Loss of T cell responses following long-term cryopreservation

Pros and Cons of Cryopreserving Allogeneic Stem Cell Products

The COVID-19 pandemic has precipitously changed the practice of transplanting fresh allografts. The safety measures adopted during the pandemic prompted the near-universal graft cryopreservation. However, the influence of cryopreserving allogeneic grafts on long-term transplant outcomes has emerged only in the most recent literature. In this review, the basic principles of cell cryopreservation are revised and the effects of cryopreservation on the different graft components are carefully reexamined. Finally, a literature revision on studies comparing transplant outcomes in patients receiving cryopreserved and fresh grafts is illustrated.

Post-thaw application of ROCK-inhibitors increases cryopreserved T-cell yield

Emerging cell-based therapies such as CAR-T (Chimeric Antigen Receptor T) cells require cryopreservation to store and deliver intact and viable cells. Conventional cryopreservation formulations use DMSO to mitigate cold-induced damage, but do not address all the biochemical damage mechanisms induced by cold stress, such as programmed cell death (apoptosis). Rho-associated protein kinases (ROCK) are a key component of apoptosis, and their activation contributes to apoptotic blebbing. Here we demonstrate that the ROCK inhibitor fasudil hydrochloride, when supplemented into the thawing medium of T-cells increases the overall yield of healthy cells. Cell yield was highest using 5 or 10% DMSO cryopreservation solutions, with lower DMSO concentrations (2.5%) leading to significant physical damage to the cells. After optimisation, the post-thaw yield of T-cells increased by approximately 20% using this inhibitor, a significant increase in the context of a therapy. Flow cytometry analysis did not show a significant reduction in the relative percentage of cell populations undergoing apoptosis, but there was a small reduction in the 8 hours following thawing. Fasudil also led to a reduction in reactive oxygen species. Addition of fasudil into the cryopreservation solution, followed by dilution (rather than washing) upon thaw also gave a 20% increase in cell yield, demonstrating how this could be deployed in a cell-therapy context, without needing to change clinical thawing routines. Overall, this shows that modulation of post-thaw biochemical pathways which lead to apoptosis (or other degradative pathways) can be effectively targeted as a strategy to increase T-cell yield and function post-thaw.

Different Impacts of Cryopreservation in Endothelial and Epithelial Ovarian Cells

The aim of our laboratory-based study was to investigate the extent of delayed-onset cell death after cryopreservation in endothelial and epithelial cell lines of ovarian origin. We found differences in percentages of vital cells directly after warming and after cultivation for 48 to 72 h. A granulosa cell line of endothelial origin (KGN) and an epithelial cell line (OvCar-3) were used. In both DMSO-containing and DMSO-free protocols, significant differences in vitality rates between the different cell lines when using open and closed vitrification could be shown (DMSO-containing: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.001; DMSO-free: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.031). Furthermore, there was a marked difference in the percentage of vital cells immediately after warming and after cultivation for 48 to 72 h; whereas the KGN cell line showed a loss of cell viability of 41% using a DMSO-containing protocol, the OvCar-3 cell loss was only 11% after cultivation. Using a DMSO-free protocol, the percentages of late-onset cell death were 77% and 48% for KGN and OvCar-3 cells, respectively. Our data support the hypothesis that cryopreservation-induced damage is cell type and cryoprotective agent dependent.

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.

HLA alleles, disease severity, and age associate with T-cell responses following infection with SARS-CoV-2

Memory T-cell responses following SARS-CoV-2 infection have been extensively investigated but many studies have been small with a limited range of disease severity. Here we analyze SARS-CoV-2 reactive T-cell responses in 768 convalescent SARS-CoV-2-infected (cases) and 500 uninfected (controls) Icelanders. The T-cell responses are stable three to eight months after SARS-CoV-2 infection, irrespective of disease severity and even those with the mildest symptoms induce broad and persistent T-cell responses. Robust CD4⁺ T-cell responses are detected against all measured proteins (M, N, S and S1) while the N protein induces strongest CD8⁺ T-cell responses. CD4⁺ T-cell responses correlate with disease severity, humoral responses and age, whereas CD8⁺ T-cell responses correlate with age and functional antibodies. Further, CD8⁺ T-cell responses associate with several class I HLA alleles. Our results, provide new insight into HLA restriction of CD8⁺ T-cell immunity and other factors contributing to heterogeneity of T-cell responses following SARS-CoV-2 infection.

A study of 768 convalescent SARS CoV-2-infected and 500 uninfected Icelanders reveals broad and stable T-cell responses 3-8 months from infection. HLA alleles, disease severity, and age contribute to the heterogeneity of cellular immunity.

Single-Mode Electromagnetic Resonance Rewarming for the Cryopreservation of Samples with Large Volumes: A Numerical and Experimental Study

Rapid and uniform rewarming has been proved to be beneficial, and sometimes indispensable for the survival of cryopreserved biomaterials, inhibiting ice-recrystallization-devitrification and thermal stress-induced fracture (especially in large samples). To date, the convective water bath remains the gold standard rewarming method for small samples in the clinical settings, but it failed in the large samples (e.g., cryopreserved tissues and organs) due to damage caused by the slow and nonuniform heating. A single-mode electromagnetic resonance (SMER) system was developed to achieve ultrafast and uniform rewarming for large samples. In this study, we investigated the heating effects of the SMER system and compared the heating performance with water bath and air warming. A numerical model was established to further analyze the temperature change and distribution at different time points during the rewarming process. Overall, the SMER system achieved rapid heating at 331.63 ± 8.59°C min^-1 while limiting the maximum thermal gradient to <9°C min^-1, significantly better than the other two warming methods. The experimental results were highly consistent, indicating SMER is a promising rewarming technology for the successful cryopreservation of large biosamples.

Rules of thumb to obtain, isolate, and preserve porcine peripheral blood mononuclear cells

One of the most used biospecimens in immunology are peripheral blood mononuclear cells (PBMC). PBMC are particularly useful when evaluating immunity through responses of circulating B- and T-cells, during an infection, or after a vaccination. While several reviews and research papers have been published aiming to point out critical steps when sampling, isolating, and cryopreserving human PBMC -or even analyzing any parameter before sampling that could impair the immune assays' outcomes-, there are almost no publications in swine research dealing with these topics. As it has been demonstrated, several factors, such as stress, circadian rhythmicity, or the anticoagulant used have serious negative impact, not only on the separation performance of PBMC, but also on the ulterior immune assays. The present review aims to discuss studies carried out in humans that could shed some light for swine research. When possible, publications in pigs are also discussed. The main goal of the review is to encourage swine researchers to standardize protocols to obtain, manage and preserve porcine PBMC, as well as to minimize, or at least to consider, the bias that some parameters might induce in their studies before, during and after isolating PBMC.

Comprehensive evaluation of the effects of long-term cryopreservation on peripheral blood mononuclear cells using flow cytometry

Human peripheral blood mononuclear cells (PBMCs) originate from hematopoietic stem cells in the bone marrow, which mainly includes lymphocytes (T cells, B cells, and natural killer cells) and monocytes. Cryopreserved PBMCs providing biobank resources are crucial for clinical application or scientific research. Here, we used flow cytometry to explore the influence of long-term cryopreservation on the quality of PBMCs with the aim of providing important evidence for the effective utilization of biobank resources. The PBMCs were isolated from the peripheral blood, which was collected from volunteers in the hospital. After long-term cryopreservation in liquid nitrogen, we analyzed the changes in cell numbers, viability, and multiple subtypes of PBMCs and studied the apoptosis, proliferation, activation, function, and status of T cells in comparison with freshly isolated PBMCs by flow cytometry, and then further tracked the effects of long-term cryopreservation on the same sample. Although the different cell types in the PBMCs dynamically changed compared with those in the freshly isolated samples, PBMC recovery and viability remained stable after long-term cryopreservation, and the number of most innate immune cells (e.g., monocytes and B cells) was significantly reduced compared to that of the freshly isolated PBMCs or long-term cryopreserved PBMCs; more importantly, the proportion of T cell subtypes, apoptosis, proliferation, and functional T cells, except for Tregs, were not affected by long-term cryopreservation. However, the proportions of activated T, naïve T, central memory T, effector T, and effector memory T cells dynamically changed after long-term cryopreservation. This article provides important evidence for the effective utilization of biobank resources. Long-term cryopreserved PBMCs can be partly used as biological resources for clinical research or basic studies, but the effect of cryopreservation on PBMCs should be considered when selecting cell samples, especially in research relating to activating or inhibiting function.

A cytotoxic-skewed immune set point predicts low neutralizing antibody levels after Zika virus infection

Although generating high neutralizing antibody levels is a key component of protective immunity after acute viral infection or vaccination, little is known about why some individuals generate high versus low neutralizing antibody titers. Here, we leverage the high-dimensional single-cell profiling capacity of mass cytometry to characterize the longitudinal cellular immune response to Zika virus (ZIKV) infection in viremic blood donors in Puerto Rico. During acute ZIKV infection, we identify widely coordinated responses across innate and adaptive immune cell lineages. High frequencies of multiple activated cell types during acute infection are associated with high titers of ZIKV neutralizing antibodies 6 months post-infection, while stable immune features suggesting a cytotoxic-skewed immune set point are associated with low titers. Our study offers insight into the coordination of immune responses and identifies candidate cellular biomarkers that may offer predictive value in vaccine efficacy trials aimed at inducing high levels of antiviral neutralizing antibodies.

Alignment of practices for data harmonization across multi-center cell therapy trials: a report from the Consortium for Pediatric Cellular Immunotherapy

Immune effector cell (IEC) therapies have revolutionized our approach to relapsed B-cell malignancies, and interest in the investigational use of IECs is rapidly expanding into other diseases. Current challenges in the analysis of IEC therapies include small sample sizes, limited access to clinical trials and a paucity of predictive biomarkers of efficacy and toxicity associated with IEC therapies. Retrospective and prospective multi-center cell therapy trials can assist in overcoming these barriers through harmonization of clinical endpoints and correlative assays for immune monitoring, allowing additional cross-trial analysis to identify biomarkers of failure and success. The Consortium for Pediatric Cellular Immunotherapy (CPCI) offers a unique platform to address the aforementioned challenges by delivering cutting-edge cell and gene therapies for children through multi-center clinical trials. Here the authors discuss some of the important pre-analytic variables, such as biospecimen collection and initial processing procedures, that affect biomarker assays commonly used in IEC trials across participating CPCI sites. The authors review the recent literature and provide data to support recommendations for alignment and standardization of practices that can affect flow cytometry assays measuring immune effector function as well as interpretation of cytokine/chemokine data. The authors also identify critical gaps that often make parallel comparisons between trials difficult or impossible.

The non-contact-based determination of the membrane permeability to water and dimethyl sulfoxide of cells virtually trapped in a self-induced micro-vortex

The cell-membrane permeabilities of a cell type toward water (L_p) and cryoprotective agents (P_s) provide crucial cellular information for achieving optimal cryopreservation in the biobanking industry. In this work, cell membrane permeability was successfully determined via directly visualizing the transient profile of the cell volume change in response to a sudden osmotic gradient instantaneously applied between the intracellular and extracellular environments. A new micro-vortex system was developed to virtually trap the cells of interest in flow-driven hydrodynamic circulation passively formed at the expansion region in a microfluidic channel, where trapped cells remain in suspension and flow with the streamline of the localized vortex, involving no physical contact between cells and the device structure; furthermore, this supports a pragmatic assumption of 100% sphericity and allows for the calculation of the active surface area of the cell membrane for estimating the actual cell volume from two-dimensional images. For an acute T-cell lymphoma cell line (Jurkat), moderately higher values (L_p = 0.34 μm min^-1 atm^-1 for a binary system, and L_p = 0.16 μm min^-1 atm^-1 and P_s = 0.55 × 10^-3 cm min^-1 for a ternary system) were measured than those obtained from prior methods utilizing contact-based cell-trapping techniques, manifesting the influence of physical contact on accuracy during the determination of cell membrane permeability.

Impact of Cryopreservation on Viability, Phenotype, and Functionality of Porcine PBMC

The use of frozen peripheral blood mononuclear cells (PBMC) is common in immunological studies. The impact of freezing PBMC has been assessed using human and mice cells, but little information is available regarding domestic animals. In the present study, the phenotype and functionality of frozen porcine PBMC were examined. In a preliminary experiment, three freezing media: fetal bovine serum plus 10% dimethyl sulfoxide, PSC cryopreservation kit, and Cryostor CS10, were compared regarding the preservation of cell viability and the response of PBMC to mitogens after thawing. After being stored one month in liquid nitrogen, cell viability was above 89% for all freezing media. The ELISPOT IFN-gamma (IFN-γ) results in response to PHA and of IgG ELISPOT in response to R848+IL-2 were similar to those obtained using fresh PBMC. In the second set of experiments, PBMC were obtained from five pigs vaccinated against Porcine reproductive and respiratory syndrome virus (PRRSV) and then frozen using Cryostor CS10. Recovered cells were phenotyped by flow cytometry using anti-CD3, CD4, CD8, and CD21 antibodies and were used to assess the PRRSV-specific responses in a proliferation experiment, an IFN-γ ELISPOT, and an IgG ELISPOT, and compared to the results obtained with fresh cells. The antigen-specific responses of frozen cells were significantly (p<0.05) impaired in the proliferation assay, particularly for CD4/CD8 double-positive T-cells and for CD21+ cells. Freezing resulted in decreased proliferation when Con A, but not PHA, was used. In ELISPOT, cryopreservation resulted in a decreased frequency of IFN-γ-secreting cells in response to PRRSV (p<0.05) but the response to PHA was not affected. No differences were observed in the IgG ELISPOT after polyclonal activation. Taken together, cryopreservation of porcine PBMC had a significant impact on the magnitude of recall antigen responses and therefore, it may affect the response of effector/memory cells but seems not to have a major impact on naïve T-cells. These results may help to the better use of frozen porcine PBMC, and to the interpretation of the results obtained from them.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

Characterization of humoral and SARS-CoV-2 specific T cell responses in people living with HIV

There is an urgent need to understand the nature of immune responses against SARS-CoV-2, to inform risk-mitigation strategies for people living with HIV (PLWH). Here we show that the majority of PLWH with ART suppressed HIV viral load, mount a detectable adaptive immune response to SARS-CoV-2. Humoral and SARS-CoV-2-specific T cell responses are comparable between HIV-positive and negative subjects and persist 5-7 months following predominately mild COVID-19 disease. T cell responses against Spike, Membrane and Nucleoprotein are the most prominent, with SARS-CoV-2-specific CD4 T cells outnumbering CD8 T cells. We further show that the overall magnitude of SARS-CoV-2-specific T cell responses relates to the size of the naive CD4 T cell pool and the CD4:CD8 ratio in PLWH. These findings suggest that inadequate immune reconstitution on ART, could hinder immune responses to SARS-CoV-2 with implications for the individual management and vaccine effectiveness in PLWH.

Advanced biomaterials in cell preservation: Hypothermic preservation and cryopreservation

Cell-based medicine has made great advances in clinical diagnosis and therapy for various refractory diseases, inducing a growing demand for cell preservation as support technology. However, the bottleneck problems in cell preservation include low efficiency and poor biocompatibility of traditional protectants. In this review, cell preservation technologies are categorized according to storage conditions: hypothermic preservation at 1 °C~35 °C to maintain short-term cell viability that is useful in cell diagnosis and transport, while cryopreservation at -196 °C~-80 °C to maintain long-term cell viability that provides opportunities for therapeutic cell product storage. Firstly, the background and developmental history of the protectants used in the two preservation technologies are briefly introduced. Secondly, the progress in different cellular protection mechanisms for advanced biomaterials are discussed in two preservation technologies. In hypothermic preservation, the hypothermia-induced and extracellular matrix-loss injuries to cells are comprehensively summarized, as well as the recent biomaterials dependent on regulation of cellular ATP level, stabilization of cellular membrane, balance of antioxidant defense system, and supply of mimetic ECM to prolong cell longevity are provided. In cryopreservation, cellular injuries and advanced biomaterials that can protect cells from osmotic or ice injury, and alleviate oxidative stress to allow cell survival are concluded. Last, an insight into the perspectives and challenges of this technology is provided. We envision advanced biocompatible materials for highly efficient cell preservation as critical in future developments and trends to support cell-based medicine. STATEMENT OF SIGNIFICANCE: Cell preservation technologies present a critical role in cell-based applications, and more efficient biocompatible protectants are highly required. This review categorizes cell preservation technologies into hypothermic preservation and cryopreservation according to their storage conditions, and comprehensively reviews the recently advanced biomaterials related. The background, development, and cellular protective mechanisms of these two preservation technologies are respectively introduced and summarized. Moreover, the differences, connections, individual demands of these two technologies are also provided and discussed.

Cryopreservation of NK and T Cells Without DMSO for Adoptive Cell-Based Immunotherapy

Dimethylsufoxide (DMSO) being universally used as a cryoprotectant in clinical adoptive cell-therapy settings to treat hematological malignancies and solid tumors is a growing concern, largely due to its broad toxicities. Its use has been associated with significant clinical side effects-cardiovascular, neurological, gastrointestinal, and allergic-in patients receiving infusions of cell-therapy products. DMSO has also been associated with altered expression of natural killer (NK) and T-cell markers and their in vivo function, not to mention difficulties in scaling up DMSO-based cryoprotectants, which introduce manufacturing challenges for autologous and allogeneic cellular therapies, including chimeric antigen receptor (CAR)-T and CAR-NK cell therapies. Interest in developing alternatives to DMSO has resulted in the evaluation of a variety of sugars, proteins, polymers, amino acids, and other small molecules and osmolytes as well as modalities to efficiently enable cellular uptake of these cryoprotectants. However, the DMSO-free cryopreservation of NK and T cells remains difficult. They represent heterogeneous cell populations that are sensitive to freezing and thawing. As a result, clinical use of cryopreserved cell-therapy products has not moved past the use of DMSO. Here, we present the state of the art in the development and use of cryopreservation options that do not contain DMSO toward clinical solutions to enable the global deployment of safer adoptively transferred cell-based therapies.

Effect of Warming Process on the Survival of Cryopreserved Human Peripheral Blood Mononuclear Cells

It is well known that the warming process is a critical step in cell cryopreservation, affecting the survival rate of the cryopreserved cells. However, there is a lack of understanding and optimization of the warming process for the cryopreserved human peripheral blood mononuclear cells (PBMCs) that are greatly needed for the cellular/immune therapies worldwide. In this study, the effect of the warming process on cryosurvival of the PBMCs was investigated, resulting in a recommendation of an optimal warming method. In the experiments, all PBMC samples were cooled by a fixed slow cooling process and stored in a liquid nitrogen tank. The frozen samples were then warmed in water baths with stirring at various temperatures, 37°C, 42°C, and 65°C, respectively. After thawing, PBMC's viability as well as phenotypic and functional analyses were performed and evaluated. It was shown that a relatively rapid warming process at 65°C in a water bath with stirring generated a significant improvement of cell viability, recovery, and functionality of the cryopreserved PBMCs. In addition, interferon-γ and interleukin-2 secretion were much higher in PBMCs thawed at 65°C than that in 42°C and 37°C, respectively. This study suggests that a rapid warming process at 65°C in a water bath should be used to replace the current conventional warming approach at 37°C.

A guide to investigating immune responses elicited by whole-sporozoite pre-erythrocytic vaccines against malaria

In the last few decades, considerable efforts have been made toward the development of efficient vaccines against malaria. Whole-sporozoite (Wsp) vaccines, which induce efficient immune responses against the pre-erythrocytic (PE) stages (sporozoites and liver forms) of Plasmodium parasites, the causative agents of malaria, are among the most promising immunization strategies tested until present. Several Wsp PE vaccination approaches are currently under evaluation in the clinic, including radiation- or genetically-attenuated Plasmodium sporozoites, live parasites combined with chemoprophylaxis, or genetically modified rodent Plasmodium parasites. In addition to the assessment of their protective efficacy, clinical trials of Wsp PE vaccine candidates inevitably involve the thorough investigation of the immune responses elicited by vaccination, as well as the identification of correlates of protection. Here, we review the main methodologies employed to dissect the humoral and cellular immune responses observed in the context of Wsp PE vaccine clinical trials and discuss future strategies to further deepen the knowledge generated by these studies, providing a toolbox for the in-depth analysis of vaccine-induced immunogenicity.

Potent ex vivo armed T cells using recombinant bispecific antibodies for adoptive immunotherapy with reduced cytokine release

BACKGROUND

T cell-based immunotherapies using chimeric antigen receptors (CAR) or bispecific antibodies (BsAb) have produced impressive responses in hematological malignancies. However, major hurdles remained, including cytokine release syndrome, neurotoxicity, on-target off-tumor effects, reliance on autologous T cells, and failure in most solid tumors. BsAb armed T cells offer a safe alternative.

METHODS

We generated ex vivo armed T cells (EATs) using IgG-[L]-scFv-platformed BsAb, where the anti-CD3 (huOKT3) scFv was attached to the light chain of a tumor-binding IgG. BsAb density on EAT, in vitro cytotoxicity, cytokine release, in vivo trafficking into tumors, and their antitumor activities were evaluated in multiple cancer cell lines and patient-derived xenograft mouse models. The efficacy of EATs after cryopreservation was studied, and gamma delta (γδ) T cells were investigated as unrelated alternative effector T cells.

RESULTS

The antitumor potency of BsAb armed T cells was substantially improved using the IgG-[L]-scFv BsAb platform. When compared with separate BsAb and T cell injection, EATs released less TNF-α, and infiltrated tumors faster, while achieving robust antitumor responses. The in vivo potency of EAT therapy depended on BsAb dose for arming, EAT cell number per injection, total number of EAT doses, and treatment schedule intensity. The antitumor efficacy of EATs was preserved following cryopreservation, and EATs using γδ T cells were safe and as effective as αβ T cell-EATs.

CONCLUSIONS

EATs exerted potent antitumor activities against a broad spectrum of human cancer targets with remarkable safety. The antitumor potency of EATs depended on BsAb dose, cell number and total dose, and schedule. EATs were equally effective after cryopreservation, and the feasibility of third-party γδ-EATs offered an alternative for autologous T cell sources.

Characterization of humoral and SARS-CoV-2 specific T cell responses in people living with HIV

There is an urgent need to understand the nature of immune responses against SARS-CoV-2, to inform risk-mitigation strategies for people living with HIV (PLWH). We show that the majority of PLWH, controlled on ART, mount a functional adaptive immune response to SARS-CoV-2. Humoral and SARS-CoV-2-specific T cell responses are comparable between HIV-positive and negative subjects and persist 5-7 months following predominately mild COVID-19 disease. T cell responses against Spike, Membrane and Nucleocapsid are the most prominent, with SARS-CoV-2-specific CD4 T cells outnumbering CD8 T cells. We further show that the overall magnitude of SARS-CoV-2-specific T cell responses relates to the size of the naive CD4 T cell pool and the CD4:CD8 ratio in PLWH, in whom disparate antibody and T cell responses are observed. These findings suggest that inadequate immune reconstitution on ART, could hinder immune responses to SARS-CoV-2 with implications for the individual management and vaccine effectiveness in PLWH.

A field method for cryopreservation of whole blood from a finger prick for later analysis with flow cytometry

OBJECTIVES

Flow cytometry is a powerful tool for investigating immune function, allowing for the quantification of leukocytes by subtype. Yet it has not been used extensively for field work due to perishable reagents and the need for immediate analysis of samples. To make flow cytometry more accessible, we devise and evaluate a field protocol for freezing capillary blood.

MATERIALS AND METHODS

We collected finger prick blood samples from 110 volunteers, age 18 to 42. Blood samples were analyzed immediately for 18 cell surface markers. Aliquots of whole blood were frozen in the vapor phase of a liquid nitrogen tank with 10% dimethyl sulfoxide in medium. Samples were analyzed on a Guava EasyCyte HT flow cytometer after 2, 4, or 14 weeks.

RESULTS

Major lymphocyte fractions in frozen samples were correlated with fresh values (T-cells: r = 0.82; Natural Killer [NK] cells: r = 0.64; CD4: r = 0.67; CD8: r = 0.82; Naïve CD4: r = 0.73, Naïve CD8: r = 0.71; B-cells: r = 0.73; all p < 0.001), and mean values were similar to those from fresh samples. However, correlations for smaller subsets of CD4 and B cells were generally poor. Some differences resulted from changes in non-specific binding for some antibody-conjugate pairs. Cryopreservation also resulted in a reduction in granulocytes more than lymphocytes.

DISCUSSION

Our results suggest that antibody/fluorochrome combinations should be validated before use on frozen samples, and that functional changes in cells may affect some cell markers. However, this simple freezing protocol utilizing finger pricks, whole blood, and a liquid nitrogen shipping tank is viable for obtaining samples for flow cytometry under field conditions.

Characterization of humoral and SARS-CoV-2 specific T cell responses in people living with HIV

There is an urgent need to understand the nature of immune responses generated against SARS-CoV-2, to better inform risk-mitigation strategies for people living with HIV (PLWH). Although not all PLWH are considered immunosuppressed, residual cellular immune deficiency and ongoing inflammation could influence COVID-19 disease severity, the evolution and durability of protective memory responses. Here, we performed an integrated analysis, characterizing the nature, breadth and magnitude of SARS-CoV-2-specific immune responses in PLWH, controlled on ART, and HIV negative subjects. Both groups were in the convalescent phase of predominately mild COVID-19 disease. The majority of PLWH mounted SARS-CoV-2 Spike- and Nucleoprotein-specific antibodies with neutralizing activity and SARS-CoV-2-specific T cell responses, as measured by ELISpot, at levels comparable to HIV negative subjects. T cell responses against Spike, Membrane and Nucleocapsid were the most prominent, with SARS-CoV-2-specific CD4 T cells outnumbering CD8 T cells. Notably, the overall magnitude of SARS-CoV-2-specific T cell responses related to the size of the naive CD4 T cell pool and the CD4:CD8 ratio in PLWH, in whom disparate antibody and T cell responses were observed. Both humoral and cellular responses to SARS-CoV-2 were detected at 5-7 months post-infection, providing evidence of medium-term durability of responses irrespective of HIV serostatus. Incomplete immune reconstitution on ART and a low CD4:CD8 ratio could, however, hamper the development of immunity to SARS-CoV-2 and serve as a useful tool for risk stratification of PLWH. These findings have implications for the individual management and potential effectiveness of vaccination against SARS-CoV-2 in PLWH.

TCF-1 regulates HIV-specific CD8+ T cell expansion capacity

Although many HIV cure strategies seek to expand HIV-specific CD8+ T cells to control the virus, all are likely to fail if cellular exhaustion is not prevented. A loss in stem-like memory properties (i.e., the ability to proliferate and generate secondary effector cells) is a key feature of exhaustion; little is known, however, about how these properties are regulated in human virus-specific CD8+ T cells. We found that virus-specific CD8+ T cells from humans and nonhuman primates naturally controlling HIV/SIV infection express more of the transcription factor TCF-1 than noncontrollers. HIV-specific CD8+ T cell TCF-1 expression correlated with memory marker expression and expansion capacity and declined with antigenic stimulation. CRISPR-Cas9 editing of TCF-1 in human primary T cells demonstrated a direct role in regulating expansion capacity. Collectively, these data suggest that TCF-1 contributes to the regulation of the stem-like memory property of secondary expansion capacity of HIV-specific CD8+ T cells, and they provide a rationale for exploring the enhancement of this pathway in T cell-based therapeutic strategies for HIV.

An easy and reliable whole blood freezing method for flow cytometry immuno-phenotyping and functional analyses

BACKGROUND

Immune profiling by flow cytometry is not always possible on fresh blood samples due to time and/or transport constraints. Furthermore, the cryopreservation of peripheral blood mononuclear cells (PBMC) requires on-site specialized lab facilities, thus severely restricting the extent to which blood immune monitoring can be applied to multicenter clinical studies. These major limitations can be addressed through the development of simplified whole blood freezing methods.

METHODS

In this report, we describe an optimized easy protocol for rapid whole blood freezing with the CryoStor® CS10 solution. Using flow cytometry, we compared cellular viability and composition on cryopreserved whole blood samples to matched fresh blood, as well as fresh and frozen PBMC.

RESULTS

Though partial loss of neutrophils was observed, leucocyte viability was routinely >75% and we verified the preservation of viable T cells, NK cells, monocytes, dendritic cells, and eosinophils in frequencies similar to those observed in fresh samples. A moderate decrease in B cell frequencies was observed. Importantly, we validated the possibility to analyze major intracellular markers, such as FOXP3 and Helios in regulatory T cells. Finally, we demonstrated good functional preservation of CS10-cryopreserved cells through the analysis of intracellular cytokine production in ex vivo stimulated T cells (IFNg, IL-4, IL-17A,) and monocytes (IL-1b, IL-6, TNFa).

CONCLUSIONS

In conclusion, our protocol provides a robust method to apply reliable immune monitoring studies to cryopreserved whole blood samples, hence offering new important opportunities for the design of future multicenter clinical trials.

Cryopreservation of peripheral blood mononuclear cells for use in proliferation assays: First step towards potency assays

Investigational cell-based therapeutics are rapidly heading towards pivotal clinical trials. The premise is that the scientific rationale is well defined, and that product quality reflects exactly this. In vitro potency assays are necessary tools for evaluating cell products, and with potency assays comes high demands for standardization and reproducibility of the methods involved. For demonstrating principles of cell therapeutics for allogeneic use or with claimed immunosuppressive efficacies, assays involving peripheral blood mononuclear cells (PBMC) are critical. Establishment of a cryopreserved bank of PBMC favors standardization, as it allows repeated use of a single donor and simultaneous testing of several donors. The first step to fulfil such potential is to ensure optimum conditions for preservation of PBMC function, and secondly to design assays which heightens the reproducibility. Emphasis should be put on application of the assay. The objective of the present study was to establish a methodological foundation for cell therapeutics to be tested, and several aspects were factored in, including cell concentrations and partial changes of medium. PBMC were isolated and cryopreserved in six formulations of cryoprotective medium consisting of fetal bovine serum (90%, 60%, and 30%) in combination with dimethyl sulfoxide (10% or 5%). The proliferative capacity of the cryopreserved cells was assayed by labeling with carboxyfluorescein succinimidyl ester and stimulation by phytohemagglutinin or in mixed lymphocyte reactions, analyzed by flow cytometry. To counter an eventual lag phase post thaw, the assays were designed to include two durations and to explore the possibility of reducing cell numbers, two cell concentrations. Qualitative and quantitative aspects of the staining were affected by formulation as well as design, stressing the importance of basic optimization for assay development. We conclude that the established methods allow for optimized preservation of function and will serve as a platform for further development of robust functional assays.

Robust T Cell Immunity in Convalescent Individuals with Asymptomatic or Mild COVID-19

SARS-CoV-2-specific memory T cells will likely prove critical for long-term immune protection against COVID-19. Here, we systematically mapped the functional and phenotypic landscape of SARS-CoV-2-specific T cell responses in unexposed individuals, exposed family members, and individuals with acute or convalescent COVID-19. Acute-phase SARS-CoV-2-specific T cells displayed a highly activated cytotoxic phenotype that correlated with various clinical markers of disease severity, whereas convalescent-phase SARS-CoV-2-specific T cells were polyfunctional and displayed a stem-like memory phenotype. Importantly, SARS-CoV-2-specific T cells were detectable in antibody-seronegative exposed family members and convalescent individuals with a history of asymptomatic and mild COVID-19. Our collective dataset shows that SARS-CoV-2 elicits broadly directed and functionally replete memory T cell responses, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19.

Cryopreservation of peripheral blood mononuclear cells using uncontrolled rate freezing

Peripheral blood mononuclear cells are widely used as source material for anticancer immunotherapies. The conventional cryopreservation method for peripheral blood mononuclear cells is time-consuming and expansive, which involves controlled rate freezing followed by storage in liquid nitrogen. Instead, the convenient uncontrolled rate freezing cryopreservation method had been reported successfully in peripheral blood hematopoietic stem cells and peripheral blood progenitor cells. Therefore, we hypothesized that uncontrolled rate freezing cooling method maybe also applied to peripheral blood mononuclear cells cryopreservation. In this study, we evaluated the performance of uncontrolled rate freezing and controlled rate freezing cooling methods through cell recovery rate, viability, differentiation potential into cytokine-induced killer cells and the cellular properties of the cultured cytokine-induced killer cells. The results showed similar post-thaw viability and recovery rate in both controlled rate freezing and uncontrolled rate freezing cryopreserved peripheral blood mononuclear cells. Importantly, the uncontrolled rate freezing cryopreserved peripheral blood mononuclear cells exhibited higher growth ratio and earlier cell clustering during ex-vivo cytokine-induced killer cell culture than the controlled rate freezing ones. These two groups of expanded cytokine-induced killer cells also exhibited similar effector cell subset ratio and tumoricidal activity. In general, the performance of cryopreserved peripheral blood mononuclear cells using uncontrolled rate freezing cooling method, with the commercial cryoprotective agent CellBanker 2, was equal or better than the controlled rate freezing method. Our study implied that the combined use of cryoprotective agent CellBanker 2 and uncontrolled rate freezing could be a convenient cryopreservation method for peripheral blood mononuclear cells.

Evaluation of T-activated proteins as recall antigens to monitor Epstein-Barr virus and human cytomegalovirus-specific T cells in a clinical trial setting

BACKGROUND

Pools of overlapping synthetic peptides are routinely used for ex vivo monitoring of antigen-specific T-cell responses. However, it is rather unlikely that these peptides match those resulting from naturally processed antigens. T-activated proteins have been described as immunogenic and more natural stimulants, since they have to pass through antigen processing and comprise activation of all clinically relevant effector cell populations.

METHODS

We performed comparative analysis of numbers and cytokine expression pattern of CD4 and CD8 T cells after stimulation with recombinant, urea-formulated T-activated EBV-BZLF1, -EBNA3A, and HCMV-IE1, and -pp65 proteins or corresponding overlapping peptide pools. Freshly isolated and cryopreserved PBMC of 30 EBV- and 19 HCMV-seropositive and seven EBV- and HCMV-seronegative subjects were stimulated ex vivo and analysed for IFN-γ, TNF and IL-2 production by flow cytometry-based intracellular cytokine staining.

RESULTS

T-activated proteins showed a high specificity of 100% (EBV-BZLF1, HCMV-IE1, and -pp65) and 86% (EBV-EBNA3A), and a high T-cell stimulatory capacity of 73-95% and 67-95% using freshly isolated and cryopreserved PBMC, respectively. The overall CD4 T-cell response rates in both cohorts were comparable after stimulation with either T-activated protein or peptide pools with the exception of lower numbers of CD8 T cells detected after stimulation with T-activated EBV-EBNA3A- (p = 0.038) and HCMV-pp65- (p = 0.0006). Overall, the number of detectable antigen-specific T cells varied strongly between individuals. Cytokine expression patterns in response to T-activated protein and peptide pool-based stimulation were similar for CD4, but significantly different for CD8 T-cell responses.

CONCLUSION

EBV and HCMV-derived T-activated proteins represent innovative, highly specific recall antigens suitable for use in immunological endpoint assays to evaluate success or failure in immunotherapy clinical trials (e.g. to assess the risk of EBV and/or HCMV reactivation after allogenic hematopoietic stem cell transplantation). T-activated proteins could be of particular importance, if an impaired antigen processing (e.g. in a post-transplant setting) must be taken into account.

Comparison of allogenic stem cell transplantations performed with frozen or fresh stem cell products with regard to GVHD and mortality

PURPOSE

Stem cells are collected from donors and infused to the recipient in allogenic peripheral stem cell transplantations. The use of frozen stem cells can promote donor compatibility, and overcoming possible problems due to insufficient stem cell mobilization will also be easier. Nevertheless, studies about the use of frozen peripheral stem cells in allogenic transplantation are extremely rare. In this study, we aimed to compare the clinical outcomes of allogenic stem cell transplants from frozen or fresh stem cell products.

MATERIALS AND METHODS

This retrospective analysis was conducted between April 2004 and September 2018 in the bone marrow transplantation unit of Ankara Numune Training and Research Hospital. Clinical data of patients who received allogenic peripheral stem cell transplantations from fully matched sibling donors were compared for 42 fresh and 30 frozen stem cell transplants.

RESULTS

While the platelet engraftment period, febrile neutropenia period, hospitalization period, and 100-day mortality rates did not show any differences, the neutrophil engraftment period was longer in the frozen group (mean: 14 days vs. 16 days, p = 0.006). Acute and chronic graftversus-host disease (GVHD) rates were similar in both groups; however, the rate of grade 3 or4 chronic liver GVHD was slightly higher in transplants performed with fresh stem cells compared to the frozen group (p = 0.046). Overall survival was similar between the groups (p = 0.700).

CONCLUSION

The use of frozen peripheral stem cells in allogenic stem cell transplantation may be a reasonable option that can be applied without causing a significant change in clinical results.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Some Aspects of CD8+ T-Cell Exhaustion Are Associated With Altered T-Cell Mitochondrial Features and ROS Content in HIV Infection

BACKGROUND

Reversing or preventing T-cell exhaustion is an important treatment goal in the context of HIV disease; however, the mechanisms that regulate HIV-specific CD8 T-cell exhaustion are incompletely understood. Since mitochondrial mass (MM), mitochondrial membrane potential (MMP), and cellular reactive oxygen species (ROS) content are altered in exhausted CD8 T cells in other settings, we hypothesized that similar lesions may arise in HIV infection.

METHODS

We sampled cryopreserved peripheral blood mononuclear cells from HIV-uninfected (n = 10) and HIV-infected participants with varying levels and mechanisms of viral control: viremic (VL > 2000 copies/mL; n = 8) or aviremic (VL < 40 copies/mL) due to antiretroviral therapy (n = 11) or natural control (n = 9). We characterized the MM, MMP, and ROS content of bulk CD8 T cells and MHC class I tetramer+ HIV-specific CD8 T cells by flow cytometry.

RESULTS

We observed higher MM, MMP, and ROS content across bulk effector-memory CD8 T-cell subsets in HIV-infected compared with HIV-uninfected participants. Among HIV-specific CD8 T cells, these features did not vary by the extent or mechanism of viral control but were significantly altered in cells displaying characteristics associated with exhaustion (eg, high PD-1 expression, low CD127 expression, and impaired proliferative capacity).

CONCLUSIONS

While we did not find that control of HIV replication in vivo correlates with the CD8 T-cell MM, MMP, or ROS content, we did find that some features of CD8 T-cell exhaustion are associated with alterations in mitochondrial state. Our findings support further studies to probe the relationship between mitochondrial dynamics and CD8 T-cell functionality in HIV infection.

Efficient short-term expansion of human peripheral blood regulatory T cells for co-culture suppression assay

Regulatory T cells (Tregs) are a small population of CD4+ lymphocytes and play a key role as suppressors of the immune system, a role that can be identified by employing a co-culture suppression assay. Conventional protocol requires a long period of in vitro expansion of Treg numbers; hence, this study describes an establishment of a co-culture suppression assay using a short-term expansion of peripheral blood (PB) Tregs and autologous T cells (Tconvs) IL-2-pre-cultured in parallel for the same length of time, thereby obviating the need of freeze/thawed autologous Tconvs. Tregs and Tconvs were isolated from PB mononuclear cells employing magnetic bead-aided depletion of CD8+ cells followed by cell sorting of CD4+ CD25high+CD127low- (Treg) and CD4+ CD25-CD127+ (Tconv) cell populations. Following a 3-day co-cultivation period under optimized conditions, Treg suppression activity was monitored by comparing using flow cytometry the number of carboxyfluorescein succinimidyl ester-labeled Tconvs to that of Treg-minus control. The assay allowed significant differentiation between Treg suppression activity of patients with active rheumatoid arthritis and those in remission. This method should be more convenient and time-saving than the conventional Treg suppression assay in current use.

Cryopreservation of primary B cells minimally influences their signaling responses

Phospho flow is a powerful approach to detect cell signaling aberrations, identify biomarkers and assess pharmacodynamics, and can be performed using cryopreserved samples. The effects of cryopreservation on signaling responses and the reproducibility of phospho flow measurements are however unknown in many cell systems. Here, B lymphocytes were isolated from healthy donors and patients with the B cell malignancy chronic lymphocytic leukemia and analyzed by phospho flow using phospho-specific antibodies targeting 20 different protein epitopes. Cells were analyzed both at basal conditions and after activation of cluster of differentiation 40 (CD40) or the B cell receptor. Pharmacodynamics of the novel pathway inhibitor ibrutinib was also assessed. At all conditions, fresh cells were compared to cryopreserved cells. Minimal variation between fresh and frozen samples was detected. Reproducibility was tested by running samples from the same donors in different experiments. The results demonstrate reproducibility across different phospho flow runs and support the use of cryopreserved samples in future phospho flow studies of B lymphocytes.

Effects of cryopreservation on chimeric antigen receptor T cell functions

Chimeric antigen receptor T (CART) cell therapy has emerged as a potentially curative "drug" for cancer treatment. Cryopreservation of CART cells is necessary for their clinical application. Systematic studies on the effects of cryopreservation on the antitumor function of CART cells are lacking. Therefore, we compared the phenotypes and functions of CART cells that were cryopreserved during ex vivo expansion with those of freshly isolated populations. T cells expressing an anti-B-cell-maturation-antigen (BCMA) chimeric antigen receptor (CAR) were expanded in vitro for 10 days and then cryopreserved. After one month, the cells were resuscitated, and their transduction rates, apoptosis rates and cell subsets were examined via flow cytometry. The results indicated no significant changes in transduction rates or cell subsets, and the survival rate of the resuscitated cells was approximately 90% Furthermore, similar tumoricidal effects and degranulation functions of the resuscitated cells compared with normally cultured cells were verified by calcein release and CD107a assays. A NOD/SCID mouse model was used to estimate the differences in the in vivo antitumor effects of the cryopreserved and normally cultured T cells, but no significant differences were observed. Following co-culture with several target cell types, the cytokines released by the cryopreserved and normally cultured T cells were measured via enzyme-linked immunosorbent assays (ELISAs). The results revealed that the release of interleukin-2 (IL-2), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) was significantly decreased. These data demonstrated that with the exception of a decrease in cytokine release, the cryopreserved CART cells retained their antitumor functions.

Susceptibility of A. fumigatus-specific T-cell assays to pre-analytic blood storage and PBMC cryopreservation greatly depends on readout platform and analytes

Mould-specific T cells detectable by flow cytometry or ELISPOT were proposed as a novel biomarker in invasive aspergillosis. To define protocols facilitating sample shipment and longitudinal analysis, this study evaluated the susceptibility of different functional assays for A. fumigatus-specific T-cell quantification and characterisation to pre-analytic delays. PBMCs from 6 healthy donors were analysed after immediate isolation, after 6 hours whole blood storage or after cryopreservation using 3 different common media. Functional responses to A. fumigatus lysate stimulation were comparatively assessed by flow cytometry, ELISPOT and 14-plex cytokine assay. After 6 hours pre-analytic storage, all functional assays showed reduced detection rates, higher coefficients of variation (CV) and widely varying individual recovery indices of specific T-cell response. While cryopreservation resulted in sufficient yields and largely unaltered cellular composition, outcomes of functional readouts significantly differed from freshly processed samples. For CD154-based flow cytometry, only cryopreservation in RPMI supplemented with autologous serum resulted in satisfactory detection rates and CVs. For ELISPOT and cytokine secretion assays, none of the cryopreservation protocols provided sufficient concordance with immediately processed samples. Even using the same readout platform, individual analytes widely varied in their susceptibility to cryopreservation, highlighting that distinct optimisation is required depending on the downstream assay.

The state of T cells before cryopreservation: Effects on post-thaw proliferation and function

AIM

We aim to assess the effect of the state of T cells before cryopreservation on the post-thaw proliferative capacity, phenotype and functional response.

METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from a hepatocellular carcinoma (HCC) patient, and the T cells were frozen during cell culture according to our experimental design. After a period of re-culture, the proliferative capacity of the cryopreserved cells, the expression of T cell surface markers and the secretion of IFN-γ and IL-10 were assayed.

RESULTS

There was >90% cell viability after thaw in every group. Lymphocytes cryopreserved at day 4, 8 or 12 during the cell culture were allowed to recover for 24 h, whereas lymphocytes cryopreserved while freshly isolated were allowed to recover for 72 h. After the period of re-culture, cryopreservation at day 4, 8 or 12 during T cell culture was not found to alter the T cell subpopulation. The proportions of NKT and Treg cells were unchanged when cells were cryopreserved at day 12 during T cell culture. IFN-γ secretion was not impacted by cryopreservation, and IL-10 secretion was significantly decreased when cells were cryopreserved at day 8 or 12 during T cell culture.

CONCLUSION

The state of T cells before cryopreservation has effects on the post-thaw proliferation capacity, the phenotype and the secretion of IFN-γ and IL-10. Cryopreservation of lymphocytes at day 8 or 12 during the cell culture may be the best choice for T cell immunotherapy.

Cryopreservation-related loss of antigen-specific IFNγ producing CD4+ T-cells can skew immunogenicity data in vaccine trials: Lessons from a malaria vaccine trial substudy

Ex vivo functional immunoassays such as ELISpot and intracellular cytokine staining (ICS) by flow cytometry are crucial tools in vaccine development both in the identification of novel immunogenic targets and in the immunological assessment of samples from clinical trials. Cryopreservation and subsequent thawing of PBMCs via validated processes has become a mainstay of clinical trials due to processing restrictions inherent in the disparate location and capacity of trial centres, and also in the need to standardize biological assays at central testing facilities. Logistical and financial requirement to batch process samples from multiple study timepoints are also key. We used ELISpot and ICS assays to assess antigen-specific immunogenicity in blood samples taken from subjects enrolled in a phase II malaria heterologous prime-boost vaccine trial and showed that the freeze thaw process can result in a 3–5-fold reduction of malaria antigen-specific IFNγ-producing CD3⁺CD4⁺ effector populations from PBMC samples taken post vaccination. We have also demonstrated that peptide responsive CD8⁺ T cells are relatively unaffected, as well as CD4⁺ T cell populations that do not produce IFNγ. These findings contribute to a growing body of data that could be consolidated and synthesised as guidelines for clinical trials with the aim of increasing the efficiency of vaccine development pipelines.

Toward Optimal Cryopreservation and Storage for Achievement of High Cell Recovery and Maintenance of Cell Viability and T Cell Functionality

Cryopreservation of biological materials such as cells, tissues, and organs is a prevailing topic of high importance. It is employed not only in many research fields but also in the clinical area. Cryopreservation is of great importance for reproductive medicine and clinical studies, as well as for the development of vaccines. Peripheral blood mononuclear cells (PBMCs) are commonly used in vaccine research where comparable and reliable results between different research institutions and laboratories are of high importance. Whereas freezing and thawing processes are well studied, controlled, and standardized, storage conditions are often disregarded. To close this gap, we investigated the influence of suboptimal storage conditions during low-temperature storage on PBMC viability, recovery, and T cell functionality. For this purpose, PBMCs were isolated and exposed with help of a robotic system in a low-temperature environment from 0 up to 350 temperature fluctuation cycles in steps of 50 cycles to simulate storage conditions in large biorepositories with sample storage, removal, and sorting functions. After the simulation, the viability, recovery, and T cell functionality were analyzed to determine the number of temperature rises, which ultimately lead to significant cell damage. All studied parameters decreased with increasing number of temperature cycles. Sometimes after as little as only 50 temperature cycles, a significant effect was observed. These results are very important for all fields in which cell cryopreservation is employed, particularly for clinical and multicenter studies wherein the comparability and reproducibility of results play a crucial role. To obtain reliable results and to maintain the quality of the cells, not only the freezing and thawing processes but also the storage conditions should be controlled and standardized, and any deviations should be documented.

Virtual Global Transplant Laboratory Standard Operating Procedures for Blood Collection, PBMC Isolation, and Storage

Research on human immune responses frequently involves the use of peripheral blood mononuclear cells (PBMC) immediately, or at significantly delayed timepoints, after collection. This requires PBMC isolation from whole blood and cryopreservation for some applications. It is important to standardize protocols for blood collection, PBMC isolation, cryopreservation, and thawing that maximize survival and functionality of PBMC at the time of analysis. This resource includes detailed protocols describing blood collection tubes, isolation of PBMC using a density gradient, cryopreservation of PBMC, and thawing of cells as well as preparation for functional assays. For each protocol, we include important considerations, such as timing, storage temperatures, and freezing rate. In addition, we provide alternatives so that researchers can make informed decisions in determining the optimal protocol for their application.

Comparative phenotypical analysis of B cells in fresh and cryopreserved mononuclear cells from blood and tissue of rhesus macaques

Cryopreservation of peripheral blood mononuclear cells (PBMCs) is common for large clinical trials for which phenotypical characterization of lymphocytes is retrospectively performed in specialized core laboratories. It is therefore essential to assess the comparability between fresh and frozen samples. No side-by-side comparison of B and plasma cells of rhesus macaques (RM), which serve as useful models for several human diseases has been conducted until now. Hence, we performed an extensive comparative analysis between fresh and thawed mononuclear cells (MNCs) from blood and various tissues of healthy RM to analyze for the possible effects of cryopreservation on phenotype and functionality. Our data demonstrate that -80°C cryopreservation induces profound changes compared to fresh ex vivo-derived material. Percentages of B cells were stable in PBMCs, but were increased in all organs analyzed. The expression of CD27, a marker for differentiation between naïve and memory B cells, was massively reduced in PBMCs and MNC from organs with the most severe changes observed in cells from bone marrow (BM). Additionally, similar low percentages of CD27(+) memory B cells were detected in PBMCs and BM samples stored in liquid nitrogen. Therefore, cryopreservation is not suitable for the phenotypical and functional characterization of B cells. Further optimization of cryoconservation protocols monitoring the surface expression of CD27, which was identified as a marker for the quality of cryopreserved material of RM, will be essential.

HLA Class-II Associated HIV Polymorphisms Predict Escape from CD4+ T Cell Responses

Antiretroviral therapy, antibody and CD8⁺ T cell-mediated responses targeting human immunodeficiency virus-1 (HIV-1) exert selection pressure on the virus necessitating escape; however, the ability of CD4⁺ T cells to exert selective pressure remains unclear. Using a computational approach on HIV gag/pol/nef sequences and HLA-II allelic data, we identified 29 HLA-II associated HIV sequence polymorphisms or adaptations (HLA-AP) in an African cohort of chronically HIV-infected individuals. Epitopes encompassing the predicted adaptation (AE) or its non-adapted (NAE) version were evaluated for immunogenicity. Using a CD8-depleted IFN-γ ELISpot assay, we determined that the magnitude of CD4⁺ T cell responses to the predicted epitopes in controllers was higher compared to non-controllers (p<0.0001). However, regardless of the group, the magnitude of responses to AE was lower as compared to NAE (p<0.0001). CD4⁺ T cell responses in patients with acute HIV infection (AHI) demonstrated poor immunogenicity towards AE as compared to NAE encoded by their transmitted founder virus. Longitudinal data in AHI off antiretroviral therapy demonstrated sequence changes that were biologically confirmed to represent CD4⁺ escape mutations. These data demonstrate an innovative application of HLA-associated polymorphisms to identify biologically relevant CD4⁺ epitopes and suggests CD4⁺ T cells are active participants in driving HIV evolution.

In HIV, CD4⁺ T cells are best known as the primary targets of infection. Although emerging data has suggested a more active role in viral pathogenesis, the CD4⁺ T cell population remains relatively understudied. Using a novel computational approach, we predicted 29 different epitopes with mutations that potentially represent escape from CD4⁺ T cell responses. The predicted escaped epitopes were found to be less immunogenic than the wild type forms, suggesting that the identified escapes allow HIV to reduce its visibility to the immune system. Using longitudinal samples, we were able to show CD4⁺ T cells driving viral escape following acute infection. Overall, these findings significantly expand our knowledge of how CD4⁺ T cells can exert HIV control and influence HIV evolution, providing important implications to future vaccine development strategies.

Effect of cryopreservation of peripheral blood mononuclear cells (PBMCs) on the variability of an antigen-specific memory B cell ELISpot

The ELISpot assay is used in vaccine studies for the quantification of antigen-specific memory B cells (B(MEM)), and can be performed using cryopreserved samples. The effects of cryopreservation on B(MEM) detection and the consistency of cultured ELISpot assays when performed by different operators or laboratories are unknown. In this study, blood was taken from healthy volunteers, and a cultured ELISpot assay was used to count B(MEM) specific for 2 routine vaccine antigens (diphtheria and tetanus toxoid). Results were assessed for intra- and inter-operator variation, and the effects of cryopreservation. Cryopreserved samples were shipped to a second laboratory in order to assess inter-laboratory variation. B(MEM) frequencies were very strongly correlated when comparing fresh and frozen samples processed by the same operator, and were also very strongly correlated when comparing 2 operators in the same laboratory. Results were slightly less consistent when samples were processed in different laboratories but correlation between the 2 measurements was still very strong. Although cell viability was reduced in some cryopreserved samples due to higher temperatures during transportation, B(MEM) could still be quantified. These results demonstrate the reproducibility of the ELISpot assay across operators and laboratories, and support the use of cryopreserved samples in future B(MEM) studies.