Natural Killer Cell-mediated Immune Surveillance Research Articles

Tumoral NKG2D alters cell cycle of acute myeloid leukemic cells and reduces NK cell-mediated immune surveillance.

The stimulatory natural killer group 2 member D (NKG2D) lymphocyte receptor, initially discovered and expressed mostly on natural killer (NK) cells, T cells and natural killer T cells, can promote tumor immune surveillance. However, with increasing tumor grade, tumors themselves express NKG2D to self-stimulate oncogenic pathways. To confirm that cancer cells themselves express NKG2D, we have now investigated the role of the tumoral NKG2D in NK cell-mediated immune surveillance. Both anti-NKG2D and shRNA to that down-regulated tumoral NKG2D increased the number of cells in G1 phase and S phase, increased the expression of cyclin E-CDK2 and decreased P21. In addition, CD107a, IFN-γ and TNF-α increased when the cells were treated with anti-NKG2D which suggests that blocking tumoral NKG2D could augment tumor surveillance of NK cells. Altogether, tumoral NKG2D stimulates cell propagation and immune escape in acute myeloid leukemia cells.

NK cell-based cancer immunotherapy: from basic biology to clinical application.

Natural killer (NK) cells, which recognize and kill target cells independent of antigen specificity and major histocompatibility complex (MHC) matching, play pivotal roles in immune defence against tumors. However, tumor cells often acquire the ability to escape NK cell-mediated immune surveillance. Thus, understanding mechanisms underlying regulation of NK cell phenotype and function within the tumor environment is instrumental for designing new approaches to improve the current cell-based immunotherapy. In this review, we elaborate the main biological features and molecular mechanisms of NK cells that pertain to regulation of NK cell-mediated anti-tumor activity. We further overview current clinical approaches regarding NK cell-based cancer therapy, including cytokine infusion, adoptive transfer of autologous or allogeneic NK cells, applications of chimeric antigen receptor (CAR)-expressing NK cells and adoptive transfer of memory-like NK cells. With these promising clinical outcomes and fuller understanding the basic questions raised in this review, we foresee that NK cell-based approaches may hold great potential for future cancer immunotherapy.

Natural killer cell immune escape in acute myeloid leukemia

As central players of the innate immune system, natural killer (NK) cells can exert direct and indirect anti-tumor effects via their cytotoxic and immune regulatory capacities, pivotal in the induction of an effective adaptive anti-tumor immune response. Hence, NK cells are considered to be important in the immune surveillance of cancer. In acute myeloid leukemia (AML) patients, however, significantly impaired NK cell functions can facilitate escape from immune surveillance and affect patient outcome. Here, we review various NK cell defects and AML evasion mechanisms to escape from NK cell-mediated immune surveillance and we discuss NK cell-related parameters as prediction factors of AML patient outcome. On the basis of these observations, novel immunotherapeutic strategies capitalizing on the potentiation of NK cell functions have emerged in AML immunotherapy, as discussed in this review. Increased knowledge on AML escape routes from NK cell immune surveillance will further aid in the design of novel NK cell-based immunotherapy approaches for the treatment of AML.

Protein Kinase C-θ (PKC-θ) in Natural Killer Cell Function and Anti-Tumor Immunity

The protein kinase C-θ (PKCθ), which is essential for T cell function and survival, is also required for efficient anti-tumor immune surveillance. Natural killer (NK) cells, which express PKCθ, play a prominent role in this process, mainly by elimination of tumor cells with reduced or absent major histocompatibility complex class-I (MHC-I) expression. This justifies the increased interest of the use of activated NK cells in anti-tumor immunotherapy in the clinic. The in vivo development of MHC-I-deficient tumors is much favored in PKCθ−/− mice compared with wild-type mice. Recent data offer some clues on the mechanism that could explain the important role of PKCθ in NK cell-mediated anti-tumor immune surveillance: some studies show that PKCθ is implicated in signal transduction and anti-tumoral activity of NK cells elicited by interleukin (IL)-12 or IL-15, while others show that it is implicated in NK cell functional activation mediated by certain killer-activating receptors. Alternatively, the possibility that PKCθ is involved in NK cell degranulation is discussed, since recent data indicate that it is implicated in microtubule-organizing center polarization to the immune synapse in CD4+ T cells. The implication of PKC isoforms in degranulation has been more extensively studied in cytotoxic T lymphocyte, and these studies will be also summarized.

Reduced DNAM-1 expression on bone marrow NK cells associated with impaired killing of CD34+ blasts in myelodysplastic syndrome

Myelodysplastic syndromes (MDS) comprise a heterogeneous group of clonal stem-cell disorders characterized by ineffective hematopoiesis and risk of progression to acute myeloid leukemia. Increased apoptosis and suppressed functions of peripheral blood natural killer (NK) cells have been described in MDS patients, but only limited information is available on the phenotypic and functional integrity of NK cells in the bone marrow. In a cohort of 41 patients with distinct clinical subtypes of MDS, we here show that NK cells in the bone marrow show decreased surface expression of the activating receptors DNAM-1 and NKG2D. Notably, decreased receptor expression correlated with elevated bone marrow blast counts and was associated with impaired NK-cell responsiveness to stimulation with the K562 cell line, or co-activation by NKG2D or DNAM-1 in combination with the 2B4 receptor. Furthermore, antibody-masking experiments revealed a central role for DNAM-1 in NK cell-mediated killing of freshly isolated MDS blasts. Thus, given the emerging evidence for NK cell-mediated immune surveillance of neoplastic cells, we speculate that reduced expression of DNAM-1 on bone marrow NK cells may facilitate disease progression in patients with MDS.

Escape of monocyte-derived dendritic cells of HIV-1 infected individuals from natural killer cell-mediated lysis.

To verify whether the in vitro sensitivity of immature dendritic cells (iDC) to lysis by autologous natural killer (NK) cells from HIV-infected individuals might be correlated with HIV disease progression. Both dendritic cells (DC) and interlekin (IL)-2 activated NK cells were obtained from 13 HIV-infected individuals early after seroconversion and not receiving highly active antiretroviral therapy (HAART) and from 14 individuals with chronic HIV infection under HAART. The rate of NK cell-mediated killing of autologous iDC was correlated with classical parameters of HIV evolution. Peripheral blood monocytes obtained from the Ficoll-derived leukocyte fraction after adherence to plastic were stimulated with granulocyte-macrophage colony stimulating factor plus IL-4 to induce their differentiation into iDC to be used as target cells in a standard 4-h cytotoxicity assay. A fraction of autologous leukocytes was stimulated with IL-2 to induce activation of NK cells to be used as effector cells. During early HIV infection the extent of ex vivo lysis of monocyte-derived DC by activated autologous NK cells was inversely and directly correlated with the levels of viraemia and with the percentage of circulating CD4 T cells, respectively. In contrast, the capacity of NK cells to kill iDC was lost independently of the levels of plasma viraemia or the concurrence of HAART in chronically infected individuals. Addition of exogenous HIV Tat during the cytotoxicity assay inhibited NK cell-mediated lysis of DC. NK cell-mediated immune surveillance against infected DC may be effective only during early HIV infection and may not be restored by HAART.

Murine cytomegalovirus m02 gene family protects against natural killer cell-mediated immune surveillance.

The murine cytomegalovirus m02 gene family encodes putative type I membrane glycoproteins named m02 through m16. A subset of these genes were fused to an epitope tag and cloned into an expression vector. In transfected and murine cytomegalovirus-infected cells, m02, m04, m05, m06, m07, m09, m10, and m12 localized to cytoplasmic structures near the nucleus, whereas m08 and m13 localized to a filamentous structure surrounding the nucleus. Substitution mutants lacking the m02 gene (SMsubm02) or the entire m02 gene family (SMsubm02-16) grew like their wild-type parent in cultured cells. However, whereas SMsubm02 was as pathogenic as the wild-type virus, SMsubm02-16 was markedly less virulent. SMsubm02-16 produced less infectious virus in most organs compared to wild-type virus in BALB/c and C57BL/6J mice, but it replicated to wild-type levels in the organs of immunodeficient gamma(c)/Rag2 mice, lacking multiple cell types including natural killer cells, and in C57BL/6J mice depleted of natural killer cells. These results argue that one or more members of the m02 gene family antagonize natural killer cell-mediated immune surveillance.