vaccine candidates paper

8/6/2019 Vaccine Candidates Paper

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VACCINE CANDIDATES/MOLECULES

AGAINST MALARIA AND

TRYPANOSOMIASIS


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TABLE OF CONTENTS

1. Introduction

2. Malaria

a. Overview

b. Malaria parasite development in human host

c. Mechanisms for potential vaccine action

d. Vaccine candidates/molecules against malaria

3. Trpanosomiasis

a. Overview

b. Trpanosomiasis parasite development in human host

c. Mechanisms for potential vaccine action

d. Vaccine candidates/molecules against trpanosomiasis

!. "onclusion

#. $eferences

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INTRODUCTION

Malaria and Trpanosomiasis are two ma%or infectious diseases caused b

parasites of the phlum &roto'oa ( the proto'oans Plasmodium sp and

Trypanosoma sp. These parasites affect both human and animals) causing

severe) highl debilitating infections with resultant high mortalit and huge

economic losses recorded annuall. Various efforts have been deploed in the

control of these two diseases) including research into developing highl potent

vaccines for the prevention of these infections in human hosts. The efforts in

developing vaccines for these diseases have ielded a variet of vaccine

candidates from diverse sources with varing degrees of potential for success.

This paper does a review on the life ccle of the two causative agents of malaria

and trpanosomiasis) laing emphasis on the aspects of the mechanism of the

parasites* action in the human host that can be e+ploited for vaccine target

action. It then lists the various agents and molecules that have been identified as

potential candidates in the control of malaria and trpanosomiasis infections)

and gives an outline on the mechanisms of each and the e+tent of development

of each agent.

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MALARIA

Overview

Malaria is a disease caused b several species of the intracellular proto'oan

parasite Plasmodium. The most popular species of this parasite that cause

infection in humans are Plasmodium malariae) P. vivax) P. ovale and P.

falciparum. Malaria is prevalent in tropical and sub,tropical regions of -frica)

-sia and outh,-merica) infecting 2# million people and resulting in between

one to three million deaths annuall 0now et al.) 2#. Transmission of this

disease is b the female form of the mosuito vector Anopheleswhich infects

the human host) while taing a blood meal) with sporo'oite stage parasites that

migrate to the liver and replicate rapidl to produce mero'oites that infect the

red blood cells in the blood stream and cause them to rupture) triggering off

clinical smptoms of the disease.

Immunit to malaria does occur naturall) but onl in response to repeated

infection with multiple strains. 04anert et al.) 25. In spite of its recogni'ed

virulence) repeated infection with malaria will result in gradual acuisition of

strain,specific) short,lived) antibod, and cell,mediated immunit to blood stage

malaria with prevention of6 first) complications and death) then disease and) in

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areas of intense stable transmission) ultimatel suppression of parasitaemia to

low or undetectable levels 0Moorth and 7ill) 22. 7owever) the immunit

generated at an one stage of malaria is confined to that stage. Indeed) the

comple+ biolog of the Plasmodiumparasite and its wide antigenic diversit

has made the development of vaccine against malaria a huge challenge 08enton

and $eed) 29.

Malaria parasite development in human host

The life ccle of the malaria parasite Plasmodiumin the human host is split into

three stages ( the &re,erthroctic) :rthroctic and e+ual stages.

Pre-erythrocytic stage

This stage starts when the infective form of the malaria parasite( the sporo'oite

form ( is in%ected through the sin of a human host from the salivar glands of

the anopheline vector while the vector taes a blood meal. The sporo'oites

travel through the bloodstream to a relativel immune,protected environment

inside the liver cells of the host. 7ere) the develop for one to two wees)

undetected) without e+hibiting an smptoms or signs in the infected host. :ach

sporo'oite develops into thousands of mero'oites in the liver cell.

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Erythrocytic stage

The mero'oites generated from the sporo'oites burst out of the liver) re,enter

the bloodstream and invade red blood cells) where the continue to replicate and

develop further into ring,shaped tropho'oites and se+ual forms of the parasite.

The mero'oites continue to rupture their host blood cells and reinvade other red

blood cells in ccles that last between 2! ( 92 hours) depending on the species

of the parasite.

Sexual stage

-fter roughl 1 das) the mero'oites in the $;"s begin to mature into se+ual

forms nown as microgametoctes and macrogametoctes. These gametoctes

are ingested b the mosuito vector during a blood meal and undergo

fertili'ation and development into sporo'oites within the vector) and the ccle

continues.

Mechanisms of potential vaccine action


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each developmental stage involved in the life ccle ( each stage could have a

vaccine developed specificall to target the parasite.

Pre-erythrocytic stage vaccine action

- vaccine for this stage of the life ccle would be targeted against the

sporo'oite and the liver stages of the parasite. This vaccine could wor b either

blocing invasion of liver cells b sporo'oites 0antibod response or b

destroing infected liver cells 0cell,mediated response 0&rice and =ien) 21.

The possible antibod responses are thus blocing of hepatocte invasion and

illing of sporo'oites via complement fi+ation or opsonisation) and the possible

cell,mediated response 0Th1 response is the stimulation of " and " T,

cells) which are lmphoctes) to target and destro the infected liver cells

0


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&rotein 0T$-& inPlasmodium falciparum( the corresponding protein found

onP. yoeliiis nown as poro'oite urface &rotein 2 0&2.

Erythrocytic stage vaccine action

- vaccine for this stage of the parasite life ccle would be directed against the

mero'oites stage of the parasite) and would be e+pected to inhibit either the

invasion of red blood cells b mero'oites or the multiplication of mero'oites in

the blood cells. This would be done b either agglutinating the mero'oites

before schi'ont rupture) or illing infected $;"s via opsonisation or

phagoctotic mechanisms) or agglutinating the infected $;"s and prevent

ctoadherence of $;" membrane proteins ( which causes smptomatic

reactions 0Moorth and 7ill) 22 ( b blocing receptor,ligand interactions.

The most popular antigen identified as a potential immune response generator at

this life ccle stage is the M&1 0Mero'oite urface &rotein 1 antigen. This

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0:$-) glcophorin binding protein 08;&,13) histidine rich protein 2 07$&,

2 and erthrocte membrane proteins 1 0&f:M&1.

Sexual stage vaccine action

The vaccine generated for this last stage of the parasite life ccle would be a

transmission,blocing vaccine ( one which induces an immune response in the

human host that will bloc the parasiteAs growth in the mosuito and

conseuentl bloc transmission of the parasite 0Miura et al.) 29. This would

be done b generating antibodies that would either neutrali'e the se+ual stages

i.e. the microgametoctes and macrogametoctes ( of Plasmodium in the

human host) destro the gametoctes ( either within the $;"s or along with

their $;" host) or interfere with the fertili'ation process of the parasite. This

vaccine is not aimed at giving protection to the person inoculated with it but at

preventing further spread of malaria in the host population. -ntigens which

have been identified as being capable of inducing these reactions include P.

falciparum surface protein antigens &fs 2# and &fs 2? and the P. vivax

homologues) referred to as &vs2# and 2? 0&rice and =ien) 21. These

proteins are members of the &2# famil of csteine,rich 2#


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Vaccine candidates in the control of malaria

;ased on the various possible mechanisms for vaccine action in the control of

malaria listed above) some candidate agents/molecules have been identified and

developed. These candidate vaccines have been e+pressed and manufactured in

various was. Bntil the 15?s) all vaccines in use were live) attenuated or

inactivated whole organism vaccines mostl to viral pathogens 0Moorth and

7ill) 22. In recent times) the use of protein subunit vaccines) a product of

recombinant


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studies in malaria e+posed populations 0Toure,;alde et al.) 25. It is being

tested in various formulations 0peptides) lipopeptides and


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This was the ver first vaccine to undergo field trials. It was developed in

"olombia as a snthetic) multi,epitope) multistage peptide vaccine mi+ed with

alum as ad%uvant 0&atarroo et al.) 1552. The candidate presents a combination

of antigens from the sporo'oite 0using " repeats and mero'oite parasites. This

vaccine candidate had 9#E efficac rate during the &hase I trials and appeared

to be well tolerated b sub%ects and immunogenic. 7owever) the reported

efficac during the &hase III field trials was considered too low to warrant

further development 08alendo et al.) 2. The candidate was abandoned for a

while but is now being retested with new ad%uvants and is in the &hase I trial

0harma and &atha) 2?.

M&StDo ' (M&)t!-Sta*e DNA O+eat!on '

This is a multiple,antigen


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candidate maes use of the whole organism , an attenuated form of the whole

parasite. @ive) attenuated parasites in the form of sporo'oites are harvested from

the salivar glands of irradiated mosuitoes) purified) and used as the basis for

vaccine formulation. anaria Inc. produces radiation,attenuated sporo'oites of

P. falciparumfrom infected mosuitoes in sufficient uantit and in a wa that

meets the regulator standards reuired for their use as a vaccine 0anaria MVI

&-T7 fact sheet. This has been achieved) and &hases I/IIa clinical trials have

begun using irradiation,attenuated sporo'oites delivered b intradermal or

subcutaneous in%ection 0Target and 8reenwood) 2?.

N.VAC-#$

This multistage vaccine candidate consists of genes from seven antigens from

different stages in the parasite life ccle ( "&) sporo'oite surface protein 2

0called &f&2) @-1) M&,1) :$-) -M-,1 and &fs2#. This candidate

ielded great results when tested first on rhesus mones6 ! out of the 9

antigens produced specific antibod responses 0"&) &f&2) M&1 and &4s2#

0Malaria site website. 7owever trials in humans did not ield impressive

results. Cevertheless) research has still been ongoing on this candidate.

MS#-1

This is one of the most popular vaccine candidate studies. -ntibodies to the ",

terminus of the M&,1 protein 0the !2 and 1?


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to be associated with protection from high parasitaemia and clinical disease

0:gan et al.) 155F and have been shown to inhibit parasite growth and prevent

red cell invasion

0O*


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SERA (#12% ant!*en

This vaccine candidate is the largest parasite protein. It accumulates in the

parasitophorous vacuole of tropho'oites and schi'onts and is processed into 3

fragments ( 1?


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TBV2'-24

This vaccine candidate is a recombinant fusion protein of two ma%or

transmission,blocing antibodies , &fs2# and &fs2?. These antigens were

wored on at the CI7) B- as potential vaccines e+pressed as recombinant

protein secreted from Saccharomyces cerevisiae east 08o'ar et al.) 21.

Bnlie the other vaccine candidates) the efficac of a transmission,blocing

vaccine candidate is determined b an in,vitro membrane,feeding assa.

Immune sera generated in an animal is fed to parasite infected) laborator,raised

mosuitoes through a membrane. The mosuito gut can then be dissected to

determine the number of infectious gametoctes that developed. :ffective

transmission,blocing antibodies will prevent the development of the gametes

in the mosuito. 0Miura et al.) 29.

TR.#ANOSOMIASIS

Overview

Trpanosomiasis is a disease of both humans and animals that is e+pressed in

multiple forms based on species of parasite. There are three species that affect

humans ( Trypanosoma brucei gambiensis) which causes Dest -frican

trpanosomiasis) Trypanosoma brucei rhodensiensis) which causes :ast -frican

trpanosomiasis) and Trypanosoma crui) which causes -merican

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trpanosomiasis) or "hagas disease. -frican trpanosomiasis currentl affects

#) people worldwide and is epidemic in 39 sub,aharan countries while

"hagas disease affects appro+imatel 2 million people in outh and "entral

-merica) Me+ico and the southern Bnited tates 0;hatia et al.) 2!.

Trpanosomiasis is transmitted b two insect vectors ( the tsetse fl 0!lossina

sp transmits the -frican trpanosomiasis and the triatomid bug 0Triatoma sp)

"hodniussp andPanstrongylus sp transmits "hagas disease. Infection of the

human host with -frican trpanosomiasis occurs when the infective stage ( the

metacclic stage ( is in%ected intradermall b the tsetse fl while it taes its

blood meal. These forms rapidl transform into blood,stage trpomastigotes)

and divide b binar fission in the interstitial spaces at the site of the bite

wound) resulting in the first indicative smptom of the infection ( a chancre.

Infection with -merican trpanosomiasis slightl differs from this mode in that

the infective stage ( the trpomastigote in this case ( is released in the faeces of

the triatomid bug) which it deposits near the site of the bite wound. These

trpomastigotes are then introduced into the human host through intact mucosal

membranes as the host rubs the faeces against their sin.

The Trypanosomaparasite possesses a speciali'ed mechanism that has enabled

it overcome the obstacles of the mammalian immune sstem b varing the

glcoproteins on its surface) and this phenomenon has made vaccine

development of this disease a ma%or challenge.

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new infection sites. "linical manifestations usuall result from this infective

ccle. The bloodstream trpomastigotes do not replicate 0different from the

-frican trpanosomes. $eplication resumes when the parasites enter another

cell or are ingested b another vector.

Mechanisms for potential vaccine action

For a long time, the development of a vaccine against

trpanosomiasis ! in partic"lar #hagas disease ! $as impeded

d"e to the "ncertaint of the mechanisms involved in the

patholog of the disease %&"monteil, 2007'( )t $as not clear

$hether the tiss"e damage ca"sed * this disease $as a res"lt

of the presence and replication of intracell"lar amastigotes, or

ca"sed * the a"toimm"nit ind"ced * parasite antigens

mimic+ing host proteins, and th"s there $as conf"sion a*o"t

$hether to inhi*it the imm"ne sstem to red"ce a"toimm"nit,

or to stim"late it, to eliminate the parasite %&"monteil, 2007'(

)t is no$ accepted that the presence of parasites in cardiac

tiss"e is necessar to initiate and maintain the inammator

response, and that therape"tic treatments or vaccines aimed at

eliminating T. cruzi $o"ld facilitate the c"ring of the disease(

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-here is a gro$ing consens"s that protection against T. cruzi

relies on a -h1 imm"ne response and the activation of

ctoto.ic #&8/- cells %artin and -arleton, 2004'( In a variet of

studies to identif the effector mechanisms reuired for the control of T. crui

infection) using animal models) components of the immune sstem lie

granuloctes) C= cells) " and " T,cell subsets and ltic antibodies

have shown potential as agents in the control of the disease 0Gacs et al.) 2#.

:fforts toward subunit vaccine development against T. crui have mainl

focused on antigens that are e+pressed on the plasma membrane of the parasite)

attached b a glcoslphosphatidlinositol 08&I anchor. 8&I proteins are

considered good antigenic targets because the are abundantl e+pressed in the

infective and intracellular stages of T. cru'i 0Gacs and 8arg) 2F and were

shown to be recogni'ed b both the humoral and cellular arms of the immune

sstem in infected hosts 0@ow et al.) 155?. 8&I proteins lie cru'ipain)

amastigote surface protein 1 and 2 0-&,1 and -&,2) trpomastigote surface

protein 1 0T-,1) and trans,sialidase 0T have been identified as potential

vaccine candidates in the control of trpanosomiasis. 7owever) these antigens

represent a limited repertoire of all the possible T. crui target molecules 0Teiel

et al.) 25.

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Vaccine candidates in the control of trypanosomiasis

5S#6/7M#11

This vaccine candidate is a recombinant fusion protein comprised of

inetoplasmid membrane protein =M&11) a protein associated with the

lpophosphoglcan molecule in T. crui) and 7&9) a gene also e+pressed in

T. crui. =M&11 is located mainl in the parasite*s flagellar pocet and is

associated with ctoseletal structures responsible for the mobilit of the

parasite and its attachment to the host cell 0Thomas et al.) 2. Hensen et al.

0155? reported this candidate to be a potent inducer of immune response) and

when it was tested in murine model b &lanelles et al. 021) it was found to

generate long,lasting humoral immune response against =M&11 protein and

activate " ctoto+ic lmphoctes.

C&8!+a!n

"ru'ipain is the ma%or csteinl proteinase of Trypanosoma crui. It has been

demonstrated to be immunogenic in both man and mice. In a stud b chnapp

et al. 022) immuni'ation of mice with


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conversion of the parasite from the complement,sensitive insect,stage

epimastigote to the complement,resistant bloodstream,stage trpomastigote.

0Corris) chrimpf and 'abo) 1559. The vaccine candidate is a recombinant

vaccine derived from anE. colie+pression sstem and a plasmid encoding the

full,length crpstructural gene using an euarotic promoter. This candidate was

tested in a murine model b epulveda et al.02 and was shown to generate

Th1 tpe T,cell response.

9-Ga)acto:;)cea0!de

,8alactoslceramide is a specific ligand for activation of Catural =iller 0C=

T,cells. C= T,cells have the capacit to secrete large amounts of ctoines and

effectivel e+ert protective immune responses against infectious diseases

0mth et al.) 22. The also have the potential to accelerate the induction

and maintenance of effective " T,cell responses 0"arvalho et al.) 22

through the gamma interferon 0I4C,9 and interleuin,! 0I@,! ctoines the

secrete.


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The Tc#2 protein of Trypanosoma crui belongs to the thiol,disulfide

o+idoreductase famil) and is crucial for parasite survival and virulence) as it

e+erts immunoregulator functions. In vitro) Tc#2 in combination with I4C,

activates human macrophages) and in vivo it relieves the immunosuppression

associated with acute infection and elicits specific immune response 0Ouaissi et

al.) 22. This candidate was tested in mice as a pc


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its immunogenic portions 04u%imura et al.) 21. It was discovered that the

gene portions capable of generating both " Th1 and " Tc1 cells

produced the most effective responses. The T-,1 protein was developed as

two


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potential antigens. Dith the implementation of these advances) it is hoped that

viable vaccines would be developed for these diseases in the not too distant

future.

REFERENCES

B


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Cava)

T,cell responses against malaria liver stages.$atural

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Da&e:!e:, #, TO))o0o, B, Ben Mo


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E)-Sa and " T,"ell :pitopes

-re Important for :fficient &rotective Immunit Induced b ~ 28~


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5o)de, A A, B)ac0an, M ?, B&*

protein 1 0msp,1015 and T helper epitopes of tetanus to+oid. accine146

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Lo, 5 #, Santo:, M A, !8e), B and Ta)eton, R L (1334 -mastigote

surface proteins of Trypanosoma cruiare targets for " "T@.(ournal

of #mmunology1%661?19,1?23

Mat!n, D and Ta)eton, R (266>8eneration) specificit) and function of

" T cells in Trypanosoma crui infection. #mmunological "evie0s

261(16 3!(319

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M!;a

S, Tae&c


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No!:, 7 A, Sc

Via Toll,@ie $eceptor 2) and "onfers &rotection -gainst @ethal Infection.

The (ournal of #mmunology1%4@F3FF,F39!

#an, , 5&an*, D,


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enhances product ield) immunogenicit) and antibod,mediated inhibition

of parasite growth in vitro.(ournal of #mmunology12(166 F1F9,9!

#ae, S E, Monte!t


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protection against Trypanosoma crui infection. #nfection and #mmunity

%4(36 !5?F,!551

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Ta*ett, G and Geenood, B M (2664 Malaria vaccines and their

potential role in the elimination of malaria. %alaria (ournal (S&++) 16

1

Te!e), V, A)a-Soto, C D, Gon8J)e8 Ca++a, S M, #o:tan, M and

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Vaccination with 8enes :ncoding the -mastigote urface &rotein,2 and

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vaccine candidates paper

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