Ebba Sohlberg

Critical Role of CD2 Co-stimulation in Adaptive Natural Killer Cell Responses Revealed in NKG2C- Deficient Humans

Summary Infection by human cytomegalovirus (HCMV) leads to NKG2C-driven expansion of adaptive natural killer (NK) cells, contributing to host defense. However, approximately 4% of all humans carry a homozygous deletion of the gene that encodes NKG2C (NKG2C−/−). Assessment of NK cell repertoires in 60 NKG2C−/− donors revealed a broad range of NK cell populations displaying characteristic footprints of adaptive NK cells, including a terminally differentiated phenotype, functional reprogramming, and epigenetic remodeling of the interferon (IFN)-γ promoter. We found that both NKG2C− and NKG2C+ adaptive NK cells expressed high levels of CD2, which synergistically enhanced ERK and S6RP phosphorylation following CD16 ligation. Notably, CD2 co-stimulation was critical for the ability of adaptive NK cells to respond to antibody-coated target cells. These results reveal an unexpected redundancy in the human NK cell response to HCMV and suggest that CD2 provides “signal 2” in antibody-driven adaptive NK cell responses.

Epstein-Barr Virus Coinfection in Children Boosts Cytomegalovirus-Induced Differentiation of Natural Killer Cells

ABSTRACT During childhood, infections with cytomegalovirus (CMV) and Epstein-Barr virus (EBV) can occur in close temporal proximity. Active, as well as latent, CMV infection is associated with enlarged subsets of differentiated natural killer (NK) and cytotoxic T cells. How EBV infection may influence CMV-driven immune differentiation is not known. We found that EBV coinfection selectively influenced the NK cell compartment of CMV-seropositive (CMV+) children. Coinfected children had significantly higher proportions of peripheral-blood NKG2C+ NK cells than CMV+ EBV− children. Ex vivo NK cell degranulation after target cell stimulation and plasma IL-15 levels were significantly higher in CMV+ children. EBV coinfection was related to the highest levels of plasma interleukin-15 (IL-15) and IL-12p70. Remarkably, in vitro EBV infection of peripheral blood mononuclear cells (PBMC) from EBV− CMV+ children increased NKG2C+ NK cell proportions. A similar tendency was seen in cocultures of PBMC with EBV+ lymphoblastoid B-cell lines (LCL) and IL-15. After K562 challenge, NKG2C+ NK cells excelled in regard to degranulation and production of gamma interferon, regardless of whether there was previous coculture with LCL. Taken together, our data suggest that dual latency with these herpesviruses during childhood could contribute to an in vivo environment supporting differentiation and maintenance of distinct NK cell populations. This viral imprint may affect subsequent immune responses through altered distributions of effector cells.

Herpesvirus Seropositivity in Childhood Associates with Decreased Monocyte-Induced NK Cell IFN-γ Production

EBV infection is inversely associated with IgE sensitization in children, and this association is further enhanced by CMV coinfection. In mice, herpesvirus latency causes systemic innate activation and protection from bacterial coinfection, implying the importance of herpesviruses in skewing immune responses during latent infection. Early control of viral infections depends on IFN-γ release by NK cells, which generally requires the presence of accessory cells. We investigated IFN-γ production by NK cells in PBMCs from children seropositive (SP) for EBV alone, for both EBV and CMV, or seronegative for both viruses. The ability of classical (CD14++CD16−) and proinflammatory (CD14+CD16+) monocytes to induce autologous NK cell IFN-γ was studied by coculture experiments with enriched CD3−CD56+ cells. Transwell experiments were used to evaluate how monocytes interact with NK cells to induce IFN-γ synthesis. SP children had a significantly reduced proportion of IFN-γ+ NK cells and cognate intracellular IFN-γ levels, which was more pronounced in CMV-coinfected subjects. Also, resting PBMCs of SP children displayed lower proportions of proinflammatory monocytes. IFN-γ production by NK cells was dependent on interactions with monocytes, with the proinflammatory subset inducing the highest IFN-γ. Finally, SP children had markedly lower levels of plasma IFN-γ, concurrent with in vitro findings. Herpesvirus infections could be one contributing factor for maturation toward balanced Th1-Th2 responses. Our data indicate that early infection by herpesviruses may affect NK cell and monocyte interactions and thereby also influence the development of allergies.

Natural killer cell-mediated immunosurveillance of human cancer.

The contribution of natural killer (NK) cells to immunosurveillance of human cancer remains debatable. Here, we discuss advances in several areas of human NK cell research, many of which support the ability of NK cells to prevent cancer development and avoid relapse following adoptive immunotherapy. We describe the molecular basis for NK cell recognition of human tumor cells and provide evidence for NK cell-mediated killing of human primary tumor cells ex vivo. Subsequently, we highlight studies demonstrating the ability of NK cells to migrate to, and reside in, the human tumor microenvironment where selection of tumor escape variants from NK cells can occur. Indirect evidence for NK cell immunosurveillance against human malignancies is provided by the reduced incidence of cancer in individuals with high levels of NK cell cytotoxicity, and the significant clinical responses observed following infusion of human NK cells into cancer patients. Finally, we describe studies showing enhanced tumor progression, or increased cancer incidence, in patients with inherited and acquired defects in cellular cytotoxicity. All these observations have in common that they, either indirectly or directly, suggest a role for NK cells in mediating immunosurveillance against human cancer. This opens up for exciting possibilities with respect to further exploring NK cells in settings of adoptive immunotherapy in human cancer.

Cord blood monocyte subsets are similar to adult and show potent peptidoglycan-stimulated cytokine responses

Human monocytes can be divided into two major subpopulations, CD14++ CD16− and CD14+ CD16+ cells, which are suggested to play different roles in antimicrobial responses. In neonates, characteristics and functional responses of monocyte subsets have not previously been explored, and might contribute to the qualitative difference between neonatal and adult cytokine profiles. We report that at baseline, monocyte subsets in cord blood and adult peripheral blood are present in similar frequencies, and show similar expression of CD11c, CD80/CD86, CD163 and HLA‐DR. In response to the bacterial ligand peptidoglycan, cord blood monocytes had high inherent capacity for production of the early‐response cytokines with levels of tumour necrosis factor and interleukin‐12p70 exceeding adult levels, and also a higher phosphorylation of p38‐mitogen‐activated protein kinase. The CD14+ CD16+ cells expressed more interleukin‐12p70 than CD14++ CD16− cells and were present in a higher frequency in peptidoglycan‐stimulated cord blood mononuclear cell cultures. Together, the behaviour of cord blood CD14+ CD16+ cells following peptidoglycan stimulation might indicate a qualitative difference between the neonatal antimicrobial response and that of the adult. In addition we found that serum factors in cord blood and adult sera affected cytokine production similarly, with the exception of tumour necrosis factor, regardless of the source of serum or cells. Overall, our data provide new insights into monocyte heterogeneity in cord blood and monocyte subset responses to a bacterial ligand at birth.

Cytomegalovirus-Seropositive Children Show Inhibition of In Vitro EBV Infection That Is Associated with CD8+CD57+ T Cell Enrichment and IFN-γ

EBV, a human herpesvirus, is commonly acquired during childhood and persists latently in B cells. EBV seropositivity has been connected to immunomodulatory effects such as altered T and NK cell functional responses as well as protection against early IgE sensitization; however, owing to the asymptomatic presentation during childhood little is known regarding the infection process in children of different ages. In this study, we used mononuclear cells from cord blood and from 2- and 5-y-old EBV-naive children for in vitro EBV infection. We show that the degree of EBV-induced B cell activation and expansion differs between age groups and in particular in relationship to IFN-γ production capacity. EBV infection induced redistribution between B cell subsets with enrichment of IgD+CD27+ cells (commonly referred to as non–switched memory) in infected cord blood cell cultures, and of IgD−CD27+ cells (switched memory) in cell cultures from older children. We also related results to serostatus to CMV, a persistent herpesvirus that can affect differentiation status of T and NK cells. As compared with CMV− children, the EBV-induced enrichment of IgD−CD27+ B cells was significantly reduced in infected cell cultures from CMV+ children. This effect was associated with high levels of IFN-γ and frequencies of highly mature CD8+CD57+ T cells in CMV+ children. Our results demonstrate that both a child’s age and serostatus to CMV will have an impact on EBV-induced B cell activation and expansion, and they point to the ability of viruses with immunomodulatory functions, such as CMV, to affect immune responses within the host system.

Women with pre-eclampsia have an altered NKG2A and NKG2C receptor expression on peripheral blood natural killer cells.

Problem  Preeclampsia, a pregnancy disorder, is associated with exaggerated inflammation and increased serum monokines. Uterine natural killer (NK) cells are implicated in preeclampsia pathology, but little is known regarding peripheral NK cells in the disease.

Microchip-Based Single-Cell Imaging Reveals That CD56dimCD57−KIR−NKG2A+ NK Cells Have More Dynamic Migration Associated with Increased Target Cell Conjugation and Probability of Killing Compared to CD56dimCD57−KIR−NKG2A− NK Cells

NK cells are functionally educated by self-MHC specific receptors, including the inhibitory killer cell Ig-like receptors (KIRs) and the lectin-like CD94/NKG2A heterodimer. Little is known about how NK cell education influences qualitative aspects of cytotoxicity such as migration behavior and efficacy of activation and killing at the single-cell level. In this study, we have compared the behavior of FACS-sorted CD56dimCD57−KIR−NKG2A+ (NKG2A+) and CD56dimCD57−KIR−NKG2A− (lacking inhibitory receptors; IR−) human NK cells by quantifying migration, cytotoxicity, and contact dynamics using microchip-based live cell imaging. NKG2A+ NK cells displayed a more dynamic migration behavior and made more contacts with target cells than IR− NK cells. NKG2A+ NK cells also more frequently killed the target cells once a conjugate had been formed. NK cells with serial killing capacity were primarily found among NKG2A+ NK cells. Conjugates involving IR− NK cells were generally more short-lived and IR− NK cells did not become activated to the same extent as NKG2A+ NK cells when in contact with target cells, as evident by their reduced spreading response. In contrast, NKG2A+ and IR− NK cells showed similar dynamics in terms of duration of conjugation periods and NK cell spreading response in conjugates that led to killing. Taken together, these observations suggest that the high killing capacity of NKG2A+ NK cells is linked to processes regulating events in the recognition phase of NK–target cell contact rather than events after cytotoxicity has been triggered.

Imprint of 5-azacytidine on the natural killer cell repertoire during systemic treatment for high-risk myelodysplastic syndrome.

5-azacytidine (5-aza) is a hypomethylating agent approved for the treatment of high-risk myelodysplastic syndrome (MDS). It is assumed to act by demethylating tumor suppressor genes and via direct cytotoxic effects on malignant cells. In vitro treatment with hypomethylating agents has profound effects on the expression of killer-cell immunoglobulin-like (KIR) receptors on natural killer (NK) cells, as these receptors are epigenetically regulated via methylation of the promoters. Here we investigated the influence of 5-aza on the NK-cell repertoire during cytokine-induced proliferation in vitro and homeostatic proliferation in vivo in patients with high-risk MDS. In vitro treatment of NK cells from both healthy donors and MDS patients with low doses of 5-aza led to a significant increase in expression of multiple KIRs, but only in cells that had undergone several rounds of cell division. Proliferating 5-aza exposed NK cells exhibited increased IFN-γ production and degranulation towards tumor target cells. MDS patients had lower proportions of educated KIR-expressing NK cells than healthy controls but after systemic treatment with 5-aza, an increased proportion of Ki-67+ NK cells expressed multiple KIRs suggesting uptake of 5-aza in cycling cells in vivo. Hence, these results suggest that systemic treatment with 5-aza may shape the NK cell repertoire, in particular during homeostatic proliferation, thereby boosting NK cell-mediated recognition of malignant cells.

Complete Remission with Reduction of High-Risk Clones following Haploidentical NK-Cell Therapy against MDS and AML

Purpose: To evaluate the safety, efficacy, and immunobiological correlates of allogeneic NK-cell–based therapy in primary chemotherapy-refractory or relapsed high-risk myelodysplastic syndrome (MDS), secondary AML (MDS/AML), and de novo AML patients. Experimental Design: Sixteen patients received fludarabine/cyclophosphamide conditioning combined with total lymphoid irradiation followed by adoptive immunotherapy with IL2–activated haploidentical NK cells. Results: NK-cell infusions were well-tolerated, with only transient adverse events observed in the 16 patients. Six patients achieved objective responses with complete remission (CR), marrow CR, or partial remission (PR). Five patients proceeded to allogeneic hematopoietic stem cell transplantation (HSCT). Three patients are still free from disease >3 years after treatment. All evaluable patients with objective responses (5/5 evaluable) had detectable donor NK cells at days 7/14 following infusion and displayed reduction of tumor cell clones, some of which carried poor prognosis mutations. Residual lin−CD34+CD123+CD45RA+ blast cells in responders had increased total HLA class I and HLA-E expression. Responding patients displayed less pronounced activation of CD8+ T cells and lower levels of inflammatory cytokines following NK-cell infusion. Intriguingly, despite omission of systemic IL2, all patients displayed increased frequencies of activated Ki-67+CD127−FoxP3+CD25hiCD4+ Treg cells of recipient origin following NK-cell therapy. Conclusions: Overall, this study suggests that high-risk MDS is responsive to NK-cell therapy and supports the use of haploidentical NK-cell infusions as a bridge to HSCT in refractory patients. Objective clinical responses and reduction of high-risk clones were associated with detectable donor-derived NK cells, immunoediting of residual blast cells, and less pronounced host immune activation. Clin Cancer Res; 24(8); 1834–44. ©2018 AACR.