The influence of previous exposure to environmental mycobacteria on the interferon-gamma response to bacille Calmette-Guérin vaccination in southern England and northern Malawi

Abstract

We report a large study of the effect of BCG vaccination on the in vitro 6-day whole blood interferon-gamma (IFN-gamma) response to antigens from eight species of mycobacteria among schoolchildren in south-eastern England, where bacille Calmette-Guérin (BCG) vaccination is highly protective against pulmonary tuberculosis, and among young adults in northern Malawi, where BCG vaccination is not protective. In the UK children, BCG induced an appreciable increase in IFN-gamma response to antigens from most species of mycobacteria. The degree of change was linked to the relatedness of the species to Mycobacterium bovis BCG, and provides further evidence of the cross-reactivity of mycobacterial species in priming of the immune system. IFN-gamma responses to purified protein derivatives (PPDs) from M. tuberculosis and environmental mycobacteria were more prevalent in the Malawian than the UK group prior to vaccination; BCG vaccination increased the prevalence of responses to these PPDs in the UK group to a level similar to that in Malawi. There was no evidence that the vaccine-induced change in IFN-gamma response was dependent upon the magnitude of the initial response of the individual to environmental mycobacteria in the United Kingdom or in Malawi. These observations should assist the development and interpretation of human clinical trials of new vaccines against M. tuberculosis in areas of both low and high exposure to environmental mycobacteria.

Fig. 1

Change in interferon (IFN)-γ response between recruitment and follow-up of control and vaccinated subjects in the United Kingdom to mycobacterial purified protein derivatives (PPDs). Subjects were bled prior to vaccination and 1 year later and IFN-γ responses measured in diluted whole blood assay at 6 days. Results are presented as a frequency distribution of size of change in IFN-γ response (as outlined in Methods) for control group (n = 100) and vaccinated (Vaccine) group (n = 240) to (a) Mycobacterium tuberculosis, (b) M. bovis, (c) M. avium and (d) M. fortuitum PPDs.

Fig. 2

Effect of BCG vaccination on prevalence of interferon (IFN)-γ responses to mycobacterial purified protein derivatives (PPDs) in the United Kingdom and Malawi. Subjects were bled prior to vaccination and 1 year later and IFN-γ responses measured in diluted whole blood assay at 6 days. Results are presented as the percentage of subjects in the United Kingdom and Malawi making positive (> 62 pg/ml) IFN-γ response to PPDs from Mycobacterium tuberculosis and different environmental mycobacteria (a) before vaccination (recruitment); (b) at recruitment and 1 year later (follow-up) among control subjects; and (c) at follow-up among control and vaccinated subjects.

Fig. 3

Effect of bacille Calmette–Guérin (BCG) vaccination on magnitude of interferon (IFN)-γ response to purified protein derivatives (PPDs) from Mycobacterium tuberculosis and environmental mycobacteria in the United Kingdom and Malawi. Subjects were bled prior to vaccination and 1 year later and IFN-γ responses measured in diluted whole blood assay at 6 days. Results are presented as median IFN-γ response (pg/ml) among subjects making an IFN-γ response > 62 pg/ml at (a) recruitment and (b) follow-up 1 year later. Group sizes for responses to PPDs from M. bovis, M. tuberculosis, M. marinum, M. avium, M. intracellulare, M. scrofulaceum, M. kansasii, M. fortuitum and M. vaccae, respectively, are as follows: recruitment, UK control group, n = 15, 22, 67, 65, 45, 41, 23, 12, 19; UK vaccine group, n = 44, 65, 143, 161, 121, 125, 80, 48, 46; Malawi control group, n = 58, 108, 110, 121, 153, 156, 12, 73, 18; Malawi vaccine group, n = 112, 223, 219, 254, 280, 305, 19, 143, 30. Follow-up, UK control group, n = 12, 18, 47, 50, 37, 36, 17, 11, 11; UK vaccine group, n = 172, 198, 213, 205, 171, 178, 141, 73, 91; Malawi control group, n = 58, 101, 113, 134, 116, 127, 74, 74, 56; Malawi vaccine group, n = 162, 251, 264, 286, 255, 278, 176, 157, 121.

Fig. 4

Effect of previous interferon (IFN)-γ response to MAIS (Mycobacterium avium, M. intracellulare and M. scrofulaceum) complex purified protein derivatives (PPDs) on subsequent change in IFN-γ response to Mycobacterium tuberculosis PPD following bacille Calmette–Guérin (BCG) vaccination. Subjects were bled prior to vaccination and 1 year later and IFN-γ responses measured in diluted whole blood assay at 6 days. Results are presented as size of change (median) in IFN-γ response to M. tuberculosis PPD 1 year after BCG vaccination among individuals making ≤ 62 pg/ml response (≤ 62) to M. avium, M. intracellulare and M. scrofulaceum PPDs versus individuals making > 250 pg/ml response (≥ 250) to these PPDs at recruitment, in Malawi and the United Kingdom. Data presented are restricted to those individuals making < 250 pg/ml IFN-γ response to M. tuberculosis PPD at recruitment. In Malawi, ≤ 62 n = 36, ≥ 250 n = 19; in the United Kingdom, ≤ 62 n = 89, ≥ 250 n = 20.