Publications by authors named "Alrina Shin Min Tan"

8 Publications

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A 3D pancreatic tumor model to study T cell infiltration.

Biomater Sci 2021 Nov 9;9(22):7420-7431. Epub 2021 Nov 9.

Singapore Immunology Network, A*STAR, 8A Biomedical Groove, 138648, Singapore.

The desmoplastic nature of the pancreatic ductal adenocarcinoma (PDAC) tumor microenvironment (TME) prevents the infiltration of T cells and the penetration of chemotherapeutic drugs, posing a challenge to the validation of targeted therapies, including T cell immunotherapies. We present an 3D PDAC-TME model to observe and quantify T cell infiltration across the vasculature. In a three-channel microfluidic device, PDAC cells are cultured in a collagen matrix in the central channel surrounded, on one side, by endothelial cells (ECs) to mimic a blood vessel and, on the opposite side, by pancreatic stellate cells (PSCs) to simulate exocrine pancreas. The migration of T cells toward the tumor is quantified based on their activation state and TME composition. The presence of EC-lining drastically reduces T cell infiltration, confirming the essential role of the vasculature in controlling T cell trafficking. We show that activated T cells migrate ∼50% more than the not-activated ones toward the cancer cells. Correspondingly, in the absence of cancer cells, both activated and not-activated T cells present similar migration toward the PSCs. The proposed approach could help researchers in testing and optimizing immunotherapies for pancreatic cancer.
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http://dx.doi.org/10.1039/d1bm00210dDOI Listing
November 2021

Microbial exposure during early human development primes fetal immune cells.

Cell 2021 Jun 1;184(13):3394-3409.e20. Epub 2021 Jun 1.

Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel.

The human fetal immune system begins to develop early during gestation; however, factors responsible for fetal immune-priming remain elusive. We explored potential exposure to microbial agents in utero and their contribution toward activation of memory T cells in fetal tissues. We profiled microbes across fetal organs using 16S rRNA gene sequencing and detected low but consistent microbial signal in fetal gut, skin, placenta, and lungs in the 2 trimester of gestation. We identified several live bacterial strains including Staphylococcus and Lactobacillus in fetal tissues, which induced in vitro activation of memory T cells in fetal mesenteric lymph node, supporting the role of microbial exposure in fetal immune-priming. Finally, using SEM and RNA-ISH, we visualized discrete localization of bacteria-like structures and eubacterial-RNA within 14 weeks fetal gut lumen. These findings indicate selective presence of live microbes in fetal organs during the 2 trimester of gestation and have broader implications toward the establishment of immune competency and priming before birth.
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http://dx.doi.org/10.1016/j.cell.2021.04.039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8240556PMC
June 2021

Integrated in silico and 3D in vitro model of macrophage migration in response to physical and chemical factors in the tumor microenvironment.

Integr Biol (Camb) 2020 04;12(4):90-108

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.

Macrophages are abundant in the tumor microenvironment (TME), serving as accomplices to cancer cells for their invasion. Studies have explored the biochemical mechanisms that drive pro-tumor macrophage functions; however the role of TME interstitial flow (IF) is often disregarded. Therefore, we developed a three-dimensional microfluidic-based model with tumor cells and macrophages to study how IF affects macrophage migration and its potential contribution to cancer invasion. The presence of either tumor cells or IF individually increased macrophage migration directedness and speed. Interestingly, there was no additive effect on macrophage migration directedness and speed under the simultaneous presence of tumor cells and IF. Further, we present an in silico model that couples chemokine-mediated signaling with mechanosensing networks to explain our in vitro observations. In our model design, we propose IL-8, CCL2, and β-integrin as key pathways that commonly regulate various Rho GTPases. In agreement, in vitro macrophage migration remained elevated when exposed to a saturating concentration of recombinant IL-8 or CCL2 or to the co-addition of a sub-saturating concentration of both cytokines. Moreover, antibody blockade against IL-8 and/or CCL2 inhibited migration that could be restored by IF, indicating cytokine-independent mechanisms of migration induction. Importantly, we demonstrate the utility of an integrated in silico and 3D in vitro approach to aid the design of tumor-associated macrophage-based immunotherapeutic strategies.
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http://dx.doi.org/10.1093/intbio/zyaa007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7167463PMC
April 2020

Aneuploidy Enables Cross-Adaptation to Unrelated Drugs.

Mol Biol Evol 2019 08;36(8):1768-1782

Department of Molecular Microbiology and Biotechnology, School of Molecular Cell Biology and Biotechnology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.

Aneuploidy is common both in tumor cells responding to chemotherapeutic agents and in fungal cells adapting to antifungal drugs. Because aneuploidy simultaneously affects many genes, it has the potential to confer multiple phenotypes to the same cells. Here, we analyzed the mechanisms by which Candida albicans, the most prevalent human fungal pathogen, acquires the ability to survive both chemotherapeutic agents and antifungal drugs. Strikingly, adaptation to both types of drugs was accompanied by the acquisition of specific whole-chromosome aneuploidies, with some aneuploid karyotypes recovered independently and repeatedly from very different drug conditions. Specifically, strains selected for survival in hydroxyurea, an anticancer drug, acquired cross-adaptation to caspofungin, a first-line antifungal drug, and both acquired traits were attributable to trisomy of the same chromosome: loss of trisomy was accompanied by loss of adaptation to both drugs. Mechanistically, aneuploidy simultaneously altered the copy number of most genes on chromosome 2, yet survival in hydroxyurea or caspofungin required different genes and stress response pathways. Similarly, chromosome 5 monosomy conferred increased tolerance to both fluconazole and to caspofungin, antifungals with different mechanisms of action. Thus, the potential for cross-adaptation is not a feature of aneuploidy per se; rather, it is dependent on specific genes harbored on given aneuploid chromosomes. Furthermore, pre-exposure to hydroxyurea increased the frequency of appearance of caspofungin survivors, and hydroxyurea-adapted C. albicans cells were refractory to antifungal drug treatment in a mouse model of systemic candidiasis. This highlights the potential clinical consequences for the management of cancer chemotherapy patients at risk of fungal infections.
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http://dx.doi.org/10.1093/molbev/msz104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6657732PMC
August 2019

Experimental evolution of a fungal pathogen into a gut symbiont.

Science 2018 11;362(6414):589-595

Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), 8A Biomedical Grove Immunos #04, Singapore 138648, Singapore.

Gut microbes live in symbiosis with their hosts, but how mutualistic animal-microbe interactions emerge is not understood. By adaptively evolving the opportunistic fungal pathogen in the mouse gastrointestinal tract, we selected strains that not only had lost their main virulence program but also protected their new hosts against a variety of systemic infections. This protection was independent of adaptive immunity, arose as early as a single day postpriming, was dependent on increased innate cytokine responses, and was thus reminiscent of "trained immunity." Because both the microbe and its new host gain some advantages from their interaction, this experimental system might allow direct study of the evolutionary forces that govern the emergence of mutualism between a mammal and a fungus.
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http://dx.doi.org/10.1126/science.aat0537DOI Listing
November 2018

The Transcriptional Response of to Weak Organic Acids, Carbon Source, and Inactivation Unveils a Role for in Mediating the Fungistatic Effect of Acetic Acid.

G3 (Bethesda) 2017 11 6;7(11):3597-3604. Epub 2017 Nov 6.

Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), Singapore 138648, Singapore

is a resident fungus of the human intestinal microflora. Commonly isolated at low abundance in healthy people, outcompetes local microbiota during candidiasis episodes. Under normal conditions, members of the human gastrointestinal (GI) microbiota were shown to keep colonization under control. By releasing weak organic acids (WOAs), bacteria are able to moderate yeast growth. This mechanism displays a synergistic effect with the absence of glucose in medium of culture, which underlines the complex interactions that faces in its natural environment. Inactivation of the transcriptional regulator in results in a lack of sensitivity to this synergistic outcome. To decipher transcriptional responses to glucose, WOAs, and the role of , we performed RNA sequencing (RNA-seq) on four biological replicates exposed to combinations of these three parameters. We were able to characterize the (i) glucose response, (ii) response to acetic and butyric acid, (iii) regulation of , and (iv) genes responsible for WOA resistance. We identified a group of six genes linked to WOA sensitivity in a glucose--dependent manner and inactivated one of these genes, the putative glucose transporter , in a SC5314 wild-type background. As expected, the mutant displayed a partial complementation to WOA resistance in the absence of glucose. This result points toward a mechanism of WOA sensitivity in involving membrane transporters, which could be exploited to control yeast colonization in human body niches.
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http://dx.doi.org/10.1534/g3.117.300238DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5677169PMC
November 2017

MIG1 Regulates Resistance of Candida albicans against the Fungistatic Effect of Weak Organic Acids.

Eukaryot Cell 2015 Oct 21;14(10):1054-61. Epub 2015 Aug 21.

Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore

Candida albicans is the leading cause of fungal infections; but it is also a member of the human microbiome, an ecosystem of thousands of microbial species potentially influencing the outcome of host-fungal interactions. Accordingly, antibacterial therapy raises the risk of candidiasis, yet the underlying mechanism is currently not fully understood. We hypothesize the existence of bacterial metabolites that normally control C. albicans growth and of fungal resistance mechanisms against these metabolites. Among the most abundant microbiota-derived metabolites found on human mucosal surfaces are weak organic acids (WOAs), such as acetic, propionic, butyric, and lactic acid. Here, we used quantitative growth assays to investigate the dose-dependent fungistatic properties of WOAs on C. albicans growth and found inhibition of growth to occur at physiologically relevant concentrations and pH values. This effect was conserved across distantly related fungal species both inside and outside the CTG clade. We next screened a library of transcription factor mutants and identified several genes required for the resistance of C. albicans to one or more WOAs. A single gene, MIG1, previously known for its role in glucose repression, conferred resistance against all four acids tested. Consistent with glucose being an upstream activator of Mig1p, the presence of this carbon source was required for WOA resistance in wild-type C. albicans. Conversely, a MIG1-complemented strain completely restored the glucose-dependent resistance against WOAs. We conclude that Mig1p plays a central role in orchestrating a transcriptional program to fight against the fungistatic effect of this class of highly abundant metabolites produced by the gastrointestinal tract microbiota.
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http://dx.doi.org/10.1128/EC.00129-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4588629PMC
October 2015

The transcriptional stress response of Candida albicans to weak organic acids.

G3 (Bethesda) 2015 Jan 29;5(4):497-505. Epub 2015 Jan 29.

Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), Singapore 138648, Singapore School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore

Candida albicans is the most important fungal pathogen of humans, causing severe infections, especially in nosocomial and immunocompromised settings. However, it is also the most prevalent fungus of the normal human microbiome, where it shares its habitat with hundreds of trillions of other microbial cells. Despite weak organic acids (WOAs) being among the most abundant metabolites produced by bacterial microbiota, little is known about their effect on C. albicans. Here we used a sequencing-based profiling strategy to systematically investigate the transcriptional stress response of C. albicans to lactic, acetic, propionic, and butyric acid at several time points after treatment. Our data reveal a complex transcriptional response, with individual WOAs triggering unique gene expression profiles and with important differences between acute and chronic exposure. Despite these dissimilarities, we found significant overlaps between the gene expression changes induced by each WOA, which led us to uncover a core transcriptional response that was largely unrelated to other previously published C. albicans transcriptional stress responses. Genes commonly up-regulated by WOAs were enriched in several iron transporters, which was associated with an overall decrease in intracellular iron concentrations. Moreover, chronic exposure to any WOA lead to down-regulation of RNA synthesis and ribosome biogenesis genes, which resulted in significant reduction of total RNA levels and of ribosomal RNA in particular. In conclusion, this study suggests that gastrointestinal microbiota might directly influence C. albicans physiology via production of WOAs, with possible implications of how this fungus interacts with its host in both health and disease.
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http://dx.doi.org/10.1534/g3.114.015941DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4390566PMC
January 2015
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