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

Interleukin-15 production by monocyte-derived dendritic cells and T cell proliferation in HIV-infected patients with discordant response to highly active antiretroviral therapy

A discordant response to highly active antiretroviral therapy (HAART) occurs when CD4 T cell counts are stable or increased over time despite persistently detectable HIV-RNA levels. In order to identify immunological factors affecting discordant treatment responses, a total of 27 HIV-infected patients were studied: (a) 10 naive patients (mean CD4+ = 101.5 cells/microl; mean HIV-RNA = 4.8 log10 copies/ml); (b) seven responder patients (mean CD4+ = 908.9 cells/microl); and (c) 10 discordant patients (mean CD4+ = 396.1 cells/microl; mean HIV-RNA = 5.4 log10 copies/ml). Five healthy blood donors were included as HIV-seronegative controls. The following parameters were evaluated: interleukin (IL)-15 production by monocyte-derived dendritic cells (MDDC) after stimulation with lypopolysaccaride (LPS) and Candida albicans; recall and HIV-1-specific antigen lymphocyte proliferation (LP). Increased levels of IL-15 production by MDDC after stimulation with LPS and C. albicans were found both in discordant patients and responder patients. Conversely, a strong reduction of IL-15 levels was observed in naive patients. Discordant patients developed positive LP responses to C. albicans and HIV-1 p24. LP in response to C. albicans and HIV-1 p24 was also positive in responder patients. Decreased LP response was found in naive patients. In conclusion, HIV-infected patients with discordant viro-immunological responses to HAART present increased levels of IL-15 production by MDDC and enhanced recall and HIV-1-specific antigen LP responses, suggesting an improvement in indices of immune function.

Clinical Management of Tuberculosis in the Context of HIV Infection

Globally, the HIV and tuberculosis epidemics are stoking each other, creating a public health crisis of enormous proportions. At the level of individuals, contemporaneous infection with M. tuberculosis and HIV poses great challenges to clinical management. This chapter provides an overview of active and latent tuberculosis treatment in HIV-infected and -uninfected individuals. The discussion focuses on medication issues, including interactions between antitubercular drugs, antiretroviral drugs, and medicines used for opportunistic infections and treatment in the face of comorbidities. Clinical questions specific to coinfection are discussed, including duration and timing initiation of therapy and immune reconstitution. Most of the data presented were generated in industrialized settings and are presented to assist patient management in such settings. However, given the disproportionate amount of TB/HIV in less-developed nations and the increasing availability of antiretroviral therapy in resource-limited settings, the issues presented will become increasingly relevant globally.

Tuberculosis

Among communicable diseases, tuberculosis is the second leading cause of death worldwide, killing nearly 2 million people each year. Most cases are in less-developed countries; over the past decade, tuberculosis incidence has increased in Africa, mainly as a result of the burden of HIV infection, and in the former Soviet Union, owing to socioeconomic change and decline of the health-care system. Definitive diagnosis of tuberculosis remains based on culture for Mycobacterium tuberculosis, but rapid diagnosis of infectious tuberculosis by simple sputum smear for acid-fast bacilli remains an important tool, and more rapid molecular techniques hold promise. Treatment with several drugs for 6 months or more can cure more than 95% of patients; direct observation of treatment, a component of the recommended five-element DOTS strategy, is judged to be the standard of care by most authorities, but currently only a third of cases worldwide are treated under this approach. Systematic monitoring of case detection and treatment outcomes is essential to effective service delivery. The proportion of patients diagnosed and treated effectively has increased greatly over the past decade but is still far short of global targets. Efforts to develop more effective tuberculosis vaccines are under way, but even if one is identified, more effective treatment systems are likely to be required for decades. Other modes of tuberculosis control, such as treatment of latent infection, have a potentially important role in some contexts. Until tuberculosis is controlled worldwide, it will continue to be a major killer in less-developed countries and a constant threat in most of the more-developed countries.

Detection of latent tuberculosis among HIV-infected patients after initiation of highly active antiretroviral therapy

This cross-sectional study of 110 individuals examined skin testing for latent tuberculosis infection (LTBI) after the initiation of highly active antiretroviral therapy. Skin test reactivity to one or more of four antigens was found in 98 out of 110 subjects (89%), and was maximal in those whose CD4 cell counts recovered to >= 100 cells/mm3. Skin testing is reliable for the identification or exclusion of LTBI once the CD4 cell count recovers to >= 100 cells/mm3.

The potential for CD4 cell increases in HIV-positive individuals who control viraemia with highly active antiretroviral therapy

OBJECTIVES

To study the long-term CD4 cell responses to highly active antiretroviral therapy (HAART) in treatment-naive patients whose viral loads remained below 500 copies/ml for prolonged periods.

DESIGN

A total of 237 patients whose viral loads remained below 500 copies/ml for one year or more. Median follow-up was 1.9 years.

METHODS

CD4 cell counts were analysed to investigate long-term immunological response using mixed-effects models with the slope allowed to change after 1, 12 and 24 months of HAART.

RESULTS

The median baseline CD4 cell count was 175 cells/mm3. After an initial rapid increase in the first month after HAART (97.2 cells/mm3 a month), increases in CD4 cell counts continued less rapidly (11.6 cells/mm3 a month). This increase slowed by 2.4 cells/mm3 a month after one year. CD4 cell counts continued increasing after 2 years, but the rate of increase again slowed (estimated slope at 2 years 5.4 cells/mm3 a month; decrease in slope from year 2 compared with years 1-2 3.7 cell/mm3 a month). A total of 198 out of 211 patients (94%) with measurements at baseline and one year experienced an increase in CD4 cell counts in this interval; 81 and 67% had an increasing slope between 1 and 2 and 2 and 3 years, respectively. By the end of follow-up, CD4 cell counts had increased by 319 cells/mm3, and were more than 500 cells/mm3 in 40% of patients.

CONCLUSION

Although the rate of immune recovery slowed after 2 years, CD4 cell counts rose in most and began to return to levels seen in HIV-negative individuals.

Fatal immune restoration disease in human immunodeficiency virus type 1-infected patients with progressive multifocal leukoencephalopathy: impact of antiretroviral therapy-associated immune reconstitution

Immune reconstitution resulting from use of highly active antiretroviral therapy in patients infected with human immunodeficiency virus type 1 (HIV-1) has been associated with a significant decrease in infectious morbidity and with improved survival. Occasionally, patients with quiescent disease due to human cytomegalovirus or nontuberculous mycobacteria may experience paradoxical worsening due to "dysregulated" restitution of the immune system (that is, immune restoration disease [IRD]). Acquired immunodeficiency syndrome-related progressive multifocal leukoencephalopathy (PML) is uncommon and often improves with immune recovery. We describe 2 HIV-1-infected patients with PML that presented with paradoxical worsening after the patients had commenced active antiretroviral therapy. After they had a transient response to high-dose corticosteroid therapy, both patients died of progressive neurological deterioration. IRD in these patients with PML was unexpected and occurred soon after they had started receiving active antiretroviral therapy, during the period of improved antigen-specific T-helper cell function. Predictors of patients' proclivity for these adverse events are uncertain. Evaluation of targeted immunomodulatory therapy directed towards disease-specific IRD is critical and may play an important role in improved survival for patients who are at risk.

Discordant response to antiretroviral therapy: HIV isolation, genotypic mutations, T-cell proliferation and cytokine production

OBJECTIVE

To study virologic and immunologic factors associated with discordant treatment response in HIV-infected patients receiving highly active antiretroviral therapy (HAART).

DESIGN

Study participants included a total of 27 patients: (a) 10 discordant patients (mean CD4+ cell count, 396.1 x 10 cells/l; mean HIV-RNA, 5.4 log copies/ml); (b) seven responder patients (mean CD4+ cell count, 997.5 x 10 cells/l); and (c) 10 failing patients (mean CD4+ cell count 66.5 x 10 cells/l; mean HIV-RNA, 5.4 log copies/ml).(10) (10)

METHODS

The HIV-1 isolation rate and biological phenotype, drug resistance genotypic mutations of HIV-1 strains, recall and HIV-1-specific antigen lymphocyte proliferation (LP), and interleukin (IL)-15 production were studied.

RESULTS

Virus isolation was obtained in 30% of discordant patients, and in 100% of failing patients. A higher replication constant was reported in discordant patients. No difference in the number of drug resistance mutations and biological phenotypes of HIV-1 was found in discordant patients with respect to failing patients. Discordant patients developed positive LP responses to and HIV-1 p24. LP in response to, HIV-1 p24 and gp160 was positive in responder patients. No significant LP was found in failing patients. Increased levels of IL-15 after stimulation with lipopolysaccaride (LPS) and were found in both discordant patients and responder patients. Conversely, a strong reduction of IL-15 levels was observed in failing patients.

CONCLUSION

The present results suggest that decreased virus isolation rate, restoration of both lymphocyte proliferation and IL-15 production are factors involved in the discordant antiretroviral therapy response of HIV-infected patients.

Cytotoxic HIV-1 p55gag-specific CD4+ T cells produce HIV-inhibitory cytokines and chemokines

CD4+ T-helper cells appear to be essential in sustaining immune responses in chronic viral infections, as the maintenance of CD8+ cytotoxic T-lymphocyte responses and the control of viremia were demonstrated to depend on CD4+ T cell help. In order to investigate the function of HIV-specific CD4+ T cells in chronic HIV-1-infection, 49 chronically HIV-infected patients were analyzed before and 3 and 6 months after initiation of antiviral treatment. Ten patients showed a substantial, although weak, proliferative response to HIV-1-p55gag protein for which no improvement was observed upon initiation of HAART. From one individual, HIV-1-p55gag-specific CD4-positive T-cell clones were generated that were heterogeneous in their TCR Vbeta gene usage and HLA-DRB1*13 and DRB1*03 restricted, respectively. In addition, some CD4+ TCC produced substantial amounts of IFN-gamma and MIP-1alpha/beta were perforin-positive, and showed cytotoxic activity. These diverse functional features of HIV-specific CD4+ T cells suggest that they may exert direct antiviral activity.

Temporary restoration of immune response against Toxoplasma gondii in HIV-infected individuals after HAART, as studied in the hu-PBMC-SCID mouse model

We studied immune reconstitution against the parasite T. gondii in HIV-infected patients treated for 1 years with highly active antiretroviral therapy (HAART). We used SCID mice, humanized with peripheral blood mononuclear cells (PBMC) from patients, which were then infected with T. gondii cysts. Mice humanized with PBMC from patients before the start of HAART were highly susceptible to infection. In contrast, mice humanized with PBMC from patients who had received HAART for 6 months displayed higher survival rates, correlating with lower intracerebral parasite loads. However, this resistance was lost during follow up because mice humanized with PBMC from patients treated with HAART for 12 months survived for no longer than mice that had not been humanized. Specific lymphocyte proliferation assays showed that the increase in proliferative response depended on treatment duration and that HAART induced changes in IFN-gamma secretion in the presence of Toxoplasma antigens. Thus, our results indicate partial immune reconstitution against T. gondii in HIV-infected patients following HAART, possibly due to changes in the patterns of specific IFN-gamma production and redistribution of functional memory CD4+ cells.

Tuberculosis unleashed: the impact of human immunodeficiency virus infection on the host granulomatous response to Mycobacterium tuberculosis

The granuloma plays a critical role in the host immune response to Mycobacterium tuberculosis, containing the organism and confining it in a latent state in most infected individuals. Indeed, approximately one-third of the world's population has latent M. tuberculosis infection. However, over the past decade, the human immunodeficiency virus type 1 (HIV-1) pandemic has profoundly affected the incidence and clinicopathological features of tuberculosis. This review examines the immunological mechanisms whereby HIV-1 impairs the establishment, maintenance and function of the tuberculous granuloma.

Highly active antiretroviral therapy restores in vitro mitogen and antigen-specific T-lymphocyte responses in HIV-1 perinatally infected children despite virological failure

To analyse the effect of highly active antiretroviral therapy (HAART) on T-lymphocyte functions we selected seven HIV-1 perinatally infected children (CDC immunological category 1 or 2) who had neither a fall in their plasma HIV-1 RNA levels nor a significant rise in CD4+ lymphocyte counts while receiving HAART. Clinical signs and symptoms were monitored monthly. Plasma viral load, CD4+, CD8+, CD19+ lymphocyte counts and in vitro T-lymphocyte proliferative responses to mitogens (anti-CD3, phytohaemoagglutinin, concanavalin A and pokeweed mitogen) and recall antigens (Candida albicans and tetanus toxoid) were tested at baseline and after 1, 3, 6 and 12 months of HAART. Twenty-two healthy age-matched children were studied as controls. A gain in body weight, no worsening of the disease and no recurrence of opportunistic infections were observed. At baseline, the majority of the children had low responses to mitogens, and all of them had a defective in vitro antigen-specific T-lymphocyte response (<2 standard deviations below the mean result for controls). During HAART, a significant increase in the response to mitogens and antigens was observed in all the patients. The T-lymphocyte response was restored more consistently against antigens to which the immune system is constantly exposed (Candida albicans, baseline versus 12 months: P < 0.001) compared with a low-exposure antigen (tetanus toxoid, baseline versus 12 months: P < 0.01). HAART restores in vitro T-lymphocyte responses even in the absence of a significant viral load decrease and despite any significant increase in CD4+ lymphocyte counts. It implies that a direct mechanism might be involved in the overall immune recovery under HAART.

Plasticity of lymphoid compartments during HIV infection and treatments: hopes and limits

Immune reconstitution during antiretroviral therapy has recently been shown to depend upon multiple factors at work in T-cell homeostasis, amongst which the reduction of thymus dysfunction and of immune hyperactivation is instrumental. The restoration of host defenses against opportunistic pathogens is, however, balanced by the poor immunity restored against HIV thus giving a satisfying link between antigen stimulation and the reconstitution of immune responses to pathogens.

Human immunodeficiency virus type 1-hepatitis C virus coinfection: intraindividual comparison of cellular immune responses against two persistent viruses

Both human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) lead to chronic infection in a high percentage of persons, and an expanding epidemic of HIV-1-HCV coinfection has recently been identified. These individuals provide an opportunity for simultaneous assessment of immune responses to two viral infections associated with chronic plasma viremia. In this study we analyzed the breadth and magnitude of the CD8(+)- and CD4(+)-T-lymphocyte responses in 22 individuals infected with both HIV-1 and HCV. A CD8(+)-T-lymphocyte response against HIV-1 was readily detected in all subjects over a broad range of viral loads. In marked contrast, HCV-specific CD8(+)-T-lymphocyte responses were rarely detected, despite viral loads in plasma that were on average 1,000-fold higher. The few HCV-specific responses that were observed were relatively weak and limited in breadth. CD4-proliferative responses against HIV-1 were detected in about half of the coinfected subjects tested, but no proliferative response against any HCV protein was found in these coinfected persons. These data demonstrate a major discordance in immune responses to two persistent RNA viruses. In addition, they show a consistent and profound impairment in cellular immune responses to HCV compared to HIV-1 in HIV-1-HCV-coinfected persons.

CD4+ T-lymphocyte nadir and the effect of highly active antiretroviral therapy on phenotypic and functional immune restoration in HIV-1 infection

To evaluate the effects of the timing of highly active antiretroviral therapy (HAART) on immune reconstitution, we compared lymphocyte subpopulations and lymphocyte proliferation (LP) in response to Candida albicans, cytomegalovirus, HIV p24, Mycobacterium avium complex, pokeweed mitogen, streptokinase, and tetanus toxoid in 43 patients with pretherapy advanced, moderately advanced, and early chronic HIV-1 infection. All patients had recent CD4+ T-cell counts >450/microl and HIV RNA <400 copies/ml for >12 months. CD4+ nadirs were positively correlated with recent numbers of CD4+ T-cells (P < 0.001), memory cells (P < 0.001), and naïve CD4+ T-cells (P < 0.05) and CD4+ CD28+ T-lymphocytes (P < 0.05) and were negatively correlated with recent CD8+ T-lymphocyte counts (P < 0.05). Only CD4+ naïve T-cells normalized when HAART was initiated at lower CD4+ T-cell levels. Fifty-three percent of patients had LP responses to HIV p24 antigen. While LP responses to prevalent antigens were usually present, responses to tetanus toxoid were more common with higher CD4+ T-lymphocyte nadirs (P < 0.05). Delaying HAART may limit phenotypic and functional immune restoration in HIV-1 infection.

Immunological and virological features of HIV-infected patients with increasing CD4 cell numbers despite virological failure during protease inhibitor-based therapy

OBJECTIVES

To investigate the extent of functional T cell recovery and to characterize plasma virus and virus producing cells in patients with increasing CD4 cell counts despite virological failure during protease inhibitor (PI) based therapy.

METHODS

The study group included 13 patients who were treated for at least 12 months with a PI based regimen and were selected on the basis of a sustained immunological response (increase of > 70 CD4 cells/microL) despite virological failure (< 1 log10 copies/mL decrease in HIV-1 RNA plasma levels).

RESULTS

Compared to a historical series of 11 complete responders with less advanced disease, the proportion of memory CD4 T cells was significantly higher (67.8+/-17.8 vs. 52.8+/-11.0; P=0.045) and the proportion of naive CD4 T cells significantly lower (30.5+/-14.8 vs. 45.0+/-10.4, P=0.021) in patients who were immunological responders/virological nonresponders. In those patients, ongoing viral replication was associated with a strong activation of circulating CD8 T lymphocytes; interleukin-2 production remained decreased. CD4 T cell reactivity to cytomegalovirus proteins was observed in nine of 11 patients tested. In the study group, the proportion of infectious virus present in plasma as well as the levels of intracellular viral replication were similar to those measured in untreated patients. Virological failure in this group of patients probably resulted from pre-existing mutations in the reverse transcriptase gene.

CONCLUSIONS

This study of patients with increasing CD4 cell numbers despite virological failure shows the persistence of immune activation and partial immune restoration with no evidence of specific viral dynamics in vivo.

Immune reconstitution in HIV-1-infected individuals treated with potent antiretroviral therapy

Potent combination antiretroviral therapy that was introduced in the mid-1990s for treatment of HIV-1 infection has resulted in unprecedented decreases in HIV-1 replication and increases in CD4+ T cell counts in many individuals. Coincident with the introduction of potent combination antiretroviral therapy, substantial declines in AIDS-related morbidity and mortality have been observed. Although these declines strongly suggest that significant immune reconstitution is occurring, increasing evidence suggests that immune reconstitution is neither uniform nor complete in all treated individuals. Clinical data suggest that some HIV-1-associated malignancies have not declined despite the new therapies, and that not all treated individuals reconstitute CD4+ T cell numbers to normal values. Laboratory studies reveal that immune responses to ubiquitous antigens are reconstituted, but that responses to rarely encountered antigens, such as tetanus, are not reconstituted without repeat vaccination. Many questions remain concerning the extent and clinical significance of the immune reconstitution that occurs in the setting of antiretroviral drug therapy. A better understanding of the nature of the immune reconstitution that results from potent antiretroviral therapy is critical to the optimal clinical management of HIV-1-infected individuals, and may provide important insights into the immunopathogenesis of HIV-1 infection as well.

Highly active antiretroviral therapy in human immunodeficiency virus type 1-infected children: analysis of cellular immune responses

The present study analyzes the effect of highly active antiretroviral therapy (HAART) on restoration of cellular immunity in human immunodeficiency virus (HIV)-infected children over a 24-week period following initiation of HAART with ritonavir, nevirapine, and stavudine. The immunological parameters evaluated at four time points (at enrollment and at 4, 12, and 24 weeks of therapy) included cytokine production by monocytes as well as T-cell proliferation in response to mitogen, alloantigen, and recall antigens including HIV type 1 envelope peptides. Circulating levels of interleukin-16 (IL-16) were measured, in addition to CD4+ T-cell counts, plasma HIV RNA levels, and the delayed-type hypersensitivity (DTH) response. At enrollment the children exhibited defects in several immune parameters measured. Therapy increased CD4+ T-cell counts and decreased viral loads significantly. By contrast, the only immunological parameter that was significantly increased was IL-12 p70 production by monocytes; the DTH response to Candida albicans also showed a strong increase in patients becoming positive. In conclusion, these results demonstrate that HAART in HIV-infected children affects the dynamics of HIV replication and the CD4+ T-cell count over 24 weeks, similar to the pattern seen in HIV-infected adults. Furthermore, these data indicate improvement in antigen-presenting cell immunological function in HIV-infected children induced by HAART.

Reconstitution of CD4+ T lymphocytes in HIV-infected individuals following antiretroviral therapy

Immune reconstitution during antiretroviral therapy has recently been shown to depend upon multiple factors at work in T cell homeostasis, amongst which the reduction of thymus dysfunction and of immune hyperactivation are instrumental. The optimism that has been raised by the restoration of hosts' defenses against opportunistic pathogens is, however, balanced by the poor immunity restored against HIV; thus, innovative immune interventions are required.

Paradoxical worsening of tuberculosis in HIV-infected persons

OBJECTIVE

To determine the incidence of paradoxical worsening of tuberculosis (TB) in HIV-infected persons.

DESIGN

Observational cohort study.

SETTING

Public, urban TB clinic.

PATIENTS

HIV-infected persons treated for TB between January 1, 1996, and December 31, 1999, and followed through June 30, 2000.

INTERVENTION

Patients received standard anti-TB therapy. Antiretroviral therapy was provided by primary medical providers. Patients receiving antiretroviral therapy were given nucleoside reverse transcriptase inhibitors alone or highly active antiretroviral therapy (HAART; nucleoside reverse transcriptase inhibitors in combination with a protease inhibitor or a nonnucleoside reverse transcriptase inhibitor).

MAIN OUTCOME MEASURE

Paradoxical worsening of TB.

RESULTS

There were 82 TB cases in 76 patients. Paradoxical worsening was identified in 6 of 82 cases (7%; 95% confidence interval, 3 to 15%). Paradoxical worsening occurred in 3 of 28 cases (11%) in patients receiving HAART and in 3 of 44 cases (7%) in patients not receiving antiretroviral therapy (p = 0.67). Cases complicated by paradoxical worsening were more likely to have both pulmonary and extrapulmonary disease at initial diagnosis than cases without paradoxical worsening (83% vs 24%; p = 0.006). TB relapse occurred in 2 of 6 cases (33%) in patients with paradoxical worsening and in 4 of 76 cases (5%) in patients without paradoxical worsening (p = 0.06).

CONCLUSIONS

Paradoxical worsening of TB occurred less frequently than in previous reports and was not associated with HAART. Paradoxical worsening also appeared to be associated with an increased risk of TB relapse. Further studies are warranted to better characterize the risk factors for paradoxical worsening and the appropriate duration of anti-TB therapy in patients in whom it occurs.

Improvement of HIV-specific immunity in HIV-infected twins treated with highly active antiretroviral therapy, interleukin 2, and syngeneic adoptively transferred cells

Five HIV-seropositive twins were treated with HAART and given cycles of treatment consisting of adoptive cellular therapy from their HIV-seronegative identical twins followed by a 5-day course of intravenous IL-2. Changes in absolute and percent CD4(+) and CD8(+) cell count were monitored and compared with changes in these parameters occurring in seven age-, sex-, and disease stage-matched HIV-infected patients treated with HAART alone. Increase in the magnitude and breadth of HIV-specific immune responses was monitored in three twin subjects who received multiple treatment cycles. Absolute and percent CD4(+) cell counts rose dramatically and to significantly higher levels in the recipient twins than in control subjects treated with HAART only. The subjects who received multiple cycles of treatment developed new and increased levels of HIV-specific activated and memory cytotoxic T lymphocyte responses, and interferon gamma-secreting effector cells. Treatment consisting of HAART, adoptive cellular therapy, and IL-2 was superior to treatment with HAART alone for improving absolute and percent CD4(+) cell counts and inducing new, or increasing the magnitude of, HIV-specific immune responses in HIV infected patients.

Discontinuation of primary prophylaxis in HIV-infected patients at high risk of Pneumocystis carinii pneumonia: prospective multicentre study

OBJECTIVES

To assess the safety of discontinuation of primary prophylaxis in HIV-infected patients on antiretroviral combination therapy at high risk of developing Pneumocystis carinii pneumonia.

DESIGN

Prospective multicentre study.

PATIENTS AND METHODS

The incidence of P. carinii pneumonia after discontinuation of primary prophylaxis was studied in 396 HIV-infected patients on antiretroviral combination therapy who experienced an increase in their CD4 cell count to at least 200 x 10(6)/l and 14% of total lymphocytes; the study population included 191 patients with a history of CD4 cell counts below 100 x 10(6)/l (245 person-years) and 144 patients with plasma HIV RNA above 200 copies/ml (215 person-years).

RESULTS

There was one case of Pneumocystis pneumonia, an incidence of 0.18 per 100 person-years [95% confidence interval (CI), 0.005--1.0 per 100 person-years]. No case was diagnosed in groups with low nadir CD4 cell counts (95% CI, 0--1.2 per 100 person-years) or detectable plasma HIV RNA (95% CI, 0--1.4 per 100 person-years).

CONCLUSIONS

Discontinuation of primary prophylaxis against Pneumocystis pneumonia is safe in patients who have responded with a sustained increase in their CD4 cell count to antiretroviral combination therapy, irrespective of the CD4 cell count nadir and the viral load at the time of stopping prophylaxis.

Two long terminal repeat circles and persistent HIV-1 replication

Building on the success of combination antiretroviral drug therapy will require a better understanding of the underlying basis for viral persistence. Characterization of the therapeutic, viral, and immunological factors that influence the size and stability of viral reservoirs will foster the development of strategies to control or eliminate HIV-1 from infected individuals. Here we review recent work aimed at delineating the complex interplay between viral replication, the immune system, and viral reservoirs. Finally, we address the implications and clinical significance of the residual replication that persists in infected individuals on potent antiretroviral therapy to evaluate both the possible risks and benefits of ongoing HIV-1 replication.

Identification of novel HLA-A2-restricted human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte epitopes predicted by the HLA-A2 supertype peptide-binding motif

Virus-specific cytotoxic T-lymphocyte (CTL) responses are critical in the control of human immunodeficiency virus type 1 (HIV-1) infection and will play an important part in therapeutic and prophylactic HIV-1 vaccines. The identification of virus-specific epitopes that are efficiently recognized by CTL is the first step in the development of future vaccines. Here we describe the immunological characterization of a number of novel HIV-1-specific, HLA-A2-restricted CTL epitopes that share a high degree of conservation within HIV-1 and a strong binding to different alleles of the HLA-A2 superfamily. These novel epitopes include the first reported CTL epitope in the Vpr protein. Two of the novel epitopes were immunodominant among the HLA-A2-restricted CTL responses of individuals with acute and chronic HIV-1 infection. The novel CTL epitopes identified here should be included in future vaccines designed to induce HIV-1-specific CTL responses restricted by the HLA-A2 superfamily and will be important to assess in immunogenicity studies in infected persons and in uninfected recipients of candidate HIV-1 vaccines.

Immune restoration and CD4+ T-cell function with antiretroviral therapies

OBJECTIVES

To review the current understanding of the details and mechanisms of immune restoration that follows administration of suppressive antiretroviral therapies to persons with chronic HIV-1 infection.

SUMMARY

A first-phase cellular increase often includes increases in multiple circulating lymphocyte populations and is largely attributable to rapid redistribution of cells from lymphoid tissue. A second slower phase is largely comprised of naïve cell increases that may reflect cells newly produced in the thymus. Improvement in CD4+ cell function is demonstrable but functional restoration is incomplete. Immunization can enhance the restoration of CD4+ cell-dependent responses, and the magnitude of restoration is related in part to the degree to which HIV-1 replication and immune activation are controlled. Despite the incomplete nature of immune restoration seen after suppression of HIV-1 replication in chronic infection, clinical benefits of these responses are reflected in decreased HIV-1-related opportunistic infections and mortality. The effects of these therapies on the occurrence of non-Hodgkins lymphoma are less apparent.

CONCLUSIONS

Suppression of HIV-1 replication results in both laboratory and clinical evidence of immune restoration. Although incomplete, this immune restoration provides 'breathing room' to develop better-tolerated antiviral therapies and therapies designed to enhance immune function.

Relative resistance in the development of T cell anergy in CD4+ T cells from simian immunodeficiency virus disease-resistant sooty mangabeys

Despite high viral loads, T cells from sooty mangabey (SM) monkeys that are naturally infected with SIV but remain clinically asymptomatic, proliferate and demonstrate normal Ag-specific memory recall CD4(+) T cell responses. In contrast, CD4(+) T cells from rhesus macaques (RM) experimentally infected with SIV lose Ag-specific memory recall responses and develop immunological anergy. To elucidate the mechanisms for these distinct outcomes of lentiviral infection, highly enriched alloreactive CD4(+) T cells from humans, RM, and SM were anergized by TCR-only stimulation (signal 1 alone) and subsequently challenged with anti-CD3/anti-CD28 Abs (signals 1 + 2). Whereas alloreactive CD4(+)T cells from humans and RM became anergized, surprisingly, CD4(+) T cells from SM showed marked proliferation and IL-2 synthesis after restimulation. This resistance to undergo anergy was not secondary to a global deficiency in anergy induction of CD4(+) T cells from SM since incubation of CD4(+) T cells with anti-CD3 alone in the presence of rapamycin readily induced anergy in these cells. The resistance to undergo anergy was reasoned to be due to the ability of CD4(+) T cells from SM to synthesize IL-2 when incubated with anti-CD3 alone. Analysis of phosphorylated kinases involved in T cell activation showed that the activation of CD4(+) T cells by signal 1 in SM elicited a pattern of response that required both signals 1 + 2 in humans and RM. This function of CD4(+) T cells from SM may contribute to the resistance of this species to SIV-induced disease.

Virological and immunological characteristics of HIV treatment failure

BACKGROUND

Resistance to antiretroviral treatment is prevalent. There is limited knowledge of the determinants of disease evolution in subjects infected with multidrug-resistant HIV (MDR-HIV).

METHODS

Infectivity, replication, chemokine receptor usage, and env, gag, protease and reverse transcriptase sequence analysis was performed for MDR-HIV isolates from 14 HIV-infected individuals and compared to wild-type HIV isolates from individuals naive to antiretroviral treatment. Expression of CD45RO/RA, Ki67 and interferon-gamma and CD4 proliferative response to various antigens was determined for individuals infected with MDR-HIV and compared to that in individuals with optimal suppression of viral replication.

RESULTS

Infectivity and replication are diminished for various MDR-HIV isolates, usually in the context of an increase in CD4 and CD4+CD45RA+ T-cell counts. However, a number of MDR-HIV isolates are associated with high in vivo viraemia and pronounced immunosuppression, and display in vitro levels of infectivity and replication comparable to those of wild-type strains. No specific genetic sequence or chemokine receptor usage predicted the fitness of an MDR isolate.

CONCLUSIONS

Despite the biological diversity of resistant viruses and the range of host responses observed, our descriptive analysis indicates that viral factors play a role in determining the degree of immune damage observed in the context of MDR-HIV infection.

CD40 ligand trimer and IL-12 enhance peripheral blood mononuclear cells and CD4+ T cell proliferation and production of IFN-gamma in response to p24 antigen in HIV-infected individuals: potential contribution of anergy to HIV-specific unresponsiveness

It has been suggested that CD4+ T cell proliferative responses to HIV p24 Ag may be important in the control of HIV infection. However, these responses are minimal or absent in many HIV-infected individuals. Furthermore, while in vitro and in vivo responses to non-HIV recall Ags improve upon administration of highly active antiretroviral therapy, there does not appear to be a commensurate enhancement of HIV-specific immune responses. It is possible that CD4+ p24-specific T cells are deleted early in the course of infection. However, it is also possible that a discrete unresponsiveness, or anergy, contributes to the lack of proliferation to p24. To evaluate the possible contribution of unresponsiveness to the lack of CD4+ T cell proliferation to p24 in HIV-infected individuals, we attempted to overcome unresponsiveness. CD40 ligand trimer (CD40LT) and IL-12 significantly increased PBMC and CD4+ T cell proliferative responses to p24 Ag in HIV-infected, but not uninfected, individuals. No increase in proliferative response to CMV Ag was observed. CD40LT exerted its effect through B7-CD28-dependent and IL-12- and IL-15-independent mechanisms. Finally, the increase in proliferation with CD40LT and IL-12 was associated with an augmented production of IFN-gamma in most, but not all, individuals. These data suggest the possible contribution of HIV-specific unresponsiveness to the lack of CD4+ T cell proliferation to p24 Ag in HIV-infected individuals and that clonal deletion alone does not explain this phenomenon. They also indicate the potential for CD40LT and IL-12 as immune-based therapies for HIV infection.

Discontinuing or withholding primary prophylaxis against Mycobacterium avium in patients on successful antiretroviral combination therapy. The Swiss HIV Cohort Study

OBJECTIVE

To assess the safety of discontinuing or withholding primary prophylaxis against disseminated Mycobacterium avium infection (MAC) in HIV infected patients on successful antiretroviral combination therapy.

SETTING

National prospective multicentre cohort study.

DESIGN

HIV-infected patients were eligible for the analysis if: (i) they had a history of at least two CD4 cell counts < 50 x 10(6)/l; (ii) they had never had MAC; (iii) they had discontinued or never begun primary prophylaxis against MAC; (iv) they received antiretroviral therapy and demonstrated an increase in CD4 cell counts to > or = 100 x 10(6)/l that was sustained for at least 12 weeks. From this time point until last follow-up, incidence of disseminated MAC disease was measured, and 99% confidence intervals were calculated assuming a Poisson distribution of events.

RESULTS

Two-hundred and fifty-three patients (22.5% female; median age, 37 years, 30% injecting drug users) were eligible for analysis. Sixty-six per cent were in Centers for Disease Control and Prevention (CDC) stage C, and 28% were in CDC stage B. Their median nadir CD4 cell count was 10 x 10(6)/l, the median duration of CD4 cell count < 50 x 10(6)/l was 12 months. During a total follow-up of 364.3 patient-years there was no case of disseminated MAC. The one-sided 99% confidence limit for incidence density of MAC was 1.3 per 100 person-years.

CONCLUSION

Discontinuing or withholding primary prophylaxis against MAC is safe in patients who have a sustained increase in their CD4 cell count to > or = 100 x 10(6)/l.