T-cell receptor gene rearrangement in primary tumors: effect of genetic background and inducing agent

The stromal gene encoding the CD274 antigen as a genetic modifier controlling survival of mice with γ-radiation-induced T-cell lymphoblastic lymphomas

Using an inter-specific subcongenic strain, Nested Recombinant Haplotype 3 (NRH3), generated between two mouse strains showing extreme differences in γ-radiation-induced thymic lymphoma susceptibility (SEG/Pas and C57BL/6J), we have identified a critical region on chromosome 19 that regulates survival of mice suffering from T-cell lymphoblastic lymphomas. Mapped on this region, the gene encoding the Cd274 ligand is able to trigger an inhibitory effect that modulates T-cell receptor (TCR) signalling and affects thymocyte maturation. Interestingly, this gene shows differential expression between thymic stromal cells from both strains in early response to a single sublethal γ-ray dose, but is inhibited in T-cell lymphoblastic lymphomas. Furthermore, we have identified several polymorphisms in the complementary DNA sequence of this gene that affect the affinity for its Cd279 receptor and are able to induce a differential rate of thymocyte apoptosis. Taken together, our data are consistent with Cd274 acting as a genetic modifier that influences the survival of γ-radiation-induced T-cell lymphoma-bearing mice. The data similarly support the idea of a co-evolution of tumour cells and associated stromal cells to generate a favourable microenvironment for T-cell lymphoma growth.

Clonal evolution of N-methylnitrosourea-induced C57BL/6J thymic lymphomas by analysis of multiple genetic alterations

C57BL/6J mice were treated with N-methylnitrosourea (NMU) and the evolution of leukemic T-cells clones into frank thymic lymphomas was followed in 42 animals using serology of T-cell markers, rearrangements of the T-cell receptor genes gamma, beta1 and beta2 and detection of carcinogen-induced Ki-ras mutations and trisomy of chromosome 15. During the latent period, multiple populations of T-cell clones were present in the thymus, many contained trisomy 15, but few had detectable Ki-ras mutations. Since most frank lymphomas consisted of a single T-cell clone with both a mutation of Ki-ras and trisomy 15, the results imply that these two events are critical for the evolution of T-cell clones from the preleukemic phase to a more malignant disease stage. Progression to frank lymphomas is coincident with changes in the expression pattern of the T-cell growth factor interleukin-2 receptor, which may play a role in the selection, expansion and thymus-independent growth of a T-cell clone.