Deficient expression of class-I HLA in some cases of acute leukemia.

Leukemic cells from the blood and marrow of 25 cases of newly diagnosed acute leukemia were presented as target cells to alloreactive effector cells from unrelated normal donors in cell-mediated cytotoxicity assays. In three cases the leukemic targets were poorly killed relative to nonleukemic, HLA-identical target cells. The poor killing of the leukemic cells from one of these cases was shown by competitive inhibition to be due to deficient expression of normal class-I HLA antigens rather than resistance to lysis. Furthermore, the leukemic cells from these three patients were also deficient in binding monoclonal antibodies to nonpolymorphic determinants of class-I HLA and B2 microglobulin. Two additional cases were identified as having a less extensive deficit of HLA, and may be representative of a group with relatively subtle changes in these cell surface antigens. The possible significance of reduced expression of HLA in leukemic progression and in susceptibility to graft-vs-leukemia reactions after bone marrow transplantation is discussed.