A novel four-colour flow cytometric assay to determine natural killer cell or T-cell-mediated cellular cytotoxicity against leukaemic cells in peripheral or bone marrow specimens containing greater than 20% of normal cells

Development of Automated Separation, Expansion, and Quality Control Protocols for Clinical-Scale Manufacturing of Primary Human NK Cells and Alpharetroviral Chimeric Antigen Receptor Engineering

In cellular immunotherapies, natural killer (NK) cells often demonstrate potent antitumor effects in high-risk cancer patients. But Good Manufacturing Practice (GMP)-compliant manufacturing of clinical-grade NK cells in high numbers for patient treatment is still a challenge. Therefore, new protocols for isolation and expansion of NK cells are required. In order to attack resistant tumor entities, NK cell killing can be improved by genetic engineering using alpharetroviral vectors that encode for chimeric antigen receptors (CARs). The aim of this work was to demonstrate GMP-grade manufacturing of NK cells using the CliniMACS^® Prodigy device (Prodigy) with implemented applicable quality controls. Additionally, the study aimed to define the best time point to transduce expanding NK cells with alpharetroviral CAR vectors. Manufacturing and clinical-scale expansion of primary human NK cells were performed with the Prodigy starting with 8-15.0 × 10⁹ leukocytes (including 1.1–2.3 × 10⁹ NK cells) collected by small-scale lymphapheresis (n = 3). Positive fraction after immunoselection, in-process controls (IPCs), and end product were quantified by flow cytometric no-wash, single-platform assessment, and gating strategy using positive (CD56/CD16/CD45), negative (CD14/CD19/CD3), and dead cell (7-aminoactinomycine [7-AAD]) discriminators. The three runs on the fully integrated manufacturing platform included immunomagnetic separation (CD3 depletion/CD56 enrichment) followed by NK cell expansion over 14 days. This process led to high NK cell purities (median 99.1%) and adequate NK cell viabilities (median 86.9%) and achieved a median CD3+ cell depletion of log −3.6 after CD3 depletion and log −3.7 after immunomagnetic CD3 depletion and consecutive CD56 selection. Subsequent cultivation of separated NK cells in the CentriCult^® chamber of Prodigy resulted in approximately 4.2–8.5-fold NK cell expansion rates by adding of NK MACS^® basal medium containing NK MACS^® supplement, interleukin (IL)-2/IL-15 and initial IL-21. NK cells expanded for 14 days revealed higher expression of natural cytotoxicity receptors (NKp30, NKp44, NKp46, and NKG2D) and degranulation/apoptotic markers and stronger cytolytic properties against K562 compared to non-activated NK cells before automated cultivation. Moreover, expanded NK cells had robust growth and killing activities even after cryopreservation. As a crucial result, it was possible to determine the appropriate time period for optimal CAR transduction of cultivated NK cells between days 8 and 14, with the highest anti-CD123 CAR expression levels on day 14. The anti-CD123 CAR NK cells showed retargeted killing and degranulation properties against CD123-expressing KG1a target cells, while basal cytotoxicity of non-transduced NK cells was determined using the CD123-negative cell line K562. Time-lapse imaging to monitor redirected effector-to-target contacts between anti-CD123 CAR NK and KG1a showed long-term effector–target interaction. In conclusion, the integration of the clinical-scale expansion procedure in the automated and closed Prodigy system, including IPC samples and quality controls and optimal time frames for NK cell transduction with CAR vectors, was established on 48-well plates and resulted in a standardized GMP-compliant overall process.

Triplebody Mediates Increased Anti-Leukemic Reactivity of IL-2 Activated Donor Natural Killer (NK) Cells and Impairs Viability of Their CD33-Expressing NK Subset

Natural killer cells (NK) are essential for the elimination of resistant acute myeloid and acute lymphoblastic leukemia (AML and ALL) cells. NK cell-based immunotherapies have already successfully entered for clinical trials, but limitations due to immune escape mechanisms were identified. Therefore, we extended our established NK cell protocol by integration of the previously investigated powerful trispecific immunoligand ULBP2-aCD19-aCD33 [the so-called triplebodies (TBs)] to improve the anti-leukemic specificity of activated NK cells. IL-2-driven expansion led to strongly elevated natural killer group 2 member D (NKG2D) expressions on donor NK cells which promote the binding to ULBP2⁺ TBs. Similarly, CD33 expression on these NK cells could be detected. Dual-specific targeting and elimination were investigated against the B-cell precursor leukemia cell line BV-173 and patient blasts, which were positive for myeloid marker CD33 and B lymphoid marker CD19 exclusively presented on biphenotypic B/myeloid leukemia’s. Cytotoxicity assays demonstrated improved killing properties of NK cells pre-coated with TBs compared to untreated controls. Specific NKG2D blocking on those NK cells in response to TBs diminished this killing activity. On the contrary, the observed upregulation of surface CD33 on about 28.0% of the NK cells decreased their viability in response to TBs during cytotoxic interaction of effector and target cells. Similar side effects were also detected against CD33⁺ T- and CD19⁺ B-cells. Very preliminary proof of principle results showed promising effects using NK cells and TBs against primary leukemic cells. In summary, we demonstrated a promising strategy for redirecting primary human NK cells in response to TBs against leukemia, which may lead to a future progress in NK cell-based immunotherapies.

Efficient generation of gene-modified human natural killer cells via alpharetroviral vectors

Natural killer (NK) cells play an important role in tumor immunotherapy with their unique capability of killing transformed cells without the need for prior sensitization and without major histocompatibility complex (MHC)/peptide restriction. However, tumor cells can escape NK cell cytotoxicity by various tumor immune escape mechanisms. To overcome these escape mechanisms, NK cells can be modified to express chimeric antigen receptors (CARs), enhancing their tumor-specific cytotoxicity. To determine the most efficacious method to modify human NK cells, we compared different retroviral vector systems, retroviral pseudotypes, and transduction protocols. Using optimized transduction conditions, the highest transduction levels (up to 60%) were achieved with alpharetroviral vectors. Alpharetroviral-modified primary human NK cells exhibited no alteration in receptor expression and had similar degranulation activity as untransduced NK cells, thus demonstrating that alpharetroviral modification did not negatively affect NK cell cytotoxicity. Transduction of NK cells with an alpharetroviral vector containing a CD19 CAR expression cassette selectively enhanced NK cell cytotoxicity towards CD19-expressing leukemia cells, achieving nearly complete elimination of leukemia cells after 48 h. Taken together, alpharetroviral vectors are promising tools for NK cell-mediated cancer immunotherapy applications.

KEY MESSAGES

Efficient modification of human NK cells using alpharetroviral vectors. Anti-CD19-CAR-NK cells exhibited improved cytotoxicity towards CD19(+) leukemia cells. Alpharetroviral vectors are promising tools for immunotherapy applications using NK cells.

Advances in clinical NK cell studies: Donor selection, manufacturing and quality control

Natural killer (NK) cells are increasingly used in clinical studies in order to treat patients with various malignancies. The following review summarizes platform lectures and 2013–2015 consortium meetings on manufacturing and clinical use of NK cells in Europe and United States. A broad overview of recent pre-clinical and clinical results in NK cell therapies is provided based on unstimulated, cytokine-activated, as well as genetically engineered NK cells using chimeric antigen receptors (CAR). Differences in donor selection, manufacturing and quality control of NK cells for cancer immunotherapies are described and basic recommendations are outlined for harmonization in future NK cell studies.

Cetuximab Reconstitutes Pro-Inflammatory Cytokine Secretions and Tumor-Infiltrating Capabilities of sMICA-Inhibited NK Cells in HNSCC Tumor Spheroids

Immunosuppressive factors, such as soluble major histocompatibility complex class I chain-related peptide A (sMICA) and transforming growth factor beta 1 (TGF-β₁), are involved in tumor immune escape mechanisms (TIEMs) exhibited by head and neck squamous cell carcinomas (HNSCCs) and may represent opportunities for therapeutic intervention. In order to overcome TIEMs, we investigated the antibody-dependent cellular cytotoxicity (ADCC), cytokine release and retargeted tumor infiltration of sMICA-inhibited patient NK cells expressing Fcγ receptor IIIa (FcγRIIIa, CD16a) in the presence of cetuximab, an anti-epidermal growth factor receptor (HER1) monoclonal antibody (mAb). Compared to healthy controls, relapsed HNSCC patients (n = 5), not currently in treatment revealed decreased levels of circulating regulatory NK cell subsets in relation to increased cytotoxic NK cell subpopulations. Elevated sMICA and TGF-β₁ plasma levels correlated with diminished TNFα and IFN-γ release and decreased NKG2D (natural killer group 2 member D)-dependent killing of HNSCC cells by NK cells. Incubation of IL-2-activated patient NK cells with patient plasma containing elevated sMICA or sMICA analogs (shed MICA and recombinant MICA) significantly impaired NKG2D-mediated killing by down-regulation of NKG2D surface expression. Of note, CD16 surface expression levels, pro-apoptotic and activation markers, and viability of patient and healthy donor NK cell subpopulations were not affected by this treatment. Accordingly, cetuximab restored killing activity of sMICA-inhibited patient NK cells against cetuximab-coated primary HNSCC cells via ADCC in a dose-dependent manner. Rapid reconstitution of anti-tumor recognition and enhanced tumor infiltration of treated NK cells was monitored by 24 h co-incubation of HNSCC tumor spheroids with cetuximab (1 μg/ml) and was characterized by increased IFN-γ and TNFα secretion. This data show that the impaired NK cell-dependent tumor surveillance in relapsed HNSCC patients could be reversed by the re-establishment of ADCC-mediated effector cell activity, thus supporting NK cell-based immunotherapy in combination with antineoplastic monoclonal mAbs.

Increased sMICA and TGFβ1 levels in HNSCC patients impair NKG2D-dependent functionality of activated NK cells

Disseminated head-and-neck squamous cell carcinoma (HNSCC) escapes immune surveillance and thus frequently manifests as fatal disease. Here, we report on the distribution of distinct immune cell subpopulations, natural killer (NK) cell cytotoxicity and tumor immune escape mechanisms (TIEMs) in 55 HNSCC patients, either at initial diagnosis or present with tumor relapse. Compared to healthy controls, the regulatory NK cells and the ratio of pro/anti-inflammatory cytokines were decreased in HNSCC patients, while soluble major histocompatibility complex Class I chain-related peptide A (sMICA) and transforming growth factor β₁ (TGFβ₁) plasma levels were markedly elevated. Increased sMICA and TGFβ₁ concentrations correlated with tumor progression and staging characteristics in 7 follow-up HNSCC patients, with significantly elevated levels of both soluble factors from the time of initial diagnosis to that of relapse. Patient plasma containing elevated sMICA and TGFβ₁ markedly impaired NKG2D-dependent cytotoxicity against HNSCC cells upon incubation with patient-derived and IL-2 activated NK cells vs. those derived from healthy donors. Decreased antitumor recognition was accompanied by reduced NKG2D expression on the NK cell surface and an enhanced caspase-3 activity. In-vitro blocking and neutralization experiments demonstrated a synergistic negative impact of sMICA and TGFβ₁ on NK cell functionality. Although we previously showed the feasibility and safety of transfer of allogeneic donor NK cells in a prior clinical study encompassing various leukemia and tumor patients, our present results suggest the need for caution regarding the sole use of adoptive NK cell transfer. The presence of soluble NKG2D ligands in the plasma of HNSCC patients and the decreased NK cell cytotoxicity due to several factors, especially TGFβ₁, indicates timely depletion of these immunosuppressing molecules may promote NK cell-based immunotherapy.

Irradiated mononuclear cells express significant in vitro cytotoxic activity: promise for in vivo clinical efficacy of irradiated mismatched donor lymphocytes infusion

BACKGROUND

Relapse of the original disease remains the most common cause of treatment failure after allogeneic hematopoietic stem cell transplantation (allo-SCT). Patients who relapse post-allo-SCT can achieve prolonged remission after donor lymphocyte infusion. Donor lymphocyte infusion as well as other immunotherapeutic strategies are usually complicated by severe graft versus host disease.

AIM

In the present study, we examined the effect of irradiation on the cytotoxic activity of mononuclear cells (MNCs).

MATERIALS & METHODS

Cytotoxic activity of fresh and irradiated MNCs from healthy donors was tested against the leukemic cell line K562 and against fresh leukemic cells from patients with acute myeloid leukemia. Cytotoxicity was assessed by using a flow-cytometry assay.

RESULTS & DISCUSSION

Interestingly, we observed that 25 Gy irradiated MNCs retain significant cytotoxic activity against K562. Based on these in vitro data, the safety and efficacy of irradiated haploidentical, IL-2-activated lymphocytes were tested in six patients after allo-SCT. Acute skin graft versus host disease developed in two patients and was resolved after a short course of steroids. One patient with mixed chimera converted to full donor chimera after infusion of irradiated donor cells.

CONCLUSION

The efficacy of irradiated haploidentical lymphocytes should be further tested in a larger number of patients.

Interleukin-2-stimulated natural killer cells are less susceptible to mycophenolate mofetil than non-activated NK cells: possible consequences for immunotherapy

In a clinical phase I/II trial, pediatric patients with high-risk malignancies were treated with ex vivo IL-2-stimulated donor natural killer (NK) cells after transplantation with haploidentical stem cells. To evaluate the potential negative effects of the immunosuppressive drug mycophenolate mofetil (MMF) used for immunotherapy, the functionality and signaling of ex vivo NK cells was investigated. Our results show that during NK cell expansion, long-term (9 days) incubation with mycophenolic acid (MPA), the active metabolite of MMF, in therapeutically relevant concentrations led to the severe inhibition of NK cell proliferation. This correlated with a significantly reduced cytokine/chemokine secretion and the inhibited acquisition of surface receptors regarding cytotoxicity (e.g., NKp30, NKp44, NKp46, NKG2D), adhesion/migration (e.g., ICAM-1/CD54, LFA-1/CD11a, CD62L, CXCR3) and activation (e.g., CD25). Moreover, MPA prevented phosphorylation of the central signaling molecules STAT-3/-4/-5, AKT and ERK1/2. In contrast, short-term (24 h) MPA incubation of IL-2-stimulated NK cells had no or only marginal effects on the activated NK cell phenotype, including receptor expression, cytokine/chemokine secretion and intracellular signaling. Further, short-term MPA incubation only moderately affected the highly cytotoxic activity of previously IL-2-stimulated NK cells. In conclusion, while long-term MPA incubation significantly compromised ex vivo NK cell functionality, previously IL-2-activated NK cells seemed to be rather resistant to short-term MPA treatment. This finding supports the use of IL-2-activated NK cells as immunotherapy, especially for patients treated with MMF after haploidentical stem cell transplantation.

Flow cytometric assay detecting cytotoxicity against human endogenous retrovirus antigens expressed on cultured multiple sclerosis cells

Damage of target cells by cytotoxicity, either mediated by specific lymphocytes or via antibody-dependent reactions, may play a decisive role in causing the central nervous system (CNS) lesions seen in multiple sclerosis (MS). Relevant epitopes, antibodies towards these epitopes and a reliable assay are all mandatory parts in detection and evaluation of the pertinence of such cytotoxicity reactions. We have adapted a flow cytometry assay detecting CD107a expression on the surface of cytotoxic effector cells to be applicable for analyses of the effect on target cells from MS patients expressing increased amounts of human endogenous retrovirus antigens. MS patients also have increased antibody levels to these antigens. The target cells are spontaneously growing peripheral blood mononuclear cells (PBMCs) of B cell lineage, expressing human endogenous retrovirus HERV epitopes on their surface. Polyclonal antibodies against defined peptides in the Env- and Gag-regions of the HERVs were raised in rabbits and used in antibody-dependent cell-mediated cytotoxicity (ADCC) -assays. Rituximab® (Roche), a chimeric monoclonal antibody against CD20 expressed primarily on B cells, was used as control antibody. Without antibodies this system is suitable for analyses of natural killer cell activity. In optimization of the assay we have used effector lymphocytes from healthy donors. The most effective effector cells are CD56(+) cells. CD8(+) T cells also express CD107a in ADCC. Using the adapted assay, we demonstrate significant ADCC activity to target cells expressing HERV epitopes, and additionally a low level of NK activity.

Clinical grade purification and expansion of NK cell products for an optimized manufacturing protocol

Allogeneic natural killer (NK) cells are used for adoptive immunotherapy after stem cell transplantation. In order to overcome technical limitations in NK cell purification and activation, the following study investigates the impact of different variables on NK cell recovery, cytotoxicity, and T-cell depletion during good manufacturing practice (GMP)-grade NK cell selection. Forty NK cell products were derived from 54 unstimulated donor leukaphereses using immunomagnetic CD3 T-cell depletion, followed by a CD56 cell enrichment step. For T-cell depletion, either the depletion 2.1 program in single or double procedure (D2.1_1depl, n = 18; D2.1_2depl, n = 13) or the faster depletion 3.1 (D3.1, n = 9) was used on the CliniMACS instrument. Seventeen purified NK cell products were activated in vitro by IL-2 for 12 days. The whole process resulted in a median number of 7.59 × 10⁸ CD56⁺CD3⁻ cells with both purity and viability of 94%, respectively. The T-cell depletion was significantly better using D2.1_1depl/2depl compared to D3.1 (log 4.6/log 4.9 vs. log 3.7; p < 0.01) and double procedure in two stages led always to residual T cells below 0.1%. In contrast D3.1 was superior to D2.1_1depl/2depl with regard to recovery of CD56⁺CD3⁻ NK cells (68% vs. 41%/38%). Concomitant monocytes and especially IL-2 activation led to increased NK cell activity against malignant target cells compared to unstimulated NK cells, which correlated with both up-regulation of natural cytotoxicity receptors and intracellular signaling. Overall, wide variations in the NK cell expansion rate and the distribution of NK cell subpopulations were found. In conclusion, our results indicate that GMP-grade purification of NK cells might be improved by a sequential processing of T-cell depletion program D2.1 and D3.1. In addition NK cell expansion protocols need to be further optimized.

Pre-emptive immunotherapy with purified natural killer cells after haploidentical SCT: a prospective phase II study in two centers

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) × 10(7)/kg and 0.03 (0.004-0.72) × 10(5)/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 × 10(5) 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.

Apoptotic tumor cells induce IL-27 release from human DCs to activate Treg cells that express CD69 and attenuate cytotoxicity

Intrinsic immunosuppression is a major obstacle for successful cancer therapy. The mechanisms for the induction and regulation of immunosuppression in humans are ill defined. A microenvironmental component that might prevent antitumor immunity is the presence of dying tumor cells, which are abundant following conventional cancer ablation methods such as chemo- or radiotherapy. Shedding of apoptotic debris and/or secretion of factors to the tumor bed or draining lymph nodes thus might have a profound impact on professional phagocytes, such as DCs, and subsequent priming of lymphocytes. Here, we exposed human DCs to supernatants of live, apoptotic, or necrotic human breast cancer cells and cocultured them with autologous T cells. Priming with apoptotic debris prevented DCs from establishing cytotoxicity toward live human tumor cells by inducing a Treg-cell population, defined by coexpression of CD39 and CD69. Immunosuppression via Treg cells was transferable and required the release of sphingosine-1-phosphate (S1P) from apoptotic cells, acting via S1P receptor 4 on DCs to induce IL-27 secretion. We propose that CD69 expression on CD39(+) Treg cells enables them to interact with CD73-expressing CD8(+) T cells to generate adenosine, thereby suppressing cytotoxicity. These findings aid the understanding of how dying tumor cells limit antitumor immunity.

NK cells engineered to express a GD2 -specific antigen receptor display built-in ADCC-like activity against tumour cells of neuroectodermal origin

Treatment of high-risk neuroblastoma (NB) represents a major challenge in paediatric oncology. Alternative therapeutic strategies include antibodies targeting the disialoganglioside GD₂, which is expressed at high levels on NB cells, and infusion of donor-derived natural killer (NK) cells. To combine specific antibody-mediated recognition of NB cells with the potent cytotoxic activity of NK cells, here we generated clonal derivatives of the clinically applicable human NK cell line NK-92 that stably express a GD₂-specific chimeric antigen receptor (CAR) comprising an anti-GD₂ ch14.18 single chain Fv antibody fusion protein with CD3-ζ chain as a signalling moiety. CAR expression by gene-modified NK cells facilitated effective recognition and elimination of established GD₂ expressing NB cells, which were resistant to parental NK-92. In the case of intrinsically NK-sensitive NB cell lines, we observed markedly increased cell killing activity of retargeted NK-92 cells. Enhanced cell killing was strictly dependent on specific recognition of the target antigen and could be blocked by GD₂-specific antibody or anti-idiotypic antibody occupying the CAR’s cell recognition domain. Importantly, strongly enhanced cytotoxicity of the GD₂-specific NK cells was also found against primary NB cells and GD₂ expressing tumour cells of other origins, demonstrating the potential clinical utility of the retargeted effector cells.

Single-colour flow cytometric assay to determine NK cell-mediated cytotoxicity and viability against non-adherent human tumor cells

A flow cytometry-based cytotoxicity (FCC) assay was developed using a single fluorophore, calcein-acetoxymethyl diacetylester (calcein-AM), to measure NK cell-mediated cytotoxicity. Non-adherent human K562 and U937 target cells were individually labelled with calcein-AM and co-incubated with effector NK cells to measure calcein loss, and therefore calculate target cell cytotoxicity. This FCC assay also provided a measure of sample viability. Notably, cell viability measured by traditional calcein/7-amino-actinomycin D (7-AAD) double labelling and Trypan Blue methods were comparable to the viability calculated using calcein-loss FCC. This FCC assay may also be used with various effector and target cell types and as a multi-parameter tool to measure viability and immunophenotype cells for tissue engineering purposes.

IL-2 stimulated but not unstimulated NK cells induce selective disappearance of peripheral blood cells: concomitant results to a phase I/II study

In an ongoing clinical phase I/II study, 16 pediatric patients suffering from high risk leukemia/tumors received highly purified donor natural killer (NK) cell immunotherapy (NK-DLI) at day (+3) +40 and +100 post haploidentical stem cell transplantation. However, literature about the influence of NK-DLI on recipient's immune system is scarce. Here we present concomitant results of a noninvasive in vivo monitoring approach of recipient's peripheral blood (PB) cells after transfer of either unstimulated (NK-DLI(unstim)) or IL-2 (1000 U/ml, 9-14 days) activated NK cells (NK-DLI(IL-2 stim)) along with their ex vivo secreted cytokine/chemokines. We performed phenotypical and functional characterizations of the NK-DLIs, detailed flow cytometric analyses of various PB cells and comprehensive cytokine/chemokine arrays before and after NK-DLI. Patients of both groups were comparable with regard to remission status, immune reconstitution, donor chimerism, KIR mismatching, stem cell and NK-DLI dose. Only after NK-DLI(IL-2 stim) was a rapid, almost complete loss of CD56(bright)CD16(dim/-) immune regulatory and CD56(dim)CD16(+) cytotoxic NK cells, monocytes, dendritic cells and eosinophils from PB circulation seen 10 min after infusion, while neutrophils significantly increased. The reduction of NK cells was due to both, a decrease in patients' own CD69(-) NCR(low)CD62L(+) NK cells as well as to a diminishing of the transferred cells from the NK-DLI(IL-2 stim) with the CD56(bright)CD16(+/-)CD69(+)NCR(high)CD62L(-) phenotype. All cell counts recovered within the next 24 h. Transfer of NK-DLI(IL-2 stim) translated into significantly increased levels of various cytokines/chemokines (i.e. IFN-γ, IL-6, MIP-1β) in patients' PB. Those remained stable for at least 1 h, presumably leading to endothelial activation, leukocyte adhesion and/or extravasation. In contrast, NK-DLI(unstim) did not cause any of the observed effects. In conclusion, we assume that the adoptive transfer of NK-DLI(IL-2 stim) under the influence of ex vivo and in vivo secreted cytokines/chemokines may promote NK cell trafficking and therefore might enhance efficacy of immunotherapy.

Novel single-platform multiparameter FCM analysis of apoptosis: Significant differences between wash and no-wash procedure

FCM is a generally accepted tool to analyze apoptosis. Unfortunately, the cell preparation of all commercial kits available includes cell washing known to cause cell loss which is most likely to affect apoptotic cells in particular. To address this, we developed a seven-color single-platform no-wash analysis technique and compared the results with those from an analogous procedure including cell washing. A five-color mAb cocktail was employed to address target cells by surface labeling, Yo-PRO-1® and DAPI were used to discriminate apoptotic and necrotic from viable cells. Cells were quantified on the basis of internal-standard fluorescent beads. Jurkat cells ACC 282 treated with camptothecin were employed to establish the staining procedure, which was then applied to blood cells collected by extracorporeal apheresis and treated with UV irradiation. Data evaluation showed that although each method by itself was highly reproducible (R(2) = 0.973), the numbers of apoptotic cells detected with the no-wash procedure were significantly higher than those obtained after cell washing (P = 6.6 E(-5), Wilcoxon Test). In addition, the observed differences increased with higher cell numbers (Bland and Altmann). We conclude that the described test is a feasible and reliable tool for apoptosis measurement and it provides results that are definitely closer to the truth than those obtained from kits that require cell washing.

IL-2-activated haploidentical NK cells restore NKG2D-mediated NK-cell cytotoxicity in neuroblastoma patients by scavenging of plasma MICA

NK group 2D (NKG2D)-expressing NK cells exhibit cytolytic activity against various tumors after recognition of the cellular ligand MHC class I chain-related gene A (MICA). However, release of soluble MICA (sMICA) compromises NKG2D-dependent NK-cell cytotoxicity leading to tumor escape from immunosurveillance. Although some molecular details of the NKG2D-MICA interaction have been elucidated, its impact for donor NK (dNK) cell-based therapy of solid tumors has not been studied. Within an ongoing phase I/II trial, we used allogeneic IL-2 activated dNK cells after haploidentical stem cell transplantation for immunotherapy of patients with high-risk stage IV neuroblastoma. NKG2D levels on activated dNK cells increased strongly when compared with freshly isolated dNK cells and correlated with enhanced NK-cell cytotoxicity. Most importantly, elevated sMICA levels in patients plasma correlated significantly with impaired dNK-cell-mediated cytotoxicity. This effect could be reversed by high-dose infusion of activated dNK cells, which display high levels of surface NKG2D. Our data suggest that the provided excess of NKG2D leads to clearance of sMICA and preserves cytotoxicity of dNK cells via non-occupied NKG2D. In conclusion, our results identify this tumor immune escape mechanism as a target to improve immunotherapy of neuroblastoma and presumably other tumors.

IL-2-driven regulation of NK cell receptors with regard to the distribution of CD16+ and CD16- subpopulations and in vivo influence after haploidentical NK cell infusion

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.

New flow cytometric assays for monitoring cell-mediated cytotoxicity

The exact immunologic responses after vaccination that result in effective antitumor immunity have not yet been fully elucidated and the data from ex vivo T-cell assays have not yet defined adequate surrogate markers for clinical efficacy. A more detailed knowledge of the specific immune responses that correlate with positive clinical outcomes should help to develop better or novel strategies to effectively activate the immune system against tumors. Furthermore, clinically relevant material is often limited and, thus, precludes the ability to perform multiple assays. The two main assays currently used to monitor lymphocyte-mediated cytoxicity in cancer patients are the (51)Cr-release assay and IFN-gamma ELISpot assay. The former has a number of disadvantages, including low sensitivity, poor labeling and high spontaneous release of isotope from some tumor target cells. Additional problems with the (51)Cr-release assay include difficulty in obtaining autologous tumor targets, and biohazard and disposal problems for the isotope. The ELISpot assays do not directly measure cytotoxic activity and are, therefore, a surrogate marker of cyotoxic capacity of effector T cells. Furthermore, they do not assess cytotoxicity mediated by the production of the TNF family of death ligands by the cytotoxic cells. Therefore, assays that allow for the simultaneous measurement of several parameters may be more advantageous for clinical monitoring. In this respect, multifactor flow cytometry-based assays are a valid addition to the currently available immunologic monitoring assays. Use of these assays will enable detection and enumeration of tumor-specific cytotoxic T lymphocytes and their specific effector functions and any correlations with clinical responses. Comprehensive, multifactor analysis of effector cell responses after vaccination may help to detect factors that determine the success or failure of a vaccine and its immunological potency.

An improved bicistronic CD20/tCD34 vector for efficient purification and in vivo depletion of gene-modified T cells for adoptive immunotherapy

T-cell-based adoptive immunotherapy is widely used to treat graft rejection and relapse after stem cell transplantation (SCT). However, this approach is hampered by a high risk of life-threatening graft-versus-host-disease (GvHD). Clinical trials have demonstrated the value of suicide genes to modify T cells for the effective control of GvHD. Herewith, we show that the combination of a codon-optimized B-cell antigen (CD20op) with a selection marker based on a cytoplasmic truncated version of the human stem cell antigen CD34 (tCD34) allows the generation of highly enriched gene-modified T cells. We demonstrate coordinate co-expression of both transgenes and high expression of CD20op resulting in an increased susceptibility to Rituximab (RTX)-induced cell death. In addition, T cells partially retained their alloreactive potential and their CD4/CD8 ratio after transduction and expansion. Long-lasting transgene expression was sustained in vivo after adoptive transfer into Rag-1(-/-) mice. Moreover, gene-modified T cells were quickly and efficiently depleted from peripheral blood (PB) and secondary lymphoid organs of transplanted animals after RTX treatment. These results warrant further steps toward a clinical application of CD20op as a suicide gene for adoptive immunotherapy.

Measurement of cytotoxic T lymphocyte activity of human cytomegalovirus seropositive individuals by a highly sensitive coupled luminescent method

A coupled luminescent method (CLM) based on glyceraldehyde-3-phosphate dehydrogenase released from injured target cells was used to evaluate the cytotoxicity of antigen-specific HLA class I-restricted CTLs. In contrast to established methods, CLM does not require the pretreatment of target cells with radioactive or toxic labeling substances. CTLs from healthy HLA-A2 positive donors were stimulated by autologous dendritic cells (DCs) pulsed with HLA-A2 restricted HCMV-pp65 nonamer peptides. HLA-A2 positive T2 cells or autologous monocytes pulsed with HCMV-pp65 nonamer peptide served as target cells. Lysis was detected only in HCMV-pp65-pulsed target cells incubated with CTLs from seropositive donors stimulated by HCMV-pp65-pulsed DCs. After 3 days, stimulation 38% of T2 cells and 17% of monocytes were lysed at an effector to target ratio of 8:1. In conclusion, CLM represents a highly sensitive, fast, material-saving and non-toxic/non-radioactive method for the measurement of antigen-specific CTL cytotoxic activity.

Cellular immune reconstitution after haploidentical transplantation in children

Delayed immune reconstitution is 1 of the major contributions to the morbidity and mortality after haploidentical transplantation. Patients with a slow recovery of the innate and especially of the adaptive immune system are at high risk for severe and often lethal infections. The reason for delayed immune reconstitution after haploidentical transplantation include the T cell depletion (TCD) of the graft, the thymic dysfunction induced by pretransplant chemotherapies and by the conditioning regimens, and the occurrence of graft-versus-host disease (GVHD) and its treatment. The detailed analysis, understanding, and manipulation of the reconstitution of the cellular immune system will be of utmost importance to overcome the posttransplant immunodefcient status, and should result in a reduced risk of severe and overwhelming infections and hopefully also to a reduced risk of relapse through better immunological control of residual malignant cells.

Alloantigen-specific killing is mediated by CD8-positive T cells in fish

CD8-positive (CD8(+)) cytotoxic T lymphocytes (CTL) have antigen-specific cytotoxic activity. In fish, however, CTL expressing CD8 on their cell surface have not been identified. In order to characterize the cells involved in specific cell-mediated cytotoxicity in teleosts, we separated and sorted ginbuna kidney leucocytes into CD8alpha(+), CD4(+) and surface IgM (sIgM)(+) cells by magnetic activated cell sorting using monoclonal antibodies and examined their cytotoxic activities. Effector donor ginbuna (OB1 clone) were sensitized by allografting scales from S3N clone fish followed by injection of an allogeneic cell line (CFS) derived from S3N fish. In cytotoxic assays, target cells were labeled with CFSE and cytotoxicity was calculated based on the number of viable target cells using flow cytometry. CD8alpha(+) cells from sensitized OB1 fish showed relatively high cytotoxicity against CFS cells (immunogen) but not against allogeneic CFK cells (third party) nor isogeneic CFO cells. Pre-sensitized sIgM(+) cells exhibited cytotoxicity against not only CFS cells but also CFK cells. However, CD4(+) or CD8alpha(-) CD4(-)sIgM(-) cells as well as cells from non-sensitized fish did not show any significant cytotoxic activity. These results suggest that CD8alpha(+) cells in fish have characteristics similar to those of CTL in mammals, and that the sIgM(+) cells include NK-like cells which non-specifically killed the target cells.

A MitoTracker Green-based flow cytometric assay for natural killer cell activity: variability, the influence of platelets and a comparison of analytical approaches

OBJECTIVE

A number of flow cytometric assays for natural killer (NK) cell cytotoxicity have been described, however, the relative merits of analytical approaches and the influence of platelets on measured responses have not been systematically evaluated. Information on the time-dependent variability in measured responses is also limited.

MATERIALS AND METHODS

Human peripheral blood mononuclear cells were obtained using Nycoprep 1.077, or Nycoprep 1.077 followed by Nycoprep 1.068 (to remove platelets), and incubated for 3 hours with MitoTracker Green (MTG)-labeled K562 cells. Cells were stained with propidium iodide (PI) and the proportions of viable and nonviable target cells (MTG(+)PI(-), MTG(+)PI(+)) were determined by flow cytometry using quadrant and polygonal region analysis.

RESULTS

Platelets inhibited NK cell cytotoxicity and the response was underestimated when the nonviable target cell population was not entirely enclosed within the nonviable target cell (upper right) flow cytometric quadrant. The variability in measured NK cell cytotoxic responses in samples obtained from five individuals on three occasions over a 3-week period was 28%, 24%, 26%, and 37%, and 19%, 23%, 27%, and 32% for the quadrant and region analyses (mean coefficient of variation at effector-to-target cell ratios of 100:1, 50:1, 25:1, and 12.5:1, respectively), and 24% and 20% when data were calculated as the area under the cytotoxic curve (AUCC).

CONCLUSION

Polygonal regions and the calculation of data as the AUCC appear to be the best approach. This study will be of value to investigators that are wishing to incorporate an NK cell cytotoxicity assay into their portfolio of experimental techniques.

A novel five-colour flow cytometric assay to determine NK cell cytotoxicity against neuroblastoma and other adherent tumour cells

For the evaluation of novel therapies, and for initial in vitro testing of potential in vivo graft-versus-tumour-effects (GvT), cytotoxicity of effector cells against target tumour cells needs to be determined in a reliable fashion. Recently Zimmermann et al. [Zimmermann, S.Y., Esser, R., Rohrbach, E., Klingebiel, T., Koehl, U., 2005. A novel four-colour flow cytometric assay to determine natural killer cell or T-cell-mediated cellular cytotoxicity against leukaemia cells in peripheral or bone marrow specimens containing greater than 20% of normal cells. J. Immunol. Methods. 296(1-2), 63-76] introduced a single platform, no-wash flow cytometric assay to quantify natural killer (NK) cell cytotoxicity against leukaemia cells. Here we have optimised this method introducing a novel five-colour flow cytometric assay for the evaluation of NK cell activity against adherent tumour cells, in particular neuroblastoma cells (NB cells). Beside an enhanced cytotoxic activity corresponding to increasing effector/target (E:T) ratios, we could demonstrate an increasing cytotoxicity in a time-dependent manner over a time period of 8 h. The usefulness of this novel method was also confirmed with human tumour cells lines of various other origin including breast and ovarian carcinoma and Wilms tumour cells freshly isolated from a patient after surgery. In addition to flow cytometric analysis, we monitored NK-cell-mediated induction of target cell apoptosis via the caspase cascade in attacked NB cells by fluorescence microscopy after immunofluorescence staining of activated Caspase-3 (Casp-3) in combination with detection of CD45(+) and CD9(+) for discrimination between NK and NB cells. In summary, this novel flow cytometric cytotoxicity assay enables efficient quantification of the phenotype of both, effector and adherent target tumour cells, and therefore represents a useful tool for research on immunotherapies that rely on cytotoxic effector cells.

Rapid flow cytometric measurement of cytokine-induced phosphorylation pathways [CIPP] in human peripheral blood leukocytes

Current strategies designed to assess cells in the peripheral blood are limited to evaluation of phenotype or delayed measurement [>6 h] of function, usually quantifying cytokine production, cytolytic activity, or response to antigens. We reasoned that measurable abnormalities in signaling pathways could reflect pathological environs that cells experience in the setting of inflammatory states/cancer and could be represented in the peripheral blood. Two major pathways regulating the immune response are the JAK/STAT and MAPK/ERK pathways. These pathways are initiated by ligand-receptor binding and are rapidly propagated by subsequent protein phosphorylation cascades. We evaluated the brief application of cytokines in vitro to interrogate the early phosphorylation events of these signaling pathways in normal peripheral blood mononuclear cells (PBMC). Individual cytokine doses and time intervals of treatment were assessed to identify conditions useful in a clinical laboratory and as an initial goal to induce maximal phosphorylation. Surprisingly, all of the STAT proteins assessed and ERK1/2 are maximally phosphorylated within 15 min in human PBMC simply following addition of cytokines without preactivation of the cells. At 2 h, cells typically return to their basal phosphorylation states. For most of the cytokines tested, increased phosphorylation directly correlated with increased concentrations of the individual cytokines. These strategies will enable robust development of simple blood analyses to identify normal levels as well as impairments in STAT and MAPK/ERK signaling pathways associated with various human disease states including acute and chronic inflammatory conditions throughout clinical immunology.

Dynamic and label-free monitoring of natural killer cell cytotoxic activity using electronic cell sensor arrays

A microelectronic sensor-based platform, the RT-CES (real time electronic sensing) system, is introduced for label free assessment of natural killer (NK) cell-mediated cytotoxic activity. The RT-CES system was used to dynamically and quantitatively monitor NK-mediated cytotoxic activity towards 8 different adherent target cell lines, including cancer cell lines commonly used in laboratories. The cytotoxic activity monitored by RT-CES system was compared with standard techniques such as MTT measurement and shows good correlation and sensitivity. To test the specificity of the assay, pharmacological agents that inhibit NK cell degranulation and cytotoxic activity were employed and were shown to selectively and dose-dependently inhibit NK-mediated cytotoxic activity toward target cells. In summary, the RT-CES system offers fully automated measurement of cytotoxic activity in real time, which enables large-scale screening of chemical compounds or genes responsible for the regulation of NK-mediated cytotoxic activity.

NK sensitivity of neuroblastoma cells determined by a highly sensitive coupled luminescent method

The measurement of natural killer (NK) cells toxicity against tumor or virus-infected cells especially in cases with small blood samples requires highly sensitive methods. Here, a coupled luminescent method (CLM) based on glyceraldehyde-3-phosphate dehydrogenase release from injured target cells was used to evaluate the cytotoxicity of interleukin-2 activated NK cells against neuroblastoma cell lines. In contrast to most other methods, CLM does not require the pretreatment of target cells with labeling substances which could be toxic or radioactive. The effective killing of tumor cells was achieved by low effector/target ratios ranging from 0.5:1 to 4:1. CLM provides highly sensitive, safe, and fast procedure for measurement of NK cell activity with small blood samples such as those obtained from pediatric patients.