Pten controls B-cell responsiveness and germinal center reaction by regulating the expression of IgD BCR.

In contrast to other B-cell antigen receptor (BCR) classes, the function of IgD BCR on mature B cells remains largely elusive as mature B cells co-express IgM, which is sufficient for development, survival, and activation of B cells. Here, we show that IgD expression is regulated by the forkhead box transcription factor FoxO1, thereby shifting the responsiveness of mature B cells towards recognition of multivalent antigen. FoxO1 is repressed by phosphoinositide 3-kinase (PI3K) signaling and requires the lipid phosphatase Pten for its activation. Consequently, Pten-deficient B cells expressing knock-ins for BCR heavy and light chain genes are unable to upregulate IgD. Furthermore, in the presence of autoantigen, Pten-deficient B cells cannot eliminate the autoreactive BCR specificity by secondary light chain gene recombination. Instead, Pten-deficient B cells downregulate BCR expression and become unresponsive to further BCR-mediated stimulation. Notably, we observed a delayed germinal center (GC) reaction by IgD-deficient B cells after immunization with trinitrophenyl-ovalbumin (TNP-Ova), a commonly used antigen for T-cell-dependent antibody responses. Together, our data suggest that the activation of IgD expression by Pten/FoxO1 results in mature B cells that are selectively responsive to multivalent antigen and are capable of initiating rapid GC reactions and T-cell-dependent antibody responses.

VENTX induces expansion of primitive erythroid cells and contributes to the development of acute myeloid leukemia in mice.

Homeobox genes are key regulators in normal and malignant hematopoiesis. The human Vent-like homeobox gene VENTX, a putative homolog of the Xenopus laevis Xvent-2 gene, was shown to be highly expressed in normal myeloid cells and in patients with acute myeloid leukemia. We now demonstrate that constitutive expression of VENTX suppresses expression of genes responsible for terminal erythroid differentiation in normal CD34+ stem and progenitor cells. Transplantation of bone marrow progenitor cells retrovirally engineered to express VENTX caused massive expansion of primitive erythroid cells and partly acute erythroleukemia in transplanted mice. The leukemogenic potential of VENTX was confirmed in the AML1-ETO transplantation model, as in contrast to AML1-ETO alone co-expression of AML1-ETO and VENTX induced acute myeloid leukemia, partly expressing erythroid markers, in all transplanted mice. VENTX was highly expressed in patients with primary human erythroleukemias and knockdown of VENTX in the erythroleukemic HEL cell line significantly blocked cell growth. In summary, these data indicate that VENTX is able to perturb erythroid differentiation and to contribute to myeloid leukemogenesis when co-expressed with appropriate AML oncogenes and point to its potential significance as a novel therapeutic target in AML.

Single nucleotide polymorphisms of thymidine kinase and DNA polymerase genes in clinical herpes simplex virus type 1 isolates associated with different resistance phenotypes.

The role of mutations in the thymidine kinase (TK, UL23) and DNA polymerase (pol, UL30) genes of herpes simplex virus (HSV) for development of different resistance phenotypes has to be exactly determined before genotypic resistance testing can be implemented in patient's care. Furthermore, the occurrence of cross-resistance is of utmost clinical importance. In this study, clinical HSV-1 isolates obtained between 2004 and 2011 from 26 patients after stem cell transplantation were examined in parallel by phenotypic and genotypic resistance testing. Thirteen isolates, which were phenotypically cross-resistant to acyclovir (ACV), penciclovir (PCV) and brivudin (BVDU), exhibited consistently frameshift or non-synonymous mutations in the TK gene known to confer resistance. One of these mutations (insertion of C at the nucleotide positions 1061-1065) has not been described before. Seven strains, phenotypically resistant to ACV and PCV and, except one each, sensitive to BVDU and resistant to foscarnet (FOS), carried uniformly resistance-related substitutions in the DNA pol gene. Finally, 3 isolates, resistant to ACV, PCV and 2 out of these also resistant to BVDU, had known but also unclear substitutions in the TK and DNA pol genes, and 3 isolates were completely sensitive. In conclusion, clinical ACV-resistant HSV-1 isolates, carrying resistance-associated mutations in the TK gene, can be regarded as cross-resistant to other nucleoside analogs such as BVDU. In contrast, clinical FOS-resistant HSV-1 strains which are cross-resistant to ACV may be sensitive to BVDU. This has to be considered for drug changes in antiviral treatment in case of ACV resistance.

Fast selection of maribavir resistant cytomegalovirus in a bone marrow transplant recipient.

BACKGROUND: Human cytomegalovirus infections are still significant causes of morbidity and mortality in transplant recipients. The use of antiviral agents is limited by toxicity and evolving resistance in immunocompromised patients with ongoing viral replication during therapy. Here, we present the first documented case of genotypic resistance against maribavir in a bone marrow transplant (BMT) recipient. CASE PRESENTATION: The female 13-year-old patient was suffering from a refractory cytopenia. Ganciclovir, foscarnet, cidofovir, leflunomide and maribavir, an inhibitor of the cytomegalovirus UL97 protein, were administered to treat a therapy-resistant cytomegalovirus infection. Viral mutations conferring resistance against nucleotide and pyrophosphate analogs as well as maribavir (MBV) have evolved sequentially. Particularly, impressive was the fast emergence of multiple mutations T409M, H411Y and H411N conferring maribavir resistance after less than 6 weeks. CONCLUSION: We describe the fast emergence of cytomegalovirus variants with different maribavir resistance associated mutations in a bone marrow transplant recipient treated with MBV 400 mg p.o. twice per day. The results suggest that a high virus load permitted a selection of several but distinct therapy-resistant HCMV mutants. Since a phase II study with MBV is intended for the treatment of resistant or refractory HCMV infections in transplant recipients this has to be kept in mind in patients with high viral loads during therapy (NCT01611974).