A subject with a novel type I bare lymphocyte syndrome has tapasin deficiency due to deletion of 4 exons by Alu-mediated recombination

Abstract

HLA class I expression depends on the formation of a peptide-loading complex composed of class I heavy chain; ␤ 2 -microglobulin; the transporter associated with antigen processing (TAP); and tapasin, which links TAP to the heavy chain. Defects in TAP result in a class I deficiency called the type I bare lymphocyte syndrome (BLS). In the present study, we examined a subject with a novel type I BLS who does not exhibit apparent TAP abnormalities but who has a tapasin defect. The subject's TAPASIN gene has a 7.4-kilobase deletion between introns 3 and 7; an Alu repeat-mediated unequal homologous recombination may be the cause of the deletion. No tapasin polypeptide was detected in the subject's cells. IntroductionType I bare lymphocyte syndrome (BLS) is characterized by the lack of cell surface HLA class I. 1,2 Patients with this syndrome showed a reduced number of CD8 ϩ T cells and the lack of natural killer (NK) activities. 3,4 Type I BLS is caused by a deficiency in the transporter associated with antigen processing (TAP). 4-7 TAP transports peptides from the cytoplasm into the inner lumen of the endoplasmic reticulum (ER), and defects in TAP induce poor peptide loading on class I heavy chains (HCs), resulting in a reduction in the number of mature class I molecules on the cell surface. Peptide binding of HCs occurs on the ER by the formation of a complex that is composed of HCs, ␤ 2 -microglobulin, TAP, and tapasin. 8 Tapasin is a 48-kd transmembrane protein that has 2 immunoglobulinlike domains and the ER-retention motif. 9,10 The TAPASIN gene is located at the HLA region. 11 Tapasin binds with TAP, forms a bridge between TAP and HCs, enhances peptide loading, and retains immature HCs in the ER. 12,13 The importance of tapasin in the class I assembly has been indicated by studies using a human mutant cell line, 721.220, which has a truncated tapasin by aberrant splicing. 9,14 TAPASIN-gene-targeted mice had an impaired class I assembly, reduced level of cell surface class I expression, and impaired immune responses. 15,16 Here we analyzed a subject with a novel type I BLS who did not manifest the symptoms commonly observed in TAP-deficient subjects and found that the subject has tapasin deficiency. Study design AntibodiesAntitapasin (peptides at 313-330) and anti-TAP1 rabbit antibodies 5 were provided by K. Tanaka Cell preparationsPeripheral blood mononuclear cells (PBMCs) were isolated from a subject S.M. The B-cell line SM-LCL was established from the patient's PBMCs. The TAP1-deficient KMW-B2 cells have been described previously. 5 Polymerase chain reaction amplification and sequencingGenomic DNA and complementary DNA (cDNA) were prepared as described previously. 5 DNA sequencing was performed by means of ABI 310 (PE Applied Biosystems, Foster City, CA). Flow cytometric analysisCells were stained by fluorescein isothiocyanate (FITC)-conjugated antibodies and analyzed by means of EPICS Elite flow cytometer (Beckman Coulter, Fullerton, CA) Results and discussion S.M. was a 54-year-old woman suffering fr...

Multiple Structural and Epigenetic Defects in the Human Leukocyte Antigen Class I Antigen Presentation Pathway in a Recurrent Metastatic Melanoma Following Immunotherapy

“…Later, Yabe et al (35) described a large homozygous deletion of exons 4 -7 in TAPBP in PBMC obtained from a patient with type II bare lymphocyte syndrome. More recently, Belicha-Villanueva et al (12) revealed a tapasin-loss phenotype by the M553 melanoma cell line, although its underlying mechanism remains unclear.…”

“…In this regard, Lehmann et al (51) demonstrated that the TAs recognized by the CTLs isolated from recurrent melanoma metastases were different from those recognized by the CTLs isolated from autologous primary lesions. In addition, some of us (14) have shown a shifting of CTL specificity from HLA-A2-MART-1 [27][28][29][30][31][32][33][34][35] complexes to HLA-A2-Tyr 369 -377 complexes in two sequential melanoma metastases with distinct HLA class I abnormalities caused by a mutant ␤ 2 m protein (32). These results are consistent with the possibility that the specificity of a patient's immune response can change in response to changes in the expression of targets by melanoma cells, which have developed immunoescape mechanisms.…”

Immunity to Microbes: Lessons from Primary Immunodeficiencies

“…This contrasts with classical observations of murine models (120) which demonstrate that antiviral defense is ensured by class I-restricted CD8 ϩ T cells. Thus, patients with low levels of expression of MHC-I molecules (transporters associated with antigen processing 1 [TAP-1], TAP-2, and tapasin deficiencies) (47,69,73,115,119), as well as those with low numbers of cytotoxic CD8 ϩ ␣␤ T cells (inherited CD8 deficiency) (28), are not particularly susceptible to viral diseases. Equally surprising, patients with either TAP deficiencies or familial CD8 deficiency due to a mutation in the CD8␣ gene (28,32,45,47).…”

A human PSMB11 variant affects thymoproteasome processing and CD8+ T cell production

“…It is important to point out that this frequency of the homozygotes is overwhelmingly larger than those of extremely rare variations (reported in less than 30 patients worldwide) known to affect MHC class I-dependent generation of CD8 + T cells in humans (23)(24)(25). Those rare variations include the mutations deficient in the peptide transporter complex TAP and TAP-associated protein TAPASIN, in which patients often suffer from respiratory tract infection and skin granulomatous lesions but sometimes exhibit no clinical problems (23)(24)(25). Based on the results of this study, we would like to propose a careful and long-term analysis of health status in those rs34457782 minor allele populations, particularly in homozygotes, that carry the β5t-G49S variant, in hopes of better understanding the role of the thymoproteasome-dependent positive selection of CD8 + T cells in humans.…”

“…The frequency of the 5 homozygotes found in the 9,730 volunteers (0.051%) suggests that the β5t-G49S variation has little or no negative impact on the human populations. It is important to point out that this frequency of the homozygotes is overwhelmingly larger than those of extremely rare variations (reported in less than 30 patients worldwide) known to affect MHC class I-dependent generation of CD8 + T cells in humans (23)(24)(25). Those rare variations include the mutations deficient in the peptide transporter complex TAP and TAP-associated protein TAPASIN, in which patients often suffer from respiratory tract infection and skin granulomatous lesions but sometimes exhibit no clinical problems (23)(24)(25).…”