Evaluation of the potency of BIKEN inactivated Japanese Encephalitis vaccine and DNA vaccines in an intracerebral Japanese Encephalitis virus challenge model

Ashok, MS and Rangarajan, PN (2000) Evaluation of the potency of BIKEN inactivated Japanese Encephalitis vaccine and DNA vaccines in an intracerebral Japanese Encephalitis virus challenge model. In: Vaccine, 19 (2-3). pp. 155-157.

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Abstract

Japanese Encephalitis virus (JEV), a member of the family flaviviridae is the causative agent of acute encephalitis in humans leading to high mortality, especially in children. While effective inactivated vaccines derived from JEV-infected mouse brain are available, their high cost and allergic reactivity have necessitated the need to develop recombinant vaccines for JE [1]. Several recent reports demonstrated that immunization with plasmids containing JEV premembrane (prM) and envelope (E) genes or E gene alone as well as those containing the gene encoding non-structural protein1 (NS1) induce protective immunity against lethal JEV challenge [2, 3, 4 and 5]. Intramuscular (i.m.) immunization of ICR mice twice at 2-week intervals with 80 μg of plasmid expressing prM plus E (pJME) or NS1 (pJNS1) results in 70 and 100% protection respectively when challenged with neuroinvasive RP-9 strain of JEV administered intraperitoneally (i.p.) along with intracerebral (i.c.) injection of saline [2]. In another study, i.m. immunization of ICR mice twice at 2-week intervals with 10 or 100 μg of plasmid expressing prM plus E are protected up to 100% when challenged i.p. with Beijing P3 strain of JEV [3 and 4]. In this study, none of the mice immunized once with 0.1, 1.0 or 10 μg survived viral challenge. Thus, two immunizations with 10–100 μg DNA appears to be the optimum dose. We have reported that i.m. immunization of mice with 100 μg of plasmid (pCMXENV) expressing intracellular form of E protein twice at 2-week intervals results in 51±12% protection against i.c. challenge with P20778 strain of JEV [5]. It is to be noted that during the natural transmission of JEV by mosquito bite, JEV is inoculated directly into the bloodstream and neither the i.c. nor the peripheral challenge models employ the intravenous route of virus inoculation. Since the virus load, route of inoculation and the neuroinvasiveness of the challenge virus play a major role in determining the type of immune response mounted by the immunized host, studies on the potency of JE vaccines can yield different results depending on the challenge model employed. In this study, we compared the potency of plasmid DNA constructs pJME, pJNS1 and pCMXENV with that of mouse brain-derived BIKEN JE vaccine (Lot No. EJN*173D; Tanabe Seiyaku Co. Ltd, Osaka, Japan) in an i.c. JEV challenge model. Outbred Swiss mice at 4–5 weeks of age were inoculated i.m. with 100 μg of each of the above plasmids. Another group of mice were inoculated with 50 μg each of pJME and pJNS1 plasmids. All the DNA vaccinated mice received a repeat dose 2 weeks later. This dosage was chosen based on the fact that immunization of mice twice with 80–100 μg of DNA vaccine twice was shown to confer 100% protection against peripheral JEV challenge [2 and 3]. In case of BIKEN JE vaccine, each vial of the lyophilized vaccine was dissolved in 1.0 ml of saline and 100 μl was administered subcutaneously to each mouse, twice at an interval of 2 weeks. This dosage of BIKEN vaccine was shown to confer 100% protection in mice against peripheral JEV challenge [6]. Unimmunized mice and mice immunized with vector (pCMX) alone served as negative controls. Two weeks after the second dose, mice were challenged i.c. with 10 LD50 (100 pfu/mouse) of neurovirulent JEV P20778 strain and were monitored for survival up to 20 days. Serum was collected from all the mice before and after virus challenge by retroorbital puncture and assayed for anti-JEV antibodies by ELISA using plates coated with inactivated JEV antigen. Neutralizing antibody titres in pooled sera were measured as described [1]. The data presented in Table 1 indicate that all the mice immunized with BIKEN JE vaccine were protected against i.c. JEV challenge while 50% protection was observed in case of mice immunized with pJME or pJNS1 and 38% protection was observed in pCMXENV-immunized mice. Immunization with both pJME and pJNS1 resulted in 56% protection. None of the unimmunized mice or mice immunized with pCMX vector survived the virus challenge (data not shown). These results indicate that the BIKEN JE vaccine confers better protection against i.c. JEV challenge than DNA vaccines.

Item Type:	Journal Article
Publication:	Vaccine
Publisher:	Elsevier Science Ltd.
Additional Information:	Copyright of this article belongs to Elsevier Science Ltd.
Keywords:	Pharmacology
Department/Centre:	Division of Biological Sciences > Biochemistry
Date Deposited:	08 Oct 2007
Last Modified:	19 Sep 2010 04:40
URI:	http://eprints.iisc.ac.in/id/eprint/12151

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