CD56(dim)CD16⁻ NK cell phenotype can be induced by 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.

Human Natural Killer Cells Cryopreserved without DMSO Sustain Robust Effector Responses

Natural killer (NK) cell-based immunotherapy has benefitted from the multiple strengths that NK cells offer in adoptive transfer settings, not the least of which is their safety and potential for allogeneic use. Such use, however, necessitates the cryopreservation of NK cell-based therapy products to support logistical efforts in deploying these cells in different locations, decentralized from the point of collection or manufacturing. DMSO, the most commonly used cryoprotective agent (CPA), has been effective in protecting immune cells during freezing and thawing, but its ability to induce molecular and genetic changes to immune cells as well as its toxicity has stimulated interest in alternative CPAs. However, replacing DMSO's ability to act intracellularly has been difficult, and the sensitivity of human peripheral blood-derived NK cells to freezing and thawing-induced damage has meant that investigations into the potential of replacing DMSO are lacking. As a first step toward establishing the feasibility of cryopreserving human NK cells with CPAs' alternative to DMSO, we investigate the potential of using noncell-penetrating and cell-penetrating CPAs to recover NK cells post-thaw without DMSO. Here, we find that cryoprotection using cell-penetrating CPAs can retain the viability of human peripheral blood-derived NK cells to a comparable degree to DMSO. In addition, non-DMSO-cryopreserved human NK cells were as cytotoxic as those cryopreserved with DMSO and displayed a comparable level of surface markers of activation. In summary, we present the first example of the potential of developing non-DMSO CPA formulations that could be deployed in future cell therapy regimens.

Physicochemical Mechanisms of Protection Offered by Agarose Encapsulation during Cryopreservation of Mammalian Cells in the Absence of Membrane-Penetrating Cryoprotectants

During freeze/thaw, cells are exposed to mechanical, thermal, chemical, and osmotic stresses, which cause loss of viability and function. Cryopreservation agents such as dimethyl sulfoxide (DMSO) are deployed to minimize freeze/thaw damage. However, there is a pressing need to eliminate DMSO from cryopreservation solutions due to its adverse effects. This is of the highest priority especially for cryopreservation of infusible/transplantable cell therapy products. In order to address this issue, we introduce reversible encapsulation in agarose hydrogels in the presence of the membrane-impermeable cryoprotectant, trehalose, as a viable, safe, and effective cryopreservation method. Our findings, which are supported by IR spectroscopy and differential scanning calorimetry analyses, demonstrate that encapsulation in 0.75% agarose hydrogels containing 10-20% trehalose inhibits mechanical damage induced by eutectic phase change, devitrification, and recrystallization, resulting in post-thaw viability comparable to the gold standard 10% DMSO.

Cryopreserved PM21-Particle-Expanded Natural Killer Cells Maintain Cytotoxicity and Effector Functions In Vitro and In Vivo

There is a great interest in developing natural killer (NK) cells as adoptive cancer immunotherapy. For off-the-shelf approaches and to conduct multicenter clinical trials, cryopreserved NK cells are the preferred product. However, recent studies reported that cryopreservation of NK cells results in loss of cell motility and, as a consequence, cytotoxicity which limits the clinical utility of such products. This study assessed the impact of cryopreservation on the recovery and function of PM21-particle expanded NK cells (PM21-NK cells) as well as their antitumor activity in vitro using 2D and 3D cancer models and in vivo in ovarian cancer models, including patient-derived xenografts (PDX). Viable PM21-NK cells were consistently recovered from cryopreservation and overnight rest with a mean recovery of 73 ± 22% (N = 19). Thawed and rested NK cells maintained the expression of activating receptors when compared to expansion-matched fresh NK cells. Cryopreserved NK cells that were thawed and rested showed no decrease in cytotoxicity when co-incubated with tumor cells at varying effector-to-target (NK:T) ratios compared to expansion-matched fresh NK cells. Moreover, no differences in cytotoxicity were observed between expansion-matched cryopreserved and fresh NK cells in 3D models of tumor killing. These were analyzed by kinetic, live-cell imaging assays co-incubating NK cells with tumor spheroids. When exposed to tumor cells, or upon cytokine stimulation, cryopreserved NK cells that were thawed and rested showed no significant differences in surface expression of degranulation marker CD107a or intracellular expression of TNFα and IFNγ. In vivo antitumor activity was also assessed by measuring the extension of survival of SKOV-3-bearing NSG mice treated with fresh vs. cryopreserved NK cells. Cryopreserved NK cells caused a statistically significant survival extension of SKOV-3-bearing NSG mice that was comparable to that observed with fresh NK cells. Additionally, treatment of NSG mice bearing PDX tumor with cryopreserved PM21-NK cells resulted in nearly doubling of survival compared to untreated mice. These data suggest that PM21-NK cells can be cryopreserved and recovered efficiently without appreciable loss of viability or activity while retaining effector function both in vitro and in vivo. These findings support the use of cryopreserved PM21-NK cells as a cancer immunotherapy treatment.

Role of NK Cells in Tumor Progression

Natural Killer (NK) cells are effector lymphocytes with the ability to generate an antitumor response. NK cells encompass a diverse group of subsets with different properties and have the capacity to kill cancer cells by different means. However, tumor cells have developed several mechanisms to evade NK cell-mediated killing. In this chapter, we summarize some aspects of NK cell biology with the aim to understand the competence of these cells and explore some of the challenges that NK cells have to face in different malignancies. Moreover, we will review the current knowledge about the role of NK cells in tumor progression and describe their phenotype and effector functions in tumor tissues and peripheral blood from cancer patients. Finally, we will recapitulate several findings from different studies focused on determining the prognostic value of NK cells in distinct cancers.

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.

Reduced frequency of cytotoxic CD56dim CD16+ NK cells leads to impaired antibody-dependent degranulation in EBV-positive classical Hodgkin lymphoma

Around 30–50% of classical Hodgkin lymphoma (cHL) cases in immunocompetent individuals from industrialized countries are associated with the B-lymphotropic Epstein-Barr virus (EBV). Although natural killer (NK) cells exhibit anti-viral and anti-tumoral functions, virtually nothing is known about quantitative and qualitative differences in NK cells in patients with EBV+ cHL vs. EBV- cHL. Here, we prospectively investigated 36 cHL patients without known immune suppression or overt immunodeficiency at diagnosis. All 10 EBV+ cHL patients and 25 out 26 EBV- cHL were seropositive for EBV antibodies, and EBV+ cHL patients presented with higher plasma EBV DNA levels compared to EBV- cHL patients. We show that the CD56^dim CD16⁺ NK cell subset was decreased in frequency in EBV+ cHL patients compared to EBV- cHL patients. This quantitative deficiency translates into an impaired CD56^dim NK cell mediated degranulation toward rituximab-coated HLA class 1 negative lymphoblastoid cells in EBV+ compared to EBV- cHL patients. We finally observed a trend to a decrease in the rituximab-associated degranulation and ADCC of in vitro expanded NK cells of EBV+ cHL compared to healthy controls. Our findings may impact on the design of adjunctive treatment targeting antibody-dependent cellular cytotoxicity in EBV+ cHL.

TIGIT blockade enhances functionality of peritoneal NK cells with altered expression of DNAM-1/TIGIT/CD96 checkpoint molecules in ovarian cancer

Advanced ovarian cancer (OC) patients have a poor 5-year survival of only 28%, emphasizing the medical need for improved therapies. Adjuvant immunotherapy could be an attractive approach since OC is an immunogenic disease and the presence of tumor-infiltrating lymphocytes has shown to positively correlate with patient survival. Among these infiltrating lymphocytes are natural killer (NK) cells, key players involved in tumor targeting, initiated by signaling via activating and inhibitory receptors. Here, we investigated the role of the DNAM-1/TIGIT/CD96 axis in the anti-tumor response of NK cells toward OC. Ascites-derived NK cells from advanced OC patients showed lower expression of activating receptor DNAM-1 compared to healthy donor peripheral blood NK cells, while inhibitory receptor TIGIT and CD96 expression was equal or higher, respectively. This shift to a more inhibitory phenotype could also be induced in vitro by co-culturing healthy donor NK cells with OC tumor spheroids, and in vivo on intraperitoneally infused NK cells in SKOV-3 OC bearing NOD/SCID-IL2Rγnull (NSG) mice. Interestingly, TIGIT blockade enhanced degranulation and interferon gamma (IFNγ) production of healthy donor CD56^dim NK cells in response to OC tumor cells, especially when DNAM-1/CD155 interactions were in place. Importantly, TIGIT blockade boosted functional responsiveness of CD56^dim NK cells of OC patients with a baseline reactivity against SKOV-3 cells. Overall, our data show for the first time that checkpoint molecules TIGIT/DNAM-1/CD96 play an important role in NK cell responsiveness against OC, and provides rationale for incorporating TIGIT interference in NK cell-based immunotherapy in OC patients.

Cryopreservation impairs 3-D migration and cytotoxicity of natural killer cells

Natural killer (NK) cells are important effector cells in the immune response to cancer. Clinical trials on adoptively transferred NK cells in patients with solid tumors, however, have thus far been unsuccessful. As NK cells need to pass stringent safety evaluation tests before clinical use, the cells are cryopreserved to bridge the necessary evaluation time. Standard degranulation and chromium release cytotoxicity assays confirm the ability of cryopreserved NK cells to kill target cells. Here, we report that tumor cells embedded in a 3-dimensional collagen gel, however, are killed by cryopreserved NK cells at a 5.6-fold lower rate compared to fresh NK cells. This difference is mainly caused by a 6-fold decrease in the fraction of motile NK cells after cryopreservation. These findings may explain the persistent failure of NK cell therapy in patients with solid tumors and highlight the crucial role of a 3-D environment for testing NK cell function.

A NKp80-Based Identification Strategy Reveals that CD56neg NK Cells Are Not Completely Dysfunctional in Health and Disease

Natural killer (NK) cells are usually identified by the absence of other lineage markers, due to the lack of cell-surface-specific receptors. CD56neg NK cells, classically identified as CD56negCD16+, are very scarce in the peripheral blood of healthy people but they expand in some pathological conditions. However, studies on CD56neg NK cells had revealed different results regarding the phenotype and functionality. This could be due to, among others, the unstable expression of CD16, which hinders CD56neg NK cells' proper identification. Hence, we aim to determine an alternative surface marker to CD16 to better identify CD56neg NK cells. We have found that NKp80 is superior to CD16. Furthermore, we found differences between the functionality of CD56negNKp80+ and CD56negCD16+, suggesting that the effector functions of CD56neg NK cells are not as diminished as previously thought. We proposed NKp80 as a noteworthy marker to identify and accurately re-characterize human CD56neg NK cells.

Nanoparticle-Mediated Intracellular Protection of Natural Killer Cells Avoids Cryoinjury and Retains Potent Antitumor Functions

The ability of natural killer (NK) cells to mediate potent antitumor immunity in clinical adoptive transfer settings relies, in large part, on their ability to retain cytotoxic function following cryopreservation. To avoid potential systemic toxicities associated with infusions of NK cells into patients in the presence of dimethylsulfoxide (DMSO), interest in alternative cryoprotective agents (CPAs) with improved safety profiles has grown. Despite the development of various sugars, amino acids, polyols, and polyampholytes as cryoprotectants, their ability to promote protection from intracellular cryodamage is limited because they mostly act outside of the cell. Though ways to shuttle cryoprotectants intracellularly exist, NK cells' high aversity to manipulation and freezing has meant they are highly understudied as targets for the development of new cryopreservation approaches. Here, the first example of a safe and efficient platform for the intracellular delivery of non-DMSO CPAs to NK cells is presented. Biocompatible chitosan-based nanoparticles are engineered to mediate the efficient DMSO-free cryopreservation of NK cells. NK cells cryopreserved in this way retain potent cytotoxic, degranulation, and cytokine production functions against tumor targets. This not only represents the first example of delivering nanoparticles to NK cells, but illustrates the clinical potential in manufacturing safer allogeneic adoptive immunotherapies "off the shelf."

A study of 51 subtypes of peripheral blood immune cells in newly diagnosed young type 1 diabetes patients

Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing beta cells in pancreatic islets. Various immune cell populations are involved in disease development and natural course. However, to our knowledge, so far there are no comprehensive comparative investigations of all main immune cell populations and their most important subsets at the onset of disease. Therefore, in the current study, we analyzed 51 peripheral blood immune cell populations in 22 young T1D patients and in 25 age-matched controls using a comprehensive polychromatic flow cytometry panel developed for whole blood by the COST Action no. BM0907 ENTIRE (European Network for Translational Immunology Research and Education: From Immunomonitoring to Personalized Immunotherapy) consortium. We found that in T1D patients, frequencies and absolute counts of natural killer (NK) cells, dendritic cells (DC) and T cells, as well as their respective subsets, were significantly altered compared to controls. Further, we observed that changes in several cell populations (e.g. CD14⁺ CD16⁺ non-classical monocytes, plasmablasts) were dependent on the age of the patient. In addition to age-related changes, we also found that alterations in immune cell patterns were associated with parameters such as the presence of ketoacidosis and C-peptide serum levels. Our study provides a foundation for future studies investigating different cell lineages and their role in T1D and illustrates the value of polychromatic flow cytometry for evaluating all main peripheral immune cells and their subsets in whole blood samples.

Bioinspired Preservation of Natural Killer Cells for Cancer Immunotherapy

The ability to cryopreserve natural killer (NK) cells has a significant potential in modern cancer immunotherapy. Current cryopreservation protocols cause deterioration in NK cell viability and functionality. This work reports the preservation of human cytokine-activated NK cell viability and function following cryopreservation using a cocktail of biocompatible bioinspired cryoprotectants (i.e., dextran and carboxylated ε-poly-L-lysine). Results demonstrate that the recovered NK cells after cryopreservation and rewarming maintain their viability immediately after thawing at a comparable level to control (dimethyl sulfoxide-based cryopreservation). Although, their viability drops in the first day in culture compared to controls, the cells grow back to a comparable level to controls after 1 week in culture. In addition, the anti-tumor functional activity of recovered NK cells demonstrates higher cytotoxic potency against leukemia cells compared to control. This approach presents a new direction for NK cell preservation, focusing on function and potentially enabling storage and distribution for cancer immunotherapy.

The early expansion of anergic NKG2Apos/CD56dim/CD16neg natural killer represents a therapeutic target in haploidentical hematopoietic stem cell transplantation

Natural killer cells are the first lymphocyte population to reconstitute early after non-myeloablative and T cell-replete haploidentical hematopoietic stem cell transplantation with post-transplant infusion of cyclophosphamide. The study herein characterizes the transient and predominant expansion starting from the second week following haploidentical hematopoietic stem cell transplantation of a donor-derived unconventional subset of NKp46^neg-low/CD56^dim/CD16^neg natural killer cells expressing remarkably high levels of CD94/NKG2A. Both transcription and phenotypic profiles indicated that unconventional NKp46^neg-low/CD56^dim/CD16^neg cells are a distinct natural killer cell subpopulation with features of late stage differentiation, yet retaining proliferative capability and functional plasticity to generate conventional NKp46^pos/CD56^bright/CD16^neg-low cells in response to interleukin-15 plus interleukin-18. While present at low frequency in healthy donors, unconventional NKp46^neg-low/CD56^dim/CD16^neg cells are greatly expanded in the seven weeks following haploidentical hematopoietic stem cell transplantation, and express high levels of the activating receptors NKG2D and NKp30 as well as of the lytic granules Granzyme-B and Perforin. Nonetheless, NKp46^neg-low/CD56^dim/CD16^neg cells displayed a markedly defective cytotoxicity that could be reversed by blocking the inhibitory receptor CD94/NKG2A. These data open new and important perspectives to better understand the ontogenesis/homeostasis of human natural killer cells and to develop a novel immune-therapeutic approach that targets the inhibitory NKG2A check-point, thus unleashing natural killer cell alloreactivity early after haploidentical hematopoietic stem cell transplantation.

Natural killer-92 cells maintain cytotoxic activity after long-term cryopreservation in novel DMSO-free media

Natural killer (NK) cells are a critical part of the innate immune system, and have emerged as attractive targets for immunotherapies for various malignancies. Alongside the need for expansion of NK cells to reach clinically useful numbers, a critical component in the availability of NK cells for allogeneic therapy is cryopreservation. While a continuously-growing cell line such as NK-92 can avoid issues associated with isolating, activating, expanding, and manufacturing large numbers of peripheral blood-derived NKs, cryopreservation of these cells has not made much progress. NK cells are highly sensitive to freezing and thawing, while the use of DMSO during cryopreservation raises serious safety concerns. In this work, we evaluated a number of cryoprotectants that do not contain DMSO for their capacity to cryopreserve NK-92 cells over long-term while retaining their cytotoxic activity and viability, with the aim of identifying potential replacements to DMSO for safe clinical use of these cells.

Human Lymphoid Tissues Harbor a Distinct CD69+CXCR6+ NK Cell Population

Knowledge of human NK cells is based primarily on conventional CD56(bright) and CD56(dim) NK cells from blood. However, most cellular immune interactions occur in lymphoid organs. Based on the coexpression of CD69 and CXCR6, we identified a third major NK cell subset in lymphoid tissues. This population represents 30-60% of NK cells in marrow, spleen, and lymph node but is absent from blood. CD69(+)CXCR6(+) lymphoid tissue NK cells have an intermediate expression of CD56 and high expression of NKp46 and ICAM-1. In contrast to circulating NK cells, they have a bimodal expression of the activating receptor DNAX accessory molecule 1. CD69(+)CXCR6(+) NK cells do not express the early markers c-kit and IL-7Rα, nor killer cell Ig-like receptors or other late-differentiation markers. After cytokine stimulation, CD69(+)CXCR6(+) NK cells produce IFN-γ at levels comparable to CD56(dim) NK cells. They constitutively express perforin but require preactivation to express granzyme B and exert cytotoxicity. After hematopoietic stem cell transplantation, CD69(+)CXCR6(+) lymphoid tissue NK cells do not exhibit the hyperexpansion observed for both conventional NK cell populations. CD69(+)CXCR6(+) NK cells constitute a separate NK cell population with a distinct phenotype and function. The identification of this NK cell population in lymphoid tissues provides tools to further evaluate the cellular interactions and role of NK cells in human immunity.

NK Cell Subgroups, Phenotype, and Functions After Autologous Stem Cell Transplantation

High-dose chemotherapy with consecutive autologous stem cell transplantation (autoSCT) is a well-established treatment option for patients suffering from malignant lymphoma or multiple myeloma. Natural killer (NK) cells are an important part of the immune surveillance, and their cell number after autoSCT is predictive for progression-free and overall survival. To improve knowledge about the role of NK cells after autoSCT, we investigated different NK cell subgroups, their phenotype, and their functions in patients treated with autoSCT. Directly after leukocyte regeneration (>1000 leukocytes/μl) following autoSCT, CD56⁺⁺ NK cells were the major NK cell subset. Surprisingly, these cells showed unusually high surface expression levels of CD57 and killer Ig-like receptors (KIRs) compared to expression levels before or at later time points after autoSCT. Moreover, these NK cells strongly upregulated KIR2DL2/3/S2 and KIR3DL1, whereas KIR2DL1/S1 remained constant, indicating that this cell population arose from more immature NK cells instead of from activated mature ones. Remarkably, NK cells were already able to degranulate and produce IFN-γ and MIP-1β upon tumor interaction early after leukocyte regeneration. In conclusion, we describe an unusual upregulation of CD57 and KIRs on CD56⁺⁺ NK cells shortly after autoSCT. Importantly, these NK cells were functionally competent upon tumor interaction at this early time point.