ALBERT

Description: Most conventional methods to sensitively quantify tumor cell proliferation and viability in vitro involve processing of cells in ways that preclude continuation of the respective experiment or prevent the longitudinal collection of data. This common technical feature of conventional assays limits their ability to provide detailed insight into the kinetics of tumor cell responses to treatment(s). Additionally, these limitations hinder the use of these assays to monitor how the kinetics of treatment response can be altered by nonmalignant "accessory" cells of the tumor microenvironment (e.g. bone marrow stromal cells [BMSCs] for hematologic malignancies or bone metastases of solid tumors). To address these obstacles, we modified our previously developed tumor cell compartment-specific bioluminescence imaging (CS-BLI) platform (McMillin et al. Nat Med. 2010), to enable longitudinal assessment of tumor cell response to diverse experimental conditions; we cultured luciferase-expressing tumor cells, with or without stromal cells, in the presence of bioluminescent substrates, using optimized conditions which provide detectable bioluminescent signal even after several days of culture, while having no adverse effect on the viability of tumor or non-malignant cells in this system. This modified approach (time-lapse CSBLI, [TL-CSBLI]) preserved the linear correlation of bioluminescent signal with tumor cell viability. Furthermore, results obtained at the end of the experiment and during interim time-points are consistent with those generated using either non-time-lapse applications of CS-BLI or conventional techniques. We applied TL-CSBLI to delineate, in high-throughput manner, the temporal dynamics of the responses of tumor cells (e.g. multiple myeloma (MM) and other hematologic malignancies) to diverse treatments (e.g. conventional chemotherapeutics, glucocorticoids; proteasome inhibitors (PIs, bortezomib or carfilzomib), and kinase inhibitors). Using the time-lapse capabilities of this assay, we evaluated tumor cell responses in the presence vs. absence of stromal cells. We observed that the kinetics of tumor cell response to diverse therapeutic classes are heterogeneous, even within the same tumor type: for instance, tumor cells with pronounced responses at the end of drug incubation (e.g. 24, 48, 72, hrs after initiation of treatment with PIs, DNA-damaging chemotherapeutics, or dexamethasone respectively), can have different magnitude of responses at intermediate time points. This suggests that TL-CSBLI data can further stratify treatment-responsive tumor cells into those with early vs. late kinetics of response. We also observed that the kinetics of the proliferative / anti-apoptotic effect conferred by stromal cells on tumor cells are highly variable between different cell lines, even within the same tumor type. For instance, the time between initiation of coculture and maximum stimulation of tumor cell viability by stromal cells was variable between cell lines and did not correlate with the magnitude of stimulation by stromal cells. Importantly, TL-CSBLI identified that the response of diverse types of tumor cells to treatments can be delayed in the presence of stromal cells, compared to conventional tumor cell monocultures: this initial delay in treatment response of tumor cells in stromal co-cultures may be observed even in cases where similar cytoreductive responses are eventually observed at later time-points in both the presence and absence of stromal cells. This observation suggests that a more expansive definition of stroma-induced resistance to a given treatment may be warranted, to specifically incorporate the ability of stromal cells to delay the tumor cell response to such treatment. In summary, TL-CSBLI enables detailed characterization of the kinetics of tumor cell responses to diverse experimental conditions. Its use can provide insight into the underappreciated impact that cell-autonomous variations or stroma-induced changes in the kinetics of tumor cell response to a given anti-tumor therapy can have on determining its efficacy. This is particularly consequential for agents (e.g. PIs) which have clinical pharmacokinetic profiles associated with transient peak exposure. Disclosures McMillin: Axios Biosciences: Equity Ownership; DFCI: patent submission on stromal co-culture technologies Patents & Royalties. Negri:DFCI: patent submission on stromal co-culture technologies Patents & Royalties. Mitsiades:Johnson & Johnson: Research Funding; Amgen: Research Funding; Celgene: Consultancy, Honoraria; Millennium Pharmaceuticals: Consultancy, Honoraria; DFCI: patent submission on stromal co-culture technologies Patents & Royalties.

Description: Abstract 1838 Introduction: Graft-versus-myeloma (GvM) effect following allogeneic stem cell transplantation (allo-SCT) is well established and often accompanied by graft-versus-host disease (GVHD). Unfortunately, most patients still relapse following allo-SCT, underscoring the need for new transplant strategies. Interestingly, studies evaluating the proteasome inhibitor bortezomib combined with donor lymphocyte infusions (DLI) in myeloma patients suggest enhanced efficacy of the combination. In contrast, other reports demonstrate that bortezomib has activity in preventing GVHD in various malignancies, including myeloma. Here, we investigate the effects of bortezomib on T cell-mediated myeloma cell killing in vitro. Methods: Tumor cell compartment-specific bioluminescence imaging (CS-BLI) technology was used to monitor the cytotoxic effects of T cells on myeloma cells in the presence or absence of antimyeloma agents. To this end, myeloma cell lines were stably transduced with a firefly luciferase construct. Two different T cell clones were used: 1) the alloreactive CD8+-T cell clone allo-A2, which kills all HLA-A2-positive cells, including the myeloma cell line U266; and 2) the CD4+ T-cell clone 3AB11, generated from a myeloma patient with clinical GvM/GVHD after allo-SCT. 3AB11 cells recognize a hematopoietically restricted minor antigen, also presented by the myeloma cell line UM9. Protein expression was determined by western blot analysis. Results: The CD4+-T cell clone 3AB11 and the allo-A2 specific CD8+- T cell clone displayed a time- and dose-dependent lysis of myeloma cell lines UM9 and U266, respectively. Concurrent treatment of myeloma cells with the T cell clones and bortezomib resulted in synergistic enhancement of myeloma cell death, compared to T cells alone or bortezomib alone. This synergism was observed at 24, 48, and 72 hours (but not after 4 hours) of co-treatment. Dexamethasone, which significantly inhibited myeloma cell death induced by T cells, functioned as control. When myeloma cells were treated for 12 hours with bortezomib and then extensively washed, there was still enhancement of T cell-mediated killing. However, pre-incubation of T cells with bortezomib significantly impaired their ability to induce myeloma cell lysis. These washout experiments indicate that bortezomib sensitizes myeloma cells to T cell-mediated killing, but does not enhance the intrinsic cytotoxic activity of T cells. Mechanistic studies demonstrated that antibodies blocking FAS ligand partially impaired myeloma cell lysis by 3AB11 and allo-A2 clones. More interestingly, however, blockade of FAS/FAS ligand interactions completely abrogated the synergism between bortezomib and T cells. Antibodies against TRAIL had no such effects. Furthermore, western blot analyses revealed that in UM9 and U266 cells bortezomib reduced protein levels of FLICE inhibitory protein (cFLIP), which is a potent inhibitor of FAS ligand-induced apoptosis. These results support the idea that bortezomib enhances the sensitivity of myeloma cells toward T cell-mediated lysis by restoring apoptosis signaling via the FAS/FAS ligand pathway. Conclusion: Proteasome inhibition sensitizes myeloma cells to T cell-mediated killing via a FAS/FAS ligand-dependent mechanism. Conversely, bortezomib impairs T cell function. However, the net effect is a synergistic killing of myeloma cells when T cells and bortezomib are combined. These data support further exploration of the use of bortezomib in preclinical models, with derived clinical trials in the allogeneic setting (e.g. in combination with DLI or following allo-SCT) or in the autologous setting (e.g. in combination with a tumor vaccine) potentially warranted. (CSM and TM are joint senior authors) Disclosures: van de Donk: Celgene: Research Funding. Lokhorst:Celgene: Research Funding; Jansen-Cilag: Research Funding. Hayes:Pfizer: Research Funding; Amgen: Research Funding. Munshi:Celgene: Consultancy; Millenium: Consultancy; Novartis: Consultancy; Onyx: Consultancy. Richardson:Millennium:; Celgene:; Johnson & Johnson:; Novartis:; Bristol Myers Squibb:. Anderson:Celgene: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees; Onyx: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Acetylon: Membership on an entity's Board of Directors or advisory committees. Mitsiades:Millennium Pharmaceuticals: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Novartis Pharmaceuticals: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Merck: Consultancy, Honoraria; Kosan: Consultancy, Honoraria; Pharmion: Consultancy, Honoraria; Centocor: Consultancy, Honoraria; Amnis Therapeutics: Consultancy, Honoraria; PharmaMar: Licencing royalties; OSI Pharmaceuticals: Research Funding; Amgen: Research Funding; AVEO Pharma: Research Funding; EMD Serono: Research Funding; Sunesis: Research Funding; Gloucester Pharmaceuticals: Research Funding; Genzyme: Research Funding; Johnson & Johnson: Research Funding.

Description: Extensive preclinical studies of several groups using tumor cells co-cultured with bone marrow stromal cells (BMSCs) has documented that the potent anti-MM activity of the proteasome inhibitor bortezomib is not suppressed by BMSCs (e.g. primary and immortalized BMSCs). Using our compartment-specific bioluminescence imaging (CS-BLI) assays, we extended these observations to larger panels of MM cell lines. We observed, however, a recurrent pattern that primary CD138+ MM tumor cells from bortezomib-refractory patients recurrently exhibited substantial in vitro response to clinically-achievable concentrations and durations of bortezomib treatment. To simulate this clinicopathological observation, MM.1R-Luc+ cells were injected i.v. in SCID-beige mice and treated with bortezomib (0.5 mg/kg s.c. twice weekly for 5 weeks): diffuse MM tumors initially responded to bortezomib, but eventually became refractory. These in vivo-resistant MM cells were isolated from the mice and were treated in vitro with bortezomib, exhibiteing similar responsinveness to this agent as their isogenic bortezomib-naive MM cells, To further address the possibility that this represents a previously underexplored form of a microenvironment-induced alteration in bortezomib responsiveness, we studied how MM cells respond to pharmacological proteasome inhibition after variable times of co-culture with BMSCs prior to bortezomib exposure. We observed that prolonged tumor-stromal co-culture (48-96hrs) prior to initiation of bortezomib treatment did not affect drug sensitivity for many of the MM cell lines (OPM2, H929, UM9, KMS11, KMS18 and RPMI-8226) tested. Notably, prolonged co-cultures with BMSCs prior to bortezomib treatment enhanced the activity of this agent for other MM cell lines (e.g. OPM1, Dox40, OCI-My5, KMS12BM or KMS18). However, MM.1S and MM.1R cells, when exposed to extended co-cultures with BMSCs prior to initiation of drug exposure, exhibited significant attenuation (2-3 fold increase of IC50 values) of their response to bortezomib in several independent replicate experiments. In support of these in vitro results, heterotypic s.c. xenografts of Luc+ MM.1S cells co-implanted with Luc-negative BMSCs did not show significant reduction in MM tumor growth with bortezomib treatment (0.5 mg/kg s.c. twice weekly for 5 weeks) compared to vehicle-treated controls (p=0.13), as quantified by bioluminescence imaging. In co-cultures with BMSCs, MM.1S and MM.1R cells also exhibited suppression of their response to carfilzomib (the degree of this stroma-induced resistance was more pronounced that in the case of bortezomib for these 2 cell lines). Consistent with these observations, in vivo administration of carfilzomib in the orthotopic model of diffuse bone lesions of MM.1R-Luc+ cells was associated with less pronounced reduction in tumor growth, compared to bortezomib treatment (p

Description: Abstract 2468 In multiple myeloma (MM) and other hematologic malignancies, bone marrow stromal cells (BMSCs) confer resistance to diverse conventional or investigational therapeutics. During the last decade, data from many groups have concurred that the in vitro anti-MM activity of the proteasome inhibitor bortezomib is very similar in the presence and absence of BMSCs, including primary and immortalized BMSCs. These well-validated observations have supported the notion that novel, more effective, therapies for the treatment of MM should ideally be, similarly to bortezomib, capable of overcoming the protective effect of BMSCs. Interestingly, however, we have observed that primary CD138+ MM tumor cells isolated from patients with clinical refractoriness to bortezomib occasionally exhibit substantial in vitro response to clinically achievable concentrations of this drug. We therefore hypothesized that, under certain previously under-explored experimental settings, BMSCs may alter the threshold of MM cell response to bortezomib-induced apoptosis. To address this hypothesis in conditions that better simulate the clinical context, we conducted compartment-specific bioluminescence imaging (CS-BLI) assays to evaluate the effect of bortezomib on tumor cells co-cultured with BMSCs for different time periods prior to bortezomib administration. We observed that prolonged tumor-stromal co-culture (48–96hrs) prior to initiation of bortezomib treatment did not affect drug sensitivity for several MM cell lines (OPM2, H929, UM9, KMS11, KMS18 and RPMI-8226) tested. Prolonged co-culture of OPM1, RPMI-8226-Dox40, OCI-My5, KMS12BM and KMS18 cells prior to bortezomib treatment enhanced its activity. Importantly, extended co-culture of MM cell lines MM.1S and MM.1R with BMSCs prior to drug treatment induced significant attenuation of their response to bortezomib, as evidenced by 2–3 fold increase of IC50 values in several independent replicate experiments and a mean % area under the bortezomib dose response curve (AUC) of 5.82% vs 14.10% in the absence vs. presence of BMSCs, respectively (p=0.0079). Consistent with these in vitro results, heterotypic s.c. xenografts of Luc+ MM.1S cells mixed with Luc- BMSCs did not show statistically significant reduction in MM burden with bortezomib treatment (0.5 mg/kg s.c. twice weekly for 5 weeks) compared to vehicle-treated controls (p=0.1320), as quantified by bioluminescence imaging. In contrast, the same dose and schedule of bortezomib treatment significantly suppressed tumor burden, compared to vehicle-treated controls, of monotypic s.c. xenografts of Luc+ MM.1S cells in SCID mice (p=0.0022), as in prior experience. To evaluate the molecular mechanisms of cell non-autonomous decrease in MM cell response to bortezomib, we compared the transcriptional profiles of MM.1S cells in extended co-cultures with HS-5 BMSCs vs. MM.1S cells cultured in isolation. These studies identified a distinct transcriptional signature of stroma-induced transcripts, including several (e.g. PSMC3, ITGB7, FOS, ALDH1L2) for which transcript expression higher than the median levels for refractory MM patients correlated with shorter overall survival (p

Description: Abstract 3995 Introduction: Multiple myeloma (MM) cells suppress osteoblast (OB) maturation and function and induce osteoclast-mediated bone resorption. However, immature cells of the osteoblast lineage (e.g. pre-osteoblasts) remain present in the MM bone microenvironment and their impact on MM cell response to treatment has not been fully characterized. We therefore studied human immortalized cells of the osteoblast lineage as surrogate models for in vitro studies on the effects of pre-osteoblasts on MM cell proliferation, survival and drug resistance. Methods: Immortalized hFOB 1.19 (here referred to as hFOB) and HOBIT cells were utilized in our studies, because, in the absence of Dexamethasone or vitamin D, they express markers consistent with pre-osteoblast stage of differentiation (high type I collagen levels; and low alkaline phosphatase, osteocalcin and osteopontin expression). Monolayer cultures of hFOB cells were performed to determine drug concentrations that did not exhibit cytotoxic effects on these pre-osteoblasts. Next, co-cultures of hFOB and HOBIT cells were performed using a panel of tumor cell lines from MM (n=13), breast (n=1) and lung (n=1) cancer. Compartment-specific bioluminescence imaging (CS-BLI) assays were undertaken to quantify the proliferative responses of the tumor cells in the presence of pre-osteoblasts, and if any changes are observed in tumor cell responses to established or novel therapeutic agents. Assays with Transwell insert chambers were conducted to allow for culture of tumor cells proximate to pre-osteoblasts, but preclude their direct cell-to-cell contact, in order to determine whether paracrine factors released by pre-osteoblasts are sufficient to recapitulate the effect(s) of their co-culture with tumor cells. Finally, cytokine or cytokine receptor neutralization studies with monoclonal antibodies or selective kinase inhibitors were performed to investigate the functional contribution of IL-6 or IGF1R-mediated signalling in tumor-pre-osteoblast interactions. Results: Pharmacologically relevant doses of conventional and novel therapies did not exhibit substantial cytotoxic effects on hFOB cells. Within 48hrs of co-culture, pre-osteoblasts stimulated proliferation of several tumor cell lines, including MM.1S, MM.1R, RPMI8226 and Dox40 in co-culture with hFOB; and NCI-H929, OPM2, H23 and Dox40 with HOBIT co-culture. hFOB cells decreased the sensitivity of 8 MM cell lines to at least one established (doxorubicin, dexamethasone, lenalidomide) or novel (vorinostat, pomalidomide) therapy tested. These observations were particularly pronounced in MM.1S and KMS34 cell lines. Subsequent Transwell-based co-culture assays showed that lack of direct cell-to-cell contact significantly decreases or even completely abrogates the resistance observed in respect to doxorubicin, lenalidomide or vorinostat in mono-cultures of tumor cells with pre-osteoblasts. Finally, IL-6 neutralization with monoclonal antibody did not overcome the proliferative effect of hFOB on MM cells. The anti-MM effect of IGF1R kinase inhibitors was also suppressed by co-culture with hFOB cells. These 2 latter results taken together indicate that the protection provided by hFOB cells is independent of IL-6 and IGF-1R-signaling in tumor or pre-osteoblasts. Conclusion: Our results suggest that cells of the osteoblast lineage may play a role as promoters of MM cell survival and resistance to diverse established and investigational therapeutics. Ongoing mechanistic and functional validation studies aim to delineate new therapeutic strategies to overcome pre-osteoblast-mediated drug resistance in MM and, potentially, other neoplasias. Disclosures: Richardson: Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; Millenium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Anderson:Millennium Pharmaceuticals: Consultancy; Celgene: Consultancy; Onyx: Consultancy; Merck: Consultancy; Bristol-Myers Squibb: Consultancy; Acetylon: Membership on an entity's Board of Directors or advisory committees; Oncopep: Membership on an entity's Board of Directors or advisory committees. Mitsiades:Millennium Pharmaceuticals: Honoraria; Celgene: Honoraria; Novartis Pharmaceuticals: Honoraria; Bristol-Myers Squibb: Honoraria; Merck &Co.: Honoraria; Centocor: Honoraria; Arno Therapeutics: Honoraria; Amgen: Research Funding; AVEO Pharma: Research Funding; OSI: Research Funding; EMD Serono: Research Funding; Sunesis: Research Funding; Johnson & Johnson: Research Funding; PharmaMar: Licensing royalties Other; Axios Biosciences: Uncompensated Role as advisor Other.

Description: Abstract 1820 Proteasome inhibitors such as Bortezomib (Bort) represent a key drug class for the therapeutic management of multiple myeloma (MM). However, MM patients, even those who initially achieve complete clinical and biochemical remission with bortezomib-based regimens eventually relapse, and bortezomib-refractory disease is associated with short overall survival. Identifying the molecular basis of resistance to bortezomib is therefore crucial for the rational development of novel therapies to hopefully improve clinical outcome for advanced MM. To address this question, we generated an isogenic cell line model of bortezomib resistance by successive rounds of in vitro exposure of bortezomib-sensitive MM.1R cells to progressively increasing bortezomib concentrations. Serial dose-response analyses confirmed the generation of several clones with variable reduction in bortezomib-sensitivity (IC50 range 40–80nM vs.

Description: Background Evidence based consensus guidelines for venous thromboembolism (VTE) prevention are broadly accepted to be effective and safe for more than three decades (Clagett GP et al, 1992). However VTE continues to be associated with a major global burden of disease with 3.9 million cases of HAT during one year among 1.1 billion citizens of high income countries (Jha AK et al, 2013). Therefore prevention is the key to reduce death and disability resulting from VTE (Kahn S et al, Gould MK et al & Falck-Yitter Y et al, 2012). Ireland like many other countries has yet to implement a mandatory risk assessment tool and thromboprophylaxis (TP) policy nationally. Aims The aim of this study was to calculate the proportion of inpatients who had a VTE risk assessment performed and received appropriate TP in a large tertiary referral hospital. This information will be vital for baseline data for implementation of a new national policy for prevention of HAT. Methods This audit was performed at Cork University Hospital on 4 pre specified days between November 2014 to February 2015. All adult inpatients (Medical and Surgical) excluding maternity and psychiatric were included. Patients on therapeutic anticoagulation were also excluded. The patients' medical chart and drug prescription chart were reviewed to determine whether or not a VTE risk assessment was documented for each patient and if they had received appropriate TP. If no risk assessment had been performed, trained researchers applied the National Institute for health and Care Excellence (NICE) guidelines 92 (Jan 2010) for VTE risk assessment and prevention. Following the risk assessment patients were divided into three categories, high risk of VTE with low risk of bleeding; high risk of VTE with significant risk of bleeding and low risk of VTE. From this the proportion of patients in each group that received appropriate TP were calculated. Results A total of 1019 patients were enrolled the majority were medical patients 63.5% (n=648). The mean age of patients was 69 years. Females accounted for 52% of patients. Average length of hospitalisation for each patient at the time of the audit was 6 days (range 1-664 days). Overall, a formal TP risk assessment was documented in only 24% (n=244) of all charts reviewed however TP was prescribed in 43.2% (n=441) of patients. See table.Table 1.High Risk of VTE low risk of bleedingHigh risk of VTE significant risk of bleedingLow risk of VTENo. of pts80.3% (n=819)16.6% (n=170)2.9% (n=30)VTE risk assessment documented21.9% (n=180)28.2% (n=55)30% (n=9)Received TP46.3% (n=380)28.8% (n=49)40% (n=12) Within the high risk category patients, 64.3% (n=526) medical. TP was only administered to 46.3% (n=380) of patients in the high risk category. This was almost evenly distributed between surgical 50.1% (n=147) and medical 43.4% (n=233) patients. Conclusion This audit was done as the initial step to develop a national policy to prevent HAT. As suspected, this audit highlights that a large proportion of hospitalised patients, both surgical and medical, continue to be at high risk for VTE despite the availability of preventative measures. There is clear illustration of under prescription of safe, effective and recommended means of VTE prevention. The current overall figure of less than 50% prescription of VTE thromboprophylaxis in high risk patients is a major patient safety concern. There are numerous recognised international guidelines for prevention of VTE, and an efficient method to implement these guidelines needs to be developed. Beyond developing national guidelines for TP, we need a co-ordinated approach to implement and monitor compliance with guidelines. Once the preliminary results of this audit were available to us in March 2015, urgent measures were taken to reduce the identified risk such as the establishment of a Hospital Thrombosis Group which developed a user friendly VTE risk assessment tool and TP policy. The VTE risk assessment tool was incorporated into the patients drug prescription chart and included a pre printed prescription for TP. It is now mandatory for the all patients to have a VTE risk assessment tool and TP prescribed if appropriate within 24hrs of admission. This was successfully piloted for four weeks in the acute medical assessment unit and is now incorporated into each patients drug chart throughout the hospital. This audit will be replicated in 6 months from introduction of this initiative, with an aim of 〉90% compliance. Disclosures No relevant conflicts of interest to declare.

Description: Background: Allele specific gene expression (ASE), with the paternal allele more expressed than the maternal allele or vice versa, appears to be a common phenomenon in humans and mice. In other species the extent of ASE is unknown, and even in humans and mice there are several outstanding questions. These include; to what extent is ASE tissue specific? how often does the direction of allele expression imbalance reverse between tissues? how often is only one of the two alleles expressed? is there a genome wide bias towards expression of the paternal or maternal allele; and finally do genes that are nearby on a chromosome share the same direction of ASE? Here we use gene expression data (RNASeq) from 18 tissues from a single cow to investigate each of these questions in turn, and then validate some of these findings in two tissues from 20 cows. Results: Between 40 and 100 million sequence reads were generated per tissue across three replicate samples for each of the eighteen tissues from the single cow (the discovery dataset). A bovine gene expression atlas was created (the first from RNASeq data), and differentially expressed genes in each tissue were identified. To analyse ASE, we had access to unambiguously phased genotypes for all heterozygous variants in the cow’s whole genome sequence, where these variants were homozygous in the whole genome sequence of her sire, and as a result we were able to map reads to parental genomes, to determine SNP and genes showing ASE in each tissue. In total 25,251 heterozygous SNP within 7985 genes were tested for ASE in at least one tissue. ASE was pervasive, 89 % of genes tested had significant ASE in at least one tissue. This large proportion of genes displaying ASE was confirmed in the two tissues in a validation dataset.For individual tissues the proportion of genes showing significant ASE varied from as low as 8–16 % of those tested in thymus to as high as 71–82 % of those tested in lung. There were a number of cases where the direction of allele expression imbalance reversed between tissues. For example the gene SPTY2D1 showed almost complete paternal allele expression in kidney and thymus, and almost complete maternal allele expression in the brain caudal lobe and brain cerebellum. Mono allelic expression (MAE) was common, with 1349 of 4856 genes (28 %) tested with more than one heterozygous SNP showing MAE. Across all tissues, 54.17 % of all genes with ASE favoured the paternal allele. Genes that are closely linked on the chromosome were more likely to show higher expression of the same allele (paternal or maternal) than expected by chance. We identified several long runs of neighbouring genes that showed either paternal or maternal ASE, one example was five adjacent genes (GIMAP8, GIMAP7 copy1, GIMAP4, GIMAP7 copy 2 and GIMAP5) that showed almost exclusive paternal expression in brain caudal lobe. Conclusions: Investigating the extent of ASE across 18 bovine tissues in one cow and two tissues in 20 cows demonstrated 1) ASE is pervasive in cattle, 2) the ASE is often MAE but ranges from MAE to slight overexpression of the major allele, 3) the ASE is most often tissue specific and that more than half the time displays divergent allele specific expression patterns across tissues, 4) across all genes there is a slight bias towards expression of the paternal allele and 5) genes expressing the same parental allele are clustered together more than expected by chance, and there are several runs of large numbers of genes expressing the same parental allele.