Getting close to nature – Plasmodium knowlesi reference genome sequences from contemporary clinical isolates

Plasmodium knowlesi, a malaria parasite of old-world macaque monkeys, is used extensively to model Plasmodium biology. Recently P. knowlesi was found in the human population of Southeast Asia, particularly Malaysia. P. knowlesi causes un-complicated to severe and fatal malaria in the human host with features in common with the more prevalent and virulent malaria caused by Plasmodium falciparum. As such P. knowlesi presents a unique opportunity to inform an experimental model for malaria with clinical data from same-species human infections. Experimental lines of P. knowlesi represent well characterised genetically static parasites and to maximise their utility as a backdrop for understanding malaria pathophysiology, genetically diverse contemporary clinical isolates, essentially wild-type, require comparable characterization. The Oxford Nanopore PCR-free long-read sequencing platform was used to sequence P. knowlesi parasites from archived clinical samples. The sequencing platform and assembly pipeline was designed to facilitate capturing data on important multiple gene families, including the P. knowlesi schizont-infected cell agglutination (SICA) var genes and the Knowlesi-Interspersed Repeats (KIR) genes. The SICAvar and KIR gene families code for antigenically variant proteins that have been difficult to resolve and characterise. Analyses presented here suggest that the family members have arisen through a process of gene duplication, selection pressure and variation. Highly evolving genes tend to be located proximal to genetic elements that drive change rather than regions that support core gene conservation. For example, the virulence-associated P. falciparum erythrocyte membrane protein (PfEMP1) gene family members are restricted to relatively unstable sub-telomeric regions. In contrast the SICAvar nd KIR genes are located throughout the genome but as the study presented here shows, they occupy otherwise gene-sparse chromosomal locations. The novel methods presented here offer the malaria research community new tools to generate comprehensive genome sequence data from small clinical samples and renewed insight into these complex real-world parasites.

KIRCLE: An Analysis of Variations in KIR Genes in The Cancer Genome Atlas and UK Biobank

Background: Natural killer (NK) cells represent a critical component of the innate immune system response against cancer and viral infections, among other diseases. To distinguish healthy host cells from infected or tumor cells, killer immunoglobulin receptors (KIR) on NK cells bind and recognize Human Leukocyte Antigen (HLA) complexes on their target cells. Just like the HLAs they bind, these KIRs exhibit high allelic diversity in the human population. Results: In order to better understand these immunoreceptors, we have developed KIRCLE, a novel method for genotyping individual KIR genes from whole exome sequencing data, and used it to analyze approximately 60,000 patient samples in The Cancer Genome Atlas and UK Biobank. We were able to assess population frequencies for different KIR alleles and demonstrate that, similar to HLA alleles, KIR alleles of different individuals correlate strongly with their ethnicities. In addition, we observed associations between different KIR alleles and HLA alleles, including HLA-B*53 with KIR3DL2*013 (Fisher Exact FDR = 7.64e-51). Finally, we showcased statistically significant associations between KIR alleles and various clinical correlates, including peptic ulcer disease (Fisher Exact FDR = 0.0429) and age of onset of atopy and various KIR alleles (Mann-Whitney-U FDR = 0.0751). Conclusions: KIR polymorphism and NK cells play a critical role in many diseases, often through their interactions with HLA complexes. Peptic ulcer disease and atopy are just two diseases in which NK cells may play a role beyond their classical realm of anti-tumor and anti-viral responses.

KIR-HLAC genotyping in married couples with early reproductive losses of unknown genesis

Aim. KIR-HLAC genotyping in married couples with early idiopathic pregnancy loss. Methods. DNA extraction and purification, PCR-SSP, agarose gel electrophoresis. Results. The spectrum of KIR genes was analyzed and the frequency of KIR genotypes in women with early reproductive losses was established. The most common (77.78 %) was the AB genotype, 20.37 % had the AA genotype, and 1.85 % had the BB genotype. HLAC genotyping of couples with regular early reproductive losses showed the C1/C2 genotype of the HLAC gene in 40.74 % of women and 44.44 % of men. The frequency of C1/C1 genotype in women was 27.78% versus 38.89 % in men. The C2/C2 genotype of the HLAC gene was detected in 31.48 % of women and 12.96 % of men. According to the results of KIR-HLAC analysis of genotyping of married couples with early reproductive losses, a high/significant risk of reproductive losses of immunological genesis was found in 55.56 % of cases. Conclusions. KIR-HLAC genotyping is a genetic test that allows to assess the risks of the embryo being rejected by the maternal immune system, and thus to direct medical interventions in order to achieve a successful pregnancy. Keywords: early reproductive losses, KIR, HLAC.

Killer immunoglobulin-like receptor (KIR) genes are associated with the risk of episodes of high-level and detectable viremia among HIV controllers

Background: HIV controllers (HICs) constitute a heterogeneous group of HIV-1 individuals able to suppress plasma viremia to low or undetectable levels in the absence of antiretroviral therapy. Host genetic factors may be involved in the sustained control of viral replication observed. We investigated the distribution and the potential impact of human leukocyte antigens (HLA)-B and -C alleles, killer immunoglobulin-like receptor (KIR) genes, single nucleotide polymorphisms (SNPs) of the NLRP3, CARD8 and IL-1β inflammasome genes, and CCR5Δ32 mutation on the viral control among HICs. Methods: In total, 28 HICs were categorized as persistent elite controllers (PECs, n = 7), ebbing elite controllers (EECs, n = 7), and viremic controllers (VCs, n = 14) according to the level of natural suppression of viremia. HLA alleles were assigned by sequencing-based typing, KIR alleles by polymerase chain reaction (PCR) sequence-specific amplification, SNPs by real-time PCR, and the CCR5Δ32 mutation by PCR. Results: Significant differences were observed in the pairwise comparisons of protective HLA-B alleles, KIR Bx genotype, KIR2DL3 + C1 pair, KIR2DL5, and KIR2DS5 allelic carrier frequencies among the HIC groups. Multivariate models showed that HICs without the KIR2DL3 allele or without KIR2DL3 + C1/C2 pair, with the HLA-C*08 allele or with the NLRP3 rs10754558-G SNP had a higher mean hazard of a viral load above 2,000 copies/mL, while a lower mean hazard of this event was observed for HICs with KIR2DL5, KIR2DS1, KIR2DS5, and KIR3DS1 alleles. Moreover, HICs with the KIR2DS5 allele had less risk of undergoing viral load (VL) blips within the same normalized period than those participants without this allele, while HICs without the KIR2DL3 allele had a mean higher risk of experiencing VL blips. Conclusions: These results indicate that innate immune mechanisms may play an essential role in modulating the sustained control of viral replication in HICs.

Large-Scale Imputation of KIR Copy Number and HLA Alleles in North American and European Psoriasis Case-Control Cohorts Reveals Association of Inhibitory KIR2DL2 With Psoriasis

Killer cell immunoglobulin-like receptors (KIR) regulate immune responses in NK and CD8+ T cells via interaction with HLA ligands. KIR genes, including KIR2DS1, KIR3DL1, and KIR3DS1 have previously been implicated in psoriasis susceptibility. However, these previous studies were constrained to small sample sizes, in part due to the time and expense required for direct genotyping of KIR genes. Here, we implemented KIR*IMP to impute KIR copy number from single-nucleotide polymorphisms (SNPs) on chromosome 19 in the discovery cohort (n=11,912) from the PAGE consortium, University of California San Francisco, and the University of Dundee, and in a replication cohort (n=66,357) from Kaiser Permanente Northern California. Stratified multivariate logistic regression that accounted for patient ancestry and high-risk HLA alleles revealed that KIR2DL2 copy number was significantly associated with psoriasis in the discovery cohort (p ≤ 0.05). The KIR2DL2 copy number association was replicated in the Kaiser Permanente replication cohort. This is the first reported association of KIR2DL2 copy number with psoriasis and highlights the importance of KIR genetics in the pathogenesis of psoriasis.

Association of killer cell immunoglobulin-like receptors with endemic Burkitt lymphoma in Kenyan children

Endemic Burkitt lymphoma (eBL) is an aggressive pediatric B cell lymphoma, common in Equatorial Africa. Co-infections with Epstein-Barr virus (EBV) and Plasmodium falciparum, coupled with c-myc translocation are involved in eBL etiology. Infection-induced immune evasion mechanisms to avoid T cell cytotoxicity may increase the role of Natural killer (NK) cells in anti-tumor immunosurveillance. Killer immunoglobulin-like receptor (KIR) genes on NK cells exhibit genotypic and allelic variations and are associated with susceptibility to diseases and malignancies. However, their role in eBL pathogenesis remains undefined. This retrospective study genotyped sixteen KIR genes and compared their frequencies in eBL patients (n = 104) and healthy geographically-matched children (n = 104) using sequence-specific primers polymerase chain reaction (SSP-PCR) technique. The relationship between KIR polymorphisms with EBV loads and eBL pathogenesis was investigated. Possession of ≥ 4 activating KIRs predisposed individuals to eBL (OR = 3.340; 95% CI 1.530–7.825; p = 0.004). High EBV levels were observed in Bx haplogroup (p = 0.016) and AB genotypes (p = 0.042) relative to AA haplogroup and AA genotype respectively, in eBL patients but not in healthy controls. Our results suggest that KIR-mediated NK cell stimulation could mute EBV control, contributing to eBL pathogenesis.

Peptide: MHC-based DNA vaccination strategy to activate natural killer cells by targeting killer cell immunoglobulin-like receptors

BackgroundNatural killer (NK) cells are increasingly being recognized as agents for cancer immunotherapy. The killer cell immunoglobulin-like receptors (KIRs) are expressed by NK cells and are immunogenetic determinants of the outcome of cancer. In particular, KIR2DS2 is associated with protective responses to several cancers and also direct recognition of cancer targets in vitro. Due to the high homology between activating and inhibitory KIR genes to date, it has been challenging to target individual KIR for therapeutic benefit.MethodsA novel KIR2DS2-targeting therapeutic peptide:MHC DNA vaccine was designed and used to immunize mice transgenic for KIR genes (KIR-Tg). NK cells were isolated from the livers and spleens of vaccinated mice and then analyzed for activation by flow cytometry, RNA profiling and cytotoxicity assays. In vivo assays of NK cell function using a syngeneic cancer model (B16 melanoma) and an adoptive transfer model for human hepatocellular carcinoma (Huh7) were performed.ResultsInjecting KIR-Tg mice with the vaccine construct activated NK cells in both liver and spleens of mice, with preferential activation of KIR2DS2-positive NK cells. KIR-specific activation was most marked on the CD11b+CD27+ mature subset of NK cells. RNA profiling indicated that the DNA vaccine upregulated genes associated with cellular metabolism and downregulated genes related to histone H3 methylation, which are associated with immune cell maturation and NK cell function. Vaccination led to canonical and cross-reactive peptide:MHC-specific NK cell responses. In vivo, DNA vaccination led to enhanced antitumor responses against B16F10 melanoma cells and also enhanced responses against a tumor model expressing the KIR2DS2 ligand HLA-C*0102.ConclusionWe show the feasibility of a peptide-based KIR-targeting vaccine strategy to activate NK cells and hence generate functional antitumor responses. This approach does not require detailed knowledge of the tumor peptidomes nor HLA matching with the patient. It therefore offers a novel opportunity for targeting NK cells for cancer immunotherapy.