A Method of Targeted Cell Isolation via Glass Surface Functionalization

Summary

This protocol describes customizable surface functionalization of the desthiobiotin, streptavidin, and APTES system in order to isolate specific cell types of interest. In addition, this manuscript covers the applications, optimization, and verification of this process.

Abstract

One of the limiting factors to the adoption and advancement of personalized medicine is the inability to develop diagnostic tools to probe individual nuances in expression from patient to patient. Current methodologies that try to separate cells to fill this niche result in disruption of physiological expression, making the separation technique useless as a diagnostic tool. In this protocol, we describe the functionalization and optimization of a surface for the cellular capture and release. This functionalized surface integrates biotinylated antibodies with a glass surface functionalized with an aminosilane (APTES), desthiobiotin and streptavidin. Cell release is facilitated through the introduction of biotin, allowing the recollection and purification of cells captured by the surface. This release is done through the targeting of the secondary moiety desthiobiotin, which results in a much more gentle release paradigm. This reduction in harsh reagents and shear forces reduces changes in cellular expression. The functionalized surface captures up to 80% of cells in a single cell mixture and has demonstrated 50% capture in a dual-cell mixture. Applications of this technology to xenografts and cancer separation studies are investigated. Quantification techniques for surface verification such as plate reader and ImageJ analyses are described as well.

Introduction

Current bench-top cell separation approaches (e.g., fluorescence activated cell sorting¹, laser capture micro-dissection², immuno-magnetic bead separation¹) can take several hours of preparation and sorting. These large time scales can affect physiological response and expression levels, resulting in analyses that are not representative of the physiological response³. Systems are needed that can rapidly and efficiently isolate specific cell types without disrupting cell-surface receptor-levels in order to improve cell isolation and enrichment for biomedical applications. Therefore, the rationale for our approach is ....

Protocol

1. Cleaning the Glass Surface and Preparing Reagents

1. Place a glass surface in an oxygen plasma machine for 5 min at 50% power to clean it.
2. Prepare 2.5 ml 2% reconstituted (3-aminopropyl) triethoxysilane (APTES) solution, by adding 50 µl of APTES and 2.45 ml of ethanol in a conical tube.

2. APTES and DSB Functionalization

1. Add APTES solution to the surfaces. Pipette 150 µl per well for 8 well plates. Pipette 100 µl per well for 24 well plates. Pipette 1.1 ml for 60 x 15 mm glass dishes. Cover the surfaces to prevent evaporation and uneven distribution of APTES solution. Place the surface....

Results

Using this protocol we show cell capture (Figure 3A) and cell release (Figure 3C) of MCF7GFP cells as well as live cell controls (Figure 4). We quantified the cell capture as 60% and 80% were released (Figure 3C). When we extended this approach to a mixture of RAW 264.7 macrophages and MCF7GFP cells, 50% of RAW macrophages were captured (Fig. 3D) and 80% of RAW macrophages were release with 20 mM biotin (.......

Discussion

Improvements in cell isolation techniques furthers scientific studies in structure-function relationships in neuroscience¹⁸, stem cell programming in regenerative biology, and angiogenic signaling in vascular biology¹⁹. Indeed, primary cell culture²⁰ (e.g., HUVECs) in vascular biology is primarily done through the use of cell isolation techniques. Cell isolation was also recently used for quantitative flow (qFlow) cytometry analysis of plasma membrane receptors^{3,14,15,19,21<.......}

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
(3-Aminopropyl) triethoxysilane (APTES)	Acros Organics	919-30-2	Used to make 2% APTES solution
Plasma Cleaner Pico	Diener	Model 1	Cleans surfaces and allows for bonding of PDMS to glass
d-Desthiobiotin (DSB)	Sigma	D20655	Used as the releasing mechanism in the cellular capture surface.
dimethyl sulfoxide (DMSO)	British Drug Houses (BDH)	BDH1115-1LP	Dissolves the DSB into solution
1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)	Thermo-Scientific	5g: 22980 25g: 22981	Activates carboxylic acids and allows binding of proteins to glass surface.
uncoated 8-well culture slide	BD Falcon	Case of 24: 354118 Case of 96: 354108	Used in cellular experiments involving Zeiss fluorescence microscope such as initial capture and release quantification experiments
Glass bottom 24-well plates	MatTek	P24G-0-13-F	Used in cellular experiments involving the plate reader such as antibody and cellular titration experiments
Mercaptoethanol	Science Lab	60-24-2	Used to quench reaction between EDC and DSB
4-Morpholinoethanesulfonic acid hydrate (MES Hydrate 99%)	Fisher Scientific	AC172590250	Used to make 0.1 M MES Buffer for use in EDC reaction
Precision Oven	Thermo Scientific	11-475-153	Used in curing of PDMS and APTES layer.
Titramax 1000 Shaker	Heidolph	13-889-420	Used to ensure even distribution of APTES on surfaces.
1x Streptavidin 5 mg [e7105-5mg]	Proteo Chem	9013-20-1	Biotin-binding protein. May cause irritation.
5 cm Glass Dish	Fisher Scientific	08748A	Used in HUVEC studies as well as future profiling studies.
14 cm Petri Dish with Cover	Sigma-Aldrich	Z717231	Used to hold samples being functionalized and transport them.
MCF7-GFP cells	Cell Biolabs	AKR211	Stored in liquid nitrogen
RAW264.7 mouse macrophages	ATCC	TIB-71	Gifted to us from Smith lab at the University of Illinois. Stored in liquid nitrogen.
TrypLE	Life Technologies	12605036	Stored in 100 ml at room temperature
Dulbecco’s modified Eagle medium	Cell Media Facility at School of Chemical Sciences at UIUC	50003PC	Supplier: Corning
Nonessential amino acids	Cell Media Facility at School of Chemical Sciences at UIUC	25-025-CI	Already added into DMEM by facility. Supplier: Corning.
Cell scraper	Fisher Scientific	12-565-58	Small 23 cm 50 pack
Cell Dissociation Solution	Corning	MT-25-056CI	Used to lift cells non-enzymatically for the use in cell experiments
Hemacytometer	Hausser	02-671-54	Used to count cells for quantification of cell solutions and capture and release effectivity.
Biotin	Amresco	58-85-5	Used to release cells from surface.
HBSS	Created from Recipe	N/A	Used to keep cells alive in suspension as well as wash surfaces of non-specific binding. Adapted from Cold Spring Harbor Protocols: In 500 ml, use 4 g NaCl, 0.2 g KCl, 0.0402 g Na2PO4•7H2O, 0.03 g KH2PO4 and 0.5 g glucose. Add DI water to get to 500 ml, filter, and then refrigerate.
HLA-ABC Antibody	BioLegend	311402	Antibody used to capture MCF7gfp cells
hIgG Antibody	BioLegend	HP6017	Antibody used to capture MCF7gfp cells
MCF7 GFP cells	Cell Biolabs	AKR-211	Luminal Breast Cancer line that has been transfected with green fluorescent protein.
Assorted Conicals	Thermo-Scientific	15mL: 12-565-268	50/15 ml plastic conicals for storing solutions and aliquots.
Mini-Tube Rotators (End over End Mixer)	Fisher Scientific	05-450-127	Used to incubate antibody and mix other cellular solutions in order to mix
Axiovert 200M (Fluorescence Microscope)	Zeiss	N/A	Zeiss Axiovert 200 M inverted florescence microscope.
Zeba Desalting columns	Thermo-Scientific	PI-87770	Used to purify newly biotinylated antibodies after the use of the Biotinylation Kit. Instructions provided at: http://www.funakoshi.co.jp/data/datasheet/PCC/89894.pdf
EZ Link Sulfo NHS Low Weight Biotinylation Kit	Thermo- Scientific		Used to biotinylate antibodies to allow them to integrate with the capture surface
Plate Reader	BioTek	Synergy HTX Multimode Reader	Used to quantitatively measure fluorescent intensity in the titration experiments.