Specificities of monoclonal antibodies B-ly7 and HML-1 are identical.

In their report in BLOOD 74:320, 1989, Visser et a1 reported on a new monoclonal antibody designated B-ly7 that they suggested to be specific for hairy cells and some scattered normal B cells. Using their antibody (courtesy of Dr Poppema) we can essentially confirm the close association of B-ly7 antigen expression with hairy cell leukemia. However, regarding the specificity of this reagent we would like to add some new significant aspects. Most of the normal (scattered) B-ly7 positive lymphocytes found in the white and red pulp of the spleen and in any other lymphoid organ are not of B-cell origin. They carry a CD8+ CD3+ phenotype. In the intestine, B-ly7 MoAb consistently stains intraepithelial and interepithelial mucosal CD8 + T lymphocytes. The low number of B-ly7 positive peripheral blood lymphocytes can be greatly enlarged to approximately 60% by lectin stimulation following a slow kinetic time course with the maximum of positive cells around day 8. The majority of these cells are CD8/CD3 positive. We recently established a number of HTLVl + positive T-cell lines of which a proportion was strongly positive for B-1y7. Knowing this reactivity, which is not or incompletely described in the report by Visser et al, we were very much reminded of the reactivity pattern of the recently described MoAb HML-I that labels mucosa-associated T cells and enteropathy associated T-cell lymphomas.'.' In search of new MoAb against lymphoid activation antigens, we obtained one MoAb designated Ber-ACT8 that exhibited a similar binding pattern. Comparison of this MoAb with B-ly7 and HML-I MoAb provided firm evidence that all three MoAbs (B-ly7, H M L l , and Ber-ACT8) recognize the same antigen based on the following: ( I ) The distribution pattern on various normal Tand B-cell targets is identical; (2) all three antibodies reacted with all cases of hairy leukemia, mucosa-associated T cells, and enteropathy-associated T-cell lymphomas; and (3) all three MoAbs consistently precipitated the same molecular trimer with molecular weights (mol wts) 170,000, 140,000, and 110,000 from both hairy cell leukemias and certain permanent T-cell lines (Visser et al report only one band of 145 Kd corresponding probably to the mol wt 170,000 band, which is by far the strongest component). Identity of the HML-1, B-ly7, and Ber-ACT8 antigens was ascertained by sequential immunoprecipitation. In conclusion, the B-ly7 MoAb is neither B-lineage specific nor specific for hairy cell leukemia. Furthermore, most of the HML1 /Bly7 positive normal lymphocytes are not candidates for being the normal counterpart of hairy cell leukemia because they exhibit T-cell phenotype. However, it is not too surprising that the expression of this interesting new antigen on both hairy cell leukemia and mucosa-associated T-cell lymphoma has not yet been discovered since both types of lymphomas are rare.