Shen, R. F. Siliciano, and J. E. Clements. 2005. SIV-specific T lymphocyte responses in PBMC and lymphoid tissues of SIV-infected pigtailed macaques during suppressive combination antiretroviral therapy. J. Med. Primatol. 34:109-121.
13. Chen, Z., D. Kwon, Z. Jin, S. Monard, P. Telfer, M. S. Jones, C. Y. Lu, R. F. Aguilar, D. D. Ho, and P. A. Marx. 1998. Natural infection of a homozygous Δ24 CCR5 red-capped mangabey with an R2b-tropic simian immunodeficiency virus. J. Exp. Med. 188:2057-2065.
14. Chen, Z., P. Zhou, D. D. Ho, N. R. Landau, and P. A. Marx. 1997. Genetically divergent strains of simian immunodeficiency virus use CCR5 as a coreceptor for entry. J. Virol. 71:2705-2714.
15. Cohen, J. 2000. AIDS research. Vaccine studies stymied by shortage of animals. Science 287:959-960.
16. Fauci, A. S., M. I. Johnston, C. W. Dieffenbach, D. R. Burton, S. M. Hammer, J. A. Hoxie, M. Martin, J. Overbaugh, D. I. Watkins, A. Mahmoud, and W. C. Greene. 2008. HIV vaccine research: the way forward. Science 321:530-532.
17. Fultz, P. N., H. M. McClure, D. C. Anderson, and W. M. Switzer. 1989. Identification and biologic characterization of an acutely lethal variant of simian immunodeficiency virus from sooty mangabeys (SIV/SMM). AIDS Res. Hum. Retrovir. 5:397-409.
18. Gartner, S., Y. Liu, M. G. Lewis, V. Polonis, W. R. Elkins, P. M. Zack, J. Miao, E. A. Hunter, J. Greenhouse, and G. A. Eddy. 1994. HIV-1 infection in pigtailed macaques. AIDS Res. Hum. Retrovir. 10(Suppl. 2):S129-S133.
19. Gartner, S., Y. Liu, V. Polonis, M. G. Lewis, W. R. Elkins, E. A. Hunter, J. Miao, K. J. Corts, and G. A. Eddy. 1994. Adaptation of HIV-1 to pigtailed macaques. J. Med. Primatol. 23:155-163.
20. Gautam, R., A. C. Carter, N. Katz, I. F. Butler, M. Barnes, A. Hasegawa, M. Ratterree, G. Silvestri, P. A. Marx, V. M. Hirsch, I. Pandrea, and C. Apetrei. 2007. In vitro characterization of primary SIVsmm isolates belonging to different lineages. In vitro growth on rhesus macaque cells is not predictive for in vivo replication in rhesus macaques. Virology 362:257-270.
21. Georges-Courbot, M. C., C. Y. Lu, M. Makuwa, P. Telfer, R. Onanga, G. Dubreuil, Z. Chen, S. M. Smith, A. Georges, F. Gao, B. H. Hahn, and P. A. Marx. 1998. Natural infection of a household pet red-capped mangabey (Cercocebus torquatus torquatus) with a new simian immunodeficiency virus. J. Virol. 72:600-608.
22. +-T-cell loss in simian immunodeficiency virus SIVagm-infected pigtailed macaques: variable pathogenicity of natural SIVagm isolates. J. Virol. 79:5153-5162.
23. Gordon, S. N., R. M. Dunham, J. C. Engram, J. Estes, Z. Wang, N. R. Klatt, M. Paiardini, I. V. Pandrea, C. Apetrei, D. L. Sodora, H. Y. Lee, A. T. Haase, M. D. Miller, A. Kaur, S. I. Staprans, A. S. Perelson, M. B. Feinberg, and G. Silvestri. 2008. Short-lived infected cells support virus replication in sooty mangabeys naturally infected with simian immunodeficiency virus: implications for AIDS pathogenesis. J. Virol. 82:3725-3735.
24. Gormus, B. J., L. N. Martin, and G. B. Baskin. 2004. A brief history of the discovery of natural simian immunodeficiency virus (SIV) infections in captive sooty mangabey monkeys. Front. Biosci. 9:216-224.
25. Hirsch, V. M., G. Dapolito, P. R. Johnson, W. R. Elkins, W. T. London, R. J. Montali, S. Goldstein, and C. Brown. 1995. Induction of AIDS by simian immunodeficiency virus from an African green monkey: species-specific variation in pathogenicity correlates with the extent of in vivo replication. J. Virol. 69:955-967.
26. Hirsch, V. M., G. A. Dapolito, S. Goldstein, H. McClure, P. Emau, P. N. Fultz, M. Isahakia, R. Lenroot, G. Myers, and P. R. Johnson. 1993. A distinct African lentivirus from Sykes' monkeys. J. Virol. 67:1517-1528.
27. Hirsch, V. M., and P. R. Johnson. 1994. Pathogenic diversity of simian immunodeficiency viruses. Virus Res. 32:183-203.
28. Hu, S. L. 2005. Non-human primate models for AIDS vaccine research. Curr. Drug Targets Infect. Disord. 5:193-201.
29. Imai, T., M. Baba, M. Nishimura, M. Kakizaki, S. Takagi, and O. Yoshie. 1997. The T cell-directed CC chemokine TARC is a highly specific biological ligand for CC chemokine receptor 4. J. Biol. Chem. 272:15036-15042.
30. Imai, T., D. Chantry, C. J. Raport, C. L. Wood, M. Nishimura, R. Godiska, O. Yoshie, and P. W. Gray. 1998. Macrophage-derived chemokine is a functional ligand for the CC chemokine receptor 4. J. Biol. Chem. 273:1764-1768.
31. Jin, M. J., J. Rogers, J. E. Phillips-Conroy, J. S. Allan, R. C. Desrosiers, G. M. Shaw, P. M. Sharp, and B. H. Hahn. 1994. Infection of a yellow baboon with simian immunodeficiency virus from African green monkeys: evidence for cross-species transmission in the wild. J. Virol. 68:8454-8460.
32. Kato, H., N. Tsuchiya, S. Izumi, M. Miyamasu, T. Nakajima, H. Kawasaki, K. Hirai, and K. Tokunaga. 1999. New variations of human CC-chemokine receptors CCR3 and CCR4. Genes Immun. 1:97-104.
33. Kaur, A., R. M. Grant, R. E. Means, H. McClure, M. Feinberg, and R. P. Johnson. 1998. Diverse host responses and outcomes following simian immunodeficiency virus SIVmac239 infection in sooty mangabeys and rhesus macaques. J. Virol. 72:9597-9611.
34. Khan, A. S., T. A. Galvin, L. J. Lowenstine, M. B. Jennings, M. B. Gardner, and C. E. Buckler. 1991. A highly divergent simian immunodeficiency virus (SIVstm) recovered from stored stump-tailed macaque tissues. J. Virol. 65:7061-7065.
35. Kirchhoff, F., S. Pohlmann, M. Hamacher, R. E. Means, T. Kraus, K. Uberla, and P. Di Marzio. 1997. Simian immunodeficiency virus variants with differential T-cell and macrophage tropism use CCR5 and an unidentified cofactor expressed in CEMx174 cells for efficient entry. J. Virol. 71:6509-6516.
36. Ling, B., R. S. Veazey, A. Luckay, C. Penedo, K. Xu, J. D. Lifson, and P. A. Marx. 2002. SIV(mac) pathogenesis in rhesus macaques of Chinese and Indian origin compared with primary HIV infections in humans. AIDS 16:1489-1496.
37. Ling, B., R. S. Veazey, and P. A. Marx. 2008. Nonpathogenic CCR2-tropic SIVrcm after serial passage and its effect on SIVmac infection of Indian rhesus macaques. Virology 379:38-44.
38. Looney, D. J., J. McClure, S. J. Kent, A. Radaelli, G. Kraus, A. Schmidt, K. Steffy, P. Greenberg, S. L. Hu, W. R. Morton, and F. Wong-Staal. 1998. A minimally replicative HIV-2 live-virus vaccine protects M. nemestrina from disease after HIV-2(287) challenge. Virology 242:150-160.
39. Luo, W., H. Yang, K. Rathbun, C. P. Pau, and C. Y. Ou. 2005. Detection of human immunodeficiency virus type 1 DNA in dried blood spots by a duplex real-time PCR assay. J. Clin. Microbiol. 43:1851-1857.
40. + T cells in multiple tissues during acute SIV infection. Nature 434:1093-1097.
41. McClure, H. M., D. C. Anderson, P. N. Fultz, A. A. Ansari, E. Lockwood, and A. Brodie. 1989. Spectrum of disease in macaque monkeys chronically infected with SIV/SMM. Vet. Immunol. Immunopathol. 21:13-24.
42. McKnight, A., M. T. Dittmar, J. Moniz-Periera, K. Ariyoshi, J. D. Reeves, S. Hibbitts, D. Whitby, E. Aarons, A. E. Proudfoot, H. Whittle, and P. R. Clapham. 1998. A broad range of chemokine receptors are used by primary isolates of human immunodeficiency virus type 2 as coreceptors with CD4. J. Virol. 72:4065-4071.
43. Morgan, C., M. Marthas, C. Miller, A. Duerr, C. Cheng-Mayer, R. Desrosiers, J. Flores, N. Haigwood, S. L. Hu, R. P. Johnson, J. Lifson, D. Montefiori, J. Moore, M. Robert-Guroff, H. Robinson, S. Self, and L. Corey. 2008. The use of nonhuman primate models in HIV vaccine development. PLoS Med. 5:e173.
44. Murphey-Corb, M., L. N. Martin, S. R. Rangan, G. B. Baskin, B. J. Gormus, R. H. Wolf, W. A. Andes, M. West, and R. C. Montelaro. 1986. Isolation of an HTLV-III-related retrovirus from macaques with simian AIDS and its possible origin in asymptomatic mangabeys. Nature 321:435-437.
45. National Research Council. 1996. Guide for the care and use of laboratory animals. National Academy Press, Washington, DC.
46. Newman, R. M., L. Hall, A. Kirmaier, L. A. Pozzi, E. Pery, M. Farzan, S. P. O'Neil, and W. Johnson. 2008. Evolution of a TRIM5-CypA splice isoform in Old World monkeys. PLoS Pathog. 4:e1000003.
47. O'Connor, D. H., T. M. Allen, and D. I. Watkins. 2001. Where have all the monkeys gone? Evaluating SIV-specific CTL in the post-Mamu-A*01 era. Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, NM.
48. O'Neil, S. P., S. P. Mossman, D. H. Maul, and E. A. Hoover. 1999. Virus threshold determines disease in SIVsmmPBj14-infected macaques. AIDS Res. Hum. Retrovir. 15:183-194.
49. Osterhaus, A. D., N. Pedersen, G. van Amerongen, M. T. Frankenhuis, M. Marthas, E. Reay, T. M. Rose, J. Pamungkas, and M. L. Bosch. 1999. Isolation and partial characterization of a lentivirus from talapoin monkeys (Myopithecus talapoin). Virology 260:116-124.
50. Pal, R., A. Garzino-Demo, P. D. Markham, J. Burns, M. Brown, R. C. Gallo, and A. L. DeVico. 1997. Inhibition of HIV-1 infection by the beta-chemokine MDC. Science 278:695-698.
51. Pandrea, I., C. Apetrei, J. Dufour, N. Dillon, J. Barbercheck, M. Metzger, B. Jacquelin, R. Bohm, P. A. Marx, F. Barre-Sinoussi, V. M. Hirsch, M. C. Muller-Trutwin, A. A. Lackner, and R. S. Veazey. 2006. Simian immunodeficiency virus SIVagm.sab infection of Caribbean African green monkeys: a new model for the study of SIV pathogenesis in natural hosts. J. Virol. 80:4858-4867.
52. + T cells is a typical feature of natural SIV hosts. Blood 109:1069-1076.
53. + T cell depletion. J. Immunol. 181:6687-6691.
54. Pandrea, I., C. Kornfeld, M. J. Ploquin, C. Apetrei, A. Faye, P. Rouquet, P. Roques, F. Simon, F. Barre-Sinoussi, M. C. Muller-Trutwin, and O. M. Diop. 2005. Impact of viral factors on very early in vivo replication profiles in simian immunodeficiency virus SIVagm-infected African green monkeys. J. Virol. 79:6249-6259.
55. Pandrea, I., R. Onanga, C. Kornfeld, P. Rouquet, O. Bourry, S. Clifford, P. T. Telfer, K. Abernethy, L. T. White, P. Ngari, M. Muller-Trutwin, P. Roques, P. A. Marx, F. Simon, and C. Apetrei. 2003. High levels of SIVmnd-1 replication in chronically infected Mandrillus sphinx. Virology 317:119-127.
56. Pandrea, I., R. M. Ribeiro, R. Gautam, T. Gaufin, M. Pattison, M. Barnes, C. Monjure, C. Stoulig, J. Dufour, W. Cyprian, G. Silvestri, M. D. Miller, A. S. Perelson, and C. Apetrei. 2008. Simian immunodeficiency virus SIVagm dynamics in African green monkeys. J. Virol. 82:3713-3724.
57. Pandrea, I., G. Silvestri, R. Onanga, R. S. Veazey, P. A. Marx, V. Hirsch, and C. Apetrei. 2006. Simian immunodeficiency viruses replication dynamics in African non-human primate hosts: common patterns and species-specific differences. J. Med. Primatol. 35:194-201.
58. + T cells is not predictive of simian immunodeficiency virus virulence. J. Immunol. 179:3035-3046.
59. Peeters, M., V. Courgnaud, B. Abela, P. Auzel, X. Pourrut, F. Bibollet-Ruche, S. Loul, F. Liegeois, C. Butel, D. Koulagna, E. Mpoudi-Ngole, G. M. Shaw, B. H. Hahn, and E. Delaporte. 2002. Risk to human health from a plethora of simian immunodeficiency viruses in primate bushmeat. Emerg. Infect. Dis. 8:451-457.
60. Perelson, A. S., A. U. Neumann, M. Markowitz, J. M. Leonard, and D. D. Ho. 1996. HIV-1 dynamics in vivo: virion clearance rate, infected cell life-span, and viral generation time. Science 271:1582-1586.
61. Reimann, K. A., R. A. Parker, M. S. Seaman, K. Beaudry, M. Beddall, L. Peterson, K. C. Williams, R. S. Veazey, D. C. Montefiori, J. R. Mascola, G. J. Nabel, and N. L. Letvin. 2005. Pathogenicity of simian-human immunodeficiency virus SHIV-89.6P and SIVmac is attenuated in cynomolgus macaques and associated with early T-lymphocyte responses. J. Virol. 79:8878-8885.
62. Silvestri, G., A. Fedanov, S. Germon, N. Kozyr, W. J. Kaiser, D. A. Garber, H. McClure, M. B. Feinberg, and S. I. Staprans. 2005. Divergent host responses during primary simian immunodeficiency virus SIVsm infection of natural sooty mangabey and nonnatural rhesus macaque hosts. J. Virol. 79:4043-4054.
63. Simon, F., S. Souquiere, F. Damond, A. Kfutwah, M. Makuwa, E. Leroy, P. Rouquet, J. L. Berthier, J. Rigoulet, A. Lecu, P. T. Telfer, I. Pandrea, J. C. Plantier, F. Barre-Sinoussi, P. Roques, M. C. Muller-Trutwin, and C. Apetrei. 2001. Synthetic peptide strategy for the detection of and discrimination among highly divergent primate lentiviruses. AIDS Res. Hum. Retrovir. 17:937-952.
64. Smith, S. M., M. Makuwa, F. Lee, A. Gettie, C. Russo, and P. A. Marx. 1998. SIVrcm infection of macaques. J. Med. Primatol. 27:94-98.
65. Staprans, S. I., and M. B. Feinberg. 2004. The roles of nonhuman primates in the preclinical evaluation of candidate AIDS vaccines. Expert Rev. Vaccines 3:S5-S32.
66. Stebbing, J., B. Gazzard, and D. C. Douek. 2004. Where does HIV live? N. Engl. J. Med. 350:1872-1880.
67. Stremlau, M., C. M. Owens, M. J. Perron, M. Kiessling, P. Autissier, and J. Sodroski. 2004. The cytoplasmic body component TRIM5α restricts HIV-1 infection in Old World monkeys. Nature 427:848-853.
68. Takehisa, J., Y. Harada, N. Ndembi, I. Mboudjeka, Y. Taniguchi, C. Ngansop, S. Kuate, L. Zekeng, K. Ibuki, T. Shimada, B. Bikandou, Y. Yamaguchi-Kabata, T. Miura, M. Ikeda, H. Ichimura, L. Kaptue, and M. Hayami. 2001. Natural infection of wild-born mandrills (Mandrillus sphinx) with two different types of simian immunodeficiency virus. AIDS Res. Hum. Retrovir. 17:1143-1154.
69. Thompson, J. D., D. G. Higgins, and T. J. Gibson. 1994. CLUSTAL W: improving the sensitivity of progressive multiple sequence alignment through sequence weighting, position-specific gap penalties and weight matrix choice. Nucleic Acids Res. 22:4673-4680.
70. Uberla, K. 2005. Efficacy of AIDS vaccine strategies in nonhuman primates. Med. Microbiol. Immunol. 194:201-206.
71. VandeWoude, S., and C. Apetrei. 2006. Going wild: lessons from naturally occurring T-lymphotropic lentiviruses. Clin. Microbiol. Rev. 19:72-62.
72. van Rensburg, E. J., S. Engelbrecht, J. Mwenda, J. D. Laten, B. A. Robson, T. Stander, and G. K. Chege. 1998. Simian immunodeficiency viruses (SIVs) from eastern and southern Africa: detection of a SIVagm variant from a chacma baboon. J. Gen. Virol. 79:1809-1814.
73. + T cells in lymphoid tissues during simian immunodeficiency virus infection. J. Virol. 74:11001-11007.
74. Watkins, D. I., D. R. Burton, E. G. Kallas, J. P. Moore, and W. C. Koff. 2008. Nonhuman primate models and the failure of the Merck HIV-1 vaccine in humans. Nat. Med. 14:617-621.
75. Zhang, L., P. J. Dailey, T. He, A. Gettie, S. Bonhoeffer, A. S. Perelson, and D. D. Ho. 1999. Rapid clearance of simian immunodeficiency virus particles from plasma of rhesus macaques. J. Virol. 73:855-860.
76. Zhang, Y., B. Lou, R. B. Lal, A. Gettie, P. A. Marx, and J. P. Moore. 2000. Use of inhibitors to evaluate coreceptor usage by simian and simian/human immunodeficiency viruses and human immunodeficiency virus type 2 in primary cells. J. Virol. 74:6893-6910.