Polyomavirus BK-specific cellular immune response in Kidney transplant recipients

Polyomavirus BK is an emerging pathogen in KT recipients. New potent immunosuppressive drugs promote reactivation and replication of BKV and progression towards PVAN. PVAN occurs in up to 10% of the KT recipients with a graft loss in up to 80% of the cases. New potent immunosuppressive drugs, as MMF) and FK506 are risk factors for developing PVAN. As no proven antiviral drugs are available, the only therapy of choice is the reduction of immunosuppressiva in order to regain BKV-replication control (H. H. Hirsch, M. Dickenmann, S. Binggeli, J. Steiger, Schweiz Med Forum 2004; 4:538–541). BKV-specific cellular and humoral immune response is not well characterized. Recent findings have shown that BKV-seropositive patients prior to transplantation are not protected from BKV-replication. In contrast, BKV-specific cellular immune response correlates with the diagnosis of PVAN (P. Comoli, S. Binggeli, F. Ginevri, H. H. Hirsch, Transplant Infectious Disease Jun 2006; 8(2):86-94, Review). The aim of this study was to investigate the interplay of BKV-specific immune response and BKV-replication in blood samples of KT recipients. We examined the BKV-specific immune response by ELISpot assay in KT. PBMC of KT recipients were stimulated with BKV LT-antigen and BKV-VP1 peptide libraries. The BKV-specific immune response was measured by the detection of IFN-γ by ELISpot assay. From the results of a pilot study with eight patients we were able to deduce that the dynamics of viral-replication rather than the viral load correlates with a protective immune response (S. Binggeli, A. Egli, M. Dickenmann, I. Binet, J. Steiger, H. H. Hirsch, American Journal of Transplantation, Sep 2006; 6(9):2218-9). To corroborate this previous observation the BKV-specific cellular immunity in 42 KT recipients and 10 HB were tested. The KT patients were divided into two groups: patient group 1 with an increasing or stable viral load (inc/hi)1 and patient group 2 with a decreasing viral load or after resolved PVAN (dec)2. Indeed patients in group 2 showed a significantly higher immune response upon stimulation with BKV-LT and BKV-VP1 than patients in group 1 (P=0.003, P=0.001, respectively, Wilcoxon, two-sided). Detailed analysis revealed a cut-off of >69 SFU/Mio PBMC for BKV LT-antigen, but not for BKV VP1, with significantly more KT patients from group 2 (dec) than from group 1 (inc/hi). This cut-off has to be validated in a prospective study and also analyzed whether such a cut-off can be used for immunosuppressive reduction guidance. BKV-specific cell expansion was tested in a short-term culture in the presence of either BKV-LT or -VP1. After 9-day culture, PBMC were restimulated with BKV-LT or -VP1 and the responses were then compared with responses to direct stimulation (without prior cultivation). BKV-LT and -VP1 specific cellular immune responses were significantly higher after 9-day cultivation than after direct stimulation (P=0.002, P=0.003, respectively, Wilcoxon, two sided). Due to high sequence homology between JCV and BKV, JCV-LT and -VP1 overlapping peptide pools were used to test PBMC-cross recognition. JCV-LT and -VP1 responses were significantly lower than BKV-mediated response (P=0.008, P<0.001, respectively, Wilcoxon, two-sided). Comparison of JCV- and BKV-specific responses after 9-day culture revealed that the BKV-VP1 response was significantly higher than the JCV-VP1 (P=0.016, Wilcoxon, two sided), but no significant difference was observed for LT-antigen (S. Binggeli, A. Egli, S. Schaub, I. Binet, M. Mayr, J. Steiger, H. H. Hirsch, American Journal of Transplantation, Mar 2007; 7:1-9). Agnoprotein, a late viral protein, is highly expressed upon infection. We investigated whether agnoprotein is able to induce a BKV-specific immune response and whether it may serve as a diagnostic marker. Immunostaining revealed that agnoprotein was highly expressed in the cytoplasm of infected cells and was only seen in combination with BKV-LT which is located in the nucleus. Interestingly, BKV-agnoprotein specific cellular and humoral immune responses were scarcely detected in HB or KT recipients. There are only few published studies concerning BKV-agnoprotein, and further investigations are necessary to fully understand the function of agnoprotein during infection. (D. Leuenberger, P. A. Andresen, R. Gosert, S. Binggeli, E. H. Ström, S. Bodaghi, C Hanssen Rinaldo, H. H. Hirsch, Clinical and Vaccine Immunology, Aug 2007; 14(8): 959-968). As no antiviral treatment is available for BKV, the only therapy is the reduction of immunosuppressive drugs in order to regain immunological control over BKV-replication and PVAN. However reduction of immunosuppressants upon PVAN diagnosis bears the risk of rejection or inflammatory response to BKV. It is difficult to distinguish between these two outcomes because specific markers are yet lacking. Therefore, it is pivotal to record the clinico-pathological course of the KT patient in order to correctly diagnose the problem as the therapies are completely different. Measuring the BKV-specific cellular immune response may support and complement other markers, such as PCR analysis and biopsies, to better distinguish between rejection and BKV-specific immune response. (S. Schaub, M. Mayr, A. Egli, S. Binggeli, B. Descoeudres, J. Steiger, M. J. Mihatsch, H. H. Hirsch, Nephrology Dialysis Transplantation, Aug 2007; 22(8): 2386-90). Finding the optimal immunosuppressive drug level is crucial for preventing rejection (under-immunosuppressed) and viral replication (over-immunosuppressed). Our current study showed a cut-off level of 6.65 ng/ml FK506 drug level in blood, dividing those KT patients with and without BKV-replication control (ROC-curve: AUC=0.897, sensitivity=78%, specificity=86%). If this cut-off is validated by a well designed prospective study, it may serve as a guideline to administrate the optimal drug level. (S. Binggeli, 2007, current results). BKV-specific epitopes have received considerable attention in the last five years. We started with the epitope mapping in a kidney patient with the most common HLA-type: HLAA* 01, HLA-B*08. First screening of BKV-LT revealed ten 15aa long peptides with immunogenic potential. Three of these ten peptides were further investigated for crossrecognition with the homologous JCV-peptides. Even though response to the three JCVpeptides was lower, cellular immune response could be clearly detected. It needs further investigation to find more BKV-specific epitopes and also to test the ability of CD8+ T-cells to kill BKV-antigen presenting cells. (S. Binggeli, 2007, current results)

Cytomegalovirus and polyomavirus BK posttransplant

Virus replication and progression to disease in transplant patients is determined by patient-, graft- and virus-specific factors. This complex interaction is modulated by the net state of immunosuppression and its impact on virus-specific cellular immunity. Due to the increasing potency of immunosuppressive regimens, graft rejections have decreased, but susceptibility to infections has increased. Therefore, cytomegalovirus (CMV) remains the most important viral pathogen posttransplant despite availability of effective antiviral drugs and validated strategies for prophylactic, preemptive and therapeutic intervention. CMV replication can affect almost every organ system, with frequent recurrences and increasing rates of antiviral resistance. Together with indirect long-term effects, CMV significantly reduces graft and patient survival after solid organ and hematopoietic stem cell transplantation. The human polyomavirus called BK virus (BKV), on the other hand, only recently surfaced as pathogen with organ tropism largely limited to the reno-urinary tract, manifesting as polyomavirus-associated nephropathy in kidney transplant and hemorrhagic cystitis in hematopoetic stem cell transplant patients. No licensed anti-polyoma viral drugs are available, and treatment relies mainly on improving immune functions to regain control over BKV replication. In this review, we discuss diagnostic and therapeutic aspects of CMV and BKV replication and disease posttransplantatio

Cytomegalovirus-specific T-cell responses and viral replication in kidney transplant recipients

<p>Abstract</p> <p>Background</p> <p>Cytomegalovirus (CMV) seronegative recipients (R-) of kidney transplants (KT) from seropositive donors (D+) are at higher risk for CMV replication and ganciclovir(GCV)-resistance than CMV R(+). We hypothesized that low CMV-specific T-cell responses are associated with increased risk of CMV replication in R(+)-patients with D(+) or D(-) donors.</p> <p>Methods</p> <p>We prospectively evaluated 73 consecutive KT-patients [48 R(+), 25 D(+)R(-)] undergoing routine testing for CMV replication as part of a preemptive strategy. We compared CMV-specific interferon-γ (IFN-γ) responses of CD4+CD3+ lymphocytes in peripheral blood mononuclear cells (PBMC) using three different antigen preparation (CMV-lysate, pp72- and pp65-overlapping peptide pools) using intracellular cytokine staining and flow cytometry.</p> <p>Results</p> <p>Median CD4+ and CD8+T-cell responses to CMV-lysate, pp72- and pp65-overlapping peptide pools were lower in D(+)R(-) than in R(+)patients or in non-immunosuppressed donors. Comparing subpopulations we found that CMV-lysate favored CD4+- over CD8+-responses, whereas the reverse was observed for pp72, while pp65-CD4+- and -CD8+-responses were similar. Concurrent CMV replication in R(+)-patients was associated with significantly lower T-cell responses (pp65 median CD4+ 0.00% vs. 0.03%, p = 0.001; CD8+ 0.01% vs. 0.03%; p = 0.033). Receiver operated curve analysis associated CMV-pp65 CD4+ responses of > 0.03% in R(+)-patients with absence of concurrent (p = 0.003) and future CMV replication in the following 8 weeks (p = 0.036). GCV-resistant CMV replication occurred in 3 R(+)-patients (6.3%) with pp65- CD4+ frequencies < 0.03% (p = 0.041).</p> <p>Conclusion</p> <p>The data suggest that pp65-specific CD4+ T-cells might be useful to identify R(+)-patients at increased risk of CMV replication. Provided further corroborating evidence, CMV-pp65 CD4+ responses above 0.03% in PBMCs of KT patients under stable immunosuppression are associated with lower risk of concurrent and future CMV replication during the following 8 weeks.</p

Dwarf galaxy populations in present-day galaxy clusters: I. Abundances and red fractions

We compare the galaxy population in the Virgo, Fornax, Coma and Perseus cluster to a state-of-the-art semi-analytic model, focusing on the regime of dwarf galaxies with luminosities from approximately 10^8 L_sun to 10^9 L_sun. We find that the number density profiles of dwarfs in observed clusters are reproduced reasonably well, and that the red fractions of model clusters provide a good match to Coma and Perseus. On the other hand, the red fraction among dwarf galaxies in Virgo is clearly lower than in model clusters. We argue that this is mainly caused by the treatment of environmental effects in the model. This explanation is supported by our finding that the colours of central ("field") dwarf galaxies are reproduced well, in contrast to previous claims. Finally, we find that the dwarf-to-giant ratio in model clusters is too high. This may indicate that the current model prescription for tidal disruption of faint galaxies is still not efficient enough.Comment: 20 pages, 10 figures. Accepted by MNRAS. Includes the modifications after referee report. Main results unchanged, interpretation slightly change

L'art suisse à Zurich

"Une petite nationale" au Kunsthaus de Zurich. Hodler, Vautier, Blanchet, Vallet, etc

From dwarf spheroidals to cDs: Simulating the galaxy population in a LCDM cosmology

We apply updated semi-analytic galaxy formation models simultaneously to the stored halo/subhalo merger trees of the Millennium and Millennium-II simulations. These differ by a factor of 125 in mass resolution, allowing explicit testing of resolution effects on predicted galaxy properties. We have revised the treatments of the transition between the rapid infall and cooling flow regimes of gas accretion, of the sizes of bulges and of gaseous and stellar disks, of supernova feedback, of the transition between central and satellite status as galaxies fall into larger systems, and of gas and star stripping once they become satellites. Plausible values of efficiency and scaling parameters yield an excellent fit not only to the observed abundance of low-redshift galaxies over 5 orders of magnitude in stellar mass and 9 magnitudes in luminosity, but also to the observed abundance of Milky Way satellites. This suggests that reionisation effects may not be needed to solve the "missing satellite" problem except, perhaps, for the faintest objects. The same model matches the observed large-scale clustering of galaxies as a function of stellar mass and colour. The fit remains excellent down to ~30kpc for massive galaxies. For M* < 6 x 10^10Msun, however, the model overpredicts clustering at scales below 1 Mpc, suggesting that the sigma_8 adopted in the simulations (0.9) is too high. Galaxy distributions within rich clusters agree between the simulations and match those observed, but only if galaxies without dark matter subhalos (so-called orphans) are included. Our model predicts a larger passive fraction among low-mass galaxies than is observed, as well as an overabundance of ~10^10Msun galaxies beyond z~0.6, reflecting deficiencies in the way star-formation rates are modelled.Comment: Accepted for publication in MNRAS. SQL databases containing the full galaxy data at all redshifts and for both the Millennium and Millennium-II simulations are publicly released at http://www.mpa-garching.mpg.de/millenniu

The first generation of Virgo cluster dwarf elliptical galaxies?

Original article can be found at: http://www.iop.org/EJ/journal/apjl Copyright American Astronomical Society DOI: 10.1088/0004-637X/706/1/L124 [Full text of this article is not available in the UHRA]In the light of the question whether most early-type dwarf (dE) galaxies in clusters formed through infall and transformation of late-type progenitors, we search for an imprint of such an infall history in the oldest, most centrally concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no signatures of disks or central residual star formation. We select dEs in a (projected) region around the central elliptical galaxies, and subdivide them by their line-of-sight velocity into fast-moving and slow-moving ones. These subsamples turn out to have significantly different shapes: while the fast dEs are relatively flat objects, the slow dEs are nearly round. Likewise, when subdividing the central dEs by their projected axial ratio into flat and round ones, their distributions of line-of-sight velocities differ significantly: the flat dEs have a broad, possibly two-peaked distribution, whereas the round dEs show a narrow single peak. We conclude that the round dEs probably are on circularized orbits, while the flat dEs are still on more eccentric or radial orbits typical for an infalling population. In this picture, the round dEs would have resided in the cluster already for a long time, or would even be a cluster-born species, explaining their nearly circular orbits. They would thus be the first generation of Virgo cluster dEs. Their shape could be caused by dynamical heating through repeated tidal interactions. Further investigations through stellar population measurements and studies of simulated galaxy clusters would be desirable to obtain definite conclusions on their origin.Peer reviewe

Human Polyomavirus Type 1 (BK Virus) Agnoprotein Is Abundantly Expressed but Immunologically Ignored▿

Impaired BK virus (BKV)-specific immunity is a key risk factor of polyomavirus-associated nephropathy. We hypothesized that BKV agnoprotein might constitute an important immune target, as it is highly expressed after infection in vitro. We demonstrate abundant expression of BKV agnoprotein in vivo by immunostaining of kidney transplant (KT) biopsy specimens. Antibody responses to the recombinant affinity-purified BKV agnoprotein, large tumor (LT), and VP1 antigens in 146 sera from 38 KT patients and in 19 sera from 16 healthy donors (HD) were compared by enzyme immunoassay. In HD, low titers of anti-agnoprotein immunoglobulin G (IgG) were found in 15% of sera, compared to 41% for anti-LT antigen and 63% for anti-VP1. No anti-BKV IgM was detectable. In KT patients, anti-agnoprotein IgG and IgM were found in 8% and 3.6% of sera, compared to 63% and 18% for anti-LT IgG and IgM and 80% and 41% for anti-VP1 IgG and IgM, respectively. Anti-LT antigen and anti-VP1, but not anti-agnoprotein, activities increased during and after BKV viremia in KT patients. To investigate specific cellular immune responses, we compared levels of gamma interferon production in peripheral blood mononuclear cells (PBMC) of 10 HD and 30 KT patients by enzyme-linked immunospot assay. In HD, the median numbers of gamma interferon spot-forming units per million PBMC for the agnoprotein, LT antigen, and VP1 peptides were 1, 23, and 25, respectively, whereas the responses in KT patients were 2, 24, and 99, respectively. We conclude that BKV agnoprotein, though abundantly expressed in vivo, is poorly recognized immunologically