Malaria Vaccine: Current Status

Presenter: Dr Pranav SoporyDepartment of Pharmacology

All India Institute of Medical SciencesNew Delhi

Mob: 9999-491-690email: pranav.sopory@gmail.com

Contents

1 Burden of Malaria

2 Need of Malaria Vaccine

3 Life Cycle of Plasmodium

4 Types of Malaria

5 Principle Targets of Malaria Vaccine

6 Vaccine currently available

7 Challenges in making an Anti-Malarial Vaccine

8 Newer formulations and their status

9 Ethical Issues

Burden of Malaria

• Worldwide Parameters

Maximum risk in Africa:• -90% of all malaria deaths.• -68% of deaths occur in children under 5 years of age.

Population at risk 3.2 billion

New cases in 2015 214 million

Deaths 438,000

Case Fatality Rate 0.2%

Malaria in India

Population at risk of Transmission (using Parasite Prevalence)

2014 %

High transmission (> 1 case per 1000 population) 27,55,00,000 22Low transmission (0–1 cases per 1000 population) 83,89,00,000 67

Malaria-free (0 cases) 13,77,00,000 11Total 1 25,21,00,000 100

Major Vectors Causes

An. Culicifacies (Rural Malaria)

An. Stephensi (Urban Malaria)

Confirmed cases (2015) 11,26,661

Reported Deaths (2015) 287

Case Fatality rate (2014) 0.2 %

Need of a Malaria Vaccine : Drug resistance

• Vaccines are the most cost-effective component of public health services.

Drug Mechanism of Action Cause of resistanceChloroquine Inhibits haem (by-product of

Hb metabolism) polymerization

Drug Efflux via PFCRT (Plasmodium Falciparum

Chloroquine-Resistance Transporter)

Sulfadoxine(S) + Pyrimethamine(P)

(Antifolates)

Enzyme Inhibition:-DHPS(S) -DHFR(P

Specific gene mutations encoding for resistance to both DHPS(S) and DHFR(P)

Atovaquone Inhibition of ETC at the Cytochrome complex

Single-point mutations in the cytochrome-b gene

Artemisinin Kill parasites by activation of free radicals.

Mutations in a gene encoded on P. falciparum

chromosome 13 Primaquine Generates free radicals

or inhibits ETC.Unknown

Life Cycle of Plasmodium

PE

BS

TBV

ATVPRGS+P

CLQART

PRQART

Types of Malaria

Plasmodium Species

Fever Prevalence

P. Falciparum Malignant Tertian Malaria (48 hrs) 65 %

P. Vivax Benign Tertian Malaria (48 hrs) 34 %

P. Malariae Quartern Malaria (72 hrs) Rare

P. Ovale Ovale Tertian Malaria Not found in India

Principle Targets of Malaria Vaccine

Based on Vector

P. Falciparum

Pre-erythrocytic (PE)

Blood Stage (BS)

Transmission Borne Vaccine

(TBV)

P. Vivax

Pre-erythrocytic (PE) Vaccine Approach (against P. Falciparum)

Target Antigen Outcome

CSP (Circumsporozoite Protein) Inhibits sporozoite adhesion to hepatocyte.

(On the hepatocyte surface: protelytic cleavage at region 1 of the N-terminus exposes the adhesive part of , thereby priming the parasites for invasion of the

liver.)

Irradiated Sporozoites Retain their immunogenicity but lose their virulence

CelTOS (Cell-traversal protein for ookinetes and sporozoites )

Abolishes hepatocyte entry of the parasite(Present in micronemes that are organelles for parasite

invasive motility. )

Blood Stage (BS) approach (against P. Falciparum)

Antigens used Outcome

EBA 175 (Erythrocyte Binding Antigen 175)

Inhibits merozoite invasion into erythrocytes via Glycophorin A

MSP 1 (Merozoite Surface Protein 1) Inhibits merozoite invasion into erythrocytes via Band 3 (Anion Exchanger

1 of the RBC)AMA 1 (Apical Membrane Antigen 1) Inhibits merozoite interaction with RBC

Transmission Blocking Vaccine (against P. Falciparum)

Target Antigen Outcome

Pfs 48/45 Ligand in the fertilisation process (exact locatin of epitope unknown)

Pfs 230 -same-

Approaches that target P. Vivax

Antigens used Outcome

CSP (Circumsporozoite Protein) Inhibits sporozoite binding to hepatocyte

DBP (Duffy Binding Protein) Prevents Duffy antigen mediated entry of merozoites into erythrocytes via DARC

(Duffy Antigen/Receptor Complex)

RTS,SA (Mosquirix)Only Anti-Malarial Vaccine approved by European Medicines Agency(EMA) in

July 2015 for use in Malaria endemic regions.

It is also the first vaccine licensed for use against any kind of parasitic disease.

Year Development

1984 Early development of RTS,S

2009 Phase 3 trials conducted in seven African countries

2011 Result of Phase 3 trial published

2014 Result of “Extended” Phase 3 trial published

2015+ WHO gives a positive regulatory approval for use in African countries as per Local Regulations

CSP is composed of• an N-terminal region that binds heparin sulfate proteoglycans• a central region containing a four-amino-acid (NANP) repeat, • and a GPI-anchored C-terminal region containing a thrombospondin-like

domain (TLD).

HBsAg particle serves as an carrier for RTS,S, which is fused to the CSP segment.

Immunogenicity is induced primarily via• One B cell epitope• Three T cell epitopes.

TLDCSP

RTS

GPI

Cont.

Recombinant vaccine is expressed in Yeast cells and includes adjuvant (AS01).

Adjuvant is composed of:• Monophosphoryl lipid (MPL): binds to TLR-4 and induces innate

immunity.• Quillaja Saponaira: induces Ig G.• Emulsion oil: mimics Lipo Polysaccharide (LPS).Nomenclature• R: central Repeat region• T: T cell epitopes• S: Surface antigen of HBV (HBsAg) attached to C-region• S: Saccharomyces cerevisiae (Yeast)• A: Adjuvant

“Extended” Phase 3 trialsCarried out between March 2009 and January 2014.Site: 11 centers in 7 countries.Total of 15,459 children.

Participants:• Children (Aged: 5-17 months)• Young Infants (Aged: 6-12 weeks)

Divided into three groups.

Randomly assigned to receive 3 doses of vaccine or a comparator/contrl at months 0, 1 and 2 and a booster dose at month 20.

Cont.

Control Vaccine: Rabies Vaccine (also endemic in these countries)Control Booster: Meningococcal Vaccine (also prevalent)

Primary Objectives • Measuring Vaccine Efficacy• Measuring Vaccine Immunogenicity• Safety (Adverse Events)

Primary Endpoint: Occurrence of Clinical Malaria i.e.• Parasitemia > 5,000/ uL• Axillary Temperature > 37.5 °C

Vaccine Efficacy15,459

participants

8,922 Children(Age: 5-17 mo.)

No. of cases of Clinical Malaria

C3C9,585

R3R6,616

Vaccine Efficacy36.3%

R3C7,396

VE28.3%

6537 Young Infants

(Age: 6-12 wk.)

No. of cases of Clinical Malaria

C3C6,170

R3R4,993

VE25.9%

R3C5,444

VE18.3%

Vaccine Efficacy (w.r.t. Severe Malaria)

15,459 participants

8,922 Children(Age: 5-17

mo.)

No. of cases of Severe Malaria

C3C171

R3R116

Vaccine Efficacy32.2%

R3C169

VE1.1%

6,537 Young Infants

(Age: 6-12 wk.)

No. of cases of Severe Malaria

C3C116

R3R96

VE17.3%

R3C104

VE10.3%

Vaccine Immunogenicity

Anti-CSP Antibody (Measured via

ELISA)

Measured at 1 month after booster dose

Children(Age: 5-17 mo.)

R3R318.2 EU/ml

R3C34.2

Young Infants(Age: 6-12 wk.)

R3R169.9

R3C6.2

12 Months after booster dose

Children(Age: 5-17 mo.)

R3R52.4

R3C19.3

Young Infants(Age: 5 -17 mo.)

R3R15.9

R3C3.7

Adverse Effects(within 30 days)

Children(Age: 5-17 mo.)

R3R+R3C

86.1%

C3C

86.8%

Young Infants(Age: 6-12 wk.)

R3R+R3C

79.4%

C3C

89.3%

Safety

Adverse Events:• Local site reactions (Pain, redness and swelling )• Drowsiness• Irritability• Loss of appetite• Fever (Most common symptom)

Serious Adverse Events:• Meningitis• Febrile Convulsions

Fever

Children(Age: 5-17 mo.)

Fever(>37.5 °C)

R3R+R3C

31.1%

C3C

13.4%

Grade 3 fever (>39 °C)

R3R+R3C

2.5%

C3C

1.1%

Young Infants(Age: 6-12 wk)

Fever(<37.5 °C)

R3R+R3C

30.6%

C3C

21.1%

Challenges in making an Anti-Malarial Vaccine

Applying the Traditional Approach

Animal Models

Waning Effect of Vaccines

1. Applying the Traditional Approach• Traditional approaches to vaccine production include

inoculation via:

• Traditional Methods have failed. All Plasmodium species have distinct forms in both human and mosquito stages for their

life cycle.

• Preventing PE stage from initiating is the only method that wards off sign and symptoms of Malaria.

Live Attenuated Vaccine

Killed Whole organisms

2. Animal Models

• Good Model: Pathological and clinical alterations should mimic the human response.

• Humans have a diverse genetic background that has a profound influence on the immune response.

• Most animal models: Inbred and homogenous.• Data resulting from experimental does not automatically extrapolate to the

disease in humans• Apart from RTS,S, other vaccine attempts have not been successful” based

on mouse models.• This limitation can be solved by the use of outbreed large animal models

that are more closely related to humans, like dogs and non-human primates.• Aotus Gri-sei-membra represents the best current malaria primate model

because of its high susceptibility to infection by blood forms and sporozoites of both species of Plasmodium

3. Waning Effect of Vaccines

Vaccine Efficacy

Phase 3 Trials(1 year after

booster dose)

Children(Age: 5-17 mo.)

55.8%

Young Infants(Age: 6-12 wk.)

31.3%

Extended Phase 3 Trials

(2009-2014)

Children(Age: 5-17 mo.)

28%

Young Infants (Age: 6-12 wk.)

18%

Newer Projects in India and their status

JAIVAC-1

JAIVAC-2

PvDBP II

PfCHMI

JAIVAC-1Indication Plasmodium Falciparum Malaria

Target Antigen RECOMBINANT VACCINE-PfMSP-119

-PfF2 (receptor-binding F2 domain of EBA175)

Route IntramuscularAdjuvant Montanide (oil emulsion)

Clinical Development Phase 1 complete (April 2015)Dose Three doses (10 μg, 25 μg and 50 μg of each antigen) on Day 0, Day

28 and Day 180

Study Endpoint -Assessment of safety of the study vaccines-Check Immunogenicity of the Antigen

Results -No serious side effect noticed.-All subjects sero-converted for PfF2 but elicited poor immune

response to PfMSP-119.-The antibodies against PfF2 were predominantly of IgG1 and IgG3

isotype.

Conclusion Antigen PfF2 should be retained as a component of a malaria vaccine but PfMSP-119 construct needs to be optimised (improve

efficiency) to improve its immunogenicity.

Anti-PfF2 and PfMSP-119 antibody levels measured by ELISA in sera collected from Day 0 to Day 365

JAIVAC-2Indication Plasmodium Falciparum Malaria

Target Antigen RECOMBINANT VACCINE-PfMSP-Fu24

-PfF2 (receptor-binding F2 domain of EBA175)

Route Intramuscular

Development Under Manufacture for Phase 1 trials

Biological Rationale PfMSP-Fu24 (Fu: Fusion):Chimeric fusion between PfMSP-119 and PfMSP-3 that contains a T-helper epitope

and B-cell epitopePre-Clinical Study Increased Efficacy (Unpublished Data)

PvDBP IIIndication Plasmodium Vivax Malaria

Target Antigen PvDBP II :39 kDa cysteine rich region on the Duffy

Binding Protein of P. VivaxRoute Intramuscular

Development Under manufacture

Biological Rationale PvDBP II is a critical domain necessary for interaction between P. Vivax to the RBC. Thus, blocking this functionally important

component prevents the erythrocytic stage of Malaria from occuring.

PF-CHMI (CONTROLLED HUMAN MALARIA INITIATIVE)

CHMI studies: Healthy volunteers are infected with Plasmodium falciparum to assess the efficacy of novel malaria vaccines.

Have become a vital tool to accelerate vaccine development. CHMI studies provide a cost-effective way to circumvent the use of large-scale field efficacy studies.

However, to date few modern CHMI studies have been performed in malaria-endemic countries.

Indication Plasmodium Falciparum Malaria Study Intervention Sporozites of P. Falciparum NF54 strain

delivered via laboratory reared An. Stephensi mosquitoes.

Route Anopheles bite on the ventral aspect of forearm

Objective To standardize the CHMI model in India

Biological Rationale Widely accepted as a safe and informative initial step in evaluating the efficacy of

pre-erythrocytic stage vaccines

Plasmodium falciparum NF54

• It is a transgenic Plasmodium parasite that expresses a luciferase transgene throughout the life cycle.

• Luciferase expression is robust and measurable at all life cycle stages, including midgut oocyst, salivary gland sporozoites and liver stages

Fluorescent Microscopy

Ethical Issues

• 1. Controlled infection studies

2. Human landing catches

1. Controlled infection studies

*• Participants often experience significant acute symptoms—including fever, headache, joint

and muscle pains, and even cardiac events—which go beyond many definitions of ‘minimal harm’ that are commonly employed in the ethical assessment of non-therapeutic research

*

• Further, malaria infection studies often involve exposure to blood products via mosquitoes or injection, which poses the risk of transmitting other infections and prion diseases. Finally, if participants are able to leave research centres while still infected, this can pose risks to the wider community. In all cases, participants must be carefully selected and informed.

*• Such studies should only occur in contexts with access to affordable quality healthcare, high

standards of research conduct, and robust ethical oversight so that the safety of participants is ensured

2. Human landing catches

*• Using human participants act as mosquito ‘traps’. • Receiving 50–100 mosquito bites in one nightshift

*

• Potential harms to a few individuals are (voluntarily consented) balanced against benefits to the wider community

*• It would nonetheless be ethically preferable to develop

alternative practices that offer no risk to human beings.

Thank You