The lymphocyte response to primary Moloney sarcoma virus tumors: definition of a non-specific component of the in vitro cellular hyporeactivity of tumor-bearing hosts

Differentiation and adaptation of natural killer cells for anti-malarial immunity

Natural killer cells employ a diverse arsenal of effector mechanisms to target intracellular pathogens. Differentiation of natural killer (NK) cell activation pathways occurs along a continuum from reliance on innate pro-inflammatory cytokines and stress-induced host ligands through to interaction with signals derived from acquired immune responses. Importantly, the degree of functional differentiation of the NK cell lineage influences the magnitude and specificity of interactions with host cells infected with viruses, bacteria, fungi, and parasites. Individual humans possess a vast diversity of distinct NK cell clones, each with the capacity to vary along this functional differentiation pathway, which - when combined - results in unique individual responses to different infections. Here we summarize these NK cell differentiation events, review evidence for direct interaction of malaria-infected host cells with NK cells and assess how innate inflammatory signals induced by malaria parasite-associated molecular patterns influence the indirect activation and function of NK cells. Finally, we discuss evidence that anti-malarial immunity develops in parallel with advancing NK differentiation, coincident with a loss of reliance on inflammatory signals, and a refined capacity of NK cells to target malaria parasites more precisely, particularly through antibody-dependent mechanisms.

Activated human primary NK cells efficiently kill colorectal cancer cells in 3D spheroid cultures irrespectively of the level of PD-L1 expression

Haploidentical Natural Killer (NK) cells have been shown as an effective and safe alternative for the treatment of haematological malignancies with poor prognosis for which traditional therapies are ineffective. In contrast to haematological cancer cells, that mainly grow as single suspension cells, solid carcinomas are characterised by a tridimensional (3D) architecture that provide specific surviving advantages and resistance against chemo- and radiotherapy. However, little is known about the impact of 3D growth on solid cancer immunotherapy especially adoptive NK cell transfer. We have recently developed a protocol to activate ex vivo human primary NK cells using B lymphoblastic cell lines, which generates NK cells able to overcome chemoresistance in haematological cancer cells. Here we have analysed the activity of these allogeneic NK cells against colorectal (CRC) human cell lines growing in 3D spheroid culture and correlated with the expression of some of the main ligands regulating NK cell activity. Our results indicate that activated NK cells efficiently kill colorectal tumour cell spheroids in both 2D and 3D cultures. Notably, although 3D CRC cell cultures favoured the expression of the inhibitory immune checkpoint PD-L1, it did not correlate with increased resistance to NK cells. Finally, we have analysed in detail the infiltration of NK cells in 3D spheroids by microscopy and found that at low NK cell density, cell death is not observed although NK cells are able to infiltrate into the spheroid. In contrast, higher densities promote tumoural cell death before infiltration can be detected. These findings show that highly dense activated human primary NK cells efficiently kill colorectal carcinoma cells growing in 3D cultures independently of PD-L1 expression and suggest that the use of allogeneic activated NK cells could be beneficial for the treatment of colorectal carcinoma.

Regulation of Murine Natural Killer Cell Development

Natural killer (NK) cells are effector lymphocytes of the innate immune system that are known for their ability to kill transformed and virus-infected cells. NK cells originate from hematopoietic stem cells in the bone marrow, and studies on mouse models have revealed that NK cell development is a complex, yet tightly regulated process, which is dependent on both intrinsic and extrinsic factors. The development of NK cells can be broadly categorized into two phases: lineage commitment and maturation. Efforts to better define the developmental framework of NK cells have led to the identification of several murine NK progenitor populations and mature NK cell subsets, each defined by a varied set of cell surface markers. Nevertheless, the relationship between some of these NK cell subsets remains to be determined. The classical approach to studying both NK cell development and function is to identify the transcription factors involved and elucidate the mechanistic action of each transcription factor. In this regard, recent studies have provided further insight into the mechanisms by which transcription factors, such as ID2, FOXO1, Kruppel-like factor 2, and GATA-binding protein 3 regulate various aspects of NK cell biology. It is also becoming evident that the biology of NK cells is not only transcriptionally regulated but also determined by epigenetic alterations and posttranscriptional regulation of gene expression by microRNAs. This review summarizes recent progress made in NK development, focusing primarily on transcriptional regulators and their mechanistic actions.

NKR-P1 biology: from prototype to missing self

Natural killer (NK) cells represent lymphocytes of the innate immune system capable of recognizing and destroying a broad array of target cells, including tumors, virus-infected cells, antibodycoated cells, foreign transplants, and "stressed" cells. NK cells eliminate their targets through two main effector mechanisms, cytokine secretion and cell-mediated cytotoxicity, which in turn depend on detection of target cells through a complex integration of stimulatory and inhibitory receptor-ligand interactions. The NKR-P1 molecules were the first family of NK cell receptors identified, yet they have remained enigmatic in their contribution to self-nonself discrimination until recently. Here, we outline a brief history of the NKR-P1 receptor family, then examine recent data providing insight into their genetic regulation, signaling function, cognate ligands, and gene organization and diversity.

Oral administration of butyrivibrio fibrisolvens, a butyrate-producing bacterium, decreases the formation of aberrant crypt foci in the colon and rectum of mice

Butyrivibrio fibrisolvens, a butyrate-producing ruminal bacterium, was evaluated for use as a probiotic to prevent colorectal cancer. Oral administration to Jcl:ICR mice of a new strain of B. fibrisolvens (MDT-1) that produces butyrate at a high rate (10(9) cfu/dose) increased the rate of butyrate production by fecal microbes, suggesting that MDT-1 can grow in the gut. The number of colorectal aberrant crypt foci (ACF), putative preneoplastic lesions induced by 1,2-dimethylhydrazine, was reduced after MDT-1 administration (10(9) cfu/dose, 3 times/wk for 4 wk). The number of aberrant crypts (ACs), number of foci having 3 or 4 ACs per focus, and the percentage of mice having 3 or 4 ACs per focus were also reduced, suggesting that the progress of lesions was suppressed by MDT-1. Interestingly, the MDT-1 cell homogenate did not have a similar beneficial effect. MDT-1 had low beta-glucuronidase activity, and administration of MDT-1 reduced the beta-glucuronidase activity in the colorectal contents. The numbers of natural killer (NK) and NKT cells in the spleen were markedly enhanced in response to MDT-1. Decreased beta-glucuronidase activity and increased numbers of NK and NKT cells and butyrate production may explain in part why MDT-1 administration suppressed ACF formation. These results suggest that colorectal cancer may be prevented or suppressed by the utilization of MDT-1 as a probiotic. Administration of MDT-1 had no harmful effect on the health of mice at least for 3 mo.

Evasion from NK cell immunity by MHC class I chain-related molecules expressing colon adenocarcinoma

Evasion of host immune responses is well documented for viruses and may also occur during tumor immunosurveillance. The mechanisms involve alterations in MHC class I expression, Ag processing and presentation, chemokine and cytokine production, and lymphocyte receptor expression. Epithelial tumors overexpress MHC class I chain-related (MIC) molecules, which are ligands for the activating receptor NKG2D on NK and T cells. We report that NK cells from patients with colorectal cancer lack expression of activating NKG2D and chemokine CXCR1 receptors, both of which are internalized. Serum levels of soluble MIC (sMIC) are elevated and are responsible for down-modulation of NKG2D and CXCR1. In contrast, high serum levels of CXC ligands, IL-8, and epithelial-neutrophil-activating peptide (ENA-78) do not down-modulate CXCR1. In vitro, internalization of NKG2D and CXCR1 occurs within 4 and 24 h, respectively, of incubating normal NK cells with sMIC-containing serum. Furthermore, natural cytotoxicity receptor NKp44 and chemokine receptor CCR7 are also down-modulated in IL-2-activated NK cells cocultured in MIC-containing serum-an effect secondary to the down-modulation of NKG2D and not directly caused by physical association with sMIC. The patients' NK cells up-regulate expression of NKG2D, NKp44, CXCR1, and CCR7 when cultured in normal serum or anti-MIC Ab-treated autologous serum. NKG2D(+) but not NKG2D(-) NK cells are tumoricidal in vitro, and in vivo they selectively traffic to the xenografted carcinoma, form immunological synapse with tumor cells, and significantly retard tumor growth in the SCID mice. These results suggest that circulating sMIC in the cancer patients deactivates NK immunity by down-modulating important activating and chemokine receptors.

Relationship of cell-mediated cytotoxicity against melanoma cells to prognosis in melanoma patients

The cell-mediated cytotoxicity (CMC) of blood mononuclear cells against cultured human melanoma cells was measured in patients after surgical removal of localized melanoma, at a time when they were considered on clinical grounds to be free of melanoma. It was found that the distribution of CMC values against melanoma cells in melanoma patients was different from that in control subjects, and several sub-populations of melanoma patients were evident on the basis of these measurements. No difference in distribution of CMC values was found against non-melanoma cells, which suggested the changes were specific for melanoma. The proportion of patients with recurrence of melanoma was compared between the patient groups with low, normal or high CMC values against cultured melanoma cells after surgery. Analysis for periods extending to 2 years showed that patients with low CMC values after surgery had a significantly higher incidence of recurrence from melanoma than patients with normal or high CMC values. These results suggest there may be a sub-group of melanoma patients who have intrinsically low CMC against melanoma cells, and that this may be an important predisposing factor in the development of recurrent melanoma.

Antibody-dependent cell-mediated cytotoxicity in the Moloney sarcoma virus system: differential activity of IgG and IgM with different subpopulations of lymphocytes

Antibody-dependent cell-mediated cytotoxicity in the Moloney sarcoma virus (MSV) system was evaluated in terms of the differential ability of IgG and IgM from MSV regressor animals to induce cytotoxicity by lymphocytes from lymph node, spleen, and thymus. The cell-mediated cytotoxicity induced by both IgM and IgG was specific for target possessing the appropriate virally determined cell surface antigen(s). IgM induced cytotoxicity by lymphocytes from all the organs tested. However, differences in magnitude and efficiency were revealed. Lymph node cells and thymocytes were most efficient against IgM-coated target cells. Against IgG-sensitized target cells, spleen and lymph node cells were about equally active, but thymocytes were inactive. Cortisone treatment of the donors of effector cells revealed that the cortisone resistant subpopulation of thymocytes, 2 days after cortisone injection, exhibited an increased cytotoxicity against target cells treated with unfractionated antiserum and its IgM fraction. This subpopulation of thymocytes was also cytotoxic against IgG-coated target cells. At 12 days after cortisone injection, the repopulated thymus showed little change in activity, compared to control thymus, against antibody-coated target cells.