Lack of common TCRA and TCRB clonotypes in CD8+/TCRαβ+ T-cell large granular lymphocyte leukemia: a review on the role of antigenic selection in the immunopathogenesis of CD8+ T-LGL

Clonal CD8⁺/T-cell receptor (TCR)αβ⁺ T-cell large granular lymphocyte (T-LGL) proliferations constitute the most common subtype of T-LGL leukemia. Although the etiology of T-LGL leukemia is largely unknown, it has been hypothesized that chronic antigenic stimulation contributes to the pathogenesis of this disorder. In the present study, we explored the association between expanded TCR-Vβ and TCR-Vα clonotypes in a cohort of 26 CD8⁺/TCRαβ⁺ T-LGL leukemia patients, in conjunction with the HLA-ABC genotype, to find indications for common antigenic stimuli. In addition, we applied purpose-built sophisticated computational tools for an in-depth evaluation of clustering of TCRβ (TCRB) complementarity determining region 3 (CDR3) amino-acid LGL clonotypes. We observed a lack of clear TCRA and TCRB CDR3 homology in CD8⁺/TCRαβ⁺ T-LGL, with only low level similarity between small numbers of cases. This is in strong contrast to the homology that is seen in CD4⁺/TCRαβ⁺ T-LGL and TCRγδ⁺ T-LGL and thus underlines the idea that the LGL types have different etiopathogenesis. The heterogeneity of clonal CD8⁺/TCRαβ⁺ T-LGL proliferations might in fact suggest that multiple pathogens or autoantigens are involved.     

A regulatory role for the cohesin loader NIPBL in nonhomologous end joining during immunoglobulin class switch recombination

DNA double strand breaks (DSBs) are mainly repaired via homologous recombination (HR) or nonhomologous end joining (NHEJ). These breaks pose severe threats to genome integrity but can also be necessary intermediates of normal cellular processes such as immunoglobulin class switch recombination (CSR). During CSR, DSBs are produced in the G1 phase of the cell cycle and are repaired by the classical NHEJ machinery. By studying B lymphocytes derived from patients with Cornelia de Lange Syndrome, we observed a strong correlation between heterozygous loss-of-function mutations in the gene encoding the cohesin loading protein NIPBL and a shift toward the use of an alternative, microhomology-based end joining during CSR. Furthermore, the early recruitment of 53BP1 to DSBs was reduced in the NIPBL-deficient patient cells. Association of NIPBL deficiency and impaired NHEJ was also observed in a plasmid-based end-joining assay and a yeast model system. Our results suggest that NIPBL plays an important and evolutionarily conserved role in NHEJ, in addition to its canonical function in sister chromatid cohesion and its recently suggested function in HR.DNA double strand breaks (DSBs) pose a severe threat to genome integrity, but can also be a necessary part of normal cellular processes, such as meiosis and Ig class switch recombination (CSR). Depending on cell cycle phase and DSB structure, different strategies are used for repair. Homologous recombination (HR) depends on a homologous DNA template for repair, preferentially the identical sister chromatid, and is therefore mainly active during the S and G2 phases. Nonhomologous end joining (NHEJ), however, is active throughout the cell cycle and is the principal pathway during the G1 phase, when there is no immediate close template for homologous repair. The classical NHEJ pathway requires not only the key components of the NHEJ machinery, i.e., Ku70/Ku80, DNA-PKcs, Artemis, XLF (Cernunnos), XRCC4, and DNA ligase IV, but also several DNA damage sensors or adaptors, such as ATM, γH2AX, 53BP1, MDC1, RNF168, and the Mre11–Rad50–NBS1 complex.Cohesin is an evolutionarily conserved multisubunit complex consisting of a heterodimer of two structural maintenance of chromosomes (SMC) proteins, SMC1A and SMC3, one kleisin protein RAD21 (MCD1 or SCC1) and SA (STAG1/2 or SCC3). The SMC proteins fold back on themselves in the hinge region to form long antiparallel coiled-coil arms, with the amino and carboxyl termini coming together to create head domains that contain ATPases. RAD21 bridges the two head domains to facilitate the formation of the proposed ring-like structure of the complex, and it also interacts with the SA subunit. The cohesin complex ensures correct chromosome segregation through cohesion between sister chromatids (Nasmyth and Haering, 2009). In addition to this canonical role, cohesin and its loading complex NIPBL/MAU2 have also been suggested to be important for regulation of gene expression and repair of DSBs through HR, presumably by facilitating proximity between the broken DNA ends and the repair template (Sjögren and Nasmyth, 2001; Vrouwe et al., 2007; Nasmyth and Haering, 2009). Smc1, the yeast SMC1A orthologue, has furthermore been suggested to coordinate the HR and NHEJ processes (Schär et al., 2004).Cornelia de Lange syndrome (CdLS) is a developmental disorder characterized by growth retardation, severe intellectual disability, gastrointestinal abnormalities, malformations, of the upper limbs and characteristic facial dysmorphisms. Heterozygous loss-of-function mutations in NIPBL, encoding the cohesin loader NIPBL, are the major cause of CdLS (Liu and Baynam, 2010). In addition, mutations in the SMC1A, SMC3, PDS5B, RAD21, and HDAC8 encoding genes, all being part of the cohesion pathway, have been found in selected CdLS patients. The multisystem dysfunctions connected to the syndrome implicate defective gene regulation during fetal development and current evidence suggests that CdLS may be caused by alterations in cohesin chromatin-binding dynamics (Liu et al., 2009). In addition, cell lines established from CdLS patients have an increased sensitivity to DNA damage that has been suggested to be caused by defective HR-mediated repair (Vrouwe et al., 2007).Here, we show an increased DNA damage sensitivity, especially after exposure to γ-rays, in B-lymphoblastoid (LCLs) and fibroblast cell lines (FBs) from NIPBL-deficient CdLS patients. However, we also observed that the majority of the patient and control cells studied were in the G1 phase of the cell cycle, where NHEJ is the principle DSB repair mechanism. We therefore investigated whether defective NHEJ could underlie the DNA damage sensitivity observed in the patient cells.     

The role of extracerebral cholesterol homeostasis and ApoE e4 in cognitive decline

We examined the associations between extracerebral markers of cholesterol homeostasis and cognitive decline over 6 years of follow-up, and studied the modifying effect of apolipoprotein E (ApoE) e4. Data were collected in the Longitudinal Aging Study Amsterdam (n = 967, with longitudinal data on cognition, ages ≥ 65 years) and analyzed using linear mixed models. General cognition (Mini-Mental State Examination; MMSE), memory (Auditory Verbal Learning Test), and information processing speed (Coding task) were measured. The results show that ApoE e4 was a significant effect modifier. Significant associations were found only in ApoE e4 noncarriers (n = 718). We found a nonlinear negative association between the ratio of lanosterol to cholesterol (≤ 189.96 ng/mg), a marker for cholesterol synthesis, and general cognition. Lower cholesterol absorption, i.e., lower ratios of campesterol and sitosterol to cholesterol, as well as a higher rate of cholesterol synthesis relative to absorption were associated with lower information processing speed. In ApoE e4 carriers, the negative association between the ratio of campesterol to cholesterol and memory reached borderline significance. Future research should focus on the interaction between (disturbed) cholesterol homeostasis and ApoE e4 status with respect to dementia.     

Does ovarian hyperstimulation in intrauterine insemination for cervical factor subfertility improve pregnancy rates?

BACKGROUND: Intrauterine insemination (IUI) can be performed with or without controlled ovarian hyperstimulation (COH). Studies in which the additional benefit of COH on IUI for cervical factor subfertility is assessed are lacking. We assessed whether COH in IUI improved pregnancy rates in cervical factor subfertility. METHODS: We performed a historical cohort study among couples with cervical factor subfertility, treated with IUI. A cervical factor was diagnosed by a well-timed, non-progressive post-coital test with normal semen parameters. We compared ongoing pregnancy rate per cycle in groups treated with IUI with or without COH. We tabulated ongoing pregnancy rates per cycle number and compared the effectiveness of COH by stratified univariable analysis. RESULTS: We included 181 couples who underwent 330 cycles without COH and 417 cycles with COH. Ongoing pregnancy rates in IUI cycles without and with COH were 9.7% and 12.7%, respectively (odds ratio 1.4; 95% confidence interval 0.85-2.2). The pregnancy rates in IUI without COH in cycles 1, 2, 3 and 4 were 14%, 11%, 6% and 15%, respectively. For IUI with COH, these rates were 17%, 15%, 14% and 16%, respectively. CONCLUSIONS: Although our data indicate that COH improves the pregnancy rate over IUI without COH, IUI without COH generates acceptable pregnancy rates in couples with cervical factor subfertility. Since IUI without COH bears no increased risk for multiple pregnancy, this treatment should be seriously considered in couples with cervical factor subfertility.     

Different chromosomal breakpoints impact the level of LMO2 expression in T-ALL

The t(11;14)(p13;q11) is presumed to arise from an erroneous T-cell receptor delta TCRD V(D)J recombination and to result in LMO2 activation. However, the mechanisms underlying this translocation and the resulting LMO2 activation are poorly defined. We performed combined in vivo, ex vivo, and in silico analyses on 9 new t(11;14)(p13;q11)-positive T-cell acute lymphoblastic leukemia (T-ALL) as well as normal thymocytes. Our data support the involvement of 2 distinct t(11;14)(p13;q11) V(D)J-related translocation mechanisms. We provide compelling evidence that removal of a negative regulatory element from the LMO2 locus, rather than juxtaposition to the TCRD enhancer, is the main determinant for LMO2 activation in the majority of t(11;14)(p13;q11) translocations. Furthermore, the position of the LMO2 breakpoints in T-ALL in the light of the occurrence of TCRD-LMO2 translocations in normal thymocytes points to a critical role for the exact breakpoint location in determining LMO2 activation levels and the consequent pressure for T-ALL development.