Poster Presentation 12th Australasian Virology Society Meeting 2024

Chronic inflammation and T-cell exhaustion ubiquitous in Central Australian HTLV-1c infection is associated with defective proviruses retaining antisense hbz gene (#167)

Ashley Hirons 1 2 , Natasha Jansz 1 2 3 , Jennifer Juno 1 2 , Nicholas Hirons 1 , Paula Ellenburg 1 4 , Ashley Yap 1 2 , Lauren Burmas 1 2 , Radwan Talukder 5 , Allegra Vickas 6 , Samantha Grimley 1 2 , John Zaunders 7 8 9 , Geoffrey Faulkner 3 , Lloyd Einsiedel 1 5 , Georges Khoury 1 2 , Damian Purcell 1 2
  1. University of Melbourne, Melbourne, Victoria, Australia
  2. Doherty Institute, Melbourne, Victoria, Australia
  3. Mater Translational Research Institute, Brisbane, Queensland, Australia
  4. Burnet Institute, Melbourne, Victoria, Australia
  5. Alice Springs Hospital, Alice Springs, Northern Territory, Australia
  6. Charles Darwin University, Darwin, Northern Territory, Australia
  7. St Vincent's Hospital, Sydney, New South Wales, Australia
  8. Kirby Institute, Sydney, New South Wales, Australia
  9. University of NSW, Sydney, New South Wales, Australia

Background

HTLV-1 subtype-C (HTLV-1c) infection is endemic in Central Australia with prevalence rates ~40% in some First Nations communities. HTLV-1c is a genetically divergent subtype and commonly associated with pulmonary disease (HAPD) and early all-cause mortality. This study determines the host-virus factors of HTLV-1c-related pathologies.

Methods

Matching plasma and PBMCs (n=77) were collected at Alice Springs Hospital. Plasma cytokine levels were measured by bead-array and PBMC proviral load (PVL) by ddPCR. HTLV-1c-specific T-cell responses were determined by activation induced marker (AIM) assay (n=40). The phenotypes of HTLV-1c-infected cells (n=34) were characterised by FACS. Integrated proviruses were amplified by limiting dilution nested PCR (n=6) and long-read sequenced using Nanopore.

Results

We observed HTLV-1c-specific T-cells and ubiquitous activation. We determined a dysfunctional cytokine network in HTLV-1c infection (positively-associated TNF-α, IL-2, age; negatively-associated IFN-γ, IL-8). Furthermore, we showed a unique HAPD cytokine profile (positively-associated IL-10, IL-6, PVL; negatively-associated IFN-γ, IL-8). We determined effector-memory T-cells are enriched for exhaustion markers, and corresponding soluble plasma markers, in HTLV-1c+ participants.

Notably, we observed activation and expansion of CCR4+CD4+ lung-homing proxy-phenotype cells correlating to PVL. All participants harboured highly-defective provirus, however HAPD+ differentially retained hbz gene. We detected exclusively replication competent provirus in CCR4-CD4+ T-cells. Proviral deletion breakpoints frequently occurred at LTR-like sequences. Lastly, we characterised novel HTLV-1c-host chimeric proviruses.

Conclusions

We identified a dysfunctional T-cell and cytokine response leading to exhaustion in all HTLV-1c-infected individuals, which may contribute to increased all-cause mortality. HTLV-1c-infected and activated cells with lung-homing potential may contribute to HAPD, however CCR4-CD4+ T-cells containing full-length provirus may facilitate transmission. Retention of hbz gene in HAPD+ subjects suggests its’ expression is crucial in driving disease. Chimeric proviruses may further contribute to cell dysfunction and pathogenesis.

Phenotypic characterisation of HTLV-1c-infected cells, and the provirus structure within, provides a focus for future studies developing therapeutic strategies.