In situ cytokine therapy: redistribution of clonally expanded T cells

Immunity to tumors relies on recirculating antigen-specific T cells. Whilst induction of antigen-specific T cells by immunotherapy has been convincing ly proven, direct evidence for recirculation of such cells is still lacking . Here, employing a recently established in situ immunotherapy model for mu rine melanoma we directly demonstrate the redistribution of clonally expand ed T cells. In this model IL-2 is targeted to the tumor microenvironment by means of specific antibody-IL-2 fusion proteins resulting in the expansion of T cells. The therapeutic effect of the fusion protein is not restricted to tumors expressing the targeted antigen, but extends to antigen negative variants of the tumor if present in the same animal. Analysis of the T cel l infiltrate by quantitative reverse transcription-PCR revealed the presenc e of highly expressed TCR BV regions in both tumor variants. TCR clonotype mapping revealed that the high expressions of these regions were caused by clonal expansions and, notably, that these specific clonotypic TCR transcri pts were identical in both tumors. Thus, T cell clones activated locally by targeted IL-2 therapy recirculate and mediate eradication of distant tumor sites not subjected to in situ cytokine therapy.