Abstract Body

Background: To evaluate the immunomodulatory effects from HDACi in HIV-infected patients, we investigated a broad range of immune pathways during a latency reversal trial with panobinostat (PANO). Further, as prolonged epigenetic modulation from HDACi treatment has been raised as safety concern, we evaluated gene expression alterations up to 24 weeks after end of PANO dosing.

Methods: Using flow cytometry, we investigated the impact of PANO on T cell activation (CD69, HLA-DR, CD38), T cell exhaustion (PD-1). Further, levels of activated regulatory T cells and their expression of suppressive markers (CD39 and CTLA4) were assessed. To determine broad changes in immune responsiveness to common stimuli, whole blood stimulations with LPS were performed and inflammatory responses by cytokine release were determined using luminex. Gene expression from purified PBMC’s was evaluated using affymetrix HTA 2.0 gene chip.

Results: A rapid increase in proportions of both CD4 and CD8 T cells expressing CD69 were observed (p<0.01) as early as 24 hrs after first PANO dosing. This was followed by a marked increase in HLA-DR+ CD4 and CD8 T cells (p<0.01) observed at day 4. At the same time point, proportions of activated regulatory T cells increased by 40 % four days after treatment initiation (p=0.003) and MFI of the suppressive markers CD39 and CTLA4 increased by 12% (p=0.009) and 25 % (p=0.0002), respectively. LPS-induced inflammatory responses as determined by IL-1b, IL-12p40, IL-6 and TNF-a secretion were all significantly down regulated four days after dosing. Importantly, all these PANO-induced immunomodulatory effects were reversible and all markers had returned to pre-treatment levels 4 weeks after end of PANO dosing. Lastly, PANO induced significant changes in the overall gene expression pattern (fold-change >1.5, FDR-corrected p<0.05). These alterations in gene expression had regressed considerably by week 4 after end of PANO treatment and normalized entirely by week 24 post-PANO therapy.

Conclusions: PANO significantly but transiently influenced T cells activation status, regulatory T cell phenotype and functional mitogen responsiveness. All measures of immune function had returned to baseline levels 4 weeks after completion of PANO and long-term follow-up revealed no sustained effect on overall gene expression. Collectively, the results suggest that PANO does not cause persistent detrimental epigenetic or immunomodulatory changes in HIV patients.