Effect of imiquimod as an adjuvant for immunotherapy of genital HSV in guinea-pigs

Novel Adjuvant S-540956 Targets Lymph Nodes and Reduces Genital Recurrences and Vaginal Shedding of HSV-2 DNA When Administered with HSV-2 Glycoprotein D as a Therapeutic Vaccine in Guinea Pigs

Herpes simplex virus type 2 (HSV-2) is a leading cause of genital ulcer disease and a major risk factor for acquisition and transmission of HIV. Frequent recurrent genital lesions and concerns about transmitting infection to intimate partners affect the quality of life of infected individuals. Therapeutic vaccines are urgently needed to reduce the frequency of genital lesions and transmission. S-540956 is a novel vaccine adjuvant that contains CpG oligonucleotide ODN2006 annealed to its complementary sequence and conjugated to a lipid that targets the adjuvant to lymph nodes. Our primary goal was to compare S-540956 administered with HSV-2 glycoprotein D (gD2) with no treatment in a guinea pig model of recurrent genital herpes (studies 1 and 2). Our secondary goals were to compare S-540956 with oligonucleotide ODN2006 (study1) or glucopyranosyl lipid A in a stable oil-in-water nano-emulsion (GLA-SE) (study 2). gD2/S-540956 reduced the number of days with recurrent genital lesions by 56%, vaginal shedding of HSV-2 DNA by 49%, and both combined by 54% compared to PBS, and was more efficacious than the two other adjuvants. Our results indicate that S-540956 has great potential as an adjuvant for a therapeutic vaccine for genital herpes, and merits further evaluation with the addition of potent T cell immunogens.

Successful application of prime and pull strategy for a therapeutic HSV vaccine

One promising approach for a herpes simplex virus vaccine uses a vaccine to prime and a chemoattractant to pull immune cells into the genital tract. We evaluated subunit vaccines (prime) and imiquimod (pull) in the guinea pig (gp) model of recurrent Herpes simplex virus type-2 (HSV-2). Following vaginal HSV-2 infection, gps were vaccinated with various combination of glycoproteins and adjuvant with or without subcutaneous or local applications of imiquimod after infection. Animals were examined daily for recurrent lesions and vaginal swabs collected for recurrent shedding. Although both the vaccines alone and imiquimod alone reduced recurrent HSV disease, the combination of local imiquimod and vaccine (Prime and Pull) was the most effective. In the first study, immunization with the trivalent vaccine alone or imiquimod alone decreased recurrent disease. However, the largest decrease was with the combination of vaccine and local imiquimod (P < 0.001 vs. placebo or vaccine alone). No effect on recurrent shedding was observed. In the second study, recurrent disease scores were similar in the PBS control group and the trivalent-immunized group treated with subcutaneous imiquimod however, significant reductions with glycoprotein vaccines and local imiquimod (p < 0.01 vs. placebo) were noted. The number of qPCR-positive recurrent swabs, ranged from 5 to 11% in the vaccinated+local imiquimod groups compared 29% in the PBS control group (P < 0.05). No recurrent swab samples from vaccinated groups were culture positive. We conclude that the strategy of prime (subunit HSV vaccine) and topical pull (intravaginal/topical imiquimod) decreased recurrent HSV more effectively than vaccine alone.

“Prime and pull” vaccination strategies involve an initial vaccination followed by the local application of a stimulant such as chemokines to recruit immune cells to infection target areas such as the mucosa. David Bernstein and colleagues investigate the efficacy of a prime and pull approach in a guinea pig model of recurrent genital Herpes simplex virus 2 (HSV-2) infection. Animals were vaccinated with HSV-2 glycoproteins in adjuvant with or without subcutaneous or topical (vaginal) exposure to the immune stimulant imiquimod to act as the “pull”. Animals with topical imiquimod show superior control of HSV-2 infection and improved recruitment of CD8⁺ T cells to the vaginal epithelium. Topical application of imiquimod demonstrates better control than subcutaneous imiquimod suggesting that “pulling” might be a useful approach in HSV vaccination.

Topical SMIP-7.7, a toll-like receptor 7 agonist, protects against genital herpes simplex virus type-2 disease in the guinea pig model of genital herpes

BACKGROUND

Development of more effective therapies for genital herpes simplex virus type-2 (HSV-2) infections remains a priority. The toll-like receptors (TLR) are attractive targets for the immunomodulation of primary and recurrent genital herpes infection. The guinea pig model of genital HSV-2 disease was therefore used to evaluate the efficacy of a new TLR-7 agonist, SMIP-7.7.

METHODS

The effects of SMIP-7.7 at concentrations between 0.90% and 0.09% were compared to the vehicle control or Aldara(®) (3M Health Care Limited, Northridge, CA, USA) as treatment for genital HSV-2 infections. Following intravaginal inoculation of Hartley guinea pigs with 10(6) pfu HSV-2 (MS strain), animals were treated intravaginally beginning at 36 h post-infection. Animals were evaluated for acute disease, acute virus replication, recurrent disease and shedding, as well as infection of the dorsal root ganglia.

RESULTS

Treatment with SMIP-7.7 significantly decreased mean total lesion scores during primary infection (all doses, P<0.01 compared with vehicle control, and similar to Aldara(®)). Vaginal virus titres were reduced in treated animals compared with vehicle control (P<0.001 for each treatment versus vehicle control on day 4). Treatment with SMIP-7.7 also significantly decreased the number of recurrent lesion days, the number of days with recurrent virus shedding and the infection of the dorsal root ganglia compared to the vehicle control, and was similar to Aldara(®). As opposed to Aldara(®), SMIP-7.7 did not induce fever or weight loss during treatment.

CONCLUSIONS

SMIP-7.7 improves the outcome of primary and recurrent HSV-2 disease comparable to Aldara(®) but without some of the side effects associated with Aldara(®).

Long-term remission of recurrent herpes labialis following topical imiquimod application on distant healthy skin: a clinical and immunological study

BACKGROUND

Given the limitations of current antiviral therapies, safer and more effective approaches to the management of recurrent herpes labialis (RHL) are needed.

METHODS

A patient with a 23-year history of RHL and 14 healthy individuals were studied. The patient applied imiquimod to distant healthy skin for 3 weeks. Peripheral blood (PB) samples were collected from the patient during treatment and 21 months after its discontinuation; samples were collected from the controls once. The distribution of lymphocyte populations in PB were analysed by flow cytometry and PB cytokine levels were measured using cytometric bead arrays.

RESULTS

The patient showed long-term remission of the disorder subsequent to a 3-week imiquimod application to distant healthy skin. Imiquimod treatment induced the activation and proliferation of T-helper and cytotoxic T-cells, B-cells and T-regulatory cells. In addition, there was a very strong transient increase of T-helper 1 cells (resulting in interferon-γ secretion) and type 1 (pro-inflammatory) polarization of the immune response accompanied by a sustainable interferon-α production. At follow-up 21 months after treatment cessation, with the patient remaining relapse-free, the patient had control levels of all cytokines, increased levels of activated cytotoxic T-cells, continuous production of new T-helper cells and B-cells and near-to-normal levels of T-regulatory cells.

CONCLUSIONS

Our results indicate that topical application of imiquimod to healthy skin is capable of causing systemic immunomodulation. This treatment might represent a new and effective alternative to established therapeutic and prophylactic regimens for RHL.

Sensing herpes: more than toll

To launch an effective antiviral immune response, cells must recognize the virus, activate a cytokine response, and initiate inflammatory processes. Herpes simplex virus 1 (HSV-1) and HSV-2 are nuclear-replicating viruses composed of a double-stranded DNA genome plus glycoproteins that are incorporated into a lipid bilayer envelope that surrounds an icosahedral capsid. Several novel receptors that mediate innate recognition of HSV and that activate the innate immune response have been identified in recent years. The host-virus interactions that lead to type I interferon (IFN), type III IFN, and cytokine production include cellular recognition of viral envelope and structural proteins, recognition of viral genomic DNA and recognition of virus-derived double-stranded RNAs. Such RNAs can interact with cellular pattern-recognition receptors, including Toll-like receptors and a number of cytoplasmic and nuclear receptors for virus DNA and virus-derived RNAs. In this review, I present a systematic overview of innate cellular recognition of HSV infection that leads to immune activation, and I discuss the implications of the known cell-host interactions. In addition, I discuss the use of innate stimulation to improve anti-HSV treatment and vaccine response and I discuss future research aims.

Intranasal delivery of Norwalk virus-like particles formulated in an in situ gelling, dry powder vaccine

The development of a vaccine to prevent norovirus infections has been focused on immunization at a mucosal surface, but has been limited by the low immunogenicity of self-assembling Norwalk virus-like particles (NV VLPs) delivered enterically or at nasal surfaces. Nasal immunization, which offers the advantage of ease of immunization, faces obstacles imposed by the normal process of mucociliary clearance, which limits residence time of applied antigens. Herein, we describe the use of a dry powder formulation (GelVac) of an inert in situ gelling polysaccharide (GelSite) extracted from Aloe vera for nasal delivery of NV VLP antigen. Powder formulations, with or without NV VLP antigen, were similar in structure in dry form or when rehydrated in simulated nasal fluids. Immunogenicity of the dry powder VLP formulation was compared to equivalent antigen/adjuvant liquid formulations in animals. For the GelVac powder, we observed superior NV-specific serum and mucosal (aerodigestive and reproductive tracts) antibody responses relative to liquid formulations. Incorporation of the TLR7 agonist gardiquimod in dry powder formulations did not enhance antibody responses, although its inclusion in liquid formulations did enhance VLP immunogenicity irrespective of the presence or absence of GelSite. We interpret these data as showing that GelSite-based dry powder formulations (1) stabilize the immunogenic structural properties of VLPs and (2) induce systemic and mucosal antibody titers which are equal or greater than those achieved by VLPs plus adjuvant in a liquid formulation. We conclude that in situ gelation of the GelVac dry powder formulation at nasal mucosal surfaces delays mucociliary clearance and thereby prolongs VLP antigen exposure to immune effector sites.

Mucosal treatments for herpes simplex virus: insights on targeted immunoprophylaxis and therapy

Herpes simplex virus (HSV) serotypes 1 and 2 establish lifelong infections that can produce reactivated pools of virus at mucosal sites where primary infections were initiated. No approved vaccines are available. To break the transmission cycle, interventions must either prevent infection or reduce infectivity at mucosal sites. This article discusses the recent experimental successes of immunoprophylactic and therapeutic compounds that enhance resistance and/or reduce viral loads at genital and ocular mucosa. Current data indicate Toll-like receptor agonists and selected immunomodulating compounds effectively increase the HSV infection threshold and hold promise for genital prophylaxis. Similarly, immunization at genital and extragenital mucosal sites is discussed. Finally, preclinical success with novel immunotherapies for ocular HSV that address herpetic keratitis and corneal blindness is reviewed.

Imiquimod: mode of action

OBJECTIVE

Since imiquimod, a nucleoside analogue of the imidazoquinoline family, has shown efficacy against many tumour entities, its mode of action has become a focus of scientific interest.

RESULTS

The major biologic effects of imiquimod are mediated through agonistic activity towards toll-like receptors (TLR) 7 and 8, and consecutively, activation of nuclear factor-kappa B (NF-kappaB). The result of this activity is the induction of pro-inflammatory cytokines, chemokines and other mediators leading to activation of antigen-presenting cells and other components of innate immunity and, eventually, the mounting of a profound T-helper (Th1)-weighted antitumoral cellular immune response. Several secondary effects on the molecular and cellular level may also be explained, at least in part, by the activation of NF-kappaB. Moreover, independent of TLR-7 and TLR-8, imiquimod appears to interfere with adenosine receptor signalling pathways, and the compound causes receptor-independent reduction of adenylyl cyclase activity. This novel mechanism may augment the pro-inflammatory activity of the compound through suppression of a negative regulatory feedback mechanism which normally limits inflammatory responses. Finally, imiquimod induces apoptosis of tumour cells at higher concentrations. The pro-apoptotic activity of imiquimod involves caspase activation and appears to depend on B cell lymphoma/leukemia protein (Bcl)-2 proteins.

CONCLUSIONS

Overall, imiquimod acts on several levels, which appear to synergistically underlie the profound antitumoral activity of the compound.

TLR7 and TLR8 as targets in cancer therapy

Small-molecule agonists at Toll-like receptor 7 (TLR7) and TLR8 have sparked a vivid interest in cancer research owing to their profound antitumoral activity. The lead compound of the imidazoquinoline family, imiquimod, is marketed as a topical formulation. It is efficacious against many primary skin tumors and cutaneous metastases. Using different imidazoquinoline species, distinct functions of TLR7 and TLR8 have been discovered. The predominant antitumoral mode of action of these agents is TLR7/8-mediated activation of the central transcription factor nuclear factor-kappaB, which leads to induction of proinflammatory cytokines and other mediators. Cutaneous dendritic cells are the primary responsive cell type and initiate a strong Th1-weighted antitumoral cellular immune response. Recent research has shown that dendritic cells themselves acquire direct antitumoral activity upon stimulation by imiquimod. In addition, there are a number of secondary effects on the molecular and cellular level that can be explained through the activation of TLR7/8. The proinflammatory activity of imiquimod, but not resiquimod, appears to be augmented by suppression of a regulatory mechanism, which normally limits inflammatory responses. This is achieved independently of TLR7/8 through interference with adenosine receptor signaling pathways. Finally, at higher concentrations imiquimod exerts Bcl-2- and caspase-dependent proapoptotic activity against tumor cells.

Immune-mediated changes in actinic keratosis following topical treatment with imiquimod 5% cream

Background

The objective of this study was to identify the molecular processes responsible for the anti-lesional activity of imiquimod in subjects with actinic keratosis using global gene expression profiling.

Methods

A double-blind, placebo-controlled, randomized study was conducted to evaluate gene expression changes in actinic keratosis treated with imiquimod 5% cream. Male subjects (N = 17) with ≥ 5 actinic keratosis on the scalp applied placebo cream or imiquimod 3 times a week on nonconsecutive days for 4 weeks. To elucidate the molecular processes involved in actinic keratosis lesion regression by imiquimod, gene expression analysis using oligonucleotide arrays and real time reverse transcriptase polymerase chain reaction were performed on shave biopsies of lesions taken before and after treatment.

Results

Imiquimod modulated the expression of a large number of genes important in both the innate and adaptive immune response, including increased expression of interferon-inducible genes with known antiviral, anti-proliferative and immune modulatory activity, as well as various Toll-like receptors. In addition, imiquimod increased the expression of genes associated with activation of macrophages, dendritic cells, cytotoxic T cells, and natural killer cells, as well as activation of apoptotic pathways.

Conclusion

Data suggest that topical application of imiquimod stimulates cells in the skin to secrete cytokines and chemokines that lead to inflammatory cell influx into the lesions and subsequent apoptotic and immune cell-mediated destruction of lesions.

The small-molecule immune response modifier imiquimod – its mode of action and clinical use in the treatment of skin cancer

Due to its good clinical efficacy against malignant skin tumours, the topical immune response modifier, imiquimod, has attracted much interest among researchers and clinicians alike. Imiquimod exerts its antitumoural effect, at least in part, through agonistic stimulation of TLR-7 and TLR-8 on dendritic cells, followed by NF-kappaB-dependent secretion of a multitude of pro-inflammatory cytokines. The net result of this pro-inflammatory activity is a profound tumour-directed cellular immune response. Recent research has revealed an additional mode of action inasmuch as imiquimod interferes with adenosine receptor signalling, even in TLR-7- and TLR-8-negative cells, thereby presumably augmenting inflammatory signalling cascades. Moreover, at higher concentrations imiquimod also exerts direct proapoptotic activity against tumour cells. This mode of action appears to be independent of membrane-bound death receptors but is mediated, at least in part, through Bcl-2-dependent release of mitochondrial cytochrome c and subsequent caspase activation. Overall, a combination of several complementary antitumoural modes of action appears to underlie the great utility of imiquimod for treating cutaneous tumours.

Imiquimod and resiquimod in a mouse model: adjuvants for DNA vaccination by particle-mediated immunotherapeutic delivery

Imiquimod, an immune response modifier and inducer of cytokines in vitro and in vivo, has been shown to have potent antiviral and antitumour activity and to act as an adjuvant for protein vaccination. We have undertaken studies in mice to investigate the potential of imiquimod and resiquimod to adjuvant DNA vaccination. These imidazoquinolines were administered by subcutaneous injection at the vaccination site immediately after particle-mediated immunotherapeutic delivery of plasmid DNA using a gene gun. Imiquimod was found to increase the number and maturation status of dendritic cells in draining lymph nodes, and to enhance antigen-specific CD4(+) and CD8(+) T cell responses, as assessed by analyses of clonal expansion, and the quantity and kinetics of cytokine production from these cells in lymph nodes and spleens collected after vaccination. A more substantial increase in IFN-gamma-producing, compared with IL-4-producing CD4(+) T cells suggested that imiquimod biased the immune response towards a predominance of Th1 cells. The analogue resiquimod was found to be to produce a similar Th1 biased immune response with a 10-fold reduced dose compared with imiquimod. Collectively, these studies suggest that both imiquimod and resiquimod may be suitable adjuvants for therapeutic DNA vaccines requiring induction of potent cytotoxic T cell responses.

Tumor-selective induction of apoptosis and the small-molecule immune response modifier imiquimod

BACKGROUND

The incidence of nonmelanoma skin cancer, basal cell carcinomas (BCCs), and squamous cell carcinomas (SCCs) is increasing, representing a major medical and economic problem. Imiquimod, a topical small-molecule immune response modifier, has shown efficacy toward BCC and actinic keratoses in clinical trials. Imiquimod acts both indirectly, via cytokine-mediated stimulation of cellular immune responses, and directly, through unknown mechanisms against tumor cells. We examined the mechanism by which imiquimod induces apoptosis in cancer cells.

METHODS

Apoptosis was assessed by enzyme-linked immunosorbent assay, western blot analysis, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays in five SCC cell lines, HaCaT cells (a spontaneously immortalized human keratinocyte cell line), and normal keratinocytes treated with imiquimod, with its analog resiquimod, or with neither. Expression of death receptors, caspases, and cytochrome c in the apoptotic signaling cascade was analyzed using western blot and flow cytometric analyses. The functional relevance of imiquimod-induced cytochrome c release was assessed by transfection of HaCaT cells with Bcl-2. Apoptosis in BCCs in vivo was assessed by TUNEL assays of imiquimod-treated and untreated tumors from three patients. Differences between treated and untreated cells and tumors were determined using a two-tailed Student's t test.

RESULTS

Imiquimod, but not resiquimod, induced apoptosis in all SCC cell lines and HaCaT cells. This induction involved activation of several caspases and Bcl-2-dependent cytosolic translocation of cytochrome c but was independent of the membrane-bound death receptors Fas, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-R1-R4 receptors, and tumor necrosis factor-R1 and -R2 receptors. Topical application of imiquimod to BCC tumors in vivo induced apoptosis.

CONCLUSION

Imiquimod has the potential to induce apoptosis in skin cancer cells, possibly by circumventing mechanisms developed by malignant tumors to resist apoptotic signals.

The imidazoquinolines and their place in the therapy of cutaneous disease

The imidazoquinolines arose from efforts to develop a nucleoside analogue. Although molecularly similar to nucleosides, the imidazoquinolines did not have nucleoside-like activity. However, the imidazoquinolines induced immune modulatory cytokines, in part, because of their ability to activate toll receptors (TLR)s. Imiquimod, the first FDA-approved imidazoquinoline, has been marketed as a 5% cream, which is approved for the therapy of genital warts. The advantage of imiquimod therapy over other therapies for genital warts is the decrease in recurrence rate with the establishment of an adaptive immunological response or immunological memory/surveillance response. As tumours and viral infections are handled similarly by the immune system, there has been great interest in the use of topical imiquimod for the treatment of cutaneous neoplasms, particularly non-melanoma skin cancers. Future efforts in imidazoquinoline research is focused around the development of analogues with modifications in the immunological profiles, potency and penetration parameters that better focus these new analogues for the therapy of specific intracellular infections and neoplasms, as well as the development of imidazoquinolines for conditions related either directly or indirectly to patterns of immune dysregulation.

Treatment of anogenital warts with imiquimod 5% cream followed by surgical excision of residual lesions

Cytodestructive or surgical therapy for patients with anogenital warts is frequently associated with recurrence. In February 1997, the US Food and Drug Administration approved imiquimod as a 5% cream for the treatment of anogenital warts. Activity of the drug results primarily from interferon alfa and other cytokine induction in the skin. These cytokines stimulate several other aspects of the innate immune response. In addition, imiquimod stimulates acquired immunity, in particular the cellular arm that is important for control of viral infections and tumors. Published studies indicate that imiquimod results in complete clearance of warts in more than 50% of patients. Residual warts can be surgically excised. Our long-term follow-up (ie, 2 to 7 years) of patients who had a 16-week course of imiquimod cream with subsequent removal of remaining warts showed a much lower rate of recurrence in comparison with those patients who were treated with surgery alone. Therefore, treatment with imiquimod followed by excision of residual lesions may provide long-term clearance of anogenital warts in those patients in whom imiquimod monotherapy is insufficient.

Immunomodulation as a treatment strategy for genital herpes: review of the evidence

In this review, we discuss the ongoing development of a new treatment option for genital herpes (GH), the disease caused by herpes simplex virus (HSV) types I and II. Following infection, the virus establishes a latent infection in peripheral neurons, which periodically activates to cause recurrent skin lesions or asymptomatic shedding in the anogenital area. A new class of drugs, the immune response modifiers (IRMs), modulates the immune system against viral infection. This approach is currently being tested as a treatment for GH. We first review the effectiveness of treatment of other viral diseases with imiquimod, the first IRM to be licensed (Aldara, imiquimod 5% cream), and one used for the treatment of external anogenital warts. We then focus on resiquimod, an analog of imiquimod, which shows early promise as a new treatment option for GH. The evidence from in vitro and in vivo studies, in particular the guinea pig model of GH, describing the effectiveness and mode of action of this novel immunopharmacological agent is presented. Resiquimod stimulates specific cells of the innate immune system (including monocytes/macrophages, dendritic cells (DC) and B lymphocytes) to produce cytokines (in particular IFN-alpha, IL-12, TNF-alpha and IFN-gamma) that initiate and drive the development of the Th1 acquired immune response against HSV-infected cells. Recent results from clinical trials and in vivo studies in animal models are consistent with the hypothesis that the development of HSV-specific cell-mediated immunity may prove to be the key in providing a long-lasting protection against GH recurrences.

Reduction of recurrent HSV disease using imiquimod alone or combined with a glycoprotein vaccine

The aim of this study is to evaluate the effects of an immune modulator, imiquimod, given alone or in combination with an HSV vaccine on HSV immune responses and as immunotherapy of a genital recurrence model. After recovery from primary genital HSV infection, animals were randomized to placebo, 21 days of imiquimod plus a placebo vaccine, or 21 days of imiquimod plus an HSV-2 glycoprotein vaccine. Placebo or HSV vaccine was given in the footpad on days 16 and 37 after HSV-2 genital inoculation. Daily imiquimod or placebo was given subcutaneously in the shoulder on days 16 through 37. Genital recurrences were monitored and HSV specific NK activity, IL-2 response and ELISA antibody were assayed. For the entire 15 week observation period, imiquimod alone reduced recurrences 62.6%, while addition of HSV vaccine to imiquimod reduced recurrences 80.6% compared to placebo/placebo. The duration of significant recurrence reduction was more notable with the addition of vaccine. Imiquimod alone significantly reduced the weekly HSV recurrent disease in the first 10 weeks (53-94% reduction, mean 75.9%), as did imiquimod plus HSV-vaccine (71-98% reduction, mean 89.5%). In weeks 10-15, imiquimod alone reduced recurrences significantly only in week 10 (20-53% reduction, mean 33%), whereas the addition of vaccine extended the significant recurrence reduction to 14 weeks (44-71% reduction, mean 56.8%). The recurrence reduction is correlated to an increased HSV-induced in vitro IL-2 response and NK activity against HSV targets in treated groups. Both imiquimod and the imiquimod/vaccine combination significantly reduced genital HSV recurrences, but the combination extended the duration and extent of protection for recurrences compared to imiquimod alone. Enhanced HSV specific immune responses correlated to the protection.

Molecular mechanisms of B lymphocyte activation by the immune response modifier R-848

The imidazoquinoline R-848, originally identified as a highly effective antiviral agent, has recently been shown to be capable of potent B lymphocyte activation. The B cell-activating properties of R-848 are strikingly similar to the effects of the CD40 ligand CD154. The present study demonstrates that this similarity extends to the intracellular signaling pathways triggered by the compound, although both overlapping and distinct mechanisms of signaling were seen. Like CD40 ligation, R-848 stimulated activation of the stress-activated protein kinases c-Jun kinase and p38 and activated the NF-kappaB family of transcription factors. Both R-848- and CD40-mediated B cell differentiation were dependent upon NF-kappaB activation, although the relative importance of individual NF-kappaB family members appeared to differ between R-848- and CD40-mediated signals. Both signals were partially dependent upon induction of TNF-alpha and IL-6, and the cytoplasmic adaptor molecule TNF receptor-associated factor 2 is involved in both R-848- and CD40-mediated differentiation.

Adjuvant activities of immune response modifier R-848: comparison with CpG ODN

R-848 and imiquimod belong to a class of immune response modifiers that are potent inducers of cytokines, including IFN-alpha, TNF-alpha, IL-12, and IFN-gamma. Many of these cytokines can affect the acquired immune response. This study examines the effects of R-848 on aspects of acquired immunity, including immunoglobulin secretion, in vivo cytokine production, and Ag-specific T cell cytokine production. Results are compared with those of Th1 CpG ODN. R-848 and CpG ODN are effective at skewing immunity in the presence of Alum toward a Th1 Ab response (IgG2a) and away from a Th2 Ab response (IgE). R-848 and CpG ODN are also capable of initiating an immune response in the absence of additional adjuvant by specifically enhancing IgG2a levels. Both R-848 and imiquimod showed activity when given subcutaneously or orally, indicating that the compound mechanism was not through generation of a depot effect. Although CpG ODN behaves similarly to R-848, CpG ODN has a distinct cytokine profile, is more effective than R-848 when given with Alum in the priming dose, and is active only when given by the same route as the Ag. The mechanism of R-848's adjuvant activity is linked to cytokine production, where increases in IgG2a levels are associated with IFN-alpha, TNF-alpha, IL-12, and IFN-gamma induction, and decreases in IgE levels are associated with IFN-alpha and TNF-alpha. Imiquimod also enhances IgG2a production when given with Ag. The above results suggest that the imidazoquinolines R-848 and imiquimod may be attractive compounds for use as vaccine adjuvants and in inhibiting pathological responses mediated by Th2 cytokines.

The immune response modifiers imiquimod and R-848 are potent activators of B lymphocytes

Imiquimod and R-848 are members of a family of immune response modifiers that stimulate cytokine production in monocyte/macrophages and dendritic cell cultures. This study evaluated the effects of the imidazoquinolines, imiquimod and R-848, on B lymphocyte activation. Both agents induced proliferation of murine T-cell-depleted and highly purified splenic B cell preparations as well as purified human B cells. Resting and activated B cells responded to these agents, with activated cells responding more efficiently. B cells from the LPS-hyporesponsive C3H/HeJ mice and guanosine-hyporesponsive SJL mice proliferated in response to imiquimod and R-848, indicating a different mechanism of action than lipopolysaccharide and guanine nucleosides. B cells were also stimulated by imiquimod and R-848 to produce increased immunoglobulin levels. Increased expression of a number of B cell activation markers were seen following imiquimod or R-848 stimulation. Finally, R-848 was shown to act as a vaccine adjuvant enhancing OVA-specific IgG2a levels while suppressing total IgE. These results indicate that R-848 and imiquimod are potent activators of B lymphocytes and are capable of augmenting antigen-specific immunoglobulin production.

Immunomodulatory and pharmacologic properties of imiquimod

Imiquimod, an imidazoquinoline amine, is an immune response modifier recently approved for the topical treatment of external genital and perianal warts. Although the majority of immunomodulatory agents available or in development inhibit pathways involved in immune activation, imiquimod is unique in that it activates immune function. The exact mechanism of imiquimod's antiviral activity is unknown; however, its effects are likely to be related to its immunomodulating properties. Although in vitro studies have shown that imiquimod has no direct antiviral effects, the drug does exhibit antiviral and antitumor effects in vivo through induction of cytokines and enhancement of cell-mediated cytolytic antiviral activity. Imiquimod stimulates the innate immune response through induction of cytokines, and the cellular arm of acquired immunity through induction of interferon-alpha (IFN-alpha), IFN-gamma, and interleukin-12. Results from animal studies have indicated a possible use for imiquimod in the prevention and treatment of herpes simplex virus infection. In addition, recent studies demonstrated that imiquimod activates Langerhans' cells and enhances allergic contact hypersensitivity.

The inhibitory effect of the imidazoquinolinamine S-28828 on the pathogenesis of a type II adenovirus in turkeys

In this study we show that a type I-IFN inducing compound, S-28828, modulated the pathogenesis of an avian type II adenovirus in turkeys. By itself, S-28828 induced a strong reaction in the spleen characterized by hyperplasia of the red and white pulps as well as an increase in lymphoid cell aggregations. Oral administration of S-28828 before the time of virus inoculation suppressed significantly (P<0.05) the replication of hemorrhagic enteritis virus (HEV) in turkeys. Two doses of 5 or 50 mg of S-28828 administered at 2 days before and at the day of virus inoculation inhibited HEV-induced pathological and histopathological lesions. Virus-induced apoptosis and reduced IgM-surface expression of B cells were suppressed by low dose S-28828 treatment. These results are of interest because mammalian adenoviruses were shown to be resistant to antiviral effects of type I IFN, the major effector cytokine induced by S-28828.

Treatment of primary herpes simplex virus infection in guinea pigs by imiquimod

Imiquimod (also known as R-837 and S-26308) is an imidazoquinoline immune response modifier and is available in the US and several other countries for the treatment of external genital warts. Imiquimod has no direct antiviral activity but demonstrates efficacy in several animal models of virus infection. The drug is recognized by antigen presenting cells including monocytes, macrophages, B-cells and dendritic cells and induces these cells to produce cytokines including interferon-alpha (IFN-alpha) and others. Imiquimod's ability to inhibit primary lesion development in the guinea pig model of Herpes simplex virus (HSV) intravaginal infection was studied. Imiquimod given intravaginally reduced primary lesions, reduced virus shedding and reduced virus content of spinal cords from HSV infected guinea pigs. A single drug application of 0.5 mg/kg reduced lesion frequency when given between 24 h before inoculation to 16 h after inoculation. A single drug application of 5 mg/kg reduced lesion frequency and severity when administered between 72 h before inoculation to 24 h after inoculation. The antiviral effect resulting from interferon induction in the animal lasts much longer than the drug itself, thus imiquimod is different than drugs having direct antiviral activity. Twice daily drug application for 4 days was effective when initiated up to 72 h after inoculation, however, once lesions began to appear, imiquimod treatment was not able to stop lesion development. Imiquimod treatment inhibited lesion development and/or virus shedding in guinea pigs inoculated with HSV-1, HSV-2 or virus isolates resistant to acyclovir. Imiquimod is currently in clinical trials for treating human HSV infections.

Herpes simplex virus vaccines

Herpes simplex virus (HSV) infections are common and produce not only a primary infection, but also latent and recurrent infections. Therefore, the goals of a HSV vaccine are different from other vaccines. In this review, the goals of both prophylactic and therapeutic HSV vaccines are discussed and related to the immunobiology of acute and recurrent HSV infections. Next, the vaccine strategies that have been and are being evaluated for control of HSV disease are described. Current approaches take advantage of many of the modern methodologies for vaccine development. Thus, as we await final evaluations of subunit HSV glycoprotein vaccines, early phase I trails are evaluating newer vaccine approaches including DNA-based vaccines and replication-impaired viruses. The definitive HSV vaccine may await increased knowledge of the optimal viral antigen(s) and routes to induce genital tract immunity.

Modulation of TH1 and TH2 cytokine production with the immune response modifiers, R-848 and imiquimod

Cytokines produced by antigen-presenting cells are known to affect the development and cytokine profile of T cells. The immune response modifiers imiquimod and R-848 were previously shown to stimulate human and mouse cultures to secrete interferon-alpha. Results from the present study demonstrate that R-848 and imiquimod are capable of inducing interleukin-12 and interferon-gamma in mouse and human cell cultures. Both CD4(+) and CD8(+) T lymphocytes were responsible for producing IFN-gamma following stimulation with R-848. Macrophages were required for induction of interferon-gamma by R-848 and the cytokines IFN-alpha and IL-12 mediated this response. R-848 and imiquimod were also found to inhibit IL-4 and IL-5 production in mouse and human culture systems. The inhibition of IL-5 in response to R-848 is seen in cultures containing CD4(+) lymphocytes and macrophages and is mediated in part by IFN-alpha. These data suggest that imiquimod and R-848 may have clinical utility in diseases where cell-mediated immune responses are important and in diseases associated with overexpression of IL-4 or IL-5 such as atopic disease.

Imiquimod applied topically: a novel immune response modifier and new class of drug

Imiquimod (S-26308, R-837) (1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4 amine), an immune response modifier, demonstrates potent antiviral and antitumor activity in animal models (see structure in Fig. 1). The drug exhibits no direct antiviral or antiproliferative activity when tested in a number of cell culture systems. Imiquimod's activity was discovered while screening for anti-herpes virus activity. One of the first analogs in the series, S-25059 was tested in the early 1980's and due to slight toxicity, caused slightly reduced herpes cytopathology in Vero cell cultures. Follow-up testing in herpes infected guinea pigs showed complete protection toward lesion development. Activity of these drugs results primarily from interferon alpha (IFN-alpha) induction and other cytokine induction. At least part of the cytokine induction is mediated through NF-kappaB activation. These cytokines stimulate several other aspects of the innate immune response. In addition, imiquimod stimulates acquired immunity, in particular the cellular arm which is important for control of viral infections and various tumors. This effect is mediated by drug induced IFN-alpha and Interleukin-12 (IL-12) and IFN-gamma induced by these cytokines. Imiquimod is expected to be effective where exogenous IFN-alpha has shown utility and where enhancement of cell-mediated immunity is needed. The following is a brief review of the preclinical pharmacology of imiquimod and the clinical results of genital wart trials. The mechanism of action of topically applied imiquimod will likely lead to benefits in several other chronic virus infections and tumors of the skin. Two other reviews on imiquimod that focus mainly on the clinical results have been published (Beutner & Geisse, 1997; Slade, Owens, Tomai & Miller, 1998).

Herpes simplex: evolving concepts

A large body of molecular biologic research has begun to clarify some basic aspects of viral latency and reactivation. The clinical definition of herpes simplex virus infection is expanding, with the recognition that the disease is largely asymptomatic and that most transmission occurs during periods of asymptomatic viral shedding. With this awareness, serologic diagnosis has become increasingly important. New treatment modalities are now available, and other promising treatments are in development.

In vivo and In vitro interferon induction in chickens by S -28828, an imidazoquinolinamine immunoenhancer

Imiquimod and its analogs belonging to a class of imidazoquinolinamines, activate immune system via cytokine induction, and have antitumor and antiviral effects in mammals. In this study, we showed that a related analog, designated S-28828, induced interferon (IFN) and macrophage activating cytokine(s) (macrophage activating factor, MAF) in chickens in vivo, ex vivo, and in vitro. IFN and MAF were detectable in the serum of chickens following oral administration. Serum IFN levels were the highest at 2 h after treatment. Although there was no detectable IFN in sera of chickens at 8, 24, and 48 h after treatment, high levels of interferon inducible enzyme, 2'-5' oligoadenylate synthase (2'5'OAS) were present at these time points. In vitro and ex vivo studies showed that spleen cells, bone marrow (BM) cells, and peripheral blood leukocytes (PBL) were capable of producing IFN and MAF, although spleen cells produced the highest levels. Our results suggest that S-28828 administered orally may be a useful immunoenhancing and antiviral agent for chickens.