Characterization of T cells that confer a high degree of protective immunity against tuberculosis in mice after vaccination with tumor cells expressing mycobacterial hsp65

Abstract

Mice vaccinated by injection with tumor cells expressing the Mycobacterium leprae gene for hsp65 acquire a remarkably high degree of protection against challenge with Mycobacterium tuberculosis. We used limiting-dilution analysis to assess the frequency of CD4+ CD8- and CD4- CD8+ splenocytes responding to mycobacterial hsp65 in such vaccinated mice. Cells of both phenotypes were present at very high and equal frequencies (approximately 1:100). Vaccination with live Mycobacterium bovis BCG also increased the frequencies of both phenotypes of hsp65-reactive cells equally (to approximately 1:2,500), whereas vaccination procedures that were not protective, with either dead BCG, hsp65 protein in incomplete Freund's adjuvant, or hsp65 mixed with tumor cells, resulted in preferential increase in CD4+ CD8- cells. Twelve CD4+ CD8- and twelve CD4- CD8+ hsp65-responsive T-cell clones were obtained and characterized. All showed conventional antigen recognition via major histocompatibility complex class II and class I pathways but differed in secretion of gamma interferon and interleukin 4 and cytotoxicity. In tests of antimycobacterial activity against M. tuberculosis, both in infected macrophages in vitro and by adoptive transfer of protection with T-cell clones injected into irradiated mice, the most effective clones were the most cytotoxic and secretion of gamma interferon made only a secondary contribution.