Fetal sex chromosome testing by maternal plasma DNA sequencing: clinical laboratory experience and biology.

OBJECTIVE: To describe the clinical experience with noninvasive prenatal testing for fetal sex chromosomes using sequencing of maternal plasma cell-free DNA in a commercial laboratory. METHODS: A noninvasive prenatal testing laboratory data set was examined for samples in which fetal sex chromosomes were reported. Available clinical outcomes were reviewed. RESULTS: Of 18,161 samples with sex chromosome results, no sex chromosome aneuploidy was detected in 98.9% and the fetal sex was reported as XY (9,236) or XX (8,721). In 4 of 32 cases in which the fetal sex was reportedly discordant between noninvasive prenatal testing and karyotype or ultrasonogram, a potential biological reason for the discordance exists, including two cases of documented co-twin demise, one case of a maternal kidney transplant from a male donor, and one case of fetal ambiguous genitalia. In the remaining 204 samples (1.1%), one of four sex chromosome aneuploidies (monosomy X, XXX, XXY, or XYY) was detected. The frequency of false positive results for sex chromosome aneuploidies is a minimum of 0.26% and a maximum of 1.05%. All but one of the discordant sex chromosome aneuploidy results involved the X chromosome. In two putative false-positive XXX cases, maternal XXX was confirmed by karyotype. For the false-positive cases, mean maternal age was significantly higher in monosomy X (P<.001) and lower in XXX (P=.008). CONCLUSION: Noninvasive prenatal testing results for sex chromosome aneuploidy can be confounded by maternal or fetal biological phenomena. When a discordant noninvasive prenatal testing result is encountered, resolution requires additional maternal history, detailed fetal ultrasonography, and determination of fetal and possibly maternal karyotypes.

A high-throughput comparison of recombinant gene expression parameters for E. coli-mediated gene transfer to P388D1 macrophage cells.

Escherichia coli strain BL21(DE3) was tested as a delivery vector for gene transfer to a murine P388D1 macrophage cell line using a 96-well high-throughput assay. Five recombinant strains of E. coli were compared to identify the effect recombinant listeriolysin O (LLO) and associated gene expression parameters had on final delivery of a luciferase reporter gene. Listeriolysin O, native to Listeria monocytogenes and used here in an effort to improve final gene delivery, was expressed from plasmid and chromosomal locations under the control of constitutive Tet or inducible T7 promoters. The E. coli vectors delivered the luciferase reporter gene to the P388D1 line with success assessed by recording luciferase luminescence activity within the macrophage cells. The assay allowed rapid analysis and evaluation of each E. coli strain tested with strain BL21(DE3) harboring a chromosomal copy of the T7-driven LLO gene showing the greatest relative measure of gene delivery. Strains were separately assayed for LLO activity and exhibited a trend of maximum gene delivery between the lowest and highest recorded LLO activities.

A comparison between polymeric microsphere and bacterial vectors for macrophage P388D1 gene delivery.

PURPOSE: The purpose of this study was to compare bacterial and polymeric gene delivery devices for the ability to deliver plasmid DNA to a murine macrophage P388D1 cell line. METHODS: An 85:15 ratio of poly(lactic-co-glycolic acid) (PLGA) and poly(beta-amino ester) polymers were formulated into microspheres that physically entrapped plasmid DNA encoding for the firefly luciferase reporter gene; whereas, the same plasmid was biologically transformed into a strain of Escherichia coli engineered to produce recombinant listeriolysin O. The two delivery devices were then tested for gene delivery and dosage effects using a macrophage cell line with both assays taking advantage of a 96-well high throughput format to quantify and compare each vector type. RESULTS: Gene delivery was comparable for both vectors at higher vector dosages while lower dosages showed an improved delivery for the microsphere vectors. Delivery efficiency (defined as luciferase measurement/mg cellular protein/ng DNA delivered) was 881 luminescence mg(-1) ng(-1) for polymeric microspheres compared to 171 luminescence mg(-1) ng(-1) for the bacterial vectors. CONCLUSION: A first head-to-head comparison between polymeric and bacterial gene delivery vectors shows a delivery advantage for polymeric microspheres that must also be evaluated in light of vector production, storage, and future potential.

Engineering bacterial vectors for delivery of genes and proteins to antigen-presenting cells.

Bacterial vectors offer a biological route to gene and protein delivery with this article featuring delivery to antigen-presenting cells (APCs). Primarily in the context of immune stimulation against infectious disease or cancer, the goal of bacterially mediated delivery is to overcome the hurdles to effective macromolecule delivery. This review will present several bacterial vectors as macromolecule (protein or gene) delivery devices with both innate and acquirable (or engineered) biological features to facilitate delivery to APCs. The review will also present topics related to large-scale manufacture, storage, and distribution that must be considered if the bacterial delivery devices are ever to be used in a global market.