The notion of a non-invasive prenatal screening test was conceived by cytogenetists in the early sixties and has been steadily moving toward reality. Scientists have documented the phenomenon of fetal cells in maternal blood, and envisioned their use in prenatal screening. The minute proportion of fetal cells found in maternal blood, can now be enriched to one per few thousand, and aneuploidies can be detected with chromosome specific DNA probes via fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR). The ultimate goal of current research in medical cytogenetics is to make low-cost, low-risk prenatal genetic screening widely available. A key limiting factor is the small number of fetal cells, which makes cell detection labor intensive, and limits accuracy. The goal of this project, is to develop a sophisticated method for enrichment and an automated system that will allow repeatable, unbiased and rapid detection of the few fetal cells in maternal blood. During the Phase I project, we implemented a two fold approach involving; (i) optimization of fetal cell enrichment methods, and (ii) development of an automated system to detect fetal cells and perform aneuploidy screening. Our experimental results indicate a mean enriched fetal cell proportion of 1.6 per 3000 maternal cells. We built a prototype automated imaging system, integrating fluorescence autofocusing, slide scanning, cell detection, and dot counting algorithms. We tested the system on samples of female blood spiked with male blood in varying proportions (mimicking actual fetal to maternal cell ratios), to obtain quantitative data on system accuracy. Finally, we estimated the cost and time savings achievable by the system and established the feasibility of our approach. In Phase II, we will further develop the prototype and test it in a clinical environment. Specifically, we will, (1) optimize the software for enhanced performance, (2) use the prototype to perform systematic studies, (3) increase the specificity of the automated system to detect fetal cells, processing samples both labeled with FISH, and stained via immunofluorescence for fetal hemoglobin, (4) test the prototype in a clinical environment, and (5) evaluate the commercial feasibility of the instrument. Phase III will focus on commercialization of the system, making fetal screening available to virtually the whole population.
The instrument developed will be incorporated into PSI's PowerGene product line of cytogenetics automation equipment, both in new systems sold and as an upgrade to existing systems already in use in cytogenetic labs. Thus commercialization of the technology developed under this project will occur quickly.
| Merchant, Fatima A; Castleman, Kenneth R (2002) Strategies for automated fetal cell screening. Hum Reprod Update 8:509-21 |
