The overall goal of this protocol, is to develop of a high efficiency, high yield method for generating dendritic cell or DCs, that fatefully reflect their in-vivo phenotypic and functional divergence. Dendritic cells exist as great populations in lymphoid organs. Therefore, we use filter ligand to increase the frequency of these essential cells in donor tissues to facilitate that isolation.
The main advantage of this technique is that it removes generation of all the DC subsets in suitable numbers for analysis using only the commercially available agents. To harvest flt-3 ligand expressing B16 melanoma cells from a 90%confluent culture, first wash the cells with PBS and incubate the culture with 05%trypsin at 37 degrees Celsius. After 5 minutes, quench the protease activity with 20 milliliters of 4 degrees Celsius complete dima medium and detach the adherent cell model layer with light tapping and gentle pipetting.
Collect the cells by centrifugation and count them. Then, re-suspend the single cell suspension to a 1 times to the 8 cells per milliliter concentration in PBS for their subcutaneous injection into C57 black 6 recipient mice. When the tumor reaches two to ten milliliters in diameter, harvest the spleens from the tumor bearing animals and place the spleens in a petri dish containing fresh RPMI medium.
Using a scalpel, cut the tissues into 0.2 square centimeters pieces, and then incubate the fragments in ten milliliters of collagenase and Dnase at 37 degrees Celsius. After 30 minutes, pour the partially digested tissue slurry onto a 70 micron cell strainer, and use a five milliliter syringe plunger to press the remaining tissue fragments through the mesh of the strainer. Rinse the filter with 10 milliliters of fresh medium, pooling the wash with the rest of the single cell suspension and pellet the cells.
We suspend the cell pellet in 2 milliliters of red blood cell lysis buffer at room temperature for 10 minutes. Then wash the cells in 10 milliliters of fresh RPMI medium, and re-suspend them at 1 times 10 to the 8 cells per milliliter in cell sorting buffer containing FC block. To isolate the plasma cytode DCs, thoroughly mix 300 microliters of biotin-labelled antibody cocktail from a plasma cytode DC isolation kit with 200 microliters of the splenic single cell suspension.
Place the cells in an ice water bath for 15 minutes, with gentle tapping every three minutes. Then wash the cells with 12 milliliters of cell sorting buffer, and re-suspend the pellet in 500 microliters of fresh sorting buffer. Next, incubate the cells in 300 microliters of anti-biotin, antibody conjugated beads for another 15 minutes in the ice water with regular tapping.
After washing the cells in fresh sorting buffer, re-suspend the pallet in 2 milliliters of cell sorting buffer, and load an appropriately sized magnetic column onto its corresponding magnet. Equilibrate the column with five milliliters of fresh 4 degree Celsius cell sorting buffer. When all of the buffer has drained from the top of the column, carefully add the cells to the center of the surface of the column head, and collect the flow-through.
Then wash the column with 10 milliliters of fresh, 4 degrees Celsius sorting buffer and collect the flow-through in the same tube. After passage though a second magnetic column, a plasma cytode dendritic cell population with a greater than 94%purity can be expected. To isolate the CD8aplha+and CD8alpha-DCs, mix the rest of the splenic cell suspension with 100 microliters of biotion conjugated antibody cocktail from a CD8alpha+dendritic cell isolation kit for 15 minutes on ice with gentle tapping, as just demonstrated.
At the end of the incubation, wash the cells in 12 milliliters of 4 degrees Celsius cell sorting buffer, and re-suspend the pellet in 150 microliters of fresh 4 degrees Celsius cell sorting buffer. Next, mix the cells with 100 microliters of the CD8alpha+dendritic cell isolation kit anti-biotin beads. After 15 minutes on ice with gentle tapping, wash the cells in 10 milliliters of 4 degrees Celsius cell sorting buffer, and re-suspend the pellet in 1 milliliter of fresh 4 degrees Celsius sorting buffer.
At the end of the incubation, sort the cells by magnetic bead separation, as just demonstrated, collecting the flow-through and the first wash. Then, spin down the cells and re-suspend the pellet in one milliliter of fresh 4 degrees Celsius cell sorting buffer. Now label the cells with 200 microliters of anti-CD8aplha conjugated magnetic beads from the kit, and pass the cells through a new column, collecting the CD8alpha-dendritic cell flow-through.
To collect the CD8alpha+DCs, transfer the column into a 15 milliliter conical tube, and plunge 5 milliliters of fresh 4 degrees Celsius cell sorting buffer though the column. After the running the cells through a second column, a greater than 96%CD8alpha+dendritic cell population can be expected. To isolate the CD8alpha-cells, spin the the CD8alpha-flow-through cell suspension.
Then label the cells with 100 microliters of anti-CD11 c-magnetic beads and collect the magnetic bead positive cell population, as just demonstrated, to obtain a greater than 97%CD8alpha-dendritic cell subset population. Finally, determine the number of live cells, by trypan blue exclusion. Once the tumor becomes palpable, the B16 flt-3 ligand tumor bearing mice consistently exhibit a dramatic increase in the splenic cellularity that correlates with the expansion of the splenic dendritic cell subsets.
Interestingly, while a 15 to 20-fold increase in the absolute cell numbers is observed for the conventional DCs in these animals, only about a 4-fold increase is observed for the plasma cytode DC subset. The different dendritic cell subsets are characterized according to their B220, CD11b, CD11c and CD8alpha expression. The cell populations also exhibit other unique subset markers, however, with mPDCA1 expressed exclusively on the plasma cytode DCs DEC205 highly expressed on the CD8alpa+DCs, and CD11b and 33D1 detected most prominently on the CD8alpha-DCs.
Using this method, we have demonstrated CD8alpa+DCs to be the most efficient in the presentation of antigens by CD bonding molecules to a specialized T-cell population known as invariant NKT cells. The most critical feature of DC isolation is to maintain strict sterility and antidoxant-free conditions. During the procedures, these T-cells are highly responsive to antidoxant.
While attempting this procedure, it is important to remember to handle the cells gently, as repeated mechnanical stimulation may alter the maturation state of dendtritic cells. Once mastered, this technique can be used to isolate a high number of all the major DC subsets from single spleen. Thanks for watching and good luck with your experiments.
