Nasal Immunization with a Malaria Transmission-Blocking Vaccine Candidate, Pfs25, Induces Complete Protective Immunity in Mice against Field Isolates of Plasmodium falciparum

Abstract

Malaria transmission-blocking vaccines based on antigens expressed in sexual stages of the parasites are considered one promising strategy for malaria control. To investigate the feasibility of developing noninvasive mucosal transmission-blocking vaccines against Plasmodium falciparum, intranasal immunization experiments with Pichia pastoris-expressed recombinant Pfs25 proteins were conducted. Mice intranasally immunized with the Pfs25 proteins in the presence of a potent mucosal adjuvant cholera toxin induced robust systemic as well as mucosal antibodies. All mouse immunoglobulin G (IgG) subclasses except IgG3 were found in serum at comparable levels, suggesting that the immunization induced mixed Th1 and Th2 responses. Consistent with the expression patterns of the Pfs25 proteins in the parasites, the induced immune sera specifically recognized ookinetes but not gametocytes. In addition, the immune sera recognized Pfs25 proteins with the native conformation but not the denatured forms, indicating that mucosal immunization induced biologically active antibodies capable of recognizing conformational epitopes of native Pfs25 proteins. Feeding Anopheles dirus mosquitoes with a mixture of the mouse immune sera and gametocytemic blood derived from patients infected with P. falciparum resulted in complete interference with oocyst development in mosquito midguts. The observed transmission-blocking activities were strongly correlated with specific serum antibody titers. Our results demonstrated for the first time that a P. falciparum transmission-blocking vaccine candidate is effective against field-isolated parasites and may justify the investigation of noninvasive mucosal vaccination regimens for control of malaria, a prototypical mucosa-unrelated mosquito-borne parasitic disease.

Protection of Mice from Rabies by Intranasal Immunization with Inactivated Rabies Virus

“…in mice administered intranasally with crV without cT, both igG 1 and igG 2a levels were generally low, and more igG 1 seemed to be induced than igG 2a . however, intranasal immunization with crV/cT, in the presence of cT, induced mixed igG 2a /igG 1 . interestingly, all mice intranasally immunized with crV/cT showed high igG 2a levels, whereas enhancement of igG 1 production was only observed in some of them.…”

“…horseradish peroxidase (hrP)-conjugated goat antimouse IgG (Gamma chain specific), HRP-conjugated goat anti-mouse igG 1 , and hrP-conjugated goat antimouse igG 2a were purchased (ZYmED, san Francisco, cA). hrP-conjugated goat anti-mouse igA (siGmA Aldrich japan, Tokyo, japan) was also used in this study.…”

“…recently, mucosal immunization using recombinant proteins or inactivated pathogens has been studied for both mucosal [15,19,22,25,26,28,29,30] and nonmucosal pathogens [1,2,16,23]. Due to the ease of administration and the efficacy against both mucosal and non-mucosal pathogens, a mucosal immunization strategy with recombinant protein is considered as one of the most promising alternative vaccination methods.…”

Alternative approaches to vaccine delivery

“…Subsequently, the same authors confirmed that intranasal immunization with the P. falciparum homologue of Pvs25, Pfs25, also induced strong serum antibodies when co-administered with CT, and the antibodies could completely block parasite transmission to mosquitoes. 67 Intranasal immunization of mice with MSP1 19 , either from P. yoelii (PyMSP1 19 ) or P. vivax (PvMSP1 19 ), was also shown to induce serum antibodies and protect the immunized mice against parasite challenge in the case of PyMSP1 19 . 69,70 For delivery via the oral route, recombinant proteins are commonly encapsulated in particulate formulations to protect them against degradation and enhance their uptake by the immune system.…”

“…Successful immunization via the intranasal route of recombinant protein in an effective mucosal adjuvant has been reported for Plasmodium antigens. [67][68][69][70] Recombinant P. vivax ookinete surface protein Pvs25 was shown to induce transmission-blocking serum antibodies when given intranasally to mice in the presence of cholera toxin (CT). 68 The level and isotype profile of the antibodies were comparable to those induced by intraperitoneal immunization with alum-adsorbed Pvs25.…”