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Whole-body immunoPET reveals active SIV dynamics
in viremic and antiretroviral therapy-treated macaques
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Nature Methods 2015 Santangelo
The detection of viral dynamics and localization in the context of controlled HIV infection remains a challenge and is limited to blood and biopsies. We developed a method to capture total-body simian immunodeficiency virus (SIV) replication using immunoPET (antibody-targeted positron emission tomography). The administration of a poly(ethylene glycol)-modified, 64Cu-labeled SIV Gp120-specific antibody led to readily detectable signals in the gastrointestinal and respiratory tract, lymphoid tissues and reproductive organs of viremic monkeys. Viral signals were reduced in aviremic antiretroviral-treated monkeys but detectable in colon, select lymph nodes, small bowel, nasal turbinates, the genital tract and lung. In elite controllers, virus was detected primarily in foci in the small bowel, select lymphoid areas and the male reproductive tract, as confirmed by quantitative reverse-transcription PCR (qRT-PCR) and immunohistochemistry. This real-time, in vivo viral imaging method has broad applications to the study of immunodeficiency virus pathogenesis, drug and vaccine development, and the potential for clinical translation. We describe the development of a non-invasive, sensitive immunoPET radiotracer and an approach to define the localization of SIV-infected tissue and free virus within live, chronically viremic, ART-treated and EC animals. The method can be repeated within the same animals (for example, before and during ART) without any adverse effect. In viremic animals, infection was concentrated within the mucosa of the gut, reiterating that these tissues are a major site of SIV replication12, 20, 21. However, we also observed discrete areas of virus replication, confirmed by qRT-PCR and IHC, both in nasal-associated tissues (post-ART) and in the reproductive tract of male animals. Within chronically infected, aviremic, ART-treated as well as EC animals, the methodology was able to detect residual virus, corroborated by qRT-PCR data. Thus, this approach provides the ability to identify novel areas of virus replication that may otherwise be difficult to sample in live animals. It may also provide a powerful tool to monitor the kinetics of viral replication in tissues over time during the application of novel therapeutic approaches. With the current efforts toward HIV eradication or functional cure, we believe that this method can be useful for determining organ-specific efficacy, which is crucial to the elimination of virally infected cells.
Our data also indicate that care must be taken when analyzing biopsies from aviremic subjects, especially ART-treated subjects, which may result in erroneous conclusions due to sampling (Supplementary Fig. 6 and Supplementary Table 3b). The detailed study of the cellular composition of these specific foci of infection, combined with site-specific drug metabolite levels and aided by the ability to image these specific sites, will likely be key to the development of directed therapies aimed at clearing infection from these sites in both controllers and individuals under ART28, 29, 30.
Although additional refinements to improve contrast and uptake are ongoing, we think that the methodology should be translatable to humans in the future because of the availability of anti-Env HIV antibodies31 and because the imaging approach is based on technologies already used in the clinic17, 18. It is applicable for studies investigating the eradication of HIV infection and targeting of virus reservoirs28, 32. Moreover, use of this technology during acute SIV infection may provide improved delineation of spatial kinetics of viral spread based on the route of infection and allow the identification of stages at which interruption of infection may be targeted using prophylactic methods33.

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