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Contains fulltext : 248611.pdf (Publisher’s version ) (Open Access), Sporozoite-based approaches currently represent the most effective vaccine strategies for induction of sterile protection against Plasmodium falciparum (Pf) malaria. Clinical development of subunit vaccines is almost exclusively centered on the circum-sporozoite protein (CSP), an abundantly expressed protein on the sporozoite membrane. Anti-CSP antibodies are able to block sporozoite invasion and development in human hepatocytes and subsequently prevent clinical malaria. Here, we have investigated whether sporozoite-induced human antibodies with specificities different from CSP can reduce Pf-liver stage development. IgG preparations were obtained from 12 volunteers inoculated with a protective immunization regime of whole sporozoites under chloroquine prophylaxis. These IgGs were depleted for CSP specificity by affinity chromatography. Recovered non-CSP antibodies were tested for sporozoite membrane binding and for functional inhibition of sporozoite invasion of a human hepatoma cell line and hepatocytes both in vitro and in vivo. Postimmunization IgGs depleted for CS specificity of 9 of 12 donors recognized sporozoite surface antigens. Samples from 5 of 12 donors functionally reduced parasite-liver cell invasion or development using the hepatoma cell line HC-04 and FRG-huHep mice containing human liver cells. The combined data provide clear evidence that non-CSP proteins, as yet undefined, do represent antibody targets for functional immunity against Pf parasites responsible for malaria.

Contains fulltext : 202100.pdf (publisher's version ) (Open Access)

Radboud University, 22 november 2018, Promotor : Sauerwein, R.W. Co-promotor : Scholzen, A., Contains fulltext : 196833.pdf (publisher's version ) (Open Access)

Contains fulltext : 191406.pdf (publisher's version ) (Open Access)

Contains fulltext : 177825.pdf (publisher's version ) (Open Access), BACKGROUND: A highly efficacious vaccine is needed for malaria control and eradication. Immunization with Plasmodium falciparum NF54 parasites under chemoprophylaxis (chemoprophylaxis and sporozoite (CPS)-immunization) induces the most efficient long-lasting protection against a homologous parasite. However, parasite genetic diversity is a major hurdle for protection against heterologous strains. METHODS: We conducted a double-blind, randomized controlled trial in 39 healthy participants of NF54-CPS immunization by bites of 45 NF54-infected (n = 24 volunteers) or uninfected mosquitoes (placebo; n = 15 volunteers) against a controlled human malaria infection with the homologous NF54 or the genetically distinct NF135.C10 and NF166.C8 clones. Cellular and humoral immune assays were performed as well as genetic characterization of the parasite clones. RESULTS: NF54-CPS immunization induced complete protection in 5/5 volunteers against NF54 challenge infection at 14 weeks post-immunization, but sterilely protected only 2/10 and 1/9 volunteers against NF135.C10 and NF166.C8 challenge infection, respectively. Post-immunization plasma showed a significantly lower capacity to block heterologous parasite development in primary human hepatocytes compared to NF54. Whole genome sequencing showed that NF135.C10 and NF166.C8 have amino acid changes in multiple antigens targeted by CPS-induced antibodies. Volunteers protected against heterologous challenge were among the stronger immune responders to in vitro parasite stimulation. CONCLUSIONS: Although highly protective against homologous parasites, NF54-CPS-induced immunity is less effective against heterologous parasite clones both in vivo and in vitro. Our data indicate that whole sporozoite-based vaccine approaches require more potent immune responses for heterologous protection. TRIAL REGISTRATION: This trial is registered in clinicaltrials.gov, under identifier NCT02098590 .

Contains fulltext : 189906.pdf (publisher's version ) (Open Access)

Contains fulltext : 154144.PDF (publisher's version ) (Open Access)

Contains fulltext : 138997.pdf (publisher's version ) (Open Access), Immunization of healthy volunteers with chloroquine ChemoProphylaxis and Sporozoites (CPS-CQ) efficiently and reproducibly induces dose-dependent and long-lasting protection against homologous Plasmodium falciparum challenge. Here, we studied whether chloroquine can be replaced by mefloquine, which is the only other licensed anti-malarial chemoprophylactic drug that does not affect pre-erythrocytic stages, exposure to which is considered essential for induction of protection by CPS immunization. In a double blind randomized controlled clinical trial, volunteers under either chloroquine prophylaxis (CPS-CQ, n = 5) or mefloquine prophylaxis (CPS-MQ, n = 10) received three sub-optimal CPS immunizations by bites from eight P. falciparum infected mosquitoes each, at monthly intervals. Four control volunteers received mefloquine prophylaxis and bites from uninfected mosquitoes. CPS-MQ immunization is safe and equally potent compared to CPS-CQ inducing protection in 7/10 (70%) versus 3/5 (60%) volunteers, respectively. Furthermore, specific antibody levels and cellular immune memory responses were comparable between both groups. We therefore conclude that mefloquine and chloroquine are equally effective in CPS-induced immune responses and protection. TRIAL REGISTRATION: ClinicalTrials.gov NCT01422954.

Contains fulltext : 136852.pdf (publisher's version ) (Open Access), BACKGROUND: Long-lasting and sterile protective immunity against Plasmodium falciparum can be achieved by immunization of malaria-naive human volunteers under chloroquine prophylaxis with sporozoites delivered by mosquito bites (CPS-immunization). Protection is mediated by sporozoite/liver-stage immunity. In this study, the capacity of CPS-induced antibodies to interfere with sporozoite functionality and development was explored. METHODS: IgG was purified from plasma samples obtained before and after CPS-immunization from two separate clinical trials. The functionality of these antibodies was assessed in vitro in gliding and human hepatocyte traversal assays, and in vivo in a human liver-chimeric mouse model. RESULTS: Whereas pre-treatment of sporozoites with 2 mg/ml IgG in the majority of the volunteers did not have an effect on in vitro sporozoite gliding motility, CPS-induced IgG showed a distinct inhibitory effect in the sporozoite in vitro traversal assay. Pre-treatment of P. falciparum sporozoites with post-immunization IgG significantly inhibited sporozoite traversal through hepatocytes in 9/9 samples when using 10 and 1 mg/ml IgG, and was dose-dependent, resulting in an average 16% and 37% reduction with 1 mg/ml IgG (p = 0.003) and 10 mg/ml IgG (p = 0.002), respectively. In vivo, CPS-induced IgG reduced liver-stage infection and/or development after a mosquito infection in the human liver-chimeric mouse model by 91.05% when comparing 11 mice receiving post-immunization IgG to 11 mice receiving pre-immunization IgG (p = 0.0008). CONCLUSIONS: It is demonstrated for the first time that CPS-immunization induces functional antibodies against P. falciparum sporozoites, which are able to reduce parasite-host cell interaction by inhibiting parasite traversal and liver-stage infection. These data highlight the functional contribution of antibody responses to pre-erythrocytic immunity after whole-parasite immunization against P. falciparum malaria.