Topical Diphenylcyclopropenone as a Measure of Immune Competence in HIV-Seropositive Subjects

Background: CD4 T cell counts are recognized as the standard method for monitoring HIV-seropositive patients and, along with viral load, are clinically important as indicators for initiating highly active antiretrovival therapy (HAART). Skin reaction scores following topical application of diphenylcyclopropenone (DPC) also demonstrate diagnostic utility as a functional measure of immune competence. Methods: We used low sensitizing doses of DPC in 40 patients applied in a non-volatile, non-irritating topical delivery system to assess immune competence in 40 HIV-seropositive subjects with a range of CD4 T cell counts. Standardized patch test reading scores were used, with 2+ or greater scores (erythema and induration) indicative of a positive response. The patch test scores were then compared with CD4 counts. Results: Application of DPC in concentrations of 0.4% and 0.2% successfully resulted in 90% sensitivity skin reaction scores in subjects with >300 CD4 T cells/microL, following a single 0.1 mL application to the inner aspect of the arm. Lower DPC concentrations of 0.1% and 0.05% were too low for initial sensitization reactions. Three subjects with CD4 counts between 150 and 300 cells/microL showed positive skin reactions indicating that this DPC test gives the clinician information on cellular immunity beyond the CD4 count. Conclusion: We conclude that a single topical application of DPC at concentrations between 0.2% and 0.4% can serve as a measure of immune competence in HIV-seropositive patients. As a functional measure of immunocompetence, this DPC test provides information beyond a CD4 count, which is particularly relevant to HIV-positive subjects with CD4 counts between 200 and 350 cells/microL.