ALLOANTIGEN PRIMING INDUCES A STATE OF UNRESPONSIVENESS IN HUMAN UMBILICAL-CORD BLOOD T-CELLS

Induction of alloreactivity in human adult and umbilical cord blood T cells was evaluated in mixed leukocyte culture by exposure to an allogeneic lymphoblastoid line that expresses known costimulatory molecules. Initial exposure to alloantigen-presenting cells (allo-APC) induced strong proliferative responses in both adult and cord blood T cells, However, in contrast to adult T cells, cord blood T cells exhibited little proliferation after restimulation with donor APC, Primed cord blood T cells could respond to interleukin 2 (IL-2), but unresponsiveness to alloantigen was not overcome by addition of exogenous IL-2, Unresponsiveness was long-lasting and appeared to be maintained by a combination of induction of anergy and activity of CD8(+) suppressor cells. This information may contribute to use of human cord blood as an allogeneic source of transplantable stem cells.