Fresh versus Frozen: Effects of Cryopreservation on CAR T Cells

Advantages of high cell concentration prior to cryopreservation of initial leukapheresis in CAR-T cell therapy

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapy is increasingly used in patients affected by B-cell lymphoma and acute lymphoblastic leukemia. For logistical reasons, initial apheresis products may be cryopreserved for shipment to manufacturing centers. Due to the characteristics of these patients, cells are often collected in large volumes, meaning more bags must be cryopreserved. This requires increased storage, time and monetary costs. In this context, we aimed to evaluate a high cell concentration cryopreservation protocol by centrifugation to standardize the initial CAR-T manufacturing procedure.

MATERIALS AND METHODS

Sixty-eight processes of leukapheresis of 57 patients affected by refractory/relapsed B cell lymphoma and 9 patients affected by acute lymphoblastic leukemia who were eligible for anti-CD19 CAR-T cell treatment performed between June 2019 and October 2022 were analyzed. Whole blood count, percentage and number of T cells were assessed on the apheresis final product. The apheresis product, which was alternatively stored overnight at 4°C, was centrifuged, adjusting the volume to approximately 40 mL. The product was immediately cryopreserved to achieve a final cell concentration of 50-200×106 cells/ml for cryopreservation.

RESULTS

Leukapheresis volume was reduced by almost fivefold (median: 185 to 40 mL), resulting in a higher product concentration in one bag. In addition, the number of non-target cells (monocytes, platelets and erythrocytes) was also reduced during the development of CAR-T cell therapy, thereby maintaining T lymphocyte levels and providing a purer starting material.

DISCUSSION

The advantages of the protocol include reducing economic costs, saving storage space, simplifying the manufacturing process, and facilitating shipping logistics. In conclusion, we present a validated, simple, and cost-effective cell enrichment processing protocol that provides high-quality cryopreserved products as starting material for the CAR-T cell manufacturing process.

CellShip: An Ambient Temperature Transport and Short-Term Storage Medium for Mammalian Cell Cultures

Cell culture is a critical platform for numerous research and industrial processes. However, methods for transporting cells are largely limited to cryopreservation, which is logistically challenging, requires the use of potentially cytotoxic cryopreservatives, and can result in poor cell recovery. Development of a transport media that can be used at ambient temperatures would alleviate these issues. In this study, we describe a novel transportation medium for mammalian cells. Five commonly used cell lines, (HEK293, CHO, HepG2, K562, and Jurkat) were successfully shipped and stored for a minimum of 72 hours and up to 96 hours at ambient temperature, after which, cells were recovered into standard culture conditions. Viability (%) and cell numbers, were examined, before, following the transport/storage period and following the recovery period. In all experiments, cell numbers returned to pretransport/storage concentration within 24-48 hours recovery. Imaging data indicated that HepG2 cells were fully adherent and had established typical growth morphology following 48 hours recovery, which was not seen in cells recovered from cryopreservation. Following recovery, Jurkat cells that had been subjected to a 96 hours transport/storage period, demonstrated a 1.93-fold increase compared with the starting cell number with >95% cell viability. We conclude that CellShip® may represent a viable method for the transportation of mammalian cells for multiple downstream applications in the Life Sciences research sector.

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.

Proline pre-conditioning of Jurkat cells improves recovery after cryopreservation

Cell therapies such as allogenic CAR T-cell therapy, natural killer cell therapy and stem cell transplants must be cryopreserved for transport and storage. This is typically achieved by addition of dimethyl sulfoxide (DMSO) but the cryoprotectant does not result in 100% cell recovery. New additives or technologies to improve their cryopreservation could have major impact for these emerging therapies. l-Proline is an amino acid osmolyte produced as a cryoprotectant by several organisms such as the codling moth Cydia pomonella and the larvae of the fly Chymomyza costata, and has been found to modulate post-thaw outcomes for several cell lines but has not been studied with Jurkat cells, a T lymphocyte cell line. Here we investigate the effectiveness of l-proline compared to d-proline and l-alanine for the cryopreservation of Jurkat cells. It is shown that 24-hour pre-freezing incubation of Jurkat cells with 200 mM l-proline resulted in a modest increase in cell recovery post-thaw at high cell density, but a larger increase in recovery was observed at the lower cell densities. l-Alanine was as effective as l-proline at lower cell densities, and addition of l-proline to the cryopreservation media (without incubation) had no benefit. The pre-freeze incubation with l-proline led to significant reductions in cell proliferation supporting an intracellular, biochemical, mechanism of action which was shown to be cell-density dependent. Controls with d-proline were found to reduce post-thaw recovery attributed to osmotic stress as d-proline cannot enter the cells. Preliminary analysis of apoptosis/necrosis profiles by flow cytometry indicated that inhibition of apoptosis is not the primary mode of action. Overall, this supports the use of l-proline pre-conditioning to improve T-cell post-thaw recovery without needing any changes to cryopreservation solutions nor methods and hence is simple to implement.

Comparison of cytotoxic potency between freshly cultured and freshly thawed cytokine-induced killer cells from human umbilical cord blood

Immune cell therapy has been incorporated into cancer therapy over the past few years. Chimeric antigen receptor T cells (Car-T cells) transplantation is a novel and promising therapy for cancer treatment and introduces a new age of immune cell therapy. However, the expensive nature of genetic modification procedures limits the accessibility of Car-T cells for cancer treatment. Cytokine-induced killer cells (CIKs) can kill the target cells in an MHC-non-restricted manner; these cells can be developed to "off-the-shelf" immune cell products for cancer treatment. However, the anti-tumor potency of freshly thawed CIKs is not well documented. This study aimed to fill this gap, evaluating the anti-tumor potency of freshly thawed CIKs compared to that of freshly cultured CIKs. CIKs were produced from the human umbilical cord blood in accordance with published protocols. CIKs were cryopreserved in xeno-free cryomedium that contains 5% DMSO, 10% human serum in phosphate buffer saline at - 86 °C. These cells were thawed and immediately utilized in assays (called freshly thawed CIKs) with freshly cultured cells are control. The expression of the surface markers of CIKs, cytokine production, and in vitro anti-tumor cytotoxic cells of freshly thawed CIKs were evaluated and compared to freshly cultured CIKs. Additionally, the freshly thawed CIKs were injected into the breast of tumor-bearing mice to assess the anti-tumor potency in vivo. The results obtained in freshly thawed CIKs and freshly cultured CIKs demonstrated that the expression of CD3, and CD56 were comparable in both cases. The production of TNF-α, IFN-γ, and IL-10 was slightly reduced in freshly thawed cells compared to the freshly cultured cells. The in vitro lysis toward MCF-7 cancer cells was similar between freshly thawed and freshly cultured CIKs. Moreover, the freshly thawed CIKs displayed anti-breast tumor activity in the breast tumor-bearing mice. The volume of tumors significantly reduced in the mice grafted with freshly thawed CIKs while, conversely, the tumor volume in mice of the placebo group gradually increased. This study substantiated that freshly thawed CIKs preserved their anti-tumor potency in both in vitro and in vivo conditions. The results initially revealed the great potential of UCB-CIKs for "off-the-shelf" CIK product manufacturing. However, further studies on the effects of cryomedia, freezing rate, and thawing procedure should be undertaken before freshly thawed off-the-shelf UCB-CIKs are utilized in clinical trials.

Should we adopt an automated de-centralized model of chimeric antigen receptor- T cells manufacturing for low-and middle-income countries? A real world perspective

Autologous chimeric antigen receptor-T (CAR-T) cell therapy has proven itself as an effective therapeutic modality for cancers, especially hematological malignancies and is emerging as a potential candidate for solid organ cancers as well. However, the accessibility to treatment has been limited due to complexities and costs associated with manufacturing a genetically modified autologous product. The centralized model of CAR-T manufacturing which has emerged as the dominant model in developed nations does not seem well-suited to the needs and realities of the developing economies. In this context, we explore the relative advantages and disadvantages of the two models from a developing nation's perspective.

Impact of cryopreservation on CAR T production and clinical response

Adoptive cell therapy with chimeric antigen receptor (CAR) T cells has become an efficient treatment option for patients with hematological malignancies. FDA approved CAR T products are manufactured in centralized facilities from fresh or frozen leukapheresis and the cryopreserved CAR T infusion product is shipped back to the patient. An increasing number of clinical centers produce CAR T cells on-site, which enables the use of fresh and cryopreserved PBMCs and CAR T cells. Here we determined the effect of cryopreservation on PBMCs and CD19 CAR T cells in a cohort of 118 patients treated with fresh CAR T cells and in several patients head-to-head. Cryopreserved PBMCs, obtained from leukapheresis products, contained less erythrocytes and T cells, but were sufficient to produce CAR T cells for therapy. There was no correlation between the recovery of PBMCs and the transduction efficacy, the number of CAR T cells obtained by the end of the manufacturing process, the in vitro reactivity, or the response rate to CAR T therapy. We could show that CAR T cells cryopreserved during the manufacturing process, stored and resumed expansion at a later time point, yielded sufficient cell numbers for treatment and led to complete remissions. Phenotype analysis including T cell subtypes, chemokine receptor and co-inhibitory/stimulatory molecules, revealed that fresh CAR T cells expressed significantly more TIM-3 and contained less effector T cells in comparison to their frozen counterparts. In addition, fresh CAR T infusion products demonstrated increased in vitro anti-tumor reactivity, however cryopreserved CAR T cells still showed high anti-tumor potency and specificity. The recovery of cryopreserved CAR T cells was similar in responding and non-responding patients. Although fresh CAR T infusion products exhibit higher anti-tumor reactivity, the use of frozen PBMCs as staring material and frozen CAR T infusion products seems a viable option, as frozen products still exhibit high in vitro potency and cryopreservation did not seem to affect the clinical outcome.

CAR-T manufactured from frozen PBMC yield efficient function with prolonged in vitro production

Chimeric antigen receptor (CAR)-T cells are engineered to identify and eliminate cells expressing a target antigen. Current manufacturing protocols vary between commercial CAR-T cell products warranting an assessment of these methods to determine which approach optimally balances successful manufacturing capacity and product efficacy. One difference between commercial product manufacturing methods is whether T cell engineering begins with fresh (unfrozen) patient cells or cells that have been cryopreserved prior to manufacture. Starting with frozen PBMC material allows for greater manufacturing flexibility, and the possibility of collecting and storing blood from patients prior to multiple lines of therapy. We prospectively analyzed if second generation anti-CD19 CAR-T cells with either CD28 or 4-1BB co-stimulatory domains have different phenotype or function when prepared side-by-side using fresh or cryopreserved PBMCs. We found that cryopreserved PBMC starting material is associated with slower CAR-T cell expansion during manufacture but does not affect phenotype. We also demonstrate that CAR-T cell activation, cytokine production and in vitro anti-tumor cytotoxicity were not different when CAR-T cells were manufactured from fresh or cryopreserved PBMC. As CAR-T cell therapy expands globally, the need for greater flexibility around the timing of manufacture will continue to grow. This study helps support the concept that cryopreservation of PBMCs could be the solution to these issues without compromising the quality of the final CAR-T product.

Impact of Cryopreservation and Freeze-Thawing on Therapeutic Properties of Mesenchymal Stromal/Stem Cells and Other Common Cellular Therapeutics

Purpose of Review

Cryopreservation and its associated freezing and thawing procedures–short “freeze-thawing”–are among the final steps in economically viable manufacturing and clinical application of diverse cellular therapeutics. Translation from preclinical proof-of-concept studies to larger clinical trials has indicated that these processes may potentially present an Achilles heel to optimal cell product safety and particularly efficacy in clinical trials and routine use.

Recent Findings

We review the current state of the literature on how cryopreservation of cellular therapies has evolved and how the application of this technique to different cell types is interlinked with their ability to engraft and function upon transfer in vivo, in particular for hematopoietic stem and progenitor cells (HSPCs), their progeny, and therapeutic cell products derived thereof. We also discuss pros and cons how this may differ for non-hematopoietic mesenchymal stromal/stem cell (MSC) therapeutics. We present different avenues that may be crucial for cell therapy optimization, both, for hematopoietic (e.g., effector, regulatory, and chimeric antigen receptor (CAR)-modified T and NK cell based products) and for non-hematopoietic products, such as MSCs and induced pluripotent stem cells (iPSCs), to achieve optimal viability, recovery, effective cell dose, and functionality of the cryorecovered cells.

Summary

Targeted research into optimizing the cryopreservation and freeze-thawing routines and the adjunct manufacturing process design may provide crucial advantages to increase both the safety and efficacy of cellular therapeutics in clinical use and to enable effective market deployment strategies to become economically viable and sustainable medicines.

Establishment of a New Cryopreservation Solution for Chimeric Antigen Receptor T Cells

Preservation and transportation are essential for the clinical application of chimeric antigen receptor T (CAR-T) cells. This study aimed to optimize a cryopreservation solution for CAR-T cells and evaluate the antitumor efficiency of CAR-T cells using this optimized solution in vitro and in vivo. First, the stability of the cryopreservation solution for CAR-T infusion was detected by the L27 (3⁷) orthogonal experiment. Subsequently, osmolality and pH were analyzed for the preservation reagent. Additionally, apoptosis and CAR expression of CAR-T cells were measured by flow cytometry, and the cytotoxicity was determined by calcein-AM staining. The results showed that cryopreservation solutions used in this study demonstrated high chemical stability, which induced only 2% CAR-T cells apoptosis in optimal solutions, which were slightly lower than other commercial solutions. Moreover, the CAR expression was not significantly affected by preservation with these solutions. There were no significant differences in the cytotoxicity between fresh and thawed CAR-T cells cryopreserved in the cryopreservation solutions in vivo and in vitro. This study developed a new cryopreservation solution for CAR-T cells, and it was safe and also had negligible effects on the CAR-T cells antitumor activity.

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

Quantitative and functional analysis of mononuclear leukocyte populations is an invaluable tool to understand the role of the immune system in the pathogenesis of a disease. Cryopreservation of mononuclear cells (MNCs) is routinely used to guarantee similar experimental conditions. Immune cells react differently to cryopreservation, and populations and functions of immune cells change during the process of freeze–thawing. To allow for a setup that preserves cell number and function optimally, we tested four different cryopreservation media. MNCs from 15 human individuals were analyzed. Before freezing and after thawing, the distribution of leukocytes was quantified by flow cytometry. Cultured cells were stimulated using lipopolysaccharide, and their immune response was quantified by flow cytometry, quantitative polymerase chain reaction (qPCR), and enzyme-linked immunosorbent assay (ELISA). Ultimately, the performance of the cryopreservation media was ranked. Cell recovery and viability were different between the media. Cryopreservation led to changes in the relative number of monocytes, T cells, B cells, and their subsets. The inflammatory response of MNCs was altered by cryopreservation, enhancing the basal production of inflammatory cytokines. Different cryopreservation media induce biases, which needs to be considered when designing a study relying on cryopreservation. Here, we provide an overview of four different cryopreservation media for choosing the optimal medium for a specific task.

Assessment of the Impact of Post-Thaw Stress Pathway Modulation on Cell Recovery following Cryopreservation in a Hematopoietic Progenitor Cell Model

The development and use of complex cell-based products in clinical and discovery science continues to grow at an unprecedented pace. To this end, cryopreservation plays a critical role, serving as an enabling process, providing on-demand access to biological material, facilitating large scale production, storage, and distribution of living materials. Despite serving a critical role and substantial improvements over the last several decades, cryopreservation often remains a bottleneck impacting numerous areas including cell therapy, tissue engineering, and tissue banking. Studies have illustrated the impact and benefit of controlling cryopreservation-induced delayed-onset cell death (CIDOCD) through various “front end” strategies, such as specialized media, new cryoprotective agents, and molecular control during cryopreservation. While proving highly successful, a substantial level of cell death and loss of cell function remains associated with cryopreservation. Recently, we focused on developing technologies (RevitalICE™) designed to reduce the impact of CIDOCD through buffering the cell stress response during the post-thaw recovery phase in an effort to improve the recovery of previously cryopreserved samples. In this study, we investigated the impact of modulating apoptotic caspase activation, oxidative stress, unfolded protein response, and free radical damage in the initial 24 h post-thaw on overall cell survival. Human hematopoietic progenitor cells in vitro cryopreserved in both traditional extracellular-type and intracellular-type cryopreservation freeze media were utilized as a model cell system to assess impact on survival. Our findings demonstrated that through the modulation of several of these pathways, improvements in cell recovery were obtained, regardless of the freeze media and dimethyl sulfoxide concentration utilized. Specifically, through the use of oxidative stress inhibitors, an average increase of 20% in overall viability was observed. Furthermore, the results demonstrated that by using the post-thaw recovery reagent on samples cryopreserved in intracellular-type media (Unisol™), improvements in overall cell survival approaching 80% of non-frozen controls were attained. While improvements in overall survival were obtained, an assessment on the impact of specific cell subpopulations and functionality remains to be completed. While work remains, these results represent an important step forward in the development of improved cryopreservation processes for use in discovery science, and commercial and clinical settings.

Making Potent CAR T Cells Using Genetic Engineering and Synergistic Agents

Immunotherapies are emerging as powerful weapons for the treatment of malignancies. Chimeric antigen receptor (CAR)-engineered T cells have shown dramatic clinical results in patients with hematological malignancies. However, it is still challenging for CAR T cell therapy to be successful in several types of blood cancer and most solid tumors. Many attempts have been made to enhance the efficacy of CAR T cell therapy by modifying the CAR construct using combination agents, such as compounds, antibodies, or radiation. At present, technology to improve CAR T cell therapy is rapidly developing. In this review, we particularly emphasize the most recent studies utilizing genetic engineering and synergistic agents to improve CAR T cell therapy.

A bioinspired and chemically defined alternative to dimethyl sulfoxide for the cryopreservation of human hematopoietic stem cells

The cryopreservation of hematopoietic cells using dimethyl sulfoxide (DMSO) and serum is a common procedure used in transplantation. However, DMSO has clinical and biological side effects due to its toxicity, and serum introduces variation and safety risks. Inspired by natural antifreeze proteins, a novel class of ice-interactive cryoprotectants was developed. The corresponding DMSO-, protein-, and serum-free cryopreservation media candidates were screened through a series of biological assays using human cell lines, peripheral blood cells, and bone marrow cells. XT-Thrive-A and XT-Thrive-B were identified as lead candidates to rival cryopreservation with 10% DMSO in serum based on post-thaw cell survival and short-term proliferation assays. The effectiveness of the novel cryopreservation media in freezing hematopoietic stem cells from human whole bone marrow was assessed by extreme limiting dilution analysis in immunodeficient mice. Stem cell frequencies were measured 12 weeks after transplant based on bone marrow engraftment of erythroid, myeloid, B-lymphoid, and CD34⁺ progenitors measured by flow cytometry. The recovered numbers of cryopreserved stem cells were similar among XT-Thrive A, XT-Thrive B, and DMSO with serum groups. These findings show that cryoprotectants developed through biomimicry of natural antifreeze proteins offers a substitute for DMSO-based media for the cryopreservation of hematopoietic stem cells.

The clinical outcomes of fresh versus cryopreserved CD19-directed chimeric antigen receptor T cells in non-Hodgkin lymphoma patients

CD19-directed chimeric antigen receptor T (CAR-T) cells have been widely reported in the therapy of relapsed/refractory non-Hodgkin lymphoma (NHL). Both cryopreserved and fresh formulations of CAR-T have been used in previous studies. However, quite a few studies investigated the effects of cryopreservation on the clinical outcomes of CAR-T cells. Here we retrospectively analyzed a phase I/II clinical trial of CD19-directed CAR-T cells in NHL patients, and compared the safety and efficacy of cryopreserved and fresh CAR-T products. All CAR-T cells were prepared using the same manufacturing process except the formulation step. Fifteen patients were infused with cryopreserved/thawed CAR-T cells, and 8 patients were treated with fresh CAR-T cells. Comparative overall response rates and in vivo expansion kinetics of CAR-T cells were observed between the cryopreserved cohort and fresh cohort. The occurrence rates of cytokine release syndrome and neurotoxicity were also similar in both groups. Patients in the fresh cohort showed higher incidence of acute hematological toxicity including anemia, hypoleukemia, and thrombocytopenia. This study demonstrated that cryopreservation showed negligible effects on the efficacy of CD19-directed CAR-T cells, but endowed CAR-T cells with higher safety in NHL patients, supporting the application of cryopreserved CAR-T products for NHL therapy.