HIV type 1 persistence in CD4- /CD8- double negative T cells from patients on antiretroviral therapy

Frequency and functional profile of circulating TCRαβ+ double negative T cells in HIV/TB co-infection

BACKGROUND

Increased frequency of circulating double negative T (DNT, CD4^-CD8^-CD3⁺) cells with protective immune function has been observed in human immunodeficiency virus (HIV) infection and tuberculosis (TB). Here the role of circulating TCRαβ⁺ DNT cells was further investigated in HIV/TB co-infection.

METHODS

A cross-sectional study was conducted to investigate the frequency and functional profiles of peripheral TCRαβ⁺ DNT cells including apoptosis, chemokine and cytokine expression among healthy individuals and patients with TB, HIV infection and HIV/TB co-infection by cell surface staining and intracellular cytokine staining combined with flow cytometry.

RESULTS

Significantly increased frequency of TCRαβ⁺ DNT cells was observed in HIV/TB co-infection than that in TB (p < 0.001), HIV infection (p = 0.039) and healthy controls (p < 0.001). Compared with TB, HIV/TB co-infection had higher frequency of Fas expression (p = 0.007) and lower frequency of Annexin V expression on TCRαβ⁺ DNT cells (p = 0.049), and the frequency of Annexin V expression on Fas⁺TCRαβ⁺ DNT cells had no significant difference. TCRαβ⁺ DNT cells expressed less CCR5 in HIV/TB co-infection than that in TB (p = 0.014), and more CXCR4 in HIV/TB co-infection than that in HIV infection (p = 0.043). Compared with healthy controls, TB and HIV/TB co-infection had higher frequency of TCRαβ⁺ DNT cells secreting Granzyme A (p = 0.046; p = 0.005). In TB and HIV/TB co-infection, TCRαβ⁺ DNT cells secreted more granzyme A (p = 0.002; p = 0.002) and perforin (p < 0.001; p = 0.017) than CD4⁺ T cells but similar to CD8⁺ T cells.

CONCLUSIONS

Reduced apoptosis may take part in the mechanism of increased frequency of peripheral TCRαβ⁺ DNT cells in HIV/TB co-infection. TCRαβ⁺ DNT cells may play a cytotoxic T cells-like function in HIV/TB co-infection.

HIV Infection and Persistence in Pulmonary Mucosal Double Negative T Cells In Vivo

The lungs are relatively unexplored anatomical human immunodeficiency virus (HIV) reservoirs in the antiretroviral therapy (ART) era. Double negative (DN) T cells are a subset of T cells that lack expression of CD4 and CD8 (CD4^- CD8^-) and may have both regulatory and effector functions during HIV infection. Notably, circulating DN T cells were previously described as cellular HIV reservoirs. Here, we undertook a thorough analysis of pulmonary versus blood DN T cells of people living with HIV (PLWH) under ART. Bronchoalveolar lavage (BAL) fluid and matched peripheral blood were collected from 35 PLWH on ART and 16 uninfected volunteers without respiratory symptoms. Both PLWH and HIV-negative (HIV^-) adults displayed higher frequencies of DN T cells in BAL versus blood, and these cells mostly exhibited an effector memory phenotype. In PLWH, pulmonary mucosal DN T cells expressed higher levels of HLA-DR and several cellular markers associated with HIV persistence (CCR6, CXCR3, and PD-1) than blood. We also observed that DN T cells were less senescent (CD28^- CD57⁺) and expressed less immunosuppressive ectonucleotidase (CD73/CD39), granzyme B, and perforin in the BAL fluid than in the blood of PLWH. Importantly, fluorescence-activated cell sorter (FACS)-sorted DN T cells from the BAL fluid of PLWH under suppressive ART harbored HIV DNA. Using the humanized bone marrow-liver-thymus (hu-BLT) mouse model of HIV infection, we observed higher infection frequencies of lung DN T cells than those of the blood and spleen in both early and late HIV infection. Overall, our findings show that HIV is seeded in pulmonary mucosal DN T cells early following infection and persists in these potential cellular HIV reservoirs even during long-term ART.IMPORTANCE Reservoirs of HIV during ART are the primary reasons why HIV/AIDS remains an incurable disease. Indeed, HIV remains latent and unreachable by antiretrovirals in cellular and anatomical sanctuaries, preventing its eradication. The lungs have received very little attention compared to other anatomical reservoirs despite being immunological effector sites exhibiting characteristics ideal for HIV persistence. Furthermore, PLWH suffer from a high burden of pulmonary non-opportunistic infections, suggesting impaired pulmonary immunity despite ART. Meanwhile, various immune cell populations have been proposed to be cellular reservoirs in blood, including CD4^- CD8^- DN T cells, a subset that may originate from CD4 downregulation by HIV proteins. The present study aims to describe DN T cells in human and humanized mice lungs in relation to intrapulmonary HIV burden. The characterization of DN T cells as cellular HIV reservoirs and the lungs as an anatomical HIV reservoir will contribute to the development of targeted HIV eradication strategies.

HIV-1 Sanctuary Sites-the Role of Membrane-Associated Drug Transporters and Drug Metabolic Enzymes

Despite significant advances in the treatment of human immunodeficiency virus-1 (HIV) infection with highly active antiretroviral drug therapy, the persistence of the virus in cellular and anatomic reservoirs is a major obstacle preventing total HIV eradication. Viral persistence could result from a variety of contributing factors including, but not limited to, non-adherence to treatment and adverse drug reactions, latently infected cells carrying replication-competent virus, drug-drug interactions, and inadequate antiretroviral drug (ARV) concentrations reached in several anatomic sites such as the brain, testis, and gut-associated lymphoid tissues. The distribution of ARVs at specific sites of infection is primarily dependent on drug physicochemical properties and drug plasma protein binding, as well as drug efflux, influx, and metabolic processes. A thorough understanding of the functional roles of drug transporters and metabolic enzymes in the disposition of ARVs in immune cell types and tissues that are characterized as HIV reservoirs and sanctuaries is critical to overcome the challenge of suboptimal drug distribution at sites of persistent HIV infection. This review summarizes the current knowledge related to the expression and function of drug transporters and metabolic enzymes in HIV cellular and anatomic reservoirs, and their potential contribution to drug-drug interactions and insufficient drug concentration at these sites.

Drug efflux transporters and metabolic enzymes in human circulating and testicular T-cell subsets: relevance to HIV pharmacotherapy

OBJECTIVES

ATP-binding cassette (ABC) drug efflux transporters and drug metabolic enzymes could reduce antiretroviral concentrations in HIV target cells. The testis has been demonstrated to be a sanctuary site, displaying suboptimal antiretroviral concentrations and persistent HIV infection. Therefore, we compared the expression and function of ABC transporters and metabolic enzymes in CD4 and CD8 T cells isolated from human testis and peripheral blood mononuclear cells (PBMCs), and assessed their expression in circulating naive and memory CD4 T-cell phenotypes.

DESIGN

Testicular tissue and blood were collected from 15 uninfected donors undergoing gender affirmation surgery. Testicular interstitial cells were isolated by enzymatic digestion, whereas PBMCs were isolated from blood by density gradient centrifugation. The expression and/or function of ABC transporters and metabolic enzymes were examined in blood and testicular T-cell subsets by flow cytometry.

RESULTS

ABC transporters (P-gp, BCRP, MRP1) and metabolic enzymes (CYP3A4, UGT1A1) were expressed in testicular and circulating CD4 and CD8 T cells, as well as in circulating naive, central, transitional, and effector memory T-cell phenotypes. MRP1 demonstrated lower frequencies in T cells from testis compared with PBMCs, as well as in circulating naive T cells compared with the memory T-cell phenotypes. Functional activity of P-gp and BCRP was detected in T-cell subsets from testis and PBMCs.

CONCLUSION

Our findings demonstrate for the first time that antiretroviral drug efflux transporters and metabolic enzymes are functionally expressed in T-cell subsets infiltrating the human testis. These transporters and enzymes can reduce antiretroviral intracellular concentrations, potentially contributing to residual HIV replication in the testis, and negatively impact HIV cure strategies.

Conversion of effector CD4+ T cells to a CD8+ MHC II-recognizing lineage

CD4⁺ and CD8⁺ T cells are dichotomous lineages in adaptive immunity. While conventionally viewed as distinct fates that are fixed after thymic development, accumulating evidence indicates that these two populations can exhibit significant lineage plasticity, particularly upon TCR-mediated activation. We define a novel CD4^-CD8αβ⁺ MHC II-recognizing population generated by lineage conversion from effector CD4⁺ T cells. CD4^-CD8αβ⁺ effector T cells downregulated the expression of T helper cell-associated costimulatory molecules and increased the expression of cytotoxic T lymphocyte-associated cytotoxic molecules. This shift in functional potential corresponded with a CD8⁺-lineage skewed transcriptional profile. TCRβ repertoire sequencing and in vivo genetic lineage tracing in acutely infected wild-type mice demonstrated that CD4^-CD8αβ⁺ effector T cells arise from fundamental lineage reprogramming of bona fide effector CD4⁺ T cells. Impairing autophagy via functional deletion of the initiating kinase Vps34 or the downstream enzyme Atg7 enhanced the generation of this cell population. These findings suggest that effector CD4⁺ T cells can exhibit a previously unreported degree of skewing towards the CD8⁺ T cell lineage, which may point towards a novel direction for HIV vaccine design.

Infrequent HIV Infection of Circulating Monocytes during Antiretroviral Therapy

Whereas human immunodeficiency virus (HIV) persists in tissue macrophages during antiretroviral therapy (ART), the role of circulating monocytes as HIV reservoirs remains controversial. Three magnetic bead selection methods and flow cytometry cell sorting were compared for their capacity to yield pure CD14⁺ monocyte populations. Cell sorting by flow cytometry provided the purest population of monocytes (median CD4⁺ T-cell contamination, 0.06%), and the levels of CD4⁺ T-cell contamination were positively correlated with the levels of integrated HIV DNA in the monocyte populations. Using cell sorting by flow cytometry, we assessed longitudinally the infection of monocytes and other cell subsets in a cohort of 29 Thai HIV-infected individuals. Low levels of HIV DNA were detected in a minority of monocyte fractions obtained before and after 1 year of ART (27% and 33%, respectively), whereas HIV DNA was readily detected in CD4⁺ T cells from all samples. Additional samples (2 to 5 years of ART) were obtained from 5 individuals in whom monocyte infection was previously detected. Whereas CD4⁺ T cells were infected at high levels at all time points, monocyte infection was inconsistent and absent in at least one longitudinal sample from 4/5 individuals. Our results indicate that infection of monocytes is infrequent and highlight the importance of using flow cytometry cell sorting to minimize contamination by CD4⁺ T cells.IMPORTANCE The role of circulating monocytes as persistent HIV reservoirs during ART is still controversial. Several studies have reported persistent infection of monocytes in virally suppressed individuals; however, others failed to detect HIV in this subset. These discrepancies are likely explained by the diversity of the methods used to isolate monocytes and to detect HIV infection. In this study, we show that only flow cytometry cell sorting yields a highly pure population of monocytes largely devoid of CD4 contaminants. Using this approach in a longitudinal cohort of HIV-infected individuals before and during ART, we demonstrate that HIV is rarely found in monocytes from untreated and treated HIV-infected individuals. This study highlights the importance of using methods that yield highly pure populations of cells as flow cytometry cell sorting to minimize and control for CD4⁺ T-cell contamination.

Impact of the SCF signaling pathway on leukemia stem cell-mediated ATL initiation and progression in an HBZ transgenic mouse model

Adult T-cell leukemia (ATL) is a malignant disease caused by human T-lymphotropic virus type 1. In aggressive ATL, the response to chemotherapy is extremely poor. We hypothesized that this poor response is due to the existence of chemotherapy-resistant cells, such as leukemic stem cells. Previously, we successfully identified an ATL stem cell (ATLSC) candidate as the c-kit⁺/CD38⁻/CD71⁻ cells in an ATL mouse model using Tax transgenic mice. Here, with a new ATL mouse model using HBZ-transgenic mice, we further discovered that the functional ATLSC candidate, which commonly expresses c-kit, is drug-resistant and has the ability to initiate tumors and reconstitute lymphomatous cells. We characterized the ATLSCs as c-kit⁺/CD4⁻/CD8⁻ cells and found that they have a similar gene expression profile as T cell progenitors. Additionally, we found that AP-1 gene family members, including Junb, Jund, and Fosb, were up-regulated in the ATLSC fraction. The results of an in vitro assay showed that ATLSCs cultured with cytokines known to promote stem cell expansion, such as stem cell factor (SCF), showed highly proliferative activity and maintained their stem cell fraction. Inhibition of c-kit–SCF signaling with the neutralizing antibody ACK2 affected ATLSC self-renewal and proliferation. Experiments in Sl/Sld mice, which have a mutation in the membrane-bound c-kit ligand, found that ATL development was completely blocked in these mice. These results clearly suggest that the c-kit–SCF signal plays a key role in ATLSC self-renewal and in ATL initiation and disease progression.

Double Negative (DN) [CD3⁺CD4⁻CD8⁻] T cells correlate with disease progression during HIV infection

Although double negative T (DNT) cells (CD3⁺CD4⁻CD8⁻) share some characteristics with T regulatory cells, the relationship between DNT cells and disease progression in HIV infection is unclear. In this study, we analyzed the relationship between DNT cells and disease progression during the first 2 years of HIV infection. We found that DNT cell numbers tended to decrease with disease progression. There was a positive correlation between DNT cells and CD4 counts. The DNT cell numbers were significantly lower in the high viral load group compared with the low viral load group. Therefore, we conclude that DNT cells correlated with disease progression in HIV infection. These data provide valuable information for further understanding of the role of DNT cells during HIV infection.

HIV Gag-specific immune response mediated by double negative (CD3(+)CD4(-)CD8(-)) T cells in HIV-exposed seronegative individuals

Double negative (DN) T cells are CD3(+), CD4(-), CD8(-) cells with either T-cell receptors (TCR) αβ or TCR γδ whose importance on protection against HIV infection is unknown. Since HIV-exposed seronegative individuals correspond to an ideal group in whom correlates of protection are expected, the role of these cells was studied in 13 HIV-serodiscordant couples in a stable relationship and reporting unprotected sexual intercourses. HIV-specific immune responses mediated by DN T-cells were evaluated by measuring intracellular IFNγ and MIP1β (CCL4) production in response to HIV-Gag peptides. Thirty-five healthy controls not exposed to HIV were tested similarly and used to define a threshold for positive responses. Interestingly, Gag-specific DN T-cell responses were found in 3/13 (23%) HIV-exposed seronegative individuals (Group A), involving both DN/αβ(+) and DN/γδ(+) T-cells through MIP1β and IFNγ production. 4/13 (30%) of partners infected with HIV (Group B) also showed Gag-specific responses but were mediated exclusively by DN/γδ(+) T-cells, mainly through IFNγ production. DN T-cells in Group A individuals can display differential HIV-specific immune responses, which might contribute to the low susceptibility to infection with HIV shown by individuals in Group A.

Double-negative T cells during HIV/SIV infections: potential pinch hitters in the T-cell lineup

PURPOSE OF REVIEW

This review summarizes the role of CD3+CD4-CD8- double-negative T cells, which have both regulatory and helper T-cell functions and may have the potential to compensate for the reduced levels of CD4 T cells during SIV/HIV infection.

RECENT FINDINGS

Double-negative T cells have been characterized in several human diseases and in murine models of autoimmunity and transplantation, where they exhibit both immunoregulatory and helper T-cell-like function. During the natural nonpathogenic SIV infection of African nonhuman primates, the lack of clinical disease progression is associated with the presence of double-negative T cells that maintain helper T-cell functions while remaining refractory to viral infection. Moreover, DN T cells may compensate for very low levels of CD4+ T cells observed in a cohort of SIV-infected sooty mangabeys that have remained free of clinical AIDS for over 10 years. These studies identify a potential for double-negative T cells to provide critical helper function during HIV infection.

SUMMARY

Double-negative T cells with some CD4+ T-cell functions are associated with a nonpathogenic outcome during SIV infection and represent a potential immune therapeutic target in HIV-infected patients.

CD4-like immunological function by CD4- T cells in multiple natural hosts of simian immunodeficiency virus

Many species of African nonhuman primates are natural hosts for individual strains of simian immunodeficiency virus (SIV). These infected animals do not, however, develop AIDS. Here we show that multiple species of African nonhuman primate species characteristically have low frequencies of CD4(+) T cells and high frequencies of both T cells that express only the alpha-chain of CD8 and double-negative T cells. These subsets of T cells are capable of eliciting functions generally associated with CD4(+) T cells, yet these cells lack surface expression of the CD4 protein and are, therefore, poor targets for SIV in vivo. These data demonstrate that coevolution with SIV has, in several cases, involved downregulation of receptors for the virus by otherwise-susceptible host target cells. Understanding the genetic factors that lead to downregulation of these receptors may lead to therapeutic interventions that mimic this modulation in progressive infections.

Human CD4- 8- T cells are a distinctive immunoregulatory subset

Human CD4(-)8(-) T cells are a minor subset quantitatively but potentially important in immunity because they are predominantly distributed at body surfaces, and their number and activities increase in autoimmune diseases and decrease with aging. Distinguishing characteristics of CD4(-)8(-) T cells are found to include a unique profile of cytokines, including Serpin E1, which is not generated by other T cells, MIF, and TGF-beta. At 2-5% of the total in mixtures with CD4 + CD8 T cells, CD4(-)8(-) T cells enhance the generation of IFN-gamma and IL-17 by up to 12- and 5-fold, respectively, without contributing either cytokine or affecting cytokine production by NK/NKT cells. CD4(-)8(-) T cell-derived MIF is their major enhancer and TGFbeta their principal inhibitor of CD4 and CD8 T cell cytokine production. Decreases in CD4(-)8(-) T cell effects may diminish protective immunity in aging, whereas increases may augment the severity of autoimmune diseases.

Selective infection of CD4+ effector memory T lymphocytes leads to preferential depletion of memory T lymphocytes in R5 HIV-1-infected humanized NOD/SCID/IL-2Rgammanull mice

To investigate the events leading to the depletion of CD4(+) T lymphocytes during long-term infection of human immunodeficiency virus type 1 (HIV-1), we infected human CD34(+) cells-transplanted NOD/SCID/IL-2Rgamma(null) mice with CXCR4-tropic and CCR5-tropic HIV-1. CXCR4-tropic HIV-1-infected mice were quickly depleted of CD4(+) thymocytes and both CD45RA(+) naïve and CD45RA(-) memory CD4(+) T lymphocytes, while CCR5-tropic HIV-1-infected mice were preferentially depleted of CD45RA(-) memory CD4(+) T lymphocytes. Staining of HIV-1 p24 antigen revealed that CCR5-tropic HIV-1 preferentially infected effector memory T lymphocytes (T(EM)) rather than central memory T lymphocytes. In addition, the majority of p24(+) cells in CCR5-tropic HIV-1-infected mice were activated and in cycling phase. Taken together, our findings indicate that productive infection mainly takes place in the activated T(EM) in cycling phase and further suggest that the predominant infection in T(EM) would lead to the depletion of memory CD4(+) T lymphocytes in CCR5-tropic HIV-1-infected mice.

Productive human immunodeficiency virus type 1 infection in peripheral blood predominantly takes place in CD4/CD8 double-negative T lymphocytes

Human immunodeficiency virus type 1 (HIV-1) transcription is subject to substantial fluctuation during the viral life cycle. Due to the low frequencies of HIV-1-infected cells, and because latently and productively infected cells collocate in vivo, little quantitative knowledge has been attained about the range of in vivo HIV-1 transcription in peripheral blood mononuclear cells (PBMC). By combining cell sorting, terminal dilution of intact cells, and highly sensitive, patient-specific PCR assays, we divided PBMC obtained from HIV-1-infected patients according to their degree of viral transcription activity and their cellular phenotype. Regardless of a patient's treatment status, the bulk of infected cells exhibited a CD4+ phenotype but transcribed HIV-1 provirus at low levels, presumably insufficient for virion production. Furthermore, the expression of activation markers on the surface of these CD4+ T lymphocytes showed little or no association with enhancement of viral transcription. In contrast, HIV-infected T lymphocytes of a CD4-/CD8- phenotype, occurring exclusively in untreated patients, exhibited elevated viral transcription rates. This cell type harbored a substantial proportion of all HIV RNA+ cells and intracellular viral RNAs and the majority of cell-associated virus particles. In conjunction with the observation that the HIV quasispecies in CD4+ and CD4-)/CD8- T cells were phylogenetically closely related, these findings provide evidence that CD4 expression is downmodulated during the transition to productive infection in vivo. The abundance of viral RNA in CD4-/CD8- T cells from viremic patients and the almost complete absence of viral DNA and RNA in this cell type during antiretroviral treatment identify HIV+ CD4-/CD8 T cells as the major cell type harboring productive infection in peripheral blood.

Development of methods for coordinate measurement of total cell-associated and integrated human immunodeficiency virus type 1 (HIV-1) DNA forms in routine clinical samples: levels are not associated with clinical parameters, but low levels of integrated HIV-1 DNA may be prognostic for continued successful therapy

We have adapted our established Alu PCR assay for proviral DNA and PCR for total cellular DNA to a real-time PCR format and applied these to human immunodeficiency virus (HIV)-positive specimens collected for routine determination of the plasma viral load (pVL). In a cohort of five patients, measurements of integrated viral load (iVL) and cell-associated viral load (cVL) in CD4(+) cells isolated by a single positive selection step were not indicative of HIV DNA levels in the circulation, and further analysis was performed on peripheral blood mononuclear cells (PBMC). In a cohort of 46 samples total cVL was quantitated in most samples, but iVL could be quantitated in only 47.8%, since in 26% iVL was undetectable and in 21.7% the results were invalid due to high levels of unintegrated HIV DNA. There was no correlation of cVL or iVL with pVL, CD4 count, or duration of successful antiretroviral treatment. Out of 26 patients with undetectable pVL, 4 patients failed therapy within the subsequent 12 months and had higher than average iVL, but this was not the case for cVL. Among nine patients with long-term undetectable pVL, no consistent decline in cVL or iVL was seen with time, and changes in cVL and iVL within a patient could be concordant or discordant. These results show that cVL and iVL can be coordinately measured in PBMC from clinical samples but do not correlate with pVL, CD4 counts, or length of suppressive antiretroviral therapy. Interestingly, a high iVL (but not a high cVL) in patients with undetectable pVL was associated with subsequent treatment failure.