Human leukocyte antigen, or HLA, is the molecular signature the immune system uses to tell its own tissue from someone else's. Transplant medicine has spent four decades learning how to match donors and recipients on these signatures so that the transplanted organ is not rejected.
We apply the same principle to cell therapy. The donors we use are HLA-homozygous, which means they carry two identical copies of each marker at the loci that matter. That homozygosity makes a single donor compatible with a far larger fraction of the population than an ordinary donor would be. Sixty-five such donors, chosen carefully, cover more than nine of every ten Americans.