Gene Expression Profiling Identifies Similar CD4⁺ and CD8⁺ T Cell Defects in TCL1 Transgenic Mice after Development of CLL to Those Observed in Patients with CLL.

The TCL1 gene at 14q32.1 is involved in chromosomal translocations and inversions in T cell leukemias, but targeted expression of the TCL1 gene in mice results in the development of a CLL like disorder in older mice resembling human B-CLL, so that deregulation of the TCL1 pathway proved to play a crucial role in CLL pathogenesis in mice. Development and progression of B-CLL is associated with immune dysregulation and in particular T cell defects. Although patients with CLL often have normal or even increased T cell numbers, there is an abnormal CD4/CD8 ratio, impaired mitogen responses and defective effector function in response to antigenic stimulation. We have previously categorized defects in the gene expression profile of CD4 and CD8 T cells in patients with CLL. We therefore sought to determine if the onset of CLL in the TCL1-transgenic mice also resulted in defects similar to those observed in patients with CLL. The aim was to determine if this murine model would mimic the impact of CLL on the normal immune system, so that we could use this model to examine in vivo the impact of steps taken to repair T cell defects. To examine this, we highly purified CD4 and CD8 T cells by positive selection from non-transgenic mice and TCL1 transgenic mice of different ages and at different stages in disease development. Total RNA was extracted, cRNA synthesized, labeled and hybridized to the Mouse 430_2 Affymetrix chip. We used DNA-Chip Analyzer (dChip) to perform an unsupervised analysis, which consisted of gene filtering, excluding genes that lacked sufficient variability across groups, and hierarchical clustering of genes and samples. This type of analysis demonstrated that CD4 and CD8 T cells of young mice without CLL clustered with non-transgenic mice of different ages, but separately from CD4 and CD8 cells from mice with developing and established CLL. Supervised analysis using Permax of the gene expression profiles of T cells in non-transgenic mice and non-tumor bearing TCL1 mice compared to CLL bearing mice identified significant differences in expression for 348 in CD4 cells and 127 genes for CD8 cells. In CD4 cells from CLL mice 202 genes were upregulated and 146 were downregulated and in CD8 cells 32 genes were upregulated and 95 genes downregulated. Analysis of the genes observed to be altered in the CLL bearing mice revealed that the majority were involved in genes regulating cytoskeleton formation, intracellular transportation, vesicle formation and transport, cell cycle control and cell differentiation. Comparison of the pathways perturbed in the mice compared to that observed in our previous study in patients with CLL demonstrated alteration in many similar pathways. The findings in human and murine CLL are in keeping with the hypothesis that interaction of the CLL cells with the normal immune function induces changes that result in decrease in T cell differentiation and effector function. It is intriguing to postulate that this effect would diminish autologous anti-tumor responses. We conclude that development of CLL in these transgenic mice induces T cell defects that mimic the defects that occur in CLL patients and that the TCL1 transgenic mouse model will serve as an ideal model to study steps to repair T cell function and their impact on CLL.