Mycobacterium vaccae reduces scratching behavior but not the rash in NC mice with eczema: a randomized, blinded,...

In a randomized, double-blinded, placebo-controlled trial, we previously showed that intra-dermal administration of a killed Mycobacterium vaccae suspension to school-aged children with atopic dermatitis ameliorates their disease. We wished to test the hypothesis that M. vaccae may also prevent the development of eczema. As it was not possible to do this in children, we studied the NC/Nga eczema mouse model. Thirty NC/Nga mice were randomized into a blinded, placebo-controlled trial where they received either 0.1 or 0.01 mg of M. vaccae (SRP299) or placebo given subcutaneously at 1 and 8 wk of age. Clinical eczema scores, as well as scratching frequency using a digital videotape system were assessed during the 26-wk study. Digital scratch scores correlated with clinical severity (p=0.001). Although there were no significant differences in age of onset or severity of the rash between the three study arms, mice injected with 0.1 mg but not 0.01 mg of SPR299 had significantly lower peak scratch frequencies than controls (Hazard ratio 0.2; 95% confidence interval 0.1-0.7; p=0.01). We conclude that in this NC/Nga mouse model, SRP299 did have a beneficial effect in reducing pruritus, a major clinical symptom of eczema, although it does not prevent the rash from developing.