Perturbation of CD4+ and CD8+ T-cell repertoires during progression to AIDS and regulation of the CD4+ repertoire during antiviral therapy

Alteration of tumor necrosis factor–α T-cell homeostasis following potent antiretroviral therapy: contribution to the development of human immunodeficiency virus–associated lipodystrophy syndrome

Highly-active antiretroviral therapy (HAART) has lead to a dramatic decrease in the morbidity of patients infected with the human immunodeficiency virus (HIV). However, metabolic side effects, including lipodystrophy-associated (LD-associated) dyslipidemia, have been reported in patients treated with antiretroviral therapy. This study was designed to determine whether successful HAART was responsible for a dysregulation in the homeostasis of tumor necrosis factor- (TNF-), a cytokine involved in lipid metabolism. Cytokine production was assessed at the single cell level by flow cytometry after a short-term stimulation of peripheral blood T cells from HIV-infected (HIV+) patients who were followed during 18 months of HAART. A dramatic polarization to TNF- synthesis of both CD4 and CD8 T cells was observed in all patients. Because it was previously shown that TNF- synthesis by T cells was highly controlled by apoptosis, concomitant synthesis of TNF- and priming for apoptosis were also analyzed. The accumulation of T cells primed for TNF- synthesis is related to their escape from activation-induced apoptosis, partly due to the cosynthesis of interleukin-2 (IL-2) and TNF-. Interestingly, we observed that LD is associated with a more dramatic TNF- dysregulation, and positive correlations were found between the absolute number of TNF- CD8 T-cell precursors and lipid parameters usually altered in LD including cholesterol, triglycerides, and the atherogenic ratio apolipoprotein B (apoB)/apoA1. Observations from the study indicate that HAART dysregulates homeostasis of TNF- synthesis and suggest that this proinflammatory response induced by efficient antiretroviral therapy is a risk factor of LD development in HIV+ patients.

Anti-human immunodeficiency virus type 1 (HIV-1) CD8(+) T-lymphocyte reactivity during combination antiretroviral therapy in HIV-1-infected patients with advanced immunodeficiency

The long-term efficacy of combination antiretroviral therapy may relate to augmentation of anti-human immunodeficiency virus type 1 (HIV-1) CD8(+) T-cell responses. We found that prolonged treatment of late-stage HIV-1-infected patients with a protease inhibitor and two nucleoside reverse transcriptase inhibitors failed to restore sustained, high levels of HIV-1-specific, HLA class I-restricted, cytotoxic-T-lymphocyte precursors and gamma interferon (IFN-gamma) production by CD8(+) T cells. In some patients, particularly those initiating three-drug combination therapy simultaneously rather than sequentially, there were early, transient increases in the frequency of anti-HIV-1 CD8(+) T cells that correlated with decreases in HIV-1 RNA and increases in T-cell counts. In the other patients, HIV-1-specific T-cell functions either failed to increase or declined from baseline during triple-drug therapy, even though some of these patients showed suppression of plasma HIV-1 RNA. These effects of combination therapy were not unique to HIV-1 specific T-cell responses, since similar effects were noted for CD8(+) T cells specific for the cytomegalovirus pp65 matrix protein. The level and breadth of CD8(+) cell reactivity to HLA A*02 HIV-1 epitopes, as determined by IFN-gamma production and HLA tetramer staining after combination therapy, were related to the corresponding responses prior to treatment. There was, however, a stable, residual population of potentially immunocompetent HIV-1-specific T cells remaining after therapy, as shown by tetramer staining of CD8(+) CD45RO(+) cells. These results indicate that new strategies will be needed to target residual, immunocompetent HIV-1-specific CD8(+) T cells to enhance the effectiveness of antiretroviral therapy in patients with advanced immunodeficiency.

Decreased CD95 expression on naive T cells from HIV-infected persons undergoing highly active anti-retroviral therapy (HAART) and the influence of IL-2 low dose administration. Irhan Study Group

The functional recovery of the immune system in HIV-infected persons receiving HAART and the role of adjuvant immune therapy are still matters of intensive investigation. We analysed the effects of HAART combined with cytokines in 22 naive asymptomatic individuals, randomized to receive HAART (n = 6), HAART plus a low dose (1000 000 U/daily) of rIL-2 (n = 8), and HAART plus rIL-2 after previous administration of granulocyte colony-stimulating factor (n = 8). After 3 months of therapy, increased CD4+ T cell counts and diminished viral loads were observed in all patients, independently of cytokine addition. A decreased expression of CD95 (Apo 1/Fas) was evident in all groups when compared with values before therapy. The percentages of peripheral blood mononuclear cells (PBMC) expressing CD95 after therapy decreased by 15%, 22% and 18% in the three treatment groups, respectively (P < 0.05). Analysis of PBMC subsets demonstrated that CD95 expression was significantly reduced on CD45RA+CD62L+ naive T cells (25.3%, 22.4%, and 18.6%, respectively; P < 0.05) in each group, after therapy. Accordingly, all patients showed a reduced rate of in vitro spontaneous apoptosis (P < 0.05). Another effect induced by HAART was a significant increase in IL-2Ralpha expression on total PBMC (P < 0.05), independently of cytokine addition. Altogether, our results suggest that very low dose administration of rIL-2 (1000 000 U/daily) may be not enough to induce a significant improvement in the immune system as regards HAART alone. The employment of higher doses of recombinant cytokines and/or different administration protocols in clinical trials might however contribute to ameliorate the immune reconstitution in patients undergoing HAART.

Shortage of circulating naive CD8+ T cells provides new insights on immunodeficiency in aging

Clinical observations indicate that elderly people are prone to severe, often lethal infectious diseases induced by novel pathogens. Since the ability to mount primary immune responses relies on the availability of naive T cells, the circulating naive T-cell reservoir was evaluated throughout the human life span. Naive T cells were identified as CD95− T lymphocytes for their phenotypic and functional features. Indeed, the lack of CD95 marker is sufficient to identify a population of naive T cells, as defined by coincidence with previously characterized CD45RA+ CD62L+ T cells. Naive CD95− T cells, as expected, require a costimulatory signal, such as CD28, to optimally proliferate after anti-CD3 stimulation. Cytofluorimetric analysis of circulating T lymphocytes from 120 healthy subjects ranging in age from 18 to 105 years revealed that naive T cells decreased sharply with age. The younger subjects had a naive T-lymphocyte count of 825 ± 48 cells/μL, and the centenarians had a naive T-lymphocyte count of 177 ± 28 cells/μL. Surprisingly, the naive T-cell count was lower in CD8+than in CD4+ subsets at any age, and the oldest individuals were almost completely depleted of circulating naive CD8+ T cells (13 ± 4 cells/μL). Concomitantly, a progressive expansion of CD28− T cells occurs with age, which can be interpreted as a compensatory mechanism. These data provide new insights into age-related T-cell–mediated immunodeficiency and reveal some analogies of T-cell dynamics between advanced aging and human immunodeficiency virus (HIV) infection. In conclusion, the exhaustion of the naive CD8+ T-cell reservoir, which has never been reported before, suggests that this T-cell pool is a major target of the aging process and may define a parameter possibly related to the life span of humans.

Direct visualization of cytokine-producing recall antigen-specific CD4 memory T cells in healthy individuals and HIV patients

We have used computer-assisted cytokine ELISA spot analysis to measure the frequencies, the type of cytokine, and the amount of cytokine produced by individual recall Ag-specific CD4 memory cells in freshly isolated blood. We studied the memory cells specific for tetanus toxoid and purified protein derivative in 18 healthy individuals and in 22 HIV-infected patients on highly active antiretroviral therapy (HAART). In healthy individuals, the frequency, cytokine signature, and cytokine production per cell of these memory cells were stable over time. Although it is presently unclear whether the maintenance of the memory T cell pool depends upon Ag persistence, cross-reactive Ag stimulation, or cytokine-driven bystander stimulations and expansions, our data strongly argue for a stable memory cell pool in healthy individuals. In HIV patients, however, the frequency of these memory cells was a function of the viral load. The decreased numbers of functional memory cells in patients with high viral loads might provide one mechanism behind the immunodeficient state. Although the cytokine output per cell was unaffected in most patients (20 of 24), in some patients (4 of 24) it was >100-fold reduced, which might provide an additional mechanism to account for the reduced immunocompetence of these patients. The ability to visualize directly and quantify the cytokine produced by the low frequency memory cells in freshly isolated blood that have been physiologically stimulated by Ag should aid comprehensive studies of the Ag-specific memory cell pool in vivo, in health and disease.

Initiation of antiretroviral therapy during primary HIV-1 infection induces rapid stabilization of the T-cell receptor β chain repertoire and reduces the level of T-cell oligoclonality

Major T-cell receptor β chain variable region (TCRBV) repertoire perturbations are temporally associated with the down-regulation of viremia during primary human immunodeficiency virus (HIV) infection and with oligoclonal expansion and clonal exhaustion of HIV-specific cytotoxic T lymphocytes (CTLs). To determine whether initiation of antiretroviral therapy (ART) or highly active antiretroviral therapy (HAART) during primary infection influences the dynamics of T-cell–mediated immune responses, the TCRBV repertoire was analyzed by semiquantitative polymerase chain reaction in serial blood samples obtained from 11 untreated and 11 ART-treated patients. Repertoire variations were evaluated longitudinally. Stabilization of the TCRBV repertoire was more consistently observed in treated as compared with untreated patients. Furthermore, the extent and the rapidity of stabilization were significantly different in treated versus untreated patients. TCRBV repertoire stabilization was positively correlated with the slope of HIV viremia in the treated group, suggesting an association between repertoire stabilization and virologic response to treatment. To test whether stabilization was associated with variations in the clonal complexity of T-cell populations, T-cell receptor (TCR) heteroduplex mobility shift assays (HMAs) were performed on sequential samples from 4 HAART-treated subjects. Densitometric analysis of HMA profiles showed a reduction in the number of TCR clonotypes in most TCRBV families and a significant decrease in the total number of clonotypes following 7 months of HAART. Furthermore, a biphasic decline in HIV-specific but not heterologous CTL clones was observed. This indicates that ART leads to a global reduction of CD8+T-cell oligoclonality and significantly modulates the mobilization of HIV-specific CTL during primary infection.

Early immune reconstitution after potent antiretroviral therapy in HIV-infected children correlates with the increase in thymus volume

DESIGN

Despite significant rises in total CD4 T cells, the process of immune reconstitution in adults with HIV infection treated with potent antiretroviral treatment results in a rather slow increase in phenotypically naive lymphocytes. In children more than in adults, thymic function may be at least partly restored when disease-induced immunosuppression is attenuated by pharmacological means.

METHODS

Twenty-five vertically infected and antiretroviral-experienced [zidovudine (ZDV)/ZDV plus didanosine (ddl)] children were prospectively followed during 12 months of treatment with lamivudine (3TC), stavudine (d4T) and indinavir (IDV). The plasma HIV viral load and phenotypic and functional cellular immunity-defining parameters were examined. The relationship between the degree of immune reconstitution and thymus volume assessed by nuclear magnetic resonance was also examined.

RESULTS

An early and steep increase in CD45RA+62L+ T cells was observed in parallel with a sustained decrease in plasma HIV RNA levels and a significant rise in total CD4 T cells. This increase was significantly greater than that observed in CD4+CD45RO+ T cells. Analysis of the CD4 T cell receptor (TCR) beta repertoire and T helper function showed the ability to reconstitute families almost completely absent at baseline, and a substantial improvement of antigen-specific responses by peripheral blood lymphocytes. The rise in CD4 cells and in CD4+CD45RA+62L+ T cells was statistically associated with changes in thymus size observed over time.

CONCLUSION

These data suggest a relevant contribution of the thymus to reconstitution of the peripheral pool of T cells in vertically HIV-infected children treated with potent antiretroviral regimens.

Normal T-cell turnover in sooty mangabeys harboring active simian immunodeficiency virus infection

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) remain healthy though they harbor viral loads comparable to those in rhesus macaques that progress to AIDS. To assess the immunologic basis of disease resistance in mangabeys, we compared the effect of SIV infection on T-cell regeneration in both monkey species. Measurement of the proliferation marker Ki-67 by flow cytometry showed that mangabeys harbored proliferating T cells at a level of 3 to 4% in peripheral blood irrespective of their infection status. In contrast, rhesus macaques demonstrated a naturally high fraction of proliferating T cells (7%) that increased two- to threefold following SIV infection. Ki-67(+) T cells were predominantly CD45RA(-), indicating increased proliferation of memory cells in macaques. Quantitation of an episomal DNA product of T-cell receptor alpha rearrangement (termed alpha1 circle) showed that the concentration of recent thymic emigrants in blood decreased with age over a 2-log unit range in both monkey species, consistent with age-related thymic involution. SIV infection caused a limited decrease of alpha1 circle numbers in mangabeys as well as in macaques. Dilution of alpha1 circles by T-cell proliferation likely contributed to this decrease, since alpha1 circle numbers and Ki-67(+) fractions correlated negatively. These findings are compatible with immune exhaustion mediated by abnormal T-cell proliferation, rather than with early thymic failure, in SIV-infected macaques. Normal T-cell turnover in SIV-infected mangabeys provides an explanation for the long-term maintenance of a functional immune system in these hosts.

Highly altered V beta repertoire of T cells infiltrating long-term rejected kidney allografts

Chronic rejection represents a major cause of long-term kidney graft loss. T cells that are predominant in long-term rejected kidney allografts (35 +/- 10% of area infiltrate) may thus be instrumental in this phenomenon, which is likely to be dependent on the indirect pathway of allorecognition only. We have analyzed the variations in T cell repertoire usage of the V beta chain at the complementary determining region 3 (CDR3) level in 18 human kidney grafts lost due to chronic rejection. We observed a strongly biased intragraft TCR V beta usage for the majority of V beta families and also a very high percentage (55%) of V beta families exhibiting common and oligoclonal V beta-C beta rearrangements in the grafts of patients with chronic rejection associated with superimposed histologically acute lesions. Furthermore, V beta 8 and V beta 23 families exhibited common and oligoclonal V beta-J beta rearrangements in 4 of 18 patients (22%). Several CDR3 amino acid sequences were found for the common and oligoclonal V beta 8-J beta 1.4 rearrangement. Quantitative PCR showed that biased V beta transcripts were also overexpressed in chronically rejected kidneys with superimposed acute lesions. In contrast, T lymphocytes infiltrating rejected allografts with chronic rejection only showed an unaltered Gaussian-type CDR3 length distribution. This pattern suggests that late graft failure associated with histological lesions restricted to Banff-defined chronic rejection does not involve T cell-mediated injury. Thus, our observation suggests that a limited number of determinants stimulates the recipient immune system in long-term allograft failure. The possibility of a local response against viral or parenchymatous cell-derived determinants is discussed.

Normal CD4 T-cell receptor repertoire in tonsillar tissue despite perturbed repertoire in peripheral blood in HIV-1 infected individuals

OBJECTIVE

To compare the T-cell receptor (TCR) repertoire of T-cell subsets in peripheral blood and lymphoid tissue from HIV-1 infected individuals.

DESIGN

Biopsies of tonsillar tissue and samples of peripheral blood were obtained from 10, mostly treatment-naive, HIV-1-infected individuals. CD4 and CD8 T-cell subsets were quantified, the TCR repertoire was analysed within 'naive' and 'memory' subsets, and results compared between identical subsets in tonsillar tissue and blood.

METHODS

Cell subsets were quantified by flow cytometry. CD4 T cells and CD8 T cells were isolated by immunomagnetic beads. Populations were in most cases further subdivided by immunomagnetic selection on the basis of CD45RO expression. TCR repertoire was studied by spectratyping of the TCR beta variable (BV) complementarity determining region 3 (CDR3) transcripts.

RESULTS

Amongst CD4 T cells, an abnormal TCR repertoire was found in median 25% (range, 0-88%) of BV families in peripheral blood, but in 0% (0-7%) in tonsillar tissue (P<0.05). Large peaks suggestive of expanded clones were common within CD8 T-cells, both in peripheral blood and tonsillar tissue. However, the expanded clones were rarely identical in the two compartments. Expanded CDR3 peaks, suggesting the presence of clonally expanded cells, were observed within both CD45RO+ and CD45RO- cells from all T-cell subsets, but, again they were mainly of different lengths.

CONCLUSION

CD4 T cells were preserved in number and TCR repertoire in tonsillar tissue compared with blood in HIV-1 infected individuals. T-cells collected from the peripheral blood may not be representative of those residing in lymphoid tissue.

Human anti-HIV-1 tat sFv intrabodies for gene therapy of advanced HIV-1-infection and AIDS

The early successes of highly active anti-retroviral therapies (HAART) for the treatment of HIV-1-infection and AIDS have raised the question as to whether there is a legitimate role for gene therapy in the treatment of this chronic infectious disease. However, in many patients the profound suppression of viral replication is short lived, particularly if patients have been treated with sequential monotherapies in the past, have been infected with a highly drug resistant isolate of HIV-1, or have temporarily discontinued therapy as a "holiday" or because of drug intolerance. In addition, life-long adherence to maintenance HAART will probably be required even in responding patients with undetectable viremia because of the reservoirs of latently infected cells that can persist for years. Gene therapy through the introduction of anti-retroviral "resistance" genes into CD4(+) T cells is one approach that could give long term protection to these HIV-1 susceptible cells in vivo. We have explored this approach by developing intrabodies to the critical HIV-1 transactivator protein, Tat that is absolutely required for HIV-1 replication. This provocative treatment approach, that will be tested in a clinical gene therapy trial, sets the groundwork for determining if anti-Tat intrabody gene therapy together with HAART can provide a treatment strategy for the immune reconstitution of HIV-1-infected patients with advanced disease.

Sexual transmission and propagation of SIV and HIV in resting and activated CD4+ T cells

In sexual transmission of simian immunodeficiency virus, and early and later stages of human immunodeficiency virus-type 1 (HIV-1) infection, both viruses were found to replicate predominantly in CD4(+) T cells at the portal of entry and in lymphoid tissues. Infection was propagated not only in activated and proliferating T cells but also, surprisingly, in resting T cells. The infected proliferating cells correspond to the short-lived population that produces the bulk of HIV-1. Most of the HIV-1-infected resting T cells persisted after antiretroviral therapy. Latently and chronically infected cells that may be derived from this population pose challenges to eradicating infection and developing an effective vaccine.

Cytomegalovirus retinitis in advanced HIV-infected patients treated with protease inhibitors: incidence and outcome over 2 years

We prospectively studied the incidence of cytomegalovirus (CMV) retinitis in 93 patients treated with highly active antiretroviral therapy (HAART) containing a protease inhibitor (PI), during a median follow-up period of 24 months. The median initial CD4+ count was 22 cells/microl (range, 1-311 cells/microl), and the median plasma HIV viral load was 5.1 log10 copies/ml (range, 2.4-6.4 log10 copies/ml). The fundus was examined monthly in patients with a history of CMV retinitis or an initial CD4+ count <50 cells/microl and every 3 months in the other patients. Of patients with previously controlled CMV retinitis, 1 of 7 relapsed. In addition, 6 of 59 patients with a CD4+ count <50 cells/microl and no history of CMV retinitis before starting PI therapy developed CMV retinitis. Of them, 3 had at least one relapse during follow-up. CD4+ counts were <40 cells/microl at the time of primary or recurrent CMV retinitis, except in two cases (147 cells/microl and 203 cells/microl). In conclusion, the incidence of CMV retinitis was 0.091 per patient-year among study subjects with advanced HIV infection who were receiving HAART (95% confidence interval [CI], 0.037-0.145). The time to progression of CMV retinitis (mean, 215 days; 95% CI, 113-317 days) was longer than reported before widespread use of PIs.

B Cell Repertoire Diversity and Clonal Expansion in Multiple Sclerosis Brain Lesions

Multiple sclerosis (MS) lesions in the CNS are characterized by disseminated demyelination with perivascular infiltrates of macrophages, T cells, and B cells. To investigate the origin and characteristics of the B cell population found in MS plaque tissue, we performed molecular studies in 10 MS patients and 4 non-MS control samples. Ig transcripts from the perivascular infiltrated brain lesions were analyzed by complementary-determining region 3 spectratyping to ascertain the B cell heavy chain gene rearrangement repertoire expressed in MS brains. Significant rearrangement diversity and deviation from the normal Ig heavy (H) chain repertoire was observed. The cloning and sequencing of RT-PCR products from families VH1 and VH4 showed a correlation with the profiles obtained by spectratyping. Generally, restricted spectratyping patterns concurred with repetition of in-frame complementary-determining region 3 identical sequences. The analysis of heavy chain variable (VH), diversity (D), and joining (JH) gene segments revealed the increased usage of VH1–69, VH4–34, and VH4–39. Similarly, gene segments from families D2, D3, and JH4 were over-represented. The presence of restricted patterns of rearranged Ig mRNA within the plaque lesion suggests that Ab production in the demyelinating plaque is a local phenomenon and supports the idea that in MS an Ag-driven immune response might be responsible for demyelination.

Functional and genetic integrity of the CD8 T-cell repertoire in advanced HIV infection

BACKGROUND

HIV-specific cytotoxic T lymphocytes (CTL) can restrict HIV replication in acute and chronic infection, but disease progression occurs in parallel with declining CTL activity. An understanding of why CTL fail to control HIV replication might reveal important mechanisms of disease progression and enhance prospects for developing effective CTL-based immunotherapies.

OBJECTIVES

To investigate the functional integrity, T-cell repertoire diversity, and HIV reactivity of CD8 T lymphocytes in individuals with advanced HIV infection.

METHODS

Individuals were considered to have progressed to advanced HIV infection if their total T-cell count was < 500 x 10(6) cells/(l) on at least two successive clinic visits. CD8 T cells from these individuals were analyzed for CTL function, HIV reactivity and T-cell receptor (TCR) diversity by chromium release assays and reverse transcriptase polymerase chain reaction.

RESULTS

CD8 T cells from all individuals with advanced HIV infection proliferated and differentiated into functional CTL in vitro. Despite extremely low T-cell counts and previous AIDS-defining illnesses, six individuals had inducible anti-HIV CTL responses. In two additional cases, HIV-specific CTL activity became detectable following significant treatment-associated remission of T-cell lymphopenia. Assessment of TCRbetaV gene family representation and betaV gene intrafamily diversity indicated CD8 T-cell repertoire diversity is maintained through advanced HIV infection.

CONCLUSIONS

These data suggest that HIV-specific CTL activity can be selectively compromised while the functional and genetic integrity of the CD8 population as a whole remains intact. A substantial fraction of individuals retain inducible anti-HIV CTL activity through advanced HIV infection and, in at least some cases, effective treatment can restore HIV-specific CTL responses even at this late stage of disease.

T cell receptor repertoire usage in allotransplantation: an overview

Lymphocytes express antigen receptors that allow the immune system to specifically recognize antigens. In transplantation, T cells play a critical role in the rejection process, and different protocols inhibiting T cell-mediated alloreactivity efficiently achieve prolongation of allograft survival. T cells can interact with alloantigens by two ways, either by the "indirect" pathway that correspond to the physiological mechanism of T cell immune recognition, or through the "direct" pathway where they recognize alloantigens directly on the surface of donor cells. If some T cells are specifically activated in allorecognition, one should be able to indirectly detect this "selection" by analyzing the T cell receptor usage that could be biased and reflect the preferential amplification of alloreactive lymphocyte subsets. Nevertheless compared with disease states such as cancer or autoimmunity the T cell receptor repertoire is still largely uncharacterized. We review the current results available on T cell repertoire usage in transplantation studies involving humans or various animal models. The T cell receptor repertoire involved in transplantation (restricted or unrestricted) and the features potentially common to alloimmune responses will be discussed.

Natural history of HIV infection in the era of combination antiretroviral therapy

BACKGROUND

The use of protease inhibitor-containing (PI) combination antiretroviral therapy has led to a reduction in the incidence of opportunistic illness and mortality (events) in HIV infection. We wished to quantify the changing incidence of these events in our clinical practice and delineate the relationship between CD4, HIV-1 RNA, and development of events in patients receiving PI combination therapy.

METHODS

We assessed HIV-infected patients with CD4 counts < or =500 cells x10(6)/l. We calculated the incidence of events from 1994 through 1998 and analyzed the association of temporal changes in event incidence and use of antiretroviral therapy. In patients on PI combination therapy, we determined the probability of achieving and maintaining an undetectable HIV-1 RNA response and determined the association of CD4, HIV-1 RNA, and developing an event.

RESULTS

The incidence of opportunistic illness declined from 23.7 events/100 person-years in 1994 to 14.0 events/100 person-years in 1998 (P<0.001). Mortality declined from 20.2 deaths/100 person-years in 1994 to 8.4 deaths/ 100 person-years in 1998 (P<0.001). Use of PI combination therapy was associated with a relative rate of opportunistic illness or death of 0.66 [95% confidence interval (CI), 0.51-0.85; P<0.001]. The relative incidence of each of 16 opportunistic illnesses was approximately the same in 1998 as in 1994 except for lymphoma, cervical cancer and wasting syndrome which do not appeared to have declined in incidence. Approximately 60% of patients who received PI therapy achieved an undetectable HIV-1 RNA, and 65% of these patients maintained durable suppression of HIV-1 RNA. Achieving an undetectable HIV-1 RNA was associated with a decreased risk of an event, and was the variable most strongly associated with an increase in CD4 level. By multivariate analysis, the concurrent CD4 level was most strongly associated with developing an event.

CONCLUSIONS

We observed a significant decline in the incidence of opportunistic illness and death from 1994 through 1998 associated with combination antiretroviral therapy. Patients who develop events while being treated with PI combination therapy were not likely to have achieved an undetectable HIV-1 RNA and are likely to have a low concurrent CD4 level.

HAART in HIV-infected patients: restoration of antigen-specific CD4 T-cell responses in vitro is correlated with CD4 memory T-cell reconstitution, whereas improvement in delayed type hypersensitivity is related to a decrease in viraemia

OBJECTIVE

To analyse prospectively the effect of highly active antiretroviral treatment (HAART) on CD4 T-cell responses in vitro and in vivo in HIV-infected patients.

DESIGN

Prospective study with 49 protease inhibitor-naive adult patients. Data were collected at baseline and after 3 and 6 months of HAART.

METHODS

In vitro CD4 T-cell reactivity was analysed by stimulation of peripheral blood mononuclear cells with several antigens. In vivo CD4 T-cell reactivity (delayed type hypersensitivity) was assessed by Multitest Merieux. Both measurements were correlated to CD4 (memory) T-cell count and HIV-1 viraemia.

RESULTS

Restoration of specific CD4 T-cell proliferation was observed in most patients. The in vitro T-cell response was restored more frequently against antigens to which the immune system is constantly exposed (Candida albicans, Mycobacterium tuberculosis, M. avium) as compared with a low-exposure antigen (tetanus toxoid). Overall, delayed type hypersensitivity detection rate increased under HAART. Multivariate analysis showed improvement of antigen-specific T-cell proliferation to be significantly associated with an increase in memory CD4 T-cells, whereas improvement of the delayed type hypersensitivity response was associated with a decrease in plasma HIV-1 RNA.

CONCLUSIONS

HAART for 6 months restored antigen-specific CD4 T-cell response to several antigens. In vitro immune reconstitution was closely correlated with an increase in memory CD4 cells. Restoration of delayed type hypersensitivity was associated with suppression of viraemia. It appears that in addition to expansion of memory CD4 cells, suppression of viraemia following HAART may allow an improved inflammatory reaction, thus providing even stronger immune reconstitution.

Latent reservoirs of HIV: obstacles to the eradication of virus

The use of highly active antiretroviral therapy (HAART) in the treatment of HIV-1-infected individuals has provided a considerable amount of information regarding the dynamics of viral replication and has resulted in enormous advances in HIV therapeutics. The profound suppression of plasma viremia in HIV-infected individuals receiving HAART has resulted in a highly beneficial clinical effect and a dramatic decrease in the death rate attributable to AIDS. Nonetheless, the persistance of reservoirs of HIV, including latently infected, resting CD4+ T cells that can give rise to infectious HIV upon stimulation in vitro, has posed a sobering challenge to the long-term control or eradication of HIV in infected individuals receiving HAART. Although a recent study has demonstrated th at the size of the pool of latently infected, resting CD4+ T cells can be markedly diminished with intermittent interleukin (IL-2) and continuous HAART, complete eradication of HiV in infected individuals remains extremely problematic. Here we discuss recent developments in studies of the latent reservoir of HIV in patients receiving HAART and implications for the long-term treatment of infected individuals and eradication of the infection.

Markers of Lymphocyte Homing Distinguish CD4 T Cell Subsets That Turn Over in Response to HIV-1 Infection in Humans

In HIV-1 infection, the abrupt rise in CD4 T cells after effective antiretroviral therapy has been viewed as a measure of HIV-1-related CD4 T cell turnover in the steady state. The early (2–4 wk) response is reportedly dominated by CD4 T cells with a memory (CD45RO) phenotype. It is controversial whether the measurement of steady-state kinetics identifies cells that otherwise would have been recruited into a short-lived, virus-producing pool or reflects lymphoid redistribution/sequestration. We performed detailed phenotypic and kinetic analysis of CD4 T cell subsets in 14 patients. Turnover occurs in memory (CD45RO) as well as naive (CD45RA) cells, if the latter are present at baseline. Most of the turnover occurs in those memory (CD45RO) and naive (CD45RA) cells that are programmed for recirculation through lymphoid organs (CD62L+ and CD44low), whereas very little turnover occurs in memory cells (CD45RO) destined for recirculation from blood to tissue (CD62L− and CD44high). Turnover occurs in both activated (CD25+ and HLA-DR+) and nonactivated populations, although it is restricted to CD38-positive cells, indicating that turnover does not measure cells that are already infected. More likely, turnover occurs in cells that replace infected cells or are on their way to becoming infected. Taken together, markers of lymphocyte trafficking better describe cell turnover related to virus replication than do naive and memory markers per se, and lymph organs, not tissue-destined cells or peripheral blood cells, appear to be the important site of virus replication and CD4 T cell turnover, destruction, and redistribution.

Measuring recent thymic emigrants in blood of normal and HIV-1-infected individuals before and after effective therapy

The role of the thymus in HIV-1 pathogenesis remains unclear. We developed an assay to quantify the number of recent thymic emigrants in blood based on the detection of a major excisional DNA byproduct (termed alpha1 circle) of T cell receptor rearrangement. By studying 532 normal individuals, we found that alpha1 circle numbers in blood remain high for the first 10-15 yr of life, a sharp drop is seen in the late teen years, and a gradual decline occurs thereafter. Compared with age-matched uninfected control individuals, alpha1 circle numbers in HIV-1-infected adults were significantly reduced; however, there were many individuals with normal alpha1 circle numbers. In 74 individuals receiving highly active antiretroviral therapy, we found no appreciable effect on alpha1 circle numbers in those whose baseline values were already within the normal range, but significant increases were observed in those with a preexisting impairment. The increases in alpha1 circle numbers were, however, numerically insufficient to account for the rise in levels of naive T lymphocytes. Overall, it is difficult to invoke thymic regenerative failure as a generalized mechanism for CD4 lymphocyte depletion in HIV-1 infection, as alpha1 circle numbers are normal in a substantial subset of HIV-1-infected individuals.

Kinetics of lymphokine production in HIV+ patients treated with highly active antiretroviral therapy and interleukin 2

This study presents the kinetics of CD4/CD25 cell numbers, serum sCD25 levels, and intracellular production and release of interleukin-2 (IL-2) and interleukin-16 (IL-16) in 11 HIV+ patients treated with six cycles of highly active antiretroviral therapy (HAART) plus six MUI of subcutaneous IL-2 compared to 10 HIV+ patients treated with HAART alone. IL-2 therapy induced moderate effects on CD4 T cell recovery and increased CD4/CD25+ cells and sCD25 levels after 2 weeks, while intracellular and secreted IL-2 was reduced and IL-16 was increased at the same time point. After 24 weeks, while HAART-treated patients had increased IL-2 production, in IL-2 treated patients, cytokine production was unaltered compared to pretreatment values. Decreased in vitro IL-2 production may depend on a feedback inhibition by IL-2 infusion. Because of its known antiviral effects, the increased IL-16 production seen after 2 weeks in IL-2-treated individuals may produce beneficial effects on HIV disease. The kinetics of cytokine production may serve to define better the use IL-2 in clinical trials.

The disruption of macaque CD4+ T-cell repertoires during the early simian immunodeficiency virus infection

T-cell receptor (TCR) complementarily determining region 3 (CDR3) spetratyping analysis was employed to assess the ability of an AIDS virus to disrupt CD4 + T-cell repertoires during the primary infection. Rhesus and pig-tailed macaques infected with simian immunodeficiency virus (SIV)mac 251 and SIVsmmFGb, respectively, were evaluated. Following SIV infection, the macaques exhibited an apparent decline of CD4 + peripheral blood lymphocyte (PBL) counts, which was associated with a change in CDR3 profiles from multiple-length distribution to one- or two-length dominance in the selected TCR Vbeta-expressing CD4 + PBL subpopulations. Molecular analysis of the perturbed cell subpopulations suggested that the CD4 + T cells bearing the dominant CDR3 length were clonally expanded. These results indicate that SIV infection can induce a disruption of macaque CD4 + T-cell repertoires during the primary infection. The finding in this study, therefore, suggests that the virus-induced clonal dominance can contribute to the disruption of CD4 + T-cell repertoires.

Effect of indinavir and higher CD4+ T-cell count on viral load response after 6 months of highly active antiretroviral therapy

This retrospective, unmasked chart review was undertaken to determine which HIV-infected patients receiving protease inhibitors (PIs) for the first time were most likely to experience a decrease in plasma viral load (PVL) and which factors were associated with a PVL < 500 copies/mL below the detectable limits after 6 months. A total of 308 patients aged > 15 years with a PVL > 500 copies/mL received therapy that included a PI in addition to other antiretroviral therapies (128 patients, saquinavir hard-gel capsule 600 mg TID; 107 patients, indinavir 800 mg TID; and 73 patients, ritonavir 600 mg BID). The choice of drug was at individual clinicians' discretion. Patients were followed for a median of 10 (range, 6 to 21) months. Of the 128 patients who received saquinavir, 45% were switched to another PI (33%, indinavir; 12%, ritonavir). Seventy percent of the 73 patients initially given ritonavir were switched (45%, indinavir; 25%, saquinavir), as were 23% of the 107 patients initially given indinavir (15%, saquinavir; 8%, ritonavir). A total of 34.1% (n = 105) of patients achieved a PVL < 500 copies/mL; in 51.6%, PVL decreased > 0.5 log copies/mL. In this subgroup, both treatment-naive patients and those who were receiving a new combination of antiretroviral therapy when they started PI treatment had a more pronounced decline in PVL (P < 0.001). After adjustment by logistic regression analysis for age, sex, mode of transmission, and duration of highly active antiretroviral therapy (HAART), CD4+ cell count and initial type of PI received were independently associated with PVL < 500 copies/mL. In the present study, the treatment success rate was low (34.1%) compared with rates observed in randomized, controlled trials. A higher CD4+ cell count and use of indinavir at the initiation of HAART are associated with a better viral load response.

An anti-HIV strategy combining chemotherapy and therapeutic vaccination

Combination chemotherapy using potent anti-retroviral agents has led to significant advances in the clinical management of human immunodeficiency virus (HIV) disease. However, the emergence of multiple drug-resistant mutants, the high need for compliance to adhere to demanding drug-dosing schemes, and the remaining toxic side-effects of drugs make the perspective of life-long treatment unattractive and possibly unrealistic. Therefore, means must be sought to shorten the time span during which treatment is necessary. Such means could be to stimulate an efficient immune response during the period of low virus load and restored CD4 + cell levels, which might be capable of keeping the virus under long-lasting control after treatment is stopped. Here we tested this concept of combined chemotherapy/ therapeutic vaccination in a non-human primate model. Rhesus macaques chronically infected with the chimeric simian/human immunodeficiency virus (SHIV) containing the HIV type 1 (HIV-1) HXBc2 gene for reverse transcriptase (RT) in the genomic background of simian immunodeficiency virus (SIV)(mac239) (RT-SHIV) were treated with (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA), a potent anti-HIV drug. When virus load had decreased significantly, we immunized with SIV genes env, gag/pol, rev, tat, and nef inserted in two different expression vector systems. Four weeks after the second immunization, drug treatment was stopped. Animals were monitored to determine if virus load stayed low or if it increased again to the original levels and if CD4+ T-cell levels remained stable. Humoral and cellular immune responses were also measured. This combined chemotherapy/ therapeutic vaccination regimen induced a significant reduction in the steady-state level of viremia in one out of two chronically infected rhesus macaques. Chemotherapeutic treatment alone did not achieve reduction of viremia in two chronically infected animals. The nature of the immune responses assumed to have been induced by vaccination in one out of the two monkeys remains to be elucidated.

Therapeutic vaccines in HIV.1 infection

In this review we address questions which must be considered if better attempts are to be made to treat all persons presently infected with human immunodeficiency virus (HIV). There are thirty million people in the world presently living with HIV, only 10% of whom are likely to be able to access currently available drug therapy. Even when available, such therapy causes considerable inconvenience and undesirable clinical side effects, and fails to eradicate virus from a small reservoir of latently infected cells. Thus, we must ask what forms of alternative therapy might be used. One strategy that may be considered is to reduce virus levels as low as possible using highly active antiretroviral therapy (HAART), followed by modulation of host immunity with immunotherapy in order to effect an appropriate and efficient response mimicking that found in long-term asymptomatic patients, with the aim of indefinitely maintaining the asymptomatic period following discontinuation of chemotherapy, or even of eradicating the virus from the latent reservoirs. In 1987, long before the advent of highly active antiretroviral therapy, J. Salk proposed the use of a 'suitable potent non-infectious (HIV) immunogen' to delay or prevent the development of AIDS in infected individuals (1). The objective of administering such an agent was to 'enhance and prolong the presence of (immunologically) protective factors'. The stated aim at that time was 'to destroy virus and viral antigen producing cells by the induction of the immune system's cytotoxic mechanisms known to rid the host of virus and virus producing cells'. Twelve years later, and after a quarter of a century living with HIV, and with the advent of HAART, is it time to use our knowledge of the host's own immune system to fight this seemingly intractable invader?

Antigen-specific cytokine response to hepatitis C virus core epitopes in HIV/hepatitis C virus-coinfected patients

OBJECTIVE

Epidemiological data indicate that hepatitis C virus (HCV) infection runs a more rapid and severe course of disease in HIV-coinfected patients, probably because of an altered immune response.

DESIGN

We investigated whether HCV-specific cytokine responses are affected by HIV coinfection.

METHODS

Using triple colour flow cytometry on peripheral blood lymphocytes after stimulation with the four major immunodominant HCV core T cell epitopes, CT1-CT4, we determined intracytoplasmic production of IFN-gamma, IL-2, IL-4, IL-10 and CD30 expression, a putative surrogate marker of type 2 cells. Fifteen patients with asymptomatic HIV/HCV coinfection (group A), 15 patients with chronic HCV infection (group B) and 10 HIV-infected patients without hepatitis C (group C) were included in the study.

RESULTS

In group A, HCV antigens induced significantly higher IL-2 and IFN-gamma production than groups B and C (P < 0.05). Groups A and B showed a similar induction of CD30, which was significantly higher than in group C (P < 0.001). Remarkably, in group A HCV antigens induced IL-4 production in addition to IL-10 and IFN-gamma in the CD30 subset, whereas in groups B and C no IL-4 induction was observed in this T cell subset (P < 0.002).

CONCLUSION

Our data suggest that asymptomatic HIV coinfection importantly alters the HCV-specific cytokine response towards a greater production of proinflammatory type 1 cytokines. Moreover, the antiviral activity of type 1 cytokines may be modified by an increased production of type 2 cytokines in the CD30 subset. The altered cytokine pattern may contribute to the adverse natural course of hepatitis C in HIV coinfection.

Long-term evaluation of T-cell subsets and T-cell function after HAART in advanced stage HIV-1 disease

OBJECTIVES

Evaluation of immunological reconstitution after 2 years of highly active antiretroviral therapy (HAART) in AIDS patients.

DESIGN

Previous data showed the effectiveness of HAART but conflicting evidence of immune reconstitution has been found in severely immunocompromised patients. Therefore, T-cell subsets and functions were analysed during 24 months of HAART in 21 AIDS patients (mean baseline CD4 cell count, 20 x 10(6)/l).

METHODS

Subjects were tested at baseline and after 4, 12 and 24 months of therapy for clinical symptoms and the following investigations were carried out: plasma HIV RNA, T-cell subsets and lymphoproliferative responses to mitogens (phytohaemagglutinin, anti-CD3), and recall antigens (Candida mannoprotein, tetanus toxoid and recombinant glycoprotein 160).

RESULTS

Increase in body weight, improvement of Karnofsky's score and reduction of opportunistic infections were observed. All patients showed an initial increase in the CD4 memory subset, whereas naive CD4 cells consistently increased only after 1 year. The magnitude of immune recovery was stronger in patients showing a significant reduction in viral load. However seven out of 21 patients who did not reach a sustained suppression of viral load showed also an increase in T-cell subsets. The majority of patients recovered lymphoproliferative responses to mitogens, whereas only four subjects showed a functional response to Candida mannoprotein. No patients showed a response to HIV recombinant glycoprotein 160 or tetanus toxoid.

CONCLUSIONS

The immune recovery observed is slower and not complete in severely immunocompromised patients. Our data suggest that HAART may be continued also in the absence of a significant HIV RNA decrease if alternative drugs are not available.

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.

Invariant or Highly Conserved TCR α Are Expressed on Double-Negative (CD3+CD4−CD8−) and CD8+ T Cells

TCR α (TCRA) expression was examined in RNA samples from PBMC and isolated populations of CD4+, CD8+, and DN T cells from 15 healthy individuals. The expressed TCR repertoire was surveyed using spectratype analysis, a technique that displays the distribution of complementarity determining region 3 (CDR3) lengths for each TCRAV gene family. The results revealed the presence of unusual populations of double-negative (DN; CD4−CD8−CD3+) T cells that express invariant or conserved TCRAV4A, AV7, AV19, and AV24 chains. Each of the conserved TCRA families was over-represented in &gt;70% of the individuals studied, and all individuals expressed at least one of the over-represented TCRAV families. Over-represented conserved AV4A or AV7 sequences were also present in CD8+ T cells from most donors. The extent of TCRA sequence conservation is unparalleled. TCRAV4A, AV19, and AV24 sequences were invariant, although AV4A and AV19 transcripts contained N region additions. TCRAV24 transcripts derived from the direct juxtaposition of V and J gene segments. TCRAV7 sequences showed some diversity in two amino acids encoded at junctions of V and J gene segments. Although derivation of DN T cells with conserved TCRA chains is puzzling, the wide-spread expression of these unusual cells suggests an important function.

Induction of Phosphorylation and Intracellular Association of CC Chemokine Receptor 5 and Focal Adhesion Kinase in Primary Human CD4+ T Cells by Macrophage-Tropic HIV Envelope

Binding of HIV-1 envelope glycoproteins to the surface of a CD4+ cell transduces intracellular signals through the primary envelope receptor, CD4, and/or the envelope coreceptor, a seven-transmembrane chemokine receptor. Macrophage-tropic strains of HIV-1 preferentially use CCR5 as an entry coreceptor, whereas T cell-tropic strains use CXC chemokine receptor-4 for entry. Intracellular signals transduced by HIV-1 envelope may have immunopathogenic consequences, including anergy, syncytium formation, apoptosis, and inappropriate cell trafficking. We demonstrate here that a recombinant envelope protein derived from an M-tropic isolate of HIV-1 can transduce CD4-dependent as well as CCR5-dependent intracellular signals in primary human CD4+ T cells. Novel HIV-induced intracellular signals that were identified include tyrosine phosphorylation of focal adhesion kinase (FAK) and CCR5, which are involved in cell adhesion and chemotaxis, respectively. HIV envelope-induced cellular association of FAK and CCR5 was also demonstrated, suggesting that ligation of CD4 and CCR5 leads to the formation of an activation complex composed of FAK and CCR5. Activation of this signaling pathway by HIV-1 envelope may be an important pathogenic mechanism of dysregulated cellular activation and trafficking during HIV infection.

Increases in T cell telomere length in HIV infection after antiretroviral combination therapy for HIV-1 infection implicate distinct population dynamics in CD4+ and CD8+ T cells

Changes in mean telomeric terminal restriction fragment (TRF) length were examined as a marker for cellular replicative history in HIV-1-infected individuals after institution of anti-retroviral therapy (ART). Increases in mean T cell TRF lengths were observed in most patients following therapy; however, the contribution of individual T cell subsets was complex. An elongation of CD8+ T cell TRF was nearly uniformly observed while changes in mean TRF length in CD4+ T cells were heterogeneous as, despite potent suppression of viral replication, CD4 cell telomeres recovered in some patients, yet continued to decline in others. Increases in CD8 cell TRF correlated with decreased memory cells, suggesting a negative selection in the periphery for CD8 cells with extensive replicative history. In contrast, increases in CD4+ T cell TRF length correlated with increases in naive cell subsets, suggesting that the CD4+ T cell TRF increase may reflect a thymic contribution in some patients. These are the first increases in somatic cell telomere length in a population of cells observed in vivo, and the findings are compatible with therapy-induced reconstitution of the lymphoid compartment with cells having a more extensive replicative potential. These findings further distinguish lymphocytes from other somatic cell populations where only decreases in TRF over time have been noted. Thus, institution of ART in persons with moderately advanced HIV-1 disease reveals distinct population dynamics of CD4 and CD8 T cell subsets and also shows that the lymphocyte replicative history is dynamic.

Biased TCR Repertoire in HIV-1-Infected Patients Due to Clonal Expansion of HIV-1-Reverse Transcriptase-Specific CTL Clones

To study whether an expansion of HIV-1-specific CTL is contributing to the skewed TCR repertoire in HIV-1-infection, we characterized the TCR usage of CTL clones specific for a conserved epitope in HIV-1 reverse transcriptase (RT/476-484). CTL clones from three HIV-1-infected patients displayed highly similar TCR usage and used the identical Vβ6.1 and Vα2.5 gene segments. CTL clones from two patients showed a very high degree of similarity within the TCR complementarity-determining region-3 (CDR-3). In accordance with the similar molecular structure, all three CTL clones also exhibited a similar functional activity with regard to recognition of variant peptides and cytokine secretion pattern. In one subject clonal expansion of a single CTL specificity could be shown over a 10-mo period. TCR spectratyping of PBMC from two patients revealed a marked expansion of CDR-3 segments of a certain length within the Vβ6-family. Sequence analysis of these CDR-3 yielded sequences identical to the RT/476-484-specific CTL previously isolated from the same patients. This analysis demonstrates that clonal expansion of HIV-1-specific CTL is contributing to the skewed TCR repertoire in HIV-1-infected patients.

Population biology of HIV-1 infection: viral and CD4+ T cell demographics and dynamics in lymphatic tissues

Human immunodeficiency virus-1 (HIV-1) is usually transmitted through sexual contact and in the very early stages of infection establishes a persistent infection in lymphatic tissues (LT). Virus is produced and stored at this site in a dynamic process that slowly depletes the immune system of CD4+ T cells, setting the stage for AIDS. In this review, I describe the changes in viral and CD4+ T cell populations in LT over the course of infection and after treatment. I present recent evidence that productively infected CD4+ T cells play an important role in establishing persistent infection from the onset, and that the LT are the major reservoir where virus is produced and stored on follicular dendritic cells (FDCs). I discuss the methods used to define the size of viral and CD4+ T cell populations in LT and the nature of virus-host cell interactions in vivo. These experimental approaches have identified populations of latently and chronically infected cells in which virus can elude host defenses, perpetuate infection, and escape eradication by highly active antiretroviral treatment (HAART). I discuss the dramatic impact of HAART on suppressing virus production, reducing the pool of stored virus, and restoring CD4+ T cell populations. I discuss the contributions of thymopoiesis and other renewal mechanisms, lymphatic homeostasis and trafficking to these changes in CD4+ T cell populations in LT, and conclude with a model of immune depletion and repopulation based on the limited regenerative capacity of the adult and the uncompensated losses of productively infected cells that treatment stems. The prediction of this model is that immune regeneration will be slow, variable, and partial. It is nonetheless encouraging to know that even in late stages of infection, control of active replication of HIV-1 provides an opportunity for the immune system to recover from the injuries inflicted by infection.

T cell response in xenorecognition and xenografts: a review

Xenotransplantation has recently become a subject of interest for the transplantation community due to the current organ shortage, which could be partially or even totally solved by the development of this strategy. The humoral response, which arises as a result of species disparities, is the major obstacle to the success of xenotransplantation. However, if the use of different strategies such as plasmapheresis, immunoadsorption, the utilization of organs from transgenic pigs for complement regulatory molecules and new immunosuppressive drugs, may allow to overcome or reduce the early antibody mediated rejections (hyperacute or acute vascular rejection), delayed responses based on cellular activations will still occur. In this review, despite the fact that different cell populations have been shown to be implicated in these phenomena (NK, granulocytes, macrophages), we will focus on recent published information concerning T cell response only, in xenorecognition.

Early reduction of the over-expression of CD40L, OX40 and Fas on T cells in HIV-1 infection during triple anti-retroviral therapy: possible implications for lymphocyte traffic and functional recovery

Fas, CD40L and OX40 are members of the tumour necrosis factor (TNF) receptor superfamily with critical roles in T cell activation and death, B cell function, dendritic cell maturation and leucocyte traffic regulation. The aim of this study was to evaluate the effects of anti-retroviral therapy (HAART) on CD40L, OX40 and Fas expression on freshly isolated peripheral blood T cells by three-colour flow cytometry and compare them with lymphoproliferative responses, peripheral blood cell counts and viral load. Fourteen asymptomatic HIV-1+ patients treated with Lamivudine, Stavudine and Nelfinavir were prospectively investigated sequentially for 48 weeks. At baseline, patients exhibited significantly enhanced proportions and counts of CD40L+ and OX40+ cells within the CD4 subset which were corrected by weeks 8-16 of HAART. Interestingly, in the five patients showing viral load rebound during therapy in spite of increasing CD4 counts, the reduction of the levels of these costimulatory molecules was similarly maintained. Therapy induced a decrease in the over-expression of Fas, particularly in the CD4 subset where normal levels were reached at week 8. This reduction occurred in parallel with the major recovery of lymphoproliferative responses. Higher basal levels and lower reduction of Fas were associated with suboptimal suppression of viraemia. In conclusion, this previously undescribed increased expression of CD40L and OX40 may play a role in the HIV-associated pan-immune activation and represent a possible target for immunointervention, as suggested for several immunologically mediated diseases. Moreover, HAART induced an early correction of the over-expression of Fas, CD40L and OX40 in CD4 T cells which could be involved in the recovery of the cell traffic disturbances and in the T cell renewal capacity.

Type 1 CD4(+) T-cell help is required for induction of antipeptide multispecific cytotoxic T lymphocytes by a lipopeptidic vaccine in rhesus macaques

We have optimized the induction of antiviral cytotoxic T lymphocytes (CTL) in rhesus macaques by a lipopeptide vaccine containing seven peptides from simian immunodeficiency virus (SIV) Nef and Gag proteins and a strong T-helper peptide from tetanus toxoid (TT) that is promiscuous in humans (peptide TT 830-846). Two of the eight immunized macaques showed T-helper (Th) cell proliferation and a specific synthesis of gamma interferon in response to TT 830-846 peptide. They also showed multispecific cytotoxic activity against three to five of the immunizing SIV peptides. These results show the importance of a strong specific type 1 Th response for inducing a multispecific CTL response in vivo, which is essential for the development of an anti-human immunodeficiency virus vaccine.

HIV-1-specific CD4+ T cells are detectable in most individuals with active HIV-1 infection, but decline with prolonged viral suppression

The role of HIV-1-specific CD4+ T-cell responses in controlling HIV-1 infection remains unclear. Previous work has suggested that such cells are eliminated in the early stages of infection in most subjects, and thus cannot substantially contribute to host defense against HIV-1. Here, using flow cytometric detection of antigen-induced intracellular cytokines, we show that significant frequencies of gag specific, T-helper-1 CD4+ memory T cells are detectable in most subjects with active/progressive HIV-1 infection (median frequency, 0.12% of memory subset; range, 0-0.66%). Median frequencies of these cells were considerably higher in nonprogressive HIV-1 disease (0.40%), but there was substantial overlap between the two groups (range of nonprogressors, 0.10-1.7%). Continuous HIV-1 suppression with anti-retroviral therapy was associated with a time-dependent reduction in median frequencies of gag-specific CD4+ memory T cells: 0.08% in subjects treated for 4-24 weeks, and 0.03% in subjects treated for 47-112 weeks. Thus, functional HIV-1-specific CD4+ T cells are commonly available for support of anti-HIV-1 effector responses in active disease, but their decline with anti-retroviral therapy indicates that immunologic participation in long-term HIV-1 control will probably require effective vaccination strategies.

Discontinuation of primary prophylaxis against Pneumocystis carinii pneumonia in HIV-1-infected adults treated with combination antiretroviral therapy. Swiss HIV Cohort Study

BACKGROUND

It is unclear whether primary prophylaxis against Pneumocystis carinii pneumonia can be discontinued in patients infected with the human immunodeficiency virus (HIV) who are successfully treated with combination antiretroviral therapy. We prospectively studied the safety of stopping prophylaxis among patients in the Swiss HIV Cohort Study.

METHODS

Patients were eligible for our study if their CD4 counts had increased to at least 200 cells per cubic millimeter and 14 percent of total lymphocytes while they were receiving combination antiretroviral therapy, with these levels sustained for at least 12 weeks. Prophylaxis was stopped at study entry, and patients were examined every three months thereafter. The development of P. carinii pneumonia was the primary end point, and the development of toxoplasmic encephalitis the secondary end point.

RESULTS

Of the 262 patients included in our analysis, 121 (46.2 percent) were positive for IgG antibodies to Toxoplasma gondii at base line. The median CD4 count at study entry was 325 per cubic millimeter (range, 210 to 806); the median nadir CD4 count was 110 per cubic millimeter (range, 0 to 240). During a median follow-up of 11.3 months (range, 3.0 to 18.8), prophylaxis was resumed in nine patients, and two patients died. There were no cases of P. carinii pneumonia or toxoplasmic encephalitis. The one-sided upper 99 percent confidence limit for the incidence of P. carinii pneumonia was 1.9 cases per 100 patient-years (based on 238 patient-years of follow-up). The corresponding figure for toxoplasmic encephalitis was 4.2 per 100 patient-years (based on 110 patient-years of follow-up).

CONCLUSIONS

Stopping primary prophylaxis against P. carinii pneumonia appears to be safe in HIV-infected patients who are receiving combination antiretroviral treatment and who have had a sustained increase in their CD4 counts to at least 200 cells per cubic millimeter and to at least 14 percent of total lymphocytes.

HIV-1 rebound during interruption of highly active antiretroviral therapy has no deleterious effect on reinitiated treatment. Comet Study Group

BACKGROUND

Potent antiretroviral therapy (ART) with a protease inhibitor-based regimen is commonly used to treat HIV-1-infected patients. Transient treatment interruptions because of drug intolerance or other reasons are not uncommon. HIV-1 dynamics during therapy interruption and its consequences for the subsequent reinitiation of therapy have not been properly studied.

METHODS

Ten antiretroviral-naive, HIV-1-infected subjects (mean baseline CD4 cell count of 414 cells/mm3 and plasma viral load of 4.8 log10 copies/ml) were treated with the triple drug ART regimen indinavir/zidovudine/lamivudine for 28 days. Therapy was then interrupted for 28 days, after which the same ART regimen was re-started.

RESULTS

HIV-1 in plasma declined during the first 7 days of therapy with T1/2 of 1.5 days, and during days 7-28 with T1/2 of 8.9 days. Once therapy was interrupted, a delay of 4-7 days was observed in all subjects, preceding a rapid viral rebound with a mean doubling time of 1.6 days. Mean viral load after 28 days of interruption was 96% of baseline. Upon reinitiation of the same ART regimen, viral load declined at rates similar to those observed during the initial therapy (T1/2 of 1.6 and 8.0 days, respectively). No resistance-conferring mutations were observed in the HIV-1 reverse transcriptase (RT) and protease regions after the interruption of therapy. Plasma viral loads were maintained below 200 copies/ml in subjects continuing therapy for 4 (n = 9) to 12 (n = 5) months, with a mean CD4 cell count increase of 145 cells/mm3.

CONCLUSIONS

The reintroduction of efficient ART therapy after a 1 month interruption shows viral kinetics similar to that of naive patients, and is not associated with the development of resistance. No deleterious effect on the reinitiated therapy was observed in patients who temporarily discontinued ART therapy. Nevertheless, because viral load rebounds back to baseline during treatment interruption, viral suppression is in effect put off by that period of time.

The in vivo effects of combination antiretroviral drug therapy on peripheral blood CD34+ cell colony-forming units from HIV type 1-infected patients

This study investigated the effects of a combination antiretroviral drug regimen (indinavir and two nucleoside analogs or ritonavir and saquinavir) on the levels of CD34+ colony-forming units (CFU-Cs) in the peripheral blood of HIV-1+ patients. Ten patients who were receiving combination antiretroviral drug therapy were studied and their peripheral blood CD34+ CFU-Cs were measured prior to, 1 month after, and 4 to 6 months after the commencement of therapy. The levels of CD4+ T cells increased significantly in these patients (paired t test, p = 0.0027) and plasma viral load became undetectable in all but one patient studied. Measurements of the CFU-Cs showed that their levels tended to increase on the commencement of therapy, and these levels became significantly higher than baseline by 4-6 months (paired t test, p = 0.0293). Analysis of the different colony phenotype demonstrated that the main contributor to this increase consisted of burst-forming unit erythroid (BFU-E) cells. These data also demonstrated that there was an inverse correlation between the rise in CFU-Cs at 4-6 months compared with CD4+ cell, CD8+ cell, and neutrophil counts, and hemoglobin concentration, at baseline. The demonstrated increase in the levels of CD34+ CFU-Cs suggests that HIV-1 may have an inhibitory effect on these cells in vivo, and that this inhibition may be abrogated by suppression of viral replication.

Immune Reconstitution and the Consequences for Opportunistic Infection Treatment and Prevention

Effective antiretroviral therapy that suppresses HIV replication is associated with dramatic increases in CD4 counts. Recent evidence suggests that this CD4 cell increase is biphasic in nature, with an initial phase (in the first 2 to 3 months) that represents redistribution of lymphocytes into the periphery and a second phase that is associated with true immunologic recovery and reconstitution. Immunologically there is evidence of increase in naive T cells, recovery of in vitro responses to microbial antigens, and repair of the damaged diversity of T cells. Clinically, this immune recovery has been characterized by decreasing morbidity and mortality from opportunistic infections, an ability to treat previously intractable infections, immune-mediated syndromes, and increasing reports of the ability to discontinue primary and secondary prophylaxis. Although there are still unresolved questions about the completeness of the immune recovery, most available evidence suggests in most patients the degree of immune reconstitution with effective antiretroviral therapy is sufficient to be protective against most opportunistic infections, and ultimately additional antimicrobial prophylaxis will be unnecessary.

T Cell Repertoire Alterations of Vascularized Xenografts

The role of T cells in the rejection of vascularized xenografts has been little explored. Because of the high potential diversity of xenoantigens, it has been suggested that xenotransplantation could induce a strong cellular response that could contribute to delayed rejection. Alternatively, alterations in molecular interactions could impair the T cell response. Because the analysis of TCR repertoire in vivo indirectly reflects the nature and the magnitude of T cell xenorecognition, we took advantage of the possibility of obtaining long term survival of hamster heart xenografts in rat recipients treated with a combination of cobra venom factor and cyclosporin A (CsA), to analyze T cell infiltration and, for the first time, Vβ TCR usage, at the complementarity-determining region 3 level, in accommodated and rejected xenografts, compared with allografts. After withdrawal of CsA (on day 40), the analysis of Vβ family expression and corresponding complementarity-determining region 3 lengths in rejected xenografts revealed a Gaussian pattern, in contrast to a much more restricted pattern in rejected allografts (p = 0.002), suggesting that, after withdrawal of CsA, all the underrepresented T cell clones are rapidly expanded in xenografts. These results correlate with the rapid kinetics of rejection (4 ± 1 days), the high number of T cells, the rapid expression of markers of activation (IL-2 receptor α-chain and class II receptor), and the strong deposit of IgG Abs in rejected xenografts. Taken together, these results suggest that the intensity and diversity of the T cell response to xenografts could be stronger than the response to allografts in vivo.

Clonal Dominance Patterns of CD8 T Cells in Relation to Disease Progression in HIV-Infected Children

CD8 T cells are important mediators of cellular immune responses as evidenced by clonal expansions in the CD8 TCR Vβ repertoire during primary HIV infection in adults. This study investigated the CD8 TCR Vβ repertoire by complementarity-determining region 3 length analysis using multiplex PCR in purified peripheral blood CD8 T cells of 22 HIV-infected children (age range was 0.75–15 yr, mean was 8.2 ± 4.1 yr). Evidence of clonal dominance in one or more Vβ families was obtained in 15 of 22 children. The patterns of clonal dominance were designated as major, minor, single, and none to indicate the involvement of three or more, two, one, or no Vβ families, respectively. A pattern of major or minor clonal dominance was observed in 12 children (group 1), whereas 10 children had single or no clonal dominance (group 2). In comparison with group 2, the children in group 1 had a higher percentage of CD4 cells (28.3 ± 11.6 vs 8.6 ± 4.8, p &lt; 0.001); a higher stimulation index in lymphoproliferative responses to Candida (92.0 ± 59.5 vs 12.3 ± 14.4, p = 0.002), tetanus (76.3 ± 51.2 vs 11.2 ± 12.7, p = 0.002), and alloantigens (178.3 ± 298.9 vs 32.9 ± 35.2, p &lt; 0.001); and a lower percentage of CD8+HLA-DR+CD38+ cells (37.4 ± 13.1 vs 54.6 ± 14.2, p &lt; 0.01). The number of dominant CD8 T cell clones was significantly correlated with the percentage of CD4 T cells (r = 0.669, p &lt; 0.001) but not with plasma HIV RNA. Compared with group 1, patients in group 2 had a 4.8 times greater probability of having &lt;15% CD4 cells. These findings indicate that CD8 clonal dominance in HIV-infected children reflects robustness of immune responses, regardless of time since infection and virus load.