vaccines in leprosy (hansens disease)

Vaccines for leprosy A short talk - Anand

• ‘Vaccine' ≈ 'la vacche' ≈ cow• Vaccines- enhances host immunity• Are perhaps the most effective means of

controlling infectious diseases by inducing active immunity

Vaccines are of 3 types-• Live vaccines• Killed vaccine• Toxoids

Attenuated Live Vaccines

• Attenuated live organisms.• Initiate an infection without causing any injury

or death• Immunity little lesser than natural infection• Lasts for several years.• Booster doses generally not required

(exception - polio).

Killed vaccine

• Killed organisms• Less immunogenic• Protection for short periods.• Repeated booster doses.

Toxoids

• Toxins of bacteria are detoxified and used as vaccines.

• Antibodies neutralize the toxin, but have no effect on organism.

Need for leprosy vaccine• New case detection rate - Not decreased.

• Large number of hidden cases continues to increase

• Even after MDT, highly bacilliferous cases (BL/LL) continue to be smear positive leading to relapses and reactions

• Therefore, combination of MDT & immunisation for active cases & in endemic areas –

Long term measure for eradication of leprosy.

Parameters for determining vaccine efficacy

• For other vaccines, usually determined by its ability to lower incidence of the disease.

• But, this parameter cannot be used for leprosy because it has long IP & will require long term trials

• Mitsuda test ---Lepromin (+)

• Aims of vaccine– Immunoprophylaxis – Immunotherapy

Effects of immunotherapy

Promotion of CD 4 Th 1 cells effective antibacterial process.

Overproduction of CD 4 Th 2 cells is switched off.

Regulatory activity of CD 8 cells is relaxed to allow Th 1 activity

More efficient killing of viable bacilli including persisters

OUTCOME– Faster clearance of dead & viable bacilli including

persistors leads to

– Duration of treatment-- Morbidity and mortality.– Transmission and relapse

– Case holding and better compliance– Clinical improvement in skin lesions– Improved Host immunity

Problems with development of vaccine for leprosy

• Long incubation period of disease.• Paucity of animal model (Armadillo)• Inability to culture bacteria in lab

Dasypus novemcinctus

CLASSIFICATION OF “CANDIDATE VACCINES

• 1st Generation

Non Cultivable (M.leprae) Cultivable M.bacteria • 1. Killed M leprae 1. BCG • 2. Killed M leprae + BCG 2. BCG + M.vaccae • 3. Acetoacetylated M leprae 3. Killed M.welchii

4. Killed ICRC 5. M.vaccae 6.

M.habana 7. M gordonnae 8. M.phlei

• Second generation (In vitro/ Animal studies only)• Subunit vaccines • Shuttle plasmid vaccines

• These are vaccines under trial• Yet to achieve the status of a vaccine

BCG

• Bacille Calmette Guerin in 1921• Living bacteria derived from an attenuated

bovine strain of tubercle bacilli• WHO recommendation - Danish 1331 strain • The most widely used vaccine

Studies with BCG vaccine• BCG was found effective against the growth of

M.leprae in foot-pads of mice

• Katoch et al (1989)– BL/LL patients treated with MDT for 2 years and who were still smear positive were given BCG which led to increased bacterial killing and clearance

• But BCG vaccination is no more considered to be a modality for immunoprophylaxis of leprosy

BCG• Indian studies -Protective efficacy ranging from 20-

70%• Almost equal to its efficacy in preventing TB• Better protection against MBL (93%)• Faster clearance of both live and dead bacilli as well

as faster histological and clinical clearance• Repeat vaccination affords further protection

especially in children less than 15 years of age• There is increased risk of type I reaction• Indicated increased risk of tuberculoid and

indeterminate leprosy after BCG vaccination

Other studies

Efficacy• Brazil - 90%• Kenya - 81% • Uganda - 80% • Myanmar- 65%

CONVIT GARCIA

Convit García’s vaccine(BCG+ Killed M.leprae)

• A Venezuelan scientist- developed a vaccine in an attempt to fight leprosy

• In 1987, Convit added heat killed M.leprae to the BCG vaccine

• The combined vaccine was tested worldwide, but was not more effective than regular BCG

• A vaccine for leishmaniasis was later developed using Convit's method

Convit vaccine

• Produced favourable clinical and histological responses in both indeterminate & LL

• Few recent trials from India -shown better lepromin conversion and faster clinical and histological cure with the use of Convit vaccine along with MDT compared to BCG with MDT.

Acetoacetylated M leprae

• Carrier modified form of M leprae.• Talwar et al gave acetoacetylated M.leprae to 13

LL patients. They observed lepromin conversion in 7/13 patients

• Acetoacetylation improves interaction of bacteria with leucocytes- in vitro studies show improved macrophage migration.

• Immunization of contacts- it made them lepromin positive.

Pathology

• Cell mediated immunity (CMI) is the dominant host defence against M.leprae and circulating anti-M.leprae antibodies have little role

• Lipid component of cell wall of M.leprae prevents the recognition of bacilli by macrophages

• Tuberculoid leprosy exhibit CMI response due to high levels of serum lipase, which removes the lipids of the cell wall

• Delipidified cell component (DCC) of M.leprae have been shown to activate macrophages and kill M.leprae in vitro.

De-lipified cel components of M leprae

• Defective macrophages of leprosy patients were able to recognize the delipified cell components as antigens.

• It led to proliferation of lymphocytes in cultures following production of the desired lymphokines.

• Mice vaccinated with delipified cell components were found to control the growth of M leprae

ICRC

• ICRC bacilli ( to MAC complex) • 1979 - Cancer Research Institute Mumbai• ICRC bacilli exhibit antigenic cross-reactivity

with M.leprae with reference to both B & T cell antigens

• Antigens of the ICRC bacilli are also more accessible, making the organism a stronger immunogen

ICRC

• From a cultivable organism & hence cheap • No contamination with animal products• Induces stable immunity • Vaccine may also act against infections caused

by these opportunistic microbes• Rapid and significant fall in BI

• Advantages:-– Enhances T cell reactivity– Induces lepromin conversion in LL patients– Faster clearing of M.leprae

• More data is available on its role in immunoprophylaxis than in immunotherapy.

• Each dose contains 1 X 108 bacilli

Mw(M.welchii)• A rapid growing mycobacterium is said to be a

cultivable saphrophytic soil bacillus• Dr. G. P. Talwar, founder- director of NII,New Delhi• Since 1998 under the trade name of ‘Leprovac’ &

is currently -‘Immuvac’• Induce lepromin conversion in BL/LL patients• The vaccine has been used in patients with MBL • ICRC and Mw are similar cell antigens Hence having similar results

Mw

• Antigenically similar to M.leprae and M tuberculosis.

• Effective and tolerable• Role in both immunotherapy and

immunoprophylaxis.• More rapid bacterial clearance• Earlier achievement BI negativity in patients

given M.w+ MDT compared to only MDT.

• Advantages:-– Earlier release of patients from treatment– Slow responders to MDT are benefited– Decreased incidence of type II reactions and neuritis

• ADR:-• Fever• Mild injection site erythema induration(7d)

ulceration(3wks) healing (4wks) scar• Loco-regional LAP

M.Vaccae

• Used in trials for immunotherapy of- TB, AD, Psoriasis, Leishmaniasis, & Adeno Ca Lung

• To induce immunoreactivity to M leprae in the form of lepromin conversion, in both in vivo and in vitro studies

• Stanford et al demonstrated lepromin conversion in humans using

BCG and killed M. vaccae

M.habana

• A photochromogen• CDRI Lucknow have shown CMI response in

mice, langur & rhesus monkeys to its vaccine• A potential candidate vaccine for both TB &

leprosy • Protect mice against MTB, M ulcerans & M leprae

2nd generation subunit vaccine• Advances in cloning -- identified many protein

antigens of M. leprae-- 70Kd, 65 Kd, 35 Kd, 31 Kd, 18 kd, 10 Kd

• Natural or recombinant form of these proteins are available.

• Peptide base vaccine can elicit humoral and CMI response.

• They are used for immunoprophylaxis, immunotherapy, immunodiagnosis.

• Chemically synthesized by recombinant DNA technology– free of biological contamination .

• Still in experimental stage- Not in humans

• Using recombinant technology, the entire genome of M.leprae has been cloned.

• Recombinant DNA clones containing gene coding for 5 immunogenic proteins have been isolated using monoclonals.

• If scientists succeed in identifying the 'protective' antigen(s) from amongst these proteins

• Clones making 'protective' antigen(s) could be a constant source of supply for the preparation of a vaccine.

HMW PP-I glycoprotein

• Fraction of sonicate of ICRC bacilli gel permeation HPLC yields HMW glycoprotein known as PP-I with molecular weight of 106 D.

• It is a strong immunogen, carrying epitopes for B & T cells.

• Brings about lepromin conversion

M lepra 35 kD protein

• M lepra 35 kD protein• Protective immunity in Guinea pigs was found

to be similar to BCG.

Other candidate Subunit vaccines

• M lepra 65 kD heat shock protein (hsp)• M lepra: lsr antigen, 12 kD antigen• M lepra groES, groEL, 70kD hsp• M lepra 35kD + M tuberculosis 85B antigen• M habana 65kD and 23 kd proteins

PLASMID EXPRESSING CYTOKINES

• Vector that expresses p35 and p40 chain of murine IL-12 when combined with M.leprae 35Kd antigen

• Increases antigen specific production of interferon γ

• Increased clearance of mycobacteria compared to M.lepra 35kD vaccine alone.

SHUTTLE PLASMID VACCINES

• Approach has been to introduce genes coding for protective antigens in BCG.

• Attempt to introduce several protective genes from diverse organisms into BCG

• Simultaneouly with aim of developing vaccines which will protect against many disease including TB, leprosy, typhoid.

Advances

• October 2003 – Identification of M. leprae antigens

• May 2005 – Completed screening of M.Leprae for proteins strongly recognized by the human immune system

• March 2006 – Identified 02 specific antigens (MLO405 and ML2331) gave a significantly greater sensitivity to PGL-1 antibody test

A vaccine for leprosy is being developed by American researchers and is set for toxicology tests towards the end of 2014 and for phase I clinical trials in human volunteers by 2015 The Guardian June 06,2014

PROBLEMS WITH THE CURRENT VACCINES

1. Very few well-performed double-blind RCTs with proper follow-up.

2. Vaccines such as Mw – 24m while MDT- 12 m3. Bacteriological cure already 100% with MDT.

Hence No additional benefits 4. Unsatisfactory results in MBL with high BI at

onset.5. Risk of type I reactions.6. Observational studies overestimate the

efficacy of vaccines

CHALLENGES FOR NEW ANTI LEPROSY VACCINES

Complex host immunological response to mycobacteria Eg:-quantity of mycobacterial protein and the timing of exposure.

Testings limited mainly to animal modelsFor testing individual vaccines takes 9 -12 mLimitations of the models for testing:- The sensitivity of mouse footpad infection

model is lowComplexity of the armadillo modelLimiting factors:-Not many new cases &

extensive infrastructure

Comparative Leprosy Vaccine Trial in South India

– Double-blind, RCT prophylactic leprosy vaccine – Compared BCG, BCG with Killed M.leprae, Mw, ICRC

with normal saline placebo.– Study population- 2,90,000.– Overall protective efficacy • BCG-34.1%• BCG with Killed M.leprae –64%• ICRC— 65%• Mw- 25.7%

– BCG with Killed M.leprae and ICRC vaccine were found to be potentially more useful as immunoprophylactic agent.

BCG BCG + killed M leprae ICRC Mw

Prophylactic efficacy 18-90% 50-64% 65.5% 25.7%

Therapeutic efficacy (combined with MDT)

BI fall @ 2.4/ yr

BI-ve at end of 3.5 yrs

BI fall @

3/ yr

BI fall @

1.7/yr

BI fall @

1.7-2.72/ yr

2. BI-ve at end of 3 yrs

Type I reaction ↑ by 10% - - ↑ by 15%

Type II reaction ↓ by 30% - - ↓ by 25%

THE FUTURE

• BCG and ICRC Vaccine- future polyvalent mycobacterial vaccine that might offer protection against a wide spectrum of mycobacterial diseases.

• Such a polyvalent mycobacterial vaccine would reduce the number of vaccinations

References:• Lepr Rev. 2004 Dec;75(4):357-66 • Bull World Health Organ1989; 67 : 389– 99.• Indian J Lepr 1998; 70 : 369–388. • Lancet 1996; 348: 17–24.• Ind J Lper 2000; 72: 21–34.• Int J Lepr Other Mycobact Dis 2001, 69: 10–13.• Int J Lepr Other Mycobact Dis 2002; 70: 174–181.