Differences In The Phenotype And In Vivo Anti-Tumor Activity Of Wti Specific And Ebv-Specific T-Cells Generated In Vitro For Adoptive Immunotherapy

Our studies in SCID mouse/human tumor xenograft models have demonstrated that T cells sensitized with autologous EBV BLCL in vitro will, following intravenous transfer into mice bearing tumors varying in HLA type and expression of EBV antigens, selectively accumulate in EBV+ tumors co-expressing the T cell’s HLA restricting allele, and will proliferate and persist in these tumors through there complete regression. In contrast while T cells sensitized against WT1 peptides presented by peptide-loaded autologous DCs or EBV BLCL in vitro also exhibit HLA-restricted accumulation in WT1+ tumor xenografts and induce significant inhibition of tumor growth, they persist only for periods of 8 days following adoptive transfer. By day 15, the T cells were no longer detectable in the tumors, following which the regrowth of WT1 expressing tumors was again observed. Accordingly, we compared T cells sensitized in vitro with autologous EBV BLCL alone or with EBV BLCL loaded either with the pool of overlapping 15-mers spanning over WT1 sequence or transduced to express WT1. Antigen-specific T cells were then characterized as to their specificity and HLA restriction. Antigen-reactive T cells were then isolated on the basis of IFNγ production in response to secondary restimulation with APCs bearing targeted peptides and the appropriate restricting HLA alleles and evaluated for their phenotype and tumor-specific activity. Both CD4+ and CD8+ EBV-specific T cells exhibited HLA-restricted lysis of EBV+ tumor cells while the CD8+ WT1 specific T cells consistently lized WT1 tumors bearing HLA restricting HLA class I allele. The CD4+ T cells were not cytotoxic. The WT1-specific and EBV-specific CD4+ T cells did not differ in phenotype. However, while CD8+ T cells specific for EBV expressed an effector memory phenotype (CD3+ CD8+ CCR7− CD45RA+ CD45RO+ CD62L+ CD25+), the WT1 specific CD8+ T cells were predominantly of a central memory type (CD3+ CD8+ CCR7+ CD45RA− CD45RO+ CD62L+ CD25+). These studies suggest that T cells generated against WT1 in vitro may be relatively deficient in effector memory T cells required to induce complete tumor regression in vivo.