A randomized double-blind Phase IIb trial to evaluate the efficacy of ChAd63-KH for the treatment of post kala-azar dermal leishmaniasis.

In a recent Phase IIa clinical trial, the candidate leishmaniasis vaccine ChAd63-KH was shown to be safe and immunogenic in Sudanese patients with post kala- azar dermal leishmaniasis. However, its value as a stand-alone therapeutic was unknown. To assess the therapeutic efficacy of ChAd63-KH, we conducted a randomized, double-blind, placebo-controlled Phase IIb trial (Clinicaltrials.gov registration: NCT03969134). Primary outcomes were safety and efficacy (≥90% improvement in clinical disease). Secondary outcomes were change in severity grade and vaccine-induced immune response. 86 participants with uncomplicated post kala azar dermal leishmaniasis of ≥ six months duration were randomised to receive ChAd63-KH (7.5x10¹⁰ viral particles once i.m.) or placebo. 75 participants (87%) completed the trial as per protocol. No severe or serious adverse events were observed. At day 90 post vaccination, 6/40 (15%) and 4/35 (11%) participants in the vaccine and placebo groups respectively showed ≥ 90% clinical improvement (RR 1.31 [95% CI, 0.40 to 4.28], p=0.742). There were also no significant differences in PKDL severity grade between study arms. Whole blood transcriptomic analysis identified transcriptional modules associated with interferon responses and monocyte and dendritic cell activation. Thus, a single vaccination with ChAd63-KH showed no therapeutic efficacy in this subset of Sudanese PKDL patients.