New vaccines against tuberculosis.

It has proved difficult to vaccinate effectively against tuberculosis with mycobacterial components or even with whole dead mycobacteria; protection was always inferior to that obtained with the live attenuated vaccine known as bacillus Calmette-Guérin (BCG). We have found that this may no longer be the case. Expression of the gene for a single mycobacterial antigen (Mycobacterium leprae hsp65) in adult BALB/c mice resulted in substantial cell-mediated protection against challenge with M. tuberculosis, but only when it was generated as an endogenous antigen within antigen-presenting cells. CD4 and CD8 T cells cloned from spleens of immunized mice passively transferred protection to non-immunized mice, and CD8 cells selectively lysed macrophages infected with M. tuberculosis. The ability of the clones to protect recipient mice against challenge infection was most strongly associated with specific cytotoxic capacity and secondarily with IFN-gamma production. Three modes of expressing the gene have been tested: a) expression from a retroviral vector (pZIPNeoSV) in implanted J774 tumor cells, b) expression from the same vector via bone marrow cells transfected in vitro and used to reconstitute irradiated mice, and c) in a preliminary experiment, from cytomegalovirus (CMV) immediate-early and hydroxymethylglutaryl Co-A reductase promoters injected as plasmid DNA into muscle.