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HLA (HLA) alleles are risk factors for CD8+ T-cell-mediated drug hypersensitivity reactions. However, as most HLA associations are incompletely predictive and/or involve risk alleles at low frequency, costly sequence-based typing can elude an economically productive cost: benefit ratio for clinical validation studies and diagnostic and/or preventative screening. Hence rapid and low-cost detection assays are now required, both for single alleles but also across risk loci associated with broader multi-disease risk; exemplified by associations with diverse alleles in HLA-B*35, including HLA-B*35:01 and green tea- or co-trimoxazole-induced liver injury. Here, we developed a cost-effective ($10USD) qPCR assay for rapid (2.5 h) clinical detection of HLA-B*35 alleles. The assay was validated using 430 DNA samples with previous American society for histocompatibility and immunogenetics-accredited sequence-based high-resolution HLA typing, positively detecting all HLA-B*35 allelic variants in our cohort, and as expected by primer design, the six samples that expressed low-frequency B*78:01. The assay did not result in positive detection for any negative control allele. With expected detection of B*35 and B*78, our assay sensitivity (95% CI, 95.07%-100.00%) and specificity (95% CI, 98.97%-100.00%) of 100% using as low as 10 ng of DNA provides a reliable HLA-B*35 screening tool for clinical validation and HLA-risk-based prevention and diagnostics.

Delayed drug hypersensitivities are CD8+ T-cell mediated reactions associated with up to 50% mortality. Human leukocyte antigen (HLA) alleles are known to predispose disease, specific to drug, reaction, and patient ethnicity, with pre-treatment screening recommended for a handful of the strongest associations to identify and prevent drug use in high-risk patients. However, an incomplete predictive value implicates other HLA-imposed risk factors, and low carriage of many identified HLA-risk alleles combined with the high cost of sequence-based typing has limited economic viability for similar recommendation of screening across drugs and healthcare systems. To mitigate, an expanding armoury of low-cost polymerase chain reaction-based screens is being developed, and HLA-imposed risk factors are being discovered. These include (1) polymorphic variants of metabolic and endoplasmic reticulum aminopeptidase enzymes, towards multi-allelic screening with increased predictivity, (2) regulation by immune checkpoint inhibitors, enabling de-tolerised animal models of human disease, and (3) immunodominant T-cell receptors (TCR) on clonally expanded CD8+ T-cells. For the latter, HLA-risk restricted TCR provides immunogenomic strategies and samples from a single patient to identify novel HLA-risk associations in underserved minority populations, tissue-relevant effector biomarkers towards earlier diagnosis and treatment, and HLA-TCR-presented immunogenic structures to aid future drug development.

Abacavir hypersensitivity syndrome (ABC HSS) is strongly associated with carriage of human leukocyte antigen (HLA)-B*57:01, which has a 100% negative predictive value for the development of ABC HSS. However, 45% of individuals who carry HLA-B*57:01 can tolerate ABC. We investigated immune and non-immune related genes in ABC HSS (n = 95) and ABC tolerant (n = 43) HLA-B*57:01 + patients to determine other factors required for the development of ABC HSS. Assignment of phenotype showed that ABC HSS subjects were significantly less likely than tolerants to carry only ERAP1 hypoactive trimming allotypes (p = 0.02). An altered self-peptide repertoire model by which abacavir activates T cells is in keeping with observation that endoplasmic reticulum aminopeptidase 1 (ERAP1) allotypes that favour efficient peptide trimming are more common in ABC HSS patients compared to patients who tolerate ABC. Independently, non-specific immune activation via soluble cluster of differentiation antigen 14 (sCD14) may also influence susceptibility to ABC HSS.

Purpose of review An update of the pharmacogenetic risk factors associated with T-cell-mediated delayed hypersensitivity reactions. Recent findings Recent HLA associations relevant to our understanding of immunopathogenesis and clinical practice include HLA-B∗13:01 with co-trimoxazole-induced SCAR, and HLA-A∗32:01 with vancomycin-DRESS, for which an extended HLA class II haplotype is implicated in glycopeptide antibiotic cross-reactivity. Hypoactive variants of ERAP1, an enzyme-trimming peptide prior to HLA loading, are now associated with protection from abacavir-hypersensitivity in HLA-B∗57:01+ patients, and single-cell sequencing has defined the skin-restricted expansion of a single, public and drug-reactive dominant TCR across patients with HLA-B∗15:02-restricted carbamazepine-induced SJS/TEN. More recent strategies for the use of HLA and other risk factors may include risk-stratification, early diagnosis, and diagnosis in addition to screening. Summary HLA is necessary but insufficient as a risk factor for the development of most T-cell-mediated reactions. Newly emerged genetic and ecological risk factors, combined with HLA-restricted response, align with underlying immunopathogenesis and drive towards enhanced strategies to improve positive-predictive and negative-predictive values. With large population-matched cohorts, genetic studies typically focus on populations that have been readily accessible to research studies, but it is now imperative to address similar risk in globally relevant and understudied populations.

All fifteen patients with HLA-A*32:01 restricted vancomycin-induced DRESS, showed negative ex vivo responses to dalbavancin however two showed cross-reactivity to teicoplanin and telavancin. Adjunctive diagnostic testing should be considered to detect potential cross-reactivity amongst glycopeptides.

Rationale Allergic contact dermatitis (ACD) is a classic delayed hypersensitivity reaction commonly associated with corticosteroids that can rarely manifest as a delayed rash following systemic administration. Methods A 50-year old woman developed local edema and delayed spreading rash following interarticular injection with dexamethasone and methylprednisolone acetate (MA). 6-months following this intradermal skin testing (IDST) was positive to MA and methylprednisolone sodium succinate, and IDST and patch test negative to other corticosteroids. She tolerated dexamethasone challenge. Cells were isolated from 4-mm punch biopsies from 48-hour positive IDST and unaffected skin with liberase digestion and sorted on CD3. scTCR and scRNA-seq were performed using plate-based assays (Smart-seq-2). Data was filtered using Seurat and analysed with Visual Genomics Analysis Studio (VGAS) software. Results Histopathology showed a superficial perivascular dermatitis with epidermal spongiosis in keeping with ACD. T-cells were 18x more prevalent in affected skin and those from both affected and unaffected sites were predominantly CD8+ T-cells that expressed CD45RO and polyclonal TCR alpha beta. Differentially expressed genes (DEG) in T-cells from affected skin reflected homing (CCR7,S1PR1), T-cell activation and proliferation (TNFRS9, GRAP2, ZYG11A, ZHX1), T-cell effector differentiation (IL-21R), and stress survival (EEF1A1, IFI6) without representation of markers of T-cell residency (ITGAE) or regulation. Conclusions We demonstrate insights into the immunopathogenesis of drug-induced ACD by showing that IDST+ methylprednisolone associated ACD is corticosteroid-specific and associated with a polyclonal population of primarily CD45RO+ memory CD8+ T-cells showing upregulation of markers of homing, T-cell activation, proliferation and differentiation but lacking markers of T-cell residency and regulation.

Infection is the leading cause of death in rheumatoid arthritis (RA). Corticosteroid (CS) use is a known and important risk factor for serious infections (SIs). Mannose binding lectin (MBL) is a genetically determined component of the innate immune system implicated in neonatal infections.Our aim was to determine whether MBL deficiency is a risk factor for SIs in RA and to compare it with CS use and also synthetic and biologic disease-modifying antirheumatic drug (DMARD) therapy.Data on 228 patients with RA were collected for up to 7 years (median = 5.9 years). Serum MBL concentrations were determined in all patients receiving synthetic (n = 96) or biologic (n = 132) DMARD therapy.High rates of SIs were observed in RA irrespective of treatment (17%). Similar rates of SIs were observed in synthetic and biologic DMARD users. The rates of single and multiple SIs were similar, irrespective of the use of a biologic agent. Undetectable MBL (56 ng/mL) concentrations and maintenance prednisolone at 10 mg per day or higher were associated with an increased risk for an SI, with incident risk ratio of 4.67 (P = .001) and 4.70 (P.001), respectively.Undetectable MBL and prednisolone confer a high risk for an SI. The use of biologic DMARDs did not confer substantial SI risk in this observational study. MBL deficiency is hitherto an unrecognized risk factor for an SI in RA.