XENOSPECIFIC CYTOTOXIC T-LYMPHOCYTES - POTENT LYSIS IN-VITRO AND IN-VIVO

As little is known about the molecular mechanisms responsible for lymp hocyte-mediated rejection of xenografts, we have studied the relative contribution of perforin and Fas pathways in cytotoxic lymphocytes gen erated in mice transplanted with human cell lines. Responder lymphocyt es generated in immunocompetent mice displayed significant lysis of hu man target cells, which suggests that mice can generate a strong lymph ocytotoxic response to human cells. Effector cells generated in immuno competent and gld (Fas ligand mutant) mice predominantly use a perfori n-mediated cytotoxic mechanism. By contrast, a Fas-mediated pathway co uld be stimulated in perforin-deficient or beta 2-microglobulin-defici ent mice, providing the human target cells were sensitive to Fas-media ted lysis, In vitro depletion of effector CD3+ CD8(+) T cells, but not CD4(+) T or NH1.1(+) cells, completely inhibited lysis of human targe t cells. This suggests that CD3(+) CD8(+) T cells were responsible for perforin-mediated xenospecific cytotoxicity, In vivo depletion of NK1 .1(+) cells and CD4(+) T cells before the final immunization abrogated the capacity of lymph node cells to generate xenospecific CD8(+) cyto toxic T lymphocytes. By contrast, in vitro depletion of CD4(+) T cells was most effective in abrogating the xenospecific Fas-mediated cytoto xicity of perforin-deficient effector cells. Xenospecific cytotoxic T cells were also capable of mediating tumor rejection when adoptively t ransferred into scid/scid mice bearing established human COLO 205 xeno grafts, Overall, these data suggested that xenospecific cytotoxic T ly mphocytes canlyse target cells via either perforin- or Fas-mediated pa thways and that these cells can provide protective and specific immuni ty against tumor xenografts in the absence of an intact humoral immune system.