Lysosomal Storage and Albinism Due to Effects of a De Novo CLCN7 Variant on Lysosomal Acidification.

Optimal lysosome function requires maintenance of an acidic pH maintained by proton pumps in combination with a counterion transporter such as the Cl-/H+ exchanger, CLCN7 (ClC-7), encoded by CLCN7. The role of ClC-7 in maintaining lysosomal pH has been controversial. In this paper, we performed clinical and genetic evaluations of two children of different ethnicities. Both children had delayed myelination and development, organomegaly, and hypopigmentation, but neither had osteopetrosis. Whole-exome and -genome sequencing revealed a de novo c.2144A>G variant in CLCN7 in both affected children. This p.Tyr715Cys variant, located in the C-terminal domain of ClC-7, resulted in increased outward currents when it was heterologously expressed in Xenopus oocytes. Fibroblasts from probands displayed a lysosomal pH approximately 0.2 units lower than that of control cells, and treatment with chloroquine normalized the pH. Primary fibroblasts from both probands also exhibited markedly enlarged intracellular vacuoles; this finding was recapitulated by the overexpression of human p.Tyr715Cys CLCN7 in control fibroblasts, reflecting the dominant, gain-of-function nature of the variant. A mouse harboring the knock-in Clcn7 variant exhibited hypopigmentation, hepatomegaly resulting from abnormal storage, and enlarged vacuoles in cultured fibroblasts. Our results show that p.Tyr715Cys is a gain-of-function CLCN7 variant associated with developmental delay, organomegaly, and hypopigmentation resulting from lysosomal hyperacidity, abnormal storage, and enlarged intracellular vacuoles. Our data supports the hypothesis that the ClC-7 antiporter plays a critical role in maintaining lysosomal pH.

A mouse model of Proteus syndrome.

Proteus syndrome is a mosaic, progressive overgrowth disorder caused by a somatic activating variant c.49G > A p.(E17K) in AKT1. The presentation in affected individuals is variable, with a diversity of tissues demonstrating abnormalities. Common manifestations include skin and bony overgrowth, vascular malformations (VMs), cysts and benign tumors. We used two methods to create mouse models that had endogenously-regulated mosaic expression of the Proteus syndrome variant. Variant allele fractions (VAFs) ranged from 0% to 50% across numerous tissues in 44 Proteus syndrome mice. Mice were phenotypically heterogeneous with lesions rarely observed before 12 months of age. VMs were the most frequent finding with a total of 69 found in 29 of 44 Proteus syndrome mice. Twenty-eight cysts and ectasia, frequently biliary, were seen in 22 of 44 Proteus syndrome mice. Varying levels of mammary hyperplasia were seen in 10 of 16 female Proteus syndrome mice with other localized regions of hyperplasia and stromal expansion noted in several additional animals. Interestingly, 27 of 31 Proteus syndrome animals had non-zero blood VAF that is in contrast to the human disorder where it is rarely seen in peripheral blood. Identification of variant-positive cells by green fluorescent protein (GFP) staining in chimeric Proteus syndrome mice showed that in some lesions, hyperplastic cells were predominantly GFP/Akt1E17K-positive and showed increased pAKT signal compared to GFP-negative cells. However, hyperplastic mammary epithelium was a mixture of GFP/Akt1E17K-positive and negative cells with some GFP/Akt1E17K-negative cells also having increased pAKT signal suggesting that the variant-positive cells can induce lesion formation in a non-cell autonomous manner.

Bi-allelic TMEM94 Truncating Variants Are Associated with Neurodevelopmental Delay, Congenital Heart Defects, and Distinct Facial Dysmorphism.

Neurodevelopmental disorders (NDD) are genetically and phenotypically heterogeneous conditions due to defects in genes involved in development and function of the nervous system. Individuals with NDD, in addition to their primary neurodevelopmental phenotype, may also have accompanying syndromic features that can be very helpful diagnostically especially those with recognizable facial appearance. In this study, we describe ten similarly affected individuals from six unrelated families of different ethnic origins having bi-allelic truncating variants in TMEM94, which encodes for an uncharacterized transmembrane nuclear protein that is highly conserved across mammals. The affected individuals manifested with global developmental delay/intellectual disability, and dysmorphic facial features including triangular face, deep set eyes, broad nasal root and tip and anteverted nostrils, thick arched eye brows, hypertrichosis, pointed chin, and hypertelorism. Birthweight in the upper normal range was observed in most, and all but one had congenital heart defects (CHD). Gene expression analysis in available cells from affected individuals showed reduced expression of TMEM94. Global transcriptome profiling using microarray and RNA sequencing revealed several dysregulated genes essential for cell growth, proliferation and survival that are predicted to have an impact on cardiotoxicity hematological system and neurodevelopment. Loss of Tmem94 in mouse model generated by CRISPR/Cas9 was embryonic lethal and led to craniofacial and cardiac abnormalities and abnormal neuronal migration pattern, suggesting that this gene is important in craniofacial, cardiovascular, and nervous system development. Our study suggests the genetic etiology of a recognizable dysmorphic syndrome with NDD and CHD and highlights the role of TMEM94 in early development.

Impaired hematopoiesis and leukemia development in mice with a conditional knock-in allele of a mutant splicing factor gene U2af1.

Mutations affecting the spliceosomal protein U2AF1 are commonly found in myelodysplastic syndromes (MDS) and secondary acute myeloid leukemia (sAML). We have generated mice that carry Cre-dependent knock-in alleles of U2af1(S34F), the murine version of the most common mutant allele of U2AF1 encountered in human cancers. Cre-mediated recombination in murine hematopoietic lineages caused changes in RNA splicing, as well as multilineage cytopenia, macrocytic anemia, decreased hematopoietic stem and progenitor cells, low-grade dysplasias, and impaired transplantability, but without lifespan shortening or leukemia development. In an attempt to identify U2af1(S34F)-cooperating changes that promote leukemogenesis, we combined U2af1(S34F) with Runx1 deficiency in mice and further treated the mice with a mutagen, N-ethyl-N-nitrosourea (ENU). Overall, 3 of 16 ENU-treated compound transgenic mice developed AML. However, AML did not arise in mice with other genotypes or without ENU treatment. Sequencing DNA from the three AMLs revealed somatic mutations homologous to those considered to be drivers of human AML, including predicted loss- or gain-of-function mutations in Tet2, Gata2, Idh1, and Ikzf1 However, the engineered U2af1(S34F) missense mutation reverted to WT in two of the three AML cases, implying that U2af1(S34F) is dispensable, or even selected against, once leukemia is established.

Prone Team: A Large-Scale Prone Position Initiative During COVID-19 Pandemic.

AIM: To identify strategies to improve time to prone in ICUs during the coronavirus disease 2019 (COVID-19) pandemic for patients meeting the criteria for prone position ventilation. BACKGROUND: Healthcare systems worldwide experienced an influx of COVID-19 patients, especially in critical care. COVID-19 patients are at risk of acute respiratory distress syndrome (ARDS). Prone position ventilation is the standard of care for mechanically ventilated patients with moderate to severe ARDS. Prone maneuvers in and of itself are time-consuming and labor-intensive, posing additional risks to patients. APPROACH: Our academic medical center developed a travel proning team to address the rapid increase in COVID-19 patients with ARDS necessitating prone positioning. EVALUATION: Over a period of 30 days, 420 ICU patients were intubated, 131 had moderate to severe ARDS and underwent prone positioning. Patients were placed in prone position or returned to supine position more than 834 times over 38 days. At the highest point, 37 procedures were done in 24 hours. CONCLUSION: This quality initiative demonstrated that utilization of a traveling proning team provides efficiency in time to prone. Developing a travel prone team allowed for efficiency in time to prone, supported the ICU clinical teams, and enhanced interdisciplinary collaboration, which is essential during times of crisis.

Regulation of erythrocyte Na+/K+/2Cl- cotransport by an oxygen-switched kinase cascade.

Many erythrocyte processes and pathways, including glycolysis, the pentose phosphate pathway (PPP), KCl cotransport, ATP release, Na+/K+-ATPase activity, ankyrin-band 3 interactions, and nitric oxide (NO) release, are regulated by changes in O2 pressure that occur as a red blood cell (RBC) transits between the lungs and tissues. The O2 dependence of glycolysis, PPP, and ankyrin-band 3 interactions (affecting RBC rheology) are controlled by O2-dependent competition between deoxyhemoglobin (deoxyHb), but not oxyhemoglobin (oxyHb), and other proteins for band 3. We undertook the present study to determine whether the O2 dependence of Na+/K+/2Cl- cotransport (catalyzed by Na+/K+/2Cl- cotransporter 1 [NKCC1]) might similarly originate from competition between deoxyHb and a protein involved in NKCC1 regulation for a common binding site on band 3. Using three transgenic mouse strains having mutated deoxyhemoglobin-binding sites on band 3, we found that docking of deoxyhemoglobin at the N terminus of band 3 displaces the protein with no lysine kinase 1 (WNK1) from its overlapping binding site on band 3. This displacement enabled WNK1 to phosphorylate oxidative stress-responsive kinase 1 (OSR1), which, in turn, phosphorylated and activated NKCC1. Under normal solution conditions, the NKCC1 activation increased RBC volume and thereby induced changes in RBC rheology. Because the deoxyhemoglobin-mediated WNK1 displacement from band 3 in this O2 regulation pathway may also occur in the regulation of other O2-regulated ion transporters, we hypothesize that the NKCC1-mediated regulatory mechanism may represent a general pattern of O2 modulation of ion transporters in erythrocytes.

Reversible binding of hemoglobin to band 3 constitutes the molecular switch that mediates O2 regulation of erythrocyte properties.

Functional studies have shown that the oxygenation state of the erythrocyte regulates many important pathways, including glucose metabolism, membrane mechanical stability, and cellular adenosine triphosphate (ATP) release. Deoxyhemoglobin (deoxyHb), but not oxyhemoglobin, binds avidly and reversibly to band 3, the major erythrocyte membrane protein. Because band 3 associates with multiple metabolic, solute transport, signal transduction, and structural proteins, the hypothesis naturally arises that the O2-dependent regulation of erythrocyte properties might be mediated by the reversible association of deoxyHb with band 3. To explore whether the band 3-deoxyHb interaction constitutes a "molecular switch" for regulating erythrocyte biology, we have generated transgenic mice with mutations in the deoxyHb-binding domain of band 3. One strain of mouse contains a "humanized" band 3 in which the N-terminal 45 residues of mouse band 3 are replaced by the homologous sequence from human band 3, including the normal human band 3 deoxyHb-binding site. The second mouse contains the same substitution as the first, except the deoxyHb site on band 3 (residues 12-23) has been deleted. Comparison of these animals with wild-type mice demonstrates that the following erythrocyte properties are controlled by the O2-dependent association of hemoglobin with band 3: (1) assembly of a glycolytic enzyme complex on the erythrocyte membrane which is associated with a shift in glucose metabolism between the pentose phosphate pathway and glycolysis, (2) interaction of ankyrin with band 3 and the concomitant regulation of erythrocyte membrane stability, and (3) release of ATP from the red cell which has been linked to vasodilation.

The COP9 signalosome is vital for timely repair of DNA double-strand breaks.

The DNA damage response is vigorously activated by DNA double-strand breaks (DSBs). The chief mobilizer of the DSB response is the ATM protein kinase. We discovered that the COP9 signalosome (CSN) is a crucial player in the DSB response and an ATM target. CSN is a protein complex that regulates the activity of cullin ring ubiquitin ligase (CRL) complexes by removing the ubiquitin-like protein, NEDD8, from their cullin scaffold. We find that the CSN is physically recruited to DSB sites in a neddylation-dependent manner, and is required for timely repair of DSBs, affecting the balance between the two major DSB repair pathways-nonhomologous end-joining and homologous recombination repair (HRR). The CSN is essential for the processivity of deep end-resection-the initial step in HRR. Cullin 4a (CUL4A) is recruited to DSB sites in a CSN- and neddylation-dependent manner, suggesting that CSN partners with CRL4 in this pathway. Furthermore, we found that ATM-mediated phosphorylation of CSN subunit 3 on S410 is critical for proper DSB repair, and that loss of this phosphorylation site alone is sufficient to cause a DDR deficiency phenotype in the mouse. This novel branch of the DSB response thus significantly affects genome stability.

Disruption of Visc-2, a Brain-Expressed Conserved Long Noncoding RNA, Does Not Elicit an Overt Anatomical or Behavioral Phenotype.

Although long noncoding RNAs (lncRNAs) are proposed to play essential roles in mammalian neurodevelopment, we know little of their functions from their disruption in vivo. Combining evidence for evolutionary constraint and conserved expression data, we previously identified candidate lncRNAs that might play important and conserved roles in brain function. Here, we demonstrate that the sequence and neuronal transcription of lncRNAs transcribed from the previously uncharacterized Visc locus are conserved across diverse mammals. Consequently, one of these lncRNAs, Visc-2, was selected for targeted deletion in the mouse, and knockout animals were subjected to an extremely detailed anatomical and behavioral characterization. Despite a neurodevelopmental expression pattern of Visc-2 that is highly localized to the cortex and sites of neurogenesis, anomalies in neither cytoarchitecture nor neuroproliferation were identified in knockout mice. In addition, no abnormal motor, sensory, anxiety, or cognitive behavioral phenotypes were observed. These results are important because they contribute to a growing body of evidence that lncRNA loci contribute on average far less to brain and biological functions than protein-coding loci. A high-throughput knockout program focussing on lncRNAs, similar to that currently underway for protein-coding genes, will be required to establish the distribution of their organismal functions.

The C-terminus of CBFß-SMMHC is required to induce embryonic hematopoietic defects and leukemogenesis.

The C-terminus of CBFß-SMMHC, the fusion protein produced by a chromosome 16 inversion in acute myeloid leukemia subtype M4Eo, contains domains for self-multimerization and transcriptional repression, both of which have been proposed to be important for leukemogenesis by CBFß-SMMHC. To test the role of the fusion protein's C-terminus in vivo, we generated knock-in mice expressing a C-terminally truncated CBFß-SMMHC (CBFß-SMMHCΔC95). Embryos with a single copy of CBFß-SMMHCΔC95 were viable and showed no defects in hematopoiesis, whereas embryos homozygous for the CBFß-SMMHCΔC95 allele had hematopoietic defects and died in mid-gestation, similar to embryos with a single-copy of the full-length CBFß-SMMHC. Importantly, unlike mice expressing full-length CBFß-SMMHC, none of the mice expressing CBFß-SMMHCΔC95 developed leukemia, even after treatment with a mutagen, although some of the older mice developed a nontransplantable myeloproliferative disease. Our data indicate that the CBFß-SMMHC's C-terminus is essential to induce embryonic hematopoietic defects and leukemogenesis.

A tissue-specific chromatin loop activates the erythroid ankyrin-1 promoter.

The human ankyrin-1 gene (ANK1) contains 3 tissue-specific alternative promoters. We have shown previously that the erythroid-specific ankyrin 1 (ANK1E) core promoter contains a 5' DNase I hypersensitive site (HS) with barrier insulator function that prevents gene silencing in vitro and in vivo. Mutations in the ANK1E barrier region lead to decreased ANK1 mRNA levels and hereditary spherocytosis. In this report, we demonstrate a second ANK1E regulatory element located in an adjacent pair of DNase I HS located 5.6 kb 3' of the ANK1E promoter at the 3' boundary of an erythroid-specific DNase I-sensitive chromatin domain. The 3' regulatory element exhibits enhancer activity in vitro and in transgenic mice, and it has the histone modifications associated with an enhancer element. One of the ANK1E 3'HS contains an NF-E2 binding site that is required for enhancer function. We show that a chromatin loop brings the 3' enhancer and NF-E2 into proximity with the 5' barrier region including the ANK1E core promoter. These observations demonstrate a model for the tissue-specific activation of alternative promoters that may be applicable to the ∼ 30% of mammalian genes with alternative promoters that exhibit distinct expression patterns.

Cbf beta-SMMHC induces distinct abnormal myeloid progenitors able to develop acute myeloid leukemia.

The acute myeloid leukemia (AML)-associated CBF beta-SMMHC fusion protein impairs hematopoietic differentiation and predisposes to leukemic transformation. The mechanism of leukemia progression, however, is poorly understood. In this study, we report a conditional Cbfb-MYH11 knockin mouse model that develops AML with a median latency of 5 months. Cbf beta-SMMHC expression reduced the multilineage repopulation capacity of hematopoietic stem cells (HSCs) while maintaining their numbers under competitive conditions. The fusion protein induced abnormal myeloid progenitors (AMPs) with limited proliferative potential but leukemic predisposition similar to that of HSCs in transplanted mice. In addition, Cbf beta-SMMHC blocked megakaryocytic maturation at the CFU-Meg to megakaryocyte transition. These data show that a leukemia oncoprotein can inhibit differentiation and proliferation while not affecting the maintenance of long-term HSCs.

The MFSD12 p.Tyr182His common variant is sufficient to alter mouse agouti coat color.

MFSD12 functions as a transmembrane protein required for import of cysteine into melanosomes and lysosomes. The MFSD12 locus has been associated with phenotypic variation in skin color across African, Latin American, and East Asian populations. The frequency of a particular MFSD12 coding variant, rs2240751 (MAF = 0.08), has been reported to correlate with solar radiation and occur at highest frequency in Peruvian (PEL MAF = 0.48) and Han Chinese (CHB MAF = 0.40) populations, suggesting it could be causative for associated phenotypic variation in skin color. We have generated a mouse knock-in allele, Mfsd12Y182H , to model the human missense p.Tyr182His human variant. We demonstrate that the variant transcript is stably expressed and that agouti mice homozygote for the variant allele are viable with an altered coat color. This in vivo data confirms that the MFSD12 p.Tyr182His variant functions as a hypomorphic allele sufficient to alter mammalian pigmentation.

The RAD51 S181P mutation shortens lifespan of female mice.

RAD51 is critical to the homologous recombination (HR) pathway that repairs DNA double strand breaks (DSBs) and protects replication forks (RFs). Previously, we showed that the S181P (SP) mutation in RAD51 causes defective RF maintenance but is proficient for DSB repair. Here we report that SP/SP female mice exhibit a shortened lifespan compared to +/+ females but not males. Histological analysis found that most mice in this study died from lymphoma, independent of genotype and sex. We propose that a potential cause for shortened lifespan in SP/SP females is due to the RF defect.

A humanized knock-in Col6a1 mouse recapitulates a deep-intronic splice-activating variant.

Antisense therapeutics such as splice-modulating antisense oligonucleotides (ASOs) are promising tools to treat diseases caused by splice-altering intronic variants. However, their testing in animal models is hampered by the generally poor sequence conservation of the intervening sequences between human and other species. Here we aimed to model in the mouse a recurrent, deep-intronic, splice-activating, COL6A1 variant, associated with a severe form of Collagen VI-related muscular dystrophies (COL6-RDs), for the purpose of testing human-ready antisense therapeutics in vivo. The variant, c.930+189C>T, creates a donor splice site and inserts a 72-nt-long pseudoexon, which, when translated, acts in a dominant-negative manner, but which can be skipped with ASOs. We created a unique humanized mouse allele (designated as "h"), in which a 1.9 kb of the mouse genomic region encoding the amino-terminus (N-) of the triple helical (TH) domain of collagen a1(VI) was swapped for the human orthologous sequence. In addition, we also created an allele that carries the c.930+189C>T variant on the same humanized knock-in sequence (designated as "h+189T"). We show that in both models, the human exons are spliced seamlessly with the mouse exons to generate a chimeric mouse-human collagen a1(VI) protein. In homozygous Col6a1 h+189T/h+189T mice, the pseudoexon is expressed at levels comparable to those observed in heterozygous patients' muscle biopsies. While Col6a1h/h mice do not show any phenotype compared to wildtype animals, Col6a1 h/h+189T and Col6a1 h+189T/h+189T mice have smaller muscle masses and display grip strength deficits detectable as early as 4 weeks of age. The pathogenic h+189T humanized knock-in mouse allele thus recapitulates the pathogenic splicing defects seen in patients' biopsies and allows testing of human-ready precision antisense therapeutics aimed at skipping the pseudoexon. Given that the COL6A1 N-TH region is a hot-spot for COL6-RD variants, the humanized knock-in mouse model can be utilized as a template to introduce other COL6A1 pathogenic variants. This unique humanized mouse model thus represents a valuable tool for the development of antisense therapeutics for COL6-RDs.

Incidence and Risk Factors for New and Recurrent Infarcts in Adults With Sickle Cell Disease.

BACKGROUND: Most adults with sickle cell disease will experience a silent cerebral infarction (SCI) or overt stroke. Identifying patient subgroups with increased stroke incidence is important for future clinical trials focused on stroke prevention. Our 3-center prospective cohort study tested the primary hypothesis that adults with sickle cell disease and SCIs have a greater incidence of new stroke or SCI compared with those without SCI. A secondary aim focused on identifying additional risk factors for progressive infarcts, particularly traditional risk factors for stroke in adults. METHODS AND RESULTS: This observational study included adults with sickle cell disease and no history of stroke. Magnetic resonance imaging scans of the brain completed at baseline and >1 year later were reviewed by 3 radiologists for baseline SCIs and new or progressive infarcts on follow-up magnetic resonance imaging. Stroke risk factors were abstracted from the medical chart. Time-to-event analysis was utilized for progressive infarcts. Median age was 24.1 years; 45.3% of 95 participants had SCIs on baseline magnetic resonance imaging. Progressive infarcts were present in 17 participants (17.9%), and the median follow-up was 2.1 years. Incidence of new infarcts was 11.95 per 100 patient-years (6.17-20.88) versus 3.74 per 100 patient-years (1.21-8.73) in those with versus without prior SCI. Multivariable Cox regression showed that baseline SCI predicts progressive infarcts (hazard ratio, 3.46 [95% CI, 1.05-11.39]; P=0.041); baseline hypertension was also associated with progressive infarcts (hazard ratio, 3.23 [95% CI, 1.16-9.51]; P=0.025). CONCLUSIONS: Selecting individuals with SCIs and hypertension for stroke prevention trials in sickle cell disease may enrich the study population with those at highest risk for infarct recurrence.

Mammalian Mst1 and Mst2 kinases play essential roles in organ size control and tumor suppression.

Control of organ size by cell proliferation and survival is a fundamental developmental process, and its deregulation leads to cancer. However, the molecular mechanism underlying organ size control remains elusive in vertebrates. In Drosophila, the Hippo (Hpo) signaling pathway controls organ size by both restricting cell growth and proliferation and promoting cell death. Here we investigated whether mammals also require the Hpo pathway to control organ size and adult tissue homeostasis. We found that Mst1 and Mst2, the two mouse homologs of the Drosophila Hpo, control the sizes of some, but not all organs, in mice, and Mst1 and Mst2 act as tumor suppressors by restricting cell proliferation and survival. We show that Mst1 and Mst2 play redundant roles, and removal of both resulted in early lethality in mouse embryos. Importantly, tumors developed in the liver with a substantial increase of the stem/progenitor cells by 6 months after removing Mst1 and Mst2 postnatally. We show that Mst1 and Mst2 were required in vivo to control Yap phosphorylation and activity. Interestingly, apoptosis induced by TNFalpha was blocked in the Mst1 and Mst2 double-mutant cells both in vivo and in vitro. As TNFalpha is a pleiotropic inflammatory cytokine affecting most organs by regulating cell proliferation and cell death, resistance to TNFalpha-induced cell death may also contribute significantly to tumor formation in the absence of Mst1 and Mst2.

Runx1-R188Q germ line mutation induces inflammation and predisposition to hematologic malignancies in mice.

Germ line mutations in the RUNX1 gene cause familial platelet disorder (FPD), an inherited disease associated with lifetime risk to hematopoietic malignancies (HM). Patients with FPD frequently show clonal expansion of premalignant cells preceding HM onset. Despite the extensive studies on the role of RUNX1 in hematopoiesis, its function in the premalignant bone marrow (BM) is not well-understood. Here, we characterized the hematopoietic progenitor compartments using a mouse strain carrying an FPD-associated mutation, Runx1R188Q. Immunophenotypic analysis showed an increase in the number of hematopoietic stem and progenitor cells (HSPCs) in the Runx1R188Q/+ mice. However, the comparison of Sca-1 and CD86 markers suggested that Sca-1 expression may result from systemic inflammation. Cytokine profiling confirmed the dysregulation of interferon-response cytokines in the BM. Furthermore, the expression of CD48, another inflammation-response protein, was also increased in Runx1R188Q/+ HSPCs. The DNA-damage response activity of Runx1R188Q/+ hematopoietic progenitor cells was defective in vitro, suggesting that Runx1R188Q may promote genomic instability. The differentiation of long-term repopulating HSCs was reduced in Runx1R188Q/+ recipient mice. Furthermore, we found that Runx1R188Q/+ HSPCs outcompete their wild-type counterparts in bidirectional repopulation assays, and that the genetic makeup of recipient mice did not significantly affect the clonal dynamics under this setting. Finally, we demonstrate that Runx1R188Q predisposes to HM in cooperation with somatic mutations found in FPDHM, using 3 mouse models. These studies establish a novel murine FPDHM model and demonstrate that germ line Runx1 mutations induce a premalignant phenotype marked by BM inflammation, selective expansion capacity, defective DNA-damage response, and predisposition to HM.

Disulfide-linked antibody-maytansinoid conjugates: optimization of in vivo activity by varying the steric hindrance at carbon atoms adjacent to the disulfide linkage.

In this report, we describe the synthesis of a panel of disulfide-linked huC242 (anti-CanAg) antibody maytansinoid conjugates (AMCs), which have varying levels of steric hindrance around the disulfide bond, in order to investigate the relationship between stability to reduction of the disulfide linker and antitumor activity of the conjugate in vivo. The conjugates were first tested for stability to reduction by dithiothreitol in vitro and for plasma stability in CD1 mice. It was found that the conjugates having the more sterically hindered disulfide linkages were more stable to reductive cleavage of the maytansinoid in both settings. When the panel of conjugates was tested for in vivo efficacy in two human colon cancer xenograft models in SCID mice, it was found that the conjugate with intermediate disulfide bond stability having two methyl groups on the maytansinoid side of the disulfide bond and no methyl groups on the linker side of the disulfide bond (huC242-SPDB-DM4) displayed the best efficacy. The ranking of in vivo efficacies of the conjugates was not predicted by their in vitro potencies, since all conjugates were highly active in vitro, including a huC242-SMCC-DM1 conjugate with a noncleavable linkage which showed only marginal activity in vivo. These data suggest that factors in addition to intrinsic conjugate potency and conjugate half-life in plasma influence the magnitude of antitumor activity observed for an AMC in vivo. We provide evidence that bystander killing of neighboring nontargeted tumor cells by diffusible cytotoxic metabolites produced from target cell processing of disulfide-linked antibody-maytansinoid conjugates may be one additional factor contributing to the activity of these conjugates in vivo.

ß+-Thalassemia trait due to a novel mutation in the ß-globin gene promoter: -26 (A>C) [HBB c.-76A>C].

We report the case of a woman with ß(+)-thalassemia (ß(+)-thal) trait, in which there were two sequence variants within the ß-globin gene promoter: -54 (G>A) [HBB c.-104G>A] and -26 (A>C) [HBB c.-76A>C]. Data from other patients indicate that the -54 substitution is a non pathogenic sequence variant. Therefore, the ß-thal phenotype is most likely due to the -26 mutation that is adjacent to the conserved ATAA box.