CD48 as a novel molecular target for antibody therapy in multiple myeloma.

Monoclonal antibody (mAb) drugs are desirable for the improvement of multiple myeloma (MM) treatment. In this study, we found for the first time that CD48 was highly expressed on MM plasma cells. In 22 out of 24 MM patients, CD48 was expressed on more than 90% of MM plasma cells at significantly higher levels than it was on normal lymphocytes and monocytes. CD48 was only weakly expressed on some CD34(+) haematopoietic stem/progenitor cells, and not expressed on erythrocytes or platelets. We next examined whether CD48 could serve as a target antigen for mAb therapy against MM. A newly generated in-house anti-CD48 mAb induced mild antibody-dependent cell-mediated cytotoxicity and marked complement-dependent cytotoxicity against not only MM cell lines but also primary MM plasma cells in vitro. Administration of the anti-CD48 mAb significantly inhibited tumour growth in severe combined immunodeficient mice inoculated subcutaneously with MM cells. Furthermore, anti-CD48 mAb treatment inhibited growth of MM cells transplanted directly into murine bone marrow. Finally and importantly, we demonstrated that the anti-CD48 mAb did not damage normal CD34(+) haematopoietic stem/progenitor cells. These results suggest that the anti-CD48 mAb has the potential to become an effective therapeutic mAb against MM.

Prognostic implication of types of tumor-associated macrophages in Hodgkin lymphoma.

To evaluate roles of tumor-associated macrophages (TAMs) for prognosis of classical Hodgkin lymphoma (CHL). Expression of markers for TAMs, CD68, HLA-DR, CD163, HLA-DR/CD68 (M1), and CD163/CD68 (M2) was immunohistochemically examined in 82 cases with CHL. Positively stained cells were counted and correlation of number of TAMs and patients' survival time was analyzed. Number of CD163+ cells and M2 cells was significantly correlated with shorter overall survival (P < 0.05), while it was marginally significant for CD68+ cells (P = 0.0827). HLA-DR + cells and M1 cells showed no significant correlation with overall survival. When confined to mixed cellularity subtype, number of M1 cells was correlated with favorable prognosis (P < 0.05), while M2 did not (P = 0.7). Older age and male sex were unfavorable factors for prognosis. At multivariate analysis, number of CD163+ cells, M2+ cells, and age were independent factors for poor overall survival (P = 0.03, 0.02, and 0.01, respectively). CD163+ cells and M2 cells might work to be tumor promotive in CHL. M1 cells might be tumor suppressive in mixed cellularity type.

Prognostic potential of detection of WT1 mRNA level in peripheral blood in adult acute myeloid leukemia.

We retrospectively analyzed the potential of Wilms' tumor gene 1 (WT1) mRNA levels in peripheral blood for predicting the prognosis of 50 patients with AML. After achieving complete remission (CR), 34 patients (69.4%) were determined to be positive and 15 (30.6%) were negative for WT1. The relapse rate of the positive and negative patients was 73.5% and 40.0% (p = 0.02), respectively. After consolidation therapy, only 15 patients (32.6%) were positive and 31 (67.4%) were negative for WT1. Although the relapse rate of the positive and negative patients was 80.0% and 54.8% (p = 0.10), respectively, the rate of relapse within 1 year was 73.3% in positive patients and only 33.3% in negative patients (p = 0.01), respectively. The disease-free survival (DFS) rate at 3 years was 20.0% for positive patients and 50.0% for negative patients (p = 0.01). The overall survival (OS) rate at 3 years was 42.8% in positive patients and 69.8% in negative patients (p = 0.04), respectively. WT1 mRNA levels in the peripheral blood can predict relapse after CR, and its levels after consolidation therapy are closely correlated with DFS, OS, and early relapse.

Prolonged accumulation of high-dose methotrexate in a case with large liver cysts.

Methotrexate (MTX) has been documented to accumulate in "third spaces'' such as pleural effusions or ascitic fluids, resulting in delayed clearance and severe toxicity. We present a case of Burkitt lymphoma possessing large liver cysts, up to the size of 7 x 7 cm, wherein clearance of high-dose MTX was severely delayed, despite normal renal and liver functions. The serum MTX concentration was higher than 0.1 microM on day 12 and remained at toxic levels, higher than 0.01 microM, even on day 25, resulting in severe neutropenia, anorexia, and diarrhea. It was presumed that MTX accumulated in the liver cysts over time and was slowly released back into the serum, resulting into prolonged high serum MTX concentrations. High dose of MTX in patients with large liver cysts induces severe toxicity by virtue of MTX accumulation in the cysts and its subsequent delayed clearance.

The lck promoter-driven expression of the Wilms tumor gene WT1 blocks intrathymic differentiation of T-lineage cells.

In the thymi of WT1-transgenic (Tg) mice with the 17AA+/KTS- spliced form of the Wilms tumor gene WT1 driven by the lck promoter, the frequencies of CD4-CD8- double-negative (DN) thymocytes were significantly increased relative to those in normal littermates. Of the 4 subsets of CD4-CD8- DN thymocytes, the DN1 (CD44+CD25-) subset increased in both frequency and absolute cell number, whereas the DN2 (CD44+CD25+) and DN3 (CD44-CD25+) subsets decreased, indicating the blocking of thymocyte differentiation from the DN1 to the DN2 subsets. Furthermore, CD4-CD8+ T-cell receptor (TCR) -gammadelta T-cells increased in both frequency and absolute cell number in the spleen and peripheral blood of the WT1-Tg mice relative to those of normal littermates. The CD8 molecules of these CD4-CD8+ TCRgammadelta T-cells were CD8alphabeta, suggesting that they originated from the thymus. These results are the first direct evidence demonstrating that the WT1 gene is involved in the development and differentiation of T-lineage cells.

Humoral immune responses against Wilms tumor gene WT1 product in patients with hematopoietic malignancies.

Wilms tumor gene WT1 is expressed at high levels in hematopoietic malignancies, such as leukemias and myelodysplastic syndromes (MDS), and in various kinds of solid tumors, including lung cancer, and it exerts an oncogenic function in these malignancies. IgM and IgG WT1 antibodies were measured by means of dot blot assay in 73 patients with hematopoietic malignancies (16 acute myeloid leukemia [AML], 11 acute lymphoid leukemia [ALL], 13 chronic myeloid leukemia [CML], and 33 MDS) and 43 healthy volunteers. Immunoglobulin IgM, IgG, and IgM+IgG WT1 antibodies were detected in 40 (54.8%), 40 (54.8%), and 24 (32.8%), respectively, of the 73 patients with hematopoietic malignancies, whereas 7 (16.2%), 2 (4.7%), and none of the 43 healthy volunteers had IgM, IgG, or IgM+IgG WT1 antibodies, respectively. Furthermore, immunoglobulin isotype class switching of WT1 antibodies from IgM to IgG occurred in conjunction with disease progression from refractory anemia (RA) to RA with excess of blasts (RAEB), and further to RAEB in transformation (RAEB-t) in MDS patients. These results showed that humoral immune responses against the WT1 protein could be elicited in patients with WT1-expressing hematopoietic malignancies, and they suggested that the helper T-cell responses needed to induce humoral immune responses and immunoglobulin isotype class switching from IgM to IgG were also generated in these patients. Our findings may provide new insight into the rationale for elicitation of cytotoxic T-cell responses against the WT1 protein in cancer immunotherapy using the WT1 vaccine.