CD82 (KAI1), a member of the tetraspan family, is expressed on early haemopoietic progenitor cells and up-regulated in distinct human leukaemias

CD82 (KAI1) is a member of the tetraspan transmembrane protein family which has been cloned from lpmphoblastoid variant cell lines. However, a role fo r CD82 in early normal and malignant haemopoiesis has not yet been characte rized. We studied the CD82 expression in 33 normal donor samples and 98 leu kaemias by fluorescence activated cell sorting (FACS) and reverse transcrip tase polymerase chain reaction (RT-PCR). We demonstrated that CD82 was mode rately expressed in the vast majority of normal granulocytes and monocytes. Ln contrast, only about one third of the peripheral blood lymphocytes were weakly CD82 positive (CD82(+)). Interestingly judgement of the CD82 transc ription and expression in various leukaemias revealed that CD82 was overexp ressed in chronic myeloid leukaemia (CML) patients in accelerated or blasti c phase (CML-AP/BP) as well as in acute myeloid leukaemia (AML) and chronic lymphocytic leukaemia (CLL) patients. Analysis of AML patients with CD34()/CD82(+) blasts prompted us to expand our studies on haemopoietic CD34(+) progenitor cells. Intriguingly, 84-95% of the CD34(+) cells isolated from h ealthy bone marrow cord blood or peripheral blood were highly CD82(+), CD82 was abundantly expressed on primitive as well as on committed haemopoietic progenitor cells. After in vitro induction of myeloid differentiation in C D34(+) peripheral blood progenitor cells (PBPC), the expression of CD82 dec reased to levels similar to those found on peripheral blood granulocytes. T hese observations suggest for the first time a role for CD82 in normal and malignant haemopoiesis.