Human NK cells confer protection against HIV-1 infection in humanized mice.

The role of NK cells against HIV-1 infections remains to be elucidated in vivo. While humanized mouse models potentially could be used to directly evaluate human NK cell responses during HIV-1 infection, improved functional development of human NK cells in these hosts is needed. Here, we report the humanized MISTRG-6-15 mouse model, in which NK cells were quick to expand and exhibit degranulation, cytotoxicity, and proinflammatory cytokine production in nonlymphoid organs upon HIV-1 infection but had reduced functionality in lymphoid organs.

Sustained Remission in Rheumatoid Arthritis: Time to Withdraw Treatment?

With increasing numbers of patients with rheumatoid arthritis achieving sustained remission, medication withdrawal is an important consideration to reduce polypharmacy and associated adverse events. An article from the journal Arthritis & Rheumatology (1) explores the treatment withdrawal options for patients on etanercept and methotrexate combination therapies and suggests methotrexate withdrawal has the least impact on disease worsening. There are limitations in the study, including the use of only one disease activity score and no assessment of radiographic progression, but, overall, the article provides a good framework for future studies on treatment withdrawal options and the possibility of medication reduction for patients.

Licensing delineates helper and effector NK cell subsets during viral infection.

Natural killer (NK) cells can be divided into phenotypic subsets based on expression of receptors that bind self-MHC-I molecules, a concept termed licensing or education. Here we show NK cell subsets with different migratory, effector, and immunoregulatory functions in dendritic cell and antigen (ag)-specific CD8+ T cell responses during influenza and murine cytomegalovirus infections. Shortly after infection, unlicensed NK cells localized in draining lymph nodes and produced GM-CSF, which correlated with the expansion and activation of dendritic cells, and resulted in greater and sustained ag-specific T cell responses.

Out-of-Sequence Signal 3 Paralyzes Primary CD4(+) T-Cell-Dependent Immunity.

Primary T cell activation involves the integration of three distinct signals delivered in sequence: (1) antigen recognition, (2) costimulation, and (3) cytokine-mediated differentiation and expansion. Strong immunostimulatory events such as immunotherapy or infection induce profound cytokine release causing "bystander" T cell activation, thereby increasing the potential for autoreactivity and need for control. We show that during strong stimulation, a profound suppression of primary CD4(+) T-cell-mediated immune responses ensued and was observed across preclinical models and patients undergoing high-dose interleukin-2 (IL-2) therapy.

Increased antitumor effects using IL-2 with anti-TGF-β reveals competition between mouse NK and CD8 T cells.

Because of increasing interest in the removal of immunosuppressive pathways in cancer, the combination of IL-2 with Abs to neutralize TGF-β, a potent immunosuppressive cytokine, was assessed. Combination immunotherapy resulted in significantly greater antitumor effects. These were correlated with significant increases in the numbers and functionality of NK cells, NK cell progenitors, and activated CD8 T cells, resulting in the observed antitumor effects.

Positive and negative regulation by NK cells in cancer.

Our understanding of NK biology has expanded immensely since the initial discovery of natural killer cells in 1975. New studies have uncovered various levels of immune regulation both on and by unique subsets of NK cells, which go well beyond simple receptor-ligand interactions between NK cells and target cancer cells. Distinct suppressor and effector populations of NK cells have been delineated in both viral and tumor models.

Utilization of mouse models to decipher natural killer cell biology and potential clinical applications.

Natural killer (NK) cells represent a key component of innate immunity. The utility of mouse models to recapitulate the human immune response has been a matter of ongoing debate, especially with regard to NK cells. However, mouse models of NK cells have provided significant advancements in our understanding of the biology of the cells that bridge these species.

Differential expression of the Ly49G(B6), but not the Ly49G(BALB), receptor isoform during natural killer cell reconstitution after hematopoietic stem cell transplantation.

Inhibitory natural killer (NK) cell receptors specific for major histocompatibility complex class I (MHC-I) molecules include Ly49 receptors in mice and killer immunoglobulin-like receptors (KIR) in humans. The "licensing" or "arming" models imply that engagement of these receptors to self MHC-I molecules during NK cell development educates NK cells to be more responsive to cancer and viral infection. We recently reported that hematopoietic stem cell transplantation (HSCT) induced rapid and preferential expansion of functionally competent Ly49G(+), but not other Ly49 family, NK cells independent of NK cell licensing via Ly49-MHC-I interactions.

Murine NK-cell licensing is reflective of donor MHC-I following allogeneic hematopoietic stem cell transplantation in murine cytomegalovirus responses.

Natural killer (NK) cells express inhibitory receptors with varied binding affinities to specific major histocompatibility complex class I (MHC-I) haplotypes. NK cells can be classified as licensed or unlicensed based on their ability or inability to bind MHC-I, respectively. The role of donor vs host MHC on their development after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is not known.

Contrasting effects of anti-Ly49A due to MHC class I cis binding on NK cell-mediated allogeneic bone marrow cell resistance.

NK subsets have activating and inhibitory receptors that bind MHC-I. Ly49A is a mouse inhibitory receptor that binds with high affinity to H2(d) in both a cis- and trans-manner. Ly49A cis-associations limit trans-interactions with H2(d)-expressing targets as well as mAb binding.

Murine natural killer cell licensing and regulation by T regulatory cells in viral responses.

Natural killer (NK) cells show differential functionality based on their capability of binding to self-MHC consistent with licensing. Here we show in vivo confirmation of the physiologic effects of licensing with differential effects of NK subsets on anti-murine cytomegalovirus (anti-MCMV) responses after syngeneic hematopoietic stem cell transplantation (HSCT) or regulatory T-cell (Treg) depletion. After HSCT, depletion of licensed NK cells led to far greater viral loads in target organs early after infection compared with nondepleted and unlicensed depleted mice.