Lymph nodes (LN) and their resident T follicular helper CD4+ T cells (Tfh) are a critical site for HIV replication and persistence. Therefore, optimizing antiviral activity in lymphoid tissues will be needed to reduce or eliminate the HIV reservoir. In this study, we treated ART-suppressed SIV-infected rhesus macaques (RM) with the lysophospholipid sphingosine-1 phosphate receptor modulator fingolimod (FTY720). With this design, we aimed at exploring the potential utility of fingolimod, approved clinically for multiple sclerosis, in retaining cytolytic lymphocytes in lymphoid sites of SIV persistence, from which they are typically excluded during ART, and to impact on the viral reservoir.
10 RMs infected with SIVmac239 started TDF/FTC/DTG treatment at day 42 post-infection; ART was continued for 9 months. Group 1 RMs (n=5) received FTY720 at 18 μg/Kg per day and group 2 (n=5) at 500 μg/Kg per day. FTY720 was administered orally once a day during the last 28 days of ART, once viremic control was achieved for all animals. Blood (PB) and lymph node (LN) were collected longitudinally for flow cytometric, histocytometry, RNAscope and DNAscope analyses. Cell-associated SIV-DNA and -RNA were quantified in CD4 T cell subsets, including Tfh, by quantitative PCR (qPCR) and reverse transcription quantitative PCR (RT-qPCR) respectively.
FTY720 treatment was safe and well tolerated, and plasma SIV levels remained undetectable (<60 RNA copies/ml) during the entire treatment. FTY720 was remarkably effective, in a dose dependent way, in reducing circulating CD4+ and CD8+ T cells (p<0.01), including those with cytolytic potential (expressing T-bet, perforin, and granzyme-B; p<0.01). FTY720 induced a transient increase in the frequencies of cycling T cells (expressing Ki-67) in blood of ART-treated, SIV-infected RMs (p<0.05). Furthermore, FTY720 promoted an increase in the number of T cells retained in LN (p=0.01), as determined directly in situ by histocytometry. Notably, the FTY720-induced inhibition of T cell egress from LN resulted in a measurable decrease of SIV-DNA and -RNA content in LN Tfh cells in most treated animals as measured by RNAscope (p=0.02; n=6) and qPCR (p=0.04; group 2).
By retaining cytolytic T cells in lymphoid sites of SIV persistence, FTY720 administration has the potential to limit a critical cellular reservoir of Tfh cells. As such, FTY720 should be considered in combined immune based interventions aimed at HIV remission.