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Cell Lines

Embryonic, Fibroblast Cell Lines and Lymphoid Tumor Cell Lines

X. laevis image

X. laevis LG15 cloned adult injected sc
with 10,000 15/0 tumor cells. A solid tumor developed
at the site of injection after 1 month (red arrow).
The frog was also grafted with white ventral skin
from a syngeneic donor (black arrow).

X. laevis is the only amphibian where true lymphoid tumors have been discovered and cell lines have been obtained opening new avenues for tumor biology and tumor immunity. These lymphoid tumor cell lines have been extensively characterized (Table 1; Robert al., 1994). They display a unique dual T/B phenotype, which, in mammals, is encountered only in rare lymphocytic leukemias.

All these cell lines express specific T-cell lineage markers (CD8, CD5 and XT-1 pan T-cell), and immature thymocytes CTX marker. They also express Rag 1, Rag 2, and TdT that are involved in Ig and TCR rearrangements, and as such, are features of undifferentiated lymphocytes. Except for the B3B3 line that has undergone unproductive gene rearrangement, all other lines express IgH and L mRNAs but do not synthesize any Ig protein (Robert et al., 1994). B3B7, 15/0 do not express MHC class I and class II mRNA or protein. However, all these different cell lines do express non-classical MHC class Ib (XNC) and b2-microglobulin mRNA.

Some of these tumor lines (15/50, 15/40 and ff-2) remain tumorigenic when transplanted in MHC compatible hosts. The 15/0 tumor line derived from the LG-15 clone (MHC a/c haplotype), grows well in LG-15 (Fig. 3) and other LG sharing the same MHC (LG6 and 7). In contrast the ff-2 tumor line grows well in F larvae but is rejected by adults. This rejection results from a thymus-dependent immune response that develops during metamorphosis.

Other types of cell lines are also available in X. laevis including: fibroblasts lines of the different strains and LG clones, and a kidney cells line (A6).

Characteristics of Tumor Cell Lines

Name of tumor cell line BB7 ff-2 15/0 15/40
Genetic background of initial tumor-bearing host Partially inbred MHC homozygous ff strain LG-15 (MHC a/c)
isogenetic clone
   
T-cell surface markers (CD8, CD5, XT-1 pan T-cell) and Thymocyte surface marker CTX +++ +++ +++ +++
lg mRNA - + + +
lg protein - - - -
TdT, Rag 1 and 2 Expression + + + +
MHC class I mRNA and protein - + - +
MHC class II mRNA and protein - - - +
Non-classical class lb mRNAs + + + +
b2-microglobulin mRNA + + + +
Tumorigenicity in syngeneic        
Larvae - + ++ +
Adult - - ++ ++