Quantification of STLV-1 Tax in various tissues of non-human primates by different PCR methods.

BackgroundHuman T-lymphotropic virus type 1 (HTLV-1) is an oncogenic retrovirus which is transmitted via cell-containing blood fluids or from mother to child via breastfeeding, leading to severe diseases such as adult T-cell leukemia/lymphoma (ATL) and neuroinflammation. Most studies focus on virus detection in peripheral blood due to limited access of tissue material, especially in infants. Thus, our understanding of viral distribution in organs, in particular along the oral route of transmission, is still a critical gap in HTLV-1 research. Methodology/Principal FindingsHere, we present an analysis of tissues from a non-human primate (NHP) colony (olive baboon: Papio anubis) naturally infected with the closely related counterpart of HTLV-1, simian T-lymphotropic virus type 1 (STLV-1). Various organs and tissues of the oropharyngeal and gastrointestinal tract including tonsils, stomach, small intestine and colon were analyzed for the presence or absence of STLV-1. Beside TaqMan qPCR measuring relative copy numbers, we established a highly sensitive and precise droplet digital (dd) PCR protocol to measure absolute copy numbers of viral Tax DNA. Tax DNA was detectable in the tonsils in two NHPs, but to a greater extent in stomach in four NHPs. We also found Tax in parts of the small intestine, i.e. duodenum and Peyers patches, in a NHP with high blood proviral load. Conclusion/SignificanceThese data provide a quantitative analysis of STLV-1 Tax in the gastrointestinal tract and are, to our knowledge, the first indication of STLV-1 detection in stomach tissue of naturally STLV-1-infected asymptomatic NHPs. Although it is unclear how infection occurred - from mother-to-child, sexual or via animal bites - our study suggests that these parts of the gastrointestinal tract might either serve as site of virus transmission or as viral reservoir. Author summaryHuman T-lymphotropic virus type 1 (HTLV-1) is a human oncogenic retrovirus being transmitted via cell-containing body fluids such as breast milk, blood, or semen. The estimated number of infected people is around 10 to 20 million. To study the viral distribution and persistence of HTLV-1 in different organs in the oropharyngeal and gastrointestinal tract, a suitable in vivo model is essential. In this study, tissues of non-human primates (NHPs, baboon: Papio anubis) naturally infected with the closely related simian counterpart of HTLV-1, simian T-lymphotropic virus type 1 (STLV-1), were analyzed for the presence or absence of the viral gene Tax. We identified the presence of STLV-1 Tax in the stomach, duodenum and Peyers patches by using two different detection methods: TaqMan-based qPCR and the more sensitive droplet digital PCR (ddPCR). Tax could be detected in tonsils in two NHPs only, but in stomach in four NHPs. Together, this is the first time that STLV-1 Tax was detected in stomach tissue of STLV-1-infected asymptomatic NHPs, highlighting the importance of investigating viral persistence and/or viral reservoirs of primate T-lymphotropic viruses independently of the entry route.