Discovery and description of the first human Retro-Giant virus

Background: Robert Gallo reported the first human retrovirus HLTV in 1980. What we report here is the first human giant virus, Mimivirus-like, with a retroviral core. Methods:   The isolation of human giant viruses from human T cells  Leukaemia was performed on 25% sucrose gradient. The purified viral pellet was examined using electron microscopy (EM), after immunolabelling with anti-FeLV gag p27 moAb, used for its ability to bind conserved epitopes among different mammalian retroviruses. RNA extracted from the viral particles was amplified with the Pan Retrovirus PCR technique that targets the most conserved VLPQG and YMDD in the Pol region of different retroviruses. The amplified genes were sequenced and analyzed with molecular phylogenetic tests. Results: EM showed the presence of ~400 nm giant viruses, mimivirus-like, specifically labelled by anti-FeLV gag p27 Ab. RNA extracted from the particles contained retroviral genes. Molecular phylogenetic analyses of 150 bp amplicon product, compared with the same size amplicons of the Pol gene of diverse retroviruses, showed that the retro-giant viruses are a distinct branch, missing from the current classification of retroviruses. Conclusions: Although sharing some of the morphological features with Mimiviruses, this human giant virus differs substantially from environmental DNA-giant viruses isolated so far, in that it manifests a unique mammalian transforming retroviral core and T cell tropism. The virus should not be confused with a classic human retrovirus nor even a large human retrovirus, but an ancestral human giant virus, mimivirus-like, with a mammalian retroviral core. Certainly, the oncogenic potential of the viral particle and its T cell tropism is of concern and further studies are needed to clarify the role of this giant virus in human diseases and evolution of archetypal retroviruses.