T-cell activation, proliferation, and memory after cardiac transplantation in vivo

Objective To study the response of alloantigen (H2K(b))-specific T cells to a H2(b+) cardiac allograft in vivo. Summary Background Data The response of T cells to alloantigen has been well characterized in vitro but has proved more difficult to assess in vivo. The aim of these experiments was to develop a model of T-cell-mediated rejection where the response of T cells after transplantation of a cardiac allograft could be followed in vivo. Methods Purified CD8(+) T cells from H2K(b)-specific TCR transgenic mice (BM3; H2(k)) were adoptively transferred into thymectomized, T-cell-depleted CBA/Ca (H2(k)) mice. These mice were then transplanted with a H2K(b+) cardiac allograft. Using four-color flow cytometry, the proliferative response, modulation of activation markers, and potential cytokine production of the H2Kb-specific T cells was assessed after transplantation. Results Consistent rejection of H2Kb+ cardiac allografts required the transfer of at least 6 x 10(6) CD8(+) H2K(b)-specific T cells. Short-term analyses revealed that the transgenic-TCR+/CD8(+) T cells proliferated and became activated after transplantation of an H2K(b+) cardiac allograft. Fifty days after transplantation, the transgenic-TCR+/CD8(+) T cells remained readily detectable, bore a predominantly memory phenotype (CD44(hi)), and rapidly produced interleukin 2 and interferon-gamma on in vitro restimulation. Conclusions These data show that the activation of alloantigen-specific T cells can be followed in vivo in short-term and long-term experiments, thereby providing a unique opportunity to study the mechanisms by which T cells respond to allografts in vivo.