Single-cell Analysis of Immunophenotype and Cytokine Production in Peripheral Whole Blood via Mass Cytometry

Here we describe a single-cell proteomic approach to evaluate immune phenotypic and functional (intracellular cytokine induction) alterations in peripheral whole blood samples, analyzed via mass cytometry.

This method can help answer questions in the autoimmunity field such as identifying cell frequency abnormalities and function differences such as production of key cytokines in the setting of autoimmune disease. The main advantage of this method is that it can capture a broad repertoire or different cell types and function differences from a easily obtainable peripheral blood sample. Generally, individuals new to this process may struggle with getting the timing of the blood processing steps right, the antibody panel design, the barcoding process itself, and analysis of high dimensional single cell data.

This systems immunology approach is particularly suitable for autoimmune diseases like SLE where immune dysregulation is pervasive and evident in peripheral blood. Visual demonstration of this method is important to clarify the timing of steps and also to show how multiple samples can be barcoded and pooled prior to mass cytometry analysis. To begin this procedure, place the labeled round bottom polystyrene tubes of five different conditions for whole blood processing on a rack.

Next, add one milliliter of 37 degree Celsius RPMI to each tube. Then, add one milliliter of whole blood to each tube and pipette up and down several times to mix thoroughly with RPMI. Subsequently, add 10 microliters of pre-diluted ruxolitinib to the tube labeled T six plus five R and mix thoroughly.

Place the rack of tubes in the incubator at 37 degrees Celsius and begin timing the incubation. To process the T zero sample, pipette the entire content of the T zero tube into a labeled conical tube containing 20 milliliters of 37 degree Celsius lyse/fix buffer at working concentration. To optimize cell recovery, rinse the tube with lyse/fix buffer and mix by inverting the conical tube.

Incubate the cells at 37 degrees Celsius for 15 minutes to allow for lysis and fixation. Then, centrifuge the cells at 500 times G for five minutes at room temperature. Afterward, decant the supernatant and re-suspend the cells in one milliliter of ice cold PBS to break up the pellet.

Then, fill the conical tube to a 15 milliliter volume with PBS. Subsequently, centrifuge the cells at 500 times G for five minutes at room temperature. Re-suspend the cells in one milliliter of CSM to break up the pellet.

Then, transfer the sample to a labeled microcentrifuge tube for antibody staining. Using an automated cell counter, count the cells with a 10 microliter sample. Next, centrifuge the cells at 500 times G for five minutes at room temperature.

Afterward, aspirate the supernatant, leaving the pellet in about 60 microliters of residual. Keep this pellet on ice until the samples from other conditions have completed processing. At T equals 30 minutes, transfer the tube rack to the tissue culture hood.

Add 10 microliters of R848 at 0.1 grams per microliter to the T six plus R848 tube and mix thoroughly. Then, add 10 microliters of LPS at 0.01 micrograms per microliter to the T six plus LPS tube and mix thoroughly. Afterward, add four microliters of protein transport inhibitor to the tubes labeled T six, T six plus five R, and T six plus LPS and return the samples to the incubator until T equals six hours.

Mix the samples thoroughly with a P1000 pipette every two hours. At T equals two hours, add four microliters of protein transport inhibitor cocktail to the T six plus R848 tube. Mix all samples and return the rack to the incubator until T equals six hours.

At T equals four hours, mix the samples with a P1000 pipette one more time. At T equals six hours, process T six, T six plus LPS, T six plus R848, and T six plus five R blood sample tubes as described for the T zero sample. Then, store the pellets in residual CSM volume at minus 80 degrees Celsius to process later.

To barcode the lysed, fixed cells, thaw the samples from the minus 80 degrees Celsius storage slowly on ice. Dilute the 10X barcoding perm buffer with PBS by one to 10 and make enough buffer for three milliliters per sample. Fill one non-sterile trough with CSM and one with the one X barcoding perm buffer.

Then, add one milliliter of ice cold CSM to the freshly thawed samples, mix thoroughly, and transfer to the respective pre-labeled polypropylene cluster tubes. Now, take a 10 microliter sample and count the cells using an automated cell counter. Normalize the cell counts in each cluster tube by removing the volume of excess cells.

Then, centrifuge the cells at 600 times G for five minutes at room temperature. Re-suspend the cells in one milliliter of one X barcoding perm buffer with a multichannel pipette and centrifuge at 600 times G for five minutes at room temperature. Afterward, aspirate off the supernatant.

Line up the cluster tubes on a rack in the same order as indicated on the barcode key so the sample matches with its barcode. Add 800 microliters of one X barcoding perm buffer by multichannel pipette to all samples in the cluster tubes without touching the cell pellet to reduce cell loss. Then, set aside the rack with the cluster tubes.

Remove the 20-plex palladium barcoding kit tube strips from minus 20 degrees Celsius and thaw at room temperature. Add 100 microliters of one X barcoding perm buffer, mix thoroughly, and transfer 120 microliters of the re-suspended barcode mix into the corresponding cell samples in the cluster tubes. Mix thoroughly by multichannel pipette so that there is no cross-contamination between individually barcoded samples.

Incubate cluster tubes for 30 minutes at room temperature to allow the barcodes to label the cells. After 30 minutes, centrifuge the samples at 600 times G for five minutes at room temperature. Aspirate the supernatant, then re-suspend them in one milliliter of CSM.

Subsequently, centrifuge and re-suspend in CSM again. Afterward, centrifuge at 600 times G for five minutes at room temperature and aspirate the supernatant. With a single pipette and using the same tip, transfer all cell pellets in about 70 to 80 microliters of residual volume to one polystyrene tube.

Do not eject the pipette tip. Set aside the single pipette with this tip. With a multichannel pipette and new tips, add 100 microliters of CSM to each original cluster tube to maximize cell recovery.

Using the single pipette with the tip that was set aside, transfer all cell pellets in 100 microliters of residual volume to the same polystyrene tube. Add CSM to top off the polystyrene tube to about three milliliters. Count and record the cell number of the pooled barcode set.

Then, centrifuge at 600 times G for five minutes at room temperature and aspirate the supernatant. Proceed to staining the barcoded samples on the same day. This schematic demonstrates the workflow for the stimulation and processing of the peripheral blood samples, including allocation of blood sample aliquots, timing of the addition of stimulation agents, protein transport inhibitor cocktail, and incubation times until the red blood cell lysis and fixation.

The choice of stimulating agents will depend on the signaling and cytokine pathways that are targeted for assessment. Following fixation and RBC lysis, the individual lysed, fixed cell samples from a healthy donor were barcoded, labeled with 26 antibodies against surface markers, permeabilized, and stained with 14 antibodies against cytokines. The limited gating strategy representing the identification of CD14 high monocytes is shown here.

From left to right, each 2D plot represented is a population subset from the parent population that is gated from the 2D plot immediately to the left. Using CD14 high monocytes as representative in eight immune cell subsets, a mass cytometry analysis was performed on peripheral blood samples from a healthy donor at time zero unstimulated and following stimulation with TLR agonist LPS and R848 and the T-cell activator PMA ionomycin. An example of the cytokine induction in CD14 high monocytes is shown and selected cytokines with specificity to the stimulating agent used are depicted.

R848 selectively induces IL-12p40 subunit and MCP1 in CD14 high monocytes while LPS does not. In contrast, PMA ionomycin does not induce cytokines in CD14 high monocytes. Once mastered, the blood stimulations can be done in about seven hours and the barcoding step can get done in just about an hour.

When attempting this procedure, it's important to be mindful of the timing of the steps and to plan ahead accordingly. Once you have this procedure in place, you can consider altering the blood stimulation conditions in the mass cytometry panel in order to assess the immune cell responses that are specific to your own research aims. After watching this video, you should have a good understanding of how to elicit cytokine responses from whole blood samples and how to pool multiple samples into a barcoded set for mass cytometry analysis.