Improvement in psoriasis after intradermal administration of heat-killed Mycobacterium vaccae

Background New treatments for psoriasis are being developed, but many are a ssociated with limited efficacy, side-effects, or rapid recurrence after di scontinuation. Thus, the aim of new agents is to induce longer term remissi ons with fewer side-effects. Preliminary studies have shown that Mycobacter ium vaccae, a nonpathogenic organism prepared as a heat-killed suspension, may induce periods of remission in some psoriasis patients when administere d intradermally. Methods To further assess the efficacy and tolerability of M. vaccae in pat ients with moderate to severe psoriasis (psoriasis area and severity index (PASI) of 12-35), we conducted an open label study whereby 24 patients rece ived two intradermal inoculations of M. vaccae in lesion-free deltoid skin, separated by a period of 3 weeks. Results Twelve weeks after starting treatment, 14 of 24 patients (58%) show ed marked improvement in the PASI score (greater than 50% reduction), two h ad moderate improvement (25-50% reduction), six were unchanged (< 25% reduc tion), and two had worsened (> 5% increase). By 24 weeks, 11 of 22 patients continued to show greater than 50% improvement. Five patients had complete clearance of skin lesions that lasted for at least 6 months. Conclusions Intradermal administration of heat-killed M. vaccae suspension was well tolerated and induced clinically significant improvement in a majo rity of psoriasis patients in this cohort. Placebo-controlled testing to fu rther define the efficacy of this treatment is warranted.