Expansion of CD8+ cytotoxic T cells in vitro and in vivo using MHC class I tetramers

The expansion of cytotoxic CD8+ T lymphocytes (CTLs) which recognize peptide epitopes of tumour or viral origin has been a major aim of immunotherapy research for the past decade. Alongside the established dendritic cell-based methods, more recent approaches using recombinant MHC class I peptide complexes have been developed.

In this study we have explored the potential of a simplified system using soluble streptavidin-linked MHC class I tetramers to expand antigen-specific CTLs in vitro and in vivo.

In vitro tetramer-mediated expansion of CD8+ CTLs recognizing HLA-2/Melan-A and HLA-A2/Gag complexes was demonstrated with PBMCs from healthy donors or HIV+ donors, respectively. With 3 weekly rounds of tetramer stimulation, cell numbers expanded 100-fold from 0.05 to 5.0%. The lytic function of HLA-A2/Melan-A-expanded cells was demonstrated in 51Cr release assays by specific killing of T2 cells pulsed with Melan-A, but not other peptides. Similarly, murine CD8+ T cells specific for the HY epitope H2-Db/Uty could be expanded in vitro over a wide range of tetramer concentrations (0.008-1.0 microg/ml), with a single exposure producing substantial T cell expansion from 0.11 to 36%. Intraperitoneal administration of H2-Db/Uty tetramers to primed C57BL/6 mice produced over 5-fold expansion of Db/Uty-specific CTL in vivo.

The results in this paper demonstrate that simple, multimeric MHC complexes may be of value in expanding CTLs in vitro for adoptive immunotherapy and also potentially in vivo. Further studies will be necessary to clarify the optimum protocols and schedules of administration for T cell expansion using recombinant MHC multimers.