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Li Z, Simin L, Jian K, Xin G, Youlin K. 4-1BB antibody enhances cytotoxic activity of natural killer cells against prostate cancer cells via NKG2D agonist combined with IL-27. Immunotherapy 2022; 14:1043-1053. [PMID: 35852136 DOI: 10.2217/imt-2021-0232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Aims: To enhance the cytotoxicity of natural killer (NK) cells against prostate cancer cells via NKG2D agonist, with 4-1BB antibody and IL-27 combination. Materials & methods: FACS was used to detect degranulation and cell surface receptors in NK cells isolated from healthy donors. Cytokine concentrations were measured using ELISA. NK-cell cytotoxicity was analyzed using Cell Counting Kit-8. Results: NKG2D agonist, 4-1BB antibody and IL-27 combination treatment improved the activating receptor expression and IFN-γ and TNF-α secretion but decreased the suppressive receptor CD158a expression and IL-10 secretion in NK cells. The combined treatment enhanced NK-cell cytotoxicity against both PC3 and DU145 cells with concurrent enhanced STAT3 activation. Conclusion: 4-1BB antibody and IL-27 improved NKG2D agonist function in NK cells against prostate cancer cells.
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Affiliation(s)
- Zhang Li
- Gastroenterology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, China
| | - Liang Simin
- Department of Urology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, China
| | - Kang Jian
- Department of Urology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, China
| | - Gou Xin
- Department of Urology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, China
| | - Kuang Youlin
- Department of Urology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, China
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2
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Gunduz M, Ataca Atilla P, Atilla E. New Orders to an Old Soldier: Optimizing NK Cells for Adoptive Immunotherapy in Hematology. Biomedicines 2021; 9:biomedicines9091201. [PMID: 34572387 PMCID: PMC8466804 DOI: 10.3390/biomedicines9091201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 08/28/2021] [Accepted: 08/30/2021] [Indexed: 12/18/2022] Open
Abstract
NK (Natural Killer) cell-mediated adoptive immunotherapy has gained attention in hematology due to the progressing knowledge of NK cell receptor structure, biology and function. Today, challenges related to NK cell expansion and persistence in vivo as well as low cytotoxicity have been mostly overcome by pioneering trials that focused on harnessing NK cell functions. Recent technological advancements in gene delivery, gene editing and chimeric antigen receptors (CARs) have made it possible to generate genetically modified NK cells that enhance the anti-tumor efficacy and represent suitable “off-the-shelf” products with fewer side effects. In this review, we highlight recent advances in NK cell biology along with current approaches for potentiating NK cell proliferation and activity, redirecting NK cells using CARs and optimizing the procedure to manufacture clinical-grade NK and CAR NK cells for adoptive immunotherapy.
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Affiliation(s)
- Mehmet Gunduz
- Department of Hematology, Biruni University, Istanbul 34010, Turkey;
| | - Pinar Ataca Atilla
- Interdisciplinary Stem Cells and Regenerative Medicine Ph.D Program, Stem Cell Institute, Ankara University, Ankara 06520, Turkey;
| | - Erden Atilla
- Department of Hematology, Mersin State Hospital, Korukent District, 96015 St., Toroslar 33240, Turkey
- Correspondence: ; Tel.: +9-05-058-213-131
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3
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Lamb MG, Rangarajan HG, Tullius BP, Lee DA. Natural killer cell therapy for hematologic malignancies: successes, challenges, and the future. Stem Cell Res Ther 2021; 12:211. [PMID: 33766099 PMCID: PMC7992329 DOI: 10.1186/s13287-021-02277-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Accepted: 03/10/2021] [Indexed: 12/20/2022] Open
Abstract
The adoptive transfer of natural killer (NK) cells is an emerging therapy in the field of immuno-oncology. In the last 3 decades, NK cells have been utilized to harness the anti-tumor immune response in a wide range of malignancies, most notably with early evidence of efficacy in hematologic malignancies. NK cells are dysfunctional in patients with hematologic malignancies, and their number and function are further impaired by chemotherapy, radiation, and immunosuppressants used in initial therapy and hematopoietic stem cell transplantation. Restoring this innate immune deficit may lead to improved therapeutic outcomes. NK cell adoptive transfer has proven to be a safe in these settings, even in the setting of HLA mismatch, and a deeper understanding of NK cell biology and optimized expansion techniques have improved scalability and therapeutic efficacy. Here, we review the use of NK cell therapy in hematologic malignancies and discuss strategies to further improve the efficacy of NK cells against these diseases.
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Affiliation(s)
- Margaret G Lamb
- Division of Hematology, Oncology, and Bone Marrow Transplant, Nationwide Children's Hospital, 700 Children's Drive, Suite 5A.1, Columbus, OH, 43205-2664, USA. .,Department of Pediatrics, The Ohio State University School of Medicine, Columbus, OH, USA.
| | - Hemalatha G Rangarajan
- Division of Hematology, Oncology, and Bone Marrow Transplant, Nationwide Children's Hospital, 700 Children's Drive, Suite 5A.1, Columbus, OH, 43205-2664, USA.,Department of Pediatrics, The Ohio State University School of Medicine, Columbus, OH, USA
| | - Brian P Tullius
- Division of Hematology, Oncology, and Bone Marrow Transplant, Nationwide Children's Hospital, 700 Children's Drive, Suite 5A.1, Columbus, OH, 43205-2664, USA.,Department of Pediatrics, The Ohio State University School of Medicine, Columbus, OH, USA
| | - Dean A Lee
- Division of Hematology, Oncology, and Bone Marrow Transplant, Nationwide Children's Hospital, 700 Children's Drive, Suite 5A.1, Columbus, OH, 43205-2664, USA.,Department of Pediatrics, The Ohio State University School of Medicine, Columbus, OH, USA
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4
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Analysis of ex vivo expanded and activated clinical-grade human NK cells after cryopreservation. Cytotherapy 2020; 22:450-457. [PMID: 32536506 DOI: 10.1016/j.jcyt.2020.05.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 04/16/2020] [Accepted: 05/02/2020] [Indexed: 12/18/2022]
Abstract
BACKGROUND AIMS Several methods to expand and activate (EA) NK cells ex vivo have been developed for the treatment of relapsed or refractory cancers. Infusion of fresh NK cells is generally preferred to the infusion of cryopreserved/thawed (C/T) NK cells because of concern that cryopreservation diminishes NK cell activity. However, there has been little head-to-head comparison of the functionality of fresh versus C/T NK cell products. METHODS We evaluated activity of fresh and C/T EA NK cells generated by interleukin (IL)-15, IL-2 and CD137L expansion. RESULTS Analysis of C/T NK cell products demonstrated decreased recovery of viable CD56+ cells, but the proportion of NK cells in the C/T EA NK cell product did not decrease compared with the fresh EA NK cell product. Fresh and C/T EA NK cells demonstrated increased granzyme B compared with NK cells pre-expansion, but only fresh EA NK cells showed increased NKG2D. Compared with fresh EA NK cells, cytotoxic ability of C/T EA NK cells was reduced, but C/T EA NK cells remained potently cytotoxic against tumor cells via both antibody-independent and antibody-dependent mechanisms within 4 h post-thaw. Fresh EA NK cells generated high levels of gamma interferon (IFN-γ), which was abrogated by JAK1/JAK2 inhibition with ruxolitinib, but C/T EA NK cells showed lower IFN-γ unaffected by JAK1/JAK2 inhibition. DISCUSSION Usage of C/T EA NK cells may be an option to provide serial "boost" NK cell infusions from a single apheresis to maximize NK cell persistence and potentially improve NK-induced responses to refractory cancer.
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5
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Lee DA. Cellular therapy: Adoptive immunotherapy with expanded natural killer cells. Immunol Rev 2019; 290:85-99. [DOI: 10.1111/imr.12793] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 06/27/2019] [Accepted: 06/29/2019] [Indexed: 12/21/2022]
Affiliation(s)
- Dean A. Lee
- Department of Hematology, Oncology, and Bone Marrow Transplantation Nationwide Children's Hospital Columbus Ohio
- Department of Pediatrics The Ohio State University Columbus Ohio
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6
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Lieberman NAP, DeGolier K, Haberthur K, Chinn H, Moyes KW, Bouchlaka MN, Walker KL, Capitini CM, Crane CA. An Uncoupling of Canonical Phenotypic Markers and Functional Potency of Ex Vivo-Expanded Natural Killer Cells. Front Immunol 2018; 9:150. [PMID: 29456538 PMCID: PMC5801405 DOI: 10.3389/fimmu.2018.00150] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 01/17/2018] [Indexed: 12/31/2022] Open
Abstract
Recent advances in cellular therapies for patients with cancer, including checkpoint blockade and ex vivo-expanded, tumor-specific T cells, have demonstrated that targeting the immune system is a powerful approach to the elimination of tumor cells. Clinical efforts have also demonstrated limitations, however, including the potential for tumor cell antigenic drift and neoantigen formation, which promote tumor escape and recurrence, as well as rapid onset of T cell exhaustion in vivo. These findings suggest that antigen unrestricted cells, such as natural killer (NK) cells, may be beneficial for use as an alternative to or in combination with T cell based approaches. Although highly effective in lysing transformed cells, to date, few clinical trials have demonstrated antitumor function or persistence of transferred NK cells. Several recent studies describe methods to expand NK cells for adoptive transfer, although the effects of ex vivo expansion are not fully understood. We therefore explored the impact of a clinically validated 12-day expansion protocol using a K562 cell line expressing membrane-bound IL-15 and 4-1BB ligand with high-dose soluble IL-2 on the phenotype and functions of NK cells from healthy donors. Following expansions using this protocol, we found expression of surface proteins that implicate preferential expansion of NK cells that are not fully mature, as is typically associated with highly cytotoxic NK cell subsets. Despite increased expression of markers associated with functional exhaustion in T cells, we found that ex vivo-expanded NK cells retained cytokine production capacity and had enhanced tumor cell cytotoxicity. The preferential expansion of an NK cell subset that is phenotypically immature and functionally pleiotropic suggests that adoptively transferred cells may persist better in vivo when compared with previous methods using this approach. Ex vivo expansion does not quell killer immunoglobulin-like receptor diversity, allowing responsiveness to various factors in vivo that may influence activation and inhibition. Collectively, our data suggest that in addition to robust NK cell expansion that has been described using this method, expanded NK cells may represent an ideal cell therapy that is longer lived, highly potent, and responsive to an array of activating and inhibitory signals.
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Affiliation(s)
- Nicole A P Lieberman
- Ben Towne Center for Childhood Cancer Research, Seattle Children's Research Institute, Seattle, WA, United States
| | - Kole DeGolier
- Ben Towne Center for Childhood Cancer Research, Seattle Children's Research Institute, Seattle, WA, United States
| | - Kristen Haberthur
- Ben Towne Center for Childhood Cancer Research, Seattle Children's Research Institute, Seattle, WA, United States
| | - Harrison Chinn
- Ben Towne Center for Childhood Cancer Research, Seattle Children's Research Institute, Seattle, WA, United States
| | - Kara W Moyes
- Ben Towne Center for Childhood Cancer Research, Seattle Children's Research Institute, Seattle, WA, United States
| | - Myriam N Bouchlaka
- Department of Pediatrics, Carbone Comprehensive Cancer Center, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Kirsti L Walker
- Department of Pediatrics, Carbone Comprehensive Cancer Center, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Christian M Capitini
- Department of Pediatrics, Carbone Comprehensive Cancer Center, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Courtney A Crane
- Ben Towne Center for Childhood Cancer Research, Seattle Children's Research Institute, Seattle, WA, United States.,Department of Neurological Surgery, University of Washington, Seattle, WA, United States
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7
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Erokhina SA, Streltsova MA, Kanevskiy LM, Telford WG, Sapozhnikov AM, Kovalenko EI. HLA-DR + NK cells are mostly characterized by less mature phenotype and high functional activity. Immunol Cell Biol 2018; 96:212-228. [PMID: 29363179 PMCID: PMC8063572 DOI: 10.1111/imcb.1032] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 11/08/2017] [Accepted: 11/15/2017] [Indexed: 12/30/2022]
Abstract
NK cells change their phenotype and functional characteristics during activation. In this work, we searched for a relationship of HLA-DR expression with differentiation stages and functional activity of NK cells ex vivo and stimulated in vitro with IL-2 challenged with gene modified feeder K562 cells expressing membrane-bound IL-21 (K562-mbIL21). This stimulation technique has been described for NK cell expansion in clinical use. We have observed that HLA-DR expression in freshly isolated circulating NK cells was mostly associated with less differentiated CD56bright CD57- cells, although in some individuals it could also be found in terminally differentiated CD57+ cells. Ex vivo HLA-DR+ NK cells possessed better capacity to produce IFN-γ in response to cytokine stimulation compared to their HLA-DR- counterparts. In vitro activation with IL-2 and K562-mbIL21 induces an increase in HLA-DR-positive NK cell proportion, again mostly among CD56bright CD57- NK cells. This happened in particular due to appearance of HLA-DR+ expression de novo in HLA-DR-negative cells. Acquired in vitro HLA-DR expression was associated with NK cell proliferation activity, more intense cytokine-induced IFN-γ production, increased degranulation toward feeder cells, and higher expression of CD86 and NKG2D. Thus, stimulation with IL-2/K562-mbIL21 causes a significant phenotype and functional shift during NK cell activation and expansion.
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Affiliation(s)
- Sofya A Erokhina
- Laboratory of Cell Interactions, Department of Immunology, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - Maria A Streltsova
- Laboratory of Cell Interactions, Department of Immunology, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - Leonid M Kanevskiy
- Laboratory of Cell Interactions, Department of Immunology, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - William G Telford
- Experimental Transplantation and Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Alexander M Sapozhnikov
- Laboratory of Cell Interactions, Department of Immunology, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - Elena I Kovalenko
- Laboratory of Cell Interactions, Department of Immunology, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
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8
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Dickinson AM, Norden J, Li S, Hromadnikova I, Schmid C, Schmetzer H, Jochem-Kolb H. Graft-versus-Leukemia Effect Following Hematopoietic Stem Cell Transplantation for Leukemia. Front Immunol 2017. [PMID: 28638379 PMCID: PMC5461268 DOI: 10.3389/fimmu.2017.00496] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The success of hematopoietic stem cell transplantation (HSCT) lies with the ability of the engrafting immune system to remove residual leukemia cells via a graft-versus-leukemia effect (GvL), caused either spontaneously post-HSCT or via donor lymphocyte infusion. GvL effects can also be initiated by allogenic mismatched natural killer cells, antigen-specific T cells, and activated dendritic cells of leukemic origin. The history and further application of this GvL effect and the main mechanisms will be discussed and reviewed in this chapter.
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Affiliation(s)
- Anne M Dickinson
- Haematological Sciences, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Jean Norden
- Haematological Sciences, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Shuang Li
- Third Faculty of Medicine, Department of Molecular Biology and Cell Pathology, Charles University, Prague, Czechia
| | - Ilona Hromadnikova
- Third Faculty of Medicine, Department of Molecular Biology and Cell Pathology, Charles University, Prague, Czechia
| | - Christoph Schmid
- Department for Hematopoietic Cell Transplantation, University Hospital Augsburg, Munich, Germany
| | - Helga Schmetzer
- Department for Hematopoietic Cell Transplantation, Internal Medicine III, Hospital of the University of Munich, Munich, Germany
| | - Hans Jochem-Kolb
- Department of Hematology-Oncology Immunology Infectious Diseases, Klinikum München-Schwabing, Munich, Germany
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9
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Pittari G, Filippini P, Gentilcore G, Grivel JC, Rutella S. Revving up Natural Killer Cells and Cytokine-Induced Killer Cells Against Hematological Malignancies. Front Immunol 2015; 6:230. [PMID: 26029215 PMCID: PMC4429635 DOI: 10.3389/fimmu.2015.00230] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Accepted: 04/29/2015] [Indexed: 01/29/2023] Open
Abstract
Natural killer (NK) cells belong to innate immunity and exhibit cytolytic activity against infectious pathogens and tumor cells. NK-cell function is finely tuned by receptors that transduce inhibitory or activating signals, such as killer immunoglobulin-like receptors, NK Group 2 member D (NKG2D), NKG2A/CD94, NKp46, and others, and recognize both foreign and self-antigens expressed by NK-susceptible targets. Recent insights into NK-cell developmental intermediates have translated into a more accurate definition of culture conditions for the in vitro generation and propagation of human NK cells. In this respect, interleukin (IL)-15 and IL-21 are instrumental in driving NK-cell differentiation and maturation, and hold great promise for the design of optimal NK-cell culture protocols. Cytokine-induced killer (CIK) cells possess phenotypic and functional hallmarks of both T cells and NK cells. Similar to T cells, they express CD3 and are expandable in culture, while not requiring functional priming for in vivo activity, like NK cells. CIK cells may offer some advantages over other cell therapy products, including ease of in vitro propagation and no need for exogenous administration of IL-2 for in vivo priming. NK cells and CIK cells can be expanded using a variety of clinical-grade approaches, before their infusion into patients with cancer. Herein, we discuss GMP-compliant strategies to isolate and expand human NK and CIK cells for immunotherapy purposes, focusing on clinical trials of adoptive transfer to patients with hematological malignancies.
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Affiliation(s)
- Gianfranco Pittari
- Department of Medical Oncology, National Center for Cancer Care and Research, Hamad Medical Corporation , Doha , Qatar
| | - Perla Filippini
- Deep Immunophenotyping Core, Division of Translational Medicine, Sidra Medical and Research Center , Doha , Qatar
| | - Giusy Gentilcore
- Deep Immunophenotyping Core, Division of Translational Medicine, Sidra Medical and Research Center , Doha , Qatar
| | - Jean-Charles Grivel
- Deep Immunophenotyping Core, Division of Translational Medicine, Sidra Medical and Research Center , Doha , Qatar
| | - Sergio Rutella
- Clinical Research Center, Division of Translational Medicine, Sidra Medical and Research Center , Doha , Qatar
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10
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IL-21: a pleiotropic cytokine with potential applications in oncology. J Immunol Res 2015; 2015:696578. [PMID: 25961061 PMCID: PMC4413888 DOI: 10.1155/2015/696578] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Revised: 03/19/2015] [Accepted: 03/25/2015] [Indexed: 12/29/2022] Open
Abstract
Interleukin- (IL-) 21 is a pleiotropic cytokine that regulates the activity of both innate and specific immunity. Indeed, it costimulates T and natural killer (NK) cell proliferation and function and regulates B cell survival and differentiation and the function of dendritic cells. In addition, IL-21 exerts divergent effects on different lymphoid cell leukemia and lymphomas, as it may support cell proliferation or on the contrary induce growth arrest or apoptosis of the neoplastic lymphoid cells. Several preclinical studies showed that IL-21 has antitumor activity in different tumor models, through mechanism involving the activation of NK and T or B cell responses. Moreover, IL-21's antitumor activity can be potentiated by its combination with other immune-enhancing molecules, monoclonal antibodies recognizing tumor antigens, chemotherapy, or molecular targeted agents. Clinical phase I-II studies of IL-21 in cancer patients showed immune stimulatory properties, acceptable toxicity profile, and antitumor effects in a fraction of patients. In view of its tolerability, IL-21 is also suitable for combinational therapeutic regimens with other agents. This review will summarize the biological functions of IL-21, and address its role in lymphoid malignancies and preclinical and clinical studies of cancer immunotherapy.
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Multiple effects of IL-21 on human NK cells in ex vivo expansion. Immunobiology 2015; 220:876-88. [PMID: 25758713 DOI: 10.1016/j.imbio.2015.01.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 01/22/2015] [Accepted: 01/22/2015] [Indexed: 11/21/2022]
Abstract
Natural killer (NK) cells (CD56(+)CD3(-)) are large, granular immunocytes that play a very pivotal role in the anti-inflammatory response and tumor surveillance. As an ideal cytotoxic lymphocyte (CTL), NK cells have attracted much attention in clinical trials. However, an insufficient number and their limited life span are bottlenecks that limit the application of NK cells in adoptive immunotherapy. Interleukins such as IL-2, IL-15 and IL-18 are recognized as factors that stimulate NK cells and have been used in NK cells ex vivo expansion. Similar to IL-2 and IL-15, IL-21 is a common γ-chain cytokine that is important in NK cell activation, maturation and proliferation. The present study aims to assess the effects of membrane-bound and soluble IL-21 on primary human NK cells during ex vivo expansion. IL-21 was found to have multiple effects on NK cells, increasing their cytotoxicity in a concentration-dependent manner by up-regulating IFN-γ and Granzyme-B expression. Nevertheless, at a high concentration (50 ng/mL), IL-21 curtailed the life span of NK cells by significantly inducing apoptosis. Moreover, when treated with IL-21, the number of NKT (CD56(+)CD3(+)) cells increased among peripheral blood mononuclear cells (PBMCs) during ex vivo expansion in a concentration-dependent manner. IL-21 also promoted expanded cells to enter into S phase of the cell cycle during the first to second weeks of culture. All these results suggest that IL-21 has multiple effects on NK cell development and functions. More attention should be given to the dosage and multiple effects of IL-21 when it was applied to NK cells in ex vivo expansion.
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