HIV infection: where have all the T cells gone?

HIV Susceptibility of human antigen-specific CD4 T cells in AIDS pathogenesis and vaccine response

HIV causes infection and progressive depletion of human CD4 T cells. Emerging data have shown that antigen-specific CD4 T-cell subsets manifest differential susceptibility to HIV, potentially leading to pathogen-specific immune failure and opportunistic infections. This concept was recently explored in context of vectors utilized in HIV vaccine trials, and the data suggest that adenovirus type 5(Ad5)-specific CD4 T cells elicited by Ad5-HIV vaccine may be particularly susceptible to HIV, potentially rendering Ad5 vaccine recipients susceptible to HIV acquisition. We here examined recent data regarding the HIV susceptibility of antigen-specific CD4 T cells induced during infection or HIV vaccination and discussed its potential impact on HIV acquisition risk posed by HIV vaccination.

Distinct gene-expression profiles associated with the susceptibility of pathogen-specific CD4 T cells to HIV-1 infection

In HIV infection, CD4 responses to opportunistic pathogens such as Candida albicans are lost early, but CMV-specific CD4 response persists. Little is currently known about HIV infection of CD4 T cells of different pathogen/antigen specificities. CFSE-labeled PBMCs were stimulated with CMV, tetanus toxoid (TT), and C albicans antigens and subsequently exposed to HIV. HIV infection was monitored by intracellular p24 in CFSE(low) population. We found that although TT- and C albicans-specific CD4 T cells were permissive, CMV-specific CD4 T cells were highly resistant to both R5 and X4 HIV. Quantification of HIV DNA in CFSE(low) cells showed a reduction of strong-stop and full-length DNA in CMV-specific cells compared with TT- and C albicans-specific cells. β-Chemokine neutralization enhanced HIV infection in TT- and C albicans-specific cells, whereas HIV infection in CMV-specific cells remained low despite increased entry by β-chemokine neutralization, suggesting postentry HIV restriction by CMV-specific cells. Microarray analysis (Gene Expression Omnibus accession number: GSE42853) revealed distinct transcriptional profiles that involved selective up-regulation of comprehensive innate antiviral genes in CMV-specific cells, whereas TT- and C albicans-specific cells mainly up-regulated Th17 inflammatory response. Our data suggest a mechanism for the persistence of CMV-specific CD4 response and earlier loss of mucosal Th17-associated TT- and C albicans-specific CD4 response in AIDS.

Manipulation of costimulatory molecules by intracellular pathogens: veni, vidi, vici!!

Some of the most successful pathogens of human, such as Mycobacterium tuberculosis (Mtb), HIV, and Leishmania donovani not only establish chronic infections but also remain a grave global threat. These pathogens have developed innovative strategies to evade immune responses such as antigenic shift and drift, interference with antigen processing/presentation, subversion of phagocytosis, induction of immune regulatory pathways, and manipulation of the costimulatory molecules. Costimulatory molecules expressed on the surface of various cells play a decisive role in the initiation and sustenance of immunity. Exploitation of the “code of conduct” of costimulation pathways provides evolutionary incentive to the pathogens and thereby abates the functioning of the immune system. Here we review how Mtb, HIV, Leishmania sp., and other pathogens manipulate costimulatory molecules to establish chronic infection. Impairment by pathogens in the signaling events delivered by costimulatory molecules may be responsible for defective T-cell responses; consequently organisms grow unhindered in the host cells. This review summarizes the convergent devices that pathogens employ to tune and tame the immune system using costimulatory molecules. Studying host-pathogen interaction in context with costimulatory signals may unveil the molecular mechanism that will help in understanding the survival/death of the pathogens. We emphasize that the very same pathways can potentially be exploited to develop immunotherapeutic strategies to eliminate intracellular pathogens.

Identification of HIV-1 epitopes that induce the synthesis of a R5 HIV-1 suppression factor by human CD4+ T cells isolated from HIV-1 immunized hu-PBL SCID mice

We have previously reported that immunization of the severe combined immunodeficiency (SCID) mice reconstituted with human peripheral blood mononuclear cells (PBMC) (hu-PBL-SCID mice) with inactivated human immunodeficiency virus type-1 (HIV-1)-pulsed-autologous dendritic cells (HIV-DC) elicits HIV-1-reactive CD4(+) T cells that produce an as yet to be defined novel soluble factor in vitro with anti-viral properties against CCR5 tropic (R5) HIV-1 infection. These findings led us to perform studies designed to identify the lineage of the cell that synthesizes such a factor in vivo and define the epitopes of HIV-1 protein that have specificity for the induction of such anti-viral factor. Results of our studies show that this property is a function of CD4(+) but not CD8(+) T cells. Human CD4(+) T cells were thus recovered from the HIV-DC-immunized hu-PBL-SCID mice and were re-stimulated in vitro by co-culture for 2 days with autologous adherent PBMC as antigen presenting cells, APC previously pulsed with inactivated HIV in IL-2-containing medium to expand HIV-1-reactive CD4(+) T cells. Aliquots of these re-stimulated CD4(+) T cells were then co-cultured with similar APC's that were previously pulsed with 10 microg/ml of a panel of HIV peptides for an additional 2 days, and their culture supernatants were examined for the production of both the R5 HIV-1 suppression factor and IFN-gamma. The data presented herein show that the HIV-1 primed CD4(+) T cells produced the R5 suppression factor in response to a wide variety of HIV-1 gag, env, pol, nef or vif peptides, depending on the donor of the CD4(+) T cells. Simultaneous production of human interferon (IFN)-gamma was observed in some cases. These results indicate that human CD4(+) T cells in PBMC of HIV-1 naive donors have a wide variety of HIV-1 epitope-specific CD4(+) T cell precursors that are capable of producing the R5 HIV-1 suppression factor upon DC-based vaccination with whole inactivated HIV-1.

The major population of PHA-stimulated PBMC infected by R5 or X4 HIV variants after a single cycle of infection is predominantly composed of CD45RO+CD4+ T lymphocytes

PHA-stimulated peripheral blood mononuclear cells (PBMCs) are widely used for investigating replication and neutralization of HIV primary isolates in vitro. The objective of this study was to identify the T lymphocyte subset(s) that are found infected after one replication cycle by either R5- or X4-HIV-1 variants in PHA-stimulated PBMCs from healthy donors. Infected T lymphocytes were detected by intracellular p24 staining and characterized by cell surface immunophenotyping using flow cytometry. The predominant lymphocyte subset expressing p24 after 24 h of infection with either R5 or X4 HIV-1 strains was found to exhibit mainly the memory CD45RO phenotype, a greater percentage of CD62L(+)CD45RO(+) central memory T lymphocytes was infected with X4 HIV strains. Although some CD45RA(+) lymphocytes were also infected, these cells co-expressed CD45RO(+). The proportion of lymphocytes expressing CD4 and CD4/CD45RO decreased by 20% after 24 h of infection. A 2-fold decrease of CD4(+)CD8(+) T lymphocytes could also be recorded, even though this subset accounted for less than 5% of total lymphocytes in control cultures. Moreover, CD4(+)CD8(+) T cells further decreased by 90% after 4 days of infection, a time at which they scored p24(+). Therefore, our results indicate that the in vitro infection system of PHA-stimulated PBMC utilized in neutralization assays provides an appropriate model for the study of infected CD45RO(+) lymphocytes but not CD45RA(+) lymphocytes.

The CCR5 and CXCR4 coreceptors--central to understanding the transmission and pathogenesis of human immunodeficiency virus type 1 infection

In this review, we will discuss what is known, what is suspected, and what still remains obscure about the central role played by coreceptor expression and usage in the transmission and pathogenic consequences of human immunodeficiency virus type 1 (HIV-1) infection. An emphasis will be on the HIV-1 phenotypic variants that are defined by their usage of the CCR5 or CXCR4 coreceptors, and how the different cellular tropism of these variants influences how and where HIV-1 replicates in vivo. We will also review what might happen when coreceptor antagonists are used clinically to treat HIV-1 infection.

T cell dynamics in HIV-1 infection

In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.

Preserved immune system in long-term asymptomatic vertically HIV-1 infected children

The objective of this study was to study immune system status in long-term asymptomatic (LTA) HIV-1-infected children. A cross-sectional study was used, involving HIV-1-infected children over 7 years of age who were rated into two groups according to their clinical and immunological classification: (a) LTA: 7 asymptomatic HIV-1-infected children in A1; (b) Rapid progressor (RP): 14 age-matched C3 HIV-1-infected children. The control group consisted of 17 age-matched uninfected children. The characterization of CD4+ T-cell subsets was determined by three-colour flow cytometry. The proliferative response and cytokine production by activated peripheral blood T-cells were also measured. IL-7 levels were measured in serum. Thymic production of T-cells was quantified by TCR rearrangement excision circles (TRECs). The LTA children showed similar proliferative responses to PHA, PWM and anti-CD3+ anti-CD28, but lower responses to tetanus toxoid and streptokinase, in comparison with the controls but always higher responses in comparison with the RP group. The production of TNF-alpha and IFN-gamma was similar in the LTA and control groups, and both were higher than the levels in the RP group. The LTA group showed a lower percentage of memory CD4+ T-cells (CD4+ CD45RO+, CD4+ CD45RA-CD62L+) than the control and RP groups. The LTA group also showed lower percentages of CD4+ CD7- cells than the controls. As for naïve CD4+ T-cells (CD4+ CD45RA+ CD62L+), CD4+ CD45RA+ and CD4+ CD62L+ cells, the LTA group showed higher values than the control and RP groups. The LTA group showed higher percentages of CD4+ HLA-DR+ CD38+ than the controls, but lower values than the RP group. In contrast, the LTA group had percentages of CD4+ HLA-DR-CD38+ T-cells higher than both the control and RP groups, whereas CD4+ CD38+ levels were only higher in the LTA group in comparison with the controls. CD4+ HLA-DR+ CD38- and CD4+ HLA-DR+ cell numbers were lower in the LTA group in comparison with the RP group. We found almost normal values of TRECs and IL-7 in the LTA group, but lower values in the RP group. Moreover, we found an inverse relation between TREC levels and IL-7 in plasma from HIV-infected children. Asymptomatic HIV-1 infected children have a well preserved immune system similar to that of control uninfected children in spite of HIV-infection for more than 7 years. Moreover, our results identified new markers of HIV disease, such as TRECs and IL-7, that could be used to monitor disease.

HIV infection in critically ill obstetrical patients

OBJECTIVES

The effect of HIV-infection on the clinical course of critically ill obstetrical patients by means of a case-control study was evaluated.

METHODS

Over one calendar year 440 patients were admitted to a high risk obstetrical unit. All patients were tested for HIV-infection. HIV-positive patients were included in the study group and two HIV-negative patients for every HIV-positive patient were included in the control group.

RESULTS

No differences were found between the two groups regarding demographic data, diagnosis, antibiotic use, mode of delivery, duration of hospital stay and mortality. More complications occurred in the HIV-negative group. Eclampsia recorded for the HIV-negative group was 17.1% and 4.7% for the HIV-positive group (P=0.04; 95% CI: -17.1%; -0.9%) and lung edema was 18.2% and 6.2%, respectively (P=0.01; 95% CI: -19.3%; -3.5%). The median CD4/CD8 ratio was significantly lower in the HIV-positive group (0.43) than the HIV-negative group (1.37) (P<0.01; 95% CI: -1.04; -0.79).

CONCLUSIONS

HIV-infection did not significantly alter the clinical course of critically ill patients in an obstetrical high care unit.

Virological and immunological effects of short-course antiretroviral therapy in primary HIV infection

BACKGROUND

National and international guidelines call for the treatment of primary HIV infection (PHI) with combination antiretroviral therapy, although the ideal timing and duration of this intervention is unknown. Recent immunological studies of antiretroviral therapy on small numbers of patients with PHI have reported preservation of HIV-specific CD4 T-helper responses, ordinarily lost in the absence of intervention. We sought to investigate whether a short course of antiretroviral therapy (SCART) at PHI was sufficient to preserve HIV-specific cellular immunity.

METHODS

Forty-five subjects with confirmed PHI were offered SCART at diagnosis. HIV specific cellular immune responses and virological parameters were assessed at monthly intervals.

RESULTS

Thirty-seven of the subjects chose SCART at PHI, and achieved a plasma viral load < 50 RNA copies/ml by a median of 10 weeks (range, 4-32 weeks). Two of the 45 individuals had evidence of genotypic HIV drug resistance at baseline, and none developed new mutations following therapy. All patients who received SCART at PHI showed preservation of HIV-specific CD4 T-helper responses up to 64 weeks off SCART.

CONCLUSION

SCART at PHI was safe, did not induce the development of drug resistance, and appeared sufficient to preserve HIV-specific CD4 T-helper responses. However, PHI is highly heterogeneous, and a large-scale randomized trial of SCART at PHI is now needed.

Production of new T cells by thymus in children: effect of HIV infection and antiretroviral therapy

The decrease in the number of CD4(+) T cells during HIV infection is the result of both peripheral destruction of cells by the virus and inadequate replacement of these cells. Aging and HIV infection lead to lower production of new T cells by the thymus, and, therefore, a complete restoration of the immune system is not generally achieved in infected adults after antiretroviral therapy. Because children have a completely functional thymus, we addressed the effects of HIV-1 infection on the production of new T cells in vertically infected children and whether the decrease of viral load after therapy results in a restoration of thymic function. To analyze the thymic function, T-cell receptor rearrangement excision circles were measured by quantitative PCR. Our results indicate that HIV-infected children have lower T-cell receptor rearrangement excision circle levels than age-matched uninfected children, likely due to an inhibitory effect of HIV on thymic function. Additionally, in some patients, the decrease in viral load after retroviral therapy allows the generation of new T cells by the thymus, thus recovering the normal number of CD4 cells.

HIV preferentially infects HIV-specific CD4+ T cells

HIV infection is associated with the progressive loss of CD4(+) T cells through their destruction or decreased production. A central, yet unresolved issue of HIV disease is the mechanism for this loss, and in particular whether HIV-specific CD4(+) T cells are preferentially affected. Here we show that HIV-specific memory CD4(+) T cells in infected individuals contain more HIV viral DNA than other memory CD4(+) T cells, at all stages of HIV disease. Additionally, following viral rebound during interruption of antiretroviral therapy, the frequency of HIV viral DNA in the HIV-specific pool of memory CD4(+) T cells increases to a greater extent than in memory CD4(+) T cells of other specificities. These findings show that HIV-specific CD4(+) T cells are preferentially infected by HIV in vivo. This provides a potential mechanism to explain the loss of HIV-specific CD4(+) T-cell responses, and consequently the loss of immunological control of HIV replication. Furthermore, the phenomenon of HIV specifically infecting the very cells that respond to it adds a cautionary note to the practice of structured therapy interruption.

Immune reconstitution in patients with HIV infection

The peripheral T cell pool is damaged by HIV-1 infection and can be regenerated by production of new T lymphocytes either from the thymus or from proliferation of post-thymic T cells. A critical question for AIDS patients is whether treatment with antiretroviral drugs can restore the capability to produce new T lymphocytes. The development of a new assay of thymus function in adults (the measurement of T cell receptor excision circles, TRECs), and studies of thymus biopsies in untreated and treated HIV-1-infected patients, have suggested that in select patients the thymus can regenerate on antiretroviral therapy. New strategies to overcome the thymic atrophy of aging are needed to improve thymic function in the majority of AIDS patients.

Evidence for increased T cell turnover and decreased thymic output in HIV infection

The effects of HIV infection upon the thymus and peripheral T cell turnover have been implicated in the pathogenesis of AIDS. In this study, we investigated whether decreased thymic output, increased T cell proliferation, or both can occur in HIV infection. We measured peripheral blood levels of TCR rearrangement excision circles (TREC) and parameters of cell proliferation, including Ki67 expression and ex vivo bromodeoxyuridine incorporation in 22 individuals with early untreated HIV disease and in 15 HIV-infected individuals undergoing temporary interruption of therapy. We found an inverse association between increased T cell proliferation with rapid viral recrudescence and a decrease in TREC levels. However, during early HIV infection, we found that CD45RO-CD27high (naive) CD4+ T cell proliferation did not increase, despite a loss of TREC within naive CD4+ T cells. A possible explanation for this is that decreased thymic output occurs in HIV-infected humans. This suggests that the loss of TREC during HIV infection can arise from a combination of increased T cell proliferation and decreased thymic output, and that both mechanisms can contribute to the perturbations in T cell homeostasis that underlie the pathogenesis of AIDS.

Increased turnover of T lymphocytes in HIV-1 infection and its reduction by antiretroviral therapy

The mechanism of CD4(+) T cell depletion in human immunodeficiency virus (HIV)-1 infection remains controversial. Using deuterated glucose to label the DNA of proliferating cells in vivo, we studied T cell dynamics in four normal subjects and seven HIV-1-infected patients naive to antiretroviral drugs. The results were analyzed using a newly developed mathematical model to determine fractional rates of lymphocyte proliferation and death. In CD4(+) T cells, mean proliferation and death rates were elevated by 6.3- and 2.9-fold, respectively, in infected patients compared with normal controls. In CD8(+) T cells, the mean proliferation rate was 7.7-fold higher in HIV-1 infection, but the mean death rate was not significantly increased. Five of the infected patients underwent subsequent deuterated glucose labeling studies after initiating antiretroviral therapy. The lymphocyte proliferation and death rates in both CD4(+) and CD8(+) cell populations were substantially reduced by 5-11 weeks and nearly normal by one year. Taken together, these new findings strongly indicate that CD4(+) lymphocyte depletion seen in AIDS is primarily a consequence of increased cellular destruction, not decreased cellular production.

Genetically modified immunocompetent cells in HIV infection

Even in the era of highly active antiretroviral therapy (HAART), gene therapy (GT) can remain a promising approach for suppressing HIV infection, especially if complemented with other forms of pharmacological and immunological intervention. A large number of vectors and targets have been studied. Here we discuss the potential of genetically treated, antigen-specific immunocompetent cells for adoptive autologous immunotherapy of HIV infection. Cellular therapies with gene-modified CD8 and CD4 lymphocytes are aimed at reconstituting the antigen-specific repertoires that may be deranged as a consequence of HIV infection. Even if complete eradication of HIV from the reservoirs cannot be achieved, reconstitution of cellular immunity specific for opportunistic pathogens and for HIV itself is a desirable option to control progression of HIV infection and AIDS pathogenesis better.

Viral phenotype affects the thymic production of new T cells in HIV-1-infected children

OBJECTIVE

To determine whether viral phenotype has any effect on thymic production of new T cells in HIV-1-infected children.

DESIGN

Differences in CD4+ T-cell counts and a marker of thymic output [T-cell antigen receptor (TCR) rearrangement excision circles (TRECs)], between HIV-1-infected children with non-syncytium-inducing (NSI) and syncytium-inducing (SI) viral strains were determined.

PATIENTS AND METHODS

A cross-sectional study in 90 samples from vertically HIV-1-infected-children (median age 4.9 years) treated with combination therapy, and a longitudinal study in three children that underwent a change from NSI to SI phenotype were carried out. Viral load, viral phenotype, CD4+ T-cell counts, and quantification of TRECs values were determined.

RESULTS

Children with SI virus showed significant lower levels of CD4+ T cells and a lower thymic production of new T cells than children with NSI. These reductions were independent of the treatment and the age of the children. However, there were no differences in viral load with the phenotype between those groups. In children with both NSI and SI viral phenotype, there was a significant correlation between CD4+ T-cell counts and TRECs values.

CONCLUSION

The decrease of CD4+ T cells in presence of T-tropic viruses would be mainly due to a lower production of new CD4+ T cells as consequence of the inhibitory effect of these T-tropic strains on thymic function. This effect is not due either to the amount of circulating virus or to the replication kinetics of those strains, but rather depends on the ability of T-tropic viruses to infect T-cell precursors using CXCR4 receptors, which are highly expressed in immature thymocytes.

Novel method for molecular detection of the two common hereditary hemochromatosis mutations

We describe a novel molecular screening technique for hereditary hemochromatosis through which HFE genotypes at codon positions 282 and 63 are simultaneously detected. The technique combines multiplex PCR and denaturing high-performance liquid chromatography (DHPLC) and allows automated high-throughput analysis. We used this method to genotype 43 previously characterized anonymous DNA specimens in blinded fashion and found multiplex PCR/DHPLC 100% accurate when compared with PCR/restriction enzyme digestion, yet far more efficient.

The role of the thymus in immune reconstitution in aging, bone marrow transplantation, and HIV-1 infection

The human thymus is a complex chimeric organ comprised of central (thymic epithelial space) and peripheral (perivascular space) components that functions well into adult life to produce naive T lymphocytes. Recent advances in identifying thymic emigrants and development of safe methods to study thymic function in vivo in adults have provided new opportunities to understand the role that the human thymus plays in immune reconstitution in aging, in bone marrow transplantation, and in HIV-1 infection. The emerging concept is that there are age-dependent contributions of thymic emigrants and proliferation of postthymic T cells to maintain the peripheral T cell pool and to contribute to T cell regeneration, with the thymus contributing more at younger ages and peripheral T cell expansion contributing more in older subjects. New studies have revealed a dynamic interplay between postnatal thymus output and peripheral T cell pool proliferation, which play important roles in determining the nature of immune reconstitution in congenital immunodeficiency diseases, in bone marrow transplantation, and in HIV-1 infection. In this paper, we review recent data on human postnatal thymus function that, taken together, support the notion that the human thymus is functional well into the sixth decade and plays a role throughout life to optimize human immune system function.

A binding pocket for a small molecule inhibitor of HIV-1 entry within the transmembrane helices of CCR5

HIV-1 entry into CD4(+) cells requires the sequential interactions of the viral envelope glycoproteins with CD4 and a coreceptor such as the chemokine receptors CCR5 and CXCR4. A plausible approach to blocking this process is to use small molecule antagonists of coreceptor function. One such inhibitor has been described for CCR5: the TAK-779 molecule. To facilitate the further development of entry inhibitors as antiviral drugs, we have explored how TAK-779 acts to prevent HIV-1 infection, and we have mapped its site of interaction with CCR5. We find that TAK-779 inhibits HIV-1 replication at the membrane fusion stage by blocking the interaction of the viral surface glycoprotein gp120 with CCR5. We could identify no amino acid substitutions within the extracellular domain of CCR5 that affected the antiviral action of TAK-779. However, alanine scanning mutagenesis of the transmembrane domains revealed that the binding site for TAK-779 on CCR5 is located near the extracellular surface of the receptor, within a cavity formed between transmembrane helices 1, 2, 3, and 7.

T-cell division in human immunodeficiency virus (HIV)-1 infection is mainly due to immune activation: a longitudinal analysis in patients before and during highly active antiretroviral therapy (HAART)

In human immunodeficiency virus (HIV)-1 infection, highly increased T-cell turnover was proposed to cause exhaustion of lymphocyte production and consequently development of AIDS. Here, we investigated cell proliferation, as measured by expression of the Ki-67 nuclear antigen, in peripheral blood CD4+ and CD8+ lymphocyte subpopulations before and during highly active antiretroviral therapy (HAART). In untreated HIV-1 infection, both the percentage and number of Ki-67+CD4+ and CD8+ lymphocytes were significantly increased, compared with values obtained from healthy individuals. A more than 10-fold increase in the percentage of dividing naive CD4+ T cells in the blood was found when the number of these cells were below 100 per μL.. HAART induced an immediate decline in Ki-67 antigen expression, despite often very low CD4+ T-cell numbers, arguing against increased proliferation being a homeostatic response. After approximately 24 weeks of HAART treatment, a transient increase in the number of proliferating cells was seen, but only in the CD4+CD27+ memory pool. In the CD8+ T-cell compartment, the number of dividing cells was elevated 20- to 25-fold. This increase was most notable in the CD27+ CD 45RO+ and CD27−CD45RO+ memory CD8+ T-cell pool, corresponding with the degree of expansion of these subsets. Reduction of plasma HIV-RNA load by HAART was accompanied by a decrease in numbers and percentages of dividing cells in all CD8+T-cell subsets. Taken together, our results indicate that peripheral T-cell proliferation is a consequence of generalized immune activation. (Blood. 2000;95:249-255)

T-cell division in human immunodeficiency virus (HIV)-1 infection is mainly due to immune activation: a longitudinal analysis in patients before and during highly active antiretroviral therapy (HAART)

In human immunodeficiency virus (HIV)-1 infection, highly increased T-cell turnover was proposed to cause exhaustion of lymphocyte production and consequently development of AIDS. Here, we investigated cell proliferation, as measured by expression of the Ki-67 nuclear antigen, in peripheral blood CD4+ and CD8+ lymphocyte subpopulations before and during highly active antiretroviral therapy (HAART). In untreated HIV-1 infection, both the percentage and number of Ki-67+CD4+ and CD8+ lymphocytes were significantly increased, compared with values obtained from healthy individuals. A more than 10-fold increase in the percentage of dividing naive CD4+ T cells in the blood was found when the number of these cells were below 100 per μL.. HAART induced an immediate decline in Ki-67 antigen expression, despite often very low CD4+ T-cell numbers, arguing against increased proliferation being a homeostatic response. After approximately 24 weeks of HAART treatment, a transient increase in the number of proliferating cells was seen, but only in the CD4+CD27+ memory pool. In the CD8+ T-cell compartment, the number of dividing cells was elevated 20- to 25-fold. This increase was most notable in the CD27+ CD 45RO+ and CD27−CD45RO+ memory CD8+ T-cell pool, corresponding with the degree of expansion of these subsets. Reduction of plasma HIV-RNA load by HAART was accompanied by a decrease in numbers and percentages of dividing cells in all CD8+T-cell subsets. Taken together, our results indicate that peripheral T-cell proliferation is a consequence of generalized immune activation. (Blood. 2000;95:249-255)