Author summary Malaria continues to be the deadliest parasitic disease worldwide, and an effective vaccine yielding sterile immunity does not yet exist. Attenuated parasites can induce sterile... Show moreAuthor summary Malaria continues to be the deadliest parasitic disease worldwide, and an effective vaccine yielding sterile immunity does not yet exist. Attenuated parasites can induce sterile protection in both human and rodent models for malaria, but these vaccines need to be administered directly into the bloodstream in order to convey protection; administration via the skin results in a much-reduced efficacy. We hypothesized this is caused by an early immune regulation initiated at the first site of contact with the immune system: the skin. However, the human skin stage of malaria has not been investigated to date. We used human antigen presenting cells as well as whole human skin explants to investigate (dermal) immune responses and found thatPlasmodiumsporozoites are able to suppress immune responses by inducing regulatory macrophages. Our study provides new insights in the mechanism of early immune regulation exploited byPlasmodiumparasites and can help to explain why intradermal vaccination using whole attenuated sporozoites results in reduced protection.Professional antigen-presenting cells (APCs), like macrophages (M phi s) and dendritic cells (DCs), are central players in the induction of natural and vaccine-induced immunity to malaria, yet very little is known about the interaction of SPZ with human APCs. Intradermal delivery of whole-sporozoite vaccines reduces their effectivity, possibly due to dermal immunoregulatory effects. Therefore, understanding these interactions could prove pivotal to malaria vaccination. We investigated human APC responses to recombinant circumsporozoite protein (recCSP), SPZ and anti-CSP opsonized SPZ both in monocyte derived MoDCs and MoM phi s. Both MoDCs and MoM phi s readily took up recCSP but did not change phenotype or function upon doing so. SPZ are preferentially phagocytosed by MoM phi s instead of DCs and phagocytosis greatly increased after opsonization. Subsequently MoM phi s show increased surface marker expression of activation markers as well as tolerogenic markers such as Programmed Death-Ligand 1 (PD-L1). Additionally they show reduced motility, produce interleukin 10 and suppressed interferon gamma (IFN gamma) production by antigen specific CD8(+)T cells. Importantly, we investigated phenotypic responses to SPZ in primary dermal APCs isolated from human skin explants, which respond similarly to their monocyte-derived counterparts. These findings are a first step in enhancing our understanding of pre-erythrocytic natural immunity and the pitfalls of intradermal vaccination-induced immunity. Show less
Winkel, B.M.F.; Korne, C.M. de; Oosterom, M.N. van; Staphorst, D.; Meijhuis, M.; Baalbergen, E.; ... ; Roestenberg, M. 2019
Given the number of global malaria cases and deaths, the need for a vaccine against Plasmodium falciparum (Pf) remains pressing. Administration of live, radiation-attenuated Pf sporozoites can... Show moreGiven the number of global malaria cases and deaths, the need for a vaccine against Plasmodium falciparum (Pf) remains pressing. Administration of live, radiation-attenuated Pf sporozoites can fully protect malaria-naive individuals. Despite the fact that motility of these attenuated parasites is key to their infectivity and ultimately protective efficacy, sporozoite motility in human tissue (e.g. skin) remains wholly uncharacterized to date. We show that the ability to quantitatively address the complexity of sporozoite motility in human tissue provides an additional tool in the development of attenuated sporozoite vaccines. We imaged Pf movement in the skin of its natural host and compared wild-type and radiation-attenuated GFP-expressing Pf sporozoites. Using custom image analysis software and human skin explants we were able to quantitatively study their key motility features. This head-to-head comparison revealed that radiation attenuation impaired the capacity of sporozoites to vary their movement angle, velocity and direction, promoting less refined movement patterns. Understanding and overcoming these changes in motility will contribute to the development of an efficacious attenuated parasite malaria vaccine. Show less
Langenberg, M.C.C.; Hoogerwerf, M.A.; Janse, J.J.; Lieshout, L. van; Corstjens, P.L.A.M.; Roestenberg, M.; ... ; CoHSI Clinical Trial Team 2019
