ACTIVATION OF PREEXISTING T-CELL CLONES BY TARGETED INTERLEUKIN-2 THERAPY

The induction of an immunological antitumor response capable of eradic ating metastatic tumors is the ultimate goal of immunotherapy, We have recently shown that this can be achieved by interleukin 2 (IL-2) ther apy directed to the tumor microenvironment by a recombinant antibody-I L-2 fusion protein. It is not known, however, whether this curative tr eatment is associated with a predominance of T cells carrying specific T cell receptor variable beta regions (TCRBV) or the presence of clon ally expanded T cells, To address this question, we have used a quanti tative reverse transcriptase-coupled PCR method to analyze the TCRBV r egion repertoire in tumor-infiltrating lymphocytes of treated and untr eated animals. As controls the TCRBV region repertoire was analyzed in blood and skin from disease-free animals, The results indicate an ove rexpression of TCRBV5 in the tumors of all treated mice and an additio nal overexpression of individual regions in each tumor, Direct sequenc ing of these TCRBV regions did not reveal any evidence of clonal expan sions. However, since clonal expansions could exist as subpopulations in highly expressed regions, not detectable by direct sequencing, a de naturing gradient gel electrophoresis assay was used for clonal analys is of TCRBV PCR products, Denaturing gradient gel electrophoresis anal ysis of selected TCRBV regions revealed the presence of clonotypic T c ells in tumors from both treated and untreated animals, These data ind icate that targeted IL-2 therapy in this model does not induce clonal T cell responses de novo, rather it acts as an activator for an alread y existing population of clonotypic T cells.