Nature Biotechnology pp 405 - 409

Sometimes the body needs a little prompting to heal itself. Scientists think they might have come up with a way of artificially stimulating the immune system into action against tumors and infectious agents using genetic engineering. By introducing human proteins into cultured mouse cells, they have created artificial cells that mimic natural antigen-presenting cells' ability to activate the body's immune system against tumors cells or pathogenic viruses. These artificial antigen-presenting cells are not only much easier to culture and handle than the body's own antigen-presenting cells, they also appear more effective at activating the immune system against influenza and tumor antigens.

The idea behind cellular therapies against cancer or infectious disease is that foreign antigen on the surface of antigen-presenting cells can be used to awaken the immune system's sentinels-cytotoxic T cells-so that they seek out and destroy a tumor or pathogenic agent. Currently, this approach involves the isolation and purificaction not only of cytotoxic T cells that do the killing, but also the antigen-presenting cells required to stimulate them. The problem is that the purification of donated natural antigen-presenting dendritic cells from bone marrow or blood is a labor-intensive process and these cells must be immune matched to the patient's body-that is, contain the same human leukocyte antigen (HLA) type.

Now Michel Sadelain and Jean-Baptiste Latouche have come up with an alternative: They have engineered mouse fibroblast cells to express human HLA class I (A2.1) together with several other accessory proteins-B7.1, LFA-3, and intracellular adhesion molecule 1 (ICAM-1). With assistance from B7.1, LFA-3 and ICAM-1, the HLA class I molecule complex orientates foreign antigen in such a way that it can be recognized by cytotoxic T cells. Thus, artificial antigen presenting cells can be grown in the laboratory and used to stimulate T cells of any patient of a given human leukocyte antigen (HLA) type. When the resultant artificial antigen-presenting cells are loaded with foreign antigen (influenza antigen, tumor antigens MART1, or tumor antigen gp100) and cultured with a patient's cytotoxic T cells, the T cells show potent responses against target cells bearing the foreign antigens, as measured by the release of a radioactive isotope.

The authors suggest that the approach will be very useful for studying the process of cytotoxic T cell activation and in particular for the development of antigen-specific T cells for use in therapies against cancer.

Nature Biotechnology pp 410 - 414 and p 383

Thinking small can sometimes be advantageous. Ralph Weissleder and colleagues have designed tiny, nanometer-sized magnetic particles that slip unnoticed into cells where they can serve as beacons for tracking the progress and movement of cells throughout the body. Using these particles, it should be possible to learn how cells migrate through the body and contribute to processes such as immune responses, the growth of blood vessels, and embryonic development.

A technique called magnetic resonance imaging (MRI), commonly used to map activity in the brain, provides a window both for following processes that occur deep within the body at the tissue or cellular level. For cellular tracking, however, current MRI methods require magnetic beads to be attached to the cell of interest, which results in their rapid recognition as foreign particles and subsequent elimination from the circulation.

To get around this, Weissleder and his collaborators have used tiny ~45 nm magnetic particles derivatized with an unusual protein, termed Tat, from the human immunodeficiency virus (HIV). This protein has the extraordinary property of chaperoning molecules from the outside to the inside of the cell by a mechanism as yet unknown. Reasoning that Tat-coated nanoparticles would be efficiently internalized by cells, Weissleder's team attached a triple magnetic, fluorescent, and isotopic label to Tat, and showed that the labeled, Tat-coated nanoparticles were efficiently taken up by both hematopoietic and neural progenitor cells. After injection into mice, the magnetic hematopoietic cells homed to bone marrow, and once the bone marrow was harvested, the cells could be detected by MRI at single cell resolution and then recaptured with magnetic separation columns.

The authors state that the technique should facilitate the detailed analysis of specific stem cell and organ interactions critical for the therapeutic use of stem cells.

Nature Biotechnology pp 438 - 441 and pp 384 - 385

Bubble-Jet printers have found a new application. This time they have moved out of the office and into the laboratory. A team of Japanese researchers, led by Nobuko Yamamoto, has adapted the Bubble-Jet printing head for printing spots of DNA onto glass slides to create microarrays. Although still in preliminary development, compared with the current pen-spotting method widely adopted for creating DNA microarrays, the Bubble-Jet approach may be more reliable and substantially increase the density of DNA spots that can be deposited on the array surface. Ultimately, this technology may enable the spotting of an entire mammalian genome on a single DNA chip.

Current formats for DNA microarrays include commercial chips created using photolithographic DNA synthesis or the robotic printing (via a pen) of DNA onto a chemically treated microscope slide. Each of these systems has its advantages, but neither combines optimal sensitivity, reproducibility, specificity, spot density, and cost.

In the new approach, Yamamoto's team set out to ascertain whether a Bubble-Jet printer head could be adapted for use in microarray synthesis. The process involves loading a dissolved DNA fragment of interest into the Bubble Jet printer head, which then heats the liquid up, producing a bubble that forces out a drop of DNA fragment solution onto the chip surface. In preliminary tests on a Bubble-Jet fabricated array of a fragment of the p53 tumor suppressor gene, the researchers were able to successfully distinguish single base mismatches from perfect matches,

In an accompanying commentary, Geoffrey Childs and his colleagues discuss significance of the new technology, comparing it with other formats and indicating refinements that will be required before the technology can be widely adopted.