Expression of extra class I major histocompatibility antigens on T-cell acute lymphoblastic leukemia (ALL) lymphoblasts.

The presence of extra HLA antigens has been demonstrated, serologically and biochemically, on the surface of lymphoblasts from a patient with acute lymphoblastic leukemia of the T-cell subtype (T-ALL). Family analysis of this patient revealed the presence of the expected antigens, plus an additional HLA antigen (A24) which could be demonstrated by cytotoxicity on the lymphoblasts. Absorption studies revealed that the lymphoblasts had the ability to remove cytotoxic antibodies from alloantisera; similarly, absorption of these alloantisera with normal cells removed the reaction against the extra antigen from the lymphoblasts. The extra HLA molecules were also demonstrated by one-dimensional IEF. Two heavy chain-like molecules, together with the beta 2m subunit, were obtained after removal of appropriate antigens from externally labeled leukemia cells by the use of monoclonal antibody W6/32, which detects a class I specific determinant. The pI of the one heavy chain was shown to be very similar to that of the serologically detected A24. Our data thus suggest that the extra antigens detected by serological reagents may have been due to activation of silent class I MHC gene(s) at the protein level.