MALARIA -VACCINES

1. MALARIA -VACCINES

2. 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 !!!!!!!!!!

3. “GLOBAL BURDEN OF MALARIA”

4. “ 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)

6. 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)

7. “MALARIA BURDEN IN INDIA”

8. 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

9. 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

10. “LIFE-CYCLE OF MALARIA PARASITE”

12. “PREVENTION STRATEGIES”

13. Integrated vector-control - insecticide-treated bed-nets - residual house spraying(with DDT) Improved diagnosis (e.g. blood film examination, rapid diagnostic methods) Prophylactic and therapeutic chemotherapy (e.g. Chloroquine, Artemesinin derivatives, Primaquine, Doxycycline) VACCINATION

14. A PROPHYLACTIC VACCINE FOR HUMANS IS POSSIBLE!!!! (EVIDENCE FROM THE PAST)

15. 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

16. 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

17. “DIFFICULTIES IN VACCINE DEVELOPMENT”

18. 4 life stages • Over 5000 potential antigenic targets • Complex organism • Stage-specific expression of antigens

19. Ability to adapt to its environment and confound the immune system by • Antigenic variation between strains • Sequence polymorphisms of critical larger epitopes • Poor understanding of protective immunity in malaria • Lack of reliable and predictive animal models

20. IMMUNITY IN MALARIA Anti-disease immunity PREMUNITION Anti-parasite immunity Protection against the clinical disease Protection against new infection by maintaining a low grade and generally asymptomatic parasitemia Protection against parasitemia Risk and morbidity asso. with parasite density reduced Decreased parasite density

21. NEW BORN protected up to 6 months by maternal transfer of anti-bodies SCHOOL AGE Anti disease immunity/ clinical tolerance NATURAL ACQUIRED IMMUNITY Stage of premunition Stage of complete, sterile immunity never achieved, even in ADULTS

22. “POTENTIAL VACCINE CANDIDATES”

23. CSP Pf/Pv25 Pf/Pv28 Pf48/45 Pv30 LSA 1 LSA 3 STARP SALSA AMA 1 MSP 1 MSP 3 RESA GLURP SERA

26. “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

27. 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)

29. 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

30. 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))

31. 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)

32. “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 ed PROTECTION AGAINST DISEASE

33. Generation of antibodies Preventing binding of infected RBC to vascular endothelia Against RBC surface receptors and inhibiting their invasion by merozoites Binding to merozoite surface antigens and mediating agglutination and facilitating their phagocytosis Destroying intra-erythrocytic parsites by monocytes

34. 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

35. TARGET ANTIGENS AMA-1 MSP-1 PfEMP-1 MSP-2 MSP-3 MSP-4 MSP-5 MSP-8 • Mediates cytoadherence by binding to chondriotin sulphate receptors in placenta whole molecule 19 kDa fragment 42 kDa C-terminal moiety EBA-15 • Largest parasite protein • Accumulates in the parasitophorous vacuole of trophozoites and schizonts

38. 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 DSMalaria (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)

39. “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

40. 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 Pf230 Pf48/45 Pf11.1 Pfs25 Pv25

41. 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)

42. Irradiated sporozoite, whole organism approach GENETICALLY MODIFIED SPOROZOITES DNA vaccine Subunit vaccine

43. 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

45. 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

46. Conjugating recombinant proteins to Pseudomonas aeruginosa exoProtein A: a strategy for enhancing immunogenicity of malaria vaccine candidates (Feng Qian et al.2007.Vaccine)

47. “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

48. 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

49. “PROBLEMS TO BE ADDRESSED”

50. 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