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Natural killer (NK) cells belong to the family of innate immune cells with the capacity to recognize and kill tumor cells. Different phenotypes and functional properties of NK cells have been described in tumor patients, which could be shaped by the tumor microenvironment. The discovery of HLA class I-specific inhibitory receptors controlling NK cell activity paved the way to the fundamental concept of modulating immune responses that are regulated by an array of inhibitory receptors, and emphasized the importance to explore the potential of NK cells in cancer therapy. Although a whole range of NK cell-based approaches are currently being developed, there are still major challenges that need to be overcome for improved efficacy of these therapies. These include escape of tumor cells from NK cell recognition due to their expression of inhibitory molecules, immune suppressive signals of NK cells, reduced NK cell infiltration of tumors, an immune suppressive micromilieu and limited in vivo persistence of NK cells. Therefore, this review provides an overview about the NK cell biology, alterations of NK cell activities, changes in tumor cells and the tumor microenvironment contributing to immune escape or immune surveillance by NK cells and their underlying molecular mechanisms as well as the current status and novel aspects of NK cell-based therapeutic strategies including their genetic engineering and their combination with conventional treatment options to overcome tumor-mediated evasion strategies and improve therapy efficacy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Seliger and Koehl.)

State-of-the-art treatment strategies have drastically ameliorated the outcome of patients affected by cancer. However, resistant and recurrent solid tumors are generally nonresponsive to conventional therapies. A central factor in the sequence of events that lead to cancer is an alteration in antitumor immune surveillance, which results in failure to recognize and eliminate the transformed tumor cell. A greater understanding of the dysregulation and evasion of the immune system in the evolution and progression of cancer provides the basis for improved therapies. Targeted strategies, such as T-cell therapy, not only generally spare normal tissues, but also use alternative antineoplastic mechanisms that synergize with other therapeutics. Despite encouraging success in hematologic malignancies, adaptive cellular therapies for solid tumors face unique challenges because of the immunosuppressive tumor microenvironment, and the hurdle of T-cell trafficking within scarcely accessible tumor sites. This review provides a brief overview of current cellular therapeutic strategies for solid tumors, research carried out to increase efficacy and safety, and results from ongoing clinical trials., (© The Author(s) 2019. Published by Oxford University Press on behalf of the European Society for Medical Oncology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Background Aims: Natural killer (NK) cells, either naive or genetically engineered, are increasingly considered for cellular therapy of patients with malignancies. When using NK cells from peripheral blood, the number of expanded NK cells can be highly variable and the need for NK cell enrichment can make the process expensive. The NK-92 cell line (CD56+/CD3-) that was isolated from a patient with lymphoma has predictable high cytotoxic activity and can be expanded under good manufacturing practice conditions in recombinant interleukin-2., Methods: Fifteen patients (age, 9-71 years) with advanced, treatment-resistant malignancies, either solid tumors/sarcomas (n = 13) or leukemia/lymphoma (n = 2), received two infusions of NK-92 cells, given 48 h apart. Three cohorts of patients were treated with escalating doses of NK-92 cells (n = 7 at 1 × 10(9), n = 6 at 3 × 10(9) and n = 2 at 1 × 10(10) cells/m(2))., Results: No infusion-related or long-term side effects were observed. The dose of 10(10) cells/m(2) was considered the maximum expandable cell dose with the use of an established culture bag system. Three fourths of patients with lung cancer had some anti-tumor response. Only one patient of seven had development of human leukocyte antigen antibodies. The persistence of NK-92 cells (male origin) in the circulation was confirmed by Y chromosome-specific polymerase chain reaction in two female patients., Conclusions: Infusions of NK-92 cells up to 10(10) cells/m(2) were well tolerated. Despite the allogeneic nature of NK-92, development of human leukocyte antigen antibodies in these patients with cancer appears to be rare. The cells can persist in the recipient's circulation for at least 48 h. Some encouraging responses were seen in patients with advanced lung cancer., (Copyright © 2013 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

Despite the availability of new antifungal compounds, morbidity and mortality of invasive fungal disease in allogeneic hematopoietic stem cell recipients are still unacceptably high. Over the past decade, one could witness an exciting improvement of the understanding of the molecular pathogenesis and of the complexity of host antifungal immune responses. This, in turn, provides critical information to augment host immunity against fungal pathogens. Strategies for enhancing the immune system include the administration of effector and regulatory cells (e.g., granulocytes, antigen-specific T cells, dendritic cells) as well as the administration of recombinant cytokines, interferons and growth factors (e.g., interferon-γ, keratinocyte growth factor, granulocyte- and granulocyte-macrophage colony stimulating factor). One has to recognize at the same time, however, that data of in vitro assays and animal models cannot necessarily be transferred into the clinical setting. In addition, meaningful clinical trials in allogeneic stem cell recipients suffering from invasive fungal disease require sufficiently large and homogenous cohorts of patients and can only be performed in international collaboration, but may ultimately improve the outcome of allogeneic transplant recipients with invasive fungal disease.

To characterize natural killer (NK) cell subpopulations during activation, we analyzed the NK cell receptor repertoire and functionality of purified clinical scale CD56CD3 donor NK cells during stimulation with 1000 U/mL interleukin (IL)-2 for up to 14 days. In a phase I/II trial, we investigated the efficacy and feasibility of nonidentical NK cell infusion in patients with neuroblastoma after haploidentical stem cell transplantation. After IL-2 stimulation, large differences in the distribution of CD16 and CD16 subpopulations were found in 12 donors. Thereby, surface expression for all natural cytotoxicity receptors (NCRs) and NKG2D increased. In addition, killer cell immunoglobulin-like receptor (KIR) NK cells were overgrown by KIR proportion and the homing receptor CD62L was lost during stimulation. NK cell cytotoxicity against K562 and neuroblastoma cells increased and significantly higher cytokine secretion (eg, interferon-gamma, tumor necrosis factor-beta, macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta) was observed after IL-2 stimulation compared with freshly isolated NK cells. However, NK cells of donors showing an initially enhanced cytotoxicity combined with NCR and CD69 expression, seemed to be exhausted and did not favor a stimulation period over 9 days. When IL-2-stimulated NK cells were given to transplant recipients, they induced a decrease of peripheral blood NK, in particular of CD56-NK cells. Our data indicate that IL-2 stimulation increases the expression of activating receptors and emphasizes mechanisms beside KIR/human leukocyte antigen. Furthermore, the results suggest that the expansion period of purified NK cells has to be individualized to optimize NK cell immunotherapy.

A monoclonal chimeric antibody ch.MK1 was generated by immunizing F004 mice expressing human instead of murine IgG1/kappa immunoglobulin constant regions. The novel antibody specifically binds cell surface-expressed human neural cell adhesion molecule (NCAM) as shown by immunoprecipitation, flow cytometry and cytospins. Functional analysis revealed nearly complete absence of complement-dependent cytolysis in ch.MK1 and in all other anti-NCAM antibodies tested for reference (UJ13a, ERIC1, 123C3, ch.5A2, B159), indicating an unexpected and group-specific property of anti-NCAM antibodies. As a most plausible mechanism, posttranslational modification of NCAM by complement-inhibiting polysialic acid is discussed. The antibody ch.MK1 demonstrated significant in vivo activity against NCAM-positive neuroblastoma in SCID mice in presence of human peripheral blood mononuclear cell. In absence of human peripheral blood mononuclear cell no distinct antitumor activity of the antibody alone was observed. In ch.MK1 the cellular component of the immune system seems to be the dominant effector mechanism, whereas complement-dependent cytolysis seems not to be necessarily required for antitumor activity. These observations help us to understand immunotherapeutic mechanisms of native anti-NCAM antibodies and may additionally contribute to the understanding of results of currently ongoing clinical studies with conjugated anti-NCAM antibodies.

Changes of the immune system can be a consequence of an underlying malignancy or induced by antineoplastic treatment. Both influence the risk for infectious complications and relapse. Over the past decade, there have been a series of major developments in the laboratory assessment of immune dysfunction, particularly as it relates to the complex interactions of the distinct components of the immune system. In addition, several new therapeutic strategies that modulate the immune system have been introduced. We review new findings that can affect clinical decision making. Better insights into the impairment of host response could provide the rationale for the development of new therapeutic strategies, for both supportive care and anticancer treatment.

Immunotherapy of childhood malignancies has a magic aura of promising an easy way to cure. It is not only the public, but also the medical community, which has caused this hope. Therefore, it was worthwhile to bring together a panel of experts working in the field of immunotherapy in order to discuss ongoing projects, and to show hopes and disappointments. The result was a fascinating symposium sponsored by The Kind Philipp Leukemia Foundation (Mönchengladbach, Germany). The symposium took place in the Reissensburg near Ulm (Germany) which gives the ideal location for such an event.

Adoptive immunotherapy using natural killer (NK) cells may prove useful, especially in situations where infusion of T cells is impractical such as in recipients of haploidentical stem cell transplantation (HSCT) from haploidentical donors. NK cells may induce potent antileukemic and possibly antirejection activity and may even mitigate graft versus host disease (GvHD). Whether such effects are clinically important and whether they are mediated mainly or exclusively by KIR-HLA class I interactions remains to be determined. Recent advances in graft engineering provide for methods to isolate large numbers of purified NK cells. Several groups have shown that clinical grade NK cells up to a dose of 10(7)/kg may be collected and purified for the purpose of infusion to patients. Early results, in a limited number of patients, show that these cell doses may be administered without adverse events and without inducing GvHD. Whether such infusions will be useful in preventing graft rejection, or exerting graft versus leukemia effects and hastening immune recovery requires further study.

Monocyte-derived conventional dendritic cells (ConvDCs) loaded with melanoma antigens showed modest responses in clinical trials. Efficacy studies were hampered by difficulties in ConvDC manufacturing and low potency. Overcoming these issues, we demonstrated higher potency of lentiviral vector (LV)-programmed DCs. Monocytes were directly induced to self-differentiate into DCs (SmartDC-TRP2) upon transduction with a tricistronic LV encoding for cytokines (granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4)) and a melanoma antigen (tyrosinase-related protein 2 (TRP2)). Here, SmartDC-TRP2 generated with monocytes from five advanced melanoma patients were tested in autologous DC:T cell stimulation assays, validating the activation of functional TRP2-specific cytotoxic T lymphocytes (CTLs) for all patients. We described methods compliant to good manufacturing practices (GMP) to produce LV and SmartDC-TRP2. Feasibility of monocyte transduction in a bag system and cryopreservation following a 24-h standard operating procedure were achieved. After thawing, 50% of the initial monocyte input was recovered and SmartDC-TRP2 self-differentiated in vitro, showing uniform expression of DC markers, detectable LV copies and a polyclonal LV integration pattern not biased to oncogenic loci. GMP-grade SmartDC-TRP2 expanded TRP2-specific autologous CTLs in vitro. These results demonstrated a simpler GMP-compliant method of manufacturing an effective individualized DC vaccine. Such DC vaccine, when in combination with checkpoint inhibition therapies, might provide higher specificity against melanoma. [ABSTRACT FROM AUTHOR]

Adoptive immunotherapy with allogeneic purified natural killer (NK) cell products might exert graft-versus-tumor alloreactivity with little risk of GVHD. In a prospective phase II study in two centers, we administered purified NK cell products to high-risk patients treated with haploidentical T-cell-depleted SCT. Sixteen patients received a total of 29 NK cell infusions on days +3, +40 and +100 after transplantation. Median doses (and ranges) of infused NK- and T-cells per product were 1.21 (0.3-3.8) × 107/kg and 0.03 (0.004-0.72) × 105/kg, respectively. With a median follow-up of 5.8 years 4/16 patients are alive. Cause of death was relapse in five, GVHD in three, graft failure in three, and transplant related neurotoxicity in one patient. Four patients developed acute GVHDgrade II, all receiving a total of 0.5 × 105 T cells/kg. Compared with historical controls, NK cell infusions had no apparent effect on the rates of graft failure or relapse. Adoptive transfer of allogeneic NK cells is safe and feasible, but further studies are needed to determine the optimal dose and timing of NK cell therapy. Moreover, NK cell activation/expansion may be required to attain clinical benefit, while careful consideration must be given to the number of T cells infused. [ABSTRACT FROM AUTHOR]

Invasive aspergillosis is a major cause of morbidity and mortality in patients undergoing allogeneic hematopoietic SCT. There is a growing body of evidence that T cells are important in the host defense against Aspergillus, and adoptively transferred anti-Aspergillus T-helper 1 (TH) 1 cells might reduce infectious mortality in hematopoietic transplant recipients. Here we present for the first time a simple and rapid method for the clinical-scale generation of functionally active anti-Aspergillus T cells according to good manufacturing practice conditions. A total of 1.1 × 109 WBCs derived from a leukapheresis product were incubated with Aspergillus antigens. Stimulated cells were selected by means of the IFN-γ secretion assay and expanded. In three independent experiments, a median number of 2 × 107 CD3+CD4+cells (range, 0.9–3.2 × 107) were obtained within 13 days. The cultured CD3+CD4+ cells exhibited almost exclusively a memory activated T-helper cell phenotype. Upon restimulation, the generated T cells produced IFN-γ, but no IL-4 or IL-10, indicating a TH1-cell population. Additionally, the cells proliferated upon restimulation and showed reduced alloreactivity compared to unselected CD4+ cells. This method of generating is suitable for future prospective trials designed to evaluate the effect of adoptive immunotherapy in hematopoietic transplant recipients with invasive aspergillosis.Bone Marrow Transplantation (2009) 43, 13–19; doi:10.1038/bmt.2008.271; published online 1 September 2008 [ABSTRACT FROM AUTHOR]