Monoclonal antibody HML‐1 reactivity with adult T‐cell leukaemia/lymphoma and other lymphomas

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Abstract
Human T‐cell leukaemia/lymphoma virus type 1 (HTLV‐1), a causative virus of adult T‐cell leukaemia/lymphoma (ATLL), is known to be transmitted by breast‐feeding. Using a monoclonal antibody HML‐1 which labels human intestinal intra‐epithelial T lymphocytes, we have immunohistochemically examined ATLL tissues in order to evaluate the possibility that HTLV‐1 infected intestinal T cells are the origin of ATLL cells. Previously this antibody was reported to react with intestinal T‐cell malignant lymphomas but not with peripheral tumours, or any B‐cell lymphomas. We investigated 181 patients with malignant lymphomas and found that 19 out of 113 ATLLs were positive for HML‐1. T‐cell malignant lymphomas excluding ATLL also reacted with HML‐1 (7/24), but all the B‐cell lymphomas 0/33) and non‐neoplastic lymph node and skin lesions (0/10) were negative for HML‐1. In patients with ATLL and other T‐cell malignant lymphomas, the positivity level of HML‐1 was relatively higher in stomach (3/7) and tonsil (2/6) than that in lymph nodes (15/100) and skin (8/47). We observed one HML‐1 positive ATLL patient with tumour formation in the skin and lymphadenopathy and marked infiltration of the large intestine but minimal involvement of other organs. Although HML‐1 was frequently expressed in gastric infiltration of ATLL, the level of positivity was too low in lymph nodes to support the hypothesis that HTLV‐1 infected intestinal T cells are the origin of ATLL cells. Some of the HML‐1 positive ATLL cases co‐expressed CD30. Furthermore, three of six cases of Ki‐1 lymphoma (large anaplastic cell lymphoma) were positive for HML‐1. We conclude that expression of HML‐1 in ATLL reflects an activated state of the lymphoma cells, but not the intestinal origin of ATLL cells.