Changes in CD8 cell subpopulations induced by antiretroviral therapy in human immunodeficiency virus infected patients

Increased HIV-1 transcriptional activity and infectious burden in peripheral blood and gut-associated CD4+ T cells expressing CD30

HIV-1-infected cells persist indefinitely despite the use of combination antiretroviral therapy (ART), and novel therapeutic strategies to target and purge residual infected cells in individuals on ART are urgently needed. Here, we demonstrate that CD4⁺ T cell-associated HIV-1 RNA is often highly enriched in cells expressing CD30, and that cells expressing this marker considerably contribute to the total pool of transcriptionally active CD4⁺ lymphocytes in individuals on suppressive ART. Using in situ RNA hybridization studies, we show co-localization of CD30 with HIV-1 transcriptional activity in gut-associated lymphoid tissues. We also demonstrate that ex vivo treatment with brentuximab vedotin, an antibody-drug conjugate (ADC) that targets CD30, significantly reduces the total amount of HIV-1 DNA in peripheral blood mononuclear cells obtained from infected, ART-suppressed individuals. Finally, we observed that an HIV-1-infected individual, who received repeated brentuximab vedotin infusions for lymphoma, had no detectable virus in peripheral blood mononuclear cells. Overall, CD30 may be a marker of residual, transcriptionally active HIV-1 infected cells in the setting of suppressive ART. Given that CD30 is only expressed on a small number of total mononuclear cells, it is a potential therapeutic target of persistent HIV-1 infection.

Previous studies have shown that higher levels of soluble CD30 are associated with HIV-1 disease progression. Many of these studies, however, were performed prior to the implementation of combination ART, and the relationship between surface CD30 expression, soluble CD30 and HIV-1 infection in ART suppressed individuals, or those with viremic control off ART, is not known. We demonstrate that cell-associated HIV-1 RNA is highly enriched in CD4⁺ T cells expressing CD30, a member of the tumor necrosis factor receptor superfamily. These findings were observed in several HIV-1 infected donor groups, regardless of whether or not the participants were receiving suppressive ART. Furthermore, we demonstrate that ex vivo treatment with brentuximab vedotin, an antibody-drug conjugate that targets CD30, reduces the total amount of HIV-1 DNA in PBMC obtained from infected individuals. Finally, we show through in situ RNA hybridization studies that CD30 and HIV transcriptional activity co-localize in cells from gut biopsies obtained from HIV-1 infected donors. These data suggest that CD30 may be a marker of residual, transcriptionally active HIV-1 infected cells in the setting of suppressive ART.

HIV-1 persistence following extremely early initiation of antiretroviral therapy (ART) during acute HIV-1 infection: An observational study

BACKGROUND

It is unknown if extremely early initiation of antiretroviral therapy (ART) may lead to long-term ART-free HIV remission or cure. As a result, we studied 2 individuals recruited from a pre-exposure prophylaxis (PrEP) program who started prophylactic ART an estimated 10 days (Participant A; 54-year-old male) and 12 days (Participant B; 31-year-old male) after infection with peak plasma HIV RNA of 220 copies/mL and 3,343 copies/mL, respectively. Extensive testing of blood and tissue for HIV persistence was performed, and PrEP Participant A underwent analytical treatment interruption (ATI) following 32 weeks of continuous ART.

METHODS AND FINDINGS

Colorectal and lymph node tissues, bone marrow, cerebral spinal fluid (CSF), plasma, and very large numbers of peripheral blood mononuclear cells (PBMCs) were obtained longitudinally from both participants and were studied for HIV persistence in several laboratories using molecular and culture-based detection methods, including a murine viral outgrowth assay (mVOA). Both participants initiated PrEP with tenofovir/emtricitabine during very early Fiebig stage I (detectable plasma HIV-1 RNA, antibody negative) followed by 4-drug ART intensification. Following peak viral loads, both participants experienced full suppression of HIV-1 plasma viremia. Over the following 2 years, no further HIV could be detected in blood or tissue from PrEP Participant A despite extensive sampling from ileum, rectum, lymph nodes, bone marrow, CSF, circulating CD4+ T cell subsets, and plasma. No HIV was detected from tissues obtained from PrEP Participant B, but low-level HIV RNA or DNA was intermittently detected from various CD4+ T cell subsets. Over 500 million CD4+ T cells were assayed from both participants in a humanized mouse outgrowth assay. Three of 8 mice infused with CD4+ T cells from PrEP Participant B developed viremia (50 million input cells/surviving mouse), but only 1 of 10 mice infused with CD4+ T cells from PrEP Participant A (53 million input cells/mouse) experienced very low level viremia (201 copies/mL); sequence confirmation was unsuccessful. PrEP Participant A stopped ART and remained aviremic for 7.4 months, rebounding with HIV RNA of 36 copies/mL that rose to 59,805 copies/mL 6 days later. ART was restarted promptly. Rebound plasma HIV sequences were identical to those obtained during acute infection by single-genome sequencing. Mathematical modeling predicted that the latent reservoir size was approximately 200 cells prior to ATI and that only around 1% of individuals with a similar HIV burden may achieve lifelong ART-free remission. Furthermore, we observed that lymphocytes expressing the tumor marker CD30 increased in frequency weeks to months prior to detectable HIV-1 RNA in plasma. This study was limited by the small sample size, which was a result of the rarity of individuals presenting during hyperacute infection.

CONCLUSIONS

We report HIV relapse despite initiation of ART at one of the earliest stages of acute HIV infection possible. Near complete or complete loss of detectable HIV in blood and tissues did not lead to indefinite ART-free HIV remission. However, the small numbers of latently infected cells in individuals treated during hyperacute infection may be associated with prolonged ART-free remission.

The HIV-1 protease inhibitor nelfinavir activates PP2 and inhibits MAPK signaling in macrophages: a pathway to reduce inflammation

The HIV-1 PI NFV has off-target effects upon host enzymes, including inhibition of the 20S proteasome, resulting in activation of PP1. HIV-1-associated monocyte/macrophage activation, in part a result of systemically elevated levels of microbial products including LPS, is associated with risk of mortality, independent of viremia or CD4 T cell loss. This study tested the hypothesis that activation of protein phosphatases by NFV would reduce activation of monocytes/macrophages through dephosphorylation of signal transduction proteins. NFV uniquely blocked LPS-induced production by human monocyte-derived macrophages of the inflammatory cytokines TNF and IL-6, as well as sCD14. Although NFV failed to modulate NF-κB, NFV treatment reduced phosphorylation of AKT and MAPKs. Inhibition of PP2 with okadaic acid blocked the anti-inflammatory effect of NFV, whereas the PP1 inhibitor calyculin A failed to counter the anti-inflammatory effects of NFV. For in vivo studies, plasma sCD14 and LPS were monitored in a cohort of 31 pediatric HIV-1 patients for over 2 years of therapy. Therapy, including NFV, reduced sCD14 levels significantly compared with IDV or RTV, independent of ΔLPS levels, VL, CD4 T cell frequency, or age. The hypothesis was supported as NFV induced activation of PP2 in macrophages, resulting in disruption of inflammatory cell signaling pathways. In vivo evidence supports that NFV may offer beneficial effects independent of antiviral activity by reducing severity of chronic innate immune activation in HIV-1 infection.

HIV patients treated with low-dose prednisolone exhibit lower immune activation than untreated patients

Background

HIV-associated general immune activation is a strong predictor for HIV disease progression, suggesting that chronic immune activation may drive HIV pathogenesis. Consequently, immunomodulating agents may decelerate HIV disease progression.

Methods

In an observational study, we determined immune activation in HIV patients receiving low-dose (5 mg/day) prednisolone with or without highly-active antiretroviral therapy (HAART) compared to patients without prednisolone treatment. Lymphocyte activation was determined by flow cytometry detecting expression of CD38 on CD8(+) T cells. The monocyte activation markers sCD14 and LPS binding protein (LBP) as well as inflammation markers soluble urokinase plasminogen activated receptor (suPAR) and sCD40L were determined from plasma by ELISA.

Results

CD38-expression on CD8+ T lymphocytes was significantly lower in prednisolone-treated patients compared to untreated patients (median 55.40% [percentile range 48.76-67.70] versus 73.34% [65.21-78.92], p = 0.0011, Mann-Whitney test). Similarly, we detected lower levels of sCD14 (3.6 μg/ml [2.78-5.12] vs. 6.11 μg/ml [4.58-7.70]; p = 0.0048), LBP (2.18 ng/ml [1.59-2.87] vs. 3.45 ng/ml [1.84-5.03]; p = 0.0386), suPAR antigen (2.17 μg/ml [1.65-2.81] vs. 2.56 μg/ml [2.24-4.26]; p = 0.0351) and a trend towards lower levels of sCD40L (2.70 pg/ml [1.90-4.00] vs. 3.60 pg/ml [2.95-5.30]; p = 0.0782). Viral load in both groups was similar (0.8 × 10⁵ ng/ml [0.2-42.4 × 10⁵] vs. 1.1 × 10⁵ [0.5-12.2 × 10⁵]; p = 0.3806). No effects attributable to prednisolone were observed when patients receiving HAART in combination with prednisolone were compared to patients who received HAART alone.

Conclusions

Patients treated with low-dose prednisolone display significantly lower general immune activation than untreated patients. Further longitudinal studies are required to assess whether treatment with low-dose prednisolone translates into differences in HIV disease progression.

MyD88-dependent immune activation mediated by human immunodeficiency virus type 1-encoded Toll-like receptor ligands

Immune activation is a major characteristic of human immunodeficiency virus type 1 (HIV-1) infection and a strong prognostic factor for HIV-1 disease progression. The underlying mechanisms leading to immune activation in viremic HIV-1 infection, however, are not fully understood. Here we show that, following the initiation of highly active antiretroviral therapy, the immediate decline of immune activation is closely associated with the reduction of HIV-1 viremia, which suggests a direct contribution of HIV-1 itself to immune activation. To propose a mechanism, we demonstrate that the single-stranded RNA of HIV-1 encodes multiple uridine-rich Toll-like receptor 7/8 (TLR7/8) ligands that induce strong MyD88-dependent plasmacytoid dendritic cell and monocyte activation, as well as accessory cell-dependent T-cell activation. HIV-1-encoded TLR ligands may, therefore, directly contribute to the immune activation observed during viremic HIV-1 infection. These data provide an initial rationale for inhibiting the TLR pathway to directly reduce the chronic immune activation induced by HIV-1 and the associated immune pathogenesis.

CD8+ cell noncytotoxic anti-HIV response: restoration by HAART in the late stage of infection

Highly active antiretroviral therapy (HAART) is currently the best HIV infection management strategy. However, its effects on the CD8+ T cell noncytotoxic anti-HIV response (CNAR) are not well known. We investigated if HAART has different effects on CNAR in patients at the intermediate and late stages of HIV infection. Untreated healthy HIV-infected subjects with a mean CD4+ T cell count of 606 cells/microl were examined as a reference group. Plasma viral load, CD4+ T cell count, and CNAR activity were measured at baseline and regular intervals for at least 48 weeks following initiation of HAART. Baseline CNAR activity in all subjects correlated inversely with viral load and directly with CD4 T+ cell counts. The level of CNAR in the latestage group was significantly lower than in the intermediate-stage and the healthy reference group (p < 0.01). Following initiation of HAART, substantial increases in CD4+ T cell counts and decreases in viral loads were observed in both groups, indicating treatment success. CNAR activity was found to be increased significantly during HAART, but only in the late-stage group (p < 0.01). This increase in CD8+ cell function was seen within 4 weeks of treatment initiation and resulted in levels of CNAR activity almost equal to those observed in the healthy reference subjects. Our findings suggest a beneficial effect on CNAR in those individuals with reduced activity, typically in late-stage infection.

T-cell activation and memory phenotypes in cerebrospinal fluid during HIV infection

We characterized T cell phenotypes in 74 paired blood and cerebrospinal fluid (CSF) samples of HIV-infected and uninfected persons using four-color flow cytometry. CD4+ and CD8+ T cells subsets were further characterized by identifying activated/resting and memory/naive subsets in CSF and blood using the markers CD38/HLA-DR and CD45RA/CD62L, respectively. With and without HIV-infection, the proportion of CD4+ T cells and memory T cells among T cells in CSF was higher compared to blood. In HIV-infection, activated CD4+ and CD8+ T cells in CSF were more abundant than in uninfected controls. As expected, combination antiretroviral therapy (ART) reduced T cell activation in CSF and blood.

Parallel decline of CD8+/CD38++ T cells and viraemia in response to quadruple highly active antiretroviral therapy in primary HIV infection

OBJECTIVES

To monitor changes in the numbers of CD8 lymphocytes expressing the activated CD38++ phenotype in peripheral blood samples from patients with primary HIV infection (PHI) treated with highly active antiretroviral therapy (HAART).

METHODS

Zidovudine, lamivudine, abacavir and amprenavir were initiated during PHI as part of the Quest study. Absolute numbers of CD8+/CD38++ T cells were determined using three-colour flow cytometry, and plasma viral load (VL) was measured using the Roche Amplicor method.

RESULTS

The median, pre-therapy CD8+/CD38++ T cell count was 461/mm(3)(interquartile range 216, 974) in 131 patients compared with normal control values of less than 20 cells/mm(3). Levels fell markedly in parallel with VL within the first 2 weeks of HAART initiation, to a median of 47 cells/mm(3) at 28 weeks (median 436 cell decline; P < 0.001). At that time, 80% of patients had a VL less than 50 copies/ml, and 16.3% of all patients had less than 20 CD8+/CD38++ T cells/mm(3). A continued decrease in CD8+/CD38++ T cell count occurred in 67.2% of patients whose VL was maintained below 50 copies/ml (median change from first to last value -18 cells/mm(3); P < 0.001).

CONCLUSION

After the initiation of HAART in PHI, CD8+/CD38++ lymphocytes declined rapidly in parallel with VL, and allowed for a normalization of CD8+/CD38++ T cell numbers in a subset of patients at week 28. Cell numbers continued to decline in patients who maintained VL below 50 copies/ml, indicating that the CD8+/CD38++ T cell count may represent a marker of residual viral replication when VL falls below detectable levels after HAART intervention.

Highly active antiretroviral therapy induces specific changes in effector and central memory T cell sub-populations

Highly active antiretroviral therapy (HAART) improves the immunodeficiency of HIV-infected individuals. In this report we show that HAART increases both naive (CD45RA+CD62L+) and central memory (CD45RO+CD62L+) CD4 lymphocytes. On CD8 lymphocytes, HAART induces an increase of naive cells associated with a consistent decrease of effector cells (CD45 RO+CD62L-). No specific differences in phenotypic changes were observed with different HAART regimens, suggesting that, once viral suppression is achieved, the pharmacological class of antiretroviral drugs does not affect immune reconstitution.

Association of immune complexes and plasma viral load with CD4+ cell depletion, CD8+ DR+ and CD16+ cell counts in HIV+ hemophilia patients. Implications for the immunopathogenesis of HIV-induced CD4+ lymphocyte depletion

OBJECTIVE

There is evidence that HIV induces CD4+ depletion in part by the formation of immune complexes (IC) that attach to CD4+ blood lymphocytes. In the present study we examined the relationship of IC-coated CD4+ blood cells with retroviral replication in HAART-treated patients.

PATIENTS AND METHODS

52 hemophilia patients were studied from 1997 to 1999. Lymphocyte subsets, IgM, IgG and gp120 on CD4+ blood cells, in vitro responses of lymphocytes to mitogens, plasma neopterin and plasma viral load were measured.

RESULTS

Patients with detectable viral replication and without ICs on CD4+ blood lymphocytes had a lower viral load (4100 versus 21000 HIV-1 mRNA copies/ml; P = 0.079) and higher CD4+ cell counts (310/microl versus 161/microl; P = 0.035) than patients with ICs on circulating CD4+ lymphocytes. Among patients with < 80 HIV-1 mRNA copies/ml, IC- individuals had slightly higher CD4+ lymphocyte counts than IC+ patients (384/microl versus 316/microl; n.s.). Further evidence for the clinical relevance of the ICs was obtained when 18 patients who had an undetectable viral load at previous investigations were analyzed. Among patients with a stable undetectable viral load, CD4+ counts increased in 6 of 8 IC- but in none of 2 IC+ individuals. In patients whose viral load increased during the observation period, 5 of 6 IC- but none of 2 IC+ individuals showed higher CD4+ cell counts. Impaired virus killing is suggested by lower CD16+ (35/microl versus 107/microl; P = 0.016), higher CD3+ DR+ (178/microl versus 66/microl; P = 0.006), and higher CD8+ DR+ (142/microl versus 34/microl; P = 0.017) cell counts in IC(-) patients compared to IC- patients without detectable viral load. Strong retroviral replication induced strong T cell dysfunctions. Fewer CD3+ 25+ blood lymphocytes (19/microl versus 47/microl; P = 0.006) and a lower in vitro response of T lymphocytes to the mitogens Con A (RR: 0.3 versus 1.2; P=0.023) and CD3 mab (RR: 0.5 versus 2.4; P = 0.012) was observed in IC+ patients with detectable versus undetectable viral load.

CONCLUSION

Our data suggest that ICs on circulating CD4+ blood lymphocytes are primarily associated with CD4+ lymphocyte depletion whereas the plasma viral load is primarily associated with decreased T lymphocyte activation, lower CD16+ counts, and higher CD8+ DR+ lymphocytes which might be the effector cells for virus elimination.

Early changes in peripheral blood T cell subsets induced by antiretroviral treatment of human immunodeficiency virus-1 positive individuals

Human immunodeficiency virus (HIV)-1 infection causes a gradual decline in peripheral blood CD4+ T cells. Shortly after the primary infection, an expansion of the activated memory CD8+ T-cell pool is also observed paralleling increased levels of plasma viraemia. In the present study we investigated the immediate effects of zidovudine therapy on peripheral blood T-cell subsets during the first 3 weeks of therapy in a group of HIV-1 positive individuals receiving influenza vaccine. HIV-1 positive individuals who received vaccine, but no treatment, were included as controls. Both the number of CD4+ and CD8+ T cells increased during the first week of therapy in parallel with a decline in plasma viraemia. The majority of CD4+ T cells contributing to this expansion expressed CD28, CD45RO and Fas, whereas the expanded CD8+ T cells were predominantly CD28-, CD45RO+, CD38+, Fas+ and Fas+ (CD95). We propose that the increase in the number of activated memory T cells observed in peripheral blood immediately after the onset of antiretroviral treatment is most likely caused by the redistribution of cells from various lymphoid organs in response to decreased levels of viral load in these compartments. The degree of T-cell redistribution is probably dependent on the magnitude of virus suppression.

Activation of CD8 T cells normalizes and correlates with the level of infectious provirus in tonsils during highly active antiretroviral therapy in early HIV-1 infection

OBJECTIVES

To study the effects of antiretroviral therapy on T cell activation in blood and tonsils from HIV-1 infected individuals in relation to CD4 cell count, plasma viremia, and infectious HIV-1 provirus.

DESIGN

A 48-week study of viral load and T cell subsets in blood and tonsils from 12 HIV-1-positive individuals with a mean CD4 cell number of 400 x 10(6) cells/l treated with a combination of zidovudine, lamivudine, and indinavir.

METHODS

Tonsil biopsies and blood samples were collected at regular intervals. Lymphocytes were phenotyped and quantified by three-color flow cytometry; infectious provirus was quantified by a limiting dilution assay. HIV-1-negative individuals were included as controls.

RESULTS

The fraction of tonsillar CD8 T cells expressing CD69, CD38, or HLA-DR in the patients with suppressed virus replication declined to levels comparable with that in controls by 48 weeks and showed a strong positive correlation with tonsillar infectious provirus and plasma viremia. The level of CD4 T cell activation was within normal range in tonsils throughout the study. The fraction of HLA-DR+ cells within CD4 and CD8 T cells in blood declined rapidly in parallel with plasma viremia but remained slightly higher compared with that in uninfected individuals.

CONCLUSION

Antiretroviral therapy normalizes tonsillar CD8 T cell activation in HIV-1-positive individuals in parallel with suppression of viral replication, indicating reduced CD8 cell turnover. Normal tonsillar CD4 T cell activation suggests limited CD4 cell turnover in early HIV infection. Activated CD8 T cells in lymphoid tissue is superior to that in blood as an immunological marker for the virological response to antiretroviral therapy.

Niacin as a potential AIDS preventive factor

A pentad of findings consistent with niacin depletion have been described in patients with AIDS. There are also clinical and laboratory data to support the potential benefit of niacin in HIV infection. In this paper, it is hypothesized that HIV infection induces niacin depletion, and that therapeutic niacin will act as an AIDS preventive factor. While viral inhibition is incontrovertibly the primary 'AIDS preventive factor', costly antiretroviral medications are simply out of reach for the majority of the world's HIV-infected people. Along with antiviral research, investigation must go forward to look at strategies to overcome the massive metabolic disruption caused by the production of approximately one billion virus particles per day. Niacin, the same B complex vitamin found in the early part of this century to be the 'pellagra preventive factor', is proposed here as a secondary 'AIDS preventive factor' in HIV-infected persons.

Unscheduled cyclin B expression and p34 cdc2 activation in T lymphocytes from HIV-infected patients

OBJECTIVE

To study the role of cell cycle regulation during HIV infection by investigating in vivo and in vitro cyclin B and p34 cdc kinase expression.

METHODS

Cyclin B expression was analysed by Western blot in CD4 and CD8 cells from 25 HIV-infected patients and 24 uninfected individuals. In eight patients, a sequential analysis was performed after initiation of antiretroviral therapy (ART), and correlations with CD4 cell count and HIV viremia were studied. Sequential changes in cyclin B expression and p34 cdc kinase expression and activity were also studied in lymphocytes activated in vitro with phytohaemagglutinin (PHA).

RESULTS

Lymphocytes from untreated HIV-infected patients demonstrate persistent in vivo overexpression of cyclin B in both CD4 and CD8 cell subpopulations. When cells are stimulated to proliferate in vitro, biochemical events that characterize the entrance into the cell cycle [ornithine decarboxylase (ODC) activity, interleukin 2 production, interleukin 2 alpha-chain receptor (IL-2R, CD25) expression, total protein synthesis, total DNA synthesis] show similar timing and sequence in lymphocytes from HIV-infected and uninfected individuals. However, in peripheral blood lymphocytes (PBL) from HIV-infected patients, cyclin B and p34 cdc kinase show premature expression during the cell cycle. Both in vivo cyclin B overexpression and in vitro unscheduled cyclin B expression were almost completely reversed 2-4 weeks after initiation of effective ART.

CONCLUSION

Increased and unscheduled expression of cyclin B and p34 cdc kinase is consistently observed in CD4 and CD8 cells from HIV-infected patients, both in vivo and after in vitro mitogenic stimulation. These alterations correlate with the level of viremia and may provide a link between the perturbation of lymphocyte proliferative homeostasis and the exaggerated propensity towards apoptosis.

The importance of lymphocyte trafficking in regulating blood lymphocyte levels during HIV and SIV infections

In humans, blood is commonly monitored to provide surrogates of disease progression and assess immune status. However, the varied, rapid and atypical alterations in lymphocyte subsets which may occur in blood in response to pathogens, are not predictive of changes in the bulk of the immune system. A hallmark of human and simian immunodeficiency virus (SIV) infections is the profound loss of blood CD4(+) lymphocytes, a feature widely accepted as being a consequence of direct or indirect viral killing of CD4(+) cells throughout the body. However, in recording declining CD4 counts and CD4/8 ratios in the blood, little attention has been paid to migratory behaviour or the composition and tissue distribution of various lymphocyte subsets. This article compares the lymphocyte subsets in blood and various tissues in normal and virus-infected individuals prior to and following drug treatment and indicates an absence of selective CD4(+) cell decreases or increases, highlighting the importance of lymphocyte trafficking and compartmentalization in regulating blood T cell levels and suggesting a reevaluation of the currently favoured paradigm.

Expression of CD28 and CD38 by CD8+ T lymphocytes in HIV-1 infection correlates with markers of disease severity and changes towards normalization under treatment. The Swiss HIV Cohort Study

The relationship between blood CD8+ T lymphocyte subsets, as defined by CD28 and CD38 expression, and plasma viraemia and CD4+ T cells in HIV-1 infection was investigated. In a cross-sectional study of 46 patients with either no or stable anti-retroviral treatment, there was a strong negative correlation between the percentage of CD8+CD28- and the percentage of CD4+ T cells (r = -0.75, P < 0.0001), and a positive correlation between absolute numbers of CD8+CD28+ and CD4+ T cells (r = 0.56, P < 0.0001). In contrast, the expression of CD38 by CD8+ T lymphocytes correlated primarily with plasma viraemia (e.g. the percentage of CD38+ in CD8bright cells, r = 0.76, P < 0.0001). In the 6 months following triple therapy initiation in 32 subjects, there was a close correlation between changes (delta) in CD8+CD28+ or CD8+CD28- and in CD4+ T cells (e.g. delta % CD8+CD28+ versus delta % CD4+, r = 0.37, P = 0.0002; delta % CD8+CD28- versus delta % CD4+, r = -0.66, P < 0.0001). A marked decline of the number of CD8+ T cells expressing CD38 was also observed. These results suggest the existence of a T cell homeostasis mechanism operating in blood with CD4+ and CD8+CD28+ cells on the one hand, and with CD8+CD28- cells on the other. In addition, the percentage of CD38+ cells in CD8+ cells, generally considered an independent prognostic factor, could merely reflect plasma viral load.