Interleukin-2 enhances the depressed natural killer and cytomegalovirus-specific cytotoxic activities of lymphocytes from patients with the acquired immune deficiency syndrome

Immuno-Diagnostic Interest in Monitoring CD16+CD56+ (Natural Killer) Cells and CD19+CD45+ (B Lymphocytes) in Individuals Newly Diagnosed with HIV in a Tertiary Care Center

BACKGROUND/OBJECTIVE

Monitoring multiple cellular markers of immune cells may provide a more accurate evaluation of the immune status of people living with human immunodeficiency virus (PLHIV). This study assessed the value of CD16+CD56+ cells (NK cells) and CD19+ lymphocytes (B cells) phenotyping in indicating viral load, AIDS status, and treatment efficacy.

METHOD

A retrospective, laboratory-based study was conducted at the Diagnostic immunology division of a referral tertiary hospital. It involved 82 newly diagnosed HIV patients treated between 2009-2016. We explored three objectives: (1) the paired change in CD16+CD56+ and CD19+CD45+ cells counts and percentages from baseline to 2-to-6 months after treatment; (2) the association of these phenotypes with 5 gradual categories of viral load; and (3) the accuracy of CD16+CD56+ and CD19+CD45+ cells counts in indicating AIDS stage defined as CD4+ < 200 cells/mm3. The second and third objectives were tested using a pooled analysis (N = 300-373).

RESULT

The median CD19+CD45+ and CD16+CD56+ counts increased by 1.9-fold and 1.3-fold after treatment respectively (p < 0.001). A negative correlation of viral load with both CD16+CD56+ (ρ = -0.29, p < 0.001) and CD19+CD45+ (ρ = -0.34, p < 0.001) counts was observed. CD16+CD56+ count < 73 cells/mm3 and CD19+CD45+ count < 166.5 were indicative for AIDS with 95.5% and 63.6% sensitivity respectively.

CONCLUSIONS

Findings advocate for the usefulness of CD16+CD56+ and CD19+CD45+ phenotyping in characterizing the severity of HIV infection and its impact on both the humoral and cellular immunity, as well as monitoring the effectiveness of treatment.

Host Immune Response and Associated Clinical Features in a Primary Cytomegalovirus Eye Infection Model Using Anterior Chamber Inoculation

Purpose

To investigate the pathogenesis of cytomegalovirus (CMV)-associated anterior segment infection in immunocompetent hosts and evaluate the effects of ganciclovir and glucocorticoid treatment in management of the disease.

Methods

We used an inoculation model to reproduce CMV anterior segment infection in immunocompetent rats. Flow cytometry, cytokine analysis, histopathological sections, and quantitative polymerase chain reaction were performed to investigate the immune response after CMV infection. The effects of ganciclovir and glucocorticoid treatment were also assessed.

Results

Anterior chamber inoculation of CMV in rats provoked characteristic pathological features of human CMV anterior segment infection. The innate and adaptive immunity sequentially developed in an anterior segment after inoculation, and the elevation of intraocular pressure (IOP) was highly associated with ocular infiltration and inflammation. Early ocular immune response reduced virus DNA in the anterior segment and alleviated viral lymphadenopathy. Early intervention with ganciclovir enhanced the release of cytokines associated with T response and facilitated recruitment of NKT and T cells in drainage lymph nodes. Glucocorticoid treatment, alone or combined with ganciclovir, decreased elevation of IOP but also impeded DNA clearance.

Conclusions

The inoculation model reproduced characteristic pathological features of human CMV anterior segment infection. The use of glucocorticoid in current practice may hinder viral clearance, and ganciclovir therapy can assist cytokine expression to combat the virus.

Bracing NK cell based therapy to relegate pulmonary inflammation in COVID-19

The contagiosity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has startled mankind and has brought our lives to a standstill. The treatment focused mainly on repurposed immunomodulatory and antiviral agents along with the availability of a few vaccines for prophylaxis to vanquish COVID-19. This seemingly mandates a deeper understanding of the disease pathogenesis. This necessitates a plausible extrapolation of cell-based therapy to COVID-19 and is regarded equivalently significant. Recently, correlative pieces of clinical evidence reported a robust decline in lymphocyte count in severe COVID-19 patients that suggest dysregulated immune responses as a key element contributing to the pathophysiological alterations. The large granular lymphocytes also known as natural killer (NK) cells play a heterogeneous role in biological functioning wherein their frontline action defends the body against a wide array of infections and tumors. They prominently play a critical role in viral clearance and executing immuno-modulatory activities. Accumulated clinical evidence demonstrate a decrease in the number of NK cells in circulation with or without phenotypical exhaustion. These plausibly contribute to the progression of pulmonary inflammation in COVID-19 pneumonia and result in acute lung injury. In this review, we have outlined the present understanding of the immunological response of NK cells in COVID-19 infection. We have also discussed the possible use of these powerful biological cells as a therapeutic agent in view of preventing immunological harms of SARS-CoV-2 and the current challenges in advocating NK cell therapy for the same.

Establishing the reference intervals of NK cell functions in healthy adults

Natural killer (NK) cells play a key role in host defense against microbial pathogens. Establishing the reference intervals (RIs) of NK cell functions would be valuable in assessing the immune status of hosts. We evaluated the NK cell activity in healthy adults. We further established and validated the RIs of representative NK cell functions. Flow cytometry was used to evaluate the cytokine production and CD107a degranulation of NK cells. Levels of soluble IFN-γ in the culture supernatants were evaluated by ELISA. Our results demonstrated that the intracellular IFN-γ production of NK cells was positively correlated with CD107a expression and soluble IFN-γ levels. There were no significant differences in NK cell functions between different age and gender groups. The mean values and RIs of representative NK cell functions are as following: IFN-γ(+) NK cells (%): 28.09 (11.3-51.95); CD107a(+) NK cells (%): 17.90 (9.852-27.56); soluble IFN-γ (pg/ml): 330.4 (41.38-717.8). In addition, the intracellular IFN-γ production and degranulation activity of NK cells in patients with colorectal cancer were significantly lower than that in healthy adults. Our study has established the RIs of NK cell functions in healthy adults, which might be used for monitoring the immune status of the hosts.

Mucosal immunity in the female genital tract, HIV/AIDS

Mucosal immunity consists of innate and adaptive immune responses which can be influenced by systemic immunity. Despite having been the subject of intensive studies, it is not fully elucidated what exactly occurs after HIV contact with the female genital tract mucosa. The sexual route is the main route of HIV transmission, with an increased risk of infection in women compared to men. Several characteristics of the female genital tract make it suitable for inoculation, establishment of infection, and systemic spread of the virus, which causes local changes that may favor the development of infections by other pathogens, often called sexually transmitted diseases (STDs). The relationship of these STDs with HIV infection has been widely studied. Here we review the characteristics of mucosal immunity of the female genital tract, its alterations due to HIV/AIDS, and the characteristics of coinfections between HIV/AIDS and the most prevalent STDs.

Expression of interleukin-15 and interleukin-15Rα in monocytes of HIV type 1-infected patients with different courses of disease progression

Interleukin-15 (IL-15) enhances the effector mechanisms of anti-HIV immune responses and thus is considered a potential adjuvant of HIV-1 vaccine. However, there are a lack of data concerning the relationships between IL-15 expression and regulation in HIV-1-infected patients and the course of disease progression. We found that IL-15, but not IL-15Rα, is expressed at significantly higher levels in the CD14(+) monocytes [stimulated or not with interferon (IFN)-γ] of long-term nonprogressors (LTNP) than in those of HIV-1 progressors or healthy controls. There was no between-group difference in the amounts of soluble IL-15 released from the cells. We also found that like the healthy controls, the LTNP expressed the IL-15 and IL-15Rα genes in a more coordinated manner than the progressors. Our findings show that there are significant differences in IL-15 expression between patients with different courses of HIV infection, and that the coordinated expression of the IL-15 and IL-15Rα genes is dysregulated in patients with progressive disease. They also provide important information concerning the mechanisms of infection and the potential use of IL-15 as a therapeutic agent.

Loss of NK stimulatory capacity by plasmacytoid and monocyte-derived DC but not myeloid DC in HIV-1 infected patients

Dendritic cells (DC) are potent inducers of natural killer (NK) cells. There are two distinct populations in blood, myeloid (mDC) and plasmacytoid (pDC) but they can also be generated In vitro from monocytes (mdDC). Although it is established that blood DC are lost in HIV-1 infection, the full impact of HIV-1 infection on DC-NK cell interactions remains elusive. We thus investigated the ability of pDC, mDC, and mdDC from viremic and anti-retroviral therapy-treated aviremic HIV-1+ patients to stimulate various NK cell functions. Stimulated pDC and mdDC from HIV-1+ patients showed reduced secretion of IFN-α and IL-12p70 respectively and their capacity to stimulate expression of CD25 and CD69, and IFN-γ secretion in NK cells was also reduced. pDC activation of NK cell degranulation in response to a tumour cell line was severely reduced in HIV-1+ patients but the ability of mDC to activate NK cells was not affected by HIV-1 infection, with the exception of HLA-DR induction. No differences were observed between viremic and aviremic patients indicating that anti-retroviral therapy had minimal effect on restoration on pDC and mdDC-mediated activation of NK cells. Results from this study provide further insight into HIV-1 mediated suppression of innate immune functions.

Natural killer cells: versatile roles in autoimmune and infectious diseases

Natural killer (NK) cells are essential members of innate immunity and they rapidly respond to a variety of insults via cytokine secretion and cytolytic activity. Effector functions of NK cells form an important first line of innate immunity against viral, bacterial and parasitic infections, as well as an important bridge for the activation of adaptive immune responses. The control of NK-cell activation and killing is now understood to be a highly complex system of diverse inhibitory and activatory receptor-ligand interactions, sensing changes in MHC expression. NK cells have a functional role in innate immunity as the primary source of NK-cell-derived immunoregulatory cytokines, which have been identified in target organs of patients suffering from autoimmune diseases, and play a critical role in early defense against infectious agents. This review focuses on recent research of NK cells, summarizing their potential immunoregulatory role in modulating autoimmunity and infectious diseases.

Impaired plasmacytoid dendritic cell (PDC)-NK cell activity in viremic human immunodeficiency virus infection attributable to impairments in both PDC and NK cell function

Human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infections impair plasmacytoid dendritic cell (PDC) and natural killer (NK) cell subset numbers and functions, though little is known about PDC-NK cell interactions during these infections. We evaluated PDC-dependent NK cell killing and gamma interferon (IFN-gamma) and granzyme B production, using peripheral blood mononuclear cell (PBMC)-based and purified cell assays of samples from HCV- and HIV-infected subjects. CpG-enhanced PBMC killing and IFN-gamma and granzyme B activity (dependent on PDC and NK cells) were impaired in viremic HIV infection. In purified PDC-NK cell culture experiments, CpG-enhanced, PDC-dependent NK cell activity was cell contact and IFN-alpha dependent, and this activity was impaired in viremic HIV infection but not in HCV infection. In heterologous PDC-NK cell assays, impaired PDC-NK cell killing activity was largely attributable to an NK cell defect, while impaired PDC-NK cell IFN-gamma-producing activity was attributable to both PDC and NK cell defects. Additionally, the response of NK cells to direct IFN-alpha stimulation was defective in viremic HIV infection, and this defect was not attributable to diminished IFN-alpha receptor expression, though IFN-alpha receptor and NKP30 expression was closely associated with killer activity in viremic HIV infection but not in healthy controls. These data indicate that during uncontrolled HIV infection, PDC-dependent NK cell function is impaired, which is in large part attributable to defective IFN-alpha-induced NK cell activity and not to altered IFN-alpha receptor, NKP30, NKP44, NKP46, or NKG2D expression.

Accessory cell dependent NK cell mediated PBMC IFN-gamma production is defective in HIV infection

HCV and HIV infections impair dendritic cell function. We evaluated the impact of HCV, HIV, and HCV-HIV infection on MDC-NK interactions by analyzing CD3 depleted PBMC for NK cell IFN-gamma in response to IL-12 or poly (I:C). Purified MDC and NK cells were analyzed for TLR ligand-dependent, MDC-dependent NK activity. In HIV infection, IFN-gamma production by CD3 depleted PBMC was reduced in response to poly (I:C), while response to IL-12 was intact in HCV and HIV infections. Poly (I:C) induced activity was dependent on MDC and partially dependent on IL-12, consistent with accessory cell help. In purified MDC-NK co-cultures, MDC dependent NK IFN-gamma and Granzyme B was intact in both HCV and HIV infections, while MDC numerical defects were observed in HIV infection. These data indicate that during viral infection with HIV, accessory cell dependent NK function in the periphery is impaired. This impairment may be related to the identified MDC numerical defect.

A pilot study evaluating time to CD4 T-cell count <350 cells/mm(3) after treatment interruption following antiretroviral therapy +/- interleukin 2: results of ACTG A5102

BACKGROUND

Although an intermittent antiviral treatment (ART) strategy may limit long-term toxicity and cost, there is concern about the risk for virologic failure, selection of drug resistance mutations, and disease progression. By boosting CD4 T-cell counts, interleukin 2 (IL-2) could safely prolong the duration of treatment interruption (TI) in a CD4-driven strategy.

METHODS

The AIDS Clinical Trials Group (ACTG) study A5102 evaluated 3 cycles of IL-2 before TI, on clinical and immunologic outcomes, using a CD4 T-cell count of <350 cells/mm as the threshold for restarting ART. Forty-seven HIV-infected subjects on potent ART with CD4 T-cell counts of > or =500 cells/mm or more and HIV RNA levels of less than 200 copies/mL were randomized to arm A (ART + three 5-day cycles of IL-2 at 4.5 million U, Sc, BID every 8 weeks, n = 23) or arm B (ART alone, n = 24) for 18 weeks (step 1). At the end of step 1, subjects with a CD4 T-cell count of > or =500 cells/mm or more stopped ART until a CD4 count of <350 cells/mm (step 2). CD4 T-cell count, time to return of viremia, and the emergence of drug resistance mutations after TI were compared between study arms.

RESULTS

IL-2 recipients maintained higher CD4 counts during TI for 48 weeks with a waning of the CD4 effect by 72 weeks. A sustained CD4 T-cell count of more than 350 cells/mm and more durable TI were associated with a higher nadir CD4 T-cell count before ART and higher naive CD4 T-cell count at entry. After TI, a higher viral set point and drug resistance mutations at virologic rebound were associated with a shorter time to CD4 T-cell count of less than 350 cell/mm. There were no differences in the magnitude of virologic rebound (at week 8 of step 2, median log10 HIV RNA level was 4.23 for arm A and 4.21 for arm B) or the steady-state HIV-1 RNA level after week 8.

CONCLUSIONS

IL-2 before TI did not prolong time to CD4 of less than 350 cells/mm. A TI strategy utilizing a CD4 T-cell threshold of less than 350 cells/mm for restarting ART appears generally safe with most subjects in both arms remaining off ART for more than 1 year. Implications of our results for TI strategies include the potential advantage of starting ART at higher CD4 T-cell levels while avoiding any drug resistance and evaluating immunomodulators or drugs to reduce T-cell activation and HIV-1 RNA rebound during the TI.

Interleukin-2 reconstitutes defective human immunodeficiency virus (HIV), and cytomegalovirus (CMV) specific CD8+ T cell proliferation in HIV infection

Recent studies indicate that a defective proliferative response of HIV-specific CD8+ T cells is associated with the lack of virologic control in chronic HIV infection in humans. The possible mechanisms that might be responsible for the reduced proliferative potential of HIV-specific CD8+ T cells and conditions conducive to the proliferation of CD8+ T cells were examined in 14 HIV-infected individuals and 7 HIV-uninfected controls using CFSE labeling and flow cytometry techniques, and analyzed data using 2 quantitative measurements: the percentages of proliferating CD8+ T cells (Tp), and the maximum number of cell divisions (Dm) after stimulation. It was found that CD8+ T cells from HIV-infected and -uninfected subjects proliferated equally well after polyclonal stimulation by phylohemagglutinin A (PHA); both groups reached a Tp of 92%-96% and a Dm of 5-8. However, in HIV-infected subjects, proliferation of HIV- and CMV-specific CD8+ T cells was significantly reduced compared to proliferation of CMV- specific CD8+ T cells from HIV-uninfected subjects. These defective proliferative responses of HIV- and CMV-specific CD8+ T cells were restored by the addition of IL-2 at the time of stimulation. These results may have implications for the design of immune modulation strategies in vivo.

NK cells in HIV infection: Paradigm for protection or targets for ambush

Natural killer cells are a crucial component of the innate immune response to certain tumours and to various viruses, fungi, parasites and bacteria. HIV has infected more than 60 million people worldwide and has led to more than 23 million deaths. At present, there are approximately 40 million people who are living with HIV infection, and there were 5 million new infections in 2004. As part of the innate immune system, natural killer cells might have an important role in host defence against HIV infection, as well as in the control of HIV replication in vivo. In this regard, it is important to understand how natural killer cells and HIV interact. This Review focuses on the role of natural killer cells in controlling HIV infection and on the impact of HIV and HIV-viraemia-induced immune activation on natural-killer-cell function.

The Use of Interleukin-2 in Human Immunodeficiency Virus Infection

Advances in antiretroviral therapy for human immunodeficiency virus (HIV) have led to reductions in HIV-related morbidity and mortality. Although antiretroviral therapy has shown success in suppressing viral loads, it does not adequately restore the immune system in all individuals infected with HIV. In light of this incomplete success, interleukin (IL)-2 is being evaluated as adjunctive therapy to antiretroviral therapy. The agent has demonstrated mixed yet promising results in restoring immune function in patients who are HIV positive.

Induction and maintenance therapy with intermittent interleukin-2 in HIV-1 infection

Studies establishing that intermittent subcutaneous interleukin-2 (IL-2) therapy can lead to substantial CD4 cell increases in many HIV-infected patients have generally been of limited duration. We studied 77 patients participating in active longitudinal studies of subcutaneous IL-2 therapy at our center in order to determine the long-term feasibility of this approach. Following initial induction, patients in each trial were eligible to receive intermittent 5-day cycles of subcutaneous IL-2 treatment at individualized doses and frequencies capable of maintaining CD4 counts at postinduction levels. The mean duration of study participation to date is 5.9 years (range, 1.0-9.3 years). Mean baseline CD4 cell count and CD4 percent values of 0.521 × 109/L (521 cells/μL) and 27% have risen to 1.005 × 109/L (1005 cells/μL) and 38%, respectively, at 90 months. The mean number of subcutaneous IL-2 cycles required to achieve and maintain these increases was 10 cycles (range, 3-29 cycles), and the current mean interval of cycling required to maintain these elevations is 39 months (median, 35 months; range, 2-91 months). We conclude that subcutaneous IL-2 therapy is capable of maintaining CD4 cell increases for an extended period using a remarkably low frequency of intermittent cycling. These observations may contribute to patients' acceptance of subcutaneous IL-2 as a favorable long-term treatment strategy. (Blood. 2004;103:3282-3286)

Non-AIDS-defining cancer in HIV-infected people

Since the advent of HAART, the natural history of HIV disease has been changing, with decreased risk of life-threatening opportunistic infections and prolonged survival. Concurrently, a variety of non-AIDS-defining cancers have been reported with increased incidence in HIV-infected adults, including anal cancer, Hodgkin's disease, head and neck cancer, testicular cancer, lung cancer, colon cancer, basal cell cancer, squamous cell cancer of the skin, and melanoma. It appears that these tumors may have a more aggressive clinical course in HIV-infected people. Available data, however, suggest that antitumor response and survival in HIV-infected people with malignancy are improved in people with higher CD4 counts. The possible mechanisms for the increased incidence and altered clinical course of these malignancies in HIV-infected people remain unclear.

Loss of the perforin cytotoxic pathway predisposes mice to experimental cytomegalovirus retinitis

AIDS-related human cytomegalovirus (HCMV) retinitis continues to be a chronic ophthalmologic problem among human immunodeficiency virus type 1 (HIV-1)-infected patients who do not respond to highly active antiretroviral therapy. Although HCMV retinitis occurs during HIV-1-induced immunosuppression, the precise effector mechanism(s) that fails during the immunopathogenesis of AIDS to allow onset and progression of HCMV retinal disease remains unclear. We therefore performed a series of experiments to explore the relative roles of distinct pathways of lymphocyte-mediated cytotoxicity in either resistance or susceptibility to experimental murine cytomegalovirus (MCMV) retinitis in mice. Whereas mutant C57BL/6 mice deficient in the Fas/FasL cytotoxic pathway (gld mice) were identical to normal C57BL/6 mice and exhibited absolute resistance to retinal necrosis following subretinal MCMV inoculation, knockout C57BL/6 mice deficient in the perforin cytotoxic pathway (PKO mice) were susceptible to MCMV retinitis. Susceptibility of PKO mice to MCMV retinitis correlated with increased ocular MCMV titers when compared with ocular MCMV titers of gld and normal mice. Since mice with retrovirus-induced immunodeficiency syndrome (MAIDS) exhibited a frequency and severity of MCMV retinitis that were equivalent to those observed in PKO mice, we hypothesized that susceptibility to MCMV retinitis during MAIDS correlates with a decrease in the perforin cytotoxic pathway. To test this hypothesis, we developed a quantitative competitive reverse transcription-PCR assay to measure mouse perforin mRNA levels in the splenic T lymphocytes and MCMV-inoculated eyes of normal mice or mice with MAIDS. Perforin mRNA levels in splenic T lymphocytes were significantly decreased during MAIDS, by approximately 100-fold, from perforin mRNA levels in normal mice. Moreover, MCMV-inoculated eyes destined to develop retinitis during MAIDS also showed a significant decrease in perforin mRNA levels from the perforin mRNA levels of MCMV-inoculated eyes of normal mice destined to be resistant to retinitis. As expected, perforin mRNA could not be detected in unmanipulated and uninfected eyes of normal mice. These results provide the first evidence that the perforin cytotoxic pathway is more important than the Fas/FasL cytotoxic pathway in providing resistance to experimental MCMV retinitis and that loss of the perforin cytotoxic pathway predisposes to MCMV retinitis.

Augmentation of local antitumor immunity in liver by interleukin-2 gene transfer via portal vein

Metastasis to the liver remains an important problem in the treatment of patients with gastrointestinal cancer. We examined the mechanism and effect on liver metastasis of in vivo interleukin-2 (IL-2) gene transfer to the liver. RCN-9 cells derived from F344 rat colon adenocarcinoma were injected into syngeneic rats via the ileocecal vein to induce liver tumors. A total of 2.5x10(9) pfu of adenovirus vector harboring the human IL-2 gene (AdCMVhIL-2), or 2.5x10(9) pfu of control vector encoding beta-galactosidase was administered before RCN-9 cell challenge. On day 14, mean tumor weight was 4.0+/-2.4 g in the control group, whereas IL-2-transduced livers had no tumors. Survival of AdCMVhIL-2-treated rats was significantly longer than that of control rats (P<.01). Flow cytometry demonstrated that the proportion of natural killer (NK) cells had increased among sinusoidal cells collected from IL-2-transduced livers. These cells were highly cytotoxic to RCN-9 cells in vitro in the presence of a physiological high concentration of recombinant IL-2. Preventative effects of IL-2 transduction of the liver against liver metastasis were lost after depletion of NK cells by treatment with anti-asialo GM1 antibodies. Our results indicate that IL-2 gene transfer to the liver prevents liver metastasis by continuously providing physiological high concentrations of IL-2 in the liver, thereby activating sinusoidal NK cells.

Effects of interleukin-2 plus highly active antiretroviral therapy on HIV-1 replication and proviral DNA (COSMIC trial)

BACKGROUND

The effect of interleukin-2 (IL-2) in combination with antiretroviral therapy on HIV-1 replication and reservoirs was investigated.

METHODS

In a prospective, open-label trial, 56 asymptomatic HIV-1-infected subjects (CD4 T cell count > 350 x 10(6) cells/l) were randomized to highly active antiretroviral therapy (HAART: stavudine, lamivudine, nelfinavir, saquinavir) with or without IL-2 (9 megaunits daily for 5 days in 6-weekly intervals for a total of eight cycles). Productive and latent infection were analysed in peripheral blood, and residual virus replication in the lymphoid tissue and in the cerebrospinal fluid. The influence of IL-2 on viral rebound after treatment discontinuation was studied.

RESULTS

Virus replication was detected in 21 of 31 on-treatment lymph nodes despite undetectable plasma viraemia. Viral RNA was found in resting as well as in proliferating cells. RNA-negative patients tended towards more rapid proviral DNA elimination. Supplementary IL-2 led to a greater increase in CD4 T cell counts than HAART alone (P < 0.001), resulting in normalization in approximately 90% of IL-2-treated patients compared with approximately 50% HAART-only subjects. IL-2 had no beneficial effect on virus replication and on proviral DNA in peripheral blood.

CONCLUSIONS

Viral persistence during HAART is partly a result of continued low-level replication, calling for more active regimens. IL-2 accelerates the normalization of CD4 T cell counts but does not impact on virus production or latency.

Cytokine therapy or structured treatment interruptions in HIV infection: which is best?

Continuous highly active antiretroviral therapy (HAART) is the treatment of choice for HIV patients in order to prevent opportunistic infection or AIDS-related morbidity and mortality. However, new HIV treatment strategies are needed to face the emerging problems related to long-term toxicities and failures of HAART. Moreover, total eradication and complete restoration of immune system function cannot be achieved by HAART alone. Therefore, in an attempt to increase the natural immunity of HIV-infected patients, immune-based therapies have been investigated. This review is intended to provide an update on the use of immune-based therapies, in particular structured treatment interruptions and cytokines, such as IL-2 and IFN-alpha, as potential stimulants of the immune system of patients with HIV-infections and to discuss risks and benefits of each alternative. Ongoing and future clinical trials will provide a rationale for their use in clinical practice and will determine how these strategies can be combined to optimise HAART.

Complex effects of interferon-alpha on the cytokine network in HIV infection--possible contribution to immunosuppression

Since interleukin (IL-)2, IL-10 and IL-12 may contribute to the pathogenesis of human immune deficiency virus (HIV) infection we examined the effect of interferon (IFN)-alpha on these cytokines in cultures of various subsets of peripheral blood mononuclear cells (PBMC) in ten HIV-infected patients and ten healthy controls. Our main findings were: (1) IFN-alpha markedly enhanced IL-10 levels in a dose-dependent manner in both lipopolysaccharide (LPS)- and phytohaemagglutinin (PHA)-stimulated PBMC, as well as in anti-CD3- and anti-CD3/anti-CD28-stimulated T cells in both HIV-infected patients and controls. (2) In contrast, IFN-alpha had a downregulatory effect on IL-10 levels in Candida -stimulated PBMC,with particularly strong suppressive effect in HIV-infected patients. (3) Furthermore, IFN-alpha had a significant but modest stimulatory effect on IL-2 levels in PHA- and Candida -stimulated PBMC and anti-CD3-stimulated T cells. (4) IFN-alpha enhanced IL-12 levels in a dose-dependent manner in LPS-stimulated PBMC in both patients and controls. Our findings that IFN-alpha markedly enhanced IL-10 and modestly enhanced IL-2 and IL-12, suggest a net immunosuppressive effect of IFN-alpha in HIV-infected patients, possibly contributing to progression of immunodeficiency in these patients.

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

The ability of IL-2 to induce expansion of the CD4(+) T lymphocyte pool has made it the most studied cytokine in the treatment of HIV infection. The majority of trials have used an empirical regimen of 5-day IL-2 cycles given every 8 weeks--a regimen based upon early pharmacodynamic studies and patient preference. To better define optimal duration and frequency of cycles, a randomized trial was conducted in which patients who received this "standard" regimen were compared to patients who received cycles of variable duration (based on individual patterns of cell cycle progression) and to patients who received cycles of variable frequency (based on individual CD4(+) T lymphocyte responses to previous cycles). Twenty-two patients with HIV-1 infection and CD4(+) T lymphocyte counts > 200 cells/mm(3) were randomized to one of three treatment groups for 32 weeks of study. Eight participants received four 5-day IL-2 cycles (controls) every 8 weeks; 7 participants received four cycles of longer duration (mean 7.7-days); and 7 participants received an increased frequency of 5-day cycles (every 4.1 weeks on average). All three groups experienced significant increases in mean CD4(+) T lymphocytes. However, there were no statistically significant differences in CD4(+) T lymphocyte increases between the group that received longer cycles (median increase 239 cells/mm(3), P = 0.78) or between the group that received more frequent cycles (median increase 511 cells/mm(3), P = 0.54) and the control group (median 284 cells/mm(3)). HIV-1 viral loads decreased during the study period in all three groups. Our inability to demonstrate a significant advantage of increased frequency or duration of IL-2 administration provides corroborating experimental evidence for the use of an IL-2 regimen consisting of 5-day cycles administered no more frequently than every 8 weeks in future clinical trials aimed at expanding the CD4(+) T lymphocyte pool.

Effects of subcutaneous IL-2 therapy on telomere lengths in PBMC in HIV-infected patients

In this study we investigated the effect of interleukin-2 (IL-2) on mean terminal restriction fragment (TRF) lengths in peripheral blood mononuclear cells (PBMC). Ten human immunodeficiency virus (HIV)-infected individuals were included and IL-2 was administered subcutaneously with 3 x 106 IU three times a week for 24 weeks. Mean TRF length was decreased on average by 267 bp at week 4 (P = 0.03) and 286 bp at week 8 (P = 0.09). Individual TRF changes at weeks 12, 16, 20 and 24 were highly variable. However, in the 12 weeks following therapy, TRF lengths generally increased reaching baseline levels by the end of the study. At baseline, mean TRF lengths were positively correlated to the ratio of naïve and memory phenotype within both CD4+ and CD8+ cells. This study shows that IL-2 treatment induces transient shortened mean TRF lengths in PBMC from HIV-infected individuals, indicating that IL-2 enhances the lymphocyte count by peripheral proliferation or recruitment of memory T cells into the blood.

A randomized, controlled 24-week study of intermittent subcutaneous interleukin-2 in HIV-1 infected patients in Thailand

OBJECTIVES

To assess the immunological and virological effects, safety profile and feasibility of subcutaneous interleukin-2 (scIL-2) therapy in an HIV-infected Thai population.

DESIGN

Seventy-two patients with baseline CD4 cell count of > or = 350 x 10(6)/l and no history of opportunistic infection were randomized to receive antiretroviral therapy plus scIL-2 (scIL-2 group) or antiretroviral therapy alone (control group). scIL-2 was administered at one of three doses for at least 24 weeks. The main measure of treatment efficacy was change in CD4 cell count.

RESULTS

The time-weighted mean change in CD4 cell count from baseline to week 24 was + 252 x 10(6)/l for the scIL-2 group compared with + 42 x 10(6)/l for the control group (P< 0.0001). Changes in plasma HIV RNA were not significantly different between the groups over the same time period: there was a 0.83 log10 copies/ml decrease for the scIL-2 group and a 0.70 log copies/ml decrease for the control group (P= 0.362).

CONCLUSIONS

This study provides the most extensive experience of scIL-2 therapy in HIV-1 infected women and Asians, and demonstrates the immunological efficacy, tolerability and feasability of scIL-2 therapy in this population. Data from this study were instrumental in guiding the selection of the scIL-2 dosing regimen for ongoing phase III trials.

Cytokines and their receptors in cardiovascular diseases--role of gp130 signalling pathway in cardiac myocyte growth and maintenance

Interleukin (IL)-6-related cytokines share gp130 as the signal-transducing protein. Cardiac myocytes produce various kinds of cytokines including IL-6 and cardiotrophin-1. Activation of gp130 transduces hypertrophic and cytoprotective signals in cardiac myocytes via JAK/STAT, MAP kinase and PI-3 kinase pathways. Besides various well-established mechanisms by which cardiac growth and myocardial remodeling are regulated, gp130 signalling may be a newly discovered mechanism that regulates these events in association with cytoprotective effect in myocardial diseases.

A risk-benefit assessment of interleukin-2 as an adjunct to antiviral therapy in HIV infection

Immunomodulation has become a major focus of HIV research in an effort to augment, boost or restore the patient's damaged immune system. Recombinant interleukin-2 is currently being studied in phase II/III trials in HIV-infected patients. Several clinical studies have demonstrated that intermittent regimens are associated with marked rises in CD4+ cell counts without an increase in viral load. Most of these studies employ 5 consecutive days of interleukin-2 therapy by continuous intravenous infusion or subcutaneous injection, repeated every 8 weeks. An alternative strategy is the daily administration of low doses of interleukin-2, but clinical experience with this regimen is limited. Interleukin-2 administration can adversely affect virtually every organ system, requiring aggressive supportive care. A variety of administration strategies and interventions are being evaluated to minimise toxicity. Currently, no clinical end-point data are available for interleukin-2 in HIV-infected patients. Until phase III studies are completed, interleukin-2 can be used in the research setting as an immunomodulator and adjunct to antiretroviral therapy. Its potential to activate latently infected cells and promote HIV eradication from reservoir sites is also an important area for further study. If clinical benefit can be demonstrated, interleukin-2 could be useful as an adjunct to antiretroviral therapy if adverse effects can be minimised and therapy can be given infrequently on an outpatient basis.

Constitutive Activation of STATs Upon In Vivo Human Immunodeficiency Virus Infection

Infection by the human immunodeficiency virus (HIV) either upregulates or downregulates the expression of several cytokines and interferons (IFNs) that use the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway for signal transduction. However, very little is known on the state of activation of the JAK/STAT pathway after HIV infection either in vivo or in vitro. In this regard, we report here that a constitutive activation of a C-terminal truncated STAT5 (STAT5▵) and of STAT1 occurs in the majority (∼75%) of individuals with progressive HIV disease. We have further demonstrated that, among peripheral blood mononuclear cells (PBMCs), STAT5▵ is activated preferentially in CD4+ T cells. In contrast to a published report, expression of STATs from PBMCs of infected individuals was comparable with that of seronegative donors. In addition, in vitro infection of mitogen-activated PBMCs with a panel of laboratory-adapted and primary HIV strains characterized by differential usage of chemokine coreceptors did not affect STAT protein levels. However, enhanced activation of STAT was observed after in vitro infection of resting PBMCs and nonadherent PBMCs by different viral strains. Thus, constitutive STAT activation in CD4+T lymphocytes represents a novel finding of interest also as a potential new marker of immunological reconstitution of HIV-infected individuals.

Constitutive Activation of STATs Upon In Vivo Human Immunodeficiency Virus Infection

Infection by the human immunodeficiency virus (HIV) either upregulates or downregulates the expression of several cytokines and interferons (IFNs) that use the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway for signal transduction. However, very little is known on the state of activation of the JAK/STAT pathway after HIV infection either in vivo or in vitro. In this regard, we report here that a constitutive activation of a C-terminal truncated STAT5 (STAT5▵) and of STAT1 occurs in the majority (∼75%) of individuals with progressive HIV disease. We have further demonstrated that, among peripheral blood mononuclear cells (PBMCs), STAT5▵ is activated preferentially in CD4+ T cells. In contrast to a published report, expression of STATs from PBMCs of infected individuals was comparable with that of seronegative donors. In addition, in vitro infection of mitogen-activated PBMCs with a panel of laboratory-adapted and primary HIV strains characterized by differential usage of chemokine coreceptors did not affect STAT protein levels. However, enhanced activation of STAT was observed after in vitro infection of resting PBMCs and nonadherent PBMCs by different viral strains. Thus, constitutive STAT activation in CD4+T lymphocytes represents a novel finding of interest also as a potential new marker of immunological reconstitution of HIV-infected individuals.

Limitations of adenovirus-mediated interleukin-2 gene therapy for oral cancer

OBJECTIVE/HYPOTHESIS

Adenoviral interleukin-2 (AdV-IL-2) gene therapy has previously not proven effective in treating established murine oral cancer. We hypothesize that the intratumoral level of IL-2 expression is a major limiting factor in treatment outcome.

METHODS

A microscopic disease and established oral cancer murine model was used to test this hypothesis. IL-2 gene transfer was performed with a recombinant adenovirus vector.

RESULTS

Tumor cells were transduced in vitro with AdV-IL-2 and subsequently implanted into the floor of the mouth in C3H/HeJ mice. IL-2 expression in vitro ranged from 990 to 1,050 pg/10(6) tumor cells. This microscopic disease treatment resulted in either complete tumor regression or a dramatic decrease in tumor progression. Cytolytic T-cell (CTL) assays demonstrated a predominance of CD8-specific, T-cell-mediated tumor killing. Reducing IL-2 expression by half with a mixture of 1:1 transduced to nontransduced tumor cells eliminated the antitumor effect and decreased the CTL response. These findings support the presence of a critical "threshold" of IL-2 expression. Adenovirus repurification and amplification allowed isolation of a twofold-higher-titer AdV-IL-2 vector. Treatment of established tumors with the higher-titer AdV-IL-2 at a new maximal dose of 1.4 x 10(9) plaque-forming units (pfu) increased in vivo IL-2 expression to 1,127 pg/10(6) cells and generated a significant antitumor response. Complete regression of established tumors, however, could not be achieved, and we noted a decrease in IL-2 expression well below the threshold at 1 week after treatment. Upon repeat maximal AdV-IL-2 injection in vivo, a greater antitumor effect and increased CTL response was seen, but also, 28% of the animals died of IL-2 toxicity.

CONCLUSION

Although limited by expression and toxicity as a single-treatment strategy for established tumors, AdV-IL-2 gene therapy should be considered a potential component of combination therapy strategies.

Dynamics of provirus load and lymphocyte subsets after interleukin 2 treatment in HIV-infected patients

The association of antiretroviral agents plus interleukin 2 (IL-2) represents an efficient approach to the treatment of HIV+ subjects. While the effects of IL-2 on the immune system have been investigated, little is known concerning its impact on HIV dynamics. Two antiretroviral drugs control HIV viremia, but have minimal effects on the proviral load, a predictor of disease progression and response to therapy. The aim of this study was to define the effect of rIL-2 on HIV proviral copy numbers and its relationship to changes in CD4+ and CD8+ subsets. Twelve HIV+ patients with CD4 cell counts between 200 and 500 cells/mm3 were treated with six cycles of subcutaneous rIL-2, in combination with zidovudine and didanosine. This regimen resulted in a rapid and durable decrease in proviral load in the peripheral blood, in an increase in CD8+ lymphocytes, and in the emergence of a CD4+CD45RA+ T subset. These results demonstrate that the rationale for IL-2 administration to HIV+ patients may depend not only on its effects on the immune system, but also on the reduction of the number of infected cells, reinforcing the notion that IL-2 can have a favorable impact on the natural history of HIV infection.

Intralymphatic interleukin-2 in combination with zidovudine for the therapy of patients with AIDS

In a pilot study the safety and therapeutic effects of an immunostimulatory intralymphatic treatment with natural human interleukin-2 (IL-2) in combination with zidovudine were evaluated in nine patients with AIDS. Therapy with IL-2 consisted of one subcutaneous injection of 0.1 microgram/kg IL-2, followed by four intralymphatic IL-2 infusions of 0.1 microgram/kg each within a period of up to 15 days. Enlargement of lymph nodes was seen in six and a transient increase of CD4 cells in five out of nine persons in association with the IL-2 therapy. An increase of HIV p24-antigenemia was observed only in the two patients in whom zidovudine dosage had to be reduced because of side effects. Moderate clinical side effects occurred in eight of the nine patients. Four patients developed zidovudine associated anemia. Six participants showed a favourable course of disease with survival of 25 to 54 months (median 30 months) despite a previous diagnosis of manifest AIDS before IL-2 therapy. This pilot study demonstrates that a combination therapy with intralymphatic IL-2 and zidovudine can induce positive immunomodulatory effects, even in the presence of manifest AIDS. Further studies should explore the tolerability and effects of a prolonged therapy with IL-2 in combination with a more potent antiviral drug combination therapy.

Pharmacokinetic modeling of recombinant interleukin-2 in patients with human immunodeficiency virus infection

A novel model was developed to characterize the time-varying clearance of recombinant interleukin-2 (IL-2). Sixty-eight patients with human immunodeficiency virus infection received 83 cycles of IL-2 either by continuous infusion or by subcutaneous injection for 5 days. IL-2 concentrations after intravenous infusions peaked at 24 hours and then declined by 55% to 78% during the remainder of the infusion. Soluble IL-2 receptors increased greater than 10-fold before gradually returning to baseline. Subcutaneous administration showed a dose-dependent decrease in area under the concentration-time curve (AUC) between days 1 and 5. A model was developed in 9 patients who had IL-2 concentrations and soluble IL-2 receptors determined by ELISA. Concentrations were fitted by an indirect stimulatory pharmacodynamic model. An additional 59 patients with only IL-2 concentrations were fitted to a simplified empiric model. Both models provided an overall r2 of 0.99 for the plot of observed versus fitted concentrations. The time-dependent increase in IL-2 clearance, likely receptor-mediated, was well described with use of an indirect-effects pharmacokinetic-pharmacodynamic model.

Lymphokine-activated killer (LAK) cell anti-HIV-1 ADCC reactivity: a potential strategy for reduction of virus-infected cellular reservoirs

Lymphocytes from HIV-1-seropositive and -seronegative individuals were examined to determine whether HIV-1 infection interfered with the ability to generate a lymphokine-activated killer (LAK) cell response. Following a 3-day ex vivo incubation in the presence of 1000 U/ml of recombinant interleukin-2, lymphocytes from seropositive individuals exhibited a LAK cell response which was equivalent to or greater than that of seronegative controls as measured against Daudi cell targets. LAK cells from seropositive and seronegative donors showed no specific cytolytic activity against gp120-coated or HIV-1-infected targets. However, in the presence of patient sera, significant levels of virus-specific LAK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) were observed. The level of this specific LAK cell-mediated ADCC was greater than that mediated under similar conditions by freshly isolated peripheral blood mononuclear cells. The greatest improvement in ADCC over baseline activity was seen with lymphocytes from AIDS patients after the 3-day ex vivo activation, suggesting that this patient population might benefit the most from adaptive LAK cell therapy.

Effects of IL-2 therapy in asymptomatic HIV-infected individuals on proliferative responses to mitogens, recall antigens and HIV-related antigens

The effects of IL-2 therapy on lymphoproliferative responses to mitogens, recall antigens and HIV epitopes were studied in asymptomatic HIV-infected patients enrolled in a phase II study of intermittent continuous intravenous (Ci.v.) IL-2 and subcutaneous infusions of polyethylene glycol-modified (PEG) IL-2. Sixteen consecutive patients randomized to receive Ci.v. IL-2 (n = 5), PEG IL-2 (n = 7) or anti-viral therapy alone (n = 4) were studied. All patients were vaccinated with tetanus toxoid (TT) before receiving therapy. Proliferative responses to phytohaemagglutinin (PHA), soluble anti-CD3, TT, streptokinase/streptodornase (SK/SD) and 11 previously described HIV-specific T-helper epitopes from gag and env were studied at weeks 0, 16, 30 and 48. Median CD4+ lymphocyte increases of 272 and 255CD4+ cells/microl were observed in the Ci.v. IL-2 and PEG IL-2 groups at week 48, while decreasing by 104 cells/microl in the anti-retroviral therapy alone group. At each time point proliferative responses to PHA, anti-CD3, TT and SK/SD were not different between treatment arms. Similarly, no differences in responses to HIV epitopes were found between the groups and no new responses to HIV epitopes were detected. IL-2 therapy results in a significant increase in peripheral blood CD4+ lymphocyte count, but this increase is not associated with quantifiable improvements in lymphoproliferative responses to mitogens, recall or HIV antigens.

Induction of HIV-1 replication by type 1-like cytokines, interleukin (IL)-12 and IL-15: effect on viral transcriptional activation, cellular proliferation, and endogenous cytokine production

Cytokine dysregulation is evident in HIV-1 infection and it may play an important role in HIV-1 pathogenesis. Administration of T helper cytokines potentially may restore the functional abnormalities to the HIV-1 immune response. Type 1-like cytokines, IL-2, IL-12, and IL-15, are candidates for immune-based therapy for HIV. Given their potential therapeutic use, we determined the effects of IL-2, IL-12, and IL-15 on HIV-1 replication in both primary blood mononuclear cells (PBMC) and the T-cell line, Kit 225-K6. We demonstrate that both IL-2 and IL-12 induce a similar level of HIV-1 replication (9- and 11-fold, respectively) in mitogen-stimulated PBMC. The effect of IL-2 plateaued by day 6, while that of IL-12 continued to increase HIV-1 expression. IL-15 induced a 2.5-fold increase in HIV-1 expression that remained at the same level through day 6. In Kit 225-K6, an IL-2-dependent T cell line, IL-12 and IL-15 enhanced HIV-1 replication by 5- and 3.5-fold over IL-2-treated cultures, respectively. IL-2-, IL-12-, and IL-15-mediated induction of HIV was independent of direct HIV-1 LTR activation, since none of the cytokines induced LTR activity from transfected reporter gene constructs. The cytokine-mediated induction of HIV-1 expression was also independent of cellular proliferation. In PBMC, the IL-12-mediated effect was partially mediated by endogenous cytokine production of IL-1beta and IL-7, whereas in Kit 225-K6, TNFalpha, INFgamma, IL-1beta, and IL-7 did not contribute significantly to the IL-12-mediated effect. IL-15 effect on HIV-1 in PBMC was independent of endogenous cytokine production. However, in Kit 225-K6, neutralizing antibodies to IL-7 had a significant effect on HIV-1 expression. These data suggest that IL-2, IL-12, and IL-15 increase HIV-1 replication predominantly through a posttranscriptional mechanism that may be enhanced by endogenous cytokine production.

AIDS-related bronchogenic carcinoma: fact or fiction?

OBJECTIVE

Case reviews and retrospective analyses have raised the possibility of an increased frequency of primary lung carcinoma in HIV- and AIDS-infected patients. Conclusions have often been controversial and conflicting. We conducted a population-based epidemiologic study to assess the incidence of lung neoplasms in an HIV/AIDS cohort.

MATERIALS AND METHODS

The Texas Department of Health generated descriptive data on lung neoplasms in HIV-AIDS patients whose conditions were diagnosed between 1990 and 1995. The cancer registry matched against all patients whose conditions were diagnosed during the same time interval. Relative risk was measured through standardized incidence ratios of lung neoplasms in the HIV-AIDS population as compared with that of the US population.

RESULTS

The HIV-AIDS data file included 26,181 cases. A total of 76 lung cancer cases were identified, of which 36 (47.4%) were primary lung cancers. All major histologies were represented. The observed (36)/expected (5.6) ratio (standard incidence ratio) for primary lung cancer compared to the US population was 6.5 (4.5 to 8.9, 95% confidence interval).

CONCLUSIONS

Our data indicate a 6.5-fold increased incidence of primary lung cancer in HIV- and AIDS-infected patients. We present the results of our study, a review of the work of other investigators, and address a potentially even greater public health problem in the HIV/AIDS population than previously realized.

The role of interleukin-2 in combination adenovirus gene therapy for head and neck cancer

Interleukin-2 (IL-2) gene therapy alone and in combination with the herpes thymidine kinase gene (tk) was used to evaluate immunological responses and antitumor effects in head and neck cancer. Established floor of mouth squamous cell carcinomas in C3H/HeJ mice were directly injected with recombinant adenoviral vectors carrying both therapeutic and control genes. One week after adenoviral gene transfer, only the animals treated with combination IL-2+tk or tk alone demonstrated significant tumor regression. Residual tumors were harvested for microscopic evaluation and immunohistochemistry staining, which revealed a predominance of CD8+ lymphocytes in the tumor beds of the animals treated with IL-2. To evaluate the systemic immune effects of IL-2, animals treated with single or combination gene therapy received a second site challenge with parental tumor cells or a heterologous but syngeneic sarcoma cell line. Mice treated with combination IL-2 and tk demonstrated a protective systemic immunity specific to the parental tumor cell line, whereas no systemic immune response was evident in mice receiving IL-2 alone. In a separate experiment, a range of concentrations of the adenovirus IL-2 vector were used to treat established tumors. Even with the maximal single-dose adenovirus concentration, IL-2 alone was ineffective as a single therapy. These results support the use of adenovirus-mediated gene transfer of IL-2 as an effective immunotherapy when used adjuvantly with the tk "suicide gene".

Antiviral activity of biological response modifiers in a murine model of AIDS. Requirement for augmentation of natural killer cell activity and synergy with oral AZT

We employed the Rauscher murine leukemia virus (RMuLV) as a murine retrovirus model of AIDS, to test biological response modifiers (BRM) and antiviral agents for potential therapeutic activity against the human immunodeficiency virus (HIV). We examined the relationship between the augmentation of natural killer (NK) cell activity and antiviral efficacy of a series of BRM, most of which are known inducers of interferon, in this model. Poly [I,C]-LC, MVE-2, and CL 246,738, but not Ampligen, soluble glucan, or 7-thia-8-oxoguanosine, consistently produced antiviral activity. In addition, the combination of suboptimal doses of oral 3'-azido-3'-deoxythymidine (AZT) (in drinking water) and poly [I,C]-LC produced a synergistic antiviral effect. With all the BRM tested, a consistent pattern emerged, namely that antiviral activity always correlated with the augmentation of splenic NK cell activity in infected animals. For instance, poly [I,C]-LC boosted NK activity much more in infected mice treated therapeutically (treatment initiated after infection) than prophylactically (treatment initiated before infection), and it had greater antiviral activity therapeutically than prophylactically. For the BRM tested, antiviral activity did not occur without augmentation of NK activity in infected mice. In contrast, augmentation of NK activity in uninfected mice bore no relationship to antiviral activity. Furthermore, elimination of NK cells by treating mice with anti-asialo GM1 abolished the antiviral activity of poly [I,C]-LC. Although splenic NK activity was ablated by anti-asialo GM1, serum interferon levels were not affected by this treatment. These results point to a causal connection between the augmentation of NK cell activity and the antiviral efficacy of these BRM in this murine AIDS model. NK cells thus appear to play a key role in resistance to this retrovirus, as has been suggested for HIV.