The rat sodium iodide symporter gene permits more effective radioisotope concentration than the human sodium iodide symporter gene in human and rodent cancer cells.

Expression of the sodium iodide symporter (NIS) gene in tumor cells may provide a novel mechanism for treating cancer. The NIS mediates the normal physiological transport of iodide across the thyroid cell membrane. This mechanism of iodide uptake has been used to both diagnose and treat thyroid cancer. Tissue expression of the NIS is largely limited to the thyroid; therefore, expression of the NIS gene in cancer cells would allow for specific iodine uptake, radioisotope accumulation, and treatment. In this study, we directly compared the human and rat NIS (rNIS) for their ability to concentrate radioisotope into human and rodent cancer cells. Perchlorate-sensitive (125)I uptake in multiple cell lines was demonstrated following transduction with retroviral vectors expressing either the human or rNIS gene. Surprisingly, iodine uptake was consistently higher with the rNIS gene, up to 5-fold greater, when compared to the human gene, even within a variety of human tumor cell lines. This iodine uptake allowed for cell killing following (131)I treatment in NIS-transduced cells when assayed by in vitro clonogenic assays. These results demonstrate that the rNIS gene provides superior iodine uptake ability, and may be preferable for use in designing anticancer gene therapy approaches.

Dominant, hierarchical induction of peripheral tolerance during foreign antigen-driven B cell development.

We created mice expressing transgene-encoded BCRs with "dual reactivity" for the hapten Ars and nuclear autoantigens. Expression of transgene-encoded BCRs was not evident in the memory compartment despite observation of transgene-expressing B cells in germinal centers following Ars immunization. In contrast, dual reactive mAbs were readily obtained from mice with enforced expression of Bcl-2 following secondary Ars immunization. However, while these mAbs were hypermutated and displayed increased affinity for Ars, all had reduced avidity for DNA and intracellular autoantigens. Thus, Bcl-2 alters dominant-negative selection of dual reactive B cells during the Ars response, but this is restricted to those with lowered autoreactivity, demonstrating a hierarchy of peripheral tolerance during memory B cell development.

Level of B cell antigen receptor surface expression influences both positive and negative selection of B cells during primary development.

To examine the effect of B cell Ag receptor (BCR) surface density on B cell development, we studied multiple lines of mice containing various copy numbers of an IgH micro delta transgene. The V(H) gene in this transgene encodes multireactive BCRs with low affinity for self Ags. These BCRs promote differentiation to a B cell subpopulation that shares some, but not all of the properties of marginal zone (MZ) B cells. Surface BCR level was found to be related to transgene gene copy number in these mice. In mice containing 1-15 copies of the transgene, elevated surface BCR levels were correlated with increased numbers of B cells in the MZ-like subset. However, in mice containing 20-30 copies of the transgene, massive clonal deletion of B cells was observed in the bone marrow, few B cells populated the spleen, and B cells were essentially absent from the lymph nodes. These data support the idea that autoantigens mediate not only negative, but positive selection of developing B cells as well. More importantly, they illustrate the profound influence of BCR surface density on the extent to which either of these selective processes take place.