CYTOTOXIC LYMPHOCYTES REQUIRE GRANZYME-B FOR THE RAPID INDUCTION OF DNA FRAGMENTATION AND APOPTOSIS IN ALLOGENEIC TARGET-CELLS

We have generated H-2b mice with a homozygous null mutation in the gra nzyme (gzm) B gene. Gzm B is a neutral serine protease with Aspase act ivity that is found only in the granules of activated cytolytic T cell s, natural killer cells, and lymphokine-activated killer cells. Gzm B- /- mice develop normally and have normal hematopoiesis and lymphopoies is. In vitro, cytotoxic T lymphocytes (CTL) derived from gzm B-/- anim als are able to induce Cr-51 release from allotarget cells, but with r educed efficiency. However, gzm B-/- CTL have a profound defect in the ir ability to induce rapid DNA fragmentation and apoptosis in allogene ic target cells. This defect is kinetic since DNA fragmentation is par tially compensated and Cr-51 release is completely rescued with long i ncubation times. We conclude that gzm B serves a critical and nonredun dant role for the rapid induction of target cell DNA fragmentation and apoptosis by alloreactive cytotoxic T lymphocytes.