Apicomplexan parasites are attenuated by low-energy electron irradiation in an automated microfluidic system and protect against infection with Toxoplasma gondii

Abstract

Radiation-attenuated intracellular parasites are promising immunization strategies. The irradiated parasites are able to invade host cells but fail to fully replicate, which allows for the generation of an efficient immune response. Available radiation technologies such as gamma rays require complex shielding constructions and are difficult to be integrated into pharmaceutical production processes. In this study, we evaluated for the first time low-energy electron irradiation (LEEI) as a method to generate replication-deficient Toxoplasma gondii and Cryptosporidium parvum. Similar to other radiation technologies, LEEI mainly damages nucleic acids; however, it is applicable in standard laboratories. By using a novel, continuous, and microfluidic-based LEEI process, tachyzoites of T. gondii and oocysts of C. parvum were irradiated and subsequently analyzed in vitro. The LEEI-treated parasites invaded host cells but were arrested in intracellular replication. Antibody-based analysis of surface proteins revealed no significant structural damage due to LEEI. Similarly, excystation rates of sporozoites from irradiated C. parvum oocysts were similar to those from untreated controls. Upon immunization of mice, LEEI-attenuated T. gondii tachyzoites induced high levels of antibodies and protected the animals from acute infection. These results suggest that LEEI is a useful technology for the generation of attenuated Apicomplexan parasites and has potential for the development of anti-parasitic vaccines.

Influenza Virus Inactivated by Heavy Ion Beam Irradiation Stimulates Antigen-Specific Immune Responses

“…In the case of ionizing radiation, radioprotectors such as a reconstituted Mn-decapeptide (MDP) antioxidant complex have been implemented to limit the damage [ 35 , 36 ]. Other alternatives to γ-irradiation rely on low- [ 37 , 38 ] and high-energy [ 39 ] electrons. While low-energy electrons are safer in terms of radioprotection compared to high-energy electrons, which require large and complex shielding to prevent release of radioactive radiation, their impact level is limited, making large-scale vaccine production impossible [ 24 ].…”

Mucosal immunization with a low-energy electron inactivated respiratory syncytial virus vaccine protects mice without Th2 immune bias

“…The RSV-A samples were irradiated in a research LEEI prototype (21) in a module based on a microfluidic system as previously described (25). In short, RSV [in PBS with 12% (w/v) trehalose] was filled into a disposable syringe which was inserted into the system and connected to a microfluidic chip (MFC) made of titan with eight parallel channels (180 µm in depth) milled into it.…”

“…LEEI was used as a non-toxic and non-probe-harming inactivation method with improved safety compared to chemical inactivation or other radiation methods. It has been used successfully for the generation of several viral, bacterial, and parasitic vaccine candidates (19)(20)(21)(22)(23)(24)(25).…”

Mucosal Application of a Low-Energy Electron Inactivated Respiratory Syncytial Virus Vaccine Shows Protective Efficacy in an Animal Model

“…Virus inactivation approaches, especially those using physical methods, are safe and have low production costs [ 38 , 39 , 40 ]. We have shown previously that low-energy electron irradiation (LEEI) is a safe, non-toxic, and non-probe harming inactivation method [ 41 , 42 , 43 , 44 , 45 , 46 ]. The advantage over other irradiation methods is that the emission of secondary photon radiation is minimal, reducing the need for extensive shielding and making LEEI-technologies applicable in standard laboratories [ 43 , 47 ].…”

“…The advantage over other irradiation methods is that the emission of secondary photon radiation is minimal, reducing the need for extensive shielding and making LEEI-technologies applicable in standard laboratories [ 43 , 47 ]. Since the penetration depth of low-energy electrons is highly limited [ 48 , 49 ], we have developed automated processes that generate thin liquid films, enabling the efficient LEEI of pathogens in suspension up to multi-liter scales [ 41 , 42 , 43 , 46 ]. LEEI has advantages over other radiation types such as ultraviolet (UV) light.…”