Evaluation of the effect of storage condition on cell extraction and flow cytometric analysis from intestinal biopsies

Effect of storage time on peripheral blood mononuclear cell isolation from blood collected in vacutainer CPT™ tubes

BACKGROUND

Clinical trials of novel therapies for the treatment of ulcerative colitis (UC) may benefit from immune cell profiling, however implementation of this methodology is limited in the multicenter trial setting by necessity of timely (within 6 to 8 h) isolation and processing of peripheral blood mononuclear cells (PBMC) from whole blood samples. Becton Dickinson Vacutainer CPT™ Cell Preparation Tubes (CPT™) limit required processing prior to shipping to a central lab to an initial centrifugation step within 24 h of sample collection. As shipping may delay final processing beyond 24 h, we analyzed cell viability and T cell composition in whole blood stored in CPT™ to determine if their use may accommodate processing delays typical for multicenter clinical trials.

METHODS

Whole blood samples from 3 patients with UC were collected in CPT™ (15 tubes/patient) and PBMC were processed at various timepoints (24-96 h). Cell viability and T cell composition (26 types) were evaluated by flow cytometry. Variability between technical and biological replicates was evaluated in the context of cell-type abundance, delayed processing time, and data normalization.

RESULTS

Total cell viability was <50% when processing was delayed to 48 h after collection and was further reduced at later processing timepoints. The effect of delayed processing on cell abundance varied widely across cell types, with CD4+, CD8+, naïve effector CD8+, and Tcm CD4 + T cells displaying the least variability in abundance with delayed processing. Normalization of cell counts to cell types other than total T cells corrected for the effect of delayed processing for several cell types, particularly Th17.

CONCLUSIONS

Based on these data, processing of PBMC in CPT™ should ideally be performed within 48 h. Delayed processing of PBMC in CPT™ may be considered for cell types that are robust to these conditions. Normalization of cell abundance to different parental cell-types may reduce variability in quantitation and should be used in conjunction with the expected effect size to meet the experimental goals of a multicenter clinical trial.

Optimizing Flow Cytometric Analysis of Immune Cells in Samples Requiring Cryopreservation from Tumor-Bearing Mice

Most shared resource flow cytometry facilities do not permit analysis of radioactive samples. We are investigating low-dose molecular targeted radionuclide therapy (MTRT) as an immunomodulator in combination with in situ tumor vaccines and need to analyze radioactive samples from MTRT-treated mice using flow cytometry. Further, the sudden shutdown of core facilities in response to the COVID-19 pandemic has created an unprecedented work stoppage. In these and other research settings, a robust and reliable means of cryopreservation of immune samples is required. We evaluated different fixation and cryopreservation protocols of disaggregated tumor cells with the aim of identifying a protocol for subsequent flow cytometry of the thawed sample, which most accurately reflects the flow cytometric analysis of the tumor immune microenvironment of a freshly disaggregated and analyzed sample. Cohorts of C57BL/6 mice bearing B78 melanoma tumors were evaluated using dual lymphoid and myeloid immunophenotyping panels involving fixation and cryopreservation at three distinct points during the workflow. Results demonstrate that freezing samples after all staining and fixation are completed most accurately matches the results from noncryopreserved equivalent samples. We observed that cryopreservation of living, unfixed cells introduces a nonuniform alteration to PD1 expression. We confirm the utility of our cryopreservation protocol by comparing tumors treated with in situ tumor vaccines, analyzing both fresh and cryopreserved tumor samples with similar results. Last, we use this cryopreservation protocol with radioactive specimens to demonstrate potentially beneficial effector cell changes to the tumor immune microenvironment following administration of a novel MTRT in a dose- and time-dependent manner.