Bioengineered small extracellular vesicles deliver multiple SARS-CoV-2 antigenic fragments and drive a broad immunological response.

The COVID-19 pandemic highlighted the clear risk that zoonotic viruses pose to global health and economies. The scientific community responded by developing several efficacious vaccines which were expedited by the global need for vaccines. The emergence of SARS-CoV-2 breakthrough infections highlights the need for additional vaccine modalities to provide stronger, long-lived protective immunity. Here we report the design and preclinical testing of small extracellular vesicles (sEVs) as a multi-subunit vaccine. Cell lines were engineered to produce sEVs containing either the SARS-CoV-2 Spike receptor-binding domain, or an antigenic region from SARS-CoV-2 Nucleocapsid, or both in combination, and we tested their ability to evoke immune responses in vitro and in vivo. B cells incubated with bioengineered sEVs were potent activators of antigen-specific T cell clones. Mice immunised with sEVs containing both sRBD and Nucleocapsid antigens generated sRBD-specific IgGs, nucleocapsid-specific IgGs, which neutralised SARS-CoV-2 infection. sEV-based vaccines allow multiple antigens to be delivered simultaneously resulting in potent, broad immunity, and provide a quick, cheap, and reliable method to test vaccine candidates.

Polymorphic KIR3DL3 expression modulates tissue-resident and innate-like T cells.

Most human killer cell immunoglobulin-like receptors (KIR) are expressed by natural killer (NK) cells and recognize HLA class I molecules as ligands. KIR3DL3 is a conserved but polymorphic inhibitory KIR recognizing a B7 family ligand, HHLA2, and is implicated for immune checkpoint targeting. The expression profile and biological function of KIR3DL3 have been somewhat elusive, so we searched extensively for KIR3DL3 transcripts, revealing highly enriched expression in γδ and CD8+ T cells rather than NK cells. These KIR3DL3-expressing cells are rare in the blood and thymus but more common in the lungs and digestive tract. High-resolution flow cytometry and single-cell transcriptomics showed that peripheral blood KIR3DL3+ T cells have an activated transitional memory phenotype and are hypofunctional. The T cell receptor (TCR) usage is biased toward genes from early rearranged TCR-α variable segments or Vδ1 chains. In addition, we show that TCR-mediated stimulation can be inhibited through KIR3DL3 ligation. Whereas we detected no impact of KIR3DL3 polymorphism on ligand binding, variants in the proximal promoter and at residue 86 can reduce expression. Together, we demonstrate that KIR3DL3 is up-regulated alongside unconventional T cell stimulation and that individuals may vary in their ability to express KIR3DL3. These results have implications for the personalized targeting of KIR3DL3/HHLA2 checkpoint inhibition.

Comparison of NK alloreactivity prediction models based on KIR-MHC interactions in haematopoietic stem cell transplantation.

The biological processes underlying NK cell alloreactivity in haematopoietic stem cell transplantation (HSCT) remain unclear. Many different models to predict NK alloreactivity through KIR and MHC genotyping exist, raising ambiguities in its utility and application for clinicians. We assessed 27 predictive models, broadly divided into six categories of alloreactivity prediction: ligand-ligand, receptor-ligand, educational, KIR haplotype-based, KIR matching and KIR allelic polymorphism. The models were applied to 78 NGS-typed donor/recipient pairs undergoing allogeneic HSCT in genoidentical (n=43) or haploidentical (n=35) matchings. Correlations between different predictive models differed widely, suggesting that the choice of the model in predicting NK alloreactivity matters. For example, two broadly used models, educational and receptor-ligand, led to opposing predictions especially in the genoidentical cohort. Correlations also depended on the matching fashion, suggesting that this parameter should also be taken into account in the choice of the scoring strategy. The number of centromeric B-motifs was the only model strongly correlated with the incidence of acute graft-versus-host disease in our set of patients in both the genoidentical and the haploidentical cohorts, suggesting that KIR-based alloreactivity, not MHC mismatches, are responsible for it. To our best knowledge, this paper is the first to experimentally compare NK alloreactivity prediction models within a cohort of genoidentical and haploidentical donor-recipient pairs. This study helps to resolve current discrepancies in KIR-based alloreactivity predictions and highlights the need for deeper consideration of the models used in clinical studies as well as in medical practice.

KIR in Allogeneic Hematopoietic Stem Cell Transplantation: Need for a Unified Paradigm for Donor Selection.

Allogeneic hematopoietic stem cell transplantation (aHSCT) is a lifesaving therapy for hematological malignancies. For years, a fully matched HLA donor was a requisite for the procedure. However, new immunosuppressive strategies have enabled the recruitment of viable alternative donors, particularly haploidentical donors. Over 95% of patients have at least two potential haploidentical donors available to them. To identify the best haploidentical donor, the assessment of new immunogenetic criteria could help. To this end, the clinical benefit of KIR genotyping in aHSCT has been widely studied but remains contentious. This review aims to evaluate the importance of KIR-driven NK cell alloreactivity in the context of aHSCT and explain potential reasons for the discrepancies in the literature. Here, through a non-systematic review, we highlight how the studies in this field and their respective predictive models or scoring strategies could be conceptually opposed, explaining why the role of NK cells remains unclear in aHCST outcomes. We evaluate the limitations of each published prediction model and describe how every scoring strategy to date only partly delivers the requirements for optimally effective NK cells in aHSCT. Finally, we propose approaches toward finding the optimal use of KIR genotyping in aHSCT for a unified criterion for donor selection.

KIR copy number variations in dengue-infected patients from northeastern Thailand.

Killer immunoglobulin-like receptors (KIRs) are a family of receptors expressed on Natural killer (NK) cells. The extensive polymorphism of KIR is involved in the immune responses of NK cells and influences dengue infections. We investigated the diversity of KIR copy numbers in dengue-infected patients from northeastern Thailand. Copy numbers of KIRs were determined by quantitative polymerase chain reaction in 137 dengue-infected patients, comprising 63 dengue fever (DF) and 74 dengue hemorrhagic fever (DHF). The distribution of KIRs was observed to be between 0 and 4 copies. The KIR AA genotype with heterozygous KIR2DS4D/WT was the most common in dengue patients, 25.4% DF and 23% DHF. Forty KIR profiles were determined in dengue patients, including 31 usual, 6 expanded, and 3 contracted profiles. Investigation of KIR copy number and dengue severity indicated that two copies of KIR2DL3 combined with HLA-C1C1 associated with an increased risk of DHF (OR 2.32, 95% CI 1.159-4.624, P = 0.016), whereas one copy of KIR2DL2 and KIR2DL3 together with HLA-C1C1 associated with a reduced risk of DHF (OR 0.17, 95% CI 0.058-0.482, P < 0.001). The outcomes of this study will contribute to the understanding of KIR complexity and innate immune responses in dengue infections.

Sialic acid-binding immunoglobulin-like lectin (Sigelac)-15 is a rapidly internalised cell-surface antigen expressed by acute myeloid leukaemia cells.

Sialic acid-binding immunoglobulin-like lectin (Siglec)-15 has recently been identified as a critical tumour checkpoint, augmenting the expression and function of programmed death-ligand 1. We raised a monoclonal antibody, A9E8, specific for Siglec-15 using phage display. A9E8 stained myeloid leukaemia cell lines and peripheral cluster of differentiation (CD)33+ blasts and CD34+ leukaemia stem cells from patients with acute myeloid leukaemia (AML). By contrast, there was minimal expression on healthy donor leucocytes or CD34+ stem cells from non-AML donors, suggesting targeting Siglec-15 may have significant therapeutic advantages over its fellow Siglec CD33. After binding, A9E8 was rapidly internalised (half-life of 180 s) into K562 cells. Antibodies to Siglec-15 therefore hold therapeutic potential for AML treatment.

Diversity of KIR genes and their HLA-C ligands in Ugandan populations with historically varied malaria transmission intensity.

BACKGROUND: Malaria is one of the most serious infectious diseases in the world. The malaria burden is greatly affected by human immunity, and immune responses vary between populations. Genetic diversity in KIR and HLA-C genes, which are important in immunity to infectious diseases, is likely to play a role in this heterogeneity. Several studies have shown that KIR and HLA-C genes influence the immune response to viral infections, but few studies have examined the role of KIR and HLA-C in malaria infection, and these have used low-resolution genotyping. The aim of this study was to determine whether genetic variation in KIR and their HLA-C ligands differ in Ugandan populations with historically varied malaria transmission intensity using more comprehensive genotyping approaches. METHODS: High throughput multiplex quantitative real-time PCR method was used to genotype KIR genetic variants and copy number variation and a high-throughput real-time PCR method was developed to genotype HLA-C1 and C2 allotypes for 1344 participants, aged 6 months to 10 years, enrolled from Ugandan populations with historically high (Tororo District), medium (Jinja District) and low (Kanungu District) malaria transmission intensity. RESULTS: The prevalence of KIR3DS1, KIR2DL5, KIR2DS5, and KIR2DS1 genes was significantly lower in populations from Kanungu compared to Tororo (7.6 vs 13.2%: p = 0.006, 57.2 vs 66.4%: p = 0.005, 33.2 vs 46.6%: p < 0.001, and 19.7 vs 26.7%: p = 0.014, respectively) or Jinja (7.6 vs 18.1%: p < 0.001, 57.2 vs 63.8%: p = 0.048, 33.2 vs 43.5%: p = 0.002, and 19.7 vs 30.4%: p < 0.001, respectively). The prevalence of homozygous HLA-C2 was significantly higher in populations from Kanungu (31.6%) compared to Jinja (21.4%), p = 0.043, with no significant difference between Kanungu and Tororo (26.7%), p = 0.296. CONCLUSIONS: The KIR3DS1, KIR2DL5, KIR2DS5 and KIR2DS1 genes may partly explain differences in transmission intensity of malaria since these genes have been positively selected for in places with historically high malaria transmission intensity. The high-throughput, multiplex, real-time HLA-C genotyping PCR method developed will be useful in disease-association studies involving large cohorts.

Investigation of CD26, a potential SARS-CoV-2 receptor, as a biomarker of age and pathology.

OBJECTIVE: In some individuals, coronavirus severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection leads to a variety of serious inflammatory symptoms, including blood clotting and acute respiratory distress. Death due to COVID-19 shows a steep rise in relation to age. Comorbidities such as type 2 diabetes mellitus (T2DM), hypertension, and cardiovascular disease also increase susceptibility. It has been reported that T-cell regulatory dipeptidyl peptidase 4 (DPP4; cluster of differentiation 26 (CD26)) binds to the external spike (S) glycoprotein of SARS-CoV-2 as a receptor, for the viral entry into the host cell. CD26 is expressed on many cells, including T and natural killer (NK) cells of the immune system, as a membrane-anchored form. A soluble form (sCD26) is also found in the blood plasma and cerebrospinal fluid (CSF). Approach and results: To investigate a possible relationship between sCD26 levels, age and pathology, serum samples were collected from control, T2DM and age-related dementia (ARD) subjects. A significant reduction in serum sCD26 levels was seen in relation to age. ARD and T2DM were also associated with lower levels of sCD26. The analysis of blood smears revealed different cellular morphologies: in controls, CD26 was expressed around the neutrophil membrane, whereas in T2DM, excessive sCD26 was found around the mononucleated cells (MNCs). ARD subjects had abnormal fragmented platelets and haemolysis due to low levels of sCD26. CONCLUSIONS: These findings may help to explain the heterogeneity of SARS-CoV-2 infection. High serum sCD26 levels could protect from viral infection by competively inhibiting the virus binding to cellular CD26, whereas low sCD26 levels could increase the risk of infection. If so measuring serum sCD26 level may help to identify individuals at high risk for the COVID-19 infection.

LILRB3 (ILT5) is a myeloid cell checkpoint that elicits profound immunomodulation.

Despite advances in identifying the key immunoregulatory roles of many of the human leukocyte immunoglobulin-like receptor (LILR) family members, the function of the inhibitory molecule LILRB3 (ILT5, CD85a, LIR3) remains unclear. Studies indicate a predominant myeloid expression; however, high homology within the LILR family and a relative paucity of reagents have hindered progress toward identifying the function of this receptor. To investigate its function and potential immunomodulatory capacity, a panel of LILRB3-specific monoclonal antibodies (mAbs) was generated. LILRB3-specific mAbs bound to discrete epitopes in Ig-like domain 2 or 4. LILRB3 ligation on primary human monocytes by an agonistic mAb resulted in phenotypic and functional changes, leading to potent inhibition of immune responses in vitro, including significant reduction in T cell proliferation. Importantly, agonizing LILRB3 in humanized mice induced tolerance and permitted efficient engraftment of allogeneic cells. Our findings reveal powerful immunosuppressive functions of LILRB3 and identify it as an important myeloid checkpoint receptor.

Variations in killer-cell immunoglobulin-like receptor and human leukocyte antigen genes and immunity to malaria.

Malaria is one of the deadliest infectious diseases in the world. Immune responses to Plasmodium falciparum malaria vary among individuals and between populations. Human genetic variation in immune system genes is likely to play a role in this heterogeneity. Natural killer (NK) cells produce inflammatory cytokines in response to malaria infection, kill intraerythrocytic Plasmodium falciparum parasites by cytolysis, and participate in the initiation and development of adaptive immune responses to plasmodial infection. These functions are modulated by interactions between killer-cell immunoglobulin-like receptors (KIRs) and human leukocyte antigens (HLAs). Therefore, variations in KIR and HLA genes can have a direct impact on NK cell functions. Understanding the role of KIRs and HLAs in immunity to malaria can help to better characterize antimalarial immune responses. In this review, we summarize the different KIRs and HLAs associated with immunity to malaria thus far.

KIR Variation in Iranians Combines High Haplotype and Allotype Diversity With an Abundance of Functional Inhibitory Receptors.

Natural killer (NK) cells are innate lymphocytes that eliminate infected and transformed cells. They discriminate healthy from diseased tissue through killer cell Ig-like receptor (KIR) recognition of HLA class I ligands. Directly impacting NK cell function, KIR polymorphism associates with infection control and multiple autoimmune and pregnancy syndromes. Here we analyze KIR diversity of 241 individuals from five groups of Iranians. These five populations represent Baloch, Kurd, and Lur, together comprising 15% of the ethnically diverse Iranian population. We identified 159 KIR alleles, including 11 not previously characterized. We also identified 170 centromeric and 94 telomeric haplotypes, and 15 different KIR haplotypes carrying either a deletion or duplication encompassing one or more complete KIR genes. As expected, comparing our data with those representing major worldwide populations revealed the greatest similarity between Iranians and Europeans. Despite this similarity we observed higher frequencies of KIR3DL1*001 in Iran than any other population, and the highest frequency of HLA-B*51, a Bw4-containing allotype that acts as a strong educator of KIR3DL1*001+ NK cells. Compared to Europeans, the Iranians we studied also have a reduced frequency of 3DL1*004, which encodes an allotype that is not expressed at the NK cell surface. Concurrent with the resulting high frequency of strong viable interactions between inhibitory KIR and polymorphic HLA class I, the majority of KIR-A haplotypes characterized do not express a functional activating receptor. By contrast, the most frequent KIR-B haplotype in Iran expresses only one functional inhibitory KIR and the maximum number of activating KIR. This first complete, high-resolution, characterization of the KIR locus of Iranians will form a valuable reference for future clinical and population studies.

Genetics of antigen processing and presentation.

Immune response to disease requires coordinated expression of an army of molecules. The highly polymorphic MHC class I and class II molecules are key to control of specificity of antigen presentation. Processing of the antigen, to peptides or other moieties, requires other sets of molecules. For classical class I, this includes TAP peptide transporters, proteasome components and Tapasin, genes which are encoded within the MHC. Similarly, HLA-DO and -DM, which influence presentation by HLA class II molecules, are encoded in the MHC region. Analysis of MHC mutants, including point mutations and large deletions, has been central to understanding the roles of these genes. Mouse genetics has also played a major role. Many other genes have been identified including those controlling expression of HLA class I and class II at the transcriptional level. Another genetic approach that has provided insight has been the analysis of microorganisms, including viruses and bacteria that escape immune recognition by blocking these antigen processing and presentation pathways. Here, we provide a brief history of the genetic approaches, both traditional and modern, that have been used in the quest to understand antigen processing and presentation.

Inhibitory killer cell immunoglobulin-like receptors strengthen CD8+ T cell-mediated control of HIV-1, HCV, and HTLV-1.

Killer cell immunoglobulin-like receptors (KIRs) are expressed predominantly on natural killer cells, where they play a key role in the regulation of innate immune responses. Recent studies show that inhibitory KIRs can also affect adaptive T cell-mediated immunity. In mice and in human T cells in vitro, inhibitory KIR ligation enhanced CD8+ T cell survival. To investigate the clinical relevance of these observations, we conducted an extensive immunogenetic analysis of multiple independent cohorts of HIV-1-, hepatitis C virus (HCV)-, and human T cell leukemia virus type 1 (HTLV-1)-infected individuals in conjunction with in vitro assays of T cell survival, analysis of ex vivo KIR expression, and mathematical modeling of host-virus dynamics. Our data suggest that functional engagement of inhibitory KIRs enhances the CD8+ T cell response against HIV-1, HCV, and HTLV-1 and is a significant determinant of clinical outcome in all three viral infections.

Report from the Killer-cell Immunoglobulin-like Receptors (KIR) component of the 17th International HLA and Immunogenetics Workshop.

The goals of the KIR component of the 17th International HLA and Immunogenetics Workshop (IHIW) were to encourage and educate researchers to begin analyzing KIR at allelic resolution, and to survey the nature and extent of KIR allelic diversity across human populations. To represent worldwide diversity, we analyzed 1269 individuals from ten populations, focusing on the most polymorphic KIR genes, which express receptors having three immunoglobulin (Ig)-like domains (KIR3DL1/S1, KIR3DL2 and KIR3DL3). We identified 13 novel alleles of KIR3DL1/S1, 13 of KIR3DL2 and 18 of KIR3DL3. Previously identified alleles, corresponding to 33 alleles of KIR3DL1/S1, 38 of KIR3DL2, and 43 of KIR3DL3, represented over 90% of the observed allele frequencies for these genes. In total we observed 37 KIR3DL1/S1 allotypes, 40 for KIR3DL2 and 44 for KIR3DL3. As KIR allotype diversity can affect NK cell function, this demonstrates potential for high functional diversity worldwide. Allelic variation further diversifies KIR haplotypes. We determined KIR3DL3 ∼ KIR3DL1/S1 ∼ KIR3DL2 haplotypes from five of the studied populations, and observed multiple population-specific haplotypes in each. This included 234 distinct haplotypes in European Americans, 191 in Ugandans, 35 in Papuans, 95 in Egyptians and 86 in Spanish populations. For another 35 populations, encompassing 642,105 individuals we focused on KIR3DL2 and identified another 375 novel alleles, with approximately half of them observed in more than one individual. The KIR allelic level data gathered from this project represents the most comprehensive summary of global KIR allelic diversity to date, and continued analysis will improve understanding of KIR allelic polymorphism in global populations. Further, the wealth of new data gathered in the course of this workshop component highlights the value of collaborative, community-based efforts in immunogenetics research, exemplified by the IHIW.

High-Resolution Genetic and Phenotypic Analysis of KIR2DL1 Alleles and Their Association with Pre-Eclampsia.

Killer-cell Ig-like receptor (KIR) genes are inherited as haplotypes. They are expressed by NK cells and linked to outcomes of infectious diseases and pregnancy in humans. Understanding how genotype relates to phenotype is difficult because of the extensive diversity of the KIR family. Indeed, high-resolution KIR genotyping and phenotyping in single NK cells in the context of disease association is lacking. In this article, we describe a new method to separate NK cells expressing allotypes of the KIR2DL1 gene carried by the KIR A haplotype (KIR2DL1A) from those expressing KIR2DL1 alleles carried by the KIR B haplotype (KIR2DL1B). We find that in KIR AB heterozygous individuals, different KIR2DL1 allotypes can be detected in both peripheral blood and uterine NK cells. Using this new method, we demonstrate that both blood and uterine NK cells codominantly express KIR2DL1A and KIR2DL1B allotypes but with a predominance of KIR2DL1A variants, which associate with enhanced NK cell function. In a case-control study of pre-eclampsia, we show that KIR2DL1A, not KIR2DL1B, associates with increased disease risk. This method will facilitate our understanding of how individual KIR2DL1 allelic variants affect NK cell function and contribute to disease risk.

Regulation of Human γδ T Cells by BTN3A1 Protein Stability and ATP-Binding Cassette Transporters.

Activation of human Vγ9/Vδ2 T cells by "phosphoantigens" (pAg), the microbial metabolite (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP) and the endogenous isoprenoid intermediate isopentenyl pyrophosphate, requires expression of butyrophilin BTN3A molecules by presenting cells. However, the precise mechanism of activation of Vγ9/Vδ2 T cells by BTN3A molecules remains elusive. It is not clear what conformation of the three BTN3A isoforms transmits activation signals nor how externally delivered pAg accesses the cytosolic B30.2 domain of BTN3A1. To approach these problems, we studied two HLA haplo-identical HeLa cell lines, termed HeLa-L and HeLa-M, which showed marked differences in pAg-dependent stimulation of Vγ9/Vδ2 T cells. Levels of IFN-γ secretion by Vγ9/Vδ2 T cells were profoundly increased by pAg loading, or by binding of the pan-BTN3A specific agonist antibody CD277 20.1, in HeLa-M compared to HeLa-L cells. IL-2 production from a murine hybridoma T cell line expressing human Vγ9/Vδ2 T cell receptor (TCR) transgenes confirmed that the differential responsiveness to HeLa-L and HeLa-M was TCR dependent. By tissue typing, both HeLa lines were shown to be genetically identical and full-length transcripts of the three BTN3A isoforms were detected in equal abundance with no sequence variation. Expression of BTN3A and interacting molecules, such as periplakin or RhoB, did not account for the functional variation between HeLa-L and HeLa-M cells. Instead, the data implicate a checkpoint controlling BTN3A1 stability and protein trafficking, acting at an early time point in its maturation. In addition, plasma membrane profiling was used to identify proteins upregulated in HMB-PP-treated HeLa-M. ABCG2, a member of the ATP-binding cassette (ABC) transporter family was the most significant candidate, which crucially showed reduced expression in HeLa-L. Expression of a subset of ABC transporters, including ABCA1 and ABCG1, correlated with efficiency of T cell activation by cytokine secretion, although direct evidence of a functional role was not obtained by knockdown experiments. Our findings indicate a link between members of the ABC protein superfamily and the BTN3A-dependent activation of γδ T cells by endogenous and exogenous pAg.

Novel KIR genotypes and gene copy number variations in northeastern Thais.

KIR (Killer Immunoglobulin-like Receptor) variants influence immune responses and are genetic factors in disease susceptibility. Using sequence-specific priming PCR, we have previously described the diversity of KIR genes in term of presence/absence in northeastern Thais (NETs). To provide additional resolution beyond conventional methods, quantitative PCR was applied to determine KIR copy number profiles. Novel expanded and contracted KIR copy number profiles were identified at cumulatively high frequencies. These all comprise haplotypes with duplication (6·9%) or deletion (2·7%) of KIR3DL1/S1 along with adjacent genes. Five expanded KIR profiles comprised haplotypes with duplications of KIR2DP1, 2DL1, 3DP1, 2DL4, 3DL1/S1 and 2DS1/4, whereas two contracted profiles contained only a single copy of KIR3DP1, 3DL1/S1 and 2DL4. Using a KIR haplotype prediction program (KIR Haplotype Identifier), 14% of NET haplotypes carried atypical haplotypes based on the gene copy number data.

Introduction: MHC/KIR and governance of specificity.

The MHC controls specificity, to ensure that appropriate immune responses are mounted to invading pathogens whilst maintaining tolerance to the host. It encodes molecules that act as sentinels, providing a snapshot of the health of the interior and exterior of the cell for immune surveillance. To maintain the ability to respond appropriately to any disease requires a delicate balance of expression and function, and many subtleties of the system have been described at the gene, individual and population level. The main players are the highly polymorphic classical MHC class I and class II molecules, as well as some non-classical loci of both types. Transporter associated with antigen processing (TAP) peptide transporters, proteasome components and Tapasin, encoded within the MHC, are also involved in selection of peptide for presentation. The plethora of mechanisms microorganisms use to subvert immune recognition, through blocking these antigen processing and presentation pathways, attests to the importance of HLA in resistance to infection. There is continued interest in MHC genetics in its own right, as well as in relation to KIR, to transplantation, infection, autoimmunity and reproduction. Also of topical interest, cancer immunotherapy through checkpoint inhibition depends on highly specific recognition of cancer peptide antigen and continued expression of HLA molecules. Here, we briefly introduce some background to the MHC/KIR axis in man. This special issue of immunogenetics expands on these topics, in humans and other model species.

Modulation of Human Leukocyte Antigen-C by Human Cytomegalovirus Stimulates KIR2DS1 Recognition by Natural Killer Cells.

The interaction of inhibitory killer cell Ig-like receptors (KIRs) with human leukocyte antigen (HLA) class I molecules has been characterized in detail. By contrast, activating members of the KIR family, although closely related to inhibitory KIRs, appear to interact weakly, if at all, with HLA class I. KIR2DS1 is the best studied activating KIR and it interacts with C2 group HLA-C (C2-HLA-C) in some assays, but not as strongly as KIR2DL1. We used a mouse 2B4 cell reporter system, which carries NFAT-green fluorescent protein with KIR2DS1 and a modified DAP12 adaptor protein. KIR2DS1 reporter cells were not activated upon coculture with 721.221 cells transfected with different HLA-C molecules, or with interferon-γ stimulated primary dermal fibroblasts. However, KIR2DS1 reporter cells and KIR2DS1+ primary natural killer (NK) cells were activated by C2-HLA-C homozygous human fetal foreskin fibroblasts (HFFFs) but only after infection with specific clones of a clinical strain of human cytomegalovirus (HCMV). Active viral gene expression was required for activation of both cell types. Primary NKG2A-KIR2DS1+ NK cell subsets degranulated after coculture with HCMV-infected HFFFs. The W6/32 antibody to HLA class I blocked the KIR2DS1 reporter cell interaction with its ligand on HCMV-infected HFFFs but did not block interaction with KIR2DL1. This implies a differential recognition of HLA-C by KIR2DL1 and KIR2DS1. The data suggest that modulation of HLA-C by HCMV is required for a potent KIR2DS1-mediated NK cell activation.