UV-Induced B-Cell Lymphomas in p53 Heterozygous Mice.

Abstract

The association between ultraviolet (UV) irradiation and skin cancer induction is well known. Recently, UV exposure was associated with the induction of internal lymphoid malignancies in UV-irradiated p53 heterozygous mice. Here we characterize the non-skin cancer that develops in the lymphoid organs of UV-irradiated mice and found that UV exposure promotes the induction of a B-cell lymphoma. p53 heterozygous mice were exposed to UVB irradiation (10KJ/m2; three times a week) supplied by a bank of FS40 sunlamps. After thirty weeks, we collected spleen cells from 5 irradiated mice, prepared single suspensions, pooled the cells and injected 2X106 cells/flank (subcutaneous injection) into Rag2−/−mice. The subcutaneous tumors that developed in the Rag2−/−mice were successfully transplanted into other Rag2−/−mice and adapted to grow in vitro. Flow cytometric analysis indicated that enlarged cells were positive for CD19, B220, IgM, CD24, CD40, B7-1, B7-2, but negative for CD43, BP-1, CD127, CD3, CD4, CD8, CD49b, NK1.1, Thy1.2, Gr-1. This phenotype is compatible with a mature B cell but also express CD5, CD11b, CD117. Immunohistchemical analysis confirmed that the tumor cells were of B-cell origin and southern blot analysis demonstrated rearrangement of Immunoglobulin heavy chain. Chromosomal analysis revealed a translocations, t (14;19). Subcutaneous injection of the tumor cells into Rag2−/− mice resulted in an aggressive tumor that infiltrated into the lymph nodes, the spleen and the bone marrow. After establishing the cell line from this B-cell lymphoma, we transfected GFP by using lentiviral vector to mark and injected into Rag2−/− mice. First, the cells bearing GFP infiltrated into the lymph nodes, and then into the spleen and the bone marrow. We also found that this cell line produced IL-10, which can promote lymphoma growth and can cause systemic immunosuppression (Masood et al., 1995 Blood 85:3423–30; Rivas et al., 1994 J Leukoc Biol. 59:769–75). The B-cell lymphoma, which grew progressively in immune compromised Rag2−/−mice, was rejected when injected into wild type mice and syngeneic UV-irradiated C57Bl/6 mice. This data indicates that UV induced B-cell lymphoma in p53 heterozygous mice does not express UV common antigen found on UV-induced skin cancer because UV irradiated mice are unable to reject UV induced tumor cells bearing this antigen as previously reported (Kripke et al., 1974 J.Natl Cancer Inst. 53:1333–6). Since sunlight exposure has been associated with the development of non-Hodgkin's lymphomas in humans, tumor development in UV-irradiated p53 heterozygous mice may provide a useful animal model for lymphoma development in humans.