Dynamics of natural killer cell homeostasis : implications for cell-based cancer Immunotherapy

Natural killer (NK) cells comprise a central role within the innate immune system, eliminating virally infected, foreign and transformed cells through their natural cytotoxic capacity. Release of their cytotoxic granules is tightly controlled through the balance of a large repertoire of inhibitory and activating receptors, and it is the unique combination of these receptors on individual cells that confers them their immense diversity both in phenotype and functionality. This thesis aimed to investigate the mechanisms sustaining NK cell homeostasis with the aim of translating these findings into more efficient NK cell-based immunotherapies against cancer. In paper I, we set out to define a transcriptional timeline for NK cell differentiation through the use of single-cell RNA sequencing of unique differentiation subsets ranging from CD56bright to adaptive NKG2C+CD56dim NK cells. Transcriptional differentiation was concentrated within the surprisingly diverse CD56bright subset which gradually transitioned into CD56dim NK cells before terminal differentiation into adaptive CD56dim NK cells. The vastly diverse yet unique NK cell repertoire within an individual is surprisingly stable over time considering the constant renewal of these cells at steady state. In paper II, we performed an in-depth analysis of homeostatic proliferation in human NK cells. We identified a high degree of intra-lineage plasticity combined with transcriptional reprogramming associated with the acquired phenotype as the underlying mechanisms maintaining repertoire stability at steady state. In paper III, we examined the role of NK cells in a setting of perturbed homeostasis, namely patients with high-risk myelodysplastic syndrome undergoing immunomodulatory treatment with 5-azacytidine. We identified a role for 5-azacytidine in modifying the global NK cell repertoire, as uptake of the drug by proliferating NK cells resulted in increased expression of killer cell immunoglobulin-like receptors (KIR) and improved functionality. In paper IV we identified a dose-dependent cytokine addiction in IL-15 expanded NK cells, leading to the induction of apoptosis upon cytokine withdrawal. A proliferation-dependent induction of the short splice variant of BIM, combined with an altered BCL-2/BIM ratio resulted in sensitization to cell death post withdrawal. This thesis provides new insights into the dynamic nature of NK cell homeostasis, from understanding NK cell differentiation at the transcriptional level to perturbations after cytokine stimulation and immunomodulatory therapies

Remodeling of secretory lysosomes during education tunes functional potential in NK cells

Inhibitory signaling during natural killer (NK) cell education translates into increased responsiveness to activation;however, the intracellular mechanism for functional tuning by inhibitory receptors remains unclear. Secretory lysosomes are part of the acidic lysosomal compartment that mediates intracellular signalling in several cell types. Here we show that educated NK cells expressing self-MHC specific inhibitory killer cell immunoglobulin-like receptors (KIR) accumulate granzyme B in dense-core secretory lysosomes that converge close to the centrosome. This discrete morphological phenotype is independent of transcriptional programs that regulate effector function, metabolism and lysosomal biogenesis. Meanwhile, interference of signaling from acidic Ca2+ stores in primary NK cells reduces target-specific Ca2+-flux, degranulation and cytokine production. Furthermore, inhibition of PI (3,5) P-2 synthesis, or genetic silencing of the PI(3,5) P-2-regulated lysosomal Ca2+-channel TRPML1, leads to increased granzyme B and enhanced functional potential, thereby mimicking the educated state. These results indicate an intrinsic role for lysosomal remodeling in NK cell education

You have got a fast car:Chimeric antigen receptor nk cells in cancer therapy

The clinical success stories of chimeric antigen receptor (CAR)-T cell therapy against B-cell malignancies have contributed to immunotherapy being at the forefront of cancer therapy today. Their success has fueled interest in improving CAR constructs, identifying additional antigens to target, and clinically evaluating them across a wide range of malignancies. However, along with the exciting potential of CAR-T therapy comes the real possibility of serious side effects. While the FDA has approved commercialized CAR-T cell therapy, challenges associated with manufacturing, costs, and related toxicities have resulted in increased attention being paid to implementing CAR technology in innate cytotoxic natural killer (NK) cells. Here, we review the current landscape of the CAR-NK field, from successful clinical implementation to outstanding challenges which remain to be addressed to deliver the full potential of this therapy to more patients

Pan-cancer profiling of tumor-infiltrating natural killer cells through transcriptional reference mapping

<p>We generated a comprehensive reference atlas of human NK cells, based on single-cell RNA sequencing profiles from 72,129 cells obtained from bulk (12 donors) and sorted phenotypically-defined NK cell subsets (2 donors) and tissue-resident NK cells (TrNK, 136 donors). 38,862 tumor-infiltrating NK cells (TiNK) were extracted from datasets comprising seven solid tumor types (427 patients) and incorporated into our reference map using transfer learning. Both the NK data as well as the data form tumors/tissues with all the other cell types can be found here.</p&gt

Pan-cancer profiling of tumor-infiltrating natural killer cells through transcriptional reference mapping

<p>We generated a comprehensive reference atlas of human NK cells, based on single-cell RNA sequencing profiles from 72,129 cells obtained from bulk (12 donors) and sorted phenotypically-defined NK cell subsets (2 donors) and tissue-resident NK cells (TrNK, 136 donors). 38,862 tumor-infiltrating NK cells (TiNK) were extracted from datasets comprising seven solid tumor types (427 patients) and incorporated into our reference map using transfer learning. Both the NK data as well as the data form tumors/tissues with all the other cell types can be found here.</p&gt

Deciphering natural killer cell homeostasis

Natural killer (NK) cells have a central role within the innate immune system, eliminating virally infected, foreign and transformed cells through their natural cytotoxic capacity. Release of their cytotoxic granules is tightly controlled through the balance of a large repertoire of inhibitory and activating receptors, and it is the unique combination of these receptors expressed by individual cells that confers immense diversity both in phenotype and functionality. The diverse, yet unique, NK cell repertoire within an individual is surprisingly stable over time considering the constant renewal of these cells at steady state. Here we give an overview of NK cell differentiation and discuss metabolic requirements, intra-lineage plasticity and transcriptional reprogramming during IL-15-driven homeostatic proliferation. New insights into the regulation of NK cell differentiation and homeostasis could pave the way for the successful implementation of NK cell-based immunotherapy against cancer

Intra-lineage plasticity and functional reprogramming maintain natural killer cell repertoire diversity

Natural killer (NK) cell repertoires are made up of phenotypically distinct subsets with different functional properties. The molecular programs involved in maintaining NK cell repertoire diversity under homeostatic conditions remain elusive. Here, we show that subset-specific NK cell proliferation kinetics correlate with mTOR activation, and global repertoire diversity is maintained through a high degree of intra-lineage subset plasticity during interleukin (IL)-15-driven homeostatic proliferation in vitro. Slowly cycling sorted KIR+CD56dim NK cells with an induced CD57 phenotype display increased functional potential associated with increased transcription of genes involved in adhesion and immune synapse formation. Rapidly cycling cells upregulate NKG2A, display a general loss of functionality, and a transcriptional signature associated with increased apoptosis/cellular stress, actin-remodeling, and nuclear factor κB (NF-κB) activation. These results shed light on the role of intra-lineage plasticity during NK cell homeostasis and suggest that the functional fate of the cell is tightly linked to the acquired phenotype and transcriptional reprogramming

Human anaplastic thyroid carcinoma cells are sensitive to NK cell-mediated lysis via ULBP2/5/6 and chemoattract NK cells

PURPOSE: Anaplastic thyroid carcinoma (ATC) is one of the most aggressive forms of cancer with no curative therapies available. To date, strategies to target ATC by immunotherapy have not been evaluated. We investigated whether ATC would be a suitable target for natural killer (NK) cell-based immunotherapy.EXPERIMENTAL DESIGN: We first established seven new cell lines from ATC tumors, three from papillary thyroid carcinoma tumors and analyzed them together with eight additional ATC cell lines. Cells were analyzed for sensitivity to lysis by NK cells and their ability to chemoattract and regulate the activity of NK cells. In addition, fresh tumor samples and peripheral blood from six patients with ATC were analyzed for NK cell infiltration and phenotype.RESULTS: We observed that ATC cell lines are sensitive to lysis by ex vivo expanded NK cells and that the lysis was abrogated upon blockade of NKG2D. Sensitivity of thyroid cancer cell lines to NK cell-mediated lysis correlated with surface expression of UL16-binding protein 2 on tumor cells. Moreover, ATC cell lines produced high levels of CXCL10 and stimulated migration of expanded NK cells and ATC tumors were enriched for NK cells expressing the cognate chemokine receptor CXCR3. However, compared with NK cells in peripheral blood, ATC tumor-derived NK cells displayed a suppressed phenotype with a downregulated expression of NKG2D. In vitro, suppression of NK cell-mediated lysis and NKG2D expression by ATC cells was restored upon neutralization of prostaglandin-E2.CONCLUSIONS: ATC cell lines are sensitive to NK cell-mediated lysis via ULBP2/5/6 and chemoattract CXCR3-positive NK cells. Patients with ATC may benefit from NK cell-based immunotherapy

Perturbed NK Cell Homeostasis Associated with Disease Severity in Chronic Neutropenia

Abstract Neutrophils have been thought to play a critical role in terminal differentiation of NK cells. Whether this effect is direct or a consequence of global immune changes with effects on NK-cell homeostasis remains unknown. In this study, we used high-resolution flow and mass cytometry to examine NK-cell repertoires in 64 patients with neutropenia and 27 healthy age- and sex-matched donors. A subgroup of patients with chronic neutropenia showed severely disrupted NK-cell homeostasis manifesting as increased frequencies of CD56bright NK cells and a lack of mature CD56dim NK cells. These immature NK-cell repertoires were characterized by expression of the proliferation/exhaustion markers Ki-67, Tim-3, and TIGIT and displayed blunted tumor target cell responses. Systems-level immune mapping revealed that the changes in immunophenotypes were confined to NK cells, leaving T-cell differentiation intact. RNA sequencing of NK cells from these patients showed upregulation of a network of genes, including TNFSF9, CENPF, MKI67, and TOP2A, associated with apoptosis and the cell cycle, but different from the conventional CD56bright signatures. Profiling of 249 plasma proteins showed a coordinated enrichment of pathways related to apoptosis and cell turnover, which correlated with immature NK-cell repertoires. Notably, most of these patients exhibited severe-grade neutropenia, suggesting that the profoundly altered NK-cell homeostasis was connected to the severity of their underlying etiology. Hence, although our data suggest that neutrophils are dispensable for NK-cell development and differentiation, some patients displayed a specific gap in the NK repertoire, associated with poor cytotoxic function and more severe disease manifestations