title: Isolation and characterization of CD6- T cells from peripheral blood.
abstract: Antibodies to the CD6 Ag have been described as having pan-T cell reactivity. We have recently demonstrated, however, that after treatment of PBL with an anti-CD6-blocked ricin-conjugated immunotoxin, clonal populations of CD3+, CD6- cells can be identified. Herein we show that through dual parameter staining of freshly isolated E-rosette+ cells, an average of 5 to 6% of either CD3+ or CD5+ cells express little or no CD6 on their surface. After negative selection by antibody-coated paramagnetic bead depletion, expanded CD6- T cells were shown to be CD1a-, CD2+, CD3+, CD5+, CD16-, CD56-, TCR-gamma/delta-, and consisted of both CD4+ and CD8+ cells. Furthermore, staining of digitonin permeabilized cells showed no cytoplasmic expression of the CD6 Ag and CD6 mRNA was not detected by Northern blot analysis. Identical staining patterns were observed for T cell clones isolated through bead depletion or immunotoxin treatment and expanded with either PHA or immobilized anti-CD3 mAb. It was also found that, relative to unfractionated T cells, the surface expression of CD5 was significantly diminished on CD6- T cells. Functionally, freshly isolated CD6- T cells showed substantially reduced alloreactivity in MLR compared with unfractionated E-rosette+ cells, yet both gave similar proliferative responses to either PHA or soluble tetanus toxin Ag. We conclude that there exists a minor subpopulation of mature T cells in peripheral blood that lack CD6. The diminished alloreactivity of these cells may help to explain the low incidence of graft-vs-host disease, despite high levels of engraftment, that has been reported in allogeneic bone marrow transplant patients receiving marrow treated with anti-CD6 (T12) mAb plus C'.
authors.affiliation: Division of Tumor Immunology, Dana Farber Cancer Institute, Boston, MA 02115.
authors.forename: R A
authors.initials: RA
authors.lastname: Rasmussen
authors.forename: S L
authors.initials: SL
authors.lastname: Counts
authors.forename: J F
authors.initials: JF
authors.lastname: Daley
authors.forename: S F
authors.initials: SF
authors.lastname: Schlossman
mesh_terms: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D016827:CD8 Antigens / Q000032:analysis; D002469:Cell Separation; D003602:Cytotoxicity, Immunologic; D006801:Humans; D008213:Lymphocyte Activation; D008212:Lymphocyte Depletion; D012397:Rosette Formation; D016176:T-Lymphocyte Subsets / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; C062279:CD6 antigen; D016827:CD8 Antigens