Optimization of bead-free polyclonal expansion of regulatory T cells

Problem: Currently the expansion of regulatory T cells (Tregs) is being carried out using MACS GMP ExpAct Beads (Miltenyi Biotec, Auburn, CA) (1). These beads are large 3.5 µm particles preloaded with CD3 and CD28 antibodies, and therefore, need to be removed using the CliniMACS System prior to infusion of the product into patients. This incurs substantial expenses involving supplies, reagents and personnel and facilities charges. Moreover, there is a loss of the product that can be as high as 25%, which in turn requires higher numbers purified Tregs are to be used at the culture initiation in order to obtain sufficient clinically usable numbers of expanded Tregs. Sometimes this might not even be feasible due to the medical and/or physical conditions of the patients. Also, some Treg cultures may not expand well resulting in insufficient numbers of the target product; this can be catastrophic for the patient as well as the effort and expenses incurred for the expansion would become a complete waste. Therefore, avoiding the use of the ExpAct Beads for the stimulation of the Treg cultures becomes attractive, provided another reagent that results in equivalent numbers of expanded Tregs can be utilized. Potential Solution: Miltenyi Biotech has another reagent that is standardized for the expansion of effector T cells and CART cells for cancer treatment. It is called TransAct and “is a polymeric nanomatrix conjugated to humanized recombinant CD3 and CD28 agonists ensuring successful activation of resting T cells from hematological cell populations”. The nanomatrix is so small that it can be sterile filtered and can be removed from the cell cultures by just washing the cells. However, since it is this reagent has not been used for the expansion of human Tregs, the culture conditions have to be optimized in the laboratory and then the technology has to be transferred to the GMP facility. A similar reagent that is available with Stem Cell Technologies (Cambridge, MA