Poster Presentation 8th Australasian Virology Society Meeting and 11th Annual Meeting of the Australian Centre for Hepatitis & HIV Virology Meeting 2015

Novel features of the human T-lymphotropic virus type-1 (HTLV-1) subtype C infecting indigenous Australians (#175)

Georges Khoury 1 , Hai Pham 2 , Megan Crane 1 , Stirling Dick 3 , Kim Wilson 3 , Lloyd Einsiedal 2 , Damian FJ Purcell 4
  1. Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, VIC, Australia
  2. Territory Rural Clinical School/Flinders University, Alice Springs, NT, Australia
  3. National Reference Laboratory, St. Vincent’s Hospital, Melbourne, VIC, Australia
  4. Department of Microbiology and Immunology, University of Melbourne, Parkville, VIC, Australia

Human T-cell lymphotropic virus type-1 (HTLV-1) infects CD4+ and CD8+ T-cells of an estimated 20 million people worldwide and the globally common cosmopolitan subtype A causes a fatal T- cell leukaemia and inflammatory conditions, such as HTLV-1-associated myelopathy, in some individuals after a long incubation. HTLV-1 subtype C is highly endemic in PNG, the Pacific Islands and in remote indigenous Central Australians where some communities have the prevalence above 60%. These HTLV-1c infections are associated with immunopathogenic conditions, such as bronchiectasis, that may be driven by dysregulated immune function of infected T-cells containing integrated HTLV-1 provirus (HTLV-1 proviral load, PVL). We studied the unique genomic structure of HTLV-1c from 30 patients from the Alice Springs Hospital HTLV-1 cohort. We also developed a digital-droplet PCR (ddPCR) that could determine the absolute quantification of PVL in T-cells using DNA extracted from buffy coat cells (BCCs) and from one DNA sample from the bronchoalveolar lavage (BAL) infiltrates from a bronchiectasis patient to determine the involvement of HTLV-1 infected T-cells in clinical illness.
Genomic DNA was extracted and full length HTLV-1c sequence from 24 patients demonstrated mutations that impinge upon expression of the p12 accessory protein. Overall HTLV-1c DNA sequences diverged by ~7.5%, except in the p12 and HBZ genes regions that diverged by 20% and 14% respectively. The HTLV-1c PVL was quantified with gag/tax primers and FAM/MGB probes relative to an internal reference gene standard, RPP30, or negative threshold controls using only VIC/MGB probe. Of the 30 patient BCC samples, the PVL ranged between 194 – 2.35 x 106 proviral copies per 106 cells. The sensitivity (or limit of detection) of our ddPCR assay is 65 copies of proviral DNA per 106 cells. This technique offers logistic advantages in studying relationships between PVL from HTLV-1 patient’s DNA samples.
In conclusion, the highly prevalent HTLV-1c infections in indigenous central Australians can reach very high PVL in T-cells and this potentially causes novel effects on immune function through the expression of mutant versions of the p12 and HBZ proteins.