Intralesional immunotherapy for common warts is effective and safe

May 16 2005

Injection of skin test antigens (preparations used in skin tests for immunity) into warts appears to stimulate the immune system and successfully treat the injected wart and also helps to treat distant non-injected warts, according to a study in the May issue of Archives of Dermatology.

Warts are unsightly and often tender or painful, causing most patients with warts to seek treatment. Primary treatment usually involves destruction of the wart using one of a number of different techniques, including cutting it out, applying salicylic acid, freezing it with liquid nitrogen and laser vaporization, according to background information provided in the article. Because wart proliferation is controlled by the immune system, various methods have been tried to stimulate an immune response to the human papillomavirus (HPV), the cause of skin warts. Previous studies have shown that injecting a wart with an antigen preparation of mumps, Candida (a cause of yeast infections) or Trichophyton (a cause of fungal infections) clears the wart and other distant and distinct warts. These skin test antigens, although they can not cause or promote infection themselves, cause a reaction on the skin if a person has been previously exposed to mumps, Candida or Trichophyton, and are used to test for immunity.

Thomas D. Horn, M.D., of the University of Arkansas for Medical Sciences, Little Rock, and colleagues conducted a randomized, clinical trial to determine the effectiveness of wart treatment with injection of skin test antigen. Warts were injected with antigen alone, antigen plus interferon alfa-2b (a chemical produced by the immune system), interferon alfa-2b alone or normal saline. Patients who had more than one wart were also tested for an immune response to HPV. Because interferon alfa-2b had no impact on the results, the patient data were analyzed in two groups, those who had received antigen and those who did not.

Of the 201 patients enrolled in the study, 95 received injections of antigen and 106 received injections of either saline or interferon alfa-2b alone. "Fifty-seven subjects injected with antigen were judged to have 100 percent resolution of warts at study conclusion, 21 of whom had more than one wart and experienced 100 percent resolution of all distant warts," the authors report. "In the interferon alfa-2b and saline groups, these numbers were 25 and 11, respectively." The researchers also found that patients who responded to treatment were much more likely to have an immune response to HPV.

"Our repeated observation that untreated warts resolve after injection of only one wart prompts the speculation that intralesional [injection into the wart] immunotherapy induces HPV-directed immunity," the authors write. "Indeed we have observed resolution of hundreds of flat warts in individual patients after injection of only one lesion. . It is possible that local and distant responses of warts in subjects who received saline or interferon alfa-2b alone develop by the same mechanism as when antigen is injected and that many triggers of an immune response to HPV exist. While injection of saline is an appropriate control, it is not a true placebo. That noted, local and systemic responses to saline injection in this study were far less likely than when antigen was used."

"Intralesional immunotherapy for common warts is effective and safe," the authors conclude. "It is unique in affording many patients a therapeutic response in untreated warts and may, through stimulation of HPV-directed immunity, provide fewer recurrent warts. While useful in any patient with warts, intralesional immunotherapy may be particularly useful in patients with numerous lesions or lesions covering large surface areas."