Isolation of a T-Cell Clone Showing HLA-DRB1*0405-Restricted Cytotoxicity for Hematopoietic Cells in a Patient With Aplastic Anemia

Abstract

The existence of T cells capable of inhibiting in vitro hematopoiesis has been shown in aplastic anemia (AA), although whether such inhibition is mediated by a specific immune reaction involving an HLA allele remained unknown. We isolated a CD4+ Vβ21+ T-cell clone that was most dominant among Vβ21+ T cells in the bone marrow (BM) of an AA patient whose HLA-DRB1 alleles included 1501 and 0405. The T-cell clone named NT4.2 lysed an autologous Epstein-Barr virus-transformed lymphoblastoid cell line (LCL) and phytohemagglutinin-stimulated lymphocytes (PHA-blasts) as well as allogeneic LCLs sharing HLA-DRB1*0405. Cytotoxicity against LCL cells and PHA-blasts by NT4.2 was blocked by anti–HLA-DR monoclonal antibody (MoAb) or anti-CD3 MoAb. NT4.2 also lysed autologous BM mononuclear cells enriched with CD34+ cells that had been cultured for one week in the presence of colony-stimulating factors as well as allogeneic CD34+ cells of a normal individual carrying HLA-DRB1*0405, cultured in the same way. Moreover, NT4.2 strongly inhibited colony formation by hematopoietic progenitor cells derived from cultured CD34+ cells sharing HLA-DRB1*0405. These results indicate that the AA patient has T cells capable of killing hematopoietic cells in an HLA-DRB1*0405-restricted manner and that such cytotoxic T cells may contribute to the pathogenesis of AA.

Decreased expression of transcription factor GATA‐2 in haematopoietic stem cells in patients with aplastic anaemia

“…Immunological mechanisms have been thought to be involved in disease development and, in support of this concept, immunosuppressive treatments are effective in many cases (Marsh et al, 1999). However, an aberrant immunological effect on stem cells could only be demonstrated in a few cases (Nakao et al, 1997), and only a few studies using in vitro colony assay methods have been carried out to define the pathological features of haematopoietic stem cells in this disease. In this study, we examined the levels of mRNA for three transcription factors, which are indispensable in the development of early haematopoiesis, in bone marrow cells from patients with aplastic anaemia and compared their levels with those of patients with ITP and normal individuals.…”

Hydroxyurea upregulates NKG2D ligand expression in myeloid leukemia cells synergistically with valproic acid and potentially enhances susceptibility of leukemic cells to natural killer cell‐mediated cytolysis

“…NK cell cytotoxicity against leukemic cell lines was assessed using the standard chromium release assay, as described previously. (23) In blocking experiments, anti-NKG2D Abs were added to the NK cell suspension at 10 lg ⁄ mL and incubated at 37°C for 30 min before the addition of target cells. The percentage of specific lysis was calculated using the formula: 100 · (count per minute [cpm] released from test sample ) cpm spontaneous release) ⁄ (cpm maximum release ) cpm spontaneous release).…”

The complex pathophysiology of acquired aplastic anaemia

“…Nevertheless, the existing data support the potential influence of HLA polymorphism on the pathophysiology of aAA (summarized in Table 1). HLA alleles that are associated with increased [4][5][6][7][8][9] or decreased [7,10] susceptibility to aAA have been reported. In addition, certain HLA alleles appear to play a role in predicting responses to IST [4,11].…”

“…How do specific HLA alleles confer susceptibility to AA? Nakao et al isolated a CD4 1 Vbeta21 1 T cell clone in a patient with aAA that was capable of killing haematopoietic cells in an HLA-DRB1*0405-restricted pattern, indicating that cytotoxic T cells may contribute to the pathogenesis of aAA [6]. This observation suggests that certain HLA alleles may play a role in the activation of autoreactive T cell clones in patients with aAA.…”