Interventions for Tuberculosis Control and Elimination 2002

this type of vaccine may not only protect against subsequent infection with
M. tuberculosis, but may stimulate the immune response even among experimental
animals with active disease. 1205 There are indications that the combination
of priming with a DNA vaccine followed by a booster with BCG
might induce higher protective efficacy in mice than BCG vaccination
alone. 1206
Recombinants
Recombinant vaccines use existing microorganisms, e.g., vaccinia viruses 1207
or BCG, 1208,1209 which are genetically modified to produce additional antigens
thought to enhance the immune response. 1185 This approach is fairly
recent and needs further research, which will most likely be aided by the
deciphering of the entire sequence of the M. tuberculosis genome. 1210 In
vitro, BCG engineered to secrete recombinant human interferon-alpha was
substantially more active than unaltered BCG in inducing interferon gamma
in human peripheral blood mononuclear cells 1209 In a guinea pig model,
such a recombinant vaccine was superior than two BCG strains in preventing
gross lesions and dissemination. 1211
Subunits
Particular components (subunits) of M. tuberculosis may be better suited to
inducing protective immunity than an entire organism. Recent research is
thus evaluating the protective efficacy of such subunits. 1212 Preliminary
experimental studies appear to be promising, providing protection similar
to that obtained with BCG vaccination. 1213,1214 Subunits are potentially specific
and safe. A disadvantage of subunit vaccines is their limited persistence
and thus potentially reduced duration of immune response. 1215 In
experimental mice models, re-challenge with a mycloyl transferase protein
significantly boosted the protection against challenge with M. tuberculosis
in animals whose immune protection had waned following BCG vaccination
at birth. 1216
169