T-cell subsets and suppressor cells in human bone marrow

To characterize immune suppressive and hematopoietic features of enriched subsets of human marrow cells, we separated these cells on Percoll density gradients. CD4+ and CD8+ T cells (CD3+) were enriched in the high-density marrow cell fractions and reduced in low-density fractions. CD4-CD8- (CD3+) T cells expressing the alpha beta T-cell antigen receptor were at least 10 times less numerous than the CD4+ and CD8+ T cells in all fractions. Purified populations of the CD4-CD8- alpha beta + T cells obtained by flow cytometry suppressed the mixed leukocyte reaction (MLR). Another population of suppressor cells that expressed neither T-cell (CD3) nor natural killer cell (CD16) surface markers was also identified. The latter cells had the phenotypic and functional characteristics of "natural suppressor" cells. Suppressor cell activity was enriched in the low-density fractions along with hematopoietic progenitors (colony-forming unit-granulocyte-macrophage and burst-forming unit-erythroid). The progenitor and suppressor cell activities were depleted in high-density fractions. The latter fractions made vigorous responses in the MLR. The low-density fractions, which accounted for less than 10% of the input marrow cells, suppressed the MLR and did not respond. Further evaluation of the low-density fractions may be of value in allogeneic bone marrow transplantation due to the reduction of CD4+ and CD8+ T cells and the enrichment of hematopoietic progenitors as well as immune suppressor cells that may inhibit graft-versus-host disease.