TCR-ligand koff rate correlates with the protective capacity of antigen-specific CD8+ T cells for adoptive transfer.

Adoptive immunotherapy is a promising therapeutic approach for the treatment of chronic infections and cancer. T cells within a certain range of high avidity for their cognate ligand are believed to be most effective. T cell receptor (TCR) transfer experiments indicate that a major part of avidity is hardwired within the structure of the TCR. Unfortunately, rapid measurement of structural avidity of TCRs is difficult on living T cells. We developed a technology where dissociation (koff rate) of truly monomeric peptide-major histocompatibility complex (pMHC) molecules bound to surface-expressed TCRs can be monitored by real-time microscopy in a highly reliable manner. A first evaluation of this method on distinct human cytomegalovirus (CMV)-specific T cell populations revealed unexpected differences in the koff rates. CMV-specific T cells are currently being evaluated in clinical trials for efficacy in adoptive immunotherapy; therefore, determination of koff rates could guide selection of the most effective donor cells. Indeed, in two different murine infection models, we demonstrate that T cell populations with lower koff rates confer significantly better protection than populations with fast koff rates. These data indicate that koff rate measurements can improve the predictability of adoptive immunotherapy and provide diagnostic information on the in vivo quality of T cells.

MHC multimer-guided and cell culture-independent isolation of functional T cell receptors from single cells facilitates TCR identification for immunotherapy.

Adoptive therapy using T cells redirected to target tumor- or infection-associated antigens is a promising strategy that has curative potential and broad applicability. In order to accelerate the screening process for suitable antigen-specific T cell receptors (TCRs), we developed a new approach circumventing conventional in vitro expansion-based strategies. Direct isolation of paired full-length TCR sequences from non-expanded antigen-specific T cells was achieved by the establishment of a highly sensitive PCR-based T cell receptor single cell analysis method (TCR-SCAN). Using MHC multimer-labeled and single cell-sorted HCMV-specific T cells we demonstrate a high efficacy (approximately 25%) and target specificity of TCR-SCAN receptor identification. In combination with MHC-multimer based pre-enrichment steps, we were able to isolate TCRs specific for the oncogenes Her2/neu and WT1 even from very small populations (original precursor frequencies of down to 0.00005% of CD3(+) T cells) without any cell culture step involved. Genetic re-expression of isolated receptors demonstrates their functionality and target specificity. We believe that this new strategy of TCR identification may provide broad access to specific TCRs for therapeutically relevant T cell epitopes.

Novel serial positive enrichment technology enables clinical multiparameter cell sorting.

A general obstacle for clinical cell preparations is limited purity, which causes variability in the quality and potency of cell products and might be responsible for negative side effects due to unwanted contaminants. Highly pure populations can be obtained best using positive selection techniques. However, in many cases target cell populations need to be segregated from other cells by combinations of multiple markers, which is still difficult to achieve--especially for clinical cell products. Therefore, we have generated low-affinity antibody-derived Fab-fragments, which stain like parental antibodies when multimerized via Strep-tag and Strep-Tactin, but can subsequently be removed entirely from the target cell population. Such reagents can be generated for virtually any antigen and can be used for sequential positive enrichment steps via paramagnetic beads. First protocols for multiparameter enrichment of two clinically relevant cell populations, CD4(high)/CD25(high)/CD45RA(high) 'regulatory T cells' and CD8(high)/CD62L(high)/CD45RA(neg) 'central memory T cells', have been established to determine quality and efficacy parameters of this novel technology, which should have broad applicability for clinical cell sorting as well as basic research.