Lytic Granules Research Articles

LYST controls the biogenesis of the endosomal compartment required for secretory lysosome function.

Chediak-Higashi syndrome (CHS) is caused by mutations in the gene encoding LYST protein, the function of which remains poorly understood. Prominent features of CHS include defective secretory lysosome exocytosis and the presence of enlarged, lysosome-like organelles in several cell types. In order to get further insight into the role of LYST in the biogenesis and exocytosis of cytotoxic granules, we analyzed cytotoxic T lymphocytes (CTLs) from patients with CHS. Using confocal microscopy and correlative light electron microscopy, we showed that the enlarged organelle in CTLs is a hybrid compartment that contains proteins components from recycling-late endosomes and lysosomes. Enlargement of cytotoxic granules results from the progressive clustering and then fusion of normal-sized endolysosomal organelles. At the immunological synapse (IS) in CHS CTLs, cytotoxic granules have limited motility and appear docked while nevertheless unable to degranulate. By increasing the expression of effectors of lytic granule exocytosis, such as Munc13-4, Rab27a and Slp3, in CHS CTLs, we were able to restore the dynamics and the secretory ability of cytotoxic granules at the IS. Our results indicate that LYST is involved in the trafficking of the effectors involved in exocytosis required for the terminal maturation of perforin-containing vesicles into secretory cytotoxic granules.

The effect of clinically therapeutic plasma concentrations of lidocaine on natural killer cell cytotoxicity.

Natural killer (NK) cells can induce death in cancer cells. Previous studies suggest that lidocaine may decrease the function of NK cells. However, it is unknown whether lower concentrations of lidocaine, usually found in patients managed with continuous infusions, also impair the function of NK cells. We hypothesized that lidocaine at low concentrations preserves the function of NK cells. Cytotoxicity assays were performed to assess the function of NK cells treated with different concentrations of lidocaine (0.01-50 μM) against K562, THP-1, and OCI-AML3 cells. Similar experiments were repeated with neutralizing NK group 2, member D (NKG2D) receptor antibody or granzyme B inhibitor. The concentrations of interferon-γ, perforin, and granzyme B and the expression of NKG2D receptor ligands (major histocompatibility I complex antigen and UL16-binding protein) were measured by enzyme-linked immunosorbent assay or Western blot. Values of P < 0.05 were considered statistically significant. In vitro, lidocaine enhanced the NK cell cytotoxicity against K562 at 0.01 and 0.1 μM (P = 0.001) and against THP-1 (P = 0.0013) and OCI-AML3 (P = 0.0043) cells at all tested concentrations. This observed effect was inhibited by the addition of a granzyme B inhibitor and NKG2D receptor blocker (THP-1, P = 0.0005 and P = 0.0001; and OCI-AML3, P = 0.0862 and P = 0.0133). Lidocaine did not induce major histocompatibility I complex antigen or UL16-binding protein. Our findings suggest that clinically relevant concentrations of lidocaine enhance the in vitro function of NK cells via the release of lytic granules.

Skin fibroblasts from individuals with Chediak-Higashi Syndrome (CHS) exhibit hyposensitive immunogenic response.

BackgroundChediak-Higashi Syndrome (CHS) is a rare autosomal recessive disease characterized by immunodeficiency, oculocutaneous albinism, neurological dysfunction, and early death. Individuals with CHS present with increased susceptibility to infections of the skin, upper-respiratory tract, gastrointestinal tract, and oral tissues. Classical CHS is caused by mutations in the gene encoding lysosomal trafficking regulator (LYST). Although defects in cytotoxic T cell lytic secretory granule secretion and neutrophil phagocytosis are suggested to contribute to the immunodeficiency in CHS, the underlying molecular mechanisms are unknown. We hypothesized that skin fibroblasts from CHS subjects exhibit impaired immune response due to defective trafficking of inflammatory factors.Methods and resultsPrimary skin fibroblasts from CHS subjects or healthy controls were assessed for genes encoding inflammatory response factors using PCR array. At baseline, we found CD14, IL1R1 and TLR-1 were down-regulated significantly (≥2 fold change) and the genes encoding TLR-3, IL-1β and IL-6 were up-regulated in CHS cells compared to control cells. When challenged with E. coli lipopolysaccharide (LPS), CHS cells were less responsive than control cells, with only 8 genes significantly up-regulated (3–68 fold change) compared to baseline values, whereas 28 genes in control cells were significantly up-regulated at a much higher magnitude (3–4,629 fold change). In addition, 50% of the genes significantly up-regulated in LPS-treated control cells were significantly lower in LPS-treated CHS cells. IL-6, a fibroblast-derived proinflammatory cytokine essential for fighting infections was significantly lower in culture media of CHS cells with or without LPS. Furthermore, Western blot and immunofluorescent staining revealed that TLR-2 and TLR-4 were diminished on cell membranes of CHS cells and dissociated from Rab11a.ConclusionsFor the first time, results from our study indicate defective trafficking of TLR-2 and TLR-4 contributes to the hyposensitive response of CHS skin fibroblasts to immunogenic challenge, providing a potential therapeutic target for clinical intervention in CHS.

Midline 1 controls polarization and migration of murine cytotoxic T cells.

Midline 1 (MID1) is a microtubule-associated ubiquitin ligase that regulates protein phosphatase 2 A levels. Loss-of-function mutations in MID1 lead to the human X-linked Opitz G/BBB (OS) syndrome characterized by defective midline development during embryogenesis. We have recently shown that MID1 is strongly up-regulated in murine cytotoxic T lymphocytes (CTLs), and that it has a significant impact on exocytosis of lytic granules and the killing capacity of CTLs. The aims of the present study were to determine the localization of MID1 in migrating CTLs, and to investigate whether MID1 affects CTL polarization and migration. We found that MID1 mainly localizes to the uropod of migrating CTLs and that it has a substantial impact on CTL polarization and migration in vitro. Furthermore, analysis of contact hypersensitivity responses supported that MID1 controls effector functions of CTLs in hapten-challenged skin in vivo. These results provide significant new knowledge on the role of MID1 in CTL biology.

ERDR1 enhances human NK cell cytotoxicity through an actin-regulated degranulation-dependent pathway

Erythroid differentiation regulator 1 (ERDR1), which is a stress-related survival factor, exhibits anti-cancer effects against melanoma. However, the function of ERDR1 on immune cells has not been examined. We investigated whether ERDR1 regulates the cytotoxic ability of human natural killer (NK) cells, which are known as innate effector lymphocytes. In this study, treatment with recombinant ERDR1 resulted in enhanced NK cell cytotoxicity through the secretion of lytic granules. Furthermore, actin modulation was involved in the ERDR1-enhanced NK cell cytotoxicity. ERDR1 stimulated actin accumulation at the immunological synapse, which was induced by the activation of Vav-1 in NK cells. These findings suggest new insight into the function of ERDR1 function in the human immune system.

A signaling network stimulated by β2 integrin promotes the polarization of lytic granules in cytotoxic cells.

Cytotoxic lymphocytes kill target cells through the polarized release of the contents of intracellular perforin-containing granules. In natural killer (NK) cells, the binding of β2 integrin to members of the intercellular adhesion molecule family is sufficient to promote not only the adhesion of NK cells to target cells but also the polarization of intracellular lytic granules toward the target. We used NK cells in an experimental system designed to enable us to study the polarization of lytic granules in the absence of their release through degranulation, as well as β2 integrin signaling independently of inside-out signals from other receptors. Through a proteomics approach, we identified a signaling network centered on an integrin-linked kinase (ILK)-Pyk2-paxillin core that was required for granule and microtubule-organizing center (MTOC) polarization. The conserved Cdc42-Par6 signaling pathway, which controls cell polarity, was also activated by ILK and was required for granule polarization toward the target cell. A subset of the signaling components required for polarization contributed also to the convergence of granules on the MTOC. These results delineate two connected signaling networks that are stimulated upon β2 integrin engagement and control the polarization of the MTOC and associated lytic granules toward the site of contact with target cells to mediate cellular cytotoxicity.

Distinct integrin-dependent signals define requirements for lytic granule convergence and polarization in natural killer cells.

Lytic granules in natural killer (NK) cells represent a dangerous cargo that is targeted for secretion to destroy diseased cells. The appropriate management of these organelles enables the mounting of a precise and valuable host defense. The process of NK cell adhesion to a target cell through engagement of the integrin LFA-1 (lymphocyte function-associated antigen 1) promotes lytic granule organization through complex cellular mechanics and a signaling pathway characterized by Zhang et al. in this issue of Science Signaling. A set of signaling molecules was defined for their ability to promote the polarization of NK cell lytic granules and the microtubule organizing center (MTOC) toward the interface with a target cell. A subset of these signaling molecules was also required for the convergence of lytic granules on the MTOC.

Acute myeloid leukemia impairs natural killer cells through the formation of a deficient cytotoxic immunological synapse.

Acute myeloid leukemia (AML) cells are killed by allogeneic NK cells. However, autologous NK cells from AML patients express decreased levels of activating receptors, and show reduced cytotoxicity. Here, we investigated how interactions between NK and AML cells might cause loss of NK-cell activity in patients. Our results show that AML cell lines and primary blasts alter the NK-cell phenotype, reducing their cytotoxic potential upon prolonged contact. Downregulation of NK-cell-activating receptors was contact-dependent and correlated with conjugate formation. Time-lapse imaging of HL60 AML cell line and NK-cell interactions showed a high proportion of noncytolytic contacts. Studies of NK-cell immunological synapses revealed a defect in lytic synapse formation. Namely, despite correct F-actin and LFA-1 recruitment, polarization of lytic granules toward primary blasts or AML cell lines was reduced. The NK-AML cell line synapses showed impairment of CD3ζ recruitment. Attempts to correct these synapse defects by cytokine stimulation of NK cells improved conjugate formation, but not granule polarization. Pretreatment of AML cell lines with the immunomodulating molecule lenalidomide significantly enhanced granule polarization. We speculate that combining immunomodulatory drugs and cytokines could increase AML cell sensitivity to autologous NK cells and reinforce the activity of allogeneic NK cells in adoptive immunotherapy.

Midline 1 directs lytic granule exocytosis and cytotoxicity of mouse killer T cells.

Midline 1 (MID1) is a microtubule-associated ubiquitin ligase that regulates protein phosphatase 2A activity. Loss-of-function mutations in MID1 lead to the X-linked Opitz G/BBB syndrome characterized by defective midline development during embryogenesis. Here, we show that MID1 is strongly upregulated in murine cytotoxic lymphocytes (CTLs), and that it controls TCR signaling, centrosome trafficking, and exocytosis of lytic granules. In accordance, we find that the killing capacity of MID1(-/-) CTLs is impaired. Transfection of MID1 into MID1(-/-) CTLs completely rescued lytic granule exocytosis, and vice versa, knockdown of MID1 inhibited exocytosis of lytic granules in WT CTLs, cementing a central role for MID1 in the regulation of granule exocytosis. Thus, MID1 orchestrates multiple events in CTL responses, adding a novel level of regulation to CTL activation and cytotoxicity.

Molecular mechanisms regulating cytotoxic lymphocyte development and function, and their associations to human diseases.

Molecular mechanisms regulating cytotoxic lymphocyte development and function, and their associations to human diseases.

Transcriptional regulation of Munc13-4 expression in cytotoxic lymphocytes is disrupted by an intronic mutation associated with a primary immunodeficiency.

Autosomal recessive mutations in UNC13D, the gene that encodes Munc13-4, are associated with familial hemophagocytic lymphohistiocytosis type 3 (FHL3). Munc13-4 expression is obligatory for exocytosis of lytic granules, facilitating cytotoxicity by T cells and natural killer (NK) cells. The mechanisms regulating Munc13-4 expression are unknown. Here, we report that Munc13-4 is highly expressed in differentiated human NK cells and effector CD8(+) T lymphocytes. A UNC13D c.118-308C>T mutation, causative of FHL3, disrupted binding of the ETS family member ELF1 to a conserved intronic sequence. This mutation impairs UNC13D intron 1 recruitment of STAT4 and the chromatin remodeling complex component BRG1, diminishing active histone modifications at the locus. The intronic sequence acted as an overall enhancer of Munc13-4 expression in cytotoxic lymphocytes in addition to representing an alternative promoter encoding a novel Munc13-4 isoform. Mechanistically, T cell receptor engagement facilitated STAT4-dependent Munc13-4 expression in naive CD8(+) T lymphocytes. Collectively, our data demonstrates how chromatin remodeling within an evolutionarily conserved regulatory element in intron 1 of UNC13D regulates the induction of Munc13-4 expression in cytotoxic lymphocytes and suggests that an alternative Munc13-4 isoform is required for lymphocyte cytotoxicity. Thus, mutations associated with primary immunodeficiencies may cause disease by disrupting transcription factor binding.

Adaptor protein Crk-like (CrkL) controls natural killer cell function via regulating the accumulation of activating receptors and phosphorylated Vav-1 molecules at immunological synapses (INM2P.433)

Abstract Very few studies have addressed how CrkL, a ubiquitous adaptor protein, regulates the immune response, especially in NK cells. Previous studies indicate that CrkL is required for NKG2D-mediated cellular cytotoxicity (NC) and CD16 signaling triggered antibody mediated cellular cytotoxicity (ADCC). However, how CrkL protein controls NK cell cytotoxicity remains unclear. Here we used lentiviral inducible shRNA to silence CrkL in human NK cell line and primary NK cells. Inducible knockdown of CrkL significantly reduced NK-target conjugation, degranulation, and cytotoxicity in both NC- and ADCC-mediated immune responses. Further investigation on the function and signaling transduction at the NK cytotoxic immunological synapse (IS) reveals that polarization of lytic granules, and accumulation of both F-actin and phosphorylated Vav-1 at the IS were greatly reduced in CrkL-silenced NK cells. NK cell activation involves in actin-dependent activating receptor clustering. CrkL silencing resulted in reduced accumulation of ligands for CD16 and NKG2D on the lipid bilayer. Similar results were obtained in NK cells from DiGeorge Syndrome patients (CrkL gene deletion). We thus propose a new model for adaptor protein CrkL function in NK cell activation: CrkL controls NK cell cytotoxicity via promoting F-actin accumulation and lytic granule polarization by modulating the accumulation of activating receptors and phosphorylated Vav-1 molecules at the IS.

NKp46 modulates NK immune synapse function (INC6P.346)

Abstract Natural killer cells play an important role in the first-line defense against tumor and virus-infected cells. The activity of NK cells is tightly regulated by a repertoire of cell-surface expressed inhibitory and activating receptors. NKp46 is a major NK cell activating receptor that is involved in the elimination of viral infected cells. NKp46 also regulates interactions with other immune cells including T cells and dendritic cells. Recent studies revealed that complex integration of NK receptor signaling controls the cytoskeleton rearrangement and other immune synapse related events. However the distinct nature by which NKp46 participates in NK immunological synapse formation and function remains unknown. In this study we found that NKp46 forms microcluster structures at the immune synapse between NK cells and target cells. Labeling of F-actin showed that higher expression of NKp46 is correlated with increased accumulation of actin mesh at the immune synapse. Concordantly, knock-down of NKp46 in primary NK cells abridged recruitment of F-actin to the synapse. Live cell imaging experiments showed a linear correlation between NKp46 expression and lytic granule polarization to the immune synapse. Taken together, our data suggests that NKp46 signaling directly effects both the early formation and late function of the NK lytic immune synapse. Moreover, this is a continuous rather than threshold effect of activation vs non-activation.

Lytic immune synapse function requires filamentous actin deconstruction by Coronin 1A.

Lytic immune effector function depends upon directed secretion of cytolytic granules at the immunological synapse (IS) and requires dynamic rearrangement of filamentous (F)-actin. Coronin 1A (Coro1A) is the hematopoietic-specific member of the Coronin family of actin regulators that promote F-actin disassembly. Here, we show that Coro1A is required for natural killer (NK) cell cytotoxic function in two human NK cell lines and ex vivo cells from a Coro1A-deficient patient. Using superresolution nanoscopy to probe the IS, we demonstrate that Coro1A promotes the deconstruction of F-actin density that facilitates effective delivery of lytic granules to the IS. Thus, we show, for the first time to our knowledge, a critical role for F-actin deconstruction in cytotoxic function and immunological secretion and identify Coro1A as its mediator.

The Perforin Pore Facilitates the Delivery of Cationic Cargos

Cytotoxic lymphocytes eliminate virally infected or neoplastic cells through the action of cytotoxic proteases (granzymes). The pore-forming protein perforin is essential for delivery of granzymes into the cytoplasm of target cells; however the mechanism of this delivery is incompletely understood. Perforin contains a membrane attack complex/perforin (MACPF) domain and oligomerizes to form an aqueous pore in the plasma membrane; therefore the simplest (and best supported) model suggests that granzymes passively diffuse through the perforin pore into the cytoplasm of the target cell. Here we demonstrate that perforin preferentially delivers cationic molecules while anionic and neutral cargoes are delivered inefficiently. Furthermore, another distantly related pore-forming MACPF protein, pleurotolysin (from the oyster mushroom), also favors the delivery of cationic molecules, and efficiently delivers human granzyme B. We propose that this facilitated diffusion is due to conserved features of oligomerized MACPF proteins, which may include an anionic lumen.

Human Immunodeficiency Syndromes Affecting Human Natural Killer Cell Cytolytic Activity

Natural killer (NK) cells are lymphocytes of the innate immune system that secrete cytokines upon activation and mediate the killing of tumor cells and virus-infected cells, especially those that escape the adaptive T cell response caused by the down regulation of MHC-I. The induction of cytotoxicity requires that NK cells contact target cells through adhesion receptors, and initiate activation signaling leading to increased adhesion and accumulation of F-actin at the NK cell cytotoxic synapse. Concurrently, lytic granules undergo minus-end directed movement and accumulate at the microtubule-organizing center through the interaction with microtubule motor proteins, followed by polarization of the lethal cargo toward the target cell. Ultimately, myosin-dependent movement of the lytic granules toward the NK cell plasma membrane through F-actin channels, along with soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent fusion, promotes the release of the lytic granule contents into the cleft between the NK cell and target cell resulting in target cell killing. Herein, we will discuss several disease-causing mutations in primary immunodeficiency syndromes and how they impact NK cell-mediated killing by disrupting distinct steps of this tightly regulated process.

T Lymphocytes Expressing a CD16 Signaling Receptor Exert Antibody-Dependent Cancer Cell Killing

To expand applications for T-cell-based immunotherapy in cancer, we designed a receptor that binds the Fc portion of human immunoglobulins and delivers activation signals. The construct included the high-affinity CD16 (FCGR3A) V158 variant, CD8α hinge, and transmembrane domains, along with signaling domains from CD3ζ and 4-1BB (TNFRSF9), forming a chimeric receptor termed CD16V-BB-ζ. After retrovirus-mediated expression in human T cells, CD16V-BB-ζ bound humanized antibodies with higher affinity than a control receptor containing the more common F158 variant. Engagement of CD16V-BB-ζ provoked T-cell activation, exocytosis of lytic granules, and sustained proliferation, with a mean cell recovery after 4-week coculture with Daudi lymphoma cells and rituximab of nearly 70-fold relative to input cells. In contrast, unbound antibody alone produced no effect. CD16V-BB-ζ T cells specifically killed lymphoma cells and primary chronic lymphocytic leukemia cells in combination with rituximab at a low effector:target ratio, even when assayed on mesenchymal cells. Trastuzumab triggered CD16V-BB-ζ-mediated killing of HER2 (ERBB2)(+) breast and gastric cancer cells; similar results were obtained with an anti-GD2 antibody in neuroblastoma and osteosarcoma cells. Furthermore, coadministration of CD16V-BB-ζ T cells with immunotherapeutic antibodies exerted considerable antitumor activity in vivo. Signaling mediated by 4-1BB-CD3ζ induced higher T-cell activation, proliferation, and cytotoxicity than CD3ζ or FcεRIγ, and the receptor was expressed effectively after mRNA electroporation without viral vectors, facilitating clinical translation. Our results offer preclinical proof of concept for CD16V-BB-ζ as a universal, next-generation chimeric receptor with the potential to augment the efficacy of antibody therapies for cancer.

Syntaxin11 serves as a t‐SNARE for the fusion of lytic granules in human cytotoxic T lymphocytes

CTLs kill target cells via fusion of lytic granules (LGs) at the immunological synapse (IS). Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) function as executors of exocytosis. The importance of SNAREs in CTL function is evident in the form of familial hemophagocytic lymphohistiocytosis type 4 that is caused by mutations in Syntaxin11 (Stx11), a Qa-SNARE protein. Here, we investigate the molecular mechanism of Stx11 function in primary human effector CTLs with high temporal and spatial resolution. Downregulation of endogenous Stx11 resulted in a complete inhibition of LG fusion that was paralleled by a reduction in LG dwell time at the IS. Dual color evanescent wave imaging suggested a sequential process, in which first Stx11 is transported to the IS through a subpopulation of recycling endosomes. The resulting Stx11 clusters at the IS then serve as a platform to mediate fusion of arriving LGs. We conclude that Stx11 functions as a t-SNARE for the final fusion of LG at the IS, explaining the severe phenotype of familial hemophagocytic lymphohistiocytosis type 4 on a molecular level.

Immune Cell Phenotype and Function After Treatment With Blinatumomab For Childhood Relapsed B-Cell Precursor Acute Lymphoblastic Leukemia (BCP-ALL)

BackgroundBlinatumomab is a bi-specific monoclonal antibody designed to engage and tether cytotoxic T-cells (CTL) to CD19-expressing target B cells. An ongoing phase I multicenter study in pediatric patients with relapsed/refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL) has shown that blinatumomab induces morphological and molecular remissions, defined as minimal residual disease (MRD) levels <10-4, in 47% of patients [Gore L, et al. J Clin Oncol 31, 2013 (suppl; abstr 10007)]. It is presently unknown whether and to what extent blinatumomab affects T-cell phenotype and function in pediatric patients with BCP-ALL. Patients and MethodsEight children diagnosed with relapsed/refractory BCP-ALL at the Bambino Gesù Children's Hospital in Rome (median age at diagnosis 5.8 years, range 0.5-14.6) received blinatumomab as continuous intravenous infusion for 28 consecutive days, followed by a 2-week drug-free period. Four out of 8 patients were given repeated treatment courses. Peripheral blood samples were collected before treatment (day 0) and weekly thereafter, for 4 consecutive weeks. Bone marrow (BM) aspirates were available on days 0 and +29 of each drug course. Peripheral blood mononuclear cells (PBMC) were labeled with appropriate combinations of fluorochrome-conjugated monoclonal antibodies to quantitate naïve/memory T cells, αβ/γδ-expressing T cells and other immune effectors with potential anti-leukemia activity, such as CD3+CD56+ natural killer (NK) T cells and CD3-CD56+ NK cells. T-cell production of interferon (IFN)-γ, interleukin (IL)-4 and IL-17 was measured at the single-cell level, after short-term (4-hour) stimulation with phorbol myristate acetate (PMA) and ionomycin. The TCR-Vβ Repertoire Kit® (Beckman Coulter, Milan, Italy) allowed the flow cytometry analysis of 24 different Vβ specificities on T cells, thus covering approximately 70% of the normal human TCR-Vβ repertoire. ResultsPeripheral blood lymphocytes reached their nadir on day +1 (median 300/µL of blood [inter-quartile range 40-380] compared with 1,080/µL of blood at baseline [inter-quartile range 360-2,310]; p=0.0037 by Mann-Whitney U test for paired data), expanded within 7 days up to 3.5-fold above baseline, and included both CD4+ and CD8+ T cells. By contrast, the frequency of both CD3+CD56+ NK T cells and CD3-CD56+ NK cells remained unchanged compared to baseline. IFN-γ production by patient-derived CD4+ T cells exceeded that observed in CD4+ T cells from healthy controls by 2-fold, indicating robust T helper type 1 (Th1) polarization. The frequency of Th2/Th17 cells, defined as CD4+IL-4+ and CD4+IL-17+ cells, respectively, was not different after treatment compared to baseline. CD31 expression on recovering CD45RA+ naïve T cells, a surrogate phenotypic feature for recent thymic emigrants (RTEs), suggested that thymic output may contribute to T-cell expansion after blinatumomab administration. Non-significant changes in the relative proportion of TCR-αβ and TCR-γδ-expressing CD3+ T cells were detected after treatment (median 79.5% TCR-αβ+ T cells and 19.3% TCR-γδ+ T cells among total CD3+ cells) compared with baseline (median 87.4% TCR-αβ+ T cells and 12.2% TCR-γδ+ T cells among total CD3+ cells). Importantly, both CD3+CD8bright T cells and NK cells expressed lytic granule proteins, such as perforin and granzyme-B, at levels that increased during treatment. The analysis of Vβ TCR repertoire revealed a restricted usage of single Vβ domains by BM-resident CD8+ T cells, but not by CD4+ T cells. Specifically, the sum of Vβ within CD8+ T cells in the BM averaged 56.7±6.2% after blinatumomab, compared with 78±5.1% in healthy controls (p=0.04; Mann-Whitney U test for unpaired data). ConclusionsBlinatumomab expands both CD31+CD45RA+ thymic-naïve and memory T cells with heightened IFN-γ production and is highly effective at clearing MRD in children with BCP-ALL. Skewing of the Vβ repertoire within BM-resident CD8+ T cells may be consistent with clonal expansions. Disclosures:Zugmaier:Amgen: Employment.

Stem Cell and T-Cell Gene Therapy Using SIN-Lentiviral Vector In Type 3 Familial Hemophagocytic Lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is the genetic form of hemophagocytic lymphohistiocytosis with an autosomal recessive form of inheritance and early onset. FHL is characterized by prolonged fever, hepatosplenomegaly and pancytopenia. Type 3 of FHL (FHL3) which accounts for 30-35 % of all FHL patients, results from mutations in UNC13D gene encoding Munc13-4 protein. Munc13-4 controls fusion of lytic granules with the plasma membrane in cytotoxic lymphocytes and its defect leads to impaired cytotoxic activity in T and NK lymphocytes. The only curative method for FHL3 is allogenic hematopoietic stem cell (HSC) transplantation. For those patients without compatible bone marrow donor, gene therapy could represent a therapeutic option.Our study is based on a comparative analysis to investigate the efficacy and safety of stem cell and T-cell gene therapy for FHL3. To this end we have generated SIN-lentiviral constructs expressing Munc13-4 and used them to produce either VSVG or T-cell specific pseudotyped lentiviral vectors. We also could obtain functionally mature T-cells in vitro, derived from umbilical cord blood HSCs which respond to TCR stimulation and show cytotoxic effect. Using these approaches, first we demonstrated that our SIN-lentiviral constructs are able to transduce efficiently human T-cells and HSCs. We used then these vectors to complement the FHL3 patient's cells. Transduction of FHL3 CD8 effector cells restored their cytotoxic function that was comparable to that of control cells. In addition we noted that the overexpression of Munc 13-4 in normal human HSCs didn't alter in vitro differentiation of these cells towards T-cells. The effect of this overexpression on B-cells and myeloid differentiation is currently under investigation.These preliminary results will be followed by ex vivo gene transfer experiments in Munc13-4 deficient “Jinx” mice to further investigate the functional restoration as well as toxic effects. This strategy, if approved, could offer a safe therapeutic method not only for FHL3 patients but also for other genetic or acquired dysfunctions of T-lymphocytes. Disclosures:No relevant conflicts of interest to declare.