Methods and reagents for improved selection of biological materials

A method for selecting a pre-determined target population of cells or subpopulation thereof from a fluid sample, which method comprises:

• a. A first step of providing a plurality of magnetic particles in a size range of about 500 nanometers to about 1500 nanometers and having bound thereto a binding agent that binds specifically to said target population or subpopulation of cells, said cells having low and high antigen density receptors, said particles having a density at least two-fold more than the density of the target cell, and said particles being made of a material of the type in which the particles become magnetized upon exposure to a magnetic field and remain magnetized following the removal of a magnetic field;
• b. A second step of mixing for about 2 seconds to about 4 minutes said sample with said particles and said particles being further characterized as being of a size and density such that said particles pass through a substantial portion of said sample as a result of said mixing to allow enough time for formation of particle-cell complexes;
• and said sample being further characterized as having a volume of at least 0.01 ml;
• and
• c. A third step of separating said sample including a non-target population or subpopulation of cells, from said particle-cell complex binding low and high antigen density receptors by placing said sample in said magnetic field with a magnetic configuration to cause the particles to move said particle-cell complex, resulting in a target population having negligible amount carry-over of non-targeted populations, wherein a containment vessel is provided for said sample and said magnetic field is created with said magnetic configuration that enables said particle-cell complexes to form as substantially a single layer along a wall of said containment vessel.