Phenotypic studies of natural killer cell subsets in human transporter associated with antigen processing deficiency

SHP-1 localization to the activating immune synapse promotes NK cell tolerance in MHC class I deficiency

Natural killer (NK) cells recognize virally infected cells and tumors. NK cell function depends on balanced signaling from activating receptors, recognizing products from tumors or viruses, and inhibitory receptors (such as KIR/Ly49), which recognize major histocompatibility complex class I (MHC-I) molecules. KIR/Ly49 signaling preserves tolerance to self but also conveys reactivity toward MHC-I-low target cells in a process known as NK cell education. Here, we found that NK cell tolerance and education were determined by the subcellular localization of the tyrosine phosphatase SHP-1. In mice lacking MHC-I molecules, uneducated, self-tolerant Ly49A⁺ NK cells showed accumulation of SHP-1 in the activating immune synapse, where it colocalized with F-actin and the signaling adaptor protein SLP-76. Education of Ly49A⁺ NK cells by the MHC-I molecule H2D^d led to reduced synaptic accumulation of SHP-1, accompanied by augmented signaling from activating receptors. Education was also linked to reduced transcription of Ptpn6, which encodes SHP-1. Moreover, synaptic SHP-1 accumulation was reduced in NK cells carrying the H2D^d-educated receptor Ly49G2 but not in those carrying the noneducating receptor Ly49I. Colocalization of Ly49A and SHP-1 outside of the synapse was more frequent in educated compared with uneducated NK cells, suggesting a role for Ly49A in preventing synaptic SHP-1 accumulation in NK cell education. Thus, distinct patterning of SHP-1 in the activating NK cell synapse may determine NK cell tolerance.

Altered Signatures of Plasma Inflammatory Proteins and Phonotypic Markers of NK Cells in Kidney Transplant Patients upon CMV Reactivation

Cytomegalovirus (CMV) reactivation remains a common opportunistic infection with a prominent role in immune reconstitution in organ transplant recipients. CMVs as important drivers of natural killer (NK) cell differentiation has been indicated to prompt several phenotypic and functional alteration in these cells. We aimed to monitor the reconstitution of NK cells and change the signature of inflammatory proteins at the critical phase of CMV reactivation over six months after kidney transplantation. The present study indicated that CMV reactivation is associated with the development of IL-6, IL-10, and cytotoxic granules, including granzyme-B and granulysin, and the drop in the frequency of CD16 + NKG2A-CD57 + NK cell subset in kidney transplant recipients (KTRs) with reactivation versus non- reactivated ones. Our findings describe distinct immune signatures that emerged with CMV reactivation after kidney transplantation, which may be helpful in the timely management of CMV infection in KTRs.

Alessandro Moretta and Transporter Associated With Antigen Processing (TAP) Deficiency: On Giant's Shoulders

The laboratory hosting me for my Ph.D. described in 1994 the first human cases of TAP deficiency in two siblings with recurrent bacterial airway infections and a negative Human Leukocyte Antigen class I (HLA) serotyping. At this time, it became clear that natural killer (NK) cells interact with HLA class I molecules which inhibit them. Inhibitory receptors were postulated, and Alessandro Moretta was the first to generate monoclonal anti-human NK cell antibodies that bound to such molecules, which he characterized in detail (Killer Immunoglobulin-like receptors—KIR). Natural killer cells from healthy donors preferentially kill targets with absent HLA class I molecules (“missing self” concept), whereas we observed that the NK cells from the TAP-deficient patients were hypo-responsive and did not lyse the HLA class I-negative leukemia cell line K562. Moreover, they were not very active in antibody-dependent cellular cytotoxicity assays. To address the question if such NK cells would express KIR or not, my thesis supervisor requested the anti-KIR antibodies from Alessandro Moretta, who was kind enough to provide us generously with aliquots. It turned out that the NK cells from the TAP-deficient individuals expressed most of these inhibitory receptors normally. We then had the privilege to receive almost every new antibody generated in the Moretta lab and to complete the phenotypic studies of the NK cells from our patients. I had the great chance to meet Alessandro Moretta at several occasions. He deeply impressed me each time and strongly influenced my way of thinking.

Human CD56dimCD16dim Cells As an Individualized Natural Killer Cell Subset

Human natural killer (NK) cells can be subdivided in several subpopulations on the basis of the relative expression of the adhesion molecule CD56 and the activating receptor CD16. Whereas blood CD56^brightCD16^dim/− NK cells are classically viewed as immature precursors and cytokine producers, the larger CD56^dimCD16^bright subset is considered as the most cytotoxic one. In peripheral blood of healthy donors, we noticed the existence of a population of CD56^dimCD16^dim NK cells that was frequently higher in number than the CD56^bright subsets and even expanded in occasional control donors but also in transporter associated with antigen processing-deficient patients, two familial hemophagocytic lymphohistiocytosis type II patients, and several common variable immunodeficiency patients. This population was detected but globally reduced in a longitudinal cohort of 18 HIV-1-infected individuals. Phenotypically, the new subset contained a high percentage of relatively immature cells, as reflected by a significantly stronger representation of NKG2A⁺ and CD57⁻ cells compared to their CD56^dimCD16^bright counterparts. The phenotype of the CD56^dimCD16^dim population was differentially affected by HIV-1 infection as compared to the other NK cell subsets and only partly restored to normal by antiretroviral therapy. From the functional point of view, sorted CD56^dimCD16^dim cells degranulated more than CD56^dimCD16^bright cells but less than CD56^dimCD16⁻ NK cells. The population was also identified in various organs of immunodeficient mice with a human immune system (“humanized” mice) reconstituted from human cord blood stem cells. In conclusion, the CD56^dimCD16^dim NK cell subpopulation displays distinct phenotypic and functional features. It remains to be clarified if these cells are the immediate precursors of the CD56^dimCD16^bright subset or placed somewhere else in the NK cell differentiation and maturation pathway.

Human natural killer cell maturation defect supports in vivo CD56(bright) to CD56(dim) lineage development

Two populations of human natural killer (NK) cells can be identified in peripheral blood. The majority are CD3⁻CD56^dim cells while the minority exhibits a CD3⁻CD56^bright phenotype. In vitro evidence indicates that CD56^bright cells are precursors of CD56^dim cells, but in vivo evidence is lacking. Here, we studied NK cells from a patient that suffered from a melanoma and opportunistic fungal infection during childhood. The patient exhibited a stable phenotype characterized by a reduction in the frequency of peripheral blood CD3⁻CD56^dim NK cells, accompanied by an overt increase in the frequency and absolute number of CD3⁻CD56^bright cells. These NK cells exhibited similar expression of perforin, CD57 and CD158, the major activating receptors CD16, NKp46, NKG2D, DNAM-1, and 2B4, as well as the inhibitory receptor CD94/NKG2A, on both CD56^bright and CD56^dim NK cells as healthy controls. Also, both NK cell subpopulations produced IFN-γ upon stimulation with cytokines, and CD3⁻CD56^dim NK cells degranulated in response to cytokines or K562 cells. However, upon stimulation with cytokines, a substantial fraction of CD56^dim cells failed to up-regulate CD57 and CD158, showed a reduction in the percentage of CD16⁺ cells, and CD56^bright cells did not down-regulate CD62L, suggesting that CD56^dim cells could not acquire a terminally differentiated phenotype and that CD56^bright cells exhibit a maturation defect that might result in a potential altered migration pattern. These observations, support the notion that NK cells of this patient display a maturation/activation defect that precludes the generation of mature NK cells at a normal rate accompanied by CD56^dim NK cells that cannot completely acquire a terminally differentiated phenotype. Thus, our results provide evidence that support the concept that in vivo CD56^bright NK cells differentiate into CD56^dim NK cells, and contribute to further understand human NK cell ontogeny.

CD56bright natural killer (NK) cells: an important NK cell subset

Human natural killer (NK) cells can be subdivided into different populations based on the relative expression of the surface markers CD16 and CD56. The two major subsets are CD56(bright) CD16(dim/) (-) and CD56(dim) CD16(+), respectively. In this review, we will focus on the CD56(bright) NK cell subset. These cells are numerically in the minority in peripheral blood but constitute the majority of NK cells in secondary lymphoid tissues. They are abundant cytokine producers but are only weakly cytotoxic before activation. Recent data suggest that under certain conditions, they have immunoregulatory properties, and that they are probably immediate precursors of CD56(dim) NK cells. CD56(bright) NK cell percentages are expanded or reduced in a certain number of diseases, but the significance of these variations is not yet clear.

HLA class I deficiency syndrome mimicking Wegener's granulomatosis

Herein we report the case of a 20-year-old woman who presented with multiple skin ulcers on her legs, severe pansinusitis, and chronic lung disease. She was initially thought to have Wegener's granulomatosis (WG). However, serologic studies indicated an HLA class I deficiency, which was confirmed by flow cytometry. Complementation studies and reverse transcriptase-polymerase chain reaction followed by direct DNA sequencing revealed a mutation in the gene encoding subunit 1 of the peptide transporter associated with antigen processing (TAP1). This mutation, which has not been previously described in the literature, results in a stop codon in the catalytic domain of TAP1. Although TAP mutations are rare, clinicians may encounter them in the evaluation of patients with suspected WG. In patients with WG-like symptoms it is important to consider this alternative genetic diagnosis as early as possible, not only so that appropriate antibiotic therapy can be initiated to prevent bronchiectasis, but also to avoid inappropriate immunosuppressive therapy that worsens the disease.