BY55 monoclonal antibody delineates within human cord blood and bone marrow lymphocytes distinct cell subsets mediating cytotoxic activity.

Abstract

We had previously reported, using BY55 monoclonal antibody, a cell surface 80-kDa protein restricted to human functional peripheral blood cytotoxic lymphocytes with either natural killer CD3-or cytotoxic T lymphocyte CD3+CD8+ phenotype. In the present report, we studied the cytotoxic lymphocytes in adult bone marrow and newborn cord blood as these organs are commonly used as sources of hematological stem cells for allogeneic transplantation. Our results showed that BYS mAb labeled only 5-10% of the bone marrow lymphocytes, which included a major proportion of CD3+CD8+ cytotoxic T lymphocytes. Interestingly, within cord blood cells, BY55+ lymphocytes represented 20-35% of the lymphocytes corresponding exclusively to a CD3-cell subset. Furthermore, we detected in cord blood no cytotoxic T lymphocyte activity but we demonstrated that the CD3-BY55+ cell subset contained the whole natural killer activity.Natural killer (NK) cells are circulating lymphocytes found within the large granular lymphocyte population (1, 2). The characteristic surface markers expressed by circulating NK cells are CD56 (3, 4), CD16 (5-7), CD11b (8, 9), and CD122 (interleukin 2 receptor p75) (10, 11). To further delineate circulating cells with cytotoxic activity, we developed a monoclonal antibody (mAb) obtained by repeated immunization with YT2C2, a human cell line with NK functional characteristics (12). This mAb, termed BY55, reacts with a 80-kDa protein structure expressed exclusively by circulating cytotoxic lymphocytes (13,14). In normal human peripheral blood, cytotoxic lymphocytes labeled with BY55 mAb corresponded to 20-25% of cells, including mostly CD3 negative lymphocytes, the majority of T-cell receptor (TCR) yS positive T lymphocytes, and a minor subset of CD8+afB+ with cytotoxic T-lymphocyte (CTL) activity.Bone marrow transplantation for hematopoietic reconstitution is the unique treatment for some inherited diseases or for various bone marrow malignancies. However, graftversus-host disease (GVHD), which can be lethal and involves cytotoxic lymphocytes from the donor, is the major limitation to the frequent usage ofthis therapeutic procedure. We had recently reported that umbilical cord blood appeared to be a source of transplantable stem cells without causing severe GVHD (15, 16). Therefore, it was important to analyze the cytotoxic lymphocyte subsets within bone marrow and cord blood. Furthermore, conflicting results were reported concerning the cytotoxic function of the lymphocytes isolated from cord blood (17)(18)(19). In the present study, we used BY55 mAb to delineate the cytotoxic lymphocyte population within newborn cord blood and adult bone mar- Sorted populations were collected as described (20), washed twice, and tested as effector cells in cytotoxic assays. Trypan blue exclusion was performed on the unsorted population and sorted populations, and the viability was always >90%.mAb. BY55 mAb was obtained as described elsewhere (13). Other mAb such as CD3, CD4, CD8, CD11b, and TCRa,3 were produced locally. The...

A Soluble Form of the MHC Class I-Specific CD160 Receptor Is Released from Human Activated NK Lymphocytes and Inhibits Cell-Mediated Cytotoxicity

“…This confirms our initial findings obtained by flow cytometry using the anti-CD160 mAb BY55, which demonstrated that BY55-reactive lymphocytes corresponded to NK cells and to cytotoxic CD8 ϩ T lymphocytes in bone marrow, cord, and PB (18,42). Furthermore, we reported that the intestinal intraepithelial lymphocytes, which spontaneously exhibit a cytotoxic activity, are reactive with BY55 mAb (20).…”

Regulatory T cells differentially modulate the maturation and apoptosis of human CD8+ T-cell subsets

“…Accordingly, Treg cells inhibited the expression of secretion of cytotoxic granules detected by surface expression of CD107 30 (data not shown) and CD160, a marker of circulating highly cytotoxic CD8 ϩ T cells. 31,32 At the same time, the effect of Treg cells on IL-2 expression was not significant in conditions of TCR polyclonal stimulation. Keeping in mind that IL-2 is the predominant cytokine secreted by M CD8 ϩ T cells, in line with their highly proliferative and self-renewing capacity, 5 this result confirmed that Treg cells differentially affect M and E CD8 ϩ T cells.…”

Engagement of CD160 receptor by HLA-C is a triggering mechanism used by circulating natural killer (NK) cells to mediate cytotoxicity

“…Further, using the original anti-CD160 mAb BY55 to separate circulating CD160 ϩ NK lymphocytes, we demonstrated that the latter cells corresponded to the effector cytotoxic population (8,9). However, because the BY55 anti-CD160 mAb did not inhibit cytotoxicity of the separated peripheral blood NK (PB-NK) lymphocytes, we were unable to assess whether the structure recognized by BY55 mAb was involved in the target cell recognition (8,9). In the present study, we investigated the function of CD160 expressed on NK cells by using another anti-CD160 mAb, CL1-R2, which inhibits the binding of CD160 receptor to its MHC class I ligands (10).…”