This article reports eight primary mediastinal tumors occurring in young adults (19 to 43 years, mean 29.4 years), predominantly female (six of eight) adults. Most patients responded badly to aggressive therapy. Progression is presently noted in one patient; five patients died 10, 11, 13, 18, and 22 months after diagnosis. No patient developed leukemia. The tumors were highly proliferative, had a diffuse growth pattern, and comprised clear cells of variable size. They could not be classified histologically, but could, however, be immunohistologically characterized as B cell lymphomas. In all cases, the immunophenotype was LC+, cALLa-, CD19+, CD20+, CD21-, Ig (surface/cytoplasm)-, and PC-1+. In addition, the neoplastic cells exhibited variable defects in the expression of HLA-A,B,C and HLA-DR and inconstant expression of other B cell-restricted/associated antigens. This combination of immunophenotypical and clinical features suggests that the mediastinal clear cell lymphoma (MCCL) is a previously undescribed type of B cell lymphoma corresponding to the terminal steps of B cell differentiation.

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In this study the authors have evaluated B-cell function after autologous peripheral-blood stem cell transplantation (ABSCT) and autologous bone marrow (ABMT) transplantation. The B-enriched fractions of peripheral blood from ten normal subjects and 22 autografted patients (11 patients after ABMT, eight patients after ABSCT, and three patients after ABSCT followed by ABMT) were investigated. Time postgrafting ranged from 1 to 34 months. Proliferative responses to anti-mu antibody, Staphylococcus aureus Cowan 1 (SAC), and low molecular weight (mol wt) 12-Kd B-cell growth factor (BCGF) were measured. Differentiative responses to the same factors were assessed by quantifying in vitro immunoglobulin (IgG/IgM) production. The authors found no difference in B-cell function between the ABMT and the ABSCT patient groups. Compared to the B cells of normal subjects, only five out of 22 autografted patients showed a normal proliferative response to all agents used, while nine out of 22 did not respond to any signals. Eight out of 22 patients displayed various defects of B- cell response. However, in vitro IgG/IgM secretion of predominantly IgG subclass was normal in 19 out of 22 patients. This in vitro ability to produce Ig was reflected by the patients' normal serum IgG/IgM levels, whereas serum IgA levels were low. The authors speculate that there may be 2 B-cell populations: the normal in vitro Ig production and in vivo serum IgG may come from the stimulation of a small number of re-infused pre-committed memory B cells while, in parallel, immature B cells develop from autografted hematopoietic progenitor cells.

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The B cell-restricted antigen HD39, whose cell surface expression is limited to resting and activated human B lymphocytes, is described in this report. The monoclonal antibody HD39 detects a two-chain glycoprotein with apparent molecular weights of 130,000 and 140,000. During B cell ontogeny, HD39 is first expressed in the cytoplasm of bone marrow derived pre-B cells, then appears on the cell surface of sIgM+ B cells, and finally on the majority of sIgM+ sIgD+ resting B cells. After activation in vitro, the expression of HD39 on the cell surface first increases, and then the antigen is lost as cells begin to differentiate. HD39 is weakly expressed on very few non-T cell ALL and B cell CLL, on approximately 50% of B cell lymphomas, and not on Waldenström's macroglobulinemias and myelomas. In contrast, it is strongly expressed on all hairy cell leukemias. Its limited cell surface expression in B cell ontogeny suggests that HD39 may be important in the events that regulate the activation of the human resting B lymphocytes.