Herpesvirus papio: state and properties of intracellular viral DNA in baboon lymphoblastoid cell lines

My journey to DNA repair

I completed my medical studies at the Karolinska Institute in Stockholm but have always been devoted to basic research. My longstanding interest is to understand fundamental DNA repair mechanisms in the fields of cancer therapy, inherited human genetic disorders and ancient DNA. I initially measured DNA decay, including rates of base loss and cytosine deamination. I have discovered several important DNA repair proteins and determined their mechanisms of action. The discovery of uracil-DNA glycosylase defined a new category of repair enzymes with each specialized for different types of DNA damage. The base excision repair pathway was first reconstituted with human proteins in my group. Cell-free analysis for mammalian nucleotide excision repair of DNA was also developed in my laboratory. I found multiple distinct DNA ligases in mammalian cells, and led the first genetic and biochemical work on DNA ligases I, III and IV. I discovered the mammalian exonucleases DNase III (TREX1) and IV (FEN1). Interestingly, expression of TREX1 was altered in some human autoimmune diseases. I also showed that the mutagenic DNA adduct O⁶-methylguanine (O⁶mG) is repaired without removing the guanine from DNA, identifying a surprising mechanism by which the methyl group is transferred to a residue in the repair protein itself. A further novel process of DNA repair discovered by my research group is the action of AlkB as an iron-dependent enzyme carrying out oxidative demethylation.

Increased antibody responses to Herpes virus papio (HVP) antigens in pre-lymphomatous baboons (Papio hamadryas) of the Sukhumi high lymphoma stock

Antibody responses to Herpes virus papio (HVP) antigens were studied in 21 pre-lymphoma baboons (which subsequently died of malignant lymphoma), 21 paired controls, i.e. age-, sex- and population-matched healthy baboons, and 185 randomly selected healthy baboons of the same population. The sera were all collected at the same time and were tested blind in the fixed-cell indirect immunofluorescence test against HVP viral capsid antigen (VCA)-positive, early antigen (EA)-positive cell targets before and after absorption with HVP. Eleven of the pre-lymphoma sera were anti-EA-positive whereas none of the paired controls contained anti-EA. Anti-VCA titers of pre-lymphoma sera were higher than those of paired controls in thirteen cases. Only in four cases were anti-VCA titers of pre-lymphoma sera lower than those of paired controls. Qualitatively, the same results were obtained when anti-VCA and anti-EA titers of pre-lymphoma sera were compared with respective mean population values. The differences between pre-lymphoma group and control groups, especially in the case of anti-EA, were statistically highly significant. Thus, elevated anti-HVP titers in healthy baboons of the Sukhumi lymphoma-prone stock can be considered as a marker of high risk for development of malignant lymphoma.

Induction of target antigens and conversion to susceptible phenotype of NK-cell-resistant lymphoid cell line

Two autologous Herpesvirus papio producer lymphoid cell lines and one autologous non-producer line were compared for susceptibility to natural killer (NK) cell-mediated lysis. The non-producer cell line, 26CB-1, was more resistant to NK cell killing compared to one viral producer counterpart 13CB-1, but equally resistant when compared to another, 8CB-1. Treatment with chemical agents that affect differentiation or activate the viral cycle, including n-butyrate, IuDR, 5-azacytidine and tunicamycin, increased the susceptibility to killing of the non-producer line but had less effect on the 13CB-1 producer line. The increase in susceptibility was due to induction of new target antigens: activated 26CB-1 cells were more effective at inhibiting NK-cell-mediated lysis and were bound by more NK cells than untreated control cells. The expression of NK target structures may be related to the differentiated state rather than to the viral production status to target cells.

Transfer of Epstein-Barr virus receptors to receptor-negative cells permits virus penetration and antigen expression

Epstein-Barr virus (EBV) receptors were implanted into the membranes of receptor-negative cells, using Sendai virus envelopes as vehicles. The presence of the receptors in the target cell membrane was demonstrated by monitoring the fate of radioiodinated donor membranes. Receptors could be detected for at least 36 hr after implantation. [3H]Thymidine-labeled EBV bound efficiently to receptor-implanted cells but not to control cells. Binding was inhibited by an excess of nonlabeled virus. Of the [3H]thymidine-labeled EBV DNA, 50-75% was found inside the receptor-implanted, EBV-exposed cells 24 hr after the infection. The viral genome was functionally active in B lymphocyte-derived cell lines of human, murine, and baboon origin; in T lymphocyte-derived lines of human and murine origin; in mouse fibroblasts; and in freshly explanted mouse lymphocytes, as shown by the expression of EBV-determined nuclear, early, and viral capsid antigens.