Regulatory T (Treg) cells as
modulators of the immune system are an interesting target for adoptive cell
therapy. Initial clinical trials of adoptive transfer of Treg cells in patients
with graft-versus-host disease (GvHD) were shown to be safe. However, obtaining
sufficient numbers of highly pure and functional Treg cells with minimal
contamination remains a challenge. We developed a novel approach to isolate
untouched Treg cells from healthy donors based on depletion of CD49d- and CD127-expressing
cells. This procedure, based on an antibody cocktail and magnetic beads for
separation in an automated system (RoboSep), was scaled up and adapted to be
compatible with GMP conditions. With this setup we performed six Treg
isolations from large-scale leukapheresis samples in a GMP facility. These runs
yielded sufficient numbers of untouched Treg cells for immediate use in clinical
applications. The cell preparations consisted of viable highly pure FoxP3
positive Treg cells that were functional in suppressing the proliferation of
effector T cells. Contamination with CD4 effector T cells was below 10%. All
other cell types (CD8, NK cells, NKT cells, B cells, monocytes, granulocytes,
erythrocytes) did not exceed 2% in the final product. Remaining isolation
reagents were reduced to levels which are considered safe. Treg cells isolated
with this procedure will be used in a phase I clinical trial of adoptive
transfer into leukemia patients developing GvHD after stem cell
transplantation.