Dynamic analysis of immune and cancer cell interactions at single cell level in microfluidic droplets

Cell-cell communication mediates immune responses to physiological stimuli at local and systemic levels. Intercellular communication occurs via a direct contact between cells as well as by secretory contact-independent mechanisms. However, there are few existing methods that allow quantitative resolution of contact-dependent and independent cellular processes in a rapid, precisely controlled, and dynamic format. This study utilizes a high-throughput microfluidic droplet array platform to analyze cell-cell interaction and effector functions at single cell level. Controlled encapsulation of distinct heterotypic cell pairs was achieved in a single-step cell loading process. Dynamic analysis of dendritic cell (DC)-T cell interactions demonstrated marked heterogeneity in the type of contact and duration. Non-stimulated DCs and T cells interacted less frequently and more transiently while antigen and chemokine-loaded DCs and T cells depicted highly stable interactions in addition to transient and sequential contact. The effector function of CD8⁺ T cells was assessed via cytolysis of multiple myeloma cell line. Variable cell conjugation periods and killing time were detected irrespective of the activation of T cells, although activated T cells delivered significantly higher cytotoxicity. T cell alloreactivity against the target cells was partially mediated by secretion of interferon gamma, which was abrogated by the addition of a neutralizing antibody. These results suggest that the droplet array-based microfluidic platform is a powerful technique for dynamic phenotypic screening and potentially applicable for evaluation of novel cell-based immunotherapeutic agents.

Generation and functional assessment of 3D multicellular spheroids in droplet based microfluidics platform

Here we describe a robust, microfluidic technique to generate and analyze 3D tumor spheroids, which resembles tumor microenvironment and can be used as a more effective preclinical drug testing and screening model. Monodisperse cell-laden alginate droplets were generated in polydimethylsiloxane (PDMS) microfluidic devices that combine T-junction droplet generation and external gelation for spheroid formation. The proposed approach has the capability to incorporate multiple cell types. For the purposes of our study, we generated spheroids with breast cancer cell lines (MCF-7 drug sensitive and resistant) and co-culture spheroids of MCF-7 together with a fibroblast cell line (HS-5). The device has the capability to house 1000 spheroids on chip for drug screening and other functional analysis. Cellular viability of spheroids in the array part of the device was maintained for two weeks by continuous perfusion of complete media into the device. The functional performance of our 3D tumor models and a dose dependent response of standard chemotherapeutic drug, doxorubicin (Dox) and standard drug combination Dox and paclitaxel (PCT) was analyzed on our chip-based platform. Altogether, our work provides a simple and novel, in vitro platform to generate, image and analyze uniform, 3D monodisperse alginate hydrogel tumors for various omic studies and therapeutic efficiency screening, an important translational step before in vivo studies.

Phenotypic drug profiling in droplet microfluidics for better targeting of drug-resistant tumors

Acquired drug resistance is a key factor in the failure of chemotherapy. Due to intratumoral heterogeneity, cancer cells depict variations in intracellular drug uptake and efflux at the single cell level, which may not be detectable in bulk assays. In this study we present a droplet microfluidics-based approach to assess the dynamics of drug uptake, efflux and cytotoxicity in drug-sensitive and drug-resistant breast cancer cells. An integrated droplet generation and docking microarray was utilized to encapsulate single cells as well as homotypic cell aggregates. Drug-sensitive cells showed greater death in the presence or absence of Doxorubicin (Dox) compared to the drug-resistant cells. We observed heterogeneous Dox uptake in individual drug-sensitive cells while the drug-resistant cells showed uniformly low uptake and retention. Dox-resistant cells were classified into distinct subsets based on their efflux properties. Cells that showed longer retention of extracellular reagents also demonstrated maximal death. We further observed homotypic fusion of both cell types in droplets, which resulted in increased cell survival in the presence of high doses of Dox. Our results establish the applicability of this microfluidic platform for quantitative drug screening in single cells and multicellular interactions.

Development of a highly sensitive, field operable biosensor for serological studies of Ebola virus in central Africa

We describe herein a newly developed optical immunosensor for detection of antibodies directed against antigens of the Ebola virus strains Zaire and Sudan. We employed a photo immobilization methodology based on a photoactivatable electrogenerated poly(pyrrole-benzophenone) film deposited upon an indium tin oxide (ITO) modified conductive surface fiber-optic. It was then linked to a biological receptor, Ebola virus antigen in this case, on the fiber tip through a light driven reaction. The photochemically modified optical fibers were tested as an immunosensor for detection of antibodies against Ebola virus, in animal and human sera, by use of a coupled chemiluminescent reaction. The immunosensor was tested for sensitivity, specificity, and compared to standard chemiluminescent ELISA under the same conditions. The analyte, anti-Ebola IgG, was detected at a low titer of 1:960,000 and 1:1,000,000 for subtypes Zaire and Sudan, respectively. While the same serum tested by ELISA was one order (24 times) less sensitive.

Optical Fiber Immunosensor Based on a Poly(pyrrole−benzophenone) Film for the Detection of Antibodies to Viral Antigen

We describe herein a newly developed optical microbiosensor for the diagnosis of hepatitis C virus (HCV) by using a novel photoimmobilization methodology based on a photoactivable electrogenerated polymer film deposited upon surface-conductive fiber optics, which are then used to link a biological receptor to the fiber tip through light mediation. This fiber-optic electroconductive surface modification is done by the deposition of a thin layer of indium tin oxide on the silica surface of the fiber optics. Monomers are then electropolymerized onto the conductive metal oxide surface; thereafter, the fibers are immersed in a solution containing HCV-E2 envelope protein antigen and illuminated with UV light (wavelength approximately 345 nm). As a result of the photochemical reaction, a thin layer of the antigen becomes covalently bound to the benzophenone-modified surface. The photochemically modified fiber optics were tested as immunosensors for the detection of anti-E2 protein antibody analyte that was measured through chemiluminescence reaction. The biosensor was tested for sensitivity, specificity, and overall practicality. Our results suggest that the detection of anti-E2 antibodies with this microbiosensor may enhance significantly HCV serological standard testing especially among patients during dialysis, which were diagnosed as HCV negative, by standard immunological tests, but were known to carry the virus. If transformed into an easy to use procedure, this assay might be used in the future as an important clinical tool for HCV screening in blood banks.