Establishment of a monoclonal antibody to plasma cells: a comparison with CD38 and PCA-1

The identification of irreversible rituximab-resistant lymphoma caused by CD20 gene mutations

C-terminal mutations of CD20 constitute part of the mechanisms that resist rituximab therapy. Most CD20 having a C-terminal mutation was not recognized by L26 antibody. As the exact epitope of L26 has not been determined, expression and localization of mutated CD20 have not been completely elucidated. In this study, we revealed that the binding site of L26 monoclonal antibody is located in the C-terminal cytoplasmic region of CD20 molecule, which was often lost in mutated CD20 molecules. This indicates that it is difficult to distinguish the mutation of CD20 from under expression of the CD20 protein. To detect comprehensive CD20 molecules including the resistant mutants, we developed a novel monoclonal antibody that recognizes the N-terminal cytoplasm region of CD20 molecule. We screened L26-negative cases with our antibody and found several mutations. A rituximab-binding analysis using the cryopreserved specimen that mutation was identified in CD20 molecules indicated that the C-terminal region of CD20 undertakes a critical role in presentation of the large loop in which the rituximab-binding site locates. Thus, combination of antibodies of two kinds of epitope permits the identification of C-terminal CD20 mutations associated with irreversible resistance to rituximab and may help the decision of the treatment strategy.

Phenotypic and molecular analysis of six human cell lines derived from patients with plasma cell dyscrasia

Cell lines RPMI 8226, JJN3, U266 B1, NCI-H929 (all EBV-) and ARH77 and HS-Sultan (both EBV+) have been extensively characterized in this study. EBV- lines expressed the phenotype (CD138-, CD19+, CD20+) whereas EBV+ were (CD138+, CD19-, CD20-). CD56 expression was restricted to EBV- cell lines, with the exception of U266 B1, whereas PCA-1 was strongly expressed on five of the six cell lines. Only EBV+ cell lines bound peanut-agglutinin (PNA). However, all cell lines bound the lectin Jacalin that binds the same receptor as PNA, irrespective of the receptors sialylation status. By RT-PCR and direct sequencing of their IgH V/D/J domains, ARH77 was demonstrated to use the germline sequence VH4-34/dm1/JH6b, whereas no arrangement was demonstrated for RPMI 8226, suggesting IgH gene deletion or mutation. HLA class I and II antigens were detected using HLA typing on all cell lines warranting their use as suitable targets for HLA-restricted cytotoxic T cells. By sensitive RT-PCR, mRNA for IL-6, IL-6R and TNFbeta was found expressed in all cell lines. IL-1 mRNA expression was predominantly associated with the EBV+ phenotype. Although mRNA for IL-3 and GM-CSF was never detected, transcripts for c-kit ligand and, more commonly, its receptor were. Likewise GM-CSF, M-CSF and erythropoietin mRNA transcripts were detected in the majority of cell lines.

A new multiple myeloma cell line, MEF-1, possesses cyclin D1 overexpression and the p53 mutation

BACKGROUND

The t(11;14)(q13;q32) translocation with cyclin D1 overexpression commonly is found in multiple myeloma (MM) and in mantle cell lymphoma (MCL). Several reports have shown that p53 mutations in MCL lead to blastoid transformation and a worse prognosis; however, the role of p53 mutations in MM with t(11;14) is unclear.

METHODS

In this study the authors describe a patient with MM with t(11;14) and a p53 mutation at presentation and characterized a cell line, MEF-1, established from this patient. Immunohistochemical analysis of p53 and cyclin D1 proteins was performed. The p53 gene was analyzed by polymerase chain reaction-single strand conformation polymorphism and direct sequencing. The expression of cyclin D1 mRNA was examined by Northern blot analysis.

RESULTS

MEF-1 had t(11;14) with overexpression of cyclin D1 mRNA and produced immunoglobulin kappa-light chain. MEF-1 had a mutation in exon 7 (codon 255-257) of the p53 gene, which was noted in the patient's myeloma cells.

CONCLUSIONS

p53 mutations may be important genetic events in disease progression of MM with t(11;14). The MEF-1 cell line may be a useful tool to study mechanisms of progression in MM based on abnormalities of the cyclin D1 gene.

Establishment of a monoclonal antibody to human myeloma cell: relation to chemotherapy and extramedullar infiltration

Resistance of myeloma cells to melphalan (L-PAM) is a serious problem. To investigate mechanisms of drug resistance, we generated a monoclonal antibody, clone O3, to melphalan-resistant myeloma cells, KHM-11R. Western blot analysis showed that molecular weight of O3 antigen was approximately 90 kDa. Expression of O3 antigen was approximately two times higher in KHM-11R than in parental melphalan sensitive cell line, KHM-11. O3 was preferentially expressed in plasma cell, B-cell, and monocytic cell lines, but not in T-cell lines. Analysis of bone marrow samples from myeloma patients revealed that 13 of 23 samples expressed O3 antigen at various levels, and that O3 antigen expression in patients correlate with preceding chemotherapy, advanced clinical stage and extramedullar invasion of myeloma cells. Furthermore, patients expressing O3 antigen at the time of diagnosis tended to have poor prognosis. The investigation of O3 antigen in myeloma cells will be useful to reveal the pathophysiology of extramedullar invasion and the mechanism of cell killing by melphalan.

Distribution of plasma cell markers and intracellular IgE in cell line U266

The IgE-producing plasma cell line U266 was used to study intracellular IgE and the distribution of the plasma cell markers CD38 and PCA-1. We found two separate clusters of U266 based on the differences in their light scatter properties in the flow cytometer. One cluster displayed high scatter signals (high SS), whereas the other showed low scatter signals (low SS). Most (75%) of the cells in the low SS cluster were positive for intracellular IgE. In contrast, high SS cells had a higher expression of surface IgE and a considerably lower proportion of these cells expressed intracellular IgE. Different patterns of expression of the plasma cell antigens CD38 and PCA-1 were observed. While the low SS cluster displayed a high (76%) expression of PCA-1 and a low (5%) CD38 expression, the high SS cluster expressed 21 and 42%, respectively. About 2/3 of the cells in the low SS cluster appeared to be in the G1 phase of the cell cycle while 1/3 were in the S/G2 phase. In the high SS cluster the opposite distribution (2/3 in S/G2) was observed. Taken together our results indicate an association between cell cycle stages, expression of intracellular IgE and plasma cell markers.

Immunotherapy of multiple myeloma

In 1994, an estimated 12,700 new cases of multiple myeloma (MM) will be diagnosed in the USA and 9,800 patients will die from this disease. At present, a cure for MM has not been achieved with any chemotherapeutic regimen. Therefore, it is important to develop novel therapeutic approaches to treat this fatal disease. This review focuses on new concepts in the immunotherapy of MM. Thus far, interferons and anti-human interleukin (IL)-6 monoclonal anti-bodies (MAbs) have been used to treat patients with this disease. Bone marrow transplantation using autologous marrow purged with MAbs and complement, with anti-myeloma immunotoxins (ITs), or MAb-magnetic bead conjugates has been reported. Adoptive cellular therapy, in vivo with anti-CD3 and IL-2, as well as transplantation of purified autologous CD34+ peripheral blood stem cells, is now being evaluated in clinical trials. Anti-human IL-6 receptor (IL-6R) and anti-CD54 (ICAM-1) MAbs have shown promising results in the therapy of human myeloma cell lines in SCID mice, while an IL-6 antagonist protein, anti-gp130 MAbs, recombinant soluble gp130, anti-B7, anti-HLA-DR, and recombinant soluble CD16 also inhibit the growth of myeloma cell lines in vitro. These experimental therapeutic modalities hold promise for use in humans and may also provide further insights into the pathogenesis of MM.