Comparison of IFN-gamma responses to mycobacterial antigens as markers of response to BCG vaccination.

An increase in interferon-gamma (IFN-gamma) production to Mycobacterium tuberculosis purified protein derivative (Mtb PPD), as measured in the cultured diluted whole blood assay, is one indicator of a protective immune response to BCG vaccine. We have explored the potential for this assay to be improved by measuring IFN-gamma responses to more defined antigens of M. tuberculosis (short-term and mid-term culture filtrates, ESAT-6, 38 kDa), Mycobacterium bovis (MPB70), M. bovis BCG (Antigen 85) and Mycobacterium leprae (35 kDa), in UK teenagers before and 1 year after BCG vaccination (or no vaccination as controls). There was a significant increase in response to the culture filtrates post-vaccination, but this was no greater than that to Mtb PPD. Many teenagers responded to the purified antigens, in particular to Antigen 85, prior to vaccination, and BCG vaccination could only augment this pre-existing response to a limited extent; prior exposure to environmental mycobacteria can thus induce cross-reactive responses to antigens which complicate interpretation of in vitro assays of vaccine response. In contrast, ESAT-6 was recognised by only one teenager prior to vaccination, and, as expected, responses were not boosted by BCG. We therefore conclude that Mtb PPD is the antigen preparation of choice for assessing the immunogenicity of BCG vaccination.

Identification of immunological biomarkers which may differentiate latent tuberculosis from exposure to environmental nontuberculous mycobacteria in children.

A positive gamma interferon (IFN-γ) response to Mycobacterium tuberculosis early secretory antigenic target-6 (ESAT-6)/culture filtrate protein-10 (CFP-10) has been taken to indicate latent tuberculosis (TB) infection, but it may also be due to exposure to environmental nontuberculous mycobacteria in which ESAT-6 homologues are present. We assessed the immune responses to M. tuberculosis ESAT-6 and cross-reactive responses to ESAT-6 homologues of Mycobacterium avium and Mycobacterium kansasii. Archived culture supernatant samples from children at 3 years post-BCG vaccination were tested for cytokine/chemokine responses to M. tuberculosis antigens. Furthermore, the IFN-γ responses to M. tuberculosis antigens were followed up for 40 children at 8 years post-BCG vaccination, and 15 TB patients were recruited as a control group for the M. tuberculosis ESAT-6 response in Malawi. IFN-γ enzyme-linked immunosorbent assays (ELISAs) on supernatants from diluted whole-blood assays, IFN-γ enzyme-linked immunosorbent spot (ELISpot) assays, QuantiFERON TB Gold-In Tube tests, and multiplex bead assays were performed. More than 45% of the responders to M. tuberculosis ESAT-6 showed IFN-γ responses to M. avium and M. kansasii ESAT-6. In response to M. tuberculosis ESAT-6/CFP-10, interleukin 5 (IL-5), IL-9, IL-13, and IL-17 differentiated the stronger IFN-γ responders to M. tuberculosis ESAT-6 from those who preferentially responded to M. kansasii and M. avium ESAT-6. A cytokine/chemokine signature of IL-5, IL-9, IL-13, and IL-17 was identified as a putative immunological biosignature to differentiate latent TB infection from exposure to M. avium and M. kansasii in Malawian children, indicating that this signature might be particularly informative in areas where both TB and exposure to environmental nontuberculous mycobacteria are endemic.

Vitamin a supplementation does not affect infants' immune responses to polio and tetanus vaccines.

It has been suggested that administering vitamin A with the measles vaccine may reduce the vaccine's immunogenicity. This trial examined the effect of supplementing vitamin A during the early months of life on infants' immune responses to tetanus and polio vaccines. Young infants (n = 1085) were enrolled and individually randomized into 1 of 4 groups in a factorial, double-blind, placebo-controlled trial. Three vitamin A supplementation strategies were investigated: 1) supplementation of breast-feeding mothers with 60 mg retinol equivalent (RE) vitamin A within 4 wk of delivery; 2) Expanded Program on Immunization (EPI)-linked supplementation of infants with 7.5 mg RE vitamin A at 6, 10, and 14 wk; and 3) combined mother and child supplementations. A 4th group in which mother and child were given placebos served as controls. Blood samples were collected from each child at 6 wk and 6 mo of age to measure antipolio antibody titer, antitetanus toxoid antibodies, and avidity of antibodies to tetanus. Of the infants randomized into the 4 arms of the study, 767 (71%) completed follow-up at 6 mo of age. Follow-up rates were similar in all 4 arms (69-72%, P = 0.8). Antibody titers were relatively high in all 4 groups at both 6 wk and 6 mo of age, with no differences among the groups. We found no evidence that vitamin A supplementation affects infants' antibody responses to tetanus toxoid or oral polio vaccine delivered at EPI contacts.