Identification and characterization of protective T cells in hsp65 DNA-vaccinated and Mycobacterium tuberculosis-infected mice

Immunization by intramuscular injection of plasmid DNA expressing mycobacterial 65-kDa heat shock protein (hsp65) protects mice against challenge with virulent Mycobacterium tuberculosis H37Rv. During infection or after immunization, CD4(+)/CD8(-) and CD8(+)/CD4(-) hsp65-reactive T cells increased equally in spleens, During infection, the majority of these cells were weakly CD44 positive (CD44(lo)) and produced interleukin 4 (IL-4) whereas after immunization the majority were highly CD44 positive (CD44(hi)) and produced gamma interferon (IFN-gamma). In adoptive transfer of protection to naive mice, the total CD8(+)/CD4(-) cell population purified from spleens of immunized mice aas more protective than that from infected mice, When the cells mere separated into CD4(+)/CD8(-) and CD8(+)/CD4(-) types and then into CD44(hi) and CD44(lo) types, CD44(lo) cells were essentially unable to transfer protection, the most protective CD44(hi) cells were CD8(+)/CD4(-), and those from immunized mice were much more protective than those from infected mice. Thus, whereas the CD44(lo) IL-4-producing phenotype prevailed during infection, protection was associated with the CD8(+)/CD44(hi) IFN-gamma-producing phenotype that predominated after immunization. This conclusion was confirmed and extended by analysis of 16 hsp65-reactive T cell clones from infected mice and 16 from immunized mice; the most protective clones, in addition, displayed antigen-specific cytotoxicity.