Ki‐67 is a commercially available monoclonal antibody that reacts with a nuclear antigen detectable in proliferating cells only. Since its first description, it has been widely used as a “universal” proliferation marker and few groups have questioned the validity of the initially described reactivity, although this was tested only on very restricted experimental models. We wanted to check its reactivity on normal bone marrow (BM) samples using a multiparameter flow cytometric analysis. Although we were able to reproduce the findings of Ki‐67 positivity on cultured and stimulated cells, we could not detect any convincing Ki‐67 positivity on nuclei of normal BM samples. These samples all had a noticeable proliferating compartment as evidenced by their DNA content. These data are in contrast with the data we obtained starting from stressed marrows and marrows cultured in the presence of hematopoietic growth factors, where we found a marked Ki‐67 positivity.
This discrepancy suggests that bone marrow cells, growing and proliferating under steady‐state conditions and guided by natural control mechanisms, may lose their Ki‐67 expression upon exiting the progenitor compartment and entering the differentiating compartment.
Hypoplastic acute leukemia (HAL) is characterized by pancytopenia and by hypocellularity of the bone marrow. The marrow contains equal to or more than 30% myeloblasts. Absence of tissue infiltrates and/or tumor masses is mandatory. Eight patients are described here. They do not fit into the FAB classification for either acute nonlymphocytic leukemia (ANLL) or myelodysplastic syndrome (MDS), except for one patient who subsequently proved to have a chronic myelomonocytic leukemia (CMML). The median age is 65 years. Two patients, including the CMML patient, are alive, 22 and 6 months from diagnosis. Six patients have died. The median survival is 8 months. Normal bone marrow cells cultured either with HAL sera or with HAL peripheral blood mononuclear cells as feeders and exogenous GM-CSF yielded subnormal CFU-GM counts. This might indicate inhibitory activity of HAL serum and defective stimulatory activity of HAL peripheral blood mononuclear cells.
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