Application of a topical immune response modifier, resiquimod gel, to modify the recurrence rate of recurrent genital herpes: a pilot study

Evolution of rational vaccine designs for genital herpes immunotherapy

Immunotherapeutic vaccines have emerged as a novel treatment modality for genital herpes, a sexually transmitted disease mainly caused by herpes simplex virus type 2. The approaches to identify potential vaccine antigens have evolved from classic virus attenuation and characterization of antibody and T cell responses in exposed, but seronegative individuals, to systematic screens for novel T cell antigens. Combined with implementation of novel vaccine concepts revolving around immune evasion and local recruitment of immune effectors, the development of a safe and effective therapeutic vaccine is within reach. Here, we describe the vaccine approaches that currently show promise at clinical and pre-clinical stages and link them to the evolving scientific strategies that led to their identification.

The Imidazoquinoline Toll-Like Receptor-7/8 Agonist Hybrid-2 Potently Induces Cytokine Production by Human Newborn and Adult Leukocytes

Background

Newborns and young infants are at higher risk for infections than adults, and manifest suboptimal vaccine responses, motivating a search for novel immunomodulators and/or vaccine adjuvants effective in early life. In contrast to most TLR agonists (TLRA), TLR8 agonists such as imidazoquinolines (IMQs) induce adult-level Th1-polarizing cytokine production from human neonatal cord blood monocytes and are candidate early life adjuvants. We assessed whether TLR8-activating IMQ congeners may differ in potency and efficacy in inducing neonatal cytokine production in vitro, comparing the novel TLR7/8-activating IMQ analogues Hybrid-2, Meta-amine, and Para-amine to the benchmark IMQ resiquimod (R848).

Methods

TLRA-induced NF-κB activation was measured in TLR-transfected HEK cells. Cytokine production in human newborn cord and adult peripheral blood and in monocyte-derived dendritic cell cultures were measured by ELISA and multiplex assays. X-ray crystallography characterized the interaction of human TLR8 with Hybrid-2.

Results

Hybrid-2 selectively activated both TLR7 and 8 and was more potent than R848 in inducing adult-like levels of TNF-α, and IL-1β. Consistent with its relatively high in vitro activity, crystallographic studies suggest that absence in Hybrid-2 of an ether oxygen of the C2-ethoxymethyl substituent, which can engage in unfavorable electrostatic and/or dipolar interactions with the carbonyl oxygen of Gly572 in human TLR8, may confer greater efficacy and potency compared to R848.

Conclusions

Hybrid-2 is a selective and potent TLR7/8 agonist that is a candidate adjuvant for early life immunization.

Immunomodulator-based enhancement of anti smallpox immune responses

Background

The current live vaccinia virus vaccine used in the prevention of smallpox is contraindicated for millions of immune-compromised individuals. Although vaccination with the current smallpox vaccine produces protective immunity, it might result in mild to serious health complications for some vaccinees. Thus, there is a critical need for the production of a safe virus-free vaccine against smallpox that is available to everyone. For that reason, we investigated the impact of imiquimod and resiquimod (Toll-like receptors agonists), and the codon-usage optimization of the vaccinia virus A27L gene in the enhancement of the immune response, with intent of producing a safe, virus-free DNA vaccine coding for the A27 vaccinia virus protein.

Methods

We analyzed the cellular-immune response by measuring the IFN-γ production of splenocytes by ELISPOT, the humoral-immune responses measuring total IgG and IgG2a/IgG1 ratios by ELISA, and the TH1 and TH2 cytokine profiles by ELISA, in mice immunized with our vaccine formulation.

Results

The proposed vaccine formulation enhanced the A27L vaccine-mediated production of IFN-γ on mouse spleens, and increased the humoral immunity with a TH1-biased response. Also, our vaccine induced a TH1 cytokine milieu, which is important against viral infections.

Conclusion

These results support the efforts to find a new mechanism to enhance an immune response against smallpox, through the implementation of a safe, virus-free DNA vaccination platform.

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(®).

Three phase III randomized controlled trials of topical resiquimod 0.01-percent gel to reduce anogenital herpes recurrences

Resiquimod, a Toll-like receptor 7 and 8 agonist, stimulates production of cytokines that promote an antigen-specific T helper type 1 acquired immune response. Animal and phase II human trials showed posttreatment efficacy in reducing recurrent herpes lesion days and/or time to first recurrence. Three phase III randomized, double-blind, vehicle-controlled trials of topical resiquimod to reduce anogenital herpes recurrences were conducted in healthy adults with ≥4 recurrences within the prior year. Participants applied resiquimod 0.01% gel or vehicle gel 2 times per week for 3 weeks to each recurrence for 12 months. Trials 1 and 2 had 2:1 resiquimod-vehicle randomization. Trial 3 had 1:1:1 randomization for resiquimod and 500 mg valacyclovir orally twice daily for 5 days (RESI-VAL), resiquimod and oral placebo (RESI-PLA), and vehicle and oral placebo (VEH-PLA). The median time to first recurrence was similar for resiquimod and vehicle (trial 1, 60 and 56 days, P=0.7; trial 2, 54 and 48 days, P=0.47; trial 3, 51 [RESI-VAL], 55 [RESI-PLA], and 44 [VEH-PLA] days, P=not significant [NS]). The median time to healing of initial treated recurrence was longer for resiquimod (trial 1, 18 compared to 10 days, P<0.001; trial 2, 19 compared to 13 days, P=0.16; trial 3, 14 [RESI-VAL], 16 [RESI-PLA], and 8 [VEH-PLA] days, P<0.001). In trials 1 and 2, moderate to severe erythema and erosion/ulceration at the application site were more common in resiquimod recipients. In conclusion, no posttreatment efficacy of resiquimod 0.01% gel was observed. Increased application site reactions and initial recurrence healing time are consistent with resiquimod-induced cytokine effects.

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.

Targeting of Toll-like receptors: a decade of progress in combating infectious diseases

Toll-like receptors (TLRs) recognise highly conserved molecular structures, collectively known as pathogen-associated molecular patterns. In the past two decades, development and clinical implementation of TLR ligands-ie, chemically modified synthetic derivatives of naturally occurring ligands and fully synthetic small molecules-have been topics of intense research. Targeted manipulation of TLR signalling has been applied clinically to boost vaccine effectiveness, promote a robust T helper 1-predominant immune response against viral infection, or dampen the exaggerated inflammatory response to bacterial infection. Use of these new therapeutic molecules as adjuncts to conventional pharmacotherapy or stand-alone treatments might offer solutions to unmet clinical needs or could replace existing partly effective therapeutic strategies.

Toll-like receptor modulation: a novel therapeutic strategy in cardiovascular disease?

BACKGROUND

Toll-like receptors (TLRs) have been recently recognised as primary receptors in the innate immune system. Apart from initiating a prompt immune response against invading pathogens, TLRs are also considered to be an important link between innate immunity, inflammation and a variety of clinical disorders, including cardiovascular diseases. TLR signalling manipulation with novel drugs could offer important opportunities for cardiovascular disease modification.

OBJECTIVE

To present the latest knowledge supporting the involvement of TLRs in the pathogenesis and progress of cardiovascular diseases and explore the role of TLRs as potential targets for therapeutic intervention in cardiovascular territory.

METHODS

A review of the literature documenting implication of TLR signalling in cardiovascular disorders. Current progress in TLR-targeting drug development and the potential role of such a treatment strategy in cardiovascular disorders are discussed.

CONCLUSIONS

A growing body of evidence supports a role for TLRs in cardiovascular disease initiation and progression. Altering TLR signalling with novel drugs could be a beneficial therapeutic strategy for patients with cardiovascular disorders.

Clinical investigations of Toll-like receptor agonists

BACKGROUND

Toll-like receptors (TLR) represent a family of surface molecules that function as primary sensors of the innate immune system to recognize microbial pathogens. Ligand binding to TLR results in activation of cellular signaling pathways that regulate expression of genes involved in inflammation and immunity.

OBJECTIVE

Use of synthetic TLR ligands (agonists) for treatment and prevention of infectious and neoplastic diseases.

METHODS

Review of literature about clinical investigations of agonists of TLR 4, 7, 8, and 9.

RESULTS/CONCLUSIONS

Imiquimod was the first TLR agonist approved for treatment of anogenital warts, actinic keratosis and superficial basal cell carcinoma in humans. Several other agonists of TLRs 4, 7, 8 and 9 were also shown to be effective for treatment of infections and cancers and, furthermore, were used as adjuvants for vaccination. Based on safety and efficacy of the TLR agonists used to date, applications are likely to increase in the future.

Immunostimulatory activity of Toll-like receptor 8 agonists towards human leucocytes: basic mechanisms and translational opportunities

TLR8 (Toll-like receptor 8) is activated by ssRNAs (single-stranded RNAs) and synthetic imidazoquinoline compounds that resemble purines and have immunostimulatory activity. TLR8 agonists are particularly effective at inducing Th1-polarizing responses from human monocytes and myeloid dendritic cells, with the magnitude of response substantially exceeding that induced by agonists of other TLRs. Mechanisms underlying the remarkable efficacy of TLR8 agonists may include: (i) particularly robust activation of intracellular signalling cascades culminating in nuclear translocation of NF-kappaB (nuclear factor kappaB), (ii) activation of BTK (Bruton's tyrosine kinase), and (iii) the ability of some imidazoquinolines to induce TLR-independent effects via antagonism of adenosine receptors. The strong agonist activities of TLR8 agonists also extend to human neonatal leucocytes, which usually display impaired Th1-polarizing responses to many diverse stimuli including agonists of other TLRs. Their strong Th1-polarizing properties render TLR8 agonists attractive targets of biopharmaceutical development as agents that may induce protective immune responses in diverse populations, including newborns.

Pyrazolopyridines with potent activity against herpesviruses: effects of C5 substituents on antiviral activity

Synthesis of a series of 5-substituted as well as 5,7-disubstituted 3-[2-(cyclopentylamino)-4-pyrimidinyl]-2-phenylpyrazolo[1,5-a]pyridin-7-amines with potent activity against herpes simplex viruses is described. Synthetic approaches allowing for variation of the substitution pattern are outlined and resulting changes in antiviral activity are highlighted. Several compounds with in vitro antiviral activity similar to or better than acyclovir are described.

Resiquimod and other immune response modifiers as vaccine adjuvants

Synthetic immune response modifiers, such as resiquimod, are Toll-like receptor 7 and 8 agonists that act as vaccine adjuvants, enhancing antigen-specific antibody production and skewing immunity towards a Th1 response. These compounds stimulate dendritic cells to secrete cytokines, upregulate costimulatory molecule expression and enhance antigen presentation to T cells. The compounds have demonstrated vaccine adjuvant properties in a number of animal models. The adjuvant effects can be enhanced by measures that allow the drug to stay localized with the vaccine without quickly entering the systemic circulation. Clinical studies demonstrate that topical application of resiquimod and analogs is safe and effective at activating the local immune response. For injection, resiquimod or a similar compound may need to be formulated to allow for local immune activation without induction of systemic cytokines.

Recognition of nucleic acid and nucleic acid analogs by Toll-like receptors 7, 8 and 9

The mammalian immune system senses pathogens through pattern recognition receptors (PRR) and responds with activation. Toll-like receptors (TLRs) that are expressed on immune and non-immune cells play a critical role in this process. As part of the innate immune response, TLRs lead to cellular activation and cytokine production with subsequent initiation of an adaptive immune response. TLR7-9 recognize single-stranded RNA, nucleoside analogs and single-stranded CpG-DNA, respectively, and their activation initiates the immune response against viruses and bacteria. Furthermore, the stimulation of these TLRs may be exploited for adjuvant therapy, vaccination and anti-tumor responses. However, a role in the generation or perpetuation of autoimmune diseases such as systemic lupus erythematosus (SLE) has also been suggested.

Effect of resiquimod 0.01% gel on lesion healing and viral shedding when applied to genital herpes lesions

Resiquimod, a Toll-like receptor 7/8 agonist developed as a topical treatment to decrease recurrences of anogenital herpes, induces proinflammatory cytokines that may delay lesion healing. Adults with frequently recurring anogenital herpes were randomized within 24 h of onset of a recurrence to vehicle or resiquimod 0.01% gel two times per week for 3 weeks. Subjects underwent daily lesion assessments and sampling for herpes simplex virus DNA PCR for 21 days or until investigator-determined healing of lesion(s). Eighty-two subjects with a mean age of 39 +/- 10.5 years and a median of seven recurrences per year were enrolled in the study. The qualifying recurrence was positive by PCR for herpes simplex virus in 68% of subjects. No difference was observed between the vehicle (39 subjects) and resiquimod (43 subjects) groups with respect to time to healing (median of 7.0 days versus median of 6.5 days, respectively; Cox proportional hazard model ratio of 1.229; 95% confidence interval, 0.778 to 1.942; P = 0.376). The distributions of maximum severity scores for any investigator-assessed local skin signs and for subject-assessed local symptoms were similar between treatment groups (P = 0.807 and P = 0.103, respectively). For subjects with at least one positive PCR result, no difference was observed for time to cessation of viral shedding (median of 7 days versus median of 5 days for vehicle and resiquimod groups, respectively; Cox proportional hazard model ratio of 1.471; 95% confidence interval, 0.786 to 2.754; P = 0.227). Application of resiquimod 0.01% two times per week for 3 weeks did not delay the healing of genital herpes lesions or reduce acute viral shedding.

Management of recurrent oral herpes simplex infections

The literature has been reviewed for evidence of the efficacy of antiviral agents in both the prophylaxis and treatment of recurrent oral herpes simplex virus (HSV) infections and discussed by a panel of experts. Emphasis was given to randomized controlled trials. Management of herpes-associated erythema multiforme and Bell palsy were also considered. The evidence suggests that 5% acyclovir (ACV) in the cream base may reduce the duration of lesions if applied early. Recurrent herpes labialis (RHL) and recurrent intraoral HSV infections can be effectively treated with systemic ACV 400 mg 3 times a day or systemic valacyclovir 500 to 1000 mg twice a day for 3 to 5 days (longer in the immunocompromised). RHL in the immunocompetent can be effectively prevented with (1) sunscreen alone (SPF 15 or above), (2) systemic ACV 400 mg 2 to 3 times a day, or (3) systemic valacyclovir 500 to 2000 mg twice a day. Valacyclovir 500 mg twice a day is also effective in suppressing erythema multiforme triggered by HSV. Further studies are needed to compare treatment efficacy between topical penciclovir, docosanol, and ACV cream for RHL.

Imidazo[1,2-a]pyridines with potent activity against herpesviruses

Synthesis of a series of 2-aryl-3-pyrimidyl-imidazo[1,2-a]pyridines with potent activity against herpes simplex viruses is described. Synthetic approaches allowing for variation of the 2-aryl, 3-heteroaryl as well as other imidazopyridine substituents are outlined and resulting effects on antiviral activity are highlighted. Several compounds with in vitro antiviral activity similar or better than acyclovir are described.

Current and future drugs targeting one class of innate immunity receptors: the Toll-like receptors

Innate immunity receptors are germline-encoded receptors that can sense molecular signatures of pathogens and cancer cells. Recent advances in immunology demonstrate the key role of these receptors in inflammation and initiation of subsequent immune responses, including adaptive immunity. Pharmaceutical interest in this field has grown with the retrospective demonstration that some marketed drugs targeting cancer or infectious diseases act via those receptors. In this review, I present an update on the scientific rationale for targeting one class of innate immunity receptor, the Toll-like receptors, and an update on the development status of corresponding drug candidates in infectious diseases, cancer, allergy and vaccines.

[Herpes simplex virus vaccines: perspectives]

PURPOSE

Despite effective antiviral therapy, infection with herpes simplex virus (HSV) is a critical public health issue, particularly genital herpes by its social and psychological burden and its contribution to the neonatal herpes and possibly to the HIV/AIDS pandemic.

CURRENT KNOWLEDGE

Many prophylactic and therapeutic vaccination approaches have been explored but no effective vaccine is presently available. In fact, as members of the Herpesviridae family, both HSV-1 and 2 types have genes involved in immune evasion.

FUTURE PROSPECTS

Further research is needed to define determinants of immunity in order to design more effective vaccines.

Microbial nucleic acids pay a Toll in kidney disease

Nucleic acids provide more than the genetic code that determines the morphological and functional phenotype of microbes and eukaryotes. In fact, nucleic acids have immunomodulatory functions as they are recognized by a set of pattern-recognition receptors that initiate and modulate immune responses in the host. Toll-like receptor (TLR)-3 recognizes double-stranded RNA, TLR7 and TLR8 recognize single-stranded RNA, CpG-DNA is a ligand for TLR9, and all of these TLRs are expressed in the nephritic kidney. In this review, we summarize recent advances in this field and discuss new hypotheses for the pathogenesis of kidney diseases that are triggered by infectious organisms.

Toll-like receptor modulation in cardiovascular disease: a target for intervention?

Toll-like receptors (TLRs) form a family of pattern recognition receptors that have emerged as key mediators of innate immunity. These receptors sense invading microbes and initiate the immune response. TLR-mediated inflammation is an important pathogenic link between innate immunity and a diverse panel of clinical disorders. Among the processes in which TLRs play a role are cardiovascular disorders such as cardiac ischaemia, coronary artery disease, ventricular remodelling, cancer angiogenesis or transplant rejection. From these, many important opportunities for disease modification through TLR signalling manipulation can be imagined. Their role as potential targets for therapeutic intervention is just beginning to be appreciated and this article reviews the current status of these treatment strategies for cardiovascular disease.

Eczema herpeticatum

Eczema herpeticum is an acute, disseminated herpes simplex virus infection which remains a feared complication of eczematous skin diseases, especially atopic dermatitis. The vesicular and erosive clinical picture is often accompanied by systemic signs and symptoms. Why some atopic patients experience multiple attacks of eczema herpeticum and others never have the disorder remains a mystery. Patients with severe or untreated atopic dermatitis are more likely to be affected. The pathogenesis appears to involve a complex interplay of factors, including demasking of binding sites for the virus through the dermatitis, failure to up-regulate antiviral proteins and a lack of plasmacytoid dendritic cells. Treatment of choice is systemic acyclovir therapy.

A randomized controlled trial of a replication defective (gH deletion) herpes simplex virus vaccine for the treatment of recurrent genital herpes among immunocompetent subjects

BACKGROUND

A replication incompetent herpes virus lacking the glycoprotein H gene has been developed as a potential therapeutic vaccine for genital herpes.

GOAL

To determine vaccine efficacy on reducing HSV reactivation and clinical disease among immunocompetent persons with recurrent genital HSV-2 infection.

STUDY DESIGN

Randomized multicenter placebo-controlled trial. Healthy volunteers who had six or more recurrences of genital herpes per year were randomized to receive injections of vaccine at 0 and 8 or 0, 4, and 8 or 0, 2, 4, and 8 weeks or placebo and were followed for subsequent recurrences for 1 year.

RESULTS

The median times to first recurrence of genital herpes (40 days versus 30 days versus 37 days versus 42 days, respectively), mean number of recurrences (3 versus 3 versus 2.4 versus 1.9, respectively), and time to lesion healing of the first recurrence (8 days versus 7.8 days versus 7.4 days versus 7.5 days, respectively), were similar for all treatment groups. Asymptomatic viral shedding was detected by PCR in 61/74 (82%) persons performing daily sample collection following completion of the vaccination series. No differences were noted in the proportion of days with shedding between treatment groups (11.9% versus 17.2% versus 13.1% versus 16.4%, respectively).

CONCLUSION

This replication incompetent HSV-2 vaccine lacking the glycoprotein H gene was safe but had no clinical or virologic benefit in the amelioration of genital HSV-2 disease among immunocompetent men and women.

Synthesis of novel substituted 2-phenylpyrazolopyridines with potent activity against herpesviruses

Herpesviruses are a significant source of human disease; amongst these herpes simplex virus 1 (HSV-1) and HSV-2 are very prevalent and cause recurrent infections. We recently identified a pyrazolo[1,5-a]pyridine scaffold that showed promising activity against HSV-1 and HSV-2 in Vero cell antiviral assays. Here, we describe the synthesis and anti-herpetic activity of several 3-pyrimidinyl-2-phenylpyrazolo[1,5-a]pyridines with differing 2-phenyl substitution patterns. Approaches to rapidly access a number of analogs with different 2-phenyl substitution patterns are outlined. Several of the compounds described have comparable activity to acyclovir against HSV-1 and HSV-2.

Evaluation of imiquimod 5% cream to modify the natural history of herpes labialis: a pilot study

BACKGROUND

Imiquimod is currently approved for the treatment of genital warts and has been shown to decrease recurrences of genital herpes in the guinea pig model of genital herpes. Therefore, we evaluated the safety and potential of topical imiquimod to decrease the rate of recurrence in humans with a history of recurrent herpes labialis.

METHODS

Forty-seven subjects with recurrent herpes labialis applied imiquimod 5% (n=30) or vehicle cream (n=17) to recurrent lesion(s) on days 1, 3, and 5 of the study (day 1 of observation occurred within 48 h after recurrence of lesion). Subjects were seen at the study centers between each dose and 3 days after application of the final dose or until resolution of the lesion.

RESULTS

After application to recurrent lesions, local erythema, edema, scabbing and/or flaking, pain, burning, and maximal lesion size were significantly greater in the imiquimod group than in the vehicle group. The study was terminated early because of severe local adverse events that occurred in 5 recipients of imiquimod. The median time until the next recurrence was, however, increased from 50 days in the vehicle group to 91 days in the imiquimod group (P=.018).

CONCLUSIONS

Application of imiquimod 5% cream to herpes labialis lesions was associated with a delay in the time to the first recurrence after treatment, but severe local inflammation occurred in some individuals.

Advances in Antiviral Therapy

Infections with five of the herpesviruses (herpes simplex virus 1 [HSV-1], HSV-2, varicella zoster virus, Epstein-Barr virus, and cytomegalovirus) are treated with topical or systemic antiviral therapies. There are more than 100 genotypes of human papillomaviruses (HPVs), which may manifest as warts, skin cancers, cervical cancer, anogenital cancers, and upper digestive tract cancers. Molluscum contagiosum (MC) is a common, benign viral infection of the skin. Immunomodulating agents, such as imiquimod, act on HPV and MC indirectly by inducing host immune responses, such as cytokines and cell-mediated immunity, and thereby reduce recurrences. There are multiple vaccines available for certain viral diseases and others in development for HSV-2 and HPV.

Therapy of other viral infections: herpes to hepatitis

Over the past several years, there has been an increase in knowledge pertaining to the diagnosis and management strategies for the herpes family (Types 1-8), the pox viruses, mumps, measles, rubella, and parvovirus B19 as well as the viral etiologies of hepatitis. Various antiviral treatments, such as nucleoside analogs and interferon therapy, have been available to reduce the signs and symptoms of these common viral infections. This article summarizes the preferred treatment strategies to be employed for each of the viruses for reducing severity, duration, recurrences (notably in the herpes family), transmission rates, as well as preventive alternatives. The majority of the therapeutic options attenuate the course of disease. Treatment decisions are driven by knowledge of the natural history and often are tailored to incorporate clinical circumstances for individual patients. Promotion of community awareness and the development of vaccines should be emphasized in the battle against these common viruses, particularly the herpes simplex viruses, the pox viruses, and hepatitis B.

Imiquimod as a dermatological therapy

Imiquimod is the first of a new class of drugs (immune response modifiers) to become commercially available. It is approved in many countries for the treatment of genital warts caused by the human papilloma virus infection. However, there are reports of its use in a variety of dermatological conditions, such as basal cell carcinomas, actinic keratoses, lentigo maligna, common warts and molluscum contagiosum. Its mechanism of action is through stimulation of the T helper cell Type 1 (Th1) immune response via activation of cell surface pathogen recognition receptors (mainly toll-like receptor 7). This activation stimulates the immune system's own defence mechanism against both virally infected and tumour cells. Imiquimod and other analogues show promise in the prophylactic treatment of skin tumours in some patients, especially those who are immunocompromised.

Emerging therapies for herpes viral infections (types 1 – 8)

There are eight members of the herpesviridae family: herpes simplex virus-1 (HSV-1), HSV-2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, human herpes virus-6, human herpes virus-7 and human herpes virus-8. The diseases caused by viruses of the herpesviridae family are treated with and managed by systemic and topical antiviral therapies and immunomodulating drugs. Because these viruses establish a latent state in hosts, antiherpetic agents, such as nucleoside analogues, only control symptoms of disease or prevent outbreaks, and cannot cure the infections. There is a need for treatments that require less frequent dosing, can be taken even when lesions are more advanced than the first signs or symptoms, and can treat resistant strains of the viruses without the toxicities of existing therapies. Immunomodulating agents, such as resiquimod, can act on the viruses indirectly by inducing host production of cytokines, and can thereby reduce recurrences of herpes. The new helicase primase inhibitors, which are the first non-nucleoside antiviral compounds, are being investigated for treatment of HSV disease, including infections resistant to existing therapy.

The road to new antiviral therapies

Viral diseases continue to pose some of the greatest challenges to modern medicine. For many viral diseases, prophylactic vaccines are unlikely to be developed in the near future. Fortunately, effective antiviral therapies have been developed for many of these viruses. In this review, I will focus on antiviral therapy for herpes simplex virus, human immunodeficiency virus, hepatitis C virus, and human papillomavirus. The development of compounds targeting these viruses illustrates many of the principles driving current antiviral development. It is likely that our increasing understanding of viral replication and the virus-host interaction will lead to more rapid development of new antivirals in the future.

Topical Immunomodulation in Dermatology: Potential of Toll-like Receptor Agonists

BACKGROUND

Topical immunomodulators include both immunostimulatory and immunosuppressive agents. If successful, topical immunotherapy may represent an important improvement in the therapy of inflammatory dermatoses, viral infections, and cancers of the skin and genital mucosa. Topical immunotherapy using obligate contact sensitizers such as diphencyprone or dinitrochlorobenzene has been used against viral (e.g., common warts) and autoimmune diseases (e.g., alopecia areata).

RESULTS

Newer agents such imidazoquinolines (imiquimod and resiquimod) act by cytokine secretion from monocytes/macrophages (interferon-alpha, interleukin-12, tumor-necrosis factor-alpha). The locally generated immune milieu leads to a Th1-dominance and cell-mediated immunity that have been clinically used to treat viral infections such as human papillomavirus, herpes simplex virus, and mollusca. Although these agents improve antigen presentation by dendritic cells, they also act on B cells leading to the synthesis of antibodies such as IgG2a. We have also introduced this treatment against cancerous lesions including initial squamous cell and basal cell carcinoma in immunocompetent and immunosuppressed patients. We provide examples of successful treatment of squamous cell cancer using topical imiquimod.

CONCLUSION

The available and additional Toll-like receptor agonists will help to improve the specific dermatologic therapy. Topical immunotherapy with both immunostimulatory and immunosuppressive agents bears potential for effective and patient friendly treatment of inflammatory, infectious, and cancerous skin diseases. Long-term evaluation will define the tolerability and safety profile of these novel topical agents.

Eczema herpeticatum

Patients affected by atopic dermatitis tend to develop viral infections. Probably the most feared complication of atopic dermatitis is eczema herpeticum, a disseminated infection with herpes simplex virus. A monomorphic eruption of dome-shaped blisters, pustules and erosions in the eczematous skin lesions along with severe systemic illness leads to the diagnosis. The clinical diagnosis may be confirmed by polymerase chain reaction, viral culture, electron microscopy with negative staining, Tzanck test, immunofluorescence tests or serology. While intravenous acyclovir is still regarded as standard treatment of eczema herpeticum, several recently-developed antiviral drugs provide therapeutic options.

Death receptor-independent apoptosis in malignant melanoma induced by the small-molecule immune response modifier imiquimod

Bypassing molecular mechanisms of apoptosis deficiency may be of great utility for the successful treatment of malignant tumors. We have discovered that imiquimod, a small-molecule immunomodulator, exerts rather tumor-selective direct pro-apoptotic activity in vivo and in vitro towards cutaneous metastases of malignant melanoma, an aggressive skin tumor. This pro-apoptotic activity was not detectable with resiquimod, a closely related structural analogue whose pro-inflammatory activity is even greater than that of imiquimod. Unresponsiveness of some melanoma metastases to imiquimod in vivo corresponded to resistance towards imiquimod-induced apoptosis in vivo and in vitro. At the molecular level, the pro-apoptotic activity of imiquimod was independent of membrane-bound death receptors, but depended on Bcl-2 expression as demonstrated by overexpression of Bcl-2 in melanoma cells. Imiquimod is the first topical compound with the potential to bypass molecular mechanisms of apoptosis deficiency, a concept that may be relevant for other tumors as well.

Herpes simplex virus type 2 vaccines: new ground for optimism?

The development of effective prophylactic and therapeutic vaccines against genital herpes has proven problematic. Difficulties are associated with the complexity of the virus life cycle (latency) and our relatively poor understanding of the mechanism of immune control of primary and recurrent disease. The types of effector cells and the mechanisms responsible for their activation and regulation are particularly important. Studies from my and other laboratories have shown that recurrent disease is prevented by virus-specific T helper 1 (Th1) cytokines (viz., gamma interferon) and activated innate immunity. Th2 cytokines (viz., interleukin-10 [IL-10]) and regulatory (suppressor) T cells downregulate this immune profile, thereby allowing unimpeded replication of reactivated virus and recurrent disease. Accordingly, an effective therapeutic vaccine must induce Th1 immunity and be defective in Th2 cytokine production, at least IL-10. These concepts are consistent with the findings of the most recent clinical trials, which indicate that (i) a herpes simplex virus type 2 (HSV-2) glycoprotein D (gD-2) vaccine formulated with a Th1-inducing adjuvant has prophylactic activity in HSV-2- and HSV-1-seronegative females, an activity attributed to the adjuvant function, and (ii) a growth-defective HSV-2 mutant (ICP10DeltaPK), which is deleted in the Th2-polarizing gene ICP10PK, induces Th1 immunity and has therapeutic activity in both genders. The ICP10DeltaPK vaccine prevents recurrent disease in 44% of treated subjects and reduces the frequency and severity of recurrences in the subjects that are not fully protected. Additional studies to evaluate these vaccines are warranted.

Chapter 17: Genital human papillomavirus infections--current and prospective therapies

Many therapies are available for the treatment of human papillomavirus (HPV)-associated disease, particularly external genital warts. However, at present, these therapies aim to remove the lesion rather than specifically target HPV infection. When disease and infection are local, as in cervical intraepithelial neoplasia (CIN), excisional therapies removing lesion and transformation-susceptible cells are highly effective. However, when infection is regional, as is usually the case for the anogenital warts, vulval intraepithelial neoplasia (VIN), anal intraepithelial neoplasia (AIN), penile intraepithelial neoplasia, and vaginal intraepithelial neoplasia, then current treatments are generally inadequate, with high recurrence rates. Future therapies will be directly or indirectly antiviral, targeting HPV protein functions or enhancing the ability of the immune system to resolve infection or inducing apoptosis indirectly in HPV-infected cells. In the short to the medium term, immunotherapies for low-grade disease are the most likely to be in the clinic. Vaccines targeting the E1 and E2 early proteins combined with immunomodulators or conventional adjuvants that induce a strong cell-mediated HPV antigen-specific response and good immune memory would be the predicted combination. Vaccines designed to target high-grade intraepithelial disease, even when used in combination with immunomodulators, are unlikely to effect lesion clearance in more than a fraction of the cases. However, they may have a role as adjunct therapy after cervical conization to prevent the recurrence of CIN or HPV reinfection. They certainly appear to have a role in multifocal disease, such as VIN and AIN, where partial clearance may be effected and lesion size reduced enough for effective ablative or excisional therapy. It seems unlikely that anti-HPV chemotherapies specifically targeting HPV protein functions will be in the clinic in the medium term. However, agents such as indole-3-carbinol have shown efficacy in small clinical trials, and if these effects are confirmed in larger, randomized, placebo-controlled trials, they could be clinically useful.

Changing paradigms in dermatology: antivirals in dermatology

Almost all of the approved antiviral drugs have become available during the past two decades. Approximately one half of these agents are for the treatment of human immunodeficiency virus (HIV) infections and comprise five classes. The first three classes all act to inhibit reverse transcriptase: nucleoside analogs; nonnucleoside analogs; and nucleotide analogs. The fourth class, protease inhibitors, prevent viral packaging; the fifth class, fusion inhibitors, prevent fusion between HIV and the target cell. Four nucleoside analogs, acyclovir, valacyclovir, famciclovir and penciclovir, are approved for the therapy of herpes simplex and varicella zoster infections. Interferon alpha is approved in the injectable form for condyloma acuminatum and Kaposi's sarcoma, but the more efficient method of delivering this agent is via interferon induction following topical use of imiquimod cream. Antiviral agents are also approved for infections with cytomegalovirus, hepatitis B and C, respiratory syncytial virus, and influenza viruses. Most of these antiviral drugs are virastatic and not viracidal. Vaccines and public health measures are much more effective and cost effective than antiviral drugs and must be promoted accordingly in the defense against viral infections.

Current and potential therapies for the treatment of herpes-virus infections

Human herpesviruses are found worldwide and are among the most frequent causes of viral infections in immunocompetent as well as in immunocompromised patients. During the past decade and a half a better understanding of the replication and disease-causing state of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), and human cytomegalovirus (HCMV) has been achieved due in part to the development of potent antiviral compounds that target these viruses. While some of these antiviral therapies are considered safe and efficacious (acyclovir, penciclovir), some have toxicities associated with them (ganciclovir and foscarnet). In addition, the increased and prolonged use of these compounds in the clinical setting, especially for the treatment of immunocompromised patients, has led to the emergence of viral resistance against most of these drugs. While resistance is not a serious issue for immunocompetent individuals, it is a real concern for immunocompromised patients, especially those with AIDS and the ones that have undergone organ transplantation. All the currently approved treatments target the viral DNA polymerase. It is clear that new drugs that are more efficacious than the present ones, are not toxic, and target a different viral function would be of great use especially for immunocompromised patients. Here, an overview is provided of the diseases caused by the herpesviruses as well as the replication strategy of the better studied members of this family for which treatments are available. We also discuss the various drugs that have been approved for the treatment of some herpesviruses in terms of structure, mechanism of action, and development of resistance. Finally, we present a discussion of viral targets other than the DNA polymerase, for which new antiviral compounds are being considered.

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.

[Topical immunomodulators in dermatology]

Immunomodulators include both immunostimulatory and immunosuppressive agents. Obligate contact sensitizers such as diphencyprone or dinitrochlorobenzene have been used against viral and autoimmune diseases. Newer agents such as the toll-like receptor agonists imiquimod and resiquimod have been clinically used to treat viral infections and skin cancers in immunocompetent and immunosuppressed patients. On the other hand, the topical immunosuppressive agents tacrolimus and pimecrolimus have been used with great success in the treatment of chronic inflammatory diseases in children and adults. The introduction of this new class of drugs (i.e. Calcineurin inhibitors) marked the beginning of the post-cortisone era in clinical dermatology. Toll-like receptor agonists and calcineurin antagonists will supplement corticosteroids to improve specific dermatological therapy. Topical immunotherapy with both immunostimulatory and immunosuppressive agents show potential for effective and patient-friendly treatment of inflammatory, infectious and neoplastic skin diseases. Long-term evaluation will define the tolerability and the safety profile.

Imiquimod

PURPOSE OF REVIEW

Imiquimod is the first member of a new class of immune response modifiers; it was first approved in 1997 for the topical treatment of external genital and perianal warts. It is an imidazoquinoline, a novel synthetic compound which is an immune response stimulator, enhancing both the innate and acquired immune pathways (particularly T helper cell type 1-mediated immune responses) resulting in antiviral, antitumour and immunoregulatory activities. The mechanism of action of imiquimod involves cytokine induction in the skin, which then triggers the host's immune system to recognize the presence of a viral infection or tumour, ultimately to eradicate the associated lesion.

RECENT FINDINGS

Imiquimod, a patient-applied topical 5% cream is clinically efficacious and safe in the management of condylomata acuminata and other warty manifestations of human papillomavirus infections. Although not licensed for use against other viral skin infections, preliminary data suggest imiquimod's success against molluscum contagiosum, caused by a poxvirus. Initial studies with imiquimod for the management of HPV-related intraepithelial dysplasias (bowenoid papulosis/vulvar intraepithelial neoplasia) as well as for ultraviolet-induced skin lesions such as actinic keratoses, Bowen's disease, and basal cell carcinomas show great promise in immunocompetent and immunosuppressed patients.

SUMMARY

In the future, imiquimod and newer generations of imidazoquinolines (resiquimod) require further investigation for potential clinical utility in treating other cutaneous and mucosal viral infections, dysplasias and neoplasia, as well as potential vaccine adjuvants.

Management of acyclovir-resistant herpes simplex virus

In immunocompetent patients, HSV is controlled rapidly by the human host's immune system, and recurrent lesions are small and short lived. When treated with antiviral agents, these patients rarely develop resistance to these drugs. In contrast immunocompromised patients might not be able to control HSV infection. Thus, frequent and severe reactivations are often seen and might lead to fatal herpetic encephalitis or disseminated HSV infection. Treatment in these patients is limited because immunocompromised hosts often develop severe herpes disease refractory to antiviral drug therapy. It is therefore imperative that physicians develop regimens to deal with both receptive and refractory HSV disease. The following treatment protocol (modified from Balfour and colleagues) might serve as a guide until further investigation of new drugs is performed. In all patients standard oral ACV therapy should be initiated at a dose of 200 mg orally, five times a day for the first 3 to 5 days. Prior to treatment, cultures the lesions should be obtained to verify HSV etiology. If the response is poor, the dose of oral ACV should be increased to 800 mg five times a day. If no response seen after 5 to 7 days, it is unlikely that the lesion will respond to intravenous ACV (or chemically and structurally related drugs such as VCV or famciclovir), so an alternative regimen must be assigned. First, repeat cultures for vital, fungal, and bacterial pathogens must be performed. In addition, ACV susceptibility studies should be ordered, if available. If the mucocutaneous lesion is accessible for topical treatment, TFT (as ophthalmic solution) should be applied to the area three to four times a day until the lesion is completely healed. If the lesion is inaccessible or if the response to TFT is poor, therapy with intravenous foscarnet should be given for 10 days or until complete resolution of the lesions. The dosage of foscarnet should be 40 milligrams per kilogram three times per day or 60 milligrams per kilogram twice daily. If foscarnet fails to achieve clinical clearing, consideration should be given to use of intravenous cidofovir (or application of compounded 1% to 3% topical cidofovir ointment). Vidarabine is reserved for situations in which all of these therapies fail. If lesions reoccur in the same location following clearing, the patient should started on high-dose oral ACV (800 mg, five times daily) or intravenous foscarnet (40 mg/kg tid or 60 mg/kg bid) as soon as possible. When lesions occur in a different location, the patient should be treated initially with standard doses of oral ACV (200 mg, five times daily) and the above protocol should be followed should there be clinical failure. In the future, new treatment options for patients with documented HSV resistance will be important in reducing the clinical impact of HSV.

Therapeutic Options for Herpes Simplex Infections

Herpes simplex viruses are responsible for a number of disease states in infected individuals. Capable of establishing latent infection, herpes simplex can reactivate, causing pain, discomfort, and psychosocial consequences. Because no cure is available, treatment modalities for herpes simplex infection are required, from both personal and public health standpoints. To date, therapy has centered around the use of antiviral drugs to control infection and suppress recurrences. To expand the scope of available treatments, efforts have focused on the development of vaccines against herpes simplex virus and new agents such as immune response modifiers. Recent data suggest that these new agents are promising in their therapeutic potential.

The novel synthetic immune response modifier R-848 (Resiquimod) shifts human allergen-specific CD4+ TH2 lymphocytes into IFN-gamma-producing cells

BACKGROUND

In experimental models, imidazoquinolines exhibit several immunomodulatory activities via Toll-like receptor signaling on cells of the innate immunity.

OBJECTIVE

The aim of our study was to investigate whether R-848 (Resiquimod), a small-molecular-weight synthetic compound belonging to the imidazoquinoline family and known for its ability to substantially delay the onset of recurrent genital herpes lesions in both animals and human beings, could influence, at least in vitro, the cytokine production profile of human hapten- or allergen-specific T cells.

METHODS

Ampicillin- and Der p 1-specific T-cell lines were derived from peripheral blood of allergic donors in the absence or presence of R-848 and assessed by flow cytometry at the single-cell level for their ability to produce IL-4 and/or IFN-gamma.

RESULTS

R-848 induced both hapten- and allergen-specific circulating T cells, including T(H)2 effectors, to produce IFN-gamma and even to lose the ability to produce IL-4, thus shifting their phenotype of cytokine production to a type 0 (T(H)0) or even T(H)1 profile. This effect was associated with an increase in the production of IL-12, IFN-alpha, IL-18, TNF-alpha, IL-10, and IL-15 by CD14(+) cells, as well as an increase in the proportions of IFN-gamma-producing CD3(-)CD16(+) (natural killer) cells.

CONCLUSIONS

These results suggest that R-848, and probably other imidazoquinolines, might be used as adjuvants in view of novel allergen-specific immunotherapeutic regimens for the treatment of allergic disorders.

Novel agents and strategies to treat herpes simplex virus infections

The quiet pandemic of herpes simplex virus (HSV) infection has plagued humanity since ancient times, causing mucocutaneous infection, such as herpes labialis and herpes genitalis. Disease symptoms often interfere with everyday activities and occasionally HSV infections are the cause of life-threatening or sight-impairing disease, especially in neonates and the immunocompromised patient population. After primary or initial infection the virus persists for life in a latent form in neurons of the host, periodically reactivating and often resulting in significant psychosocial distress for the patient. Currently, no cure is available. In the mid-1950s the first antiviral, idoxuridine, was developed for topical treatment of herpes disease and, in 1978, vidarabine was licensed for systemic use to treat HSV encephalitis. Acyclovir (Zovirax), a potent, specific and tolerable nucleosidic inhibitor of the herpes DNA polymerase, was a milestone in the development of antiviral drugs in the late 1970s. In the mid-1990s, when acyclovir became a generic drug, valacyclovir (Valtrex) and famciclovir (Famvir), prodrugs of the gold standard and penciclovir (Denavir), Vectavir), a close analogue, were launched. Though numerous approaches and strategies were tested and considerable effort was expended in the search of the next generation of an antiherpetic therapy, it proved difficult to outperform acyclovir. Notable in this regard was the award of a Nobel Prize in 1988 for the elucidation of mechanistic principles which resulted in the development of new drugs such as acyclovir. Vaccines, interleukins, interferons, therapeutic proteins, antibodies, immunomodulators and small-molecule drugs with specific or nonspecific modes of action lacked either efficacy or the required safety profile to replace the nucleosidic drugs acyclovir, valacyclovir, penciclovir and famciclovir as the first choice of treatment. Recently though, new inhibitors of the HSV helicase-primase with potent in vitro antiherpes activity, novel mechanisms of action, low resistance rates and superior efficacy against HSV in animal models have been discovered. This review summarises the current therapeutic options, discusses the potential of preclinical or investigational drugs and provides an up-to-date interpretation of the challenge to establish novel treatments for herpes simplex disease.

Recent progress in herpes simplex virus immunobiology and vaccine research

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) cause prevalent, chronic infections that have serious outcomes in some individuals. Neonatal herpes may occur when the infant traverses the cervix during maternal genital herpes. Genital herpes is a major risk factor for human immunodeficiency virus type 1 transmission. Considerable efforts have been made to design and test vaccines for HSV, focusing on genital infection with HSV-2. Several protein subunit vaccines based on HSV-2 envelope glycoproteins have reached advanced-phase clinical trials. These antigens were chosen because they are the targets of neutralizing-antibody responses and because they elicit cellular immunity. Encouraging results have been reported in studies of treatment of HSV-seronegative women with a vaccine consisting of truncated glycoprotein D of HSV-2 and a novel adjuvant. Because most sexual HSV transmission occurs during asymptomatic shedding, it is important to evaluate the impact of vaccination on HSV-2 infection, clinically apparent genital herpes, and HSV shedding among vaccine recipients who acquire infection. There are several other attractive formats, including subunit vaccines that target cellular immune responses, live attenuated virus strains, and mutant strains that undergo incomplete lytic replication. HSV vaccines have also been evaluated for the immunotherapy of established HSV infection.