Bone marrow cytotoxic precursor T cells: Alloantigen-induced cytotoxic T-cell responses by murine bone marrow cells in vitro

Abstract

When bone marrow cells, obtained from C57BL/6 mice, were incubated in vitro with irradiated BALB/c spleen cells, cytotoxic activity against P815 tumor cells developed at 5–7 days of culture. This cytotoxic activity was T cell mediated and specific for the H-2 type of the allogeneic spleen cells used as stimulators. The generation of this cytotoxic T-cell activity was dependent on T cells present in the bone marrow since T-cell-depleted bone marrow cells failed to generate a cytotoxic response in vitro. The correct ratio of bone marrow cells to allogeneic stimulator cells was critical for demonstrating an in vitro cytotoxic response. Further, bone marrow cells incubated in culture medium not supplemented with 2-mercaptoethanol (2-ME) failed to generate alloantigen induced cytotoxic responses. Cytotoxic activity generated by bone marrow cells was always lower than the cytotoxic activity generated by alloantigen stimulated spleen cells. However, the level of cytotoxic activity generated by bone marrow cells was not in proportion to the initial low number of T cells present in that tissue. Before in vitro culture with alloantigen, 3% of the bone marrow cells were Thy-1.2 + as compared to 40% of the spleen cells being Thy-1.2 +. After 5 days of culture with alloantigen, 28% of the bone marrow cells were Thy-1.2 +, representing a sixfold increase in the absolute number of T cells. The possibility that differentiation of pre-T cells into cytotoxic effector T cells is taking place in this in vitro response is considered.