Bortezomib, a proteasome inhibitor with efficacy in multiple myeloma, is associated with thrombocytopenia, the cause and kinetics of which are different from those of standard cytotoxic agents. We assessed the frequency, kinetics, and mechanism of thrombocytopenia following treatment with bortezomib 1.3 mg/m 2 in 228 patients with relapsed and/or refractory myeloma in 2 phase 2 trials. The mean platelet count decreased by approximately 60% during treatment but recovered rapidly between treatments in a cyclic fashion. Among responders, the pretreatment platelet count increased significantly during subsequent cycles of therapy. The mean percent reduction in platelets was independent of baseline platelet count, M-protein concentration, and marrow plasmacytosis. Plasma thrombopoietin levels inversely correlated with platelet count. Murine studies demonstrated a reduction in peripheral platelet count following a single bortezomib dose without negative effects on megakaryocytic cellularity, ploidy, or morphology. These data suggest that bortezomib-induced thrombocytopenia is due to a reversible effect on megakaryocytic function rather than a direct cytotoxic effect on megakaryocytes or their progenitors. The exact mechanism underlying bortezomib-induced thrombocytopenia remains unknown but it is unlikely to be related to marrow injury or decreased thrombopoietin production. (Blood. 2005; 106:3777-3784)

Abstract The intestinal microbiota in allogeneic bone marrow transplant (allo-BMT) recipients modulates graft-versus-host disease (GVHD), a systemic inflammatory state initiated by donor T cells that leads to colitis, a key determinant of GVHD severity. Indole or indole derivatives produced by tryptophan metabolism in the intestinal microbiota limit intestinal inflammation caused by diverse stressors, so we tested their capacity to protect against GVHD in murine major histocompatibility complex–mismatched models of allo-BMT. Indole effects were assessed by colonization of allo-BMT recipient mice with tryptophanase positive or negative strains of Escherichia coli, or, alternatively, by exogenous administration of indole-3-carboxaldehyde (ICA), an indole derivative. Treatment with ICA limited gut epithelial damage, reduced transepithelial bacterial translocation, and decreased inflammatory cytokine production, reducing GVHD pathology and GVHD mortality, but did not compromise donor T-cell-mediated graft-versus-leukemia responses. ICA treatment also led to recipient-strain-specific tolerance of engrafted T cells. Transcriptional profiling and gene ontology analysis indicated that ICA administration upregulated genes associated with the type I interferon (IFN1) response, which has been shown to protect against radiation-induced intestinal damage and reduce subsequent GVHD pathology. Accordingly, protective effects of ICA following radiation exposure were abrogated in mice lacking IFN1 signaling. Taken together, these data indicate that indole metabolites produced by the intestinal microbiota act via type I IFNs to limit intestinal inflammation and damage associated with myeloablative chemotherapy or radiation exposure and acute GVHD, but preserve antitumor responses, and may provide a therapeutic option for BMT patients at risk for GVHD.

IntroductionDonor T cells are responsible for both GVHD and GVL reactions after allogeneic HSCT. The activation status of T cells is modulated by dendritic cells (DCs), the most potent and professional antigenpresenting cells (APCs). 1,2 Both host and donor DCs have been shown to play critical roles in regulating GVHD and GVL effects after MHC-mismatched HSCT. 3-7 GVHD can be initiated by residual APCs that directly present host antigen (Ag) to donor T cells, 5 whereas GVHD intensity can be modulated by donor APCs that present host Ag to donor T cells via indirect antigen presentation. 1,3,8 However, despite extensive investigations of the role of host DCs on GVHD pathophysiology, much less is known about the mechanisms by which donor APCs activate and regulate donor T cells. A previous study by MacDonald et al 9 demonstrated that depleting CD11c ϩ donor conventional DCs (CDCs) reduced the severity of GVHD in mice. The same group then demonstrated that conventional donor cDCs isolated from the spleen are the most effective population in presenting alloantigen and stimulating naive donor T-cell responses early post-bone marrow transplantation (BMT). 3 Recently, using 2 allogeneic murine BMT models (C57BL/ 63B10.BR and C3H3C57BL/6), we showed that addition of donor bone marrow cells enriched for pre-pDCs to a graft composed of purified HSC and T cells significantly improved long-term leukemia-free survival without increasing GVHD compared with recipients of donor HSC and T cells. 10 Of note, higher numbers of IFN-␥-producing donor T cells were seen among recipients of pDCs. 10 The aim of the present work was to further define the mechanism by which donor pre-pDCs modulate the alloreactivity of donor T cells. Based on the marked up-regulation of IFN-␥ in donor T cells cotransplanted with bone marrow enriched for pre-pDCs, 10,11 we hypothesized that IFN-␥-responsive genes in donor pre-pDCs might be involved in their immunomodulatory activity.Using highly purified populations of donor pre-pDCs, we observed that IFN-␥ signaling by donor T cells to donor pre-pDCs led to increased indoleamine-2,3-dioxygenase (IDO) expression in donor pDCs and that IDO production by donor pDCs suppressed the GVHD activity of donor T cells and changed the balance between regulatory and inflammatory donor T cells. These data support a new paradigm for immune regulation in allogeneic HSCT in which donor DCs first activate donor T cells and then subsequently limit GVHD through IDO-dependent modulation of inflammation. Methods Mice B10.BR (H-2K k ), C57BL/6 (B6, H-2K b ), and FVB (H-2K q ) mice, as well as congenic strains of B6 expressing CD45.1 or CD90.1, and IFN-␥, IFN-␥ receptor, and IDO1 knockout strains on the B6 background (IFN-␥ Ϫ/Ϫ , IFNGR1 Ϫ/Ϫ , and IDO1 Ϫ/Ϫ ), were purchased from The Jackson Laboratory. A congenic strain of B10.BR (H-2K k ) expressing CD90.1, named BA.B10, For personal use only. on May 10, 2018. by guest www.bloodjournal.org From was generated by crossing B6 CD90.1 and B10.BR mice and then backcrossing 10 generatio...

Many tumors exhibit extensive chromosomal instability, but karyotypic alterations will be significant in carcinogenesis only by influencing specific oncogenes or tumor suppressor loci within the affected chromosomal segments. In this investigation, the specificity of chromosomal rearrangements attributable to radiation-induced genomic instability is detailed, and a qualitative and quantitative correspondence with mutagenesis is demonstrated. Chromosomal abnormalities preferentially occurred near the site of prior rearrangements, resulting in complex abnormalities, or near the centromere, resulting in deletion or translocation of the entire chromosome arm, but no case of an interstitial chromosomal deletion was observed. Evidence for chromosomal instability in the progeny of irradiated cells also included clonal karyotypic heterogeneity. The persistence of instability was demonstrated for at least 80 generations by elevated mutation rates at the heterozygous, autosomal marker locus tk. Among those TK- mutants that showed a loss of heterozygosity, a statistically significant increase in mutation rate was observed only for those in which the loss of heterozygosity encompasses the telomeric region. This mutational specificity corresponds with the prevalence of terminal deletions, additions, and translocations, and the absence of interstitial deletions, in karyotypic analysis. Surprisingly, the elevated rate of TK- mutations is also partially attributable to intragenic base substitutions and small deletions, and DNA sequence analysis of some of these mutations is presented. Complex chromosomal abnormalities appear to be the most significant indicators of a high rate of persistent genetic instability which correlates with increased rates of both intragenic and chromosomal-scale mutations at tk.

Imatinib mesylate (Gleevec) inhibits Abl1, c-Kit, and related protein tyrosine kinases (PTKs) and serves as a therapeutic for chronic myelogenous leukemia and gastrointestinal stromal tumors. Imatinib also has efficacy against various pathogens, including pathogenic mycobacteria, where it decreases bacterial load in mice, albeit at doses below those used for treating cancer. We report that imatinib at such low doses unexpectedly induces differentiation of hematopoietic stem cells and progenitors in the bone marrow, augments myelopoiesis but not lymphopoiesis, and increases numbers of myeloid cells in blood and spleen. Whereas progenitor differentiation relies on partial inhibition of c-Kit by imatinib, lineage commitment depends upon inhibition of other PTKs. Thus, imatinib mimics “emergency hematopoiesis,” a physiological innate immune response to infection. Increasing neutrophil numbers by adoptive transfer sufficed to reduce mycobacterial load, and imatinib reduced bacterial load of Franciscella spp., which do not utilize imatinib-sensitive PTKs for pathogenesis. Thus, potentiation of the immune response by imatinib at low doses may facilitate clearance of diverse microbial pathogens.