Background
The persistence of HIV-1 in a transcriptionally silent latent form in long-lasting memory CD4+ T cells remains one of the main barriers to cure AIDS. One strategy to eradicate HIV-1 reservoirs is the so-called “shock and kill” approach. It aims to reactivate latent HIV by administration of latency reserving agents (LRAs) to render infected cells vulnerable to elimination, while preventing de novo infections by cART. Thus far, however, it failed to clearly reduce the majority of latently HIV-infected cells. Thus, novel LRAs are urgently needed.
Methods
To discover novel endogenous compounds that reactivate latent HIV-1 proviruses, we screened a human hemofiltrate-derived peptide library containing essentially all the peptides and small proteins circulating in blood. To this purpose, we used J-Lat cells, a very well-established model system for HIV-1 latency involving Jurkat-derived T cell lines containing an integrated HIV-R7/E-/GFP genome. Viral protein induction in cART-suppressed PBMCs was assessed using HIV-1 Gag-p24 Simoa (PMID: 33796087), following 72 hours treatment with the test agent (RBP4) or anti-CD3/CD28 positive control.
Results
Multiple rounds of peptide separation and screening revealed that the human Retinol Binding Protein 4 (RBP4), a small protein that transports vitamin A (retinol) in blood, potently reactivates latent HIV in a variety of Jurkat T cell lines (p<0.001). Carrier-free RBP4 as well as free forms of retinoids (all-trans retinal, retinol and retinoic acid) do not reactivate HIV. Thus, the complex retinol-RBP4 (Holo-RBP4), which is very abundant in the circulation, seems essential for its activity as LRA. Notably, RBP4 significantly reactivates latent HIV-1 in primary T cells isolated from infected individuals under effective cART at physiological concentrations (p<0.05). Finally, JNK signalling pathway was identified to be relevant for RBP4-mediated activation of latent reservoirs.
Conclusions
We identified RBP4 as an endogenous and abundant circulating HIV-1 latency reversing agents that may modulate the size of the viral reservoirs in vivo.
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