K562-HLA transfectant cells. HLA-negative K562 cells were transfected with cDNAs encoding single HLA class I alleles. After single-cell cloning and expansion in selection medium, K562-HLA cell clones were analyzed by flow cytometry. Monoclonal Abs used recognized either the corresponding HLA allele or myeloid antigen CD65, respectively. Representative data obtained with the K562-HLA-B*0702 cell clone are shown. Comparably strong HLA transgene and CD65 expression levels were found on K562 clones transfected with HLA-A*0201, HLA-A*0301, HLA-B*0801, HLA-B*3501, or HLA-Cw*0702 (data not shown).