Differential survival of transferred CD8 T cells and host reconstitution depending on TCR avidity for host-expressed alloantigen

We transferred naive alloreactive CD8 T cells from TCR transgenic mice to irradiated recipients expressing a partial (H-2K(bm8)) or a full (H-2K(b)) agonist alloantigen (alloAg). The consequences were strikingly distinct, resulting in acceleration of host lymphopoiesis in the former group, but in strong graft-vs-host reaction, preventing host lymphocyte reconstitution in the latter group. This was correlated, respectively, with long-term persistence and with rapid disappearance of the transferred CD8 T cells. Analysis of transferred T cells showed that initial T cell expansion and modulation of expression of activation markers CD44 and CD62L, as well as induction of cytotoxic function, were similar in both groups. However, IL-2 production and subsequent up-regulation of CD25, early perforin-independent cytolysis, and early down-regulation of Bcl-2 expression were detected only in T cells transferred in hosts expressing full agonist alloAg. Expansion of transferred CD8 T cells was not dependent on either IL-2 or CD25 expression. This expansion could lead to either accelerated host reconstitution or to strong graft-vs-host, depending on the nature of the alloAg. Thus, the extent of Ag stimulation may be a crucial parameter in protocols of alloreactive T cell immunotherapy.