MALARIA -VACCINES

Disease burden- World and India Plasmodium life cycle Control strategies being used Immunology of malaria Different types of vaccines Clinical trials till date Problems addressed and

remaining?? THE FUTURE !!!!!!!!!!

“GLOBAL BURDEN OF MALARIA”

“ The malaria epidemic is like loading seven Boeing 747 airliners with people everyday, and then deliberately crashing them into Mt. Kilimanjaro.”

Dr. Wen Kilama

African Malaria Network(AMANET)

ONE THIRD HUMAN MANKIND at risk World’s MOST DANGEROUS TROPICAL

disease Annual cases – 500 MILLION Mortality – 3 MILLION DEATHS Afflicted are children(1 million) aged <

5 YEARS, particularly in AFRICA MULTI-SYSTEM INVOLVEMENT in c/o

P.falciparum malaria( e.g. cerebral malaria)

“MALARIA BURDEN IN INDIA”

Outside Africa, 2/3rd cases are concentrated in INDIA, Brazil, Sri Lanka, Vietnam, Columbia, Solomon Islands

60-65% infections caused by P.vivax

35-40% by P.falciparum

Few by P. malariae [from Orissa and Tumkur & Hassan districts of Karnataka]

Estimated 10.6 million malaria cases reported from India in 2006, accounting for 60% cases of the WHO-SEAR region

Maximum burden in states of Uttar Pradesh, Bihar, Karnataka, Orissa, Rajasthan, Madhya Pradesh, Pondicherry

80% of malaria cases derived from forest- related areas and along the borders with Myanmar & India where malaria is endemic

Anopheles culicifacies- rural malaria

Anopheles stephensi- urban malaria

“LIFE-CYCLE OF MALARIA PARASITE”

“PREVENTION STRATEGIES”

Improved diagnosis (e.g. blood film examination, rapid diagnostic methods)

Prophylactic and therapeutic chemotherapy (e.g. Chloroquine, Artemesinin derivatives, Primaquine, Doxycycline)

Integrated vector-control - insecticide-treated bed-nets - residual house spraying(with DDT)

VACCINATION

A PROPHYLACTIC VACCINE FOR HUMANS IS

POSSIBLE!!!!

(EVIDENCE FROM THE PAST)

Irradiated (and thus attenuated) sporozoites

Naïve human volunteers

Protection against the experimental infection

Malaria immune volunteers

Passive transfer of hyper-immune immunoglobulins

Malaria naïve volunteers

Protection achieved

Continuous antigenic stimulation in endemic areas

Build-up of naturally acquired immunity, which affects

- the severity of clinical disease

- less incidence of parasitemia

- significant protection from death

“DIFFICULTIES IN VACCINE

DEVELOPMENT”

4 life stages

Over 5000 potential antigenic targets

Complex organism

Stage-specific expression of antigens

Ability to adapt to its environment and confound the immune system by

i. Antigenic variation between strains

ii. Sequence polymorphisms of critical larger epitopes

Poor understanding of protective immunity in malaria

Lack of reliable and predictive animal models

IMMUNITY IN MALARIA

Anti-disease immunity

Anti-parasite immunity

PREMUNITION

Protection against the clinical disease

Risk and morbidity asso. with parasite density reduced

Protection against parasitemia

Decreased parasite density

Protection against new infection by maintaining a low grade and generally asymptomatic parasitemia

NEW BORN protected up to 6 months by maternal transfer of anti-bodies

SCHOOL AGEAnti disease immunity/ clinical tolerance

Stage of premunition

Stage of complete, sterile immunity never achieved, even in ADULTS

NATURALACQUIRED IMMUNITY

“POTENTIAL VACCINE CANDIDATES”

CSP

LSA 1LSA 3STARPSALSA

AMA 1MSP 1MSP 3RESAGLURPSERA

Pf/Pv25Pf/Pv28Pf48/45Pv30

PRE-ERYTHROCYTIC ASEXUAL/BLOOD STAGE

TRANSMISSION-BLOCKING

CIRCUMSPOROZOITE PROTEIN

MEROZOITE-SURFACE ANTIGEN 1(MSP-1)

Pfs 25

LIVER-STAGE ANTIGEN 1 (LSA-1)

MEROZOITE-SURFACE PROTEIN(MSP-3)

Pfs 28

LIVER-STAGE ANTIGEN 3(LSA-3)

RING-STAGE INFECTED ERYTHROCYTE SURFACE ANTIGEN(RESA)

Pvs25

SPOROZOITE AND LIVER STAGE ANTIGEN (SALSA)

APICAL MEMBRANE ANTIGEN(AMA-1)

Pvs28

SPOROZOITE THREONINE AND ASPARAGINE RICH PROTEIN(STARP)

GLUTAMINE-RICH PROTEIN(GLURP)

Pfs48/45

SERINE REPEAT ANTIGEN(SERA)

Pfs30

“PRE-ERYTHROCYTIC VACCINES”Generates an

antibody response

Neutralize sporozoites

Hepatocyte invasion

prevented

Elicit a cell mediated-immune response

Interfere with the

intra-hepatic

multiplication cycle of

the parasite (by

killing the parasite

infected hepatocytes)

PROTECTION AGAINST INFECTION

Good for

- Travelers to malarious areas

- Military personnel deployed in forests

- Non- immune individuals living in non-malarious areas of countries with malaria

Specie-specific protection

No strain- specifc protection

Thousands of infected sporozoites needed for each individual (according to irradiated sporozoites model)

ANTIGEN ADJUVANT INSTITUTE PLACE EFFICACY

RTS S(CSP) ASO2 GSK+WRAIR Gambia 30%

RTS S(CSP) ASO2 PATH+MVI Mozambique 30% in 1-4 year old children

CS102(CSP based)

Montanide ISA 720

University of Lausanne+ Dictagen

- Safe, induced both cell-mediated and humoral immunity

ICC-1132(muliple antigenic peptide)

Recombinant VLP based on Hepatitis-B core particle

Apovia (USA) + MVI

- Failed in phase 2, discontinued

MuSt- DO 5(5 liver-stage specific antigens)

DNA vaccine US Dept.of Defense + Vical ,Inc

CIRCUMSPOROZOITE PROTEIN Expressed in large amounts on the surface

of the sporozoite and of the infected hepatocyte

Central area of repeated amino-acid sequences NANP that are highly immunogenic and present in all but varies among all Plasmodium species

Candidate vaccine developed by GSK and WRAIR

RTS,S

RTS,S Expressed in Saccharomyces cerevisiae RTS- corresponds to amino acids 207 to 395 of P.

falciparum CSP S- hepatocyte B virus antigen(HBsAg) ASO2A- Adjuvant mixture based on

monophosphoryl lipid A (oil-in-water emulsion) and QS21 (a saponin derivative)

Field trials in

- Gambia (65% efficacy, for 2 months)

(Stoute JA et al.1998.J Infect Dis)

- Mozambique (35.3% to first episode & 48.6% against severe disease)

(Alonso PL et al.2005.Lancet))

INITIATIVES BY MVI AND PATH • Trials in Gabon, Ghana, Kenya, Senegal, Tanzania• Focus on infants and young children • Defining appropriate dosage schedule,

incorporating it in Expanded Program on Immunization, and the best adjuvant

RECENT ADVANCES Different adjuvants (ASO1B, Montanide ISO 720) No immune interference with concurrent

administration of LSA1/AS01B and RTS,S/AS01B at separate sites

(Pichyangkul et al.2008. Infection and Immunity)

“ASEXUAL/ BLOOD STAGE VACCINES” To elicit antibodies

that will inactivate merozoites and/or target malarial antigens expressed on the RBC surface through antibody-dependent cellular cyto-toxicity and/or complement lysis

To elicit T-cell responses able to inhibit the development of the parasite in RBC.

Merozoite multiplication

PROTECTION AGAINST DISEASE

ed

Generation of antibodies

Against RBC surface receptors and inhibiting their invasion by merozoites

Destroying intra-erythrocytic parsites by monocytes

Preventing binding of infected RBC to vascular endothelia

Binding to merozoite surface antigens and mediating agglutination and facilitating their phagocytosis

Inhibition of parasite invasion cycles

Reduced parasitemia

Decreased mortality and morbidity

Lack a human artificial challenge model

Natural challenge in field trials required to provide proof-of-concept

Polymorphism and strain variability of many asexual stage antigens

TARGET ANTIGENS

MSP-1

whole molecule

42 kDa C-terminal moiety

19 kDa fragment

AMA-1MSP-2MSP-3MSP-4MSP-5MSP-8

EBA-15

PfEMP-1

• Mediates cytoadherence by binding to chondriotin sulphate receptors in placenta

• Largest parasite protein• Accumulates in the parasitophorous

vacuole of trophozoites and schizonts

ANTIGEN ADJUVANT INSTITUTE PLACE EFFICACY

Spf66 (multi-epitope, multi-stage peptide)

Alum - Columbia by Patarrayo

Low

MSP-1+MSP-2+RESA

Montanide - Papua, new Guinea

62%reduction in parasite density

MSP-1(42 kDa fragment)

ASO2 GSK+WRAIR+ MVI

USA, Kenya, Mali

Satisfactory

AMA-1 ASO2 GSK+WRAIR - -

AMA-1(C-terminal)+MSP-1(19 kDa fragment) in Pichia pastoris

Montanide ISO 720

Shanghai - Immunogenic in rabbits and non-human primates

ANTIGEN ADJUVANT INSTITUTE PLACE EFFICACY

MSP-3 - Pasteur Institute+ EMVI

- -

GLURP Alum/ Montanide ISO 720

Staten Serum Institute+ EMVI

- -

SERA/ Pf126 - Asian-African collaboration

Solomon Islands, Brazil, Uganda, Japan

-

A Bicistronic DNA Vaccine Containing Apical Membrane Antigen 1 and Merozoite Surface Protein 4/5 Can Prime Humoral and Cellular Immune Responses and Partially Protect Mice against Virulent Plasmodium chabaudi adami DS Malaria(Rainczuk et al.2004.Infection and Immunity)

Genetic diversity of vaccine candidate antigens in Plasmodium falciparum isolates from the Amazon basin of Peru

(Chenet et al.2008.Malaria Journal) Sequence diversity and natural selection at domain 1

of AMA-1 among P.falciparum in Indian population

(More diversity in Assam, Orissa, Andaman & Nicobar islands as compared to UP & Goa)

“TRANSMISSION-BLOCKING VACCINES”

To prevent or decrease transmission of the parasite host in the community, not to prevent illness or infection in the vaccinated individual

Altruistic vaccine (does not protect the vaccinee)

Assessing their impact by the field trials in Phase 3 not possible

TARGET ANTIGENS

Pre-fertilization antigens expressed either completely or predominantly in gametocytes

Post-fertilization antigens expressing solely or predominantly on zygotes or ookinetes

Late-midgut stage antigens such as parasite-induced chitinase required for the ookinete to penetrate through the peritrophic membrane

Pf230Pf48/45 Pf11.1

Pfs25Pv25

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

(Arakawa et al.2005.Infection and Immunity)

Irradiated sporozoite, whole organism approach

Subunit vaccine

DNA vaccine

GENETICALLY MODIFIED SPOROZOITES

DNA VACCINES SAFE as they don’t contain any pathogenic

organism that may revert in virulence PLASMID DNA- A STABLE MOLECULE as

compared to recombinant or live-attenuated vaccines, making storage and distribution convenient in tropical countries, where cold chain is difficult to maintain

Simple administration (IM or ID) Multiple plasmids can be incorporated to multi-

valent vaccine

DELIVERY SYSTEMS

DNA VACCINES

Multi-stage DNA based Malaria vaccine operation (MuSt-DO)

5 different liver stage antigens-CSP, LSA 1, LSA 3, EXP1 & SSP2/TRAP

LIVE RECOMBINANT VACCINES

Attenuated modified vaccinia- Ankara strain(MVA)

Fowlpox virus(FPV) Adenovirus Sindbis virus YELLOW FEVER

VIRUS(17 D vaccine) Influenza virus

strain

Conjugating recombinant proteins to Pseudomonas aeruginosa exoProtein A: a strategy for enhancing immunogenicity of malaria vaccine candidates

(Feng Qian et al.2007.Vaccine)

“FUTURE INSIGHTS”

• Genetically-modified sporozoite vaccines

• An anti-parasite toxin vaccine that targets the parasite toxins which contribute to the disease, such as the glycosyl-phosphatidyl-inositol (GPI) anchor

GENETICALLY MODIFIED SPOROZOITES

Safe Genetically stable Cryo-preservation possible(upto 10

years) Large scale production feasible Prioritizing protective antigens and tool

for subunit vaccine development Genes targetted- UIS 3

“PROBLEMS TO BE ADDRESSED”

Designing a malaria vaccine (identification of the appropriate antigen and formulation of the adjuvant)

Obscurity about different immune mechanisms in malaria

Choice of clinical-case definitions and end-points in malaria vaccine trials

Lack of funding agencies (with no commercial intentions)

Lack of immunological memory

Lack of definite biological assays and animal models to correlate with vaccine strategy

BIBLIOGRAPHY- Girard et al. 2007. A review of human vaccine

research and development: Malaria.Vaccine.25:567-1580

- Matuschewski K.2006.Vaccine development against malaria. Current Opinion in Immunology.18:449-457

- Jones et al.1994.Malaria vaccine development. Clinical Microbiology Review.7:303-310

- Phillips R S. 2001.Current status of malaria and potential for control. Clinical Microbiology Review.14:208-226

- www.malariavaccine.org- www.who.int