Evaluation of zero-length cross-linking procedure for immuno-magnetic separation of Leptospira

Advances in rare cell isolation: an optimization and evaluation study

Background

Rare nucleated CD45 negative cells in peripheral blood may be malignant such as circulating tumor cells. Untouched isolation thereof by depletion of normal is favored yet still technological challenging. We optimized and evaluated a novel magnetic bead-based negative selection approach for enhanced enrichment of rare peripheral blood nucleated CD45 negative cells and investigated the problem of rare cell contamination during phlebotomy.

Methods

Firstly, the performance of the magnetic cell separation system was assessed using leukocytes and cultivated fibroblast cells in regard to depletion efficiency and the loss of cells of interest. Secondly, a negative selection assay was optimized for high performance, simplicity and cost efficiency. The negative selection assay consisted of; a RBC lysis step, two depletion cycles comprising direct magnetically labelling of leukocytes using anti-CD45 magnetic beads followed by magnetic capture of leukocytes using a duopole permanent magnet. Thirdly, assay evaluation was aligned to conditions of rare cell frequencies and comprised cell spike recovery, cell viability and proliferation, and CD45 negative cell detection. Additionally, the problem of CD45 negative cell contamination during phlebotomy was investigated.

Results

The depletion factor and recovery of the negative selection assay measured at most 1600-fold and 96%, respectively, leaving at best 1.5 × 10⁴ leukocytes unseparated and took 35 min. The cell viability was negatively affected by chemical RBC lysis. Proliferation of 100 spiked ovarian cancer cells in culture measured 37% against a positive control. Healthy donor testing revealed findings of nucleated CD45 negative cells ranging from 1 to 22 cells /2.5 × 10⁷ leukocytes or 3.5 mL whole blood in 89% (23/26) of the samples.

Conclusion

Our assay facilitates high performance at shortest assay time. The enrichment assay itself causes minor harm to cells and allows proliferation. Our findings suggest that rare cell contamination is unavoidable. An unexpected high variety of CD45 negative cells have been detected. It is hypothesized that a rare cell profile may translate into tumor marker independent screening.

Development of a magnetic bead fluorescence microscopy immunoassay to detect and quantify Leptospira in environmental water samples

Climate change, world population growth, and poverty have led to an increase in the incidence of leptospirosis. Leptospirosis is caused by pathogenic spirochaete bacteria that belong to the genus Leptospira. The bacteria are maintained in the renal tubules of the reservoir hosts (typically a rodent), then shed into the environment via the urine. Water is key for environmental survival and transmission, as leptospires can survive for several weeks in a moist environment. Therefore, environmental epidemiological studies are needed to study the contamination of environmental water sources. However, few such studies have been performed using cultivation of the isolates and PCR assays. But, leptospira cultivation can be easily contaminated by other organisms and takes usually several weeks. Moreover, PCR is a complex and costly analysis for the underdeveloped countries that have the highest incidence of leptospirosis. In this study, we describe two modifications of a fluorescence microscopy assay based on immuno-magnetic separation (IMS) to detect leptospires in environmental water samples that mainly differ in fluorescent dye staining. The first type uses acridine orange fluorescent dye staining combined with multiplexed IMS for sample screening. The detection limit ranged from 10(2) to 10(3) organisms per mL and largely depended on the capture efficiency (CE) of the immuno-magnetic particles. The second type uses serogroup-specific immuno-particles and direct fluorescence antibody staining (DFA) to detect leptospires; the detection limit of this second assay was approximately 10(1) cells per mL. Both assay types were applied to natural and experimentally infected water samples, which were also analysed with DFM and real-time PCR. Our data show that the fluorescent microscopy immunoassay successfully identified experimental leptospire contamination and was as sensitive as PCR. This modified immune-fluorescence assay may therefore enable epidemiological studies of leptospirosis.