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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