To study the processing of proinsulin into antigenic peptides, a myelogenous leukemia cell line, K562, that stably expresses MHC class I (HLA-A2) [23], was transduced with retroviruses carrying the (mutant) preproinsulin gene followed by an internal ribosome entry site (IRES) and an eGFP-encoding sequence. Here, INS is linked to myeloid leukemia.