Search

The human cytomegalovirus (CMV) immune evasion protein, UL40, shares an identical peptide sequence with that found in the leader sequence of many human leukocyte antigen (HLA)-C alleles and when complexed with HLA-E, can modulate NK cell functions via interactions with the CD94-NKG2 receptors. However the UL40-derived sequence can also be immunogenic, eliciting robust CD8+ T cell responses. In the setting of solid organ transplantation these T cells may not only be involved in antiviral immunity but also can potentially contribute to allograft rejection when the UL40 epitope is also present in allograft-encoded HLA. Here we assessed 15 bilateral lung transplant recipients for the presence of HLA-E-restricted UL40 specific T cells by tetramer staining of peripheral blood mononuclear cells (PBMC). UL40-specific T cells were observed in 7 patients post-transplant however the magnitude of the response varied significantly between patients. Moreover, unlike healthy CMV seropositive individuals, longitudinal analyses revealed that proportions of such T cells fluctuated markedly. Nine patients experienced low-grade acute cellular rejection, of which 6 also demonstrated UL40-specific T cells. Furthermore, the presence of UL40-specific CD8+ T cells in the blood was significantly associated with allograft dysfunction, which manifested as Bronchiolitis Obliterans Syndrome (BOS). Therefore, this study suggests that minor histocompatibility antigens presented by HLA-E can represent an additional risk factor following lung transplantation. [ABSTRACT FROM AUTHOR]

Murine natural killer (NK) cells are regulated by the interaction of Ly49 receptors with major histocompatibility complex class I molecules (MHC-I). Although the ligands for inhibitory Ly49 were considered to be restricted to classical MHC (MHCIa), we have shown that the non-classical MHC molecule (MHCIb) H2-M3 was a ligand for the inhibitory Ly49A. Here we establish that another MHC-Ib, H2-Q10, is a bona fide ligand for the inhibitory Ly49C receptor. H2-Q10 bound to Ly49C with a marginally lower affinity (~5 μM) than that observed between Ly49C and MHC-Ia (H-2Kb/H-2Dd, both ~1 μM), and this recognition could be prevented by cis interactions with H-2K in situ. To understand the molecular details underpinning Ly49· MHC-Ib recognition, we determined the crystal structures of H2-Q10 and Ly49C bound H2-Q10. Unliganded H2-Q10 adopted a classical MHC-I fold and possessed a peptide-binding groove that exhibited features similar to those found in MHC-Ia, explaining the diverse peptide binding repertoire of H2-Q10. Ly49C bound to H2-Q10 underneath the peptide binding platform to a region that encompassed residues from theα1,α2, and α3 domains, as well as the associated β2-microglobulin subunit. This docking mode was conserved with that previously observed for Ly49C·H-2Kb. Indeed, structure-guided mutation of Ly49C indicated that Ly49C·H2-Q10 and Ly49C·H-2Kb possess similar energetic footprints focused around residues located within the Ly49C β4-stand and L5 loop, which contact the underside of the peptide-binding platform floor. Our data provide a structural basis for Ly49·MHC-Ib recognition and demonstrate that MHC-Ib represent an extended family of ligands for Ly49 molecules. [ABSTRACT FROM AUTHOR]

Monitoring of donor chimerism (DC) may detect early relapse following allogeneic hematopoietic stem cell transplantation (allo-SCT) for acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Most centers use unfractionated peripheral blood or T-cells to monitor DC, although CD34 + DC may be more predictive. The limited adoption of CD34 + DC may be due to the lack of detailed, comparative studies. To address this knowledge gap, we compared peripheral blood CD34 + and CD3 + DC in 134 patients who underwent allo-SCT for AML or MDS. In July 2011, the Alfred Hospital Bone Marrow Transplantation Service adopted routine monitoring of DC in the lineage-specific CD34 + and CD3 + cell subsets from peripheral blood at 1, 2, 3, 4, 6, 9, and 12 months post-transplantation for AML or MDS. Immunologic interventions, including rapid withdrawal of immunosuppression, azacitidine, and donor lymphocyte infusion, were prespecified for CD34 + DC ≤80%. Overall, CD34 + DC ≤80% detected 32 of 40 relapses (positive predictive value [PPV], 68%; negative predictive value [NPV], 91%), compared with 13 of 40 relapses for CD3 + DC ≤80% (PPV, 52%; NPV, 75%). Receiver operating characteristic analysis showed the superiority of CD34 + DC, with the greatest value at day 120 post-transplantation. CD3 + DC provided additional value in only 3 cases, preceding CD34 + DC ≤80% by 1 month. We further show that the CD34 + DC sample can be used to detect NPM1 mut , with the combination of CD34 + DC ≤80% and NPM1 mut identifying the highest risk of relapse. Among the 24 patients in morphologic remission at the time of CD34 + DC ≤80%, 15 (62.5%) responded to immunologic interventions (rapid withdrawal of immunosuppression, azacitidine, or donor lymphocyte infusion) with recovery of CD34 + DC >80%, and 11 of these patients remained in complete remission for a median of 34 months (range, 28 to 97 months). In contrast, the other 9 patients did not respond to the clinical intervention and relapsed within a median of 59 days after detecting CD34 + DC ≤80%. The CD34 + DC was significantly higher in responders than in nonresponders (median, 72% versus 56%; P = .015, Mann-Whitney U test). Overall, monitoring of CD34 + DC was considered clinically useful (early diagnosis of relapse enabling preemptive therapy or predicting low risk of relapse) in 107 of 125 evaluable patients (86%). Our findings show that peripheral blood CD34 + DC is feasible and superior to CD3 + DC for predicting relapse. It also provides a source of DNA for measurable residual disease testing, which may further stratify the risk of relapse. If validated by an independent cohort, our results suggest that CD34 + should be used in preference to CD3 + DC for detecting early relapse and guiding immunologic interventions following allo-SCT for AML or MDS., (Copyright © 2023 The American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

Human cytomegalovirus (CMV) infection can stimulate robust human leukocyte antigen (HLA)-E-restricted CD8 + T cell responses. These T cells recognize a peptide from UL40, which differs by as little as a single methyl group from self-peptides that also bind HLA-E, challenging their capacity to avoid self-reactivity. Unexpectedly, we showed that the UL40/HLA-E T cell receptor (TCR) repertoire included TCRs that had high affinities for HLA-E/self-peptide. However, paradoxically, lower cytokine responses were observed from UL40/HLA-E T cells bearing TCRs with high affinity for HLA-E. RNA sequencing and flow cytometric analysis revealed that these T cells were marked by the expression of inhibitory natural killer cell receptors (NKRs) KIR2DL1 and KIR2DL2/L3. On the other hand, UL40/HLA-E T cells bearing lower-affinity TCRs expressed the activating receptor NKG2C. Activation of T cells bearing higher-affinity TCRs was regulated by the interaction between KIR2D receptors and HLA-C. These findings identify a role for NKR signaling in regulating self/non-self discrimination by HLA-E-restricted T cells, allowing for antiviral responses while avoiding contemporaneous self-reactivity., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Background: In lung transplant recipients, immunosuppressive medications result in impaired antiviral immunity and a propensity for cytomegalovirus (CMV) reactivation within the lung allograft. Natural killer (NK) cells play a key role in immunity to CMV, with an increase in the proportion of NK cells expressing activating CD94-NKG2C receptors in the blood being a strong correlate of CMV infection. Whether a similar increase in NKG2C NK cells occurs in lung transplant recipients following CMV reactivation in the allograft and if such cells contribute to viral control remains unclear., Methods: In this pilot study, we longitudinally assessed the frequency and phenotype of NKG2C NK cells in the blood and bronchoalveolar lavage (BAL) of lung transplant recipients and stratified recipients based on their risk of developing CMV disease., Results: We observed an increase in the proportion of NKG2C NK cells in the blood and BAL of CMV high-risk patients, coincident with both the cessation of antiviral prophylaxis and subsequent detection of actively replicating CMV in the blood and lung allograft. Additionally, these NKG2C NK cells expressed killer-cell immunoglobulin-like receptors distinct from those of other NK subsets and BAL NKG2C NK cells possessed an activated phenotype. Finally, the frequency of NKG2C NK cells in the BAL may be inversely correlated with CMV blood titers., Conclusions: Monitoring the phenotype of NK cells postlung transplant may be a useful biomarker for monitoring patient levels of CMV immunity.

Natural killer (NK) cell recognition of the nonclassical human leukocyte antigen (HLA) molecule HLA-E is dependent on the presentation of a nonamer peptide derived from the leader sequence of other HLA molecules to CD94-NKG2 receptors. However, human cytomegalovirus can manipulate this central innate interaction through the provision of a "mimic" of the HLA-encoded peptide derived from the immunomodulatory glycoprotein UL40. Here, we analyzed UL40 sequences isolated from 32 hematopoietic stem cell transplantation recipients experiencing cytomegalovirus reactivation. The UL40 protein showed a "polymorphic hot spot" within the region that encodes the HLA leader sequence mimic. Although all sequences that were identical to those encoded within HLA-I genes permitted the interaction between HLA-E and CD94-NKG2 receptors, other UL40 polymorphisms reduced the affinity of the interaction between HLA-E and CD94-NKG2 receptors. Furthermore, functional studies using NK cell clones expressing either the inhibitory receptor CD94-NKG2A or the activating receptor CD94-NKG2C identified UL40-encoded peptides that were capable of inhibiting target cell lysis via interaction with CD94-NKG2A, yet had little capacity to activate NK cells through CD94-NKG2C. The data suggest that UL40 polymorphisms may aid evasion of NK cell immunosurveillance by modulating the affinity of the interaction with CD94-NKG2 receptors.