Preclinical safety and tolerability of a repeatedly administered human leishmaniasis DNA vaccine

Riede, O; Seifert, K; Oswald, D; Endmann, A; Hock, C; Winkler, A; Salguero, F J; Schroff, M; Croft, S L; Juhls, C

In a repeated-dose toxicity study in naive mice, we tested three ascending doses of LEISHDNAVAX. The highest dose of 100 μg corresponds to a human dose of~300 mg DNA on a mg kg − 1 body weight base. Doses in published clinical trials ranged from 0.1 mg 33 to 4 mg 34 of plasmid DNA, so our study design includes a high safety margin. To further extend the safety margin, the vaccine was administered in a condensed schedule of five vaccinations (one more than the estimated maximum number for clinical application) in weekly intervals. Importantly, a No Observed Adverse Effect Level, that is, the highest dose without significant toxicity, was not reached with the doses tested. No local intolerance reactions related to the vaccine were observed. The results established in naive mice are corroborated by safety data obtained from the biodistribution study. Rats received 120 μg LEISHDNAVAX, corresponding to a human dose of~24 mg (based on mg kg − 1 body weight). There were no vaccine-related toxic effects observed either. Our results further confirm the findings of other investigators reporting excellent preclinical safety profiles of DNA vectors. 10, 11, 20, 26, 27, 30 In Leishmania-infected and diseased individuals, tolerability of the vaccine may be different than in healthy, naive vaccinees. Moreover, owing to the ability of Leishmania amastigotes to exploit host IgG as virulence factor, 35 there is the theoretical risk of vaccine-related immune-enhancement of infection and pathogenesis as discussed for other infectious diseases. 36, 37 Hence demonstration of absence of disease exacerbation was included into the development program of LEISHDNAVAX. We evaluated the tolerability of LEISHDNAVAX in two different mouse strains, chosen for their inherent differences in cytokine responses to infection with L. donovani. 38 These experiments demonstrate that LEISHDNAVAX had no effect on the kinetics of the parasite burden with no vaccine-related enhancement of infection at any of the time points investigated. The kinetic of infection corresponded to the well-documented pattern in mice with a rapid increase in hepatic parasite burden, followed by a decline in parasite numbers and clearance and a slower increase in parasite numbers in the spleen with the establishment of chronic infections. 23 Results for all other standard parameters were similar for treated and nontreated mice, demonstrating a good tolerability of the vaccine candidate in infected animals.