Quantitative and Functional Assessment of the Influence of Routinely Used Cryopreservation Media on Mononuclear Leukocytes for Medical Research

The impact of cryopreservation on cytokine secretion and polyfunctionality in human PBMCs: a comparative study

Introduction

Human peripheral blood mononuclear cells (hPBMCs) are widely used in fundamental research and clinical applications as studying their responses to in vitro activation is an effective way to uncover functional alterations and disease associated phenotypes. However, the availability of samples in large numbers at a specific time and location remains challenging, hence they often might preferably be collected and cryopreserved for later analysis. While the effect of cryopreservation on viability and cell surface expression is well established, changes in activity and cytokine secretion still lead to conflicting results as it is often measured in bulk or within the cells.

Methods

Here, we used our platform for dynamic single-cell multiplexed cytokine secretion measurement and compared it to a traditional intracellular cytokine staining to quantify the effect of cryopreservation on cytokine secretion and expression of individual hPBMCs.

Results

Following stimulation with LPS or anti-CD3/CD28 antibodies for up to 36 or 72 h incubation, we observed distinct alterations in cytokine responses due to cryopreservation when comparing to fresh samples, but also remarkable consistencies for some cytokines and parameters. In short, the frequencies of cytokine-secreting cells in cryopreserved samples were lower for IL-6 (LPS), IL1-β (CD3/CD28) and IFN-γ (CD3/CD28), while the frequency and dynamics of IL-8 secretion were strongly impacted in all cases. We observed a large disconnect between cytokine expression and secretion for TNF-α, where the expression dramatically increased after cryopreservation, but actual secretion was, in comparison, remarkably stable. The polyfunctionality of single cells was altered by cryopreservation in specific co-secreting populations led by the effects on IL-6 or IL-8 secretion. Among immune cells, cryopreservation seemed to affect lymphocytes and monocytes differently as effects appeared early on in lymphocytes while generally observed in later time points in monocytes.

Conclusion

Together, this study offers an in-depth quantitative insight into the biological behavior of immune cells in response to cryopreservation and stimulation, further providing some insights into conflicting results in the literature as well as guidelines for researchers planning to assess cytokine-secreting from frozen hPBMCs in immunological research or clinical applications.

Unlocking the secrets of Hofbauer cells in placental (patho-) physiology: Isolation and quality assessment in human term placenta

INTRODUCTION

Hofbauer cells (HBCs) are macrophages of fetal origin that reside in the villous tissue. They are the only immune cells within healthy villi. While HBCs perform innate immune functions such as phagocytosis and antigen presentation, they are increasingly recognized for their diverse roles in placental physiology e.g. vascular functionality, tissue homeostasis, tolerance. Consequently, HBCs are of utmost interest in a variety of non-physiological placental conditions.

ISOLATION

Villous tissue is collected freshly after delivery and finely minced. The resulting tissue is digested in a two-step process, using Trypsin/DNase to separate cytotrophoblasts and collagenase/DNase to penetrate deeper into the villous stroma, containing HBCs, and obtain a single cell suspension. After a density gradient centrifugation, the corresponding cell layer is collected and subjected to negative immune selection of HBCs, yielding unaffected cells that have not been activated during the isolation process.

QUALITY CONTROL

In addition to a classical immunocytochemistry (ICC) approach including macrophage markers, and markers for potentially contaminating cell types (e.g. fibroblasts, muscle, mesenchymal cells), we have developed a multi-color flow cytometry (FC) panel. This panel assesses Hofbauer cell purity and polarization states more accurately and comprehensively than qualitative ICC, using percentage analysis of parent cells to estimate the expression levels of specific markers.

DISCUSSION

The presented protocol allows us to isolate HBCs in significant numbers and high purity, even from placentae compromised by preeclampsia (PE) with limited placental volume. We have successfully developed and implemented this protocol to study healthy, diabetic and PE macrophages, aiding a better understanding of the underlying placental pathophysiology at the cellular level.

Measuring anti-islet autoimmunity in mouse and human by profiling peripheral blood antigen-specific CD4 T cells

The endocrine pancreas is one of the most inaccessible organs of the human body. Its autoimmune attack leads to type 1 diabetes (T1D) in a genetically susceptible population and a lifelong need for exogenous insulin replacement. Monitoring disease progression by sampling peripheral blood would provide key insights into T1D immune-mediated mechanisms and potentially change preclinical diagnosis and the evaluation of therapeutic interventions. This effort has been limited to the measurement of circulating anti-islet antibodies, which despite a recognized diagnostic value, remain poorly predictive at the individual level for a fundamentally CD4 T cell-dependent disease. Here, peptide-major histocompatibility complex tetramers were used to profile blood anti-insulin CD4 T cells in mice and humans. While percentages of these were not directly informative, the state of activation of anti-insulin T cells measured by RNA and protein profiling was able to distinguish the absence of autoimmunity versus disease progression. Activated anti-insulin CD4 T cell were detected not only at time of diagnosis but also in patients with established disease and in some at-risk individuals. These results support the concept that antigen-specific CD4 T cells might be used to monitor autoimmunity in real time. This advance can inform our approach to T1D diagnosis and therapeutic interventions in the preclinical phase of anti-islet autoimmunity.

Cryopreserved anti-CD22 and bispecific anti-CD19/22 CAR T cells are as effective as freshly infused cells

Cryopreservation of chimeric antigen receptor (CAR) T cells facilitates shipment, timing of infusions, and storage of subsequent doses. However, reports on the impact of cryopreservation on CAR T cell efficacy have been mixed. We retrospectively compared clinical outcomes between patients who received cryopreserved versus fresh CAR T cells for treatment of B cell leukemia across two cohorts of pediatric and young adult patients: those who received anti-CD22 CAR T cells and those who received bispecific anti-CD19/22 CAR T cells. Manufacturing methods were consistent within each trial but differed between the two trials, allowing for exploration of cryopreservation within different manufacturing platforms. Among 40 patients who received anti-CD22 CAR T cells (21 cryopreserved cells and 19 fresh), there were no differences in in vivo expansion, persistence, incidence of toxicities, or disease response between groups with cryopreserved and fresh CAR T cells. Among 19 patients who received anti-CD19/22 CAR T cells (11 cryopreserved and 8 fresh), patients with cryopreserved cells had similar expansion, toxicity incidence, and disease response, with decreased CAR T cell persistence. Overall, our data demonstrate efficacy of cryopreserved CAR T cells as comparable to fresh infusions, supporting cryopreservation, which will be crucial for advancing the field of cell therapy.

Monocyte and Macrophage Function Diversity

In the last decade, there has been a tremendous revival of interest in monocyte and macrophages [...]