Human immunodeficiency virus type 1 (HIV-1) antigen secretion by latently infected resting CD4+ T lymphocytes from HIV-1-infected individuals

Cell-to-cell transmission of HIV-1 from provirus-activated cells to resting naïve and memory human primary CD4 T cells is highly efficient and requires CD4 and F-actin but not chemokine receptors

Latently infected cells harboring replication-competent proviruses represent a major barrier to HIV-1 cure. One major effort to purge these cells has focused on developing the "shock and kill" approach for forcing provirus reactivation to induce cell killing by viral cytopathic effects, host immune responses, or both. We conducted kinetic and mechanistic studies of HIV-1 protein expression, virion production, and cell-to-cell virus transmission during provirus reactivation. Provirus-activated ACH-2 cells stimulated with romidepsin (RMD) or PMA produced Nef early, and then Env and Gag in parallel with the appearance of virions. Env on the surface of provirus-activated cells and cellular F-actin were critical in the formation of virological synapses to mediate cell-to-cell transmission of HIV-1 from provirus-activated cells to uninfected cells. This HIV-1 cell-to-cell transmission was substantially more efficient than transmission seen via cell-free virus spread and required F-actin remodeling and CD4, but not chemokine receptors. Resting human primary CD4⁺ T cells including naïve and memory subpopulations and, especially the memory CD4⁺ T cells, were highly susceptible to HIV-1 infection via cell-to-cell transmission. Cell-to-cell transmission of HIV-1 from provirus-activated cells was profoundly decreased by protease inhibitors (PIs) and neutralizing antibodies (nAbs) that recognize the CD4-binding site (CD4bs) such as VRC01, but not by reverse transcriptase (RT) inhibitor Emtricitabine (FTC). Therefore, our results suggest that PIs with potent blocking abilities should be used in clinical application of the "shock and kill" approach, most likely in combination with CD4bs nAbs, to prevent new HIV-1 infections.

Provirus activation plus CD59 blockage triggers antibody-dependent complement-mediated lysis of latently HIV-1-infected cells

Latently HIV-1-infected cells are recognized as the last barrier toward viral eradication and cure. To purge these cells, we combined a provirus stimulant with a blocker of human CD59, a key member of the regulators of complement activation, to trigger Ab-dependent complement-mediated lysis. Provirus stimulants including prostratin and histone deacetylase inhibitors such as romidepsin and suberoylanilide hydroxamic acid activated proviruses in the latently HIV-1-infected T cell line ACH-2 as virion production and viral protein expression on the cell surface were induced. Romidepsin was the most attractive provirus stimulant as it effectively activated proviruses at nanomolar concentrations that can be achieved clinically. Antiretroviral drugs including two protease inhibitors (atazanavir and darunavir) and an RT inhibitor (emtricitabine) did not affect the activity of provirus stimulants in the activation of proviruses. However, saquinavir (a protease inhibitor) markedly suppressed virus production, although it did not affect the percentage of cells expressing viral Env on the cell surface. Provirus-activated ACH-2 cells expressed HIV-1 Env that colocalized with CD59 in lipid rafts on the cell surface, facilitating direct interaction between them. Blockage of CD59 rendered provirus-activated ACH-2 cells and primary human CD4(+) T cells that were latently infected with HIV-1 sensitive to Ab-dependent complement-mediated lysis by anti-HIV-1 polyclonal Abs or plasma from HIV-1-infected patients. Therefore, a combination of provirus stimulants with regulators of complement activation blockers represents a novel approach to eliminate HIV-1.

CD4+ T cells spontaneously producing human immunodeficiency virus type I in breast milk from women with or without antiretroviral drugs

Background

Transmission of human immunodeficiency virus type 1 (HIV-1) through breast-feeding may involve both cell-free and cell-associated virus. This latter viral reservoir remains, however, to be fully explored. CD4⁺ T cell-associated virus production in breast milk was therefore investigated.

Methods

The ex vivo spontaneous production of HIV-1 antigen and HIV-1 RNA by CD4⁺ T cells was measured in paired blood and breast milk samples from 15 HIV-1 infected women treated or not with antiretroviral drugs. Spontaneous antigen secreting cells (HIV-1-AgSCs) from breast milk and blood were enumerated by an ELISpot assay, and cell-associated HIV-1 RNA was quantified by real-time PCR in supernatants of CD4⁺ T cells cultured for 18 hours without addition of polyclonal activators.

Results

Among the CD4⁺ T cells present in breast milk, memory cells expressing high levels of cell-surface activation markers were predominant. Spontaneous HIV-1-AgSCs were detected and enumerated in the breast milk of all 15 women, with a median number of 13.0 and 9.5 HIV-1- AgSCs/106 CD4⁺ T cells in aviremic (n = 7) and viremic (n = 8) women, respectively. Cell- associated HIV-1 RNA was detected in cell-free supernatants from 4/7 aviremic and 5/8 viremic individuals at median levels of 190 and 245 copies/ml, respectively.

Conclusions

Activated CD4⁺ T cells producing HIV-1 are detected in the breast milk of untreated individuals as well as those receiving highly active antiretroviral therapy. This finding strongly suggests that HIV-1 replication occurs in latently infected CD4⁺ T cells that, upon spontaneous activation, revert to productively infected cells. These cells might be responsible for a residual breast milk transmission despite maternal highly active antiretroviral therapy.

High-throughput screening uncovers a compound that activates latent HIV-1 and acts cooperatively with a histone deacetylase (HDAC) inhibitor

Current antiretroviral therapy (ART) provides potent suppression of HIV-1 replication. However, ART does not target latent viral reservoirs, so persistent infection remains a challenge. Small molecules with pharmacological properties that allow them to reach and activate viral reservoirs could potentially be utilized to eliminate the latent arm of the infection when used in combination with ART. Here we describe a cell-based system modeling HIV-1 latency that was utilized in a high-throughput screen to identify small molecule antagonists of HIV-1 latency. A more detailed analysis is provided for one of the hit compounds, antiviral 6 (AV6), which required nuclear factor of activated T cells for early mRNA expression while exhibiting RNA-stabilizing activity. It was found that AV6 reproducibly activated latent provirus from different lymphocyte-based clonal cell lines as well as from latently infected primary resting CD4(+) T cells without causing general T cell proliferation or activation. Moreover, AV6 complemented the latency antagonist activity of a previously described histone deacetylase (HDAC) inhibitor. This is a proof of concept showing that a high-throughput screen employing a cell-based model of HIV-1 latency can be utilized to identify new classes of compounds that can be used in concert with other persistent antagonists with the aim of viral clearance.

The potential impact of CD4+ T cell activation and enhanced Th1/Th2 cytokine ratio on HIV-1 secretion in the lungs of individuals with advanced AIDS and active pulmonary infection

Bronchoalveolar lavage fluid (BALF) provides a source of mucosal CD4(+) T cells. We investigated the physiological properties of T lymphocytes from BALF and blood and their role on the dynamic of HIV-1 replication among AIDS patients with active lung infections. Pulmonary CD4(+) T cells consist mainly of effector memory cells (CD45RO(+) and CCR7(-)) with increased expression of activation markers (HLA-DR(+) and CD69(+)) when compared to the blood counterpart. We observed a high frequency of BALF cells capable of secreting HIV-1-Ags suggesting that the local lung environment may support favorable conditions for CD4(+) T lymphocytes harboring HIV-1 DNA to initiate the viral cycle. Nevertheless, the high number of IFN-γ-producing cells and the predominance of Th1 immune response in the lung could limit the secretion of HIV-1 RNA. In conclusion, the capacity of activated CD4(+) T cells to produce HIV-1 is driven by both the level and quality of cellular activation in the lung.

Close association of CD8+/CD38 bright with HIV-1 replication and complex relationship with CD4+ T-cell count

BACKGROUND

Measuring lymphocyte activation provides information in addition to CD4(+) T-cell count for immune monitoring of HIV-1 infected patients. CD38 is a well-established activation marker that is generally analyzed on the whole population of CD8(+) T-cells. Focusing specifically on CD38 high expression (CD8(+)/CD38(bright)) may be an interesting surrogate gating strategy because CD38(bright) characterizes principally activated memory cells.

METHODS

CD8(+)/CD38(bright) was investigated in 1,353 HIV-1 infected patients over a one-year period to establish relevant cutoff values and clarify the relationships of this marker with HIV-1 RNA viral load (VL) and CD4(+) T-cell count.

RESULTS

The CD8(+)/CD38(bright) (>8,500 CD38 binding site per cells) is well correlated with HIV-1 VL (r = 0.87, P < 0.001) in this longitudinal follow-up of nonimmunodepressed patients that initiated antiviral therapy (ART). In aviremic patients on ART, the marker was highly predictive of VL rebound (sensitivity 93%, specificity 64% for a VL level of detection >200 copies/ml). While the CD8(+)/CD38(bright) moderately correlated with CD4(+) T-cell count independently of the VL (r = -0.37, P < 0.001), it increased dramatically in aviremic patient groups that exhibited profound CD4(+) T-cell depletion (median 39% for CD4(+) T-cell counts <50/mm(3)). This result indicates that other additional immunological and/or viral factors than readily detectable HIV-1 replication appears to be involved in T-cell activation of immunodepressed individuals.

CONCLUSIONS

CD8(+)/CD38(bright) is an effective marker for monitoring T-cell activation, which is a central factor of HIV-1 pathogenesis. This gating strategy requires only a single additional staining in conventional four color CD4 protocols.

Induction of granulysin in CD8+ T cells by IL-21 and IL-15 is suppressed by human immunodeficiency virus-1

Immunosuppression following infection with HIV-1 predisposes patients to a myriad of opportunistic pathogens, one of the most important of which is Mtb. Granulysin, expressed by NK cells and CTL, exhibits potent antimicrobial activity against Mtb and several other opportunistic pathogens associated with HIV-1 infection. The immune signals that promote granulysin expression in human CTL are not fully understood. Using primary human CD8+ T cells, in this study, we identify IL-21 as a strong inducer of granulysin, demonstrate that IL-21 and IL-15 activate granulysin expression within CD8+ CD45RO+ T cells, and establish a role for Jak/STAT signaling in the regulation of granulysin within CD8+ T cells. We show that infection of PBMC from healthy donors in vitro with HIV-1 suppresses granulysin expression by CD8+ T cells, concomitant with reduced p-STAT3 and p-STAT5, following activation with IL-15 and IL-21. Of note, simultaneous signaling through IL-15 and IL-21 could partially overcome the immunosuppressive effects of HIV-1 on granulysin expression by CD8+ T cells. These results suggest that HIV-1 infection of PBMC may reduce the antimicrobial profile of activated CD8+ T cells by disrupting signaling events that are critical for the induction of granulysin. Understanding the effects of HIV-1 on CD8+ T cell activation is essential to understanding the physiological basis for inadequate cytotoxic lymphocyte activity in HIV+ patients and for informed guidance of cytokine-based therapy to restore T cell function.

Functional Epstein-Barr virus reservoir in plasma cells derived from infected peripheral blood memory B cells

The Epstein-Barr virus (EBV) causes infectious mononucleosis, establishes latency in resting memory B lymphocytes, and is involved in oncogenesis through poorly understood mechanisms. The EBV lytic cycle is initiated during plasma cell differentiation by mRNAs transcripts encoded by BZLF1, which induce the synthesis of EBV proteins such as the immediate-early antigen ZEBRA and the late membrane antigen gp350. Therefore, we assessed the capacity of circulating EBV-infected B lymphocytes from healthy EBV-seropositive subjects to enter and complete the EBV lytic cycle. Purified B lymphocytes were polyclonally stimulated and BZLF1- or gp350-secreting cells (BZLF1-SCs or gp350-SCs) were enumerated by ELISpot assays. The number of BZLF1-SCs ranged from 50 to 480/107 lymphocytes (median, 80; 25th-75th percentiles, 70-150) and gp350-SCs from 10 to 40/107 lymphocytes (median, 17; 25th-75th percentiles, 10-20). gp350-SCs represented only 7.7% to 28.6% of BZLF1-SCs (median, 15%; 25th-75th percentiles, 10.5%-20%). This EBV functional reservoir was preferentially restricted to plasma cells derived from CD27(+) IgD(-) memory B lymphocytes. In 9 of 13 subjects, EBV DNA quantification in B-cell culture supernatants gave evidence of completion of EBV lytic cycle. These results demonstrate that EBV proteins can be secreted by EBV-infected B lymphocytes from healthy carriers, a majority generating an abortive EBV lytic cycle and a minority completing the cycle.

Biphasic decay kinetics suggest progressive slowing in turnover of latently HIV-1 infected cells during antiretroviral therapy

Background

Mathematical models based on kinetics of HIV-1 plasma viremia after initiation of combination antiretroviral therapy (cART) inferred HIV-infected cells to decay exponentially with constant rates correlated to their strength of virus production. To further define in vivo decay kinetics of HIV-1 infected cells experimentally, we assessed infected cell-classes of distinct viral transcriptional activity in peripheral blood mononuclear cells (PBMC) of five patients during 1 year after initiation of cART

Results

In a novel analytical approach patient-matched PCR for unspliced and multiply spliced viral RNAs was combined with limiting dilution analysis at the single cell level. This revealed that HIV-RNA⁺ PBMC can be stratified into four distinct viral transcriptional classes. Two overlapping cell-classes of high viral transcriptional activity, suggestive of a virion producing phenotype, rapidly declined to undetectable levels. Two cell classes expressing HIV-RNA at low and intermediate levels, presumably insufficient for virus production and occurring at frequencies exceeding those of productively infected cells matched definitions of HIV-latency. These cells persisted during cART. Nevertheless, during the first four weeks of therapy their kinetics resembled that of productively infected cells.

Conclusion

We have observed biphasic decays of latently HIV-infected cells of low and intermediate viral transcriptional activity with marked decreases in cell numbers shortly after initiation of therapy and complete persistence in later phases. A similar decay pattern was shared by cells with greatly enhanced viral transcriptional activity which showed a certain grade of levelling off before their disappearance. Thus it is conceivable that turnover/decay rates of HIV-infected PBMC may be intrinsically variable. In particular they might be accelerated by HIV-induced activation and reactivation of the viral life cycle and slowed down by the disappearance of such feedback-loops after initiation of cART.

Unintegrated HIV-1 provides an inducible and functional reservoir in untreated and highly active antiretroviral therapy-treated patients

Background

The presence of HIV-1 preintegration reservoir was assessed in an in vitro experimental model of latent HIV-1 infection, and in patients treated or not with highly active antiretroviral therapy (HAART).

Results

In resting CD4⁺ T lymphocytes latently infected in vitro with HIV-1, we demonstrated that the polyclonal activation induced a HIV-1 replication, which could be prevented by the use of an HIV-1 integrase inhibitor. We also showed that this reservoir was labile since the rescuable HIV-1-antigens production from unintegrated HIV-1 genomes declined over time. These data confirm that our experimental approach allows the characterization of a functional unintegrated HIV-1 reservoir. We then explored the preintegration reservoir in HIV-1-infected patients. This reservoir was detected in 11 of 12 untreated patients, in 4 of 10 sustained responders to HAART, and in one incomplete responder. This reservoir was also inducible, labile, and anti-HIV-1 integrase drug inhibited its induction. Finally, this reservoir was associated with the presence of spontaneous HIV-1 antigens producing CD4⁺ T cells in blood from 3 of 3 untreated patients and 2 of 2 sustained responders to HAART harboring a preintegration reservoir.

Conclusion

This preintegration phase of HIV-1 latency could be a consequence of the ongoing viral replication in untreated patients and of a residual viral replication in treated patients.

Isolation and characterization of HIV-1-infected resting CD4+ T lymphocytes in breast milk

An HIV-1 reservoir comprised primarily of latently infected resting CD4+ T lymphocytes that can be stimulated in vivo to produce virus may play a critical role in mother-to-child postnatal transmission of HIV-1 by breastfeeding. Here, we describe an experimental protocol for the detection of resting CD4+ T cell HIV-1 reservoir from breast milk. We adapted a method for the purification of resting CD4+ T lymphocytes in blood to isolate resting CD4+ T cells in breast milk from HIV-1-infected-lactating women (n=18) and from controls (n=3). Purified resting CD4+ T cells from blood and breast milk samples of HIV-1-infected-lactating women were polyclonally stimulated to characterize and enumerate HIV-1-antigen-secreting cells (HIV-1-Ag-SCs) by an enzyme-linked immunospot (ELISpot) assay. Resting CD4+ T cells represented more than 90% of purified viable breast milk cells. CD4+ T cell polyclonal stimulation combined with the ELISpot assay led to the characterization of a breast milk T cell HIV-1 reservoir greater than the blood reservoir (median 400 and 57.14 HIV-1-Ag-SCs/10(6) resting CD4+ T cells, respectively, p<0.001). Our strategy could be adapted to other body fluids and be useful for characterizing new HIV-1 reservoirs.

Detection of a large T-cell reservoir able to replicate HIV-1 actively in breast milk

In breast milk and paired blood samples of nine HIV-1-infected lactating women, we undertook a study to detect a CD4 T-cell reservoir and to investigate its capacity to enter viral production after activation. Breast milk-infected CD4 T cells have a greater capacity to produce viral particles actively than blood CD4 T cells. This observation may explain the apparent paradox of a transmissible viral infection from a body fluid with a low viral concentration.