Immunotherapy of HIV-infected patients with intermittent interleukin-2: effects of cycle frequency and cycle duration on degree of CD4(+) T-lymphocyte expansion

Cytokine therapies in HIV-1 infection: present and future

Since the introduction of highly active antiretroviral therapy (HAART), HIV-related deaths have declined dramatically in the developed world. However, HAART is neither able to eradicate the virus nor are its immunomodulatory effects sufficient to effect complete control of the virus. In addition, the long-term use of HAART is complicated by drug-related toxicities and compliance issues, both of which impact upon the development of viral resistance. The failure of structured treatment interruption strategies in those with chronic HIV-infection combined with the above limitations, has prompted renewed interest in immunotherapy. Cytokines and therapeutic vaccination have been proposed as HAART-adjunctive and HAART-sparing treatments in HIV-infection, and the current and future role of cytokine therapy in this disease will be the subject of this review.

Immunotherapeutic restoration in HIV-infected individuals

While the development of combined active antiretroviral therapy (cART) has dramatically improved life expectancies and quality of life in HIV-infected individuals, long-term clinical problems, such as metabolic complications, remain important constraints of life-long cART. Complete immune restoration using only cART is normally unattainable even in cases of sufficient plasma viral suppression. The need for immunologic adjuncts that complement cART remains, because while cART alone may result in the complete recovery of peripheral net CD4+ T lymphocytes, it may not affect the reservoir of HIV-infected cells. Here, we review current immunotherapies for HIV infection, with a particular emphasis on recent advances in cytokine therapies, therapeutic immunization, monoclonal antibodies, immune-modulating drugs, nanotechnology-based approaches and radioimmunotherapy.

Role of interleukin-2 in patients with HIV infection

Control of viral replication to below the level of quantification using combination antiretroviral therapy (ART) [cART] has led to a dramatic fall in mortality and morbidity from AIDS. However, despite the success of cART, it has become apparent that many patients do not achieve normalized CD4+ T-cell counts despite virological suppression to below the level of quantification (<50 copies/mL). Increasing data from cohort studies and limited data from clinical trials, such as the SMART study, have shown that higher CD4+ T-cell counts are associated with reductions in morbidity and mortality from both AIDS and serious non-AIDS (SNA) conditions, including cardiovascular disease. Enhancement of immune restoration over and above that achievable with ART alone, using a number of strategies including cytokine therapy, has been of interest for many years. The most studied cytokine in this setting is recombinant interleukin (IL)-2 (rIL-2). The purpose of this review is to describe the current status of rIL-2 as a therapeutic agent in the treatment of HIV-1 infection. The review focuses on the rationale underpinning the exploration of rIL-2 in HIV infection, summarizing the phase II and III findings of rIL-2 as an adjunctive therapy to ART and the phase II studies of rIL-2 as an antiretroviral-sparing agent. The phase II studies demonstrated the potential utility of continuous intravenous IL-2 and subsequently intermittent dosing with subcutaneous rIL-2 as a cytokine that could expand the CD4+ T-cell pool in HIV-1-infected patients without any significant detrimental effect on HIV viral load and with an acceptable adverse-effect profile. These data were utilized in designing the phase II studies of rIL-2 as an ART-sparing agent and, more importantly, the large phase III clinical endpoint studies of rIL-2 in HIV-1-infected adults, ESPRIT and SILCAAT. In the latter, subcutaneous rIL-2 was given intermittently (5 days of twice-daily dosing at 4.5-7.5 million international units per dose every 8 weeks) to HIV-1-infected adults receiving cART using an induction/maintenance strategy. Both studies explored the clinical benefit of intermittent subcutaneous rIL-2 with cART versus cART in HIV-infected adults with CD4+ T-cell counts > or = 300 cells/microL (ESPRIT study) and 50-299 cells/microL (SILCAAT study). Both studies showed that receipt of rIL-2 conferred no clinical benefit despite a significantly higher CD4+ T-cell count in the rIL-2 arms of both studies. Moreover, there was an excess of grade 4 clinical events in ESPRIT rIL-2 recipients. The results of the phase III clinical endpoint studies showed that rIL-2 has no place as a therapeutic agent in the treatment of HIV infection.

Immunotherapy of viral infections

Among the microorganisms that cause diseases of medical or veterinary importance, the only group that is entirely dependent on the host, and hence not easily amenable to therapy via pharmaceuticals, is the viruses. Since viruses are obligate intracellular pathogens, and therefore depend a great deal on cellular processes, direct therapy of viral infections is difficult. Thus, modifying or targeting nonspecific or specific immune responses is an important aspect of intervention of ongoing viral infections. However, as a result of the unavailability of effective vaccines and the extended duration of manifestation, chronic viral infections are the most suitable for immunotherapies. We present an overview of various immunological strategies that have been applied for treating viral infections after exposure to the infectious agent.

Immunotherapies in HIV-1 infection

PURPOSE OF REVIEW

The purpose of this review is to describe the current status of immunotherapies for the treatment of HIV-1 infection. This review is timely, as the results of the phase III clinical trials of recombinant interleukin-2 (rIL-2) as adjuncts to combination antiretroviral therapy are about to be released.

RECENT FINDINGS

For many years, the use of rIL-2 in HIV-infected individuals has been explored. Although the results of the clinical endpoint studies of rIL-2 are awaited, there are now further data for rIL-2 as a stand-alone therapy for the treatment of HIV. Maraviroc, a recently approved anti-HIV agent, is a small molecule antagonist of human chemokine receptor-5. The recent observation that maraviroc-treated patients achieved higher CD4 and CD8 T-cell counts compared with comparator regimens (without a chemokine receptor-5 antagonist) for equivalent viral load reductions has fueled interest in using these host-directed therapies to enhance immune restoration.

SUMMARY

This review summarizes the most recent clinical data for rIL-2 and reviews other immunotherapies in earlier development including cytokines rIL-7, rIL-15, rIL-21, new therapeutic vaccination approaches including infusion of overlapping HIV peptides and dendritic cell immunotherapy and novel agents including luteinizing hormone-releasing hormone analogues and vitamin D3-binding protein macrophage activating factor.

Safety, tolerability, pharmacokinetics, and efficacy of an interleukin-2 agonist among HIV-infected patients receiving highly active antiretroviral therapy

We sought to determine the safety, maximum tolerated dose, optimal dose, and preliminary dose efficacy of intermittent subcutaneously (s.c.) administered BAY 50-4798 among patients with HIV infection receiving highly active antiretroviral therapy (HAART) compared with patients receiving HAART alone. A phase I/II randomized, double-blind, dose-escalation study was conducted of the safety, tolerability, pharmacokinetics, and efficacy of s.c. BAY 50-4798 administered to HIV-infected patients already receiving stable HAART. There were no unexpected safety findings in a population of HIV-infected patients receiving HAART plus SC BAY 50-4798 as adjunctive therapy. BAY 50-4798 exhibited nearly dose-proportional pharmacokinetics, and accumulation was minimal during multiple-dose treatment. Limited efficacy data indicated that treatment with BAY 50-4798 caused at least a transient increase in CD4(+) T cell counts in some recipients, particularly at the early time points. In general, this effect appeared to increase with increasing dose. Bay 50-4798 was generally well tolerated across the dose range tested, but a lack of potent, sustained immunologic activity suggests that further optimization of dose and schedule will be necessary.

Increases in CD4+ T lymphocytes occur without increases in thymic size in HIV-infected subjects receiving interleukin-2 therapy

OBJECTIVE

To examine the potential contribution of the thymus to CD4+ T-lymphocyte increases in HIV-infected patients receiving intermittent interleukin-2 (IL-2) therapy.

DESIGN

Fifteen HIV-infected patients treated with antiretroviral regimens who were enrolled in a study of intermittent IL-2 therapy and were willing to undergo serial thymic computed tomography (CT) were prospectively studied.

METHODS

Thymic CT was performed before and approximately 6 and 12-17 months after intermittent IL-2 therapy was started. Scans were graded in a blinded manner. Changes in lymphocyte subpopulations were determined by flow cytometry.

RESULTS

Statistically significant increases in CD4+ T lymphocytes occurred with IL-2 administration, with a preferential increase in naive relative to memory CD4+ T cells. Despite this increase in naive CD4+ T cells, overall there was a modest decrease in thymic volume observed during the study period. No correlation was found between changes in thymic volume indices and total, naive, or memory CD4+ T-lymphocyte counts.

CONCLUSIONS

These findings demonstrate that the profound CD4+ T-lymphocyte increases seen with intermittent IL-2 administration are not associated with increases in thymic volume and more likely are due to peripheral expansion rather than increased thymic output.

Lymphocyte counts independently predict overall survival in advanced cancer patients: a biomarker for IL-2 immunotherapy

Interleukin-2 (IL-2) targets cells bearing IL-2 receptors and induces different degrees of lymphocytosis. This study retrospectively evaluated whether lymphocytosis, in addition to clinical characteristics at baseline and to tumor objective response, may predict overall survival in metastatic renal cell carcinoma patients who received IL-2 subcutaneously (s.c.). Overall survival, clinical characteristics, tumor response, and total lymphocyte count at baseline and during the first treatment cycle of 266 advanced renal cell cancer patients, treated with 1 of 4 different first-line s.c. IL-2-based protocols, were studied using the Cox multivariate analysis. Median IL-2 cumulative dose and length of treatment (+/-SD) were 232 +/- 282 x 10(6)/m(2) in 7 +/- 5.9 weeks, respectively. Median overall survival (os) was 13.1 months (range 0.7-86.9+) in all. Tumor outcome consisted of: 9 CR (3%) (os = NR); 35 PR (13%) (os = 19.7 months.); 117 SD (44%) (os = 15.1 months); 105 PD (39%) (os = 6.4 months). Median lymphocyte counts were 1400/mm(3) at baseline (25th-75th, 900-1900/mm(3)) and 3600/mm(3) as a maximum value (25th-75th, 2600-4800/mm(3)). Death risk significantly decreased by 11% for each 1,000 lymphocytes/mm(3) (RR 0.89; 95% CI 0.82-0.97), after correcting for clinical characteristics (PS ECOG 0 versus > or =1, time from primary diagnosis > or =2 years versus <2 years, number of metastatic sites 1 versus >1) and tumor response (CR, PR). A two-step bootstrapping procedure confirmed such predictive performance. Lymphocyte count monitoring represents a biomarker of the host response to subcutaneous IL-2 treatment useful for multimodal clinical assessment, as it predicts overall survival in advanced cancer patients independently from tumor response and from main clinical characteristics.

Interleukin-2 immunotherapy of murine cytomegalovirus retinitis during MAIDS correlates with increased intraocular CD8+ T-cell infiltration

AIDS-related human cytomegalovirus retinitis continues to be an important sight-threatening disease in AIDS patients who do not respond to highly active antiretroviral therapy. We have shown previously that systemic cytokine immunotherapy with interleukin-2 (IL-2) will protect against experimental murine cytomegalovirus (MCMV) in mice with a murine retrovirus-induced immunodeficiency syndrome (MAIDS). Since IL-2 serves as a Th1 immunoregulatory cytokine, we hypothesized that IL-2-induced protection against MCMV retinitis during MAIDS would correlate with a measurable increase in the number of natural killer (NK) cells and/or CD8+ T cells that infiltrate the eye in response to MCMV infection of the retina. We therefore performed a study to quantify and compare the number of NK cells and CD8+ T cells that infiltrate MCMV-infected eyes in untreated and IL-2-treated mice with MAIDS at 3 days and 5 days after subretinal MCMV inoculation. Double-label flow cytometric analysis revealed the detection of measurable numbers of both NK cells and CD8+ T cells in MCMV-infected eyes of untreated MAIDS mice destined to develop retinitis. In contrast, IL-2 immunotherapy during MAIDS correlated with a 10-fold increase by day 5 after inoculation in the number of CD8+ T cells in MCMV-infected eyes destined to be resistant to retinitis. However, IL-2 immunotherapy during MAIDS had no appreciable effect on the number of NK cells that infiltrated MCMV-infected eyes. Taken together, our findings suggest that function of cytotoxic lymphocytes that infiltrate the eye may be more important than absolute numbers of cytotoxic lymphocytes that infiltrate the eye when assessing the protective effects of IL-2 immunotherapy on MCMV retinitis during MAIDS.

A randomized controlled trial evaluating the efficacy and safety of intermittent 3-, 4-, and 5-day cycles of intravenous recombinant human interleukin-2 combined with antiretroviral therapy (ART) versus ART alone in HIV-seropositive patients with 100-300 CD4+ T cells

The effect of length of therapy on the safety and efficacy profile of continuous intravenous (CIV) interleukin-2 (IL-2) in combination with antiretroviral therapy (ART) was evaluated in 81 HIV-seropositive patients with CD4(+) T-cell counts of 100-300/mm(3). Patients were randomized to CIV IL-2 (12 mIU/day) for 3, 4, or 5 days plus ART every 8 weeks for six cycles, or to ART alone. The mean percent increase in CD4(+) T-cell counts was 24.5% for IL-2 recipients compared with a mean percent decrease of 30.5% for control patients (P = 0.005). Increasing duration of CIV IL-2 therapy resulted in improved CD4(+) T-cell response. The most frequent clinical adverse events and laboratory abnormalities were predominantly of grade 1 or 2 severity. However, grade 3 or 4 events were reported in 57%, 60%, and 84% of the 3-, 4-, and 5-day CIV IL-2 patients, respectively. Serious adverse events, mainly due to the requirement of hospitalization, occurred in 20% of IL-2 recipients, compared with 10% of control patients. Viral load during the course of the study was not different among the treatment groups. IL-2 therapy in cycles of 5 days resulted in an optimal increase in CD4(+) T-cell counts and is the preferred cycle length for IL-2 therapy geared toward increasing CD4(+) T-cell numbers.