While the carcinoma cells expressed low but significant amounts of free HLA-CW1 HCs at the cell surface, transfection with B2m caused a change in the antibody reactivity of the three domains of HLA-CW1 molecules, thereby providing the first experimental proof to show that assembly with B2m affects the folding of not only the αl and α2, but also of the α3 domain. The gene discussed is B2M; the disease is carcinoma.