PBMC Thawing for Immune Assays
Materials Required
Principle
PBMC thawing for immune assays recovers viable cryopreserved peripheral blood mononuclear cells for downstream functional or phenotypic readouts, including ELISPOT, intracellular cytokine staining, proliferation assays, and flow-cytometric immunophenotyping[1][2][3][4][5][6]. Cryopreserved PBMCs can support immune monitoring because antigen-specific T-cell function and major CD4/CD8 phenotypes may be retained after optimized freezing and thawing, although some lymphocyte subsets and activation or memory markers can be altered by cryopreservation[3][5][6][7]. The technical objective is rapid warming of the frozen vial followed by controlled dilution and removal of DMSO-containing cryomedium, because thawing and wash conditions measurably affect viable PBMC recovery and downstream assay performance[1][2][3]. Viability alone is insufficient for protocol evaluation because high viability may occur with low live-cell recovery, so both viable percentage and absolute live-cell recovery should be measured after thawing[2].
MCE has not independently verified the accuracy of these methods. They are for reference only.
Experimental Materials
• Use cryopreserved human PBMC aliquots as the starting sample for immune monitoring assays[1][2][3][5].
• Use pre-warmed RPMI 1640-based wash medium; RPMI 1640 at 37°C with 20% fetal bovine serum was the best-performing wash medium in one comparative thawing study[2].
• Use DMSO-containing cryopreserved PBMC only as the frozen input material; the thawing procedure should dilute and remove DMSO before immune-assay setup[1][2][3].
• Benzonase may be included in the thawing medium only when the protocol has been validated for the intended assay, because one multicenter study found that benzonase sometimes improved viable recovery and did not alter functional or immunophenotypic results, whereas the improvement was not consistent[3].
• Use a viability dye compatible with the downstream platform; 7-AAD was used to identify dead CD45+ leukocytes by flow cytometry in a PBMC thawing optimization study[2].
• For immunophenotyping, antibodies against CD45, CD3, CD4, CD8, CD19, CD14, CD16/CD56, HLA-DR, CD38, CD45RA, CCR7, and related lineage or functional markers were used in studies evaluating cryopreserved PBMC composition and T-cell status[2][6][7].
• For ELISPOT-based immune assays, IFN-γ ELISPOT kits and antigen stimulations such as CEF peptides or mumps antigen were used to evaluate antigen-specific T-cell readouts after PBMC thawing[4][5].
• Use a 37°C water bath or equivalent controlled warming device for rapid thawing of cryovials[1][2][4].
• Use 15-mL conical tubes, a centrifuge capable of 500 × g, a 37°C incubator with 5% CO2 when post-thaw incubation is being evaluated, a cell counter or flow cytometer for viability and recovery assessment, and a flow cytometer or ELISPOT reader according to the downstream immune assay[2][4][7].
• Use pre-warmed RPMI 1640-based wash medium; RPMI 1640 at 37°C with 20% fetal bovine serum was the best-performing wash medium in one comparative thawing study[2].
• Use DMSO-containing cryopreserved PBMC only as the frozen input material; the thawing procedure should dilute and remove DMSO before immune-assay setup[1][2][3].
• Benzonase may be included in the thawing medium only when the protocol has been validated for the intended assay, because one multicenter study found that benzonase sometimes improved viable recovery and did not alter functional or immunophenotypic results, whereas the improvement was not consistent[3].
• Use a viability dye compatible with the downstream platform; 7-AAD was used to identify dead CD45+ leukocytes by flow cytometry in a PBMC thawing optimization study[2].
• For immunophenotyping, antibodies against CD45, CD3, CD4, CD8, CD19, CD14, CD16/CD56, HLA-DR, CD38, CD45RA, CCR7, and related lineage or functional markers were used in studies evaluating cryopreserved PBMC composition and T-cell status[2][6][7].
• For ELISPOT-based immune assays, IFN-γ ELISPOT kits and antigen stimulations such as CEF peptides or mumps antigen were used to evaluate antigen-specific T-cell readouts after PBMC thawing[4][5].
• Use a 37°C water bath or equivalent controlled warming device for rapid thawing of cryovials[1][2][4].
• Use 15-mL conical tubes, a centrifuge capable of 500 × g, a 37°C incubator with 5% CO2 when post-thaw incubation is being evaluated, a cell counter or flow cytometer for viability and recovery assessment, and a flow cytometer or ELISPOT reader according to the downstream immune assay[2][4][7].
Experimental Procedure
• Pre-warm wash medium to 37°C before thawing, because warm RPMI 1640 with 20% fetal bovine serum improved thawing performance in one comparative study, and ice-chilled washing conditions reduced viable recovery in a systematic PBMC thawing study[1][2].
• Prepare enough wash medium to dilute each thawed vial in a 15-mL tube; one study specifically evaluated 10 mL wash medium in a 15-mL Falcon tube[2].
• Label tubes before removing PBMC vials from frozen storage, and prepare viability-counting materials before thawing because thawed cells are evaluated by both viability percentage and absolute live-cell recovery[2].
• If the downstream assay includes ELISPOT resting, decide this before thawing, because resting is not universally beneficial and may cause substantial viable-cell loss[4].
• Remove one PBMC cryovial from frozen storage and thaw rapidly at 37°C until the frozen contents are just liquefied; one practical protocol thawed a 1-mL PBMC cryovial for 60 seconds at 37°C, and another study found thawed PBMC in cryovials could remain up to 30 minutes at 37°C in the presence of DMSO before washing without loss of ELISPOT functionality under the tested conditions[1][4].
• Transfer the thawed cell suspension into a 15-mL conical tube containing pre-warmed wash medium, avoiding ice-cold wash conditions because adding ice-chilled medium to cold cells reduced viable PBMC recovery[1][2].
• When using the Hønge et al. optimized flow-cytometry condition, use RPMI 1640 at 37°C with 20% fetal bovine serum as wash medium[2].
• Dilute the thawed PBMC gently rather than abruptly when following the multicenter functional-assay protocol, because slow dropwise addition of the first 5 mL wash medium over 2-3 minutes significantly improved viable-cell recovery compared with rapid addition[3].
• Mixing method did not significantly change viability or live-cell recovery in one flow-cytometry optimization study, so no additional unsupported mixing requirement is specified here[2].
• Centrifuge the diluted PBMC suspension; one thawing optimization study using 10 mL wash medium in a 15-mL Falcon tube found that samples should be centrifuged for at least 10 minutes at 500 × g[2].
• Centrifugation temperature at 20°C or 37°C did not affect viability or recovery in that study[2].
• Remove the supernatant and resuspend the cell pellet in assay-appropriate culture or staining medium for counting and downstream use[2][4].
• If ELISPOT is performed immediately after thawing, one study resuspended PBMC at 3 × 106 PBMC/mL and plated 300,000 PBMC per well for IFN-γ ELISPOT[4].
• For post-thaw incubation, PBMC could be rested for up to 8 hours at 37°C with 5% CO2 without affecting cell counts in one flow-cytometry study, whereas 16 hours significantly decreased viability and recovery[2].
• For ELISPOT, 20-hour resting was not generally beneficial, increased responses only in selected high CEF responders, and caused about half of viable PBMC to be lost, so resting should be used only when validated for the study population and antigen system[4].
• Measure both percentage viability and absolute live-cell recovery after thawing, because thawing conditions can change these measures independently and high viability does not necessarily indicate high live PBMC recovery[2].
• For lymphocyte proliferation assays using cryopreserved PBMC, one multicenter study identified 75% viability as an acceptance parameter, but it did not identify comparable acceptance parameters for flow-cytometry results[3].
• For flow cytometry, acquire live/dead and lineage-marker data using a predefined gating strategy; published studies used CD45+ leukocyte gating with exclusion of dead events and evaluated CD4+, CD8+, B-cell, NK-cell, monocyte, activation, memory, apoptosis, proliferation, and cytokine-producing T-cell populations[2][6][7].
• Interpret cryopreserved-PBMC phenotyping with caution for labile or altered populations, because CD45RO, CD62L, activated T-cell, naïve/memory T-cell, monocyte, B-cell, and some Treg-related readouts may differ after cryopreservation[3][6][7].
• For ELISPOT, report antigen-induced spot-forming units after subtracting medium-control background when this analysis structure is used, and include replicate wells because published ELISPOT studies used triplicate antigen-stimulated wells and medium controls[4][5].
• For resting comparisons or paired thawing-condition comparisons, use paired statistical analyses such as Wilcoxon signed-rank testing when comparing matched PBMC aliquots, as reported in ELISPOT resting studies[4].
• Prepare enough wash medium to dilute each thawed vial in a 15-mL tube; one study specifically evaluated 10 mL wash medium in a 15-mL Falcon tube[2].
• Label tubes before removing PBMC vials from frozen storage, and prepare viability-counting materials before thawing because thawed cells are evaluated by both viability percentage and absolute live-cell recovery[2].
• If the downstream assay includes ELISPOT resting, decide this before thawing, because resting is not universally beneficial and may cause substantial viable-cell loss[4].
• Remove one PBMC cryovial from frozen storage and thaw rapidly at 37°C until the frozen contents are just liquefied; one practical protocol thawed a 1-mL PBMC cryovial for 60 seconds at 37°C, and another study found thawed PBMC in cryovials could remain up to 30 minutes at 37°C in the presence of DMSO before washing without loss of ELISPOT functionality under the tested conditions[1][4].
• Transfer the thawed cell suspension into a 15-mL conical tube containing pre-warmed wash medium, avoiding ice-cold wash conditions because adding ice-chilled medium to cold cells reduced viable PBMC recovery[1][2].
• When using the Hønge et al. optimized flow-cytometry condition, use RPMI 1640 at 37°C with 20% fetal bovine serum as wash medium[2].
• Dilute the thawed PBMC gently rather than abruptly when following the multicenter functional-assay protocol, because slow dropwise addition of the first 5 mL wash medium over 2-3 minutes significantly improved viable-cell recovery compared with rapid addition[3].
• Mixing method did not significantly change viability or live-cell recovery in one flow-cytometry optimization study, so no additional unsupported mixing requirement is specified here[2].
• Centrifuge the diluted PBMC suspension; one thawing optimization study using 10 mL wash medium in a 15-mL Falcon tube found that samples should be centrifuged for at least 10 minutes at 500 × g[2].
• Centrifugation temperature at 20°C or 37°C did not affect viability or recovery in that study[2].
• Remove the supernatant and resuspend the cell pellet in assay-appropriate culture or staining medium for counting and downstream use[2][4].
• If ELISPOT is performed immediately after thawing, one study resuspended PBMC at 3 × 106 PBMC/mL and plated 300,000 PBMC per well for IFN-γ ELISPOT[4].
• For post-thaw incubation, PBMC could be rested for up to 8 hours at 37°C with 5% CO2 without affecting cell counts in one flow-cytometry study, whereas 16 hours significantly decreased viability and recovery[2].
• For ELISPOT, 20-hour resting was not generally beneficial, increased responses only in selected high CEF responders, and caused about half of viable PBMC to be lost, so resting should be used only when validated for the study population and antigen system[4].
• Measure both percentage viability and absolute live-cell recovery after thawing, because thawing conditions can change these measures independently and high viability does not necessarily indicate high live PBMC recovery[2].
• For lymphocyte proliferation assays using cryopreserved PBMC, one multicenter study identified 75% viability as an acceptance parameter, but it did not identify comparable acceptance parameters for flow-cytometry results[3].
• For flow cytometry, acquire live/dead and lineage-marker data using a predefined gating strategy; published studies used CD45+ leukocyte gating with exclusion of dead events and evaluated CD4+, CD8+, B-cell, NK-cell, monocyte, activation, memory, apoptosis, proliferation, and cytokine-producing T-cell populations[2][6][7].
• Interpret cryopreserved-PBMC phenotyping with caution for labile or altered populations, because CD45RO, CD62L, activated T-cell, naïve/memory T-cell, monocyte, B-cell, and some Treg-related readouts may differ after cryopreservation[3][6][7].
• For ELISPOT, report antigen-induced spot-forming units after subtracting medium-control background when this analysis structure is used, and include replicate wells because published ELISPOT studies used triplicate antigen-stimulated wells and medium controls[4][5].
• For resting comparisons or paired thawing-condition comparisons, use paired statistical analyses such as Wilcoxon signed-rank testing when comparing matched PBMC aliquots, as reported in ELISPOT resting studies[4].
Troubleshooting
Low viable-cell recovery after thawing.
Possible cause:Wash medium was added too quickly or under cold conditions.
Literature-supported solution:
Use pre-warmed wash medium and slow dilution, because ice-chilled medium reduced viable recovery and slow dropwise dilution improved viable-cell recovery[1][3].
High viability but too few usable PBMC for the assay.
Possible cause:Viability percentage and absolute recovery diverged after thawing.
Literature-supported solution:
Evaluate both viability and absolute live-cell recovery for every thawed sample rather than relying on viability alone[2].
Reduced proliferation-assay reliability.
Possible cause:Low post-thaw PBMC viability.
Literature-supported solution:
Apply the 75% viability acceptance parameter for lymphocyte proliferation assays reported in the multicenter PBMC study[3].
ELISPOT signal does not improve after overnight resting.
Possible cause:Resting is not a generally applicable enhancer of antigen-specific ELISPOT performance and may reduce available viable PBMC.
Literature-supported solution:
Use resting only after validation for the antigen and donor population; otherwise plate freshly thawed PBMC or increase plated cell number when cell availability permits[4].
Phenotypic results differ between fresh and cryopreserved PBMC.
Possible cause:Some markers and immune subsets are altered by cryopreservation.
Literature-supported solution:
Avoid mixing fresh and cryopreserved PBMC results within the same analysis when the assay is sensitive to cryopreservation effects, and interpret CD45RO, CD62L, activation, naïve/memory, monocyte, B-cell, and Treg-related readouts with caution[3][6][7].
Références:
- [1]. Ramachandran H, et al. Optimal thawing of cryopreserved peripheral blood mononuclear cells for use in high-throughput human immune monitoring studies. Cells. 2012;1(3):313-324. [Content Brief]
- [2]. Hønge BL, et al. Optimizing recovery of frozen human peripheral blood mononuclear cells for flow cytometry. PLoS One. 2017;12(11):e0187440. [Content Brief]
- [3]. Weinberg A, Song LY, Wilkening C, Sevin A, Blais B, Louzao R, et al. Optimization and limitations of use of cryopreserved peripheral blood mononuclear cells for functional and phenotypic T-cell characterization. Clin Vaccine Immunol. 2009;16(8):1176-1186. [Content Brief]
- [4]. Kuerten S, et al. Resting of cryopreserved PBMC does not generally benefit the performance of antigen-specific T cell ELISPOT assays. Cells. 2012;1(3):409-427. [Content Brief]
- [5]. Kreher CR, et al. CD4+ and CD8+ cells in cryopreserved human PBMC maintain full functionality in cytokine ELISPOT assays. J Immunol Methods. 2003;278(1-2):79-93. [Content Brief]
- [6]. Reimann KA, et al. Preservation of lymphocyte immunophenotype and proliferative responses in cryopreserved peripheral blood mononuclear cells from human immunodeficiency virus type 1-infected donors: implications for multicenter clinical trials. Clin Diagn Lab Immunol. 2000;7(3):352-359. [Content Brief]
- [7]. Li B, Yang C, Jia G, Liu Y, Wang N, Yang F, et al. Comprehensive evaluation of the effects of long-term cryopreservation on peripheral blood mononuclear cells using flow cytometry. BMC Immunol. 2022;23(1):30. [Content Brief]
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