Nicholas M. Valiante

Human Diversity in Killer Cell Inhibitory Receptor Genes

The presence and expression of killer inhibitory receptor (KIR) and CD94:NKG2 genes from 68 donors were analyzed using molecular typing techniques. The genes encoding CD94:NKG2 receptors were present in each person, but KIR gene possession varied. Most individuals expressed inhibitory KIR for the three well-defined HLA-B and -C ligands, but noninhibitory KIR genes were more variable. Twenty different KIR phenotypes were defined. Two groups of KIR haplotypes were distinguished and occurred at relatively even frequency. Group A KIR haplotypes consist of six genes: the main inhibitory KIR, one noninhibitory KIR, and a structurally divergent KIR. Allelic polymorphism within five KIR genes was detected. Group B comprises more noninhibitory KIR genes and contains at least one additional gene not represented in group A. The KIR locus therefore appears to be polygenic and polymorphic within the human population.

Functionally and structurally distinct NK cell receptor repertoires in the peripheral blood of two human donors.

The expression of KIR and CD94:NKG2 receptors was determined for more than 100 natural killer (NK) cell clones obtained from two blood donors who differ in their HLA class I and KIR genes. More than 98% of the clones were inhibited by individual autologous class I allotypes, and every clone was inhibited by the combination of autologous allotypes. The patterns of inhibition correlate with expression of inhibitory receptors of defined specificity. One donor possesses three class I ligands for KIR, and a majority of NK cells use KIR as their inhibitory receptor; the second donor possesses only a single ligand for KIR, and a majority of NK cells use the more broadly reactive CD94:NKG2a as their inhibitory receptor. Because of these differences, the first donor has subpopulations of NK cells that kill cells of the second donor, whereas the NK cells of the second donor are universally tolerant of cells from the first donor.

Contact-dependent Stimulation and Inhibition of Dendritic Cells by Natural Killer Cells

Natural killer (NK) cells and dendritic cells (DCs) are two distinct cell types of innate immunity. It is known that the in vitro interaction of human NK cells with autologous DCs results in DC lysis. Here we show that contact-dependent interactions between activated human NK cells and immature DCs (iDCs) provides a “control switch” for the immune system. At low NK/DC ratios, this interaction dramatically amplifies DC responses, whereas at high ratios it completely turns off their responses. Specifically, culture of activated human NK cells with iDCs, at low NK/DC ratios (1:5), led to exponential increases in DC cytokine production, which were completely dependent on cell-to-cell contact. DC maturation was also driven by cognate interactions with NK cells and maturation was dependent on endogenously produced TNF-α in the culture. At slightly higher NK/DC ratios (5:1), inhibition of DC functions was the dominant feature due to potent killing by the autologous NK cells. Resting NK cells also stimulated autologous DC maturation in a TNF-α/contact-dependent manner, however, increasing the NK/DC ratio only led to an enhancement of this effect.

Inhibition of Natural Killer Cells through Engagement of CD81 by the Major Hepatitis C Virus Envelope Protein

The immune response against hepatitis C virus (HCV) is rarely effective at clearing the virus, resulting in ∼170 million chronic HCV infections worldwide. Here we report that ligation of an HCV receptor (CD81) inhibits natural killer (NK) cells. Cross-linking of CD81 by the major envelope protein of HCV (HCV-E2) or anti-CD81 antibodies blocks NK cell activation, cytokine production, cytotoxic granule release, and proliferation. This inhibitory effect was observed using both activated and resting NK cells. Conversely, on NK-like T cell clones, including those expressing NK cell inhibitory receptors, CD81 ligation delivered a costimulatory signal. Engagement of CD81 on NK cells blocks tyrosine phosphorylation through a mechanism which is distinct from the negative signaling pathways associated with NK cell inhibitory receptors for major histocompatibility complex class I. These results implicate HCV-E2–mediated inhibition of NK cells as an efficient HCV evasion strategy targeting the early antiviral activities of NK cells and allowing the virus to establish itself as a chronic infection.

New adjuvants for human vaccines.

Despite their obvious benefits, decades of research and hundreds of pre-clinical candidates, only a handful of adjuvants are approved for prophylactic vaccination of humans. The slow pace of development is due to a number of knowledge gaps, the most important of which is the complexity involved in designing adjuvants that are both potent and well tolerated. Recent advances in our understanding of innate immunity have led to the identification of immune pathways and adjuvant formulations more suitable for clinical advancement. One area of particular interest is the discovery of agonists that target the toll-like receptors. This review highlights recent progress of clinically approved vaccine adjuvants and identifies potential novel adjuvants that can broaden the development of new vaccines against infectious diseases.

Nonviral delivery of self-amplifying RNA vaccines

Despite more than two decades of research and development on nucleic acid vaccines, there is still no commercial product for human use. Taking advantage of the recent innovations in systemic delivery of short interfering RNA (siRNA) using lipid nanoparticles (LNPs), we developed a self-amplifying RNA vaccine. Here we show that nonviral delivery of a 9-kb self-amplifying RNA encapsulated within an LNP substantially increased immunogenicity compared with delivery of unformulated RNA. This unique vaccine technology was found to elicit broad, potent, and protective immune responses, that were comparable to a viral delivery technology, but without the inherent limitations of viral vectors. Given the many positive attributes of nucleic acid vaccines, our results suggest that a comprehensive evaluation of nonviral technologies to deliver self-amplifying RNA vaccines is warranted.

mTOR inhibition improves immune function in the elderly

mTOR inhibition by RAD001 improves immune responses in elderly volunteers receiving an influenza vaccination. mTOR and Human Aging Inhibition of mTOR signaling extends life span and delays the onset of aging-related diseases in all species studied to date. These findings suggest that the mTOR pathway regulates aging. However, it is unknown if mTOR inhibition has beneficial effects on aging in humans. To begin to address this question, Mannick et al. evaluated the effects of the mTOR inhibitor RAD001 on the decline in immune function that occurs during aging in humans. Their findings suggest that RAD001 improved immune function in elderly volunteers as assessed by response to influenza vaccination. It remains to be determined whether mTOR inhibition improves additional aging-related conditions in humans. Inhibition of the mammalian target of rapamycin (mTOR) pathway extends life span in all species studied to date, and in mice delays the onset of age-related diseases and comorbidities. However, it is unknown if mTOR inhibition affects aging or its consequences in humans. To begin to assess the effects of mTOR inhibition on human aging-related conditions, we evaluated whether the mTOR inhibitor RAD001 ameliorated immunosenescence (the decline in immune function during aging) in elderly volunteers, as assessed by their response to influenza vaccination. RAD001 enhanced the response to the influenza vaccine by about 20% at doses that were relatively well tolerated. RAD001 also reduced the percentage of CD4 and CD8 T lymphocytes expressing the programmed death-1 (PD-1) receptor, which inhibits T cell signaling and is more highly expressed with age. These results raise the possibility that mTOR inhibition may have beneficial effects on immunosenescence in the elderly.

Dynamics of intra‐hepatic lymphocytes in chronic hepatitis C: enrichment for Vα24+ T cells and rapid elimination of effector cells by apoptosis

Chronic viral hepatitis is characterized by a dramatic lymphocyte infiltrate in the liver. Although it is one of the most common chronic inflammatory diseases in humans, little information is available on the functional state of these intra‐hepatic lymphocytes (IHL). To address this issue, we have optimized cytofluorimetric techniques to assess directly ex vivo the functions, dynamics and repertoires of IHL isolated from biopsies of patients with chronic hepatitis C. We estimate that 1 % of the total body lymphocytes infiltrate the inflamed liver and find that, at variance with peripheral blood lymphocytes (PBL) isolated from the same patients, most IHL display an activated phenotype and produce Th1 type lymphokines when stimulated in vitro. Virtually all IHL are found in the G0/G1 state of the cell cycle, while a sizeable percentage of them is undergoing programmed cell death in vivo, as detected by the TUNEL assay performed on freshly isolated cells. In contrast again to PBL from the same patients, IHL show a preferential compartmentalization of NK and TCRγ / δ+ cells, and a remarkable (up to 20‐fold) enrichment for Vα24+ T cells. Together our data suggest that in a liver injured by chronic hepatitis C, most IHL are pro‐inflammatory activated cells which are highly enriched for effectors of innate resistance. These IHL do not undergoclonal expansion in the liver but rather display effector function and die in situ at a high rate, suggesting that maintenance of the IHL pool is dependent on continuous migration from extra‐hepatic sites.

NKp46 and NKG2D Recognition of Infected Dendritic Cells Is Necessary for NK Cell Activation in the Human Response to Influenza Infection

At an early phase of viral infection, contact and cooperation between dendritic cells (DCs) and NK cells activates innate immunity, and also influences recruitment, when needed, of adaptive immunity. Influenza, an adaptable fast-evolving virus, annually causes acute, widespread infections that challenge the innate and adaptive immunity of humanity. In this study, we dissect and define the molecular mechanisms by which influenza-infected, human DCs activate resting, autologous NK cells. Three events in NK cell activation showed different requirements for soluble mediators made by infected DCs and for signals arising from contact with infected DCs. IFN-α was mainly responsible for enhanced NK cytolysis and also important for CD69 up-regulation, whereas IL-12 was necessary for enhancing IFN-γ production. Increased CD69 expression and IFN-γ production, but not increased cytolysis, required recognition of influenza-infected DCs by two NK cell receptors: NKG2D and NKp46. Abs specific for these receptors or their known ligands (UL16-binding proteins 1–3 class I-like molecules for NKG2D and influenza hemagglutinin for NKp46) inhibited CD69 expression and IFN-γ production. Activation of NK cells by influenza-infected DCs and polyinosinic:polycytidylic acid (poly(I:C))-treated DCs was distinguished. Poly(I:C)-treated DCs did not express the UL16-binding protein 3 ligand for NKG2D, and in the absence of the influenza hemagglutinin there was no involvement of NKp46.

The repertoire of killer cell Ig-like receptor and CD94:NKG2A receptors in T cells: clones sharing identical alpha beta TCR rearrangement express highly diverse killer cell Ig-like receptor patterns.

Killer cell Ig-like receptor (KIR) and CD94:NKG2A molecules were first defined as human NK cell receptors (NKR), but now are known to be expressed and to function on subpopulations of T cells. Here the repertoires of KIR and CD94:NKG2A expression by T cells from two donors were examined and compared with their previously defined NK cell repertoires. T cell clones generated from peripheral blood of both donors expressed multiple NKR in different combinations and used the range of receptors expressed by NK cells. In both donors αβ T cells less frequently expressed the inhibitory receptors CD94:NKG2A and KIR2DL1 than either γδ T cells or NK cells. In contrast to NK cells, not all NKR+ T cells expressed an inhibitory receptor for autologous HLA class I. This lack of specific inhibitory NKR was especially apparent on αβ T cells of one donor. Overall, αβ T cells exhibited a distinct pattern of NKR expression different from that of γδ T and NK cells, which expressed highly similar NKR repertoires. In one donor, analysis of TCR rearrangement revealed a dominant subset of NKR+ T cells sharing identical TCR α- and β-chains. Remarkably, among 55 T cell clones sharing the same TCRαβ rearrangement 18 different KIR phenotypes were seen, suggesting that KIR expression was initiated subsequently to TCR rearrangement.