Improving CRISPR-Cas9 Screens in CAR T Cells: A Refined Method for Library Preparation

Our research focuses on using CRISPR screening approaches to identify targets and enhance the effectiveness of CAR T cell therapies. Current experiment challenges includes achieving reproducible laboratory methods in CRISPR screening approaches. To begin, add a predetermined amount of Lenta viral CRISPR library to a 24 well plate containing T cells.

Add poly brain at a final concentration of eight micrograms per milliliter. Mix gently to ensure even distribution. Centrifuge the cells at 700 G for 90 minutes at 32 degrees Celsius to perform spin-fection.

After centrifugation, carefully remove the plate from the centrifuge. Replace the media with fresh T-cell growth medium. After six hours, add the CAR lenta viral vector at a multiplicity of infection of three.

Incubate the cells at 37 degrees Celsius for four days. Once incubation is complete, collect the CAR T cells. Wash once with PBS.

Then stain the cells using acradine orange propidium iodide, and count them in a fluorescent cell counter. Prepare a four micromolar solution of cas9 in electroporation buffer. Resuspend five times 10 to the power six CAR T cells in 50 microliters of cas9 solution.

Then pipette 50 microliters of the cell suspension into each well of a multi-well cuvete strip without forming bubbles. Remove any visible bubbles by gently running a pipette tip along the edges of the well. Use the expand T-cell three program to nucleoffect the CAR T cells.

Place the cuvettes in an incubator at 37 degrees Celsius for 40 minutes. Resuspend the nucleoffected cells in T-cell growth medium. Then incubate again at 37 degrees Celsius for three days.

Count the cells using acradine orange propidium iodide staining in a fluorescent cell counter. After adjusting the cell density to ten to the power of six cells per milliliter, add puromycin to a final concentration of 2.5 micrograms per milliliter. After six days of incubation, assess the percentage of CAR positive cells using flow cytometry.

Then sort CAR T cell populations and store dry cell pellets at minus 80 degrees Celsius. Extract genomic DNA from the samples using a cell and tissue DNA extraction method. Measure genomic DNA concentration using a double stranded DNA quantification kit.

Next digest up to five micrograms of genomic DNA with 20 units of the selected restriction enzymes in a total volume of 50 microliters. Incubate overnight at 37 degrees Celsius in a thermocycler. The next day, prepare 10 milliliters of elution buffer containing 10 millimolartris HCL and 50 milliliters of fresh 70%ethanol.

Pipette 100 microliters of the digested product into a tube containing vortexed beads. Pipette to mix the suspension thoroughly and incubate for five minutes at room temperature before magnetizing for another five minutes. While on the magnet, discard the supernatant and pipette 200 microliters of the 70%ethanol solution without disturbing the pellet.

After 30 seconds, discard the supernatant and perform two more alcohol washes. After two washes, allow the beads to dry for two minutes, then remove them from the magnet. Add 40 microliters of elucian buffer and pipette to resuspend the beads.

Magnetize the suspension for two minutes, then transfer the supernatant into a new tube. Add one x wash binding buffer to a tube containing one milligram of vortex streptavidin magnetic beads. Pipette to resuspend the beads in the buffer.

Then place the suspension on a magnet for one minute, discard the supernatant and perform two more washes. After the third wash reuspend the beads in two x wash binding buffer. Then add five microliters of 10 micromolar biotinylated pull down primers to the purified digestion product.

Incubate the mixture in a dry bath at 96 degrees Celsius for five minutes and immediately cool on ice for five minutes. Add one milligram of pre-washed, streptavidin magnetic beads to the reaction, ensuring that both the reaction and the streptavidin beads have equal volumes. Incubate for 20 minutes at room temperature while resuspending every four minutes.

Magnetize the beads for five minutes, then wash three times with one x wash binding buffer. Finally, resuspend the beads containing bound sgRNA cassette in 50 microliters of elucian buffer. Prepare and amplify the sgRNA library and sequence it.

Following antibiotic selection, CAR T cells transduced with the CRISPR library showed continued survival and proliferation in both donors after puromycin treatment. Untransduced T-cell, and CAR T cells lacking CRISPR library transduction did not show comparable proliferation under antibiotic selection and served as negative controls. Restriction enzyme digestion with NDEL and PSPXI generated fragmented genomic DNA while preserving the single guide RNA cassette for enrichment.

Fragments containing sgRNA were then selectively amplified. Pearson and Spearman correlations showed that single guide RNA read counts and library complexity were maintained in donor genomic DNA samples compared with the plasmid library. Robust rank aggregation analysis identified genes that were significantly enriched or depleted following Cas9 editing in both donors.

Pathway enrichment analysis revealed top gene ontology terms associated with the identified genetic regulators. Our protocol offers a reliable alternative to existing laboratory techniques using CRISPR screening approaches. Our findings will advance the field by supporting the development of more reproducible and robust CRISPR screening protocols.

Our results paved the way for identifying genes and can be moderated to enhance CAR T cell phenotype and function.