The macrophage migration inhibitory factor (MIF) receptor CD74 is overexpressed in various neoplasms, mainly in hematological tumors, and currently investigated in clinical studies. CD74 is quickly internalized and recycles after antibody binding therefore it constitutes an attractive target for antibody-based treatment strategies. CD74 has been further described as one of the most upregulated molecules in human glioblastomas. To assess the potential relevance for anti-CD74 treatment we determined the cellular source and clinico-pathological relevance of CD74 expression in human gliomas by immunohistochemistry, immunofluorescence, immunoblotting, cell sorting analysis and qPCR. Furthermore, we fractionated glioblastoma cells and glioma-associated microglia/macrophages (GAMs) from primary tumors and compared CD74 expression in cellular fractions with whole tumor lysates. Our results show that CD74 is restricted to GAMs in vivo, while being absent on tumor cells, the latter strongly expressing its ligand MIF. Most interestingly, a higher amount of CD74-positive GAMs was associated with beneficial patient survival constituting an independent prognostic parameter and with an anti-tumoral M1-polarization. In summary, CD74 expression in human gliomas is restricted to GAMs and positively associated with patient survival. In conclusion, CD74 represents a positive prognostic marker most probably due to its association with a M1-polarized immune milieu in high-grade gliomas.
Cancer stem cell (CSC) biology and tumor immunology have shaped our understanding of tumorigenesis. However, we still do not fully understand why tumors can be contained but not eliminated by the immune system and whether rare CSCs are required for tumor propagation. Long latency or recurrence periods have been described for most tumors. Conceptually, this requires a subset of malignant cells which is capable of initiating tumors, but is neither eliminated by immune cells nor able to grow straight into overt tumors. These criteria would be fulfilled by CSCs. Stem cells are pluripotent, immune-privileged, and long-living, but depend on specialized niches. Thus, latent tumors may be maintained by a niche-constrained reservoir of long-living CSCs that are exempt from immunosurveillance while niche-independent and more immunogenic daughter cells are constantly eliminated. The small subpopulation of CSCs is often held responsible for tumor initiation, metastasis, and recurrence. Experimentally, this hypothesis was supported by the observation that only this subset can propagate tumors in non-obese diabetic/scid mice, which lack T and B cells. Yet, the concept was challenged when an unexpectedly large proportion of melanoma cells were found to be capable of seeding complex tumors in mice which further lack NK cells. Moreover, the link between stem cell-like properties and tumorigenicity was not sustained in these highly immunodeficient animals. In humans, however, tumor-propagating cells must also escape from immune-mediated destruction. The ability to persist and to initiate neoplastic growth in the presence of immunosurveillance - which would be lost in a maximally immunodeficient animal model - could hence be a decisive criterion for CSCs. Consequently, integrating scientific insight from stem cell biology and tumor immunology to build a new concept of "CSC immunology" may help to reconcile the outlined contradictions and to improve our understanding of tumorigenesis.
Cytokine secretion and degranulation represent key components of CD8(+) T-cell cytotoxicity. While transcriptional blockade of IFN-? and inhibition of degranulation by TGF-? are well established, we wondered whether TGF-? could also induce immune-regulatory miRNAs in human CD8(+) T cells. We used miRNA microarrays and high-throughput sequencing in combination with qRT-PCR and found that TGF-? promotes expression of the miR-23a cluster in human CD8(+) T cells. Likewise, TGF-? up-regulated expression of the cluster in CD8(+) T cells from wild-type mice, but not in cells from mice with tissue-specific expression of a dominant-negative TGF-? type II receptor. Reporter gene assays including site mutations confirmed that miR-23a specifically targets the 3'UTR of CD107a/LAMP1 mRNA, whereas the further miRNAs expressed in this cluster-namely, miR-27a and -24-target the 3'UTR of IFN-? mRNA. Upon modulation of the miR-23a cluster by the respective miRNA antagomirs and mimics, we observed significant changes in IFN-? expression, but only slight effects on CD107a/LAMP1 expression. Still, overexpression of the cluster attenuated the cytotoxic activity of antigen-specific CD8(+) T cells. These functional data thus reveal that the miR-23a cluster not only is induced by TGF-?, but also exerts a suppressive effect on CD8(+) T-cell effector functions, even in the absence of TGF-? signaling.
The ectonucleotidases CD39 and CD73 degrade ATP to adenosine which inhibits immune responses via the A2A adenosine receptor (ADORA2A) on T and NK cells. The current study investigates the potential therapeutic use of the specific anti CD39- and anti CD73-antibodies A1 (CD39) and 7G2 (CD73) as these two ectonucleotidases are overexpressed in ovarian cancer (OvCA). As expected, NK cell cytotoxicity against the human ovarian cancer cell lines OAW-42 or SK-OV-3 was significantly increased in the presence of A1 or 7G2 antibody. While this might partly be due to antibody-dependent cell-mediated cytotoxicity, a luciferase-dependent assay for quantifying biologically active adenosine further showed that A1 and 7G2 can inhibit CD39 and CD73-dependent adenosine-generation. In turn, the reduction in adenosine levels achieved by addition of A1 and 7G2 to OAW-42 or SK-OV-3 cells was found to de-inhibit the proliferation of CD4(+) T cells in coculture with OvCA cells. Likewise, blocking of CD39 and CD73 on OvCA cells via A1 and 7G2 led to an increased cytotoxicity of alloreactive primed T cells. Thus, antibodies like A1 and 7G2 could improve targeted therapy in ovarian cancer not only by specifically labeling overexpressed antigens but also by blocking adenosine-dependent immune evasion in this immunogenic malignancy.
Breast cancer is the most common cancer among women worldwide. Every year, nearly 1.4 million new cases of breast cancer are diagnosed, and about 450.000 women die of the disease. Approximately 15-25% of breast cancer cases exhibit increased quantities of the trans-membrane receptor tyrosine kinase human epidermal growth factor receptor 2 (HER2) on the tumor cell surface. Previous studies showed that blockade of this HER2 proto-oncogene with the antibody trastuzumab substantially improved the overall survival of patients with this aggressive type of breast cancer. Recruitment of natural killer (NK) cells and subsequent induction of antibody-dependent cell-mediated cytotoxicity (ADCC) contributed to this beneficial effect. We hypothesized that antibody binding to HER2-positive breast cancer cells and thus ADCC might be further improved by synergistically applying two different HER2-specific antibodies, trastuzumab and pertuzumab. We found that tumor cell killing via ADCC was increased when the combination of trastuzumab, pertuzumab, and NK cells was applied to HER2-positive breast cancer cells, as compared to the extent of ADCC induced by a single antibody. Furthermore, a subset of CD44(high)CD24(low)HER2(low) cells, which possessed characteristics of cancer stem cells, could be targeted more efficiently by the combination of two HER2-specific antibodies compared to the efficiency of one antibody. These in vitro results demonstrated the immunotherapeutic benefit achieved by the combined application of trastuzumab and pertuzumab. These findings are consistent with the positive results of the clinical studies, CLEOPATRA and NEOSPHERE, conducted with patients that had HER2-positive breast cancer. Compared to a single antibody treatment, the combined application of trastuzumab and pertuzumab showed a stronger ADCC effect and improved the targeting of breast cancer stem cells.
Inactivation of the p53 pathway that controls cell cycle progression, apoptosis and senescence, has been proposed to occur in virtually all human tumors and p53 is the protein most frequently mutated in human cancer. However, the mutational status of p53 in melanoma is still controversial; to clarify this notion we analysed the largest series of melanoma samples reported to date.
The prognosis of patients afflicted by glioblastoma remains poor. Biomarkers for the disease would be desirable in order to allow for an early detection of tumor progression or to indicate rapidly growing tumor subtypes requiring more intensive therapy. In this study, we investigated whether a blood-derived specific miRNA fingerprint can be defined in patients with glioblastoma. To this end, miRNA profiles from the blood of 20 patients with glioblastoma and 20 age- and sex-matched healthy controls were compared. Of 1158 tested miRNAs, 52 were significantly deregulated, as assessed by unadjusted Students t-test at an alpha level of 0.05. Of these, two candidates, miR-128 (up-regulated) and miR-342-3p (down-regulated), remained significant after correcting for multiple testing by Benjamini-Hochberg adjustment with a p-value of 0.025. The altered expression of these two biomarkers was confirmed in a second cohort of glioblastoma patients and healthy controls by real-time PCR and validated for patients who had received neither radio- nor chemotherapy and for patients who had their glioblastomas resected more than 6 months ago. Moreover, using machine learning, a comprehensive miRNA signature was obtained that allowed for the discrimination between blood samples of glioblastoma patients and healthy controls with an accuracy of 81% [95% confidence interval (CI) 78-84%], specificity of 79% (95% CI 75-83%) and sensitivity of 83% (95% CI 71-85%). In summary, our proof-of-concept study demonstrates that blood-derived glioblastoma-associated characteristic miRNA fingerprints may be suitable biomarkers and warrant further exploration.
The ectonucleotidases CD39 and CD73 degrade immune stimulatory ATP to adenosine that inhibits T and NK cell responses via the A(2A) adenosine receptor (ADORA2A). This mechanism is used by regulatory T cells (T(reg)) that are associated with increased mortality in OvCA. Immunohistochemical staining of human OvCA tissue specimens revealed further aberrant expression of CD39 in 29/36 OvCA samples, whereas only 1/9 benign ovaries showed weak stromal CD39 expression. CD73 could be detected on 31/34 OvCA samples. While 8/9 benign ovaries also showed CD73 immunoreactivity, expression levels were lower than in tumour specimens. Infiltration by CD4(+) and CD8(+) T cells was enhanced in tumour specimens and significantly correlated with CD39 and CD73 levels on stromal, but not on tumour cells. In vitro, human OvCA cell lines SK-OV-3 and OaW42 as well as 11/15 ascites-derived primary OvCA cell cultures expressed both functional CD39 and CD73 leading to more efficient depletion of extracellular ATP and enhanced generation of adenosine as compared to activated T(reg). Functional assays using siRNAs against CD39 and CD73 or pharmacological inhibitors of CD39, CD73 and ADORA2A revealed that tumour-derived adenosine inhibits the proliferation of allogeneic human CD4(+) T cells in co-culture with OvCA cells as well as cytotoxic T cell priming and NK cell cytotoxicity against SK-OV3 or OAW42 cells. Thus, both the ectonucleotidases CD39 and CD73 and ADORA2A appear as possible targets for novel treatments in OvCA, which may not only affect the function of T(reg) but also relieve intrinsic immunosuppressive properties of tumour and stromal cells.
Macrophage migration inhibitory factor (MIF), which inhibits apoptosis and promotes angiogenesis, is expressed in cancers suppressing immune surveillance. Its biological role in human glioblastoma is, however, only poorly understood. We examined in-vivo expression of MIF in 166 gliomas and 23 normal control brains by immunohistochemistry. MIF immunoreactivity was enhanced in neoplastic astrocytes in WHO grade II glioma and increased significantly in higher tumour grades (III-IV). MIF expression was further assessed in 12 glioma cell lines in vitro. Quantitative RT-PCR showed that MIF mRNA expression was elevated up to 800-fold in malignant glioma cells compared with normal brain. This translated into high protein levels as assessed by immunoblotting of total cell lysates and by ELISA-based measurement of secreted MIF. Wild-type p53-retaining glioma cell lines expressed higher levels of MIF, which may be connected with the previously described role of MIF as a negative regulator of wild-type p53 signalling in tumour cells. Stable knockdown of MIF by shRNA in glioma cells significantly increased tumour cell susceptibility towards NK cell-mediated cytotoxicity. Furthermore, supernatant from mock-transfected cells, but not from MIF knockdown cells, induced downregulation of the activating immune receptor NKG2D on NK and CD8+ T cells. We thus propose that human glioma cell-derived MIF contributes to the immune escape of malignant gliomas by counteracting NK and cytotoxic T-cell-mediated tumour immune surveillance. Considering its further cell-intrinsic and extrinsic tumour-promoting effects and the availability of small molecule inhibitors, MIF seems to be a promising candidate for future glioma therapy.
Growth and differentiation factor (GDF)-15 is a member of the transforming growth factor (TGF)-beta family. GDF-15 is necessary for the maintenance of pregnancy but has also been linked to other physiologic and pathologic conditions.
Relapses during multiple sclerosis (MS) are treated by administration of exogenous corticosteroids. However, little is known about the bioavailability of endogenous steroids in the central nervous system (CNS) of MS patients. We thus determined cortisol and dehydroepiandrosterone (DHEA) levels in serum and cerebrospinal fluid (CSF) samples from 34 MS patients, 28 patients with non-inflammatory neurological diseases (NIND) and 16 patients with other inflammatory neurological diseases (OIND). This revealed that MS patients - in sharp contrast to patients with OIND - show normal cortisol concentrations in serum and lowered cortisol levels in the CSF during acute relapses. This local cortisol deficit may relate to poor local activation of cortisone via 11beta-hydroxysteroid dehydrogenase type 1 (11bHSD1) or to inactivation via 11bHSD2. Accordingly, 11bHSD2 was found to be expressed within active plaques, whereas 11bHSD1 was predominantly detected in surrounding "foamy" macrophages. Our study thus provides new insights into the impaired endogenous CNS cortisol regulation in MS patients and its possible relation to MS lesion pathogenesis. Moreover, an observed upregulation of 11bHSD1 in myelin-loaded macrophages in vitro suggests an intriguing hypothesis for the self-limiting nature of MS lesion development. Finally, our findings provide an attractive explanation for the effectivity of high- vs. low-dose exogenous corticosteroids in the therapy of acute relapses.
Extracellular adenosine exerts powerful paracrine effects on immune cells. Thus, adenosine signaling has to be strictly regulated. This is achieved by its rapid internalization or enzymatic degradation. Consequently, free adenosine is extremely difficult to measure in cell culture systems and may escape from detection by time-consuming endpoint measurements like high-performance liquid chromatography (HPLC). Therefore, we have now developed a highly sensitive assay which enables the quantification of biologically relevant extracellular adenosine via the activation of an ectopically expressed Adenosine 2a-receptor (ADORA2A) in HEK-293 reporter cells. Binding of the short-lived nucleoside to this receptor induces a cAMP-dependent signal which can be detected via a cAMP-responsive luciferase construct. Tests with exogenously added adenosine confirmed that the resulting luminescence signals correlate with the respective adenosine levels and thus allow quantitative measurements in a range from 20 nM to 80 ?M free extracellular adenosine. Inhibition of adenosine uptake by dipyridamole further increased the sensitivity of the assay. We further validated our approach by quantifying the adenosine levels that are generated by regulatory T cells via ectonucleotidase-mediated cleavage of ATP. As expected, values returned to baseline when ADORA2A was inhibited. This confirmed that this new cell-based reporter assay constitutes a biologically relevant, technically easy, versatile, scalable and cost-effective approach that allows the non-radioactive quantification of adenosine as a signaling intermediate.
Glioblastoma multiforme (GBM) is paradigmatic for the investigation of cancer stem cells (CSC) in solid tumors. Growing evidence suggests that different types of CSC lead to the formation of GBM. This has prompted the present comparison of gene expression profiles between 17 GBM CSC lines and their different putative founder cells. Using a newly derived 24-gene signature, we can now distinguish two subgroups of GBM: Type I CSC lines display "proneural" signature genes and resemble fetal neural stem cell (fNSC) lines, whereas type II CSC lines show "mesenchymal" transcriptional profiles similar to adult NSC (aNSC) lines. Phenotypically, type I CSC lines are CD133 positive and grow as neurospheres. Type II CSC lines, in contrast, display (semi-)adherent growth and lack CD133 expression. Molecular differences between type I and type II CSC lines include the expression of extracellular matrix molecules and the transcriptional activity of the WNT and the transforming growth factor-beta/bone morphogenetic protein signaling pathways. Importantly, these characteristics were not affected by induced adherence on laminin. Comparing CSC lines with their putative cells of origin, we observed greatly increased proliferation and impaired differentiation capacity in both types of CSC lines but no cancer-associated activation of otherwise silent signaling pathways. Thus, our data suggest that the heterogeneous tumor entity GBM may derive from cells that have preserved or acquired properties of either fNSC or aNSC but lost the corresponding differentiation potential. Moreover, we propose a gene signature that enables the subclassification of GBM according to their putative cells of origin.
Although trastuzumab (Herceptin) has substantially improved the overall survival of patients with mammary carcinomas, even initially well-responding tumors often become resistant. Because natural killer (NK) cell-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) is thought to contribute to the therapeutic effects of trastuzumab, we have established a cell culture system to select for ADCC-resistant SK-OV-3 ovarian cancer and MCF7 mammary carcinoma cells. Ovarian cancer cells down-regulated HER2 expression, resulting in a more resistant phenotype. MCF7 breast cancer cells, however, failed to develop resistance in vitro. Instead, treatment with trastuzumab and polyclonal NK cells resulted in the preferential survival of individual sphere-forming cells that displayed a CD44(high)CD24(low) "cancer stem cell-like" phenotype and expressed significantly less HER2 compared with non-stem cells. Likewise, the CD44(high)CD24(low) population was also found to be more immunoresistant in SK-BR3, MDA-MB231, and BT474 breast cancer cell lines. When immunoselected MCF7 cells were then re-expanded, they mostly lost the observed phenotype to regenerate a tumor cell culture that displayed the initial HER2 surface expression and ADCC-susceptibility, but was enriched in CD44(high)CD24(low) cancer stem cells. This translated into increased clonogenicity in vitro and tumorigenicity in vivo. Thus, we provide evidence that the induction of ADCC by trastuzumab and NK cells may spare the actual tumor-initiating cells, which could explain clinical relapse and progress. Moreover, our observation that the "relapsed" in vitro cultures show practically identical HER2 surface expression and susceptibility toward ADCC suggests that the administration of trastuzumab beyond relapse might be considered, especially when combined with an immune-stimulatory treatment that targets the escape variants.
AEZS 112 is an orally active small molecule anticancer drug which inhibits the polymerization of tubulin at low micromolar concentrations. The current study investigates the anti-tumor effect and the mechanism of action of AEZS 112 in in vitro models of human ovarian and endometrial cancers. Four human ovarian and 2 endometrial cancer cell lines were incubated with increasing concentrations of AEZS 112 with and without multi-caspase inhibitor zVAD-FMK for 72 hours. Cytotoxic effects of AEZS 112 were analyzed using crystal violet staining, FACS analysis of DNA content as well as Annexin V/propidium iodide-double staining. AEZS 112 displayed anti-tumor activity in all six cell lines. The EC50 determined after 72-h incubation for Ishikawa and HEC 1A was 0.0312 and 0.125 microm, respectively. The EC50 was 5 microm for SKOV 3 cells, 1 microm for 0.5 microm for OAW 42 cells, 0.125 microm for OvW 1 cells and 0.0312 microm for PA 1 cells. Cytotoxic effects of AEZS 112 could not be abrogated by caspase inhibition with pan-caspase inhibitor zVAD-fmk. Annexin V/propidium iodide-double staining after treatment with AEZS 112 was indicative of necrosis-like cell death. AEZS 112 dose-dependently increased non-vital hypodiploid cells and the cytotoxic effect was least pronounced in G2 phase of the cell cycle, indicating cell death during mitosis, as determined by FACS analysis. The orally active small molecule tubulin inhibitor AEZS 112 showed anti-tumor activity in human ovarian and endometrial cancer cell lines at low micromolar concentrations, which could not be abrogated by caspase inhibition and is therefore a good candidate for in vivo studies in these tumors.
The glycoprotein macrophage migration inhibitory factor (MIF) is a cytokine that has been shown to promote tumor progression and tumor immune escape in ovarian cancer. The present study investigates MIF in uterine cervical cancer.
Ovarian cancer is generally thought of as a cancer with poor prognosis. However, prognostic appraisal of the disease is based on tumor stages, surgical features or sensibility towards platinum-based chemotherapy. There are data that also grant immunological parameters such as CD8(+) T-lymphocyte-(CD8 T-cell) infiltration in tumor tissue, a prognostic role. Macrophage migration-inhibitory factor (MIF) has been described as a tumor-derived protein which allows tumor cell immune escape from antitumoral host natural killer (NK) - and CD8 T-cells. This immune escape is functionally based on down-regulation of the receptor natural killer group 2D (NKG2D). We here report that the levels of the MIF protein which is known to be secreted in ascites and serum of patients with ovarian cancer, not only seems to correlate with common prognostic parameters such as tumor stage or platinum sensitivity, but also with CD8 T- and NK-cell infiltration in tumor tissue. We therefore believe that MIF may play a suppressive role in the host antitumor immune response, which may have a negative impact on the course of the disease. The fact that MIF levels in serum of patients at primary diagnosis correlate with platinum sensibility supports the hypothesis that serum MIF levels should be evaluated as a parameter reflecting tumor sensibility towards chemotherapy in early stages of the disease.
Immune cell infiltration varies widely between different glioblastomas (GBMs). The underlying mechanism, however, remains unknown. Here we show that TGF-beta regulates proliferation, migration, and tumorigenicity of mesenchymal GBM cancer stem cells (CSCs) in vivo and in vitro. In contrast, proneural GBM CSCs resisted TGF-beta due to TGFR2 deficiency. In vivo, a substantially increased infiltration of immune cells was observed in mesenchymal GBMs, while immune infiltrates were rare in proneural GBMs. On a functional level, proneural CSC lines caused a significantly stronger TGF-beta-dependent suppression of NKG2D expression on CD8(+) T and NK cells in vitro providing a mechanistic explanation for the reduced immune infiltration of proneural GBMs. Thus, the molecular subtype of CSCs TGF-beta-dependently contributes to the degree of immune infiltration.
As NK cell immunotherapy is still poorly successful, combinations with drugs enhancing NK cell activity are of major interest. NK large granular lymphocyte expansions associated with improved survival have been described under monotherapy with the Bcr-Abl/Src inhibitor dasatinib, which inhibits NK cell functions in vitro. As Src kinases play a major role in inhibitory and activating signaling pathways of NK cells, both outcomes appear plausible. To clarify these contradictory observations and potentially enable the use of dasatinib as adjuvant, we analyzed how clinically relevant doses promote NK cell effector functions. Polyclonal human NK cells were studied ex vivo. Functional outcomes assessed included conjugate formation, calcium flux, receptor regulation, cytokine production, degranulation, cytotoxicity, apoptosis induction and signal transduction. While dasatinib inhibits NK cell effector functions during functional assays, 24 hr pretreatment of NK cells followed by washout of dasatinib, led to dose-dependent enhancement of cytokine production, degranulation marker expression and cytotoxicity against selected lymphoma and leukemia cell lines. Mechanistically, this was neither due to an altered viability of NK cells nor increased NKG2D, LFA-1 or conjugate formation with target cells. Receptor proximal signaling events were inhibited. However, a slight time dependent enhancement of Vav phosphorylation was observed under certain circumstances. The shift in Vav phosphorylation level may be one major mechanism for NK cell activity enhancement induced by dasatinib. Our findings argue for a careful timing and dosing of dasatinib application during leukemia/lymphoma treatment to enhance NK cell immunotherapeutic efforts.
Lobaplatin as a single agent and in combination with tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is investigated in in-vitro models of p53-negative triple-negative breast cancers (TNBCs) and compared with a model of oestrogen receptor-positive p53-positive breast cancer. In addition, the induction of programmed cell death by lobaplatin is further explored. By using cell viability assays and western blotting, the cytotoxic effects of lobaplatin alone and in combination with TRAIL are compared with cisplatin in HCC 1806, HCC 1937, and MCF 7 cells. The multicaspase inhibitor z-VAD-fmk and necrostatin, an inhibitor of necroptosis, are used to demonstrate the mechanism of cell death caused by lobaplatin. Lobaplatin displayed antitumour activity in all three cell lines, which increased time dependently. Cotreatment of lobaplatin and TRAIL induced an increase in cytotoxicity by 30-50% in the different cell lines. The pan-caspase inhibitor z-VAD-fmk as well as necrostatin could weaken but not abolish the cytotoxic effect of lobaplatin and cisplatin. Lobaplatin showed substantial cytotoxic effects in two in-vitro models of p53-mutated TNBC. Cotreatment with TRAIL and platinum agents resulted in increased antitumour activity in the TNBC cell lines investigated. Cell death subsequent to treatment with cisplatin and lobaplatin occurred because of apoptosis. However, caspase-independent mechanisms of programmed cell death were also involved. It was also demonstrated that platinum compounds could induce necroptosis, although to a minor extent.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.