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Topical Imiquimod for Recurrent Acyclovir-resistant HSV Infection

2006; Elsevier BV; Volume: 119; Issue: 5 Linguagem: Inglês

10.1016/j.amjmed.2005.06.037

1555-7162

Valérie Martinez, Jean‐Michel Molina, Catherine Scieux, Patricia Ribaud, Florence Morfin,

Nail Diseases and Treatments

Herpes simplex virus (HSV) infections still represent a significant cause of morbidity in immunocompromised patients and are usually chronically recurrent. HSV infections are commonly cutaneomucous and usually localized on the face in the case of HSV type 1 (HSV-1) and in the genital region in the case of HSV type 2 (HSV-2), but other localizations may occur. Although acyclovir (ACV) has demonstrated efficacy for the treatment and prophylaxis of HSV infection in immunocompromised patients, the emergence of ACV-resistant (ACV-R) strains has been frequently reported and is closely linked to the degree of immunosuppression and the duration of exposure to ACV.1Englund J.A. Zimmerman M.E. Swierkosz E.M. Googman J.L. Scholl D.R. Balfour H.H. Herpes simplex virus resistant to acyclovir a study in a tertiary care center.Ann Intern Med. 1990; 112: 416-422Crossref PubMed Scopus (320) Google Scholar Recent surveys have reported prevalence rates of ACV-R HSV strains of 4.2% in patients with human immunodeficiency virus (HIV) infection, reaching 13.7% in bone marrow transplant recipients.1Englund J.A. Zimmerman M.E. Swierkosz E.M. Googman J.L. Scholl D.R. Balfour H.H. Herpes simplex virus resistant to acyclovir a study in a tertiary care center.Ann Intern Med. 1990; 112: 416-422Crossref PubMed Scopus (320) Google Scholar, 2Chen Y. Scieux C. Garrait V. et al.Resistant herpes simplex virus type 1 infection an emerging concern after allogeneic stem cell transplantation.Clin Infect Dis. 2000; 31: 927-935Crossref PubMed Scopus (141) Google Scholar, 3Danve-Szatanek C. Aymard M. Thouvenot D. et al.Surveillance network for herpes simplex virus resistance to antiviral drugs 3-year follow-up.J Clin Microbiol. 2004; 42: 242-249Crossref PubMed Scopus (177) Google Scholar Although foscarnet (FCV) or cidofovir (CDV) are usually effective to treat ACV-R HSV infections, both drugs are usually administered parenterally and have significant renal toxic effects.4Chatis P.A. Miller C.H. Schrager L. Crumpacker C.S. Successful treatment with foscarnet of an acyclovir resistant mucocutaneous infection with herpes simplex virus in a patient with acquired immunodeficiency syndrome.N Engl J Med. 1989; 320: 297-300Crossref PubMed Scopus (170) Google Scholar, 5Blot N. Schneider P. Young P. et al.Treatment of an acyclovir and foscarnet-resistant herpes simplex virus infection with cidofovir in a child after an unrelated bone marrow transplant.Bone Marrow Transplant. 2000; 26: 903-905Crossref PubMed Scopus (46) Google Scholar FCV-resistance (FCV-R) can also rapidly emerge in immunocompromised patients, therefore limiting therapeutic options in these patients.2Chen Y. Scieux C. Garrait V. et al.Resistant herpes simplex virus type 1 infection an emerging concern after allogeneic stem cell transplantation.Clin Infect Dis. 2000; 31: 927-935Crossref PubMed Scopus (141) Google Scholar, 3Danve-Szatanek C. Aymard M. Thouvenot D. et al.Surveillance network for herpes simplex virus resistance to antiviral drugs 3-year follow-up.J Clin Microbiol. 2004; 42: 242-249Crossref PubMed Scopus (177) Google Scholar, 5Blot N. Schneider P. Young P. et al.Treatment of an acyclovir and foscarnet-resistant herpes simplex virus infection with cidofovir in a child after an unrelated bone marrow transplant.Bone Marrow Transplant. 2000; 26: 903-905Crossref PubMed Scopus (46) Google Scholar, 6Safrin S. Kemmerly S. Plotkin B. et al.Foscarnet-resistant herpes simplex virus infection in a patient with AIDS.J Infect Dis. 1994; 169: 193-196Crossref PubMed Scopus (140) Google Scholar Topical therapy with antiviral agents such as trifluridine has been assessed in cases of antiviral drug resistance but has only partial activity.7Amin A.R. Robinson M.R. Smith D.D. Swenson C.F. Luque A.E. Trifluorothymidine 0.5% ointment in the treatment of aciclovir-resistant mucocutaneous herpes simplex in AIDS.AIDS. 1996; 10: 1051-1053Crossref PubMed Scopus (6) Google Scholar Following the report of the efficacy of topical imiquimod, an immunomodulator, in patients with ACV-unresponsive HSV infection,8Gilbert J. Drehs M.M. Weinberg J.M. Topical imiquimod for acyclovir-unresponsive herpes simplex virus 2 infection.Arch Dermatol. 2001; 137: 1015-1017PubMed Google Scholar we decided to treat with this topical agent two consecutive immunocompromised patients with cutaneomucous HSV infection that did not respond to either ACV, FCV or CDV.Case 1Patient 1 was a 37-year-old HIV-infected man who presented with a 10-year history of recurrent anogenital HSV-2 infection. Past medical history included multiple opportunistic infections such as Pneumocystis jiroveci pneumonia, disseminated cytomegalovirus disease, and microsporidial intestinal infection. His nadir CD4 cell count was 5 cells/mm3, a time at which he experienced his first anal HSV-2 infection. However, following the introduction of highly active antiretroviral therapy in 1996, HIV-1 replication in the plasma remained below detectable levels, and CD4 cell count increased up to 450 cells /mm3. No new opportunistic infections developed in this patient; however, he was still experiencing very disabling and painful chronically recurrent pseudotumoral anogenital HSV-2 infections despite daily suppressive therapy with ACV or valacyclovir (Figure 1). He received multiple courses of parenteral FCV and CDV with short-term benefit, but treatment had to be discontinued because of renal failure. Topical trifluridine was also used, again with only short-term benefit and rapid recurrence upon treatment discontinuation.We then decided to initiate topical imiquimod 5% cream. At this time, the CD4 cell count was 728/mm3 and plasma HIV RNA was below 20 copies/mL under a protease inhibitor-containing regimen. In vitro testing of the HSV-2 strain demonstrated ACV-R (inhibitory concentration 50% (IC50): 37 μM), FCV-R (IC50 >500 μM), although it remained susceptible to CDV (IC50: 3.4 μM). The patient applied imiquimod cream 3 times the first week and 2 times the second week in order to achieve topical therapy for approximately 8 to 10 hours per application, and then stopped treatment. The patient noted no adverse effects from the application of topical imiquimod cream. Two weeks later skin lesions improved significantly, and reepithelialization was seen at 1 month (Figure 2). Detection of HSV-2 by either culture or polymerase chain reaction remained negative. No recurrence was observed during a 12-month follow-up without any ACV suppressive therapy.Figure 2Improvement with reepithelialization of erosion 1 month after 3 applications of imiquimod (Patient 1).View Large Image Figure ViewerDownload (PPT)Case 2Patient 2 was a 31-year-old man with a history of acute lymphocytic leukemia first diagnosed in 1996. Following relapse, he underwent a second allogeneic unrelated stem cell transplantation in 2003. The conditioning regimen consisted of cyclophosphamide, busulfan, fludarabine and antithymocytes globulins. Post-transplant events were mild acute liver graft-versus-host disease treated with high-dose steroids and an Epstein-Barr virus-associated lymphoproliferative disorder that responded to anti-CD20 monoclonal antibodies. Despite valacyclovir prophylaxis (500 mg daily), 2 months after transplantation he developed a cutaneomucous HSV-1 infection of the mouth, lips and fingers with painful and disabling erosions. At that time, he had mild neutropenia (1000 granulocytes/mm3) but severe lymphopenia (3 CD4 cells/mm3). High-dose valacyclovir (1 g TID) and FCV, or parenteral combination of FCV plus ACV, had only partial activity. Renal insufficiency precluded CDV use. Topical trifluridine was tested with no clear benefit and persistent shedding of HSV-1 from the cutaneomucous lesions.In vitro sensitivity testing of the HSV-1 strain revealed an intermediate level of ACV susceptibility (IC50: 8.7 μM) and FCV-R (IC50: 678 μM). We then decided to change therapy and to initiate topical therapy with 5% imiquimod cream 4 times daily, while maintaining low-dose therapy with valacyclovir (500 mg per day) to prevent Varicella-Zoster virus reactivation. A significant improvement was noted 2 weeks later. Complete clinical and virological cure of the finger lesions was noted 3 weeks after treatment initiation, and mouth, lips, and throat lesions healed 1 week later. Topical imiquimod therapy was tapered after 1 month, and only one application daily was used for the following 3 months, then stopped. No adverse effect was reported during treatment. During a 10-month follow-up period, no recurrence of HSV-1 infection was noted under valacyclovir prophylaxis.Clinical isolates and HSV susceptibility testing: HSV strains were isolated in human lung fibroblast embryonic cells (MRC-5), and a virus stock was prepared in Vero cells. Typing of the HSV strains was performed by indirect immunofluorescence with monoclonal antibodies (Argène-Biosoft, Varhiles, France). Assessment of in vitro sensitivity of HSV strains to antivirals was performed using a colorimetric test based on the chessboard technique as previously described.9Langlois M. Allard J.P. Nugier F. Aymard M. A rapid and automated colorimetric assay for evaluating the sensitivity of herpes simplex strains to antiviral drugs.J Biol Stand. 1986; 14: 201-211Crossref PubMed Scopus (86) Google Scholar This phenotypic resistance test determines the antiviral concentration inhibiting viral replication by 50%. Resistance thresholds have been defined for ACV (6.5 μM for HSV-1 and 13.5 μM for HSV-2), for FCV (>400 μM for HSV-1 and HSV-2), and for CDV (>15 μM for HSV-1 and HSV-2).We report here the successful use of topical 5% imiquimod cream in 2 immunocompromised patients who presented with chronically recurrent cutaneomucous HSV infections that resisted oral and parenteral therapy with antiviral agents. Therapeutic options are limited in these patients, especially when resistance to available antiviral agents emerges and alternative treatments are warranted. Topical imiquimod treatment in these patients was initiated following the encouraging report by Gilbert et al of an HIV-infected patient with HSV-2 infection.8Gilbert J. Drehs M.M. Weinberg J.M. Topical imiquimod for acyclovir-unresponsive herpes simplex virus 2 infection.Arch Dermatol. 2001; 137: 1015-1017PubMed Google Scholar This patient presented with a 5-month history of penile HSV-2 infection that became unresponsive to acyclovir, valacyclovir and famciclovir. He was receiving antiretroviral therapy with a complete suppression of HIV-1 replication and a CD4 cell count of 200 cells/mm3. After the application of imiquimod to the lesions 3 times over the course of a week, the skin lesion improved with reepithelialization of the erosion. Imiquimod therapy was discontinued after 1 week and no recurrence was seen after 1 month of follow-up. Danielsen et al also reported the case of a 28-year-old HIV-infected man with a very painful penile erosion due to both HSV-1 and -2 infection that was clinically resistant to acyclovir, valacyclovir, famciclovir and intravenous foscarnet.10Danielsen A.G. Petersen C.S. Iversen J. Chronic erosive herpes simplex virus infection of the penis in a human immunodeficiency virus-positive man, treated with imiquimod and famciclovir.Br J Dermatol. 2002; 147: 1034-1036Crossref PubMed Scopus (21) Google Scholar The patient received a 10-week combination of topical imiquimod and systemic famciclovir, leading to a slow healing of the erosion. Famciclovir was then continued alone with no further relapse 20 months later. Finally, Christensen and Hengge reported the case of a 30-year-old woman with a 2-year history of chronically recurrent genital HSV-2 infection who received a 3-month course of imiquimod 3 times a week following a 5-day course of intravenous acyclovir and who experienced no further recurrent HSV infection after a 6-month follow-up.11Christensen B. Hengge U.R. Recurrent urogenital herpes simplex-successful treatment with imiquimod?.Sex Transm Infect. 1999; 75: 132-133PubMed Google ScholarHowever, spontaneous resolution of symptoms is found in up to 15% of patients in clinical trials aiming at preventing recurrent herpes, and a recent study in immunocompetent adults showed that imiquimod alone did not significantly alter the time to first recurrence of herpes genitalis.12Schacker T.W. Conant M. Thoming C. Stanczak T. Wang Z. Smith M. Imiquimod HSV study groupImiquimod 5-percent cream does not alter the natural history of recurrent herpes genitalis a phase II, randomized, double-blind, placebo-controlled study.Antimicrob Agents Chemother. 2002; 46: 3243-3248Crossref PubMed Scopus (49) Google Scholar Further studies need to be completed, therefore, to better assess the benefit of imiquimod in patients with recurrent HSV infections.The exact antiviral mechanism of action of imiquimod remains incompletely understood. Imiquimod is a local immunomodulator, which belongs to the family of imidazoquinolines and induces the production of various cytokines (including IL-12) and interferons. It has been shown to be effective in anogenital human papilloma virus-associated condylomata, both in acute therapy and long-term prophylaxis. Animal experiments have also indicated the effectiveness of this substance in HSV infection, in particular with respect to the prevention of recurrences.13Miller R.L. Imbertson L.M. Reiter M.J. Gerster J.F. Treatment of primary herpes simplex virus infection in guinea pigs by imiquimod.Antiviral Res. 1999; 44: 31-42Crossref PubMed Scopus (54) Google Scholar The drug has no direct antiviral activity, and its effect might be mediated through activation of monocyte-macrophages to secrete various cytokines, resulting in a T-helper 1 dominant response.14Wagner T.L. Ahonen C.L. Couture A.M. et al.Modulation of TH1 and TH2 cytokine production with the immune response modifiers, R-848 and imiquimod.Cell Immunol. 1999; 191: 10-19Crossref PubMed Scopus (252) Google Scholar It has also been shown that imiquimod induces functional maturation of human Langerhans cells. The T-helper 1 cytokine switch and the increased antigen presentation might be very helpful in patients with underlying immune deficits. Imiquimod also induces local interferon alpha production, which is known to have direct antiviral activity and which persists beyond the time of an effective concentration of the drug.Topical imiquimod therefore offers another alternative for the treatment of HSV infections, particularly in the setting of immunocompromised patients experiencing multiple recurrences or chronic infections with resistant strains. However, clinical experience is very limited so far, and further studies are clearly needed. Herpes simplex virus (HSV) infections still represent a significant cause of morbidity in immunocompromised patients and are usually chronically recurrent. HSV infections are commonly cutaneomucous and usually localized on the face in the case of HSV type 1 (HSV-1) and in the genital region in the case of HSV type 2 (HSV-2), but other localizations may occur. Although acyclovir (ACV) has demonstrated efficacy for the treatment and prophylaxis of HSV infection in immunocompromised patients, the emergence of ACV-resistant (ACV-R) strains has been frequently reported and is closely linked to the degree of immunosuppression and the duration of exposure to ACV.1Englund J.A. Zimmerman M.E. Swierkosz E.M. Googman J.L. Scholl D.R. Balfour H.H. Herpes simplex virus resistant to acyclovir a study in a tertiary care center.Ann Intern Med. 1990; 112: 416-422Crossref PubMed Scopus (320) Google Scholar Recent surveys have reported prevalence rates of ACV-R HSV strains of 4.2% in patients with human immunodeficiency virus (HIV) infection, reaching 13.7% in bone marrow transplant recipients.1Englund J.A. Zimmerman M.E. Swierkosz E.M. Googman J.L. Scholl D.R. Balfour H.H. Herpes simplex virus resistant to acyclovir a study in a tertiary care center.Ann Intern Med. 1990; 112: 416-422Crossref PubMed Scopus (320) Google Scholar, 2Chen Y. Scieux C. Garrait V. et al.Resistant herpes simplex virus type 1 infection an emerging concern after allogeneic stem cell transplantation.Clin Infect Dis. 2000; 31: 927-935Crossref PubMed Scopus (141) Google Scholar, 3Danve-Szatanek C. Aymard M. Thouvenot D. et al.Surveillance network for herpes simplex virus resistance to antiviral drugs 3-year follow-up.J Clin Microbiol. 2004; 42: 242-249Crossref PubMed Scopus (177) Google Scholar Although foscarnet (FCV) or cidofovir (CDV) are usually effective to treat ACV-R HSV infections, both drugs are usually administered parenterally and have significant renal toxic effects.4Chatis P.A. Miller C.H. Schrager L. Crumpacker C.S. Successful treatment with foscarnet of an acyclovir resistant mucocutaneous infection with herpes simplex virus in a patient with acquired immunodeficiency syndrome.N Engl J Med. 1989; 320: 297-300Crossref PubMed Scopus (170) Google Scholar, 5Blot N. Schneider P. Young P. et al.Treatment of an acyclovir and foscarnet-resistant herpes simplex virus infection with cidofovir in a child after an unrelated bone marrow transplant.Bone Marrow Transplant. 2000; 26: 903-905Crossref PubMed Scopus (46) Google Scholar FCV-resistance (FCV-R) can also rapidly emerge in immunocompromised patients, therefore limiting therapeutic options in these patients.2Chen Y. Scieux C. Garrait V. et al.Resistant herpes simplex virus type 1 infection an emerging concern after allogeneic stem cell transplantation.Clin Infect Dis. 2000; 31: 927-935Crossref PubMed Scopus (141) Google Scholar, 3Danve-Szatanek C. Aymard M. Thouvenot D. et al.Surveillance network for herpes simplex virus resistance to antiviral drugs 3-year follow-up.J Clin Microbiol. 2004; 42: 242-249Crossref PubMed Scopus (177) Google Scholar, 5Blot N. Schneider P. Young P. et al.Treatment of an acyclovir and foscarnet-resistant herpes simplex virus infection with cidofovir in a child after an unrelated bone marrow transplant.Bone Marrow Transplant. 2000; 26: 903-905Crossref PubMed Scopus (46) Google Scholar, 6Safrin S. Kemmerly S. Plotkin B. et al.Foscarnet-resistant herpes simplex virus infection in a patient with AIDS.J Infect Dis. 1994; 169: 193-196Crossref PubMed Scopus (140) Google Scholar Topical therapy with antiviral agents such as trifluridine has been assessed in cases of antiviral drug resistance but has only partial activity.7Amin A.R. Robinson M.R. Smith D.D. Swenson C.F. Luque A.E. Trifluorothymidine 0.5% ointment in the treatment of aciclovir-resistant mucocutaneous herpes simplex in AIDS.AIDS. 1996; 10: 1051-1053Crossref PubMed Scopus (6) Google Scholar Following the report of the efficacy of topical imiquimod, an immunomodulator, in patients with ACV-unresponsive HSV infection,8Gilbert J. Drehs M.M. Weinberg J.M. Topical imiquimod for acyclovir-unresponsive herpes simplex virus 2 infection.Arch Dermatol. 2001; 137: 1015-1017PubMed Google Scholar we decided to treat with this topical agent two consecutive immunocompromised patients with cutaneomucous HSV infection that did not respond to either ACV, FCV or CDV. Case 1Patient 1 was a 37-year-old HIV-infected man who presented with a 10-year history of recurrent anogenital HSV-2 infection. Past medical history included multiple opportunistic infections such as Pneumocystis jiroveci pneumonia, disseminated cytomegalovirus disease, and microsporidial intestinal infection. His nadir CD4 cell count was 5 cells/mm3, a time at which he experienced his first anal HSV-2 infection. However, following the introduction of highly active antiretroviral therapy in 1996, HIV-1 replication in the plasma remained below detectable levels, and CD4 cell count increased up to 450 cells /mm3. No new opportunistic infections developed in this patient; however, he was still experiencing very disabling and painful chronically recurrent pseudotumoral anogenital HSV-2 infections despite daily suppressive therapy with ACV or valacyclovir (Figure 1). He received multiple courses of parenteral FCV and CDV with short-term benefit, but treatment had to be discontinued because of renal failure. Topical trifluridine was also used, again with only short-term benefit and rapid recurrence upon treatment discontinuation.We then decided to initiate topical imiquimod 5% cream. At this time, the CD4 cell count was 728/mm3 and plasma HIV RNA was below 20 copies/mL under a protease inhibitor-containing regimen. In vitro testing of the HSV-2 strain demonstrated ACV-R (inhibitory concentration 50% (IC50): 37 μM), FCV-R (IC50 >500 μM), although it remained susceptible to CDV (IC50: 3.4 μM). The patient applied imiquimod cream 3 times the first week and 2 times the second week in order to achieve topical therapy for approximately 8 to 10 hours per application, and then stopped treatment. The patient noted no adverse effects from the application of topical imiquimod cream. Two weeks later skin lesions improved significantly, and reepithelialization was seen at 1 month (Figure 2). Detection of HSV-2 by either culture or polymerase chain reaction remained negative. No recurrence was observed during a 12-month follow-up without any ACV suppressive therapy. Patient 1 was a 37-year-old HIV-infected man who presented with a 10-year history of recurrent anogenital HSV-2 infection. Past medical history included multiple opportunistic infections such as Pneumocystis jiroveci pneumonia, disseminated cytomegalovirus disease, and microsporidial intestinal infection. His nadir CD4 cell count was 5 cells/mm3, a time at which he experienced his first anal HSV-2 infection. However, following the introduction of highly active antiretroviral therapy in 1996, HIV-1 replication in the plasma remained below detectable levels, and CD4 cell count increased up to 450 cells /mm3. No new opportunistic infections developed in this patient; however, he was still experiencing very disabling and painful chronically recurrent pseudotumoral anogenital HSV-2 infections despite daily suppressive therapy with ACV or valacyclovir (Figure 1). He received multiple courses of parenteral FCV and CDV with short-term benefit, but treatment had to be discontinued because of renal failure. Topical trifluridine was also used, again with only short-term benefit and rapid recurrence upon treatment discontinuation. We then decided to initiate topical imiquimod 5% cream. At this time, the CD4 cell count was 728/mm3 and plasma HIV RNA was below 20 copies/mL under a protease inhibitor-containing regimen. In vitro testing of the HSV-2 strain demonstrated ACV-R (inhibitory concentration 50% (IC50): 37 μM), FCV-R (IC50 >500 μM), although it remained susceptible to CDV (IC50: 3.4 μM). The patient applied imiquimod cream 3 times the first week and 2 times the second week in order to achieve topical therapy for approximately 8 to 10 hours per application, and then stopped treatment. The patient noted no adverse effects from the application of topical imiquimod cream. Two weeks later skin lesions improved significantly, and reepithelialization was seen at 1 month (Figure 2). Detection of HSV-2 by either culture or polymerase chain reaction remained negative. No recurrence was observed during a 12-month follow-up without any ACV suppressive therapy. Case 2Patient 2 was a 31-year-old man with a history of acute lymphocytic leukemia first diagnosed in 1996. Following relapse, he underwent a second allogeneic unrelated stem cell transplantation in 2003. The conditioning regimen consisted of cyclophosphamide, busulfan, fludarabine and antithymocytes globulins. Post-transplant events were mild acute liver graft-versus-host disease treated with high-dose steroids and an Epstein-Barr virus-associated lymphoproliferative disorder that responded to anti-CD20 monoclonal antibodies. Despite valacyclovir prophylaxis (500 mg daily), 2 months after transplantation he developed a cutaneomucous HSV-1 infection of the mouth, lips and fingers with painful and disabling erosions. At that time, he had mild neutropenia (1000 granulocytes/mm3) but severe lymphopenia (3 CD4 cells/mm3). High-dose valacyclovir (1 g TID) and FCV, or parenteral combination of FCV plus ACV, had only partial activity. Renal insufficiency precluded CDV use. Topical trifluridine was tested with no clear benefit and persistent shedding of HSV-1 from the cutaneomucous lesions.In vitro sensitivity testing of the HSV-1 strain revealed an intermediate level of ACV susceptibility (IC50: 8.7 μM) and FCV-R (IC50: 678 μM). We then decided to change therapy and to initiate topical therapy with 5% imiquimod cream 4 times daily, while maintaining low-dose therapy with valacyclovir (500 mg per day) to prevent Varicella-Zoster virus reactivation. A significant improvement was noted 2 weeks later. Complete clinical and virological cure of the finger lesions was noted 3 weeks after treatment initiation, and mouth, lips, and throat lesions healed 1 week later. Topical imiquimod therapy was tapered after 1 month, and only one application daily was used for the following 3 months, then stopped. No adverse effect was reported during treatment. During a 10-month follow-up period, no recurrence of HSV-1 infection was noted under valacyclovir prophylaxis.Clinical isolates and HSV susceptibility testing: HSV strains were isolated in human lung fibroblast embryonic cells (MRC-5), and a virus stock was prepared in Vero cells. Typing of the HSV strains was performed by indirect immunofluorescence with monoclonal antibodies (Argène-Biosoft, Varhiles, France). Assessment of in vitro sensitivity of HSV strains to antivirals was performed using a colorimetric test based on the chessboard technique as previously described.9Langlois M. Allard J.P. Nugier F. Aymard M. A rapid and automated colorimetric assay for evaluating the sensitivity of herpes simplex strains to antiviral drugs.J Biol Stand. 1986; 14: 201-211Crossref PubMed Scopus (86) Google Scholar This phenotypic resistance test determines the antiviral concentration inhibiting viral replication by 50%. Resistance thresholds have been defined for ACV (6.5 μM for HSV-1 and 13.5 μM for HSV-2), for FCV (>400 μM for HSV-1 and HSV-2), and for CDV (>15 μM for HSV-1 and HSV-2).We report here the successful use of topical 5% imiquimod cream in 2 immunocompromised patients who presented with chronically recurrent cutaneomucous HSV infections that resisted oral and parenteral therapy with antiviral agents. Therapeutic options are limited in these patients, especially when resistance to available antiviral agents emerges and alternative treatments are warranted. Topical imiquimod treatment in these patients was initiated following the encouraging report by Gilbert et al of an HIV-infected patient with HSV-2 infection.8Gilbert J. Drehs M.M. Weinberg J.M. Topical imiquimod for acyclovir-unresponsive herpes simplex virus 2 infection.Arch Dermatol. 2001; 137: 1015-1017PubMed Google Scholar This patient presented with a 5-month history of penile HSV-2 infection that became unresponsive to acyclovir, valacyclovir and famciclovir. He was receiving antiretroviral therapy with a complete suppression of HIV-1 replication and a CD4 cell count of 200 cells/mm3. After the application of imiquimod to the lesions 3 times over the course of a week, the skin lesion improved with reepithelialization of the erosion. Imiquimod therapy was discontinued after 1 week and no recurrence was seen after 1 month of follow-up. Danielsen et al also reported the case of a 28-year-old HIV-infected man with a very painful penile erosion due to both HSV-1 and -2 infection that was clinically resistant to acyclovir, valacyclovir, famciclovir and intravenous foscarnet.10Danielsen A.G. Petersen C.S. Iversen J. Chronic erosive herpes simplex virus infection of the penis in a human immunodeficiency virus-positive man, treated with imiquimod and famciclovir.Br J Dermatol. 2002; 147: 1034-1036Crossref PubMed Scopus (21) Google Scholar The patient received a 10-week combination of topical imiquimod and systemic famciclovir, leading to a slow healing of the erosion. Famciclovir was then continued alone with no further relapse 20 months later. Finally, Christensen and Hengge reported the case of a 30-year-old woman with a 2-year history of chronically recurrent genital HSV-2 infection who received a 3-month course of imiquimod 3 times a week following a 5-day course of intravenous acyclovir and who experienced no further recurrent HSV infection after a 6-month follow-up.11Christensen B. Hengge U.R. Recurrent urogenital herpes simplex-successful treatment with imiquimod?.Sex Transm Infect. 1999; 75: 132-133PubMed Google ScholarHowever, spontaneous resolution of symptoms is found in up to 15% of patients in clinical trials aiming at preventing recurrent herpes, and a recent study in immunocompetent adults showed that imiquimod alone did not significantly alter the time to first recurrence of herpes genitalis.12Schacker T.W. Conant M. Thoming C. Stanczak T. Wang Z. Smith M. Imiquimod HSV study groupImiquimod 5-percent cream does not alter the natural history of recurrent herpes genitalis a phase II, randomized, double-blind, placebo-controlled study.Antimicrob Agents Chemother. 2002; 46: 3243-3248Crossref PubMed Scopus (49) Google Scholar Further studies need to be completed, therefore, to better assess the benefit of imiquimod in patients with recurrent HSV infections.The exact antiviral mechanism of action of imiquimod remains incompletely understood. Imiquimod is a local immunomodulator, which belongs to the family of imidazoquinolines and induces the production of various cytokines (including IL-12) and interferons. It has been shown to be effective in anogenital human papilloma virus-associated condylomata, both in acute therapy and long-term prophylaxis. Animal experiments have also indicated the effectiveness of this substance in HSV infection, in particular with respect to the prevention of recurrences.13Miller R.L. Imbertson L.M. Reiter M.J. Gerster J.F. Treatment of primary herpes simplex virus infection in guinea pigs by imiquimod.Antiviral Res. 1999; 44: 31-42Crossref PubMed Scopus (54) Google Scholar The drug has no direct antiviral activity, and its effect might be mediated through activation of monocyte-macrophages to secrete various cytokines, resulting in a T-helper 1 dominant response.14Wagner T.L. Ahonen C.L. Couture A.M. et al.Modulation of TH1 and TH2 cytokine production with the immune response modifiers, R-848 and imiquimod.Cell Immunol. 1999; 191: 10-19Crossref PubMed Scopus (252) Google Scholar It has also been shown that imiquimod induces functional maturation of human Langerhans cells. The T-helper 1 cytokine switch and the increased antigen presentation might be very helpful in patients with underlying immune deficits. Imiquimod also induces local interferon alpha production, which is known to have direct antiviral activity and which persists beyond the time of an effective concentration of the drug.Topical imiquimod therefore offers another alternative for the treatment of HSV infections, particularly in the setting of immunocompromised patients experiencing multiple recurrences or chronic infections with resistant strains. However, clinical experience is very limited so far, and further studies are clearly needed. Patient 2 was a 31-year-old man with a history of acute lymphocytic leukemia first diagnosed in 1996. Following relapse, he underwent a second allogeneic unrelated stem cell transplantation in 2003. The conditioning regimen consisted of cyclophosphamide, busulfan, fludarabine and antithymocytes globulins. Post-transplant events were mild acute liver graft-versus-host disease treated with high-dose steroids and an Epstein-Barr virus-associated lymphoproliferative disorder that responded to anti-CD20 monoclonal antibodies. Despite valacyclovir prophylaxis (500 mg daily), 2 months after transplantation he developed a cutaneomucous HSV-1 infection of the mouth, lips and fingers with painful and disabling erosions. At that time, he had mild neutropenia (1000 granulocytes/mm3) but severe lymphopenia (3 CD4 cells/mm3). High-dose valacyclovir (1 g TID) and FCV, or parenteral combination of FCV plus ACV, had only partial activity. Renal insufficiency precluded CDV use. Topical trifluridine was tested with no clear benefit and persistent shedding of HSV-1 from the cutaneomucous lesions. In vitro sensitivity testing of the HSV-1 strain revealed an intermediate level of ACV susceptibility (IC50: 8.7 μM) and FCV-R (IC50: 678 μM). We then decided to change therapy and to initiate topical therapy with 5% imiquimod cream 4 times daily, while maintaining low-dose therapy with valacyclovir (500 mg per day) to prevent Varicella-Zoster virus reactivation. A significant improvement was noted 2 weeks later. Complete clinical and virological cure of the finger lesions was noted 3 weeks after treatment initiation, and mouth, lips, and throat lesions healed 1 week later. Topical imiquimod therapy was tapered after 1 month, and only one application daily was used for the following 3 months, then stopped. No adverse effect was reported during treatment. During a 10-month follow-up period, no recurrence of HSV-1 infection was noted under valacyclovir prophylaxis. Clinical isolates and HSV susceptibility testing: HSV strains were isolated in human lung fibroblast embryonic cells (MRC-5), and a virus stock was prepared in Vero cells. Typing of the HSV strains was performed by indirect immunofluorescence with monoclonal antibodies (Argène-Biosoft, Varhiles, France). Assessment of in vitro sensitivity of HSV strains to antivirals was performed using a colorimetric test based on the chessboard technique as previously described.9Langlois M. Allard J.P. Nugier F. Aymard M. A rapid and automated colorimetric assay for evaluating the sensitivity of herpes simplex strains to antiviral drugs.J Biol Stand. 1986; 14: 201-211Crossref PubMed Scopus (86) Google Scholar This phenotypic resistance test determines the antiviral concentration inhibiting viral replication by 50%. Resistance thresholds have been defined for ACV (6.5 μM for HSV-1 and 13.5 μM for HSV-2), for FCV (>400 μM for HSV-1 and HSV-2), and for CDV (>15 μM for HSV-1 and HSV-2). We report here the successful use of topical 5% imiquimod cream in 2 immunocompromised patients who presented with chronically recurrent cutaneomucous HSV infections that resisted oral and parenteral therapy with antiviral agents. Therapeutic options are limited in these patients, especially when resistance to available antiviral agents emerges and alternative treatments are warranted. Topical imiquimod treatment in these patients was initiated following the encouraging report by Gilbert et al of an HIV-infected patient with HSV-2 infection.8Gilbert J. Drehs M.M. Weinberg J.M. Topical imiquimod for acyclovir-unresponsive herpes simplex virus 2 infection.Arch Dermatol. 2001; 137: 1015-1017PubMed Google Scholar This patient presented with a 5-month history of penile HSV-2 infection that became unresponsive to acyclovir, valacyclovir and famciclovir. He was receiving antiretroviral therapy with a complete suppression of HIV-1 replication and a CD4 cell count of 200 cells/mm3. After the application of imiquimod to the lesions 3 times over the course of a week, the skin lesion improved with reepithelialization of the erosion. Imiquimod therapy was discontinued after 1 week and no recurrence was seen after 1 month of follow-up. Danielsen et al also reported the case of a 28-year-old HIV-infected man with a very painful penile erosion due to both HSV-1 and -2 infection that was clinically resistant to acyclovir, valacyclovir, famciclovir and intravenous foscarnet.10Danielsen A.G. Petersen C.S. Iversen J. Chronic erosive herpes simplex virus infection of the penis in a human immunodeficiency virus-positive man, treated with imiquimod and famciclovir.Br J Dermatol. 2002; 147: 1034-1036Crossref PubMed Scopus (21) Google Scholar The patient received a 10-week combination of topical imiquimod and systemic famciclovir, leading to a slow healing of the erosion. Famciclovir was then continued alone with no further relapse 20 months later. Finally, Christensen and Hengge reported the case of a 30-year-old woman with a 2-year history of chronically recurrent genital HSV-2 infection who received a 3-month course of imiquimod 3 times a week following a 5-day course of intravenous acyclovir and who experienced no further recurrent HSV infection after a 6-month follow-up.11Christensen B. Hengge U.R. Recurrent urogenital herpes simplex-successful treatment with imiquimod?.Sex Transm Infect. 1999; 75: 132-133PubMed Google Scholar However, spontaneous resolution of symptoms is found in up to 15% of patients in clinical trials aiming at preventing recurrent herpes, and a recent study in immunocompetent adults showed that imiquimod alone did not significantly alter the time to first recurrence of herpes genitalis.12Schacker T.W. Conant M. Thoming C. Stanczak T. Wang Z. Smith M. Imiquimod HSV study groupImiquimod 5-percent cream does not alter the natural history of recurrent herpes genitalis a phase II, randomized, double-blind, placebo-controlled study.Antimicrob Agents Chemother. 2002; 46: 3243-3248Crossref PubMed Scopus (49) Google Scholar Further studies need to be completed, therefore, to better assess the benefit of imiquimod in patients with recurrent HSV infections. The exact antiviral mechanism of action of imiquimod remains incompletely understood. Imiquimod is a local immunomodulator, which belongs to the family of imidazoquinolines and induces the production of various cytokines (including IL-12) and interferons. It has been shown to be effective in anogenital human papilloma virus-associated condylomata, both in acute therapy and long-term prophylaxis. Animal experiments have also indicated the effectiveness of this substance in HSV infection, in particular with respect to the prevention of recurrences.13Miller R.L. Imbertson L.M. Reiter M.J. Gerster J.F. Treatment of primary herpes simplex virus infection in guinea pigs by imiquimod.Antiviral Res. 1999; 44: 31-42Crossref PubMed Scopus (54) Google Scholar The drug has no direct antiviral activity, and its effect might be mediated through activation of monocyte-macrophages to secrete various cytokines, resulting in a T-helper 1 dominant response.14Wagner T.L. Ahonen C.L. Couture A.M. et al.Modulation of TH1 and TH2 cytokine production with the immune response modifiers, R-848 and imiquimod.Cell Immunol. 1999; 191: 10-19Crossref PubMed Scopus (252) Google Scholar It has also been shown that imiquimod induces functional maturation of human Langerhans cells. The T-helper 1 cytokine switch and the increased antigen presentation might be very helpful in patients with underlying immune deficits. Imiquimod also induces local interferon alpha production, which is known to have direct antiviral activity and which persists beyond the time of an effective concentration of the drug. Topical imiquimod therefore offers another alternative for the treatment of HSV infections, particularly in the setting of immunocompromised patients experiencing multiple recurrences or chronic infections with resistant strains. However, clinical experience is very limited so far, and further studies are clearly needed.