Analysis at the clonal level of T-cell phenotype and functions in severe aplastic anemia patients

The aim of this study was to analyze at the clonal level the phenotype and functions of T cells from patients with severe aplastic anemia (SAA). For this purpose we studied 175 T-cell clones obtained from peripheral blood (PB) and bone marrow (BM) of four SAA patients and 97 clones from two healthy controls. The percentage of CD8 ⁺ T-cell clones obtained from the patients' PB and BM was higher, but not significantly (P = .07 and P = .14, respectively), than that obtained in controls. A higher proportion of T-cell clones from SAA patients exhibited lectin-dependent cytolytic activity and especially natural killer-like activity when compared with controls (PB: P <.01, P <.05; BM: P <.05, P <.01, respectively). Lymphokine release was tested before and after mitogen stimulation. A number of patients' clones were able to release interferons (IFNs) spontaneously (PB: 28.6% v 0%, P <.05; BM: 28.6% v 0%, P <.10). After mitogen stimulation, patients' BM T-cell clones produced IFNs in greater proportions (90.9% v 46.7%, P <.01) and in greater quantities (PB: 25.5 arbitrary units [AU]/mL v 5.7 AU/mL, P <.03; BM: 26 AU/mL v 9.1 AU/mL, P = .011) as compared with controls. Tumor necrosis factor (TNF) activity was not found in supernatants of unprimed T-cell clones. After mitogen stimulation, PB T-cell microcultures produced TNFα in greater proportions (97.9% v 72.2%, P <.01) and, also in this case, in greater quantities (PB: 7.2 AU/mL v 1.5 AU/mL, P = .007; BM: 9.9 AU/mL v 1.5 AU/mL, P = .003) than controls. In conclusion, T-cell clones from SAA patients exhibit prodominantly a CD8 ⁺ phenotype, a greater cytotoxic activity, and can be shown to produce greater quantities of suppressor lymphokines when compared with controls.