A monoclonal antibody (TA-1) reactive with human T lymphocytes and monocytes

Several monoclonal antibodies were produced against the human T lymphocyte leukemia cell line HSB-2 by fusing spleen cells from hyperimmune mice with NS-1 myeloma cells. One clone, designated TA-1, was initially characterized for reactivity with normal and leukemic human hematopoietic cells. Using indirect immunofluorescence, TA-1 was shown to bind to ~75% of peripheral blood lymphocytes. Enrichment for T and B lymphocytes followed by double fluorochrome labeling studies revealed that most if not all E⁺ T lymphocytes and ~10% of B lymphocytes were TA-1⁺. TA-1 also reacted with ~67% of thymocytes, mixed lymphocyte culture-activated T lymphocytes, the entire peripheral blood monocyte population, and ~13% of nucleated bone marrow cells. TA-1⁺ cells in bone marrow included both phagocytic and nonphagocytic cells. TA-1 did not bind to peripheral blood granulocytes, red blood cells, or platelets. Studies of acute lymphoblastic leukemia (ALL) revealed that 6 of 11 T-ALL and 1 of 21 E^-, SIg^--ALL were TA-1⁺, whereas cells from 10 patients with chronic lymphocytic leukemia were TA-1^-. Interestingly, TA-1 was able to distinguish acute myelomonocytic leukemic cells (TA-1⁺) from acute myelocytic leukemic cells (TA-1^-). In summary, these studies demonstrate the existence of a determinant recognized by TA-1 that is primarily expressed on cells of T lymphocyte and monocyte/macrophage lineage.