Clonal expansion of CD8⁺ BV8 T lymphocytes in bone marrow characterizes thymoma-associated B lymphopenia

A subgroup of thymoma patients is affected by severe immunodeficiency clinically resembling an HIV infection (Good syndrome). These individuals are characterized by B lymphopenia with B-lymphopoiesis deficiency. To investigate the pathogenesis of this unique condition, we studied the T-cell repertoire in blood and bone marrow samples by heterogeneity length analysis of CDR3 beta variable regions of the T-cell receptor (spectratyping). While no alterations were found in the peripheral blood, we detected an oligoclonal population of β variable 8 (BV8) CD8⁺ T cells in 5 of 5 bone marrow samples. No lymphocyte expansions were found in the bone marrow of 2 thymoma patients with normal B-cell counts, 2 healthy donors, and 3 patients with diseases unrelated to thymoma. These data suggest that an immune response toward an unknown antigen is taking place in the bone marrow of B-lymphopenic thymoma patients. We propose that BV8 CD8⁺ T cells may play a role in the pathogenesis of this immunodeficiency syndrome.