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Biotech / Medical : MEDX ... anybody following? -- Ignore unavailable to you. Want to Upgrade?

To: Icebrg who wrote (828)	6/13/2004 7:26:38 AM
From: Icebrg	Respond to of 2240

In a model of tumor dormancy, long-term persistent leukemic cells have increased B7-H1 and B7.1 expression and resist CTL-mediated lysis. Blood. 2004 Jun 10 Saudemont A, Quesnel B. Unite INSERM 524, Institut de Recherche sur le Cancer de Lille, Lille, France; Institut Federatif de Recherche 114, Lille, France. In tumor dormancy, tumor cells persist in the host over a long period of time, but do not grow. We investigated in the DA1-3b mouse model of acute myeloid leukemia how leukemic cells could persist for months in spite of an effective anti-leukemic immune response. Mice were immunized with irradiated IL12- or CD154- transduced DA1-3b cells, and then challenged with wild type DA1-3b cells, and were randomly killed during one year follow-up. Quantification of residual disease one year after challenge showed that persistent leukemic cells represented less than 0.02 % of spleen cells in most animals. These residual cells were still able to kill naive hosts, even when isolated after one year of persistence. Persistent leukemic cells were more resistant to specific CTL-mediated killing, and had enhanced B7-H1 and B7.1 expression, proportional to the time they had persisted in the host. Blocking B7-H1 or B7.1/CTLA-4 interaction enhanced CTL-mediated killing of the persistent cells, and blocking B7-H1, B7.1, or CTLA-4 in vivo prolonged survival of naive mice injected with persistent leukemic cells. Thus, escape of leukemic cells from tumor immunity via over-expression of B7-H1 or B7.1 might represent a new mechanism of tumor dormancy in acute leukemia.