Presentation on theme: "Experiences with BCG vaccination in the UK and Malawi Hazel M Dockrell London School of Hygiene & Tropical Medicine."— Presentation transcript:
Experiences with BCG vaccination in the UK and Malawi Hazel M Dockrell London School of Hygiene & Tropical Medicine
We need correlates of protection to use in trials of new TB vaccines in man Can we exploit the observations that BCG vaccination can induce protection against pulmonary TB when given to adolescents in the UK, but not when given to young adults in Malawi?
In Malawi, a single BCG vaccination gives 50% or more protection against leprosy but no protection against pulmonary tuberculosis* In the UK, vaccination of schoolchildren with BCG provides 77% protection against tuberculosis *Lancet, 348,: 17 (1996) BCG protection in Malawi and the UK
Immunity to Tuberculosis Cell mediated immunity is important Interaction between activated m , CD4+, CD8+, T cells Type 1 cytokines such as IFN /IL-12 play a role in protection; also role for TNF Could whole blood assays measuring such cytokines be used as a correlate of protection?
Diluted whole blood assays to measure antigen-specific interferon- responses Heparinised blood just diluted in tissue culture medium and antigens added Cytokines measured in culture supernatants Assay proved easy, reliable and reproducible for field use when used with M.leprae antigens in Nepal It has now been used in studies in Malawi, Pakistan, The Philippines, South Africa, Uganda, China…. Weir et al J Immunol Meth 176: 93 (1994)
Interferon- responses measured in diluted whole blood cultures Black et al, Int J Tuberc Lung Dis 5: 664 (2001)
Use of positive control supernatants to control for assay variation
Field work in Malawi 633 recruited (age 10-28) (HIV-ve, BCG-ve) 562 eligible (Mantoux <10mm) 2/3 BCG vaccinated 80% follow-up at 1 year
and in Essex, UK…. 435 recruited (age 12-15, BCG scar -ve), Heaf test grade >2 excluded 2/3 given BCG vaccination 80% followed up at 1 year Rosemary Weir
Does IFN production increase in both UK and Malawian vaccinees? IFN responses to M.tuberculosis PPD tested pre vaccination and 1 year post vaccination
Pre- and post- BCG vaccination IFN responses to PPD in UK Increase in % responders Controls 19% to 21% Vaccinees 23% to 83% Black, Weir et al, Lancet 139: 1393 (2002)
Pre- and post- BCG vaccination IFN responses to PPD in Malawi Increase in % responders Placebo 60% to 76% Vaccinees 61% to 78% Black, Weir et al, Lancet 139: 1393 (2002)
1.4 vs 2.4 Increase 1.05 vs 8.3
IFN responses detected in 6 day whole blood assays are more variable in a tropical setting such as Malawi, than in the UK IFN responses to PPD: % changes over 1 year in placebo/control groups decrease no change increase Malawi UK
Distribution of IFN responses to MTb PPD 1 year after BCG vaccination in Malawi &UK The increase in IFN is associated with protection in the UK There are conflicting views about whether exposure to mycobacteria confers protection or blocks its induction
Controlling for effective vaccination: Comparison of BCG scar size of vaccinees in Malawi and UK Malawi: 98.5% scar +ve UK: 96.7% scar +ve
Choice of time point: maximal responses will be different in naive and sensitised subjects A small group of subjects were tested weeks after BCG vaccination in Malawi Results did indicate that BCG vaccination boosted the IFN response, but this increase was transient In our current study we are testing at both 3 and 12 months….
Frequency distributions of IFNγ responses to M tuberculosis PPD among 13-year olds in the UK, prior to and 3 months after receiving BCG vaccine or placebo Change: 1.3x vs 16.9x
The timing of testing is critical: 8-10 weeks after BCG, IFN responses are boosted in Malawian vaccinees Data: Gill Black PrePost IFN - pg/ml Placebo group (n=8) Vaccine group (n=17) PrePost IFN - pg/ml
IFN responses to environmental mycobacterial PPDs one year after BCG vaccination in Malawi Exposure to non-tuberculous, environmental mycobacteria appears common in Malawians, and is responsible for sensitisation to MTb PPD
BCG vaccination is given to infants at brith in most low income countries If exposure to environmental mycobacteria accounts for the differences to response in adolescents to BCG vaccination in Malawi and the UK, would infants in the two settings behave similarly?
Vaccination schedule in Malawi
BCG vaccination is inducing good IFN responses at 3 months in Malawi in infants
Frequency distributions of IFNγ responses to M tuberculosis PPD in Malawian and UK infants, three months after BCG vaccination Malawian infants vaccinated at birth give good IFN responses 3 months later Responses seem higher in the UK infants- is this real, is it because they are older (4 months vs 3 months), or ????
Before and after…... Before vaccination of adolescents/young adults, only 20% were IFN responders to PPD in UK, compared to 60% in Malawi After vaccination, approx 80% of both the UK and Malawi populations responded Are both populations equally protected? What else is different?
In Malawi, 55% of the young adults tested were infected with hookworm, 40% with Schistosoma mansoni and 25% with Schistosoma haematobium; filarial infection is also found in the north of the district
Effect of helminth infections on immune responses Odds ratios of having a strong IFNγ response (>250 pg/ml) (a) and a (“positive”) IL-5 response (>62 pg/ml) (b) to M tuberculosis PPD, streptokinase/streptodornase (SK/SD) or phytohaemagglutinin (PHA) by numbers of helminth infections (hookworm, S mansoni, S haematobium, W bancrofti). Baseline is group not infected with any helminths.
IL-5 response to M. tuberculosis PPD post-vaccination, Malawi and UK BCG vaccination does not induce increased IL-5 production in response to PPD, in Malawi or the UK IL-5 responders are high, not low, IFN producers
Differences in innate immunity: Malawians also make more IL-10 and TNF than UK subjects
Association between IFN responses and Mantoux skin test response to PPD PPD ESAT-6
Assays for IFN as an alternative to skin testing Assays are robust and perform well in field settings They identify more T cell responders than skin testing- are they more sensitive? Two responses are associated although there are discordant individuals Responses are more variable in a tropical setting (Malawi vs UK) Assays can detect responses to individual recombinant antigens
Overnight and 6 day whole blood assays compared Overnight assays require more blood, and may need to be put into culture quickly 6 day assays are similar to traditional PBMC assays, and involve cell proliferation 6 days assays require access to a tissue culture hood and CO 2 incubator In both assays cytokine can be measured by ELISA (multiplex assay, dipstick)
Conclusions In adolescents/young adults, the increase in the amount of IFN produced in cultures stimulated with PPD correlates with the protection BCG vaccination gives against TB in the UK: just measuring absolute amounts of IFN insufficient In Malawi, BCG vaccination only induces a temporary boosting in IFN responses: timing of testing critical Prior sensitivity to mycobacterial antigens in Malawi seems to result from exposure to environmental mycobacteria: implications for vaccine design and timing Other infections may influence the status of the immune system in low income countries
Whether IFN is a correlate of protection depends on whether the Malawians have protective immunity to TB equivalent to that given by BCG vaccination in the UK….. Does the immunity induced by environmental mycobacteria kill the BCG before it can induce real protection? Test mycobacterial killing… Does protection need IFN together with another key cytokine (TNF ) or without another cytokine (IL-4, IL-10, TGF )? Does protection need CD8 T cells as well as CD4 T cells?
Some implications and questions.... Diluted whole blood assays have the potential to be a useful tool for new TB vaccine trials If a new TB vaccine contains antigens cross- reactive with those in environmental mycobacteria, it may need to be given to infants There may be differences in the proportion of naïve and memory T cells, and in the maintenance of T cell memory, in tropical and non-tropical settings
BCG vaccination Malawi/UK Paul Fine Rosemary Weir, Patricia Gorak-Stolinska (UK) Gill Black, Anne Ben-Smith (Malawi) Steven Chaguluka, Huxley Kanyongoloka Mia Crampin, David Warndorff Lifted Sichali, Lorren Mwaungulu Bernadette Nazareth Sian Floyd, Lyn Bliss, Jacky Saul, Keith Branson Funded by the Wellcome Trust, LEPRA and WHO