Tenofovir and dolutegravir reduce human T-cell leukemia virus 1 transmission and de novo viral spread in vivo

Human T-leukemia virus 1 (HTLV-1) is an oncogenic retrovirus with no available curative therapy. In-vitro data suggests HTLV-1 may be susceptible to certain HIV-1 antiretroviral compounds but their value, if any, in the context of a clinically-relevant transmission model is unknown. We addressed this knowledge gap by investigating the efficacy of the anti-retroviral compounds, tenofovir and dolutegravir, in preventing HTLV-1 transmission and infection in a humanised mouse model of HTLV-1 subtype c (HTLV-1c) infection, the first of its kind. Characterisation of this model revealed that HTLV-1c and HTLV-1 subtype a (HTLV-1a) showed subtle differences in natural history of disease but not as striking as the differences observed clinically, indicating additional host and environmental contributors to human disease. Single cell RNA sequencing of CD4+ T cell VDJ transcripts revealed poly- and oligoclonal expansion of HTLV-1c-infected CD4+ T cells. We show that tenofovir significantly reduces HTLV-1 transmission in vivo at clinically relevant doses when administered as pre-exposure prophylaxis. Further, tenofovir and dolutegravir combination significantly attenuates viral spread and disease progression during early infection. Our data support the use of tenofovir and dolutegravir against HTLV-1 transmission and early infection. Routine use of these drugs as effective prophylactic agents against HIV-1 infection will facilitate their rapid translation to HTLV-1 clinical trials. Overall design: Splenocytes from 3x mock-infected and 3x HTLV-1c-infected humanised NOD-scid IL2Rgammanull mice were labelled with unique human Total-seqC oligonucleotide-conjugated 'hashtag' antibodies (BioLegend) and anti-human fluorescent antibodies against CD45 (Pecy5), CD4 (APC-H7) and CD45RO (Pe-CF594) before isolating human CD4+ memory T cells by FACS. Five samples were labelled with a unique hashtag. The sixth sample was labelled with an equal ratio combination of all five hashtags that could be identified during demultiplexing having a mixture of all five. 2,000 memory CD4+ T cells form each mouse were pooled (12,000 cells total) before single cell gel beads in emulsion (GEM) generation and barcoding in a 10X Genomics chromium controller (Chromium single cell 5' library and gel bead kit, PN-1000014). 5'-gene expression, cell surface protein (hashtag), and VDJ (Chromium single cell VDJ enrichment kit for T cells, PN-2000008/9) libraries were prepared as per manufacturer's instructions (10X Genomics). Libraries were sequenced by Illumina paired-end next generation sequencing on a NextSeq 500 machine. Data analysis was performed using R v4.0.0 (R Foundation for Statistical Computing, Vienna, Austria) and Bioconductor v3.11. Infected_1: Hashtag 1: TotalSeq-C0251 Infected_2: Hashtag 2: TotalSeq-C0252 Infected_3: Hashtag 3: TotalSeq-C0253 Uninfected_1: Hashtag 4: TotalSeq-C0254 Uninfected_2: Hashtag 5: TotalSeq-C0255 Uninfected_3: Hashtag 1,2,3,4,5: equal ratios