In Vitro Exposure to Prostratin but Not Bryostatin-1 Improves Natural Killer Cell Functions Including Killing of CD4+ T Cells Harboring Reactivated Human Immunodeficiency Virus

Abstract

In the attempt of purging the HIV-1 reservoir through the “shock-and-kill” strategy, it is important to select latency-reversing agents (LRAs) devoid of deleterious effects on the antiviral function of immune effector cells. Here, we investigated two LRAs with PKC agonist activity, prostratin (PRO) and bryostatin-1 (BRY), for their impact on the function of natural killer (NK) cells, the major effectors of innate immunity whose potential in HIV-1 eradication has emerged in recent clinical trials. Using NK cells of healthy donors, we found that exposure to either PRO or BRY potently activated NK cells, resulting in upmodulation of NKG2D and NKp44 activating receptors and matrix metalloprotease-mediated shedding of CD16 receptor. Despite PRO and BRY affected NK cell phenotype in the same manner, their impact on NK cell function was diverse and showed considerable donor-to-donor variation. Altogether, in most tested donors, the natural cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) of NK cells were either improved or maintained by PRO, while both activities were impaired by BRY. Moreover, we analyzed the effect of these drugs on the capacity of treated NK cells to kill autologous latently infected CD4+ T cells reactivated via the same treatment. First, we found that PRO but not BRY increased upmodulation of the ULBP2 ligand for NKG2D on reactivated p24+ cells. Importantly, we showed that clearance of reactivated p24+ cells by NK cells was enhanced when both targets and effectors were exposed to PRO but not to BRY. Overall, PRO had a superior potential compared with BRY as to the impact on key NK cell functions and on NK-cell-mediated clearance of the HIV-1 reservoir. Our results emphasize the importance of considering the effects on NK cells of candidate “shock-and-kill” interventions. With respect to combinative approaches, the impact on NK cells of each LRA should be re-evaluated upon combination with a second LRA, which may have analogous or opposite effects, or with immunotherapy targeting NK cells. In addition, avoiding co-administration of LRAs that negatively impact ADCC activity by NK cells might be essential for successful application of antibodies or vaccination to “shock-and-kill” strategies.

Hexamethylene bisacetamide impairs NK cell-mediated clearance of acute T lymphoblastic leukemia cells and HIV-1-infected T cells that exit viral latency

“…2C). As expected, NK cells responded to short-term IL-15 stimulation by upregulating both NKG2D and NKp44 14,22 , but not in the presence of HMBA. Thus, in NK cells HMBA suppresses cell-surface NKG2D expression and abrogates both NKG2D and NKp44 upmodulation induced by IL-15.

Figure 2HMBA downmodulates NKG2D on NK cells.

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Current Status of Latency Reversing Agents Facing the Heterogeneity of HIV-1 Cellular and Tissue Reservoirs

“…Recent studies demonstrating diverse responses of infected cells to LRAs point to their weak effect (Archin et al, 2012;Spivak et al, 2014;Elliott et al, 2015) and highlight the diversity of determinants responsible for the reservoirs' heterogeneity that were demonstrated so far to be virus genetic background- (Norton et al, 2019), cell model- (Spina et al, 2013), cell type- (Baxter et al, 2016;Grau-Expósito et al, 2019;Kula et al, 2019), silencing mechanism- (Elliott et al, 2014;Yukl et al, 2018), tissue reservoir- (Elliott et al, 2014;Telwatte et al, 2018;Yukl et al, 2018), integration site- (Chen et al, 2017;Abner et al, 2018;Battivelli et al, 2018), patient- (Darcis et al, 2017;Yukl et al, 2018), and gender- (Das et al, 2018) specific. In addition, some studies demonstrate a heterogeneous effect of LRAs on NK cells (Garrido et al, 2016) and cytotoxic T-cell lymphocyte (Walker-Sperling et al, 2016) activity with conflicting observations, suggesting either an immunosuppressive effect or a reduced impact of LRA activity on cells sensing HIV-1 reactivation (Archin et al, 2012;Jones et al, 2014;Clutton et al, 2016;Walker-Sperling et al, 2016;Desimio et al, 2017Desimio et al, , 2018. Moreover, prolonged ART treatment is associated with a significant reduction in the frequency of HIV-1-specific CD8 + T-cells (Gray et al, 1999;Casazza et al, 2001).…”

DNAM-1 Activating Receptor and Its Ligands: How Do Viruses Affect the NK Cell-Mediated Immune Surveillance during the Various Phases of Infection?

“…Latency reversing agents (LRAs), known as drugs able to induce viral production and unmask latently-infected cells, represent a promising clinical approach to cure HIV-1 [198,199]. LRAs promote “shock-and-kill” immune-mediated mechanisms, including those dependent on NK cells [200,201,202]. Interestingly, in the context of HIV-1, some LRAs have the potential to induce DNAM-1 ligands on CD4 + T cells [200]; therefore, it will be important to evaluate the contribution of DNAM-1-mediated responses of NK cells against HIV-1 infection upon the “shock-and-kill” triggering.…”