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. Although HIV-1 infection induced functional impairment of NK cells, antiretroviral therapy reinvigorated NK cells in response to HIV-1 rebound after analytic treatment interruption. Moreover, a broadly neutralizing antibody, PGT121, enhanced NK cell function in vivo, consistent with antibody-dependent cellular cytotoxicity. Monoclonal antibody depletion of NK cells resulted in higher viral loads in multiple nonlymphoid organs. Overall, our results in humanized MISTRG-6-15 mice demonstrated that NK cells provided direct anti-HIV-1 responses in vivo but were limited in their responses in lymphoid organs

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

SummaryPrimary 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. This suppression targeted naive CD4+ but not CD8+ T cells and was mediated through transient suppressor of cytokine signaling-3 (SOCS3) inhibition of the STAT5b transcription factor signaling pathway. These events resulted in complete paralysis of primary CD4+ T cell activation, affecting memory generation and induction of autoimmunity as well as impaired viral clearance. These data highlight the critical regulation of naive CD4+ T cells during inflammatory conditions

Using a Chemical Genetics Approach to Characterize the Auxin Signaling Pathway in Arabidopsis thaliana

Auxins are plant hormones involved in cell elongation, phototropism, and root development. Chemical genetics combines combinatorial synthetic chemistry, high-throughput screening, and genetic analysis to understand signaling pathways by identifying small molecules that inhibit its output. Previous work identified two small molecules, furylacrylic acid and Compound C, that attenuate auxin responses. I have determined the effect derivatives of these molecules have on auxin-induced reporter gene expression, seed germination, root elongation, and activity of the SCFTIR1-Aux/IAA auxin receptor. Collectively, these data establish the specificity and the minimal components of the biologically active molecules. Future experiments will focus on confirming putative cellular targets of these molecules

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. Interactions between NK cells and dendritic cells, T cells, and B cells also dramatically alter the overall immune response to cancer. To exploit the diverse functional abilities of NK cell subsets for cancer immunotherapies, it is important to understand NK cell biology and NK regulator mechanisms

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. Interactions between NK cells and dendritic cells, T cells, and B cells also dramatically alter the overall immune response to cancer. To exploit the diverse functional abilities of NK cell subsets for cancer immunotherapies, it is important to understand NK cell biology and NK regulator mechanisms

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. Combination immunotherapy also was accompanied by lesser toxicities than was IL-2 therapy alone. Additionally, we observed a dual competition between NK cells and activated CD8 T cells such that, after immunotherapy, the depletion of either effector population resulted in the increased total expansion of the other population and compensatory antitumor effects. This study demonstrates the efficacy of this combination immunotherapeutic regimen as a promising cancer therapy and illustrates the existence of potent competitive regulatory pathways between NK cells and CD8 T cells in response to systemic activation

Differential Expression of the Ly49GB6, but Not the Ly49GBALB, 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. We now extend these studies to evaluate expression of the two Ly49G receptor isoforms Ly49G(B6) and Ly49G(BALB), using mice with different MHC-I haplotypes that express one or both of the isoforms. NK cells from CB6F1 (H-2(bxd)) hybrid mice express two different alleles for Ly49G receptor, Ly49G(B6) and Ly49G(BALB). We found that CB6F1 mice had more Ly49G(B6+) NK cells than Ly49(BALB+) NK cells, and that only Ly49G(B6+) NK cells increased in relative numbers and in Ly49G mean fluorescence intensity values after HSCT similar to the B6 parental strain. We further observed that Ly49G(+) NK cells in BALB/c (H-2(d)) and BALB.B (H-2(b)) mice, which have the same background genes, recover slowly after HSCT, in contrast to Ly49G(+) NK cells in B6 (H-2(b)) recipients. The difference in expression of Ly49G(B6) relative to Ly49G(BALB) was linked to differences in the activity of the Pro1 promoter between the two alleles. Thus, we conclude that the Ly49G(B6) receptor dominates Ly49G expression on NK cells after HSCT in strains in which that allele is expressed. The data suggest that Ly49 allelic polymorphism within a particular Ly49 family member can differentially affect NK cell recovery after HSCT depending on the background genes of the recipient, not on the MHC-I haplotype

Increased Antitumor Effects Using IL-2 with Anti–TGF-β Reveals Competition between Mouse NK and CD8 T Cells

Due to increasing interest in the removal of immunosuppressive pathways in cancer, the combination of IL2 with antibodies to neutralize TGFβ, a potent immunosuppressive cytokine, was assessed. Combination immunotherapy resulted in significantly greater anti-tumor effects. These were correlated with significant increases in the numbers and functionality of NK cells, NK progenitors and activated CD8 T cells resulting in the observed anti-tumor effects. Combination immunotherapy was also accompanied with lesser toxicities than IL2 therapy alone. Additionally, we observed a dual competition between NK and activated CD8 T cells such that after immunotherapy, the depletion of either effector population resulted in the increased total expansion of the other population and compensatory anti-tumor effects. This study demonstrates the efficacy of this combination immunotherapeutic regimen as a promising cancer therapy and illustrates the existence of potent competitive regulatory pathways between NK and CD8 T cells in response to systemic activation