Polypeptide, cell, and method involving engineered CD16

Abstract

To provide generally a modified form of CD16, genetically-modified cells that express the modified CD16, and methods that involve the genetically-modified cells.SOLUTION: A modified form of CD16 can exhibit increased anti-tumor and / or anti-viral activity due to, at least in part, reduced susceptibility to ADAM17-mediated shedding upon NK cell stimulation.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 61 / 971,996, filed March 28, 2014, which is incorporated herein by reference. Summary of the Invention

[0002] This disclosure generally describes modified forms of CD16, genetically modified cells expressing modified CD16, and methods involving the genetically modified cells that may exhibit enhanced anti-tumor and / or anti-viral activity due, at least in part, to reduced susceptibility to metalloprotease-mediated shedding upon NK cell stimulation. Thus, in one aspect, this disclosure describes cells genetically engineered to express a CD16 polypeptide that contains a membrane proximal region and an amino acid modification within the membrane proximal region.

[0003] In another aspect, this disclosure describes a cell comprising a polynucleotide encoding a CD16 polypeptide having a membrane proximal region and an amino acid modification in the membrane proximal region. In any aspect, the amino acid drug therapy reflects the addition of one or more amino acids, the deletion of one or more amino acids, or the substitution of one or more amino acids compared to the wild-type amino acid sequence of the CD16 membrane proximal region. In some of these embodiments, the substitution of one or more amino acids comprises the substitution of a serine residue at position 197 of SEQ ID NO:1.

[0004] In any embodiment, the cell can be a natural killer (NK) cell, a neutrophil, a monocyte, or a T cell. In either embodiment, the modified CD16 polypeptide exhibits reduced susceptibility to ADAM17-mediated shedding compared to a wild-type CD16 polypeptide. In either embodiment, the modified CD16 polypeptide exhibits reduced susceptibility to cleavage upon NK cell stimulation compared to a wild-type CD1 polypeptide. In another aspect, this disclosure describes methods that typically involve administering to a patient in need of such treatment a therapy that includes (a) administering to the patient a therapeutic NK effector, and (b) administering to the patient any of the genetically modified cells of the embodiments outlined above.

[0005] In some embodiments, the therapeutic NK effector includes a therapeutic agent. In some of these embodiments, the therapeutic agent can include an antibody or a therapeutic antibody fragment. In some of these embodiments, the antibody or antibody fragment specifically binds to a viral antigen. In other embodiments, the antibody or antibody fragment specifically binds to a tumor antigen. In some embodiments, the therapeutic agent may include a bispecific killer engager (BiKE) or a trispecific killer cell engager (TriKE).

[0006] In yet another aspect, this disclosure describes a method for improving immunotherapy for a patient, which involves administering a therapeutic NK effector to the patient. Typically, the method further comprises administering to the patient any of the genetically modified cell embodiments outlined above. The foregoing summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The following description more particularly exemplifies illustrative embodiments. In several places throughout this application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited lists serve only as a representative group and should not be interpreted as an exclusive list. [Brief description of the drawings]

[0007] [Figure 1A]Location of the ectodomain cleavage site of human CD16. (A) Tryptic peptides of soluble CD16 immunoprecipitated from cell supernatants of PMA-activated human NK cells or neutrophils were subjected to mass spectrometry analysis. Four high-confidence peptides with non-tryptic C-termini were identified: one peptide derived from soluble CD16 released by NK cells (peptide no. 1, top left) and three peptides derived from soluble CD16 released by neutrophils (peptide no. 2, bottom left; peptide no. 3, top right; and peptide no. 4, bottom right). [Figure 1B] (B) Illustration of peptide numbers 1-4 (underlined) and the putative cleavage site (wedge shape) of CD16a (SEQ ID NO:1) and CD16b (SEQ ID NO:2). In the identified peptides, amino acid 176 distinguishes CD16a (F) from CD16b (V). Amino acids 1-16 indicate the predicted signal sequence of CD16a and CD16b. Amino acids 210-229 indicate the transmembrane region of CD16a. Amino acid numbering starts with the methionine in the signal sequence. The amino acid sequences of CD16a and CD16b are based on NCBI reference sequences NM_000569.6 and NM_000570.4, respectively. [Diagram 2] Schematic representation of CD16 ectodomain shedding, cleavage region, and engineered serine-197 to proline mutation. CD16a and CD16b undergo ectodomain shedding by ADAM17 in the membrane proximal region as indicated. The CD16 cleavage region in the membrane proximal region is based on mass spectrometry analysis that revealed three distinct cleavage sites (wedge-shaped) in close proximity. Site-directed mutagenesis was performed to replace serine-197 (amino acids 190-202 of SEQ ID NO: 1) of CD16 with proline (CD16 / S197P). [Diagram 3]Effect of engineered S197P mutation on CD16a and CD16b shedding. Transfected HEK293 (human embryonic kidney) cells expressed CD16b and CD16b / S197P (A) or CD16a and CD16a / S197P (B) separately at the same levels as measured by flow cytometry (left panel). Different transfectants were treated with or without PMA (15 ng / ml, 30 min at 37°C) and soluble levels of CD16 in the medium supernatant were quantified by ELISA (right panel). Each treatment condition was repeated three times for each experiment and data are representative of three independent experiments. Bar graphs show the mean ± SD. Statistical significance is indicated as ***P<0.001. (C) Transfected HEK293 cells expressed L-selectin (CD62L) or L-selectin and CD16b / S197P. Surface levels of L-selectin and CD16b / S197P on transfected and mock-transfected cells were measured using flow cytometry (histogram plots). Transfectants expressing L-selectin or L-selectin and CD16b / S197P were incubated for 30 min at 37°C in the presence or absence of PMA, and the mean fluorescence intensity (MFI) of L-selectin staining was determined (bar graphs). Each treatment condition was repeated three times for each experiment, and data represent two independent experiments. Bar graphs show the mean ± SD. Statistical significance is indicated as *P<0.05. For all histogram plots, X-axis=Log10 fluorescence and Y-axis=cell number. [Figure 4]Effect of engineered S197P mutation on CD16a shedding in NK cells. NK92 cells transduced with empty vector (vector only), CD16a, or CD16a / S197P were treated with or without PMA (100 ng / ml) (unstimulated) for 30 min at 37°C (A), with IL-12 and IL-18 (100 ng / ml and 400 ng / ml, respectively) for 24 h at 37°C (B), or with Raji cells and rituximab for 60 min at 37°C (C). Cell surface levels of CD16a were measured by flow cytometry. Antibody staining of isotype-matched negative controls is indicated by dotted lines. (D) Parental NK92 cells and transduced cells expressing CD16a or CD16a / S197P were treated with Raji cells and rituximab in the presence or absence of the ADAM17 inhibitor BMS566394 (5 μM) for 60 min at 37°C. Soluble CD16a levels were measured by ELISA. Each treatment condition was repeated three times for each experiment, and data represent three independent experiments. Bar graphs show the mean ± SD. Statistical significance is indicated as ***P<0.001. (E) NK92 cells expressing CD16a or CD16a / S197P were stained with anti-ADAM17 mAbs M220, 623, 633, or an isotype-matched negative control antibody as indicated. (F) CD56+CD45+ NK cells derived from mock-transduced iPSCs (left panel) or iPSCs expressing genetically modified CD16a or CD16a / S197P (right panel) were incubated with or without K562 target cells for 4 h at 37° C. For all histogram plots, X-axis=Log10 fluorescence and Y-axis=cell number and data represent at least three independent experiments. [Diagram 5]Effect of engineered S197P mutation on CD16a function. (A) NK92 cells expressing comparable levels of CD16a or CD16a / S197P (left panel) were treated with monomeric human IgG (0-20 μg / ml). As controls, cells were similarly treated with monomeric human IgA (20 μg / ml) and NK92 parental cells were treated with IgG (20 μg / ml) (bar graph). Antibody binding was measured by flow cytometry as described in Materials and Methods. Bar graphs show the mean ± SD of at least three separate experiments. Statistical significance is indicated as *P<0.05 versus IgG (0 μg / ml), IgA, or NK92 parental cells + IgG. (B) Mock-transduced NK92 cells or NK92 cells expressing CD16a or CD16a / S197P were incubated at 37°C in the absence (unstimulated) or presence of Raji cells treated with or without anti-CD20 rituximab for the indicated time points. NK92 cell activation was assessed by upregulation of CD107a staining by flow cytometry. For histogram plots, X-axis=Log10 fluorescence and Y-axis=cell number. Data are representative of at least three independent experiments.

[0008] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS This disclosure generally describes modified forms of CD16a, genetically engineered cells expressing modified CD16a, and methods involving the genetically engineered cells. The modified forms of CD16a may exhibit enhanced anti-tumor and / or anti-viral activity due, at least in part, to reduced susceptibility to metalloprotease-mediated shedding upon NK cell stimulation. In contrast to many solid tumor types, survival rates for women with epithelial ovarian cancer have changed little over the last 30 years. Moreover, current standard therapies for recurrent ovarian cancer have low (<20%) response rates. Despite HER2 overexpression by ovarian cancer samples, treatment with the anti-HER2 antibody trastuzumab produces only limited responses in patients with advanced ovarian cancer. This resistance to trastuzumab may result from a dysfunctional NK cell-mediated antibody-dependent cellular cytotoxicity. Thus, innovative therapeutic strategies are urgently needed. We describe a novel approach to provide a therapeutic strategy.

[0009] One concern for ovarian cancer is that the environment in which tumor cells develop is highly proinflammatory, which tends to promote CD16a cleavage on infiltrating NK cells, thereby attenuating antibody-dependent cellular cytotoxicity. Several antibodies have emerged as effective targeted therapies for treating human malignancies. Their effectiveness is due in part to antibody interaction with FcγRIIIa / CD16a on natural killer (NK) cells and induction of cancer cell killing by antibody-dependent cellular cytotoxicity. The human IgG Fc receptor CD16 (FcγRIII) consists of two isoforms: CD16a (FcγRIIIa) and CD16b (FcγRIIIb). CD16a is expressed by natural killer (NK) cells, and CD16b is expressed by neutrophils. NK cell activation results in rapid downregulation of surface levels of both CD16 isoforms by a process termed ectodomain shedding, a proteolytic event that involves the metalloprotease ADAM17 and occurs at a single extracellular domain close to the plasma membrane (Figure 1A).

[0010] As mentioned previously, ovarian cancer patients may be resistant to NK cell-mediated immunotherapy - i.e., their tumors are not sensitive to NK cell-mediated therapy. For example, ovarian cancer cells commonly express the epidermal growth factor receptor HER2, but its targeting with the therapeutic antibody trastuzumab has provided limited clinical responses. This resistance may arise, at least in part, as a result of ectodomain shedding - i.e., NK cell activation by cytokines, target cell interaction, and / or tumor infiltration may lead to CD16a cleavage and defective antibody-dependent cellular cytotoxicity. Thus, interfering with the process of ectodomain shedding may be of clinical relevance.

[0011] We used mass spectrometry to determine the cleavage sites of CD16a and CD16b and cloned the cDNAs for CD16a and CD16b from human leukocytes. Each cDNA was mutated in a directed manner to introduce a single amino acid change; serine at position 197 was changed to proline (Figure 1B). This mutation prevents cleavage of CD16a and CD16b, preventing their downregulation upon cell activation. Expression of cleavage-resistant CD16a ex vivo increased NK cells that maintained high surface levels of this IgG Fc receptor, which promoted NK cell stimulation, efficacy of therapeutic antibodies, and cancer cell killing. Although ADAM17 has many cell surface substrates, there is no consensus sequence for proteolysis that can be used to predict the site of CD16a cleavage. Therefore, we used LCMS-MS to determine the C-terminal cleavage site within soluble CD16 released from activated human peripheral blood leukocytes.

[0012] We observed three putative cleavage sites in close proximity within the membrane-proximal region of CD16 (Fig. 2, wedge shape), with one region identical between CD16a and CD16b. Although proteolysis of ADAM17 does not require a consensus sequence, the secondary structure of the cleavage region is important. In an attempt to prevent CD16a cleavage, we replaced serine-197 with proline (CD16a 197P), which introduced a conformational change. We identified the location of CD16 cleavage by immunoprecipitating CD16 from culture supernatants of activated NK cells and, separately, from culture supernatants of neutrophils. Immunoprecipitated CD16 was treated with PNGaseF to remove N-glycans, trypsin digested, and the resulting peptides subjected to mass spectrometry. We identified four distinct peptide patterns with high confidence, including a nontryptic C-terminus (Figure 1A).

[0013] For CD16 enriched from culture supernatants of activated NK cells, we observed only one peptide pattern, which corresponds to amino acids glycine-174 to alanine-195 of SEQ ID NO:1 (peptide no. 1, Fig. 1A). The membrane proximal regions of CD16a and CD16b have identical amino acid sequences except for residue 176. A phenylalanine at this position is indicative of CD16a, which was present in peptide no. 1 (Fig. 1A and B). This peptide revealed a nontryptic P1 / P1' cleavage site at alanine-195 / valine-196 (Fig. 1B).

[0014] For CD16 enriched from culture supernatants of activated neutrophils, we detected three distinct peptide patterns with nontryptic C-termini (peptides no. 2-4, Figures 1A and 1B). Peptide no. 2 corresponds to amino acids glycine-174 to alanine-195 of SEQ ID NO:2, peptide no. 3 corresponds to amino acids glycine-174 to valine-196 of SEQ ID NO:2, and peptide no. 4 corresponds to amino acids asparagine-180 to threonine-198 of SEQ ID NO:2.

[0015] Peptide #2 and #3 contained a valine at position 176, suggestive of CD16b, and revealed P1 / P1' positions at alanine-195 / valine-196 and at valine-196 / serine-197 (Figure 1B). Peptide #4 had a P1 / P1' position at threonine-198 / isoleucine-199 (Figure 1B). This peptide was derived from soluble CD16 from enriched neutrophils, but did not contain the amino acid at position 176 to identify the isoform (Figure 1B). Regardless, the high-confidence peptide revealed a third cleavage site of CD16. Taken together, these findings demonstrate the existence of a cleavage region of CD16 rather than a single specific cleavage site.

[0016] We further investigated the cleavage region of CD16 by using site-directed mutagenesis to determine whether CD16a and CD16b cleavage could be disrupted in cell-based assays. ADAM17 tends to prefer α-helical structures in the substrate region that interacts with its catalytic site. Moreover, proteomic studies on ADAM17 cleavage site specificity revealed a very low preference for proline residues at the P1', P2', or P3' positions. Therefore, we substituted serine-197 in the cleavage region of CD16a and CD16b with proline (S197P, as shown in Figure 2).

[0017] CD16b and CD16b / S197P were separately expressed in the human kidney cell line HEK293, which does not express endogenous CD16. HEK293 transfectants expressed CD16b or CD16b / S197P at the same levels on their surface (Figure 3A). High levels of CD16b were released from transfected HEK293, which were further enhanced by their treatment with PMA, as measured by ELISA (Figure 3A). However, the soluble levels of CD16b / S197P produced by untreated or PMA-treated HEK293 cells were significantly lower than that of CD16b (Figure 3A).

[0018] We also investigated the effect of the S197P mutation on CD16a shedding using the same approach. Surface expression of CD16a requires association with the γ-chain dimer. Therefore, we used HEK293 cells stably expressing the human γ-chain. In comparison to HEK293 transfectants expressing equivalent surface levels of CD16a or CD16a / S197P (Figure 3B), we measured the soluble levels of each receptor in the culture supernatants of untreated and PMA-treated cells. Compared to CD16a, we again observed significantly lower levels of soluble CD16a / S197P (Figure 3B).

[0019] To assess whether the engineered S197P mutation in CD16 could interfere with ADAM17 activity, we also transfected HEK293 cells expressing or lacking CD16b / S197P with L-selectin, a well-described ADAM17 substrate normally expressed in leukocytes. Both transfectants expressed comparable levels of L-selectin, which was similarly downregulated following their activation with PMA (Fig. 3C), demonstrating that the S197P mutation affected CD16 shedding but not ADAM17 activity.

[0020] To evaluate the effect of the S197P mutation on CD16a shedding in NK cells, we used the human NK cell line NK92 (Gong et al, 1994, Leukemia 8:652-658). These cells lack endogenous CD16a expression, but recombinant CD16a can be stably expressed. We transduced NK92 cells to express CD16a and CD16a / S197P separately. Cells expressing comparable levels of these receptors were activated with PMA, and cell surface CD16 levels were examined by flow cytometry. CD16a, but not CD16a / S197P, underwent a significant downregulation in cell surface expression (Figure 4A). IL-12 and IL-18 are physiological stimuli of NK cells that can cause CD16a shedding, either individually or in combination. We demonstrated that NK92 cells treated with IL-12 and IL-18 strongly downregulated cell surface expression of CD16a, but not CD16a / S197P (Figure 4B). Direct engagement of cell-bound IgG by CD16a may also cause shedding, which we investigated here by incubating NK92 cells expressing CD16a or CD16a / S197P with the CD20-positive Burkitt's lymphoma cell line Raji in the presence or absence of the anti-CD20 mAb, rituximab. Treatment of Raji cells with rituximab induced downregulation of CD16a, but not CD16a / S197P (Figure 4C).

[0021] BMS566394 is an ADAM17 inhibitor that is highly selective for ADAM17 over other metalloproteases by several orders of magnitude. BMS566394 prevented CD16a shedding with similar efficiency as the S197P mutation, but had no additional blocking effect on activated NK92 cells expressing CD16a / S197P (Figure 4D). These findings provide further evidence that ADAM17 is the primary sheddase that cleaves CD16a within its cleavage region. However, it is possible that ADAM17 expression levels are not equivalent to those of NK92 cells expressing CD16a or CD16a / S197P, which may account for their different shedding. Therefore, we stained NK92 cells expressing CD16a or CD16a / S197P with multiple anti-ADAM17 mAbs and observed identical cell surface levels (Figure 4E).

[0022] To establish the effect of the S197P mutation on CD16a shedding by primary NK cells, we used human iPSCs to generate genetically engineered NK cells. We previously reported the induction of functional NK cells from iPSCs and their similarity to peripheral blood NK cells (Knorr et al., 2013 Stem Cells Transl Med. 2:274-283; Ni et al, 2014, Stem Cells 32: 1021-1031). CD16a and CD16a / S197P cDNAs were cloned into Sleeping Beauty transposon plasmids for gene insertion and stable expression in iPSC cells, which were subsequently differentiated into mature NK cells.

[0023] NK cells derived from mock-transduced iPSC cells expressed low levels of endogenous CD16a, whereas transduced CD16a and CD16a / S197P were expressed at higher levels (Figure 4F). NK cell activation occurred through various receptors upon their interaction with K562 cells, including BY55 / CD160, leading to ADAM17 activation and CD16a shedding. We stimulated iPSC-derived NK cells with K562 cells and found that CD16a underwent a significant downregulation of cell surface expression, whereas CD16a / S197P expression remained stable (Figure 4F).

[0024] Endogenous and recombinant CD16a have sufficient affinity to bind monomeric IgG. To examine the effect of the S197P mutation on CD16a function, we compared the IgG-binding capacity of CD16a and CD16a / S197P. NK92 cells expressing equivalent levels of CD16a or CD16a / S197P bound IgG in a similar dose-dependent manner (Figure 5A). Controls consisted of IgA binding to NK92 cells expressing CD16a or CD16a / S197P, and IgG binding to parental NK92 cells. Both occurred at essentially background levels (Figure 5A). These findings demonstrate specific and equivalent IgG binding by CD16a and CD16a / S197P.

[0025] Since CD16a is a potent activating receptor on NK cells, we investigated whether the engineered S197P mutation affected the ability of CD16a to trigger cell activation upon engagement of antibody-treated tumor cells. NK92 cell activation occurred very rapidly by degranulation and was assessed by measuring upregulation of CD107a, a sensitive indicator of NK cell activation. Mock-transduced NK92 cells incubated with Raji cells treated with or without rituximab demonstrated low levels and similar upregulation of CD107a (Figure 5B). NK92 cells expressing CD16a or CD16a / S197P at comparable levels incubated with Raji cells alone also marginally upregulated CD107a, but their incubation with rituximab-treated Raji cells also resulted in a large upregulation of CD107a (Figure 5B). Taken together, the above findings indicate that the engineered S197P mutation in CD16a did not impair its function.

[0026] Thus, we show that engineered S197P mutations in CD16a and CD16b effectively prevented their shedding in cell-based assays with native ADAM17. The S197P mutation in CD16a also prevented receptor shedding in the human NK cell line, NK92, but did not impair receptor function. NK92 cells expressing equivalent levels of CD16a or CD16a / S197P bound monomeric IgG with similar efficiency across a range of antibody concentrations. In addition, NK92 cells expressing CD16a or CD16a / S197P upregulated the activation marker CD107a in a similar manner upon engagement of rituximab bound to Raji cells.

[0027] Pluripotent stem cells allow for genetic manipulation to generate engineered NK cells. This disclosure describes the generation of engineered NK cells from transduced iPSCs expressing wild-type CD16a or CD16a / S197P. Using NK92 cells, CD16a was shed in iPSC-derived NK cells and demonstrated normal ADAM 17 activity upon cell activation, while CD16a / S197P was not shed.

[0028] CD16a and the cytotoxic function of NK cells are significantly downregulated in cancer patients. cDNAs encoding CD16a / S197P can be used to generate stable human induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs). These stem cells can then be differentiated into primary NK cells expressing CD16a / S197P. Other cell populations expressing cleavage-resistant CD16a / S197P (e.g., monocytes) or CD16b / S197P (e.g., neutrophils) can also be derived from hESCs / iPSCs.

[0029] To create NK cell immunotherapies for use in human patients against various forms of cancer or infection, CD16a / S197P-expressing NK cells may mediate enhanced antibody-dependent cellular cytotoxicity (ADCC) activity or other CD16a-mediated activities (e.g., IFNγ and TNFα production). For example, CD16a / S197P-expressing NK cells may be combined with therapeutic antibodies (e.g., trastuzumab or rituximab), bispecific killer engagers (e.g., BiKE, CD16×CD33, CD16×CD19, or CD16×EP-CAM bispecific killer cell engagers), or trispecific killer cell engagers (TriKE). Other therapeutic cell populations (e.g., neutrophils, monocytes, T cells, etc.) may also produce enhanced CD16-mediated activities.

[0030] Expression of CD16a / S197P in human iPSCs or human ESCs can generate NK cell populations with enhanced ADCC activity against neoplastic conditions, such as HER2 ovarian cancer. In some cases, the neoplastic conditions can be treated with therapeutic antibodies, such as trastuzumab. Mature NK cells can be derived from human embryonic stem cells and iPSCs.

[0031] Wild-type CD16a and / or CD16a / S197P can be cloned to generate stable iPSC or stable ECS lines expressing individual CD16a receptors. Any suitable cloning method can be used. Exemplary cloning methods include, for example, virus-based methods, transposon vectors (e.g., Sleeping Beauty), or nucleofection.

[0032] As an example, iPSCs can be modified using the Sleeping Beauty transposon vector. The vector contains a selection system, such as a GFP / Zeocin resistance fusion protein, which allows for a dual selection system (Zeocin resistance and flow cytometric cell sorting). iPSCs are differentiated into mature NK cells as previously described (Ni et al, 2011, J. Virol. 85:43-50; Knorr et al. 2013, Stem Cells Transl Med 2:274-283; Woll et al, 2009, Blood 113:6094-6101). Expression of transgenic receptors in iPSCs can lead to high expression levels in induced NK cells. CD16 expression in undifferentiated iPSCs can halt NK cell differentiation. In such cases, CD16 expression may be delayed, for example using the CD56 or native CD16a promoter, so that CD16 expression coincides more favorably with normal NK cell differentiation.

[0033] One skilled in the art will compare NK cells expressing comparable levels of CD16a / S197P versus wild-type CD16a. Expression levels of CD16 constructs can be matched by FACS sorting based on GFP expression, which appears in a proportional manner with CD16 constructs. Matched CD16a levels can be confirmed by FACS. NK cytotoxicity against HER2-expressing ovarian cancer cells can be assessed by standard chromium release assays in the presence or absence of therapeutic antibodies, such as trastuzumab. Antibody-dependent cellular cytotoxicity can be assessed using non-chromium labeled ovarian cancer cells. One skilled in the art can assess NK cell cytokine production (e.g., IFNγ, TNF) and soluble levels of CD16a by ELISA, and cell surface levels of CD16a and other activation markers (e.g., CD107a, CD62L) by FACS.

[0034] The human tumor xenograft model described in Example 3 can be used to evaluate the anticancer activity of NK cells expressing noncleavable CD16a in vivo. Unlike human CD16, mouse CD16 does not undergo ectodomain shedding upon cell stimulation, therefore measuring the effect of CD16a shedding on NK cell-mediated ADCC cannot be modeled in normal mice. Table 1 provides representative combinations of experimental groupings and treatments.

[0035] [Table 1]

[0036] Tumor growth and / or regression may be monitored weekly by conventional methods including, for example, bioluminescence imaging, ultrasound, CT, MRI, another imaging technique, and / or weighing the mice (Woll et al, 2009, Blood 113:6094-6101). Mice may also be bled (e.g., weekly) to quantify human NK cell viability. Expression and / or cell surface levels of various effector function markers (e.g., IFNγ, CD16a) may be assessed using conventional techniques, for example, by FACS. Mice may be followed for any suitable period of time, for example, 60 days. At the time of sacrifice, internal organs (e.g., spleen, liver, lungs, kidneys, and / or ovaries) may be examined (e.g., by bioluminescence) for signs of metastatic cancer, as previously described (Woll et al, 2009, Blood 113:6094-6101).

[0037] Our analysis allows one of skill in the art to define and compare the antibody-dependent cytotoxicity activity and in vivo potency of iPSC-derived NK cells expressing CD16a / S197P versus wild-type CD16a. Thus, we herein describe modified forms of CD16a, genetically modified cells expressing modified CD16a, and methods involving genetically modified cells (e.g., NK cells, neutrophils, monocytes, T cells, etc.). For example, NK cells expressing modified forms of CD16a, CD16a / S197P, exhibit enhanced anti-ovarian cancer activity due, at least in part, to reduced susceptibility to ADAM17-mediated shedding upon NK cell stimulation. This in turn enhances antibody-dependent cytotoxicity activity upon engagement of antibody-tagged cancer cells, e.g., cancer cells tagged with therapeutic antibodies. Moreover, antibody recognition by NK cells enhances contact stability with tumor cells and potentiates NK cell activity through other activating receptors, such as NKG2D.

[0038] The term "and / or" means one or all of the listed elements or a combination of any two or more of the listed elements; the term "comprising" and variations thereof do not have a limiting meaning where these terms appear in the description and claims; unless otherwise specified, "a," "an," "the," and "at least one" are used interchangeably and mean one or more; and the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0039] In the foregoing description, specific embodiments may be described in isolation for clarity. A particular embodiment includes any combination of compatible features described herein with respect to one or more embodiments, unless expressly specified otherwise that a feature of a particular embodiment is incompatible with a feature of another embodiment. In any method disclosed herein that includes distinct steps, the steps may be performed in any feasible order, and, where appropriate, any combination of two or more steps may be performed simultaneously. The present invention is illustrated by the following examples. It should be understood that the particular examples, materials, amounts, and procedures are to be interpreted broadly in accordance with the scope and spirit of the invention described herein. Example 1

[0040] Example 1 mass spectrometry Peripheral blood collection from healthy volunteers was performed according to a protocol approved by the University of Minnesota Institutional Review Board under protocol number 9708M00134. Human neutrophil and NK cell isolation was performed as previously described (Wang et al, 2013, Biochim Biophys Acta. 1833:680-685; Long et al, 2010, J Leukoc Biol. 87: 1097-1101; Long et al, 2012, J Leukoc Biol. 92:667-672). Enriched neutrophils or NK cells (1 × 10 in PBS) were collected from 100 healthy volunteers and 100% ethanol. 7 CD16 was activated with PMA (15 ng / ml or 50 ng / ml, respectively; Sigma-Aldrich, St. Louis, MO) for 30 min at 37°C. Cell supernatants were filtered (0.45 μm pore size) and CD16 was immunoprecipitated using mAb 3G8 (BioLegend, Inc., San Diego, CA) and the Pierce Direct Immunoprecipitation Kit (Thermo Fisher Scientific, Rockford, IL) according to the manufacturer's instructions. Purified CD16 was deglycosylated with Remove-iT PNGase F (New England BioLabs, Inc., Ipswich, MA) tagged with a chitin-binding domain according to the manufacturer's instructions. Briefly, 10–20 μg of purified CD16 was denatured in the presence of 40 mM DTT at 55°C for 10 min and then incubated with 3 μl of REMOVE-IT PNGase F (New England BioLabs, Inc., Ipswich, MA) for 1 h at 37°C. REMOVE-IT PNGase F was then removed from the reaction using chitin magnetic beads.

[0041] CD16 was subjected to SDS-PAGE and the gel band corresponding to soluble CD16 was detected by krypton fluorescent protein dye (Thermo Fisher Scientific, Rockford, IL) and confirmed by CD16 immunoblot analysis of adjacent lanes of the same gel, which was then excised and subjected to standard in-gel digestion with trypsin. Digested peptides extracted from the gel were dried down and reconstituted in water:acetonitrile:formic acid, 98:2:0.01 for liquid chromatography-mass spectrometry, and <1 μg aliquots were analyzed by mass spectrometry (VELOS ORBITRAP, Thermo Fisher Scientific, Rockford, IL) in data-dependent scanning mode as previously described (Lin-Moshier et al, 2013, J Biol Chem. 288:355-367). Database searches were performed using Protein Pilot 4.5 (AB Sciex, Framingham, MA) using the Paragon scoring algorithm (Shilov et al, 2007, Mol Cell Proteomics 6: 1638-1655) against the NCBI reference sequence Homo sapiens protein FASTA database with contaminant database (thegpm.org / cRAP / index, 109 proteins). Search parameters were: cysteine ​​iodoacetamide; trypsin; instrument Orbi MS (1-3 ppm) Orbi MS / MS; biological modification ID focus (including asparagine deamidation); overall search results; and false discovery rate analysis (using reverse database).

[0042] Generation of cDNA expression constructs CD16b occurs in two allelic variants, termed NA1 and NA2, which differ by four amino acids in the N-terminal portion of its extracellular domain. Both allelic variants of CD16b are cleaved by ADAM17 with similar efficiency. For this study, we examined only the NA1 variant. There are also two allelic variants of CD16a, which have either a valine or a phenylalanine residue at position 176. These two allelic variants of CD16a were cleaved by ADAM17 with similar efficiency. For this study, we examined only the valine allelic variant CD16a.

[0043] CD16a and CD16b were amplified from human leukocyte cDNA and cloned separately into the pcDNA3.1 plasmid (Invitrogen, Carlsbad, CA) at the BamHI and EcoRI restriction enzyme sites as previously described (Wang et al, 2013, Biochim Biophys Acta. 1833:680-685; Dong et al, 2014, Arthritis Rheumatol. 66: 1291-1299). Constructs were then subjected to Quik-Change Site-directed Mutagenesis (Agilent Technologies, Santa Clara, CA) according to the manufacturer's instructions to convert the serine at position 197 of CD16a and CD16b to proline. All constructs were sequenced to confirm the presence of the planned mutations and the absence of any spontaneous mutations.

[0044] The CD16a cDNA was then cloned into the bicistronic retroviral expression vector pBMN-IRES-EGFP, provided by Dr. G. Nolan (Stanford University, Stanford, CA), at the BamHI and EcoRI restriction enzyme sites. The CD16a construct was also cloned into the bicistronic Sleeping Beauty transposon plasmid (pKT2-IRES-GFP:zeo) as previously described (Wilber et al., 2007, Stem Cells 25:2919-2927; Tian et al., 2009, Stem Cells 27:2675-2685).

[0045] Briefly, wild type CD16a and CD16a / S197P were PCR amplified using primers: 5'-CCG GAA TTC CAG TGT GGC ATC ATG TGG CAG CTG CTC-3' (sense, SEQ ID NO:XX) and 5'-CCG GAA TTC TCA TTT GTC TTG AGG GTC CTT TCT-3' (antisense, SEQ ID NO:YY). EcoRI sites are underlined. EcoRI digested CD16a and CD16a / S197P PCR fragments were cloned separately into pKT2-IRES-GFP:zeo. Correct CD16a orientation and sequence were confirmed by PCR and sequencing analysis. We previously cloned full-length human L-selectin (CD62L) cDNA (Feehan et al., 1996, J Biol Chem. 271:7019-7024; Matala et al., 2001, J Immunol. 167: 1617-1623) and transferred it into the pcDNA3.1 vector at the restriction enzyme site Xba1. Full-length human FcRγ cDNA was cloned as previously described with modifications using the pcDNA3.1 vector (Dong et al., 2014, Arthritis Rheumatol. 66: 1291-1299).

[0046] Generation of cell lines expressing recombinant L-selectin, CD16a, and CD16b HEK293 cells (human embryonic kidney cell line) and NK92 cells (human NK cell line) (ATCC, Manassas, VA) were cultured according to the supplier's instructions. HEK293 cells were transiently transfected with pcDNA3.1 with or without CD16b, CD16b / S197P, and / or L-selectin using Lipofectamine2000 (Invitrogen, Carlsbad, CA) according to the manufacturer's instructions. HEK293 cells stably expressing human FcRγ were transiently transfected with pcDNA3.1 with or without CD16a or CD16a / S197P by the same approach. NK92 cells were stably transduced with pBMN-IRES-EGFP with or without CD16a or CD16a / S197P by previously described retroviral production and infection procedures (Matala et al, 2001, J Immunol. 167: 1617-1623; Walcheck et al, 2003, J Leukoc Biol. 74:389-394; Wang et al, 2009, J Immunol. 182:2449-2457). Expression of the constructs was assessed by EGFP fluorescence and by CD16 staining as measured by flow cytometry. Human iPSCs (UCBiPS7, derived from umbilical cord blood CD34 cells) were maintained on mouse embryonic fibroblasts (Knorr et al., 2013, Stem Cells Trans I Med. 2:274-283; Ni et al, 2014, Stem Cells 32: 1021-1031). Stable expression of CD16a or CD16a / S197P was achieved using the Sleeping Beauty transposon system as previously described (Wilber et al., 2007, Stem Cells 25:2919-2927; Tian et al., 2009, Stem Cells 27:2675-2685).Briefly, iPSCs were nucleofected with pKT2-IRES-GFP:zeo combined with transposase DNA in Nucleofector Solution V (Lonza Inc., Gaithersburg, MD) using program setting B16. Nucleofected cells were immediately suspended in iPSC growth medium containing Zeocin (50 μg / ml) and plated onto mouse embryonic fibroblasts.

[0047] Induction of NK cells from CD16a-hESC and CD16a-iPSC cells Hematopoietic differentiation of hESCs and iPSCs was performed as previously described (Ng et al, 2005, Blood 106: 1601-1603; Ng et al, 2008, Nat Protoc 3:768-776; Le Garff-Tavernier et al, 2010, Aging Cell 9: 527-535). Briefly, 3000 single cells per well of a 96-well round-bottom plate were seeded in BPEL medium containing stem cell factor (SCF, 40 ng / ml), vascular endothelial growth factor (VEGF, 20 ng / ml), and bone morphogenetic protein 4 (BMP4, 20 ng / ml).BPEL medium consisted of Iscove's Modified Dulbecco's Medium (IMDM, 86 mL, Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA), F12 Nutrient Mixture with Glutmax I (86 mL, Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA), 10% deionized bovine serum albumin (BSA, 5 mL, Sigma-Aldrich, St. Louis, MO), 5% polyvinyl alcohol (10 mL, Sigma-Aldrich, St. Louis, MO), linoleic acid (20 μl of a 1 g / ml solution, Sigma), SYNTHECOL 500× solution (Sigma-Aldrich, St. Louis, MO), a-monothioglycerol (3.9 μl / 100 mL, Sigma-Aldrich, St. Louis, MO), and α-monothioglycerol (3.9 μl / 100 mL, Sigma-Aldrich, St. Louis, MO). The mixture contained 100x insulin-transferrin-selenium (Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA), protein-free hybridoma mix II (Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA), ascorbic acid (5 mg / ml, Sigma), GLUTAMAX I (Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA), insulin-transferrin-selenium 100x solution (Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA), and penicillin / streptomycin (Invitrogen, Thermo Fisher Scientific, Inc., Waltham. MA).

[0048] On day 11 of hematopoietic differentiation, spun embryoid bodies were transferred directly into 24-well plates with or without EL08-1D2 stromal cells in NK medium supplemented with cytokines (Le Garff-Tavernier et al, 2010, Aging Cell 9:527-535). After 4–5 weeks of culture, single cell suspensions were stained with APC-, PE-, FITC-, and PerCP-cy5.5-conjugated IgG or specific antibodies against human blood surface antigens: CD45-PE, CD56-APC, CD56-PE, CD16-PerCP-cy5.5, NKG2D-PE, NKp44-PE, NKp46-PE, CD158b-FITC, CD158e1 / 2-FITC (BD Pharmingen, San Jose, CA), CD158a / h-PE, and CD158i-PE (Beckman Coulter, Inc., Pasadena, CA). Antibody staining was assessed by flow cytometry.

[0049] cell stimulation HEK293 and NK92 cells in RPMI1640 medium (Mediatech, Inc., Manassas, VA) were activated with 15 ng / ml and 100 ng / ml PMA, respectively, for 30 min at 37° C. NK92 cells were activated with 100 ng / ml and 400 ng / ml IL-12 (PeproTech Inc, Rocky Hill, NJ) and IL-18 (R&D Systems, Inc., Minneapolis, MN), respectively, for the indicated time points. NK92 cell activation through CD16a was mediated by their incubation with the CD20-positive Burkitt's lymphoma cell line Raji (ATCC, cultured according to the contract manufacturer's instructions) (1:1 ratio) treated with the anti-CD20 mAb rituximab (1 μg / ml) (Genentech, Inc., South San Francisco, CA) as previously described (Romee et al., 2013, Blood 121:3599-3608). Excess rituximab was removed by washing the Raji cells. In some experiments, NK92 cells were preincubated for 30 min with the selective ADAM17 inhibitor BMS566394 (5 μM) (Bristol-Myers Squibb Company, Princeton, NJ). NK cells derived from iPSCs were stimulated with the human erythroleukemia cell line K562 (ATCC grown according to the supplier's instructions) as previously described (Romee et al., 2013, Blood 121:3599-3608). Briefly, iPSC-derived NK cells were incubated with K562 target cells (2:1 ratio) for 4 hours at 37°C.

[0050] Antibody binding assays Cells binding to monomeric human IgG and IgA (Sigma-Aldrich, St. Louis, MO) were generated as previously described with some modifications (Dong et al., 2014, Arthritis Rheumatol. 66: 1291-1299). 6NK92 parental or transduced cells expressing CD16a or CD16a / S197P at 100 / ml were incubated in triplicate with the indicated concentrations of IgG or IgA for 1 hour at 4° C. Cells were washed extensively and incubated with APC-conjugated donkey anti-human Fc (heavy and light chain) antibody (Jackson Immunoresearch, West Grove, PA) according to the manufacturer's instructions. Cells were washed and then immediately analyzed by flow cytometry.

[0051] Flow cytometry and ELISA For cell staining, nonspecific antibody binding sites were blocked, cells were stained with the indicated antibodies, and examined by flow cytometry as previously described (Wang et al., 2013, Biochim Biophys Acta. 1833:680-685; Romee et al., 2013, Blood 121 :3599-3608). Flow cytometry analysis was performed with FACSCanto and LS RII instruments (BD Biosciences, San Jose, CA). Human CD16 was detected by mAbs 3G8 (BioLegend, Inc., San Diego, CA) and DJ130c (Santa Cruz Biotech, Santa Cruz, CA). CD107a was detected by mAb H4A3 (Biolegend, Inc., San Diego, CA). ADAM17 was detected by mAbs M220 (Doedens et al, 2000, J Biol Chem. 275:14598-14607), 111633, and 111623 (R&D Systems, Inc., Minneapolis, MN). Human L-selectin was detected by mAb LAM1-116 (Ancell Corp., Stillwater, MN). Isotype-matched negative control mAbs were used to assess the level of nonspecific staining. ELISA for CD16 was performed by a custom cytometric bead assay as previously described (Wang et al, 2013, Biochim Biophys Acta. 1833:680-685).

[0052] statistical analysis Statistical analysis was performed using Prism software (GraphPad, San Diego, Calif.) using ANOVA and Student's t-tests, where appropriate. A p-value of <0.05 was considered significant.

[0053] Example 2 Comparable levels of WT CD16a and CD16a 197P Comparison of NK cells expressing (CD16a / S197P)

[0054] Expression levels of CD16 constructs are matched by FACS sorting based on GFP expression (as was done for NK92 cells described above, FIG. 2), which occurs in a proportional manner with CD16 constructs. Matched CD16a levels are confirmed by FACS for all assays. As a control, iPSC-derived NK cells modified with an empty Sleeping Beauty transposon vector (expressing only GFP) are evaluated. iPSC-derived NK cells express low levels of endogenous CD16a (data not shown). NK cytotoxicity against HER2-expressing ovarian cancer cells is evaluated by standard chromium release assay in the presence or absence of trastuzumab. Antibody-dependent cellular cytotoxicity with non-chromium-labeled ovarian cancer cells is also performed. NK cell cytokine production (e.g., IFNγ, TNFα) and soluble levels of CD16a are evaluated by ELISA. Cell surface levels of CD16a and other activation markers (e.g., CD107a, CD62L) are evaluated by FACS.

[0055] Example 3 CD16a 197P A human tumor xenograft model to test whether iPSC-derived NK cells expressing (CD16a / S197P) have enhanced anti-ovarian cancer activity in vivo in the presence of trastuzumab.

[0056] NOD / SCID / γc mice engineered to stably express firefly luciferase for bioluminescence imaging (Geller et al., 2013, Cytotherapy 15: 1297-1306) - / -A xenograft model using NSG mice and human ovarian cancer cell lines is used to test intraperitoneal (ip) delivery of NK cell activity against ovarian cancer cells. The HER2-overexpressing OVCAR3 ovarian cancer cell line is used as the in vivo target (Hellstrom et al, 2001, Cancer Res 61: 2420-2423). Sublethally irradiated (225 cGY) NSG female mice are injected with OVCAR3 (2×10 5 Tumours were allowed to grow for 7 days, after which mice were injected with 20 × 10 6 Mice are then given the indicated IL-2 (5 μg / mouse) every other day for 4 weeks to promote in vivo survival of NK cells as previously described (Woll et al, 2009, Blood 113: 6094-6101). Trastuzumab is administered intraperitoneally every week for 4 weeks at a dose of 50 μg, a dose previously used in this model (Warburton et al, 2004, Clinical cancer research 10:2512-2524). Comparable levels of WT CD16 or CD16a 197P The in vivo efficacy of iPSC-derived NK cells expressing (CDa6a / S197P) is compared. Controls include iPSC-derived NK cells expressing only GFP (vector only) and a cohort of mice fed only ovarian cancer cells. All mice receive the same IL-2 treatment.

[0057] Tumor growth / regression is monitored weekly by bioluminescence imaging and weighing of mice as previously described (Woll et al, 2009, Blood 113: 6094-6101). Mice are also bled weekly to quantify human NK cell viability. Expression / cell surface levels of various effector function markers (e.g. IFNγ, CD16a) are assessed by FACS. Mice are followed for -60 days. At the time of sacrifice, internal organs (spleen, liver, lungs, kidneys, and ovaries) are examined for signs of metastatic cancer by bioluminescence as previously described (Blood 113: Woll et al, 2009, 6094-6101).

[0058] Representative Embodiments Embodiment 1. A cell genetically engineered to express a CD16 polypeptide comprising a membrane proximal region and an amino acid modification within said membrane proximal region. Embodiment 2. A cell comprising a polynucleotide encoding a CD16 polypeptide comprising a membrane proximal region and an amino acid modification within said membrane proximal region. Embodiment 3. The cell of embodiment 1 or embodiment 2, wherein the amino acid drug therapy reflects the addition of one or more amino acids, the deletion of one or more amino acids, or the substitution of one or more amino acids compared to the wild-type amino acid sequence of the CD16 membrane proximal region.

[0059] Embodiment 4. The cell of embodiment 3, wherein the one or more amino acid substitutions include a substitution of a serine residue at position 197 of SEQ ID NO:1. Embodiment 5. The cell of any one of embodiments 1 to 4, wherein the cell is a natural killer (NK) cell. Embodiment 6. The cell of any one of embodiments 1 to 5, wherein the cell is a neutrophil. Embodiment 7. The cell of any one of embodiments 1 to 6, wherein the cell is a monocyte. Embodiment 8. The cell of any one of embodiments 1 to 7, wherein the modified CD16 polypeptide exhibits reduced susceptibility to ADAM17-mediated shedding compared to a wild-type CD16 polypeptide.

[0060] Embodiment 9. The cell of any one of embodiments 1 to 8, wherein the modified CD16 polypeptide exhibits reduced susceptibility to cleavage upon NK cell stimulation compared to a wild-type CD16 polypeptide. Embodiment 10. A patient in need of such treatment is administered the following: administering a therapeutic NK effector to said patient; and Administering the cell according to any one of claims 1 to 9 to the patient. The method comprises administering a treatment comprising:

[0061] Embodiment 11 The method of embodiment 10, wherein said therapeutic NK effector comprises a therapeutic agent. Embodiment 12 The method of embodiment 11, wherein the therapeutic agent specifically recognizes a tumor antigen. Embodiment 13. The method of embodiment 12, wherein the therapeutic agent comprises an antibody or antibody fragment that specifically recognizes a tumor antigen. Embodiment 14 The method of embodiment 13, wherein the tumor antigen comprises HER2. Embodiment 15 The method of embodiment 13 or embodiment 14, wherein the antibody comprises trastuzumab or rituximab.

[0062] Embodiment 16 The method of embodiment 10, wherein said therapeutic NK effector comprises a bispecific killer engager (BiKE). Embodiment 17. The method of embodiment 16, wherein the BiKE comprises CD16×CD33 BiKE, CD16×CD19 BiKE, or CD16×EP-CAM BiKE. Embodiment 18 The method of embodiment 10, wherein said therapeutic NK effector comprises a trispecific killer cell engager (TriKE).

[0063] Embodiment 19. The method of any one of embodiments 11 or 16-18, wherein the therapeutic agent specifically recognizes a viral target. Embodiment 20. A method of improving therapy for a patient involving administering to the patient a therapeutic NK effector comprising: Administering the cell according to any one of claims 1 to 9 to the patient. The method includes:

[0064] The entire disclosures of all patents, patent applications, and publications mentioned herein, as well as electronically available materials (e.g., nucleotide sequence deposits, e.g., GenBank and RefSeq, and amino acid sequence deposits, e.g., SwissProt, PIR, PRF, PDB, and translations from the annotated translated regions of GenBank and RefSeq) are incorporated by reference in their entirety. In the event of any inconsistency between the disclosure of this application and the disclosure of any document incorporated by reference herein, the disclosure of this application shall control. The foregoing detailed description and examples are provided merely for clarity of understanding and should not be unduly limited therefrom. The invention is not limited to the exact details shown and described, and the invention claimed in the appended claims includes modifications that would be apparent to one of ordinary skill in the art.

[0065] Unless otherwise indicated, all numerical values ​​expressing ingredients, molecular weights, and other quantities used in the specification and claims should be understood to be modified in all instances by the term "about." Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations and may vary depending upon the desired properties sought to be obtained by the present invention. Without limiting the doctrine of equivalents with respect to the scope of the claims, at the very least, the number of reported significant digits should be taken into consideration and conventional rounding techniques should be used in construing each numerical parameter.

[0066] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible, however, any numerical value necessarily contains a certain range corresponding to the standard deviation found in the corresponding testing measurements.

[0067] All headings are for the convenience of the reader and should not be used to limit the meaning of the material that follows the heading, unless specifically stated.

Claims

1. A cell comprising a polynucleotide encoding a modified CD16 polypeptide or an allelic variant thereof, comprising a substitution of a serine residue at position 197 of SEQ ID NO: 1 or 2 for proline.

2. The cell of claim 1, wherein the substitution of a serine residue at position 197 results in a structural change that inhibits CD16 cleavage.

3. The cell of claim 1, wherein the CD16 polypeptide further comprises a valine at position 176 (176V).

4. The cells are (i) natural killer (NK) cells; (ii) neutrophils; (iii) a monocyte; or (iv) Pluripotent stem cells or differentiated cells obtained from the pluripotent stem cells. The cell of claim 1 or claim 2.

5. 5. The cell of claim 4, wherein (i) the pluripotent stem cell is an induced pluripotent stem cell (iPSC) or an embryonic stem cell (ESC); or (ii) the differentiated cell generated from the pluripotent stem cell is a hematopoietic cell.

6. A modified CD16 or allelic variant thereof comprising a serine to proline substitution at position 197 of SEQ ID NO:1 or SEQ ID NO:2, compared to a CD16 polypeptide not having the same modification, (i) reduced susceptibility to ectodomain shedding; (ii) reduced susceptibility to ADAM17-mediated shedding; (iii) reduced susceptibility to cleavage upon NK cell stimulation; or (iv) increased CD16-mediated activity The cell of claim 1 , which exhibits the following:

7. NK cells comprising the modified polypeptide have at least one of the following characteristics compared to NK cells expressing a wild-type CD16 polypeptide: (a) enhanced antitumor potential; (b) enhanced antiviral capacity; (c) Improved antibody-dependent cellular cytotoxicity (d) enhanced IFNγ or TNFα production (e) enhanced CD16-mediated activity (f) High surface CD16 levels (g) Low soluble CD16 levels (h) enhanced cell stimulation; and (i) Enhanced in vivo anti-cancer activity The cell of claim 4 .

8. The cell of claim 1, further comprising a bispecific killer engager (BiKE) or a trispecific killer cell engager (TriKE).

9. The cell of claim 8, wherein the BiKE comprises CD16xCD33BiKE, CD16xCD19BiKE, or CD16xEP-CAM BiKE.

10. A pharmaceutical composition comprising a cell population, the cell population comprising the cells according to any one of claims 1 to 9.

11. The pharmaceutical composition of claim 10 , wherein the composition comprises a population of NK cells.

12. The pharmaceutical composition of claim 11 , wherein the composition is for administration to a subject receiving a therapeutic agent.

13. The therapeutic agent is one of: (i) specifically recognizes a tumor antigen; (ii) comprises an antibody or antibody fragment that specifically recognizes the tumor antigen; or (iii) specifically recognize a viral target; 13. The pharmaceutical composition of claim 12.

14. (i) the tumor antigen comprises HER2; or (ii) the antibody is trastuzumab or rituximab The pharmaceutical composition of claim 13, comprising:

15. The therapeutic agent is one of the following: (i) bispecific killer engagers (BiKEs); or (ii) Tri-specific Killer Cell Engager (TriKE) The pharmaceutical composition of claim 12, comprising:

16. 16. The pharmaceutical composition of claim 15, wherein the BiKE comprises CD16xCD33 BiKE, CD16xCD19 BiKE, or CD16xEP-CAM BiKE.

17. 10. Use of a cell according to any one of claims 1 to 9 in the manufacture of a medicament for a neoplastic condition in a subject in need of treatment.

18. A kit comprising the pharmaceutical composition according to any one of claims 10 to 16.

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