The second option approach might be more efficient, as heterologous sporozoites would evade strain-specific neutralizing immunity, thereby increasing the liver parasite burden at second and third immunizations. control serum were pre-incubated with 3-collapse serial dilutions of the 2A10 monoclonal antibody (0.027C20?g/mL), targeting the repeat region of the circumsporozoite protein (CSP), and added to primary human being hepatocyte ethnicities. Six days post-infection, the number of NF54 parasites under chemoprophylaxis (chemoprophylaxis and sporozoite (CPS)-immunization) induces the most efficient long-lasting safety against a homologous parasite. However, parasite genetic diversity is a major hurdle for safety against heterologous strains. Methods We carried out 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 illness 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 total safety in 5/5 volunteers against NF54 challenge illness 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 being 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 safeguarded against heterologous challenge were among the stronger immune responders to in vitro parasite activation. Conclusions Although highly protecting against homologous parasites, NF54-CPS-induced immunity is definitely less effective against heterologous parasite clones both in vivo and in vitro. Our data show that whole sporozoite-based vaccine methods require more potent immune reactions for heterologous safety. Trial sign up This trial is definitely authorized in clinicaltrials.gov, under identifier “type”:”clinical-trial”,”attrs”:”text”:”NCT02098590″,”term_id”:”NCT02098590″NCT02098590. Electronic supplementary material The online version of this article (doi:10.1186/s12916-017-0923-4) contains supplementary material, which is available to authorized users. NF54-infected mosquitoes followed by a challenge illness with either NF135.C10 clone from Cambodia or NF166.C8 clone from Guinea. Parasites were characterized by whole genome sequencing and CPS-induced cellular and humoral reactions were analyzed. Methods Study design and participants This solitary center, double-blind, randomized, placebo-controlled trial was carried out in the Radboud university or college medical center (Nijmegen, The Netherlands) between February and November 2015. Study participants were healthy male and woman volunteers (18C35 years old) with no history of malaria and screened for eligibility, including a complete medical and family history, physical examination, blood hematological and biochemical guidelines, and serology for HIV, hepatitis B and C, and the asexual phases of as previously explained [20]. All candidate participants provided written educated consent in the screening visit. Study authorization The study was authorized by the Central Committee for Study Involving Human Subjects of The Netherlands (CCMO NL48732.091.14) and conducted according to the principles outlined in the Declaration of Helsinki and Good Clinical Practice requirements. This trial is definitely authorized at ClinicalTrials.gov, identifier “type”:”clinical-trial”,”attrs”:”text”:”NCT02098590″,”term_id”:”NCT02098590″NCT02098590. Methods All included study subjects (n?=?41, Fig.?1) received chloroquine inside a prophylactic dose (we.e., a loading dose of 300?mg of chloroquine on each of the first 2?days, followed by 300?mg once a week), for a total duration of 13?weeks. While under chloroquine prophylaxis, study organizations 1, 2 and 3 received three immunizations with bites of 15 NF54-infected mosquitoes. PF-00562271 Organizations 4, 5 and 6 received three mock immunizations with bites of 15 uninfected mosquitoes. Open in a separate windows Fig. 1 Clinical trial profile Volunteers were followed on an outpatient basis from days 6 to 10 after each immunization. Blood was examined daily, including hemocytometry, white-blood cell counts, lactic acid dehydrogenase, and highly sensitive troponin-T. From day time 7 to 9, blood was also checked for PF-00562271 malaria parasites by solid blood smear microscopy and quantitative real-time PCR (qPCR) was performed retrospectively (after study de-blinding), as described previously [21, 22]. At 14?weeks after discontinuation of chloroquine prophylaxis, all participants were exposed to bites of five mosquitoes (Table?1). Subjects of organizations 1 and 4 were challenged with the heterologous NF135.C10 clone, organizations 2 and 5 with the heterologous NF166.C8 clone, and organizations 3 and 6 with the homologous NF54 strain. Mosquitoes were examined to verify that a blood meal was taken and the presence of sporozoites in mosquito salivary glands was confirmed by dissection. If insufficient infected mosquitoes had taken a blood meal, subjects were exposed to additional mosquitoes. Table 1 Baseline characteristics of subjects included in the analysis strain?ImmunizationNF54NF54NF54UninfectedUninfectedUninfected?ChallengeNF135NF54, NF135.C10, and NF166.C8 asexual and sexual blood phases were cultured in a semi-automated tradition system [26C29]. mosquitoes for immunizations and challenge infections were reared in the Radboud university or college medical center insectary (Nijmegen, The Netherlands) relating to standard operating procedures. Infected mosquitoes were Rabbit Polyclonal to SKIL acquired by standard PF-00562271 membrane feeding on gametocyte ethnicities of the different strains as explained previously [29]. For in vitro sporozoite infectivity assays, salivary glands from infected.