By David N. Leff

Editor¿s note: Science Scan is a roundup of recently published biotechnology-relevant research.

It didn¿t take a cabal of terrorists to launch the most efficient bacterial-warfare bug now threatening the human race. Staphylococcus aureus is everywhere on earth ¿ from indwelling plastic heart valves to the nostrils of hospital staff and their septic patients to the dirty needles of crack abusers to the doomed lungs of cystic fibrosis sufferers.

The kill rate of S. aureus is very high, and climbing higher. Its drug-resistance strategy is to the point of overwhelming vancomycin, the last and only antibiotic still effective against Staph. (See BioWorld Today, May 28, 1999, p. 1.)

Now, however, researchers at GlaxoSmithKline in Collegeville, Pa., are testing a new ploy aimed at conning S. aureus and other pathogenic bacteria into generating their own antibiotic, and thereby killing themselves ¿ like microbial suicide bombers.

¿We¿re not sure if that¿s a possibility or not,¿ observed microbiologist Gary Woodnutt, vice president of the Microbiology Group at Glaxo. ¿Our ploy identifies the targets that could then be used for antibiotic discovery. We¿re not using it at the moment as an antibiotic in its own right, albeit that that¿s the way it¿s appearing to the Staph aureus microorganism.¿

A recent paper in Science, dated Sept. 21, 2001, reports their work so far. Its title: ¿Identification of critical staphylococcal genes using conditional phenotypes generated by antisense RNA.¿ Woodnutt is the article¿s senior author.

¿One key innovation in this paper,¿ he told BioWorld Today, ¿is a system where we were not just looking at growth in vitro, on a plate, but actually using this in vivo as well ¿ in an animal infection model ¿ looking at something above and beyond in vitro bacterial growth. That, I think, is really the critical point of this paper.

¿Our strategy involved antisense technology,¿ Woodnutt continued, ¿in a regulatable gene expression system. By this method we identified more than 150 critical staphylococcal genes where antisense ablation led to lethal or growth-inhibitory effects. About 40 percent of these genes are orthologs or homologs of known essential bacterial genes.

¿To demonstrate the titration of essential genes in vivo,¿ Woodnutt recounted, ¿we chose a murine model of hematogenous pyelonephritis, which represents a localized kidney infection ¿ similar to several human renal diseases ¿ from which bacteria can be readily recovered.¿

The paper concluded: ¿The antisense system described offers a comprehensive genomic approach to readily identify and characterize growth-critical gene functions in the clinically important human pathogen, S. aureus. Each gene identified is maintained in one of a collection of conditional growth-defective/lethal isogenic strains. This set of isolates allows titratible phenotypic control over the expression of the gene¿s function in bacterial culture and in relevant models of infection.¿

¿What we¿re doing,¿ Woodnutt observed in closing, ¿is looking at the bug¿s own ability to kill itself, by using the antisense plasmids we describe. This is what an antibiotic would look like if it targeted this gene. Then if we got a true antibiotic, this is what it would appear to look like in animals and in man. Our genomic approach,¿ he concluded, ¿identifies staphylococcus gene products that could serve as targets for antibiotic discovery.¿

New Light On Long-Term T-Cell Memory Mechanism To Bolster Vaccine Design, Re-Infection Prevention

Once the human immune system encounters an infectious agent or nonliving immunogenic molecule, it never forgets the alien antigen¿s epitopic shape. How does it generate this lifetime immunological memory?

A report in Nature Immunology for August 2001 shows that white blood cells (CD4 lymphocytes), which are dedicated to conferring specific immune responses, need to be exposed to a pathogen for only a very short time in order to create the highly efficient, long-lasting memory cells that are needed for effective vaccines. (Incidentally, those CD4 lymphocytes are the first murderous targets of HIV infection, by which the AIDS virus aims at crippling its human victim¿s immune system.)

The journal paper bears the title: ¿CD⁴⁺ T cell effectors can become memory cells with high efficiency and without further division.¿ Its authors are immunologists in the Biomedical Research Laboratories of the Trudeau Institute Inc. in Saranac Lake, N.Y.

Until now, they point out, the pathways utilized by T cells to become memory cells were unknown. Their paper describes how naove T cells, which have never encountered a particular antigen, become activated (i.e., effector) lymphocytes when confronted by antigenic proteins made by pathogens. These in turn differentiate into memory T cells. The co-authors make the point that as most properties of memory cells are predetermined during effector generation, the most effective vaccine strategies will focus on generating large numbers of the right kind of effector CD⁴⁺ T cells. This new finding, they emphasize, is important for vaccine development, as well as for fending off re-infection.

A Little-Known Gene, Commonly Mutated In Human Cancers, Predisposes To Melanoma In Mouse Model

A mutation in the gene found in a hereditary form of human melanoma provides one of the best mouse models in this increasingly common, and often deadly, malignancy. It¿s reported in Nature dated Sept. 6, 2001, under the title, ¿Loss of p16^Ink4a confers susceptibility to metastatic melanoma in mice.¿ Its authors are molecular geneticists at The Netherlands Cancer Institute in Amsterdam.

A back-to-back article in the same Sept. 6 issue of Nature is titled: ¿Loss of p16^Ink4a with retention of p19^Arf predisposes mice to tumorigenesis.¿ Its authors are at the Harvard-affiliated Dana-Farber Cancer Institute in Boston.

Both papers report that knocking out the p16^Ink4a gene in mice, leaving the p19^Arf gene intact, predisposes the animals to melanoma.