In vitro inhibition of hematopoiesis by HNK1, DR-positive T cells and monocytes after allogeneic bone marrow transplantation

Blood CFU-GM and BFU-E, grown from 17 patients who had undergone allogeneic bone marrow transplantation (BMT), were studied by the plasma-clot technique before day 45, and at a time when their blood count was approximately normal. The number of colonies varied from one patient to another, but was always lower than in normal subjects. Removal of cells forming rosettes with sheep erythrocytes (E+C) increased colony growth in four out of eight cases, whereas removal of adherent cells (AC) had the same effect in five out of six cases. Addition of E+C or AC after their initial removal restored the inhibition of colony growth. This suppression was noted at a 1:1 to 8:1 cellular ratio and ranged from 25% to 75%. The phenotype of the suppressive cells was further characterized by complement-mediated lysis with monoclonal antibodies (MoAbs) and fluorescent labeling. Two types of cells associated with inhibition of colony growth were identified: the first were E+C positive, characterized by the T3, HNK1, DR, and T8 determinants; the second were identified by the MO2 MoAb, indicating their monocytic origin, together with their properties of adherence. Similar suppressor cells of CFU-GM were found in the marrow of two other allogeneic BMT patients. A direct suppressive effect of the two types of cells was demonstrated in one experiment when MO2+ and/or HNK1+ cells collected by cell sorting were added back to cultures depleted in MO2+ and HNK1+ cells by complement-mediated lysis and were both found to decrease colony growth. Purified HNK1+ cells led to moderate inhibition of colony growth, which was not enhanced by increasing their concentration. This suppressive effect of hematopoiesis could be the consequence of an allogeneic reaction, since no inhibition was affected by T cells or monocytes in seven autologous BMTs and one syngeneic BMT.