An in vivo replication-important function in the second coding exon of Tat is constrained against mutation despite cytotoxic T lymphocyte selection.
Human and simian immunodeficiency virus (HIV/SIV) Tat proteins are specified by two coding exons. Tat functions in the transcription of primate lentiviruses. A plethora of in vitro data currently suggests that the second coding exon of Tat is largely devoid of function. However, whether the second exon of Tat contributes functionally to viral pathogenesis in vivo remains unknown. To address this question directly, we compared infection of rhesus macaques with an SIV, engineered to express only the first coding exon of Tat (SIVtat1ex), to counterpart infection with wild-type SIVmac239 virus, which expresses the full 2-exon Tat. This comparison showed that the second coding exon of Tat contributes to chronic SIV replication in vivo. Interestingly, in macaques, we observed a cytotoxic T lymphocytes (CTL) response to the second coding exon of Tat, which appears to durably control SIV replication. When SIV mutated in an attempt to escape this second Tat-exon-CTL, the resulting virus was less replicatively fit and failed to populate the host in vivo. Our study provides the first evidence that the second coding exon in Tat embodies an important function for in vivo replication. We suggest the second coding exon of Tat as an example of a functionally constrained "epitope" whose elicited CTL response cannot be escaped by virus mutation without producing a virus that replicates poorly in vivo.
Smith
Stephen M
SM
Saint Michael's Medical Center, Newark, New Jersey 07102, USA. stephens@cathedralhealth.org
Pentlicky
Sara
S
Klase
Zachary
Z
Singh
Mahender
M
Neuveut
Christine
C
Lu
Chun-yi
CY
Reitz
Marvin S
MS
Yarchoan
Robert
R
Marx
Preston A
PA
Jeang
Kuan-Teh
KT
D000595:Amino Acid Sequence; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D000956:Antigens, Viral / Q000276:immunology; D018791:CD4 Lymphocyte Count; D000939:Epitopes / Q000737:chemistry; D005091:Exons / Q000235:genetics / Q000502:physiology*; D015696:Gene Products, tat / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D005818:Genetic Engineering; D015497:HIV-1 / Q000737:chemistry; D006801:Humans; D008253:Macaca mulatta / Q000821:virology; D008969:Molecular Sequence Data; D009154:Mutation; D011379:Prognosis; D016097:Simian Acquired Immunodeficiency Syndrome / Q000276:immunology / Q000503:physiopathology / Q000821:virology; D015302:Simian Immunodeficiency Virus / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014766:Viremia; D014779:Virus Replication / Q000235:genetics*; D054322:tat Gene Products, Human Immunodeficiency Virus
D000914:Antibodies, Viral; D000956:Antigens, Viral; D000939:Epitopes; D015696:Gene Products, tat; D054322:tat Gene Products, Human Immunodeficiency Virus