These iPS cells have been generated from the blood of healthy donors who are homozygous in their expression of the protein HLA-A, HLA-B, or HLA-DR

iPS cells are being made to express the most frequent HLA in Japan. Currently, a total of 27 iPS cell lines made from 7 donors who together are homozygous for 4 HLA types have been prepared. These lines cover approximately 40% of the Japanese population. The different lines give versatility in HLA typing and differentiation capacity for different diseases. Some of these cell lines have already been used in iPS cell-based clinical cell therapies.

Cells from HLA-homozygous donors can be used for cell therapies in patients who have at least one of the same HLA. In the illustration, the donor cells can be used in 4 of the 7 patients.

Currently, the HLA-homozygous iPS cells cover only 40% of the Japanese population. Thus, the cells cannot be used in the other 60% due to the high risk of an immune reaction.

HLA (human leukocyte antigen)：HLA are proteins expressed on the cell surface that allow the immune system to distinguish self and foreign cells. There are three classes, with class I (HLA-A, -B, and -C) being considered the most important when donor-patient matching. The number of HLA combinations is in the tens of thousands.