By David N. Leff

When Father Noah prepared to launch his Ark, the biblical passenger list stipulated, ¿of every living thing of all flesh, two of every sort . . . ¿

Of all these innumerable life forms, all but a single category had one pathological property in common. As Joseph Bryant puts it: ¿None of the species in the animal world, except the higher primates, such as the chimpanzee, can be infected with the AIDS virus. The lower species, of course, has never been able to be infected.¿

Bryant heads the Animal Model Division at the Institute of Human Virology¿s Biotechnology Institute in the University of Maryland, Baltimore. The virology institute¿s director is Robert Gallo, an early AIDS research pioneer, who co-coined the name of the pathogen ¿ HIV, human immunodeficiency virus.

Bryant is senior author ¿ and Gallo a co-author ¿ of a paper in today¿s Proceedings of the National Academy of Sciences (PNAS), dated July 31, 2001. The paper is titled: ¿An HIV-1 transgenic rat that develops HIV-related pathology and immunologic dysfunction.¿

¿This to our knowledge,¿ Bryant told BioWorld Today, ¿is the first HIV-type transgenic rat. We had made this rodent model¿s predecessor, the first of several transgenic mice, a decade ago, at the National Institutes of Health. Our whole purpose was to develop an animal model that we could use to study as much as possible about AIDS.

¿But with the advent of transgenic technology,¿ he continued, ¿we knew by the late ¿80s and early ¿90s, they¿d already got the HIV genome sequenced. They could take each of the genome¿s viral genes and introduce it into any one of the transgenic rodents. We did that in the mouse while we were at the NIH. That animal turned out to be a pretty good model, but it lacked something we saw in the human. Namely a key cell-division protein, cyclin D, was not present. But in the rat it was.¿

Pinch Of Mouse, Handful Of Rat

¿On the other hand,¿ he pointed out, ¿a mouse weighed only 25 grams (0.88 ounces), as compared with the rat¿s 500 grams (1.1 pounds). So that was a key component of the equation. While the rat was still a very small animal model, it was large enough to do long-term studies on, which was difficult to do on the mouse. You just couldn¿t collect very much specimen material from it. Nonetheless, we did some very good work done on our mouse models.¿

To construct their HIV rat, the co-authors deleted fragmentary gene sequences, gag and pol, from the whole HIV genome¿s infectious proviral plasmid. They microinjected these into the fertilized one-cell eggs of female rats. The resulting progeny reproduced the clinical symptoms and histological manifestations of full-blown human AIDS. What¿s more, they were delivered, and grew up, as germ-free animals.

¿These rats,¿ Bryant recounted,¿ developed a severe, chronic neurological disease, which apparently mimics some of the clinical conditions seen in AIDS patients. We started seeing a large amount of vascular disease throughout almost all the rats¿ major organs. They also incurred critical infirmities involving the heart, and skin lesions, including a large number of inflammatory psoriasis-like disease ¿ very similar to the skin-related diseases that we see in AIDS patients.

¿In this particular rat model, as it stands today,¿ Bryant went on, ¿we¿ve been able to see almost all of the chronic AIDS-associated disease and pathology that occur in human AIDS patients. These involve the body¿s major organs. There¿s a lot now involving severe nephropathy ¿ kidney disease. For some reason, 90 percent of the HIV nephropathy develops in black patients, which interests me as an African-American scientist. We¿ll have another rat-model paper in a couple of months, reporting work with a collaborator down at Children¿s Hospital, on kidney disease in AIDS infants.

¿Also,¿ Bryant added, ¿NIH has just announced that its National Institute of Diabetes & Digestive & Kidney Diseases wants to study long-term therapy in AIDS heart patients.¿ In their germ-free HIV rat model, Bryant pointed out, ¿all of our AIDS-mimicking findings are introduced without any secondary infections, such as sepsis, which therapeutic drugs might cause.¿

Several clinical investigators in cardiology, the central nervous system and neuropathy have already started using the rat model. ¿We have two researchers,¿ Bryant observed, ¿who have done some preliminary work on assaying cocaine use in our rats, and it has had some effect on their heart lining. We have another investigator who is ready to do some work on the effects of alcohol. In other words, they¿re starting to mimic some of the conditions in the AIDS population, using the rat model to speed up the process.¿

This time factor explains why the chimpanzee model of AIDS has fallen out of favor. ¿We already know the life span of the rodent ¿ a maximum of 2.5 to three years in the laboratory rat. So the direct proportion in a chimp infected 10 years ago may take another 10 before it comes down with all of the AIDS signs and symptoms.¿

The University of Maryland¿s Biotechnology Institute obtained issued patents to Bryant¿s rat colony last December.

Quick-Frozen Rat Embryos Thawed On Demand

¿We¿ve started to produce at a high level, using cryopreservation to freeze the embryos until needed,¿ Bryant recounted. ¿We are in the process now of removing gp120, HIV¿s major envelope gene, and have already made the transgenic animals. We¿re just waiting to see whether the phenotype is what we expect. The next transgene would be one called tat. It is particularly relevant to Kaposi¿s sarcoma, and has some relationship to many of the infectious gene processes of AIDS. Gallo was one of the first to work on that.

¿We are also in the course,¿ Bryant continued, ¿of creating the transgenic CD4 rat, which means taking the human gene. It marks the immune system T cell targeted for HIV infection. Our CD4 rat is already developed, but we have now tried to characterize it to make sure that the gene has been properly expressed in the animal. Then we will of course mate it to the model we have now,¿ he concluded, ¿to determine what effects the different genes will have on this human CD4.¿