Tumor cells transfected with a bacterial heat-shock gene lose tumorigenicity and induce protection against tumors.

The gene encoding a highly immunogenic mycobacterial heat-shock protein (hsp65) was transfected into the murine macrophage tumor cell line J774. The resulting hsp65-expressing cells (J774-hsp65) were no longer able to produce tumors in syngeneic mice. This loss of tumorigenicity was not mediated through T cells since the transfected cells did not produce tumors in athymic mice. If mice are first immunized with the J774-hsp65 cells and then challenged with the parent J774 cells, the mice do not develop tumors, indicating that the presence of the mycobacterial hsp65 protein greatly enhances immunological recognition of unique structures expressed by the parent tumor cells. This is further confirmed by the demonstration in vitro of T cells derived from J774-hsp65-immunized mice that are cytotoxic for the parent J774 cells. The results provide the basis for a novel strategy for enhancing the immunological recognition and decreasing the tumorigenicity of transformed cells.

Major histocompatibility complex non-restricted presentation to CD4+ T lymphocytes of Mycobacterium leprae heat-shock protein 65 antigen by macrophages transfected with the mycobacterial gene.

When the immunodominant 65,000 MW heat-shock protein of Mycobacterium leprae (ML65hsp) was expressed from the transfected mycobacterial gene in the mouse macrophage cell line J774.G8, the antigen was recognized by specifically sensitized CD4+ splenocytes in association with major histocompatibility complex (MHC) class II and CD4. Inhibition by monensin, leupeptin and chloroquine but not brefeldin A indicated dependence of presentation upon endosomal antigen processing. Although direct access of the endogenously synthesized antigen to the endosomal pathway of presentation, without extracellular release followed by endocytosis, could not be discounted, antigen was present in supernatants of the transfected cells in a form that could be presented by fixed macrophages and a form that required further processing for presentation. Each of three monoclonal antibodies (mAb) specific for widely separated linear amino acid epitopes of the antigen strongly inhibited recognition, suggesting steric interference with antigen-presenting cell (APC)-T cell interaction. Tests with splenocytes from vaccinated congenic mice indicated that recognition was not restricted by MHC haplotype. The significance and mechanism of this apparent MHC context-independent interaction of the presented antigen with specific T-cell receptor (TcR) remain to be explored.