Neoplastic Transformation of T Lymphocytes through Transgenic Expression of a Virus Host Modification Protein

Virus host evasion genes are ready-made tools for gene manipulation and therapy. In this work we have assessed the impact in vivo of the evasion gene A238L of the African Swine Fever Virus, a gene which inhibits transcription mediated by both NF-κB and NFAT. The A238L gene has been selectively expressed in mouse T lymphocytes using tissue specific promoter, enhancer and locus control region sequences for CD2. The resulting two independently derived transgenic mice expressed the transgene and developed a metastasic, angiogenic and transplantable CD4+CD8+CD69– lymphoma. The CD4+CD8+CD69– cells also grew vigorously in vitro. The absence of CD69 from the tumour cells suggests that they were derived from T cells at a stage prior to positive selection. In contrast, transgenic mice similarly expressing a mutant A238L, solely inhibiting transcription mediated by NF-κB, were indistinguishable from wild type mice. Expression of Rag1, Rag2, TCRβ-V8.2, CD25, FoxP3, Bcl3, Bcl2 l14, Myc, IL-2, NFAT1 and Itk, by purified CD4+CD8+CD69– thymocytes from A238L transgenic mice was consistent with the phenotype. Similarly evaluated expression profiles of CD4+CD8+ CD69– thymocytes from the mutant A238L transgenic mice were comparable to those of wild type mice. These features, together with the demonstration of (mono-)oligoclonality, suggest a transgene-NFAT-dependent transformation yielding a lymphoma with a phenotype reminiscent of some acute lymphoblastic lymphomas

Intermediate steps in positive selection: differentiation of CD4+8int TCRint thymocytes into CD4-8+TCRhi thymocytes.

The differentiation potential of putative intermediates between CD4+8+ thymocytes and mature T cells has been examined. Such intermediate populations were sorted, in parallel with CD4+8+ thymocytes, from three types of C57BL/6 mice: major histocompatibility complex (MHC) class II-deficient mice, mice transgenic for an alpha/beta T cell receptor (TCR) restricted by class I MHC and normal mice. The sorted populations were then transferred into the thymus of nonirradiated C57BL/Ka mice differing in Thy 1 allotype, and the progeny of the transferred cells were analyzed 2 d later. Surprisingly, with all three types of donor mice, a major proportion of the CD4+8intTCRint-derived progeny were found to be CD4-8+TCRhi cells, thus delineating a new alternative pathway for development of the CD8 lineage. In contrast, the transfer of CD4int8+TCRint thymocytes produced CD4-8+TCRhi cells but no significant proportion of CD4+8-TCRhi cells, suggesting that there is no equivalent alternative pathway for the CD4 lineage. The results negate some of the evidence for a stochastic/selective model of lineage commitment, and point to an asymmetry in the steps leading to CD4-8+ versus CD4+8- T cells