Rudolph Jaenisch

DNA Methylation by DNA Methyltransferase 1 Is Critical for Effector CD8 T Cell Expansion

Transcriptional silencing mediated by DNA methylation is a critical component of epigenetic regulation during early embryonic development in animals. However, the requirement for DNA methylation during activation and differentiation of mature CD8+ T cells into effector and memory cells is not clear. Using cre-mediated deletion of DNA methyltransferase 1 (Dnmt1) at the time of CD8+ T cell activation, we investigated the obligation for maintaining patterns of DNA methylation during the generation of Ag-specific effector and memory CD8+ T cells in response to acute viral infection of mice with lymphocytic choriomeningitis virus. Dnmt1−/− CD8+ T cells failed to undergo the massive CD8+ T cell expansion characteristic of lymphocytic choriomeningitis virus infection, leading to >80% reductions in Ag-specific effector CD8+ T cells at the height of the response. Despite this, Dnmt1−/− CD8+ T cells efficiently controlled the viral infection. Interestingly, the number of Ag-specific Dnmt1−/− memory CD8+ T cells was moderately reduced compared with the reductions seen at day 8 postinfection. Our data suggest that ablation of Dnmt1 and subsequent DNA methylation affect the finite proliferative potential of Ag-specific CD8+ T cells with moderate effects on their differentiation to effector and memory CD8+ T cells.

CD8+ T Cells from Mice Transnuclear for a TCR that Recognizes a Single H-2Kb-Restricted MHV68 Epitope Derived from gB-ORF8 Help Control Infection

To study the CD8(+) T cell response against a mouse γ-herpes virus, we generated K(b)-MHV-68-ORF8(604-612)RAG(-/-) CD8(+) T cell receptor transnuclear (TN) mice as a source of virus-specific CD8(+) T cells. K(b)-ORF8-Tet(+) CD8(+) T cells, expanded in the course of a resolving MHV-68 infection, served as a source of nucleus donors. Various in vivo and ex vivo assay criteria demonstrated the fine specificity and functionality of TN cells. TN cells proliferated extensively in response to viral infection, helped control viral burden, and exhibited a phenotype similar to that of endogenous K(b)-ORF8-Tet(+) cells. When compared to OT-1 cells, TN cells displayed distinct properties in response to lymphopenia and cognate antigen stimulation, which may be attributable to the affinity of the TCR expressed by the TN cells. The availability of MHV-68-specific CD8(+) TCR TN mice provides a new tool for investigating aspects of host-pathogen interactions unique to γ-herpes viruses.

The cloning of mammals: what are the problems?

I want to talk about a topic which is of public interest, the cloning of mammals. When you look at the media, for example the New York Times Magazin’s cover a couple of months ago, what emerges is the issue of the mad scientist, of out of space sects which believe that life came to earth by cloning, and so on. I think this is a ludicrous debate and I am not going to go further into that. There are rather serious and interesting issues behind this and these issues have been raised already half a century ago, in the seminal experiments with frogs done by Briggs and King, Gurdon, DiBernardino and by others. The principal questions which were posed then were: Does differentiation involve loss of nuclear potency, and is there nuclear differentiation? Can a nucleus of a terminally differentiated cell be reprogrammed to participate in development of an animal and the differentiation of all lineages. These are essentially the same questions we ask now, in one way or the other, and I will discuss these questions. In the second part of my talk I will actually bridge the topics of this institute. I will talk about immunology, including B and T cells.