Figure 2.

Different Tregs Good Manufacturing Product (GMP)-compatible expansion protocols and potential areas to improve for Tfr cell therapy. In the top diagram are described some of the protocols in use in our GMP facility (126, 127, 135) for the expansion of Tregs from the isolation step (using either magnetic beads or cell sorting) to the other steps such as stimulation every 12 days (with anti-CD3/CD28 beads) and feeding every 48 h. The use of IL-2 and rapamycin has been shown necessary to expand functional and stable Tregs in the absence of T effectors. In the bottom diagram is described a similar process for the generation of a Tfr product and in red are all the different steps which remains to be optimized.