WO2018047149A1

WO2018047149A1 - Cell filtration as a means of introducing exogenous material into a cell

Info

Publication number: WO2018047149A1
Application number: PCT/IB2017/055502
Authority: WO
Inventors: Ananth Annapragada; Chandreshkumar PATEL
Original assignee: Texas Children's Hospital
Priority date: 2016-09-12
Filing date: 2017-09-12
Publication date: 2018-03-15

Abstract

Disclosed are methods of delivering substances into cells by passing cells through porous membranes. Disclosed embodiments include methods of delivering a substance into cells by providing a cell suspension, passing the cell suspension through a porous membrane, and exposing the cells to the substance to be delivered into the cells.

Description

CELL FILTRATION AS A MEANS OF INTRODUCING EXOGENOUS MATERIAL

INTO A CELL

DESCRIPTION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent

Application Serial No. 62/393,498, filed September 12, 2016, hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0002] The invention generally concerns methods of introducing exogenous material into cells by means of passing cells through a porous membrane.

B. Description of Related Art

[0003] There are numerous applications where it is desirable to introduce exogenous material into cells. Some examples include gene transfection, siRNA delivery, peptide or protein delivery, particle or agglomerate delivery, and small molecule delivery. There are no universal methods available today for all these purposes. Perhaps the most commonly used application is that of gene transfection. Currently available techniques are both expensive and have very low efficiency. Some known methods for transferring genetic material into cells include the following.

[0004] Cationic lipids may be used in transfection methods. The fusogenicity of cationic lipids with cell membranes is well known. Cationic lipids with terminal amine groups are commonly used to complex naturally anionic DNA and transport it into cells. Perhaps the most common of these materials is Lipofectamine, currently marketed by Invitrogen. The process of encapsulating payload results in both encapsulated and non- encapsulated payload. Yet, only the encapsulated payload is transported into the cell. This results in wasted payload.

[0005] Calcium Phosphate transfection is another commonly used method. It requires mixing DNA with calcium chloride to produce a precipitate that can be taken up by the cells. This method requires experienced hands to produce a size and quality of the precipitate necessary for the transfection. Small changes in pH can affect transformation efficiency. Lastly, calcium phosphate cannot be used with the commonly used cell culture medium RPMI.

[0006] Cationic polymers can also be used to transfect DNA into cells. DEAE-

Dextran is a commonly used polymer that makes a DNA-polymer complex used for transfection. A high concentration of DEAE-Dextran can, however, be toxic to cells.

[0007] Electroporation is another method used for transfection. This method requires exposing cells to a high-intensity electric field, following which charged materials may be transported into the cell, carried by the electric field. Electroporation can easily kill cells, and a common problem with it is low cell viability.

[0008] Cells can also be transfected using microinjection, which involves directly injecting the DNA into the cells. A glass micropipette is used to penetrate the cell membrane under microscopic observation, and material is transferred into the cell. However, this method is tedious and must of necessity be restricted to one cell at a time.

[0009] Viral vectors are also commonly used for transfection. This method requires modifying the DNA and packing it into a viral vector. The properties of the virus, that cause infection of the cell are then taken advantage of to transfect the cell.

[0010] Another transfection technique involves inducing perturbations in cell membranes by forcing cells through microfluidic channels (WO2013/059343). However, the materials for use in this technique require costly microfluidic manufacturing techniques and can process only relatively small volumes in a given time period. In addition, this technique requires application of relatively high pressures to achieve acceptable transfection efficiencies.

SUMMARY OF THE INVENTION

[0011] A solution to the aforementioned inefficiencies of known methods of introducing exogenous materials into cells has been discovered. In some embodiments, the solution resides in passing suspended cells through a simple porous membrane and exposing the cells to the exogenous material. This technique can be performed on simple equipment using relatively low levels of applied pressure and causes exogenous materials to enter into cells at a surprisingly high level of efficiency, while also maintaining very high levels of cell viability. [0012] In one aspect of the present invention, there is disclosed a method of delivering a substance into cells, the method comprising, (a) providing cells in a suspension; (b) passing the suspension through a porous membrane; and (c) exposing the cells to a substance intended to be delivered into the cells. In some embodiments, the substance may be present with the cells in the suspension as the cells are passed through the porous membrane. In some embodiments, the cells may be exposed to the substance only after the cells are passed through the porous membrane. In some embodiments, exposing the cells to the substance comprises adding a predetermined amount of the substance to the cell suspension. In some embodiments, the substance to be delivered into the cells comprises a nucleic acid molecule. In some embodiments, exposing the cells to the substance comprises adding the nucleic acid molecule to the cell suspension to a final concentration of at least 0.5, 1, 2, 3, 4, or 5 μg/ml. In some embodiments, after being delivered into the cells, the cells express a protein encoded by the nucleic acid molecule. In some embodiments, the nucleic acid molecule comprises a gene editing construct. Other suitable substances may be delivered into cells following the method of this embodiment, including peptides, proteins, small molecules, particles, or agglomerates. In some aspects, the invention has the advantage that it can be used to deliver many different types of substances into the cells, while other methods, like viral transfection, are limited to delivering nucleic acid materials. In some embodiments, the substance to be delivered into the cells comprises molecules with molecular weights of at least 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100 kDa or more. In some embodiments, the substance to be delivered into the cells comprises molecules with molecular weights of less than 1 kDa. In some embodiments, the method further comprises detecting the substance in the cells after passing the suspension through the porous membrane. In some embodiments, detecting the substance in the cells comprises detecting expression of a nucleic acid. In some embodiments, detecting the substance in the cells comprising detecting fluorescence of a molecule delivered into the cells. In some embodiments, detecting the substance in the cells comprises detecting an effect of the substance on the function of the cells.

[0013] In some aspects, the invention involves passing cells through a porous membrane to cause the cells to be able to take up a substance. In some embodiments, the porous membrane is made of a polymer. In some embodiments, the polymer is a thermoplastic polymer. In some embodiments, the thermoplastic polymer is polycarbonate. In some embodiments, the porous membrane is hydrophilic. In some embodiments, the membrane is made from a material having a Moh's hardness below S, 4, or 3, or between 2 and 3. The membrane may also be made from other suitable materials known to persons of ordinary skill in the art. In some embodiments, the pores in the membrane have a circular cross-section. In some embodiments, the pores in the membrane have a cylindrical shape. In some embodiments, the diameters of the pores are below about, above about, or about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 μm or are between any two values selected from about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100. In some embodiments, the average diameter of the pores is below about, above about, or about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 μm or is between any two values selected from about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 μm. In some embodiments, the average diameter of the pores is between about 4 μm and 20 μm or between about 4 μm and 12 μm. In some embodiments, the average diameter of the pores is larger than the average diameter of the cells being passed through the membrane. In some embodiments all of the pores have diameters larger than the diameters of the cells. It is a particularly surprising feature of some embodiments of the invention that passing cells through a membrane having pores larger than the cells causes the cells to take up an exogenous substance. In some embodiments, the porous membrane has a pore area fraction between any two values selected from about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, and 70%. In some embodiments the membrane has a thickness of about 12 μm. In some embodiments, the membrane has a thickness between any two values selected from 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, and 30 μm. In some embodiments, it is contemplated that membranes having a woven, net-like, or lattice-like structure or being composed of threads or filaments may be excluded from the embodiments. In some embodiments, the pores have a substantially uniform diameter, resulting in short, cylindrical shapes for the pores with the height of the cylinder being approximately equal to the thickness of the membrane. In some embodiments, the ratio of the pore diameter to pore height is approximately 1:1 or is between about 1:2 and 2:1. In some embodiments, it is contemplated that pores having tapered or conical shapes or regions may be excluded.

[0014] In some embodiments, the flow rate of the cells suspension through the porous membrane is between about 0.04 ml/s-cm² and 0.7 ml/s-cm². In some embodiments, the flow rate of the suspension is about 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, 0.28, 0.32, 0.36, 0.40, 0.44, 0.48, 0.52, 0.56, 0.60, 0.64, 0.68, 0.72, 0.76, or 0.80 ml/s cm² or is between any two values selected from about 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, 0.28, 0.32, 0.36, 0.40, 0.44, 0.48, 0.52, 0.56, 0.60, 0.64, 0.68, 0.72, 0.76, and 0.80 ml/s cm².

[0015] In some embodiments, the method of delivering a substance into the cells further comprises applying a pressure differential across the membrane to accelerate flow of the cell suspension through the porous membrane. In some embodiments, the pressure differential may be achieved by applying positive pressure on one side of the membrane to push the cell suspension through the membrane or by applying a negative pressure (i.e., a vacuum) on one side of the membrane to pull the cell suspension through the membrane. The pressure may be applied by a variety of means known to persons of ordinary skill in the art including, but not limited to, a peristaltic pump, a syringe, an air compressor, or a vacuum pump. In some embodiments the absolute value of the pressure differential across the membrane is less than about or is about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, or 3.0 atm or is between any two values selected from about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, and 3.0 atm. It is a particular, and surprising, advantage of some embodiments of the invention that delivery of a substance into cells can be performed at high efficiency even at relatively low pressure differentials, such as below 0.5 or 1.0 atm. In some embodiments, no pressure differential is applied across the membrane; that is, the suspension flows through the membrane by the force of gravity and/or capillary action.

[0016] In some embodiments, after passing the cell suspension through the porous membrane the proportion of cells that remain viable is greater than 90%. In some embodiments, the proportion of cells that remain viable is greater than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, or 99%. In some embodiments, the proportion of cells that remain viable is between any two values selected from 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, and 99%. In some embodiments, the substance is delivered into at least 90% of the cells that are viable after having passed through the membrane. In some embodiments, the substance is delivered into at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, or 99% of the cells that are viable after having passed through the membrane. In some embodiments, the percentage of cells into which the substance is delivered is between any two values selected from 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, and 99%.

[0017] In some embodiments, the suspension further comprises liposomal particles.

In some embodiments, the liposomal particles comprise a matrix lipid. In some embodiments, the matrix lipid comprises L-a-phosphatidlycholine, hydrogenated ("Hydro Soy PC" or "HSPC"); dipalrnitoylphosphatidylcholine ("DPPC"); and/or l,2-distearoyl-sn-glycero-3- phophocholine ("DSPC"). In some embodiments, the liposomal particles further comprise at least one lipid-PEG conjugate. In some embodiments, the liposomal particles further comprise cholesterol. In some embodiments, the liposomal particles encapsulate an aqueous core. In some embodiments, the substance to be delivered into the cells is encapsulated within the liposomal particles. In some embodiments, the substance to be delivered into the cells is not encapsulated within the liposomal particles. In some embodiments, the liposomal particles have an average diameter of between about 80 and 500 nm. In some embodiments, the liposomal particles have an effective particle size as measured by dynamic light scattering between about 80 and 500 nm or between about 100 and 140 nm. In some embodiments, the liposomal particles are present in a concentration yielding a lipid concentration between about 0.5 and 2 mM. In some embodiments, the liposomal particles are present in a concentration yielding a lipid concentration between any two values selected from about 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 mM. In some embodiments, the liposomal particles enhance the survival rate of cells present in the suspension after the suspension is passed through the membrane. In some embodiments, the liposomal particles increase the proportion of viable cells that take up the substance as a result of passing through the membrane.

[0018] Also disclosed is a method of delivering a substance into a cell, the method comprising (a) providing a suspension comprising cells; (b) adding to the suspension a substance intended to be delivered into the cells; (c) passing the suspension through a porous membrane; and (d) detecting the substance in the cells after the suspension has been passed through the porous membrane.

[0019] It is contemplated that the method of delivering a substance into cells can be performed with a variety of different cell types. In some embodiments, the cells are of mammalian origin. In some embodiments, the cells are of non-mammalian origin. In some embodiments, the cells are immune cells, blood cells, bone marrow cells, neural cells, cancer cells, epithelial cells, muscle cells, reproductive cells, and/or egg cells. In some embodiments, the cells are known to be difficult to transfect, such as K562 leukemia cells.

[0020] The use of the word "a" or "an" when used in conjunction with the term

"comprising" in the claims or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." [0021] The words "comprising" (and any form of comprising, such as "comprise" and

"comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0022] "Effective" or any variation of this term, when used in the claims or specification, means adequate to accomplish a desired, expected, or intended result.

[0023] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0024] The methods of introducing substances into cells disclosed herein can

"comprise," "consist essentially of," or "consist of particular components, compositions, ingredients, etc. disclosed throughout the specification.

[0025] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1: Passing cells through a membrane promotes rhodamine uptake.

Rhodamine fluorescence was visualized in cells passed through a membrane (right panel) and in unfiltered control (left panel).

[0027] FIG. 2: Passing cells through a membrane promotes uptake of a GFP- encoding plasmid. DAPI and GFP fluorescence were visualized in cells passed through the membrane (right panel) and in unfiltered control (left panel).

[0028] FIG. 3: Quantification of GFP fluorescence. GFP fluorescence was quantified by imaging cytometry in cells passed through the membrane and in unfiltered control. [0029] FIG. 4: Membranes with different pore sizes. Rhodamine fluorescence was visualized in cells passed through membranes having 8, 10, or 12 μm pores (top right, bottom left, and bottom right panels, respectively). Control cells (top left panel) were not passed through a membrane.

[0030] FIG. 5: Quantification of Rhodamine fluorescence. Rhodamine fluorescence was quantified by imaging cytometry in cells passed through the membrane with the indicated pore sizes and in unfiltered control.

[0031] FIG. 6: Uptake of a gene editing construct GFP and mCherry fluorescence were visualized. Arrowheads indicate cells co-expressing GFP and mCherry.

[0032] FIG. 7: Uptake of rhodamine by K562 Leukemia cells. DAPI (left panels only) and rhodamine fluorescence (all panels) were visualized in unfiltered control cells (top two panels) and in cells passed through membrane with 10 μιη pores (bottom two panels).

[0033] FIG. 8: Uptake of GFP plasmid by K562 Leukemia cells. DAPI and GFP fluorescence were visualized in unfiltered control cells (left panel) and in cells passed through a membrane with 10 μιη pores (right panel).

[0034] FIG. 9: Effect of membrane surface properties. DAPI and rhodamine fluorescence were visualized in cells passed through a 10 μm membrane either by an infusion pump (left panels) or a gas pressure extruder (right panels). Membranes had either hydrophobic (bottom two panels) or hydrophilic (middle two panels) surfaces. Control cells (top two panels) were not passed through a membrane.

[0035] FIG. 10: Quantification of Rhodamine fluorescence. Rhodamine fluorescence was quantified by imaging cytometry in cells passed through the membrane with the indicated surface properties using an extruder and in unfiltered control.

[0036] FIG. 11: Quantification of Rhodamine fluorescence. Rhodamine fluorescence was quantified by imaging cytometry in cells passed through the membrane with the indicated surface properties using an infusion pump and in unfiltered control.

[0037] FIG. 12: Uptake of GFP plasmid by cells passed through a membrane having pores larger than the cells. DAPI and GFP fluorescence were visualized in cells passed through a membrane having 12 μm pores (panel A and bottom two panels). Panel B: control cells that were not passed through a membrane. [0038] FIG. 13: Uptake of rhodamine added after cells pass through membrane.

DAPI and rhodamine fluorescence were visualized in cells that were incubated with rhodamine before and during filtration (middle panel) and in cells that were incubated with rhodamine only after filtration. Control cells (left panel) were incubated with rhodamine but not passed through a membrane.

[0039] FIG. 14: Uptake of rhodamine added at various time points after cells pass through membrane. DAPI and rhodamine fluorescence were visualized in cells that were incubated with rhodamine before and during filtration and in cells that were incubated with rhodamine only after filtration, with the rhodamine being added at 1 min., 30 min, 1 nr., 2 nr., 3 nr., or 4 hr. after filtration, as indicated (starting at top left panel across top: control, rhodamine co-filtered sample, rhodamine added 1 min. after filtration, and rhodamine added 30 min. after filtration; starting at bottom left panel across bottom: rhodamine added 1 hr. after filtration, 2 hr. after filtration, 3 hr. after filtration, and 4 hr. after filtration ) . Control cells (top left panel) were incubated with rhodamine but not passed through the membrane. [0040] FIG. 15: Net-like membranes. Nylon (left) and polypropylene (right) membranes with 10 μm pore sizes were visualized by a light microscope.

[0041] FIG. 16: Cells captured by net-like membranes. DAPI fluorescence was visualized in cells on the surface of net-like nylon (left) or polypropylene (right) membranes.

[0042] FIG. 17 shows an embodiment of a system for delivering a substance into cells using vacuum pressure.

[0043] FIG. 18 shows an embodiment of a system for delivering a substance into cells using a container connected to tubing.

DETAILED DESCRIPTION OF THE INVENTION

[0044] Novel methods of delivering substances into cells are described herein. Current methods of doing so are limited by low efficiency, low survival rates of cells, and limited range of payload. The methods described herein provide a solution to these problems and provide a highly efficient, simple means of delivering a wide variety of substances into cells. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections. A. Systems for delivering a substance into cells

[0045] The methods of delivering substances into cells disclosed herein can be performed using systems suitable for such purpose. In one embodiment of such a system, illustrated in FIG. 17, a membrane 2 is be placed in the bottom of a container 4 such that it completely covers an opening 6 at the bottom of the container 4 so that a cell suspension 10 cannot pass through the opening 6 without first passing through the membrane 2. The container 4 is placed on top of another container 8 for capturing the cell suspension 10 after it flows through the membrane 2. The top container 4 and bottom container 8 are connected with an air-tight seal 12. Vacuum pressure is applied in the space 14 below the membrane 2 using an opening 20 into the space 14 below the membrane 2 to accelerate the flow of a cell suspension 10 through the membrane 2.

[0046] In another embodiment of a system for delivering substances into cells, illustrated in FIG. 18, the membrane 2 is placed in a container 28 having an inlet port 16 and an outlet port 18. The membrane 2 may be placed in the container 28 such that it completely covers the outlet port 18 so that a cell suspension 10 cannot pass through the outlet port 18 without first passing through the membrane 2. The inlet port 16 is connected to an inlet tube 22 in fluid communication with a cell suspension reservoir (not shown) and source of positive pressure (not shown). The outlet port 18 is connected to an outlet tube 24 in fluid communication with a container (not shown) that captures the cell suspension 10. Positive pressure may be applied by a variety of suitable means, including an infusion pump, a plunger or syringe, or a gas pressure device.

[0047] A variety of other suitable configurations can be envisioned by a person of ordinary skill in the art. In some embodiments, no pressure is applied to the system so that there is no pressure differential across the membrane. In such embodiments, the cell suspension can flow through the membrane under the force of gravity alone. In embodiments in which a pressure differential is created across the membrane (i.e. where negative pressure is applied on one side of the membrane, where positive pressure is applied on one side of the membrane, or where a combination of positive pressure on one side and negative pressure on the opposite side of the membrane are applied together), such pressure can accelerate the flow of the cell suspension through the membrane, advantageously increasing the amount of cell suspension that can be processed in a given amount of time. B. Membranes

[0048] Embodiments disclosed herein involve passing cells through porous membranes. The membranes can be made of polymers, including, for example, polycarbonate. Suitable membranes for disclosed methods can include commercially available membranes such as those sold under the trade name Nucelopore. These membranes are available with pore sizes of 0.05 to 12 μm. The pores are typically circular, and are formed by caustic etching of the membrane after exposure to high energy particles in a cyclotron wherein the crystal structure of the membrane polymer is damaged and rendered susceptible to the etch. The membranes are typically quite thin, around 1-20 μm, and the pores are therefore better classified as circular or disk like rather than cylindrical. The pore sizes are usually distributed around the nominal size quoted on the specification of the membrane. Thus, a 5μ membrane usually will exhibit pores distributed from approximately 4 to 6 μm. Similarly, the thickness of the membranes typically varies by + 10% from the stated thickness. These properties of the pores are maintained whether the membrane is hydrophobic or hydrophilic in nature, and regardless of the specific polymer the membrane is composed of.

[0049] The hardness of the membrane material can be characterized according to various hardness tests, including Moh's hardness. Moh's hardness is a means of characterizing the hardness of a substance by observing the ability of the substance to resist scratching. It has been suggested that more rigid and hard materials, such as silicon, with a Moh's hardness of approximately 7-8 (Handbook of Chemistry and Physics, CRC Press, 1993-1994, Page 12-162), are more suitable in methods of transfecting cells. {See WO2013/059343). However, the inventors have surprisingly found that porous membranes made from relatively soft materials, including those with Moh's hardness values of below 4, or of approximately 2-3, can also be successfully used in methods of delivering substances into cells. For example, membranes made from polypropylene (Moh's hardness of approximately 2-3), can be used effectively in methods disclosed herein.

[0050] The dimensions and other properties of the membranes, such as pore size, thickness, and area ratio of pores to membrane material can be varied to alter the performance of the membrane. For example, larger pore sizes can be used for larger cells. Pore size can also affect the viability of cells passing through the membrane and the efficiency at which a substance is delivered into cells. A higher area ratio of pores to membrane can be used to allow for a higher rate of flow through the membrane. The size of the membrane can be freely adjusted to adapt to containers of different sizes and configurations and to allow for high volumes of cell suspension to be processed more quickly.

[0051] In some embodiments disclosed herein, the method involves a certain rate of flow through the membrane. Flow rate through a membrane can be ascertained by measuring the amount of liquid that passes through the membrane in a given amount of time and dividing by the area of the membrane. The flow rate can be influenced by the area fraction of pores in the membrane. The flow rate through the pores themselves can be ascertained by multiplying the flow rate through the membrane by the area fraction of pores. For example, if the flow rate through a membrane having an area fraction of pores of 40% is measured to be 1 ml/s-cm², the flow rate through the pores is 0.4 ml s-cm². Embodiments disclosed herein typically have flow rates through the membranes ranging from about 0.04 ml/s-cm² to 0.7 ml/s-cm², but can be adjusted higher or lower. Pore area fractions in membranes described herein are typically between about 20 and 50%, but other values may be used as appropriate.

C. Payload

[0052] A variety of substances can be delivered into cells using the methods disclosed herein. A substance to be delivered into cells can be referred to as "payload." A common type of payload is nucleic acid molecules. DNA and RNA encoding proteins of interest can be delivered into cells and then expressed using the cell's machinery. Other nucleic acids like miRNAs can be delivered into cells to alter the expression of a gene in the cell. Nucleic acids comprising a gene editing construct can also be delivered into cells. As a non-limiting example, a nucleic acid molecule comprising a CRISPR/Cas9 gene editing construct can be delivered into cells using methods disclosed herein. A gene editing construct is intended to induce desired changes in a target DNA sequence. Nucleic acid molecules can be delivered in different forms, including, for example, as plasmids, double-stranded linear molecules, or single stranded linear molecules.

[0053] Other macromolecules such as proteins and polysaccharides can also be delivered into cells using the methods disclosed herein. These molecules can be useful in regulating gene expression or otherwise altering the function of the target cells. Payload to be delivered into the cells using the disclosed methods can vary in size from small molecules of 1 kDa or less to large molecules in excess of 100 kDa. Small molecule payload can be a drug or other therapeutic agent or may be used to alter the functioning of the cell in research applications. [0054] In some instances, the substance to be delivered into cell is comprised in a liposomal particle, or liposome. Liposomes are generally spherical vesicles having at least one lipid bilayer. Suitable liposomes for use in embodiments disclosed herein can include, for example, stealth liposomes, which include a coating of PEG. The presence of liposomes in the cell suspension can enhance survival of cells passed through a membrane and can enhance the delivery of a substance into cells. This is true even if the substance to be delivered into cells is not comprised in the liposomes. The concentration of liposomes can be characterized by a total lipid concentration that they contribute to a cell suspension. For example, a reference to a total lipid concentration of 1 mM indicates that the lipids that make up the liposomes are present at 1 millimole per liter, not that the liposomal particles themselves are present in that concentration. The size of the liposomes can be characterized in a number of ways. In one example, an effective particle size is determined by dynamic light scattering (DLS).

[0055] In particular embodiments, the substance that is desired to be delivered into the cells is added to the cell suspension before the cell suspension is passed through the membrane. Thus, the cells and the substance pass through the membrane together. In some embodiments, the substance is added to the cell suspension after the cell suspension is passed through the membrane. In these embodiments, passing the cells through the membrane causes the cells to be receptive to delivery of the substance of interest. Exposing the cells to the substance while they are in this receptive state can cause the substance to be delivered into the cells.

[0056] Delivery of a substance into cells can be detected and monitored by a variety of methods known in the art. One common way is to detect fluorescence using a microscope. In some instances, the substance itself is fluorescent and successful uptake of the substance can be detected by observing the fluorescence of the substance in cells. In some instances, the substance is a nucleic acid encoding a protein that is fluorescent, for example GFP or mCherry, so that detection of that protein's fluorescence indicates successful delivery of the nucleic acid. In addition to microscopy, fluorescence in a cell can also be detected by methods such as flow cytometry. Other means of detecting successful delivery of a substance into cells can be devised based on the characteristics of the payload and its effect on cells. Detection of delivery of a substance into cells can be direct, such as by observing the substance itself, or indirect, such as by observing an effect that the substance has on the cells. [0057] In some instances, methods disclosed herein are characterized by the efficiency at which they deliver a substance into the cells. This can be measured by, for example, determining what proportion of cells that pass through the membrane uptake the payload, by determining the proportion of viable cells in the cell suspension after passing through the membrane that have taken up the payload, or by other measures known in the art. Efficiency of delivery of substances into cells can be influenced by the size of the membrane pores, the flow rate through the membrane or pores, the surface properties of the membrane, the structure of the membrane, the pressure differential across the membrane, the type of cell, the nature of the ingredients in the cell suspension, among other factors. It is a particular advantage of embodiments described herein that they result in relatively high efficiency delivery of substances into cells.

[0058] Methods disclosed herein can also be characterized by the proportion of viable cells that are recovered after a cell suspension is passed through a membrane as compared to the number of viable cells in the suspension before being passed through the membrane. Cell viability can be detected in a variety of ways, including by trypan blue exclusion, tetrazolium reduction, resazurin reduction, and many other assays known to persons of ordinary skill in the art. It is a particular advantage of embodiments described herein that they result in high recovery of viable cells after passage through the membrane and that they result in a combination of high efficiency of delivery of a substance into cells while at the same time maintaining a high recovery of viable cells. Due to this advantage, embodiments described herein can be used to effectively deliver desired substances into cells that are sensitive to known transfection methods or are difficult to transfect for other reasons.

[0059] It is contemplated that the substance delivered into cells in the methods disclosed herein is a substance, such as, for example, a molecule or mixture of molecules, that is of particular interest and/or is intended or expected to have some specific effect on the cells that is made possible by being delivered into the cells. It is also contemplated that the effect of the substance to be delivered into the cells is not known or suspected before being delivered into the cells, and delivery into the cells is a means of ascertaining the effect of the substance, if any, on the cells. Other molecules, chemicals, solvents, solutes, and other ingredients present in the cell suspension can also enter cells along with the substance of interest. However, entry of those ingredients into cells is not considered to comprise delivery of a substance into the cells for purposes of embodiments described herein. [0060] The terms "transfection" and "transduction" as used herein refer generally to delivery of exogenous substances, or payload, into cells and can include delivery of substances or molecules into cells that would not normally be found in the cells.

D. Cell suspension

[0061] Embodiments disclosed herein involve passing a cell suspension through porous membranes. As used herein, a "cell suspension" can comprise a mixture of cells in an aqueous liquid phase. In some instances, the aqueous liquid phase can comprise buffers, nutrients, serum, and other suitable ingredients. In some instances, the aqueous liquid phase comprises growth media, such as, for example, DMEM, or buffers, such as PBS. In some instances, the aqueous liquid phase can be pure water. The cell suspension can be homogeneous or non-homogeneous, and can include mixtures in which some or all cells have settled out of suspension.

[0062] A variety of cell types can be used in the methods described herein. The cells can be cultured cells or they can be derived from living tissue. The cells can be immune cells, blood cells, bone marrow cells, neural cells, cancer cells, epithelial cells, muscle cells, reproductive cells, egg cells, and many other cell types. It is a particular advantage of some embodiments disclosed herein that they can be used to deliver a substance of interest into cells that are known to be difficult to transfect, such as, for example, K562 leukemia cells.

[0063] The terms "filtered" and "passed through a membrane" are used synonymously herein. Use of the terms 'filter" or "filtered" is not intended to indicate that some substance present in the cell suspension is prevented from passing through the membrane. That is, a cell suspension can be said to be "filtered" even if the entirety of the cell suspension passes through the membrane. Likewise, cells are said to be "filtered" if they have passed through the membrane, whether or not the membrane prevented anything from passing through.

EXAMPLES

[0064] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results. Example 1

Rhodamine liposome loading into HeLa cells [0065] Rhodamine liposomes used in this and subsequent Examples were prepared by the following procedure. A 100 mM lipid mixture consisting of l,2-dipalmitoyl-sn-glycero-3- phospho-choline (DPPC), cholesterol, l,2-distearoyl-sn-glycero-3-phosphoemanolamine-N- [methoxy (polyethylene glycol)-2000] (DSPE- MPEG2000), and Lissamine Rhodamine B l,2-Dmexadecanoyl-sn-Glycero-3-Phosphoemanolamine, Triethylammonium Salt (rhodamine DHPE) in a 58.3:40:1.5:0.20 molar ratio was dissolved in ethanol, 200 proof, at ~60°C. The ethanol lipid solution was hydrated with an 10 mM histidine/150 mM saline solution at ~60°C and then sequentially extruded on a Lipex thermoline extruder (Northern Lipids Inc., Canada), with four passes through a 200 nm Nuclepore membrane (Whatman, Newton, MA) followed by six passes through a 100 nm membrane. Dialysis was done using a 300kD Float-A-Lyzer (Spectrum Labs, Rancho Dominguez, CA) to remove any free-floating lipids. Effective particle size was determined by DLS (Brookhaven Instruments Corp, Holtville, NY), to be 121.5 nm with a polydispersity index of 0.038.

[0066] Rhodamine was delivered into cells according to the following procedure.

Cultured HeLa cells were trypsinized with a 0.25% trypsin solution containing 2.21 mM EDTA after which the cells were suspended in DMEM media with 10% FBS. The cells were then centrifuged at 500 rpm for 5 minutes, after which the supernatant was aspirated and the cells were re-suspended in 4 mL of DMEM media. 50 μΐ of 100 mM lipid concentration of stealth liposomes with 0.2 mol% lipid-Rhodamine, prepared as described above, were added to 4 ml of the cell suspension for a final lipid concentration of 1.25 mM. The cell suspension was then passed through a polycarbonate hydrophilic Nuclepore Track-Etch membrane (Whatman) having 8 μιη pores and a thickness of 12 μm thick using a Lipex thermoline extruder with -10 psi applied. The filtered suspension was incubated in Corning Falcon chambered cell culture slides overnight at 37°C with 5% CO₂. The cells were washed with 1% PBS followed by fixation in 4% paraformaldehyde for 10 minutes then washed in 1% PBS and counterstained for nuclei with DAPI, 5 μg/mL, for 10 min. The cells were then rinsed in PBS and coverslip was applied with Gel/Mount. Cells were observed under a microscope and inspected for rhodamine fluorescence. As a control, a suspension of HeLa cells was incubated with the same concentration of rhodamine-containing lipids under the same conditions but without being filtered. FIG. 1 shows that the cells passed through the membrane (right panel) took up much more rhodamine than the control (left panel). Example 2

GFP Plasmid transfection into HeLa cells [0067] HeLa cells growing in culture were trypsinized, washed, and suspended in

DMEM complete medium. 20 μg of a GFP-encoding plasmid (pCas9 GFP lOkd (OriGene) were added to 4 mL of the cell suspension. The suspension was then passed through a 8 μm polycarbonate hydrophilic membrane and plated as described in Example 1. As a control, an identical cell suspension was created and plated without being filtered. The cells were incubated overnight and fixed in 4% paraformaldehyde for 10 minutes and washed in 1% PBS. The cells were stained with DAPI and washed again. DAPI (dark gray) and GFP (light gray) fluorescence were observed under a microscope. FIG. 2 shows that the filtered cells (right panel) exhibited substantially more GFP fluorescence than the unfiltered control (left panel). Thus, filtering the cells caused substantial uptake of the GFP plasmid. This was confirmed by measuring the intensity of GFP fluorescence for individual cells in the filtered and control samples by imaging cytometry. FIG. 3 shows that filtered cells exhibited greater GFP fluorescence than the unfiltered control.

Example 3 Cell viability is dependent on the pore size of the filtration membrane

[0068] HeLa cells growing in culture were trypsinized, washed, and resuspended in 4 ml DMEM complete medium or in 4 ml of DMEM serum-free medium. Each of three 1 ml aliquots of each cell suspension was passed through a membrane with a pore size of 8, 10, or 12 μm and a thickness of 12 μιη using an extruder at 10 psi as described in Example 1. An additional 1 ml of cell-free medium (complete or serum-free to correspond to the cell suspension) was passed through each membrane to flush any retained cells. The total number of alive cells in each 1 ml cell suspension before and after being passed through the membrane was measured by a trypan blue exclusion assay (dead cells are stained blue and alive cells are unstained; cells are counted using a hemacytometer). The percent viability before and after filtration and the percent of alive cells recovered after filtration were calculated, and the results for the DMEM complete medium experiments ("Serum media") and the DMEM serum-free medium ("Serum free media") are set forth in Table 1 and Table 2, respectively. TABLE 1

TABLE 2

[0069] The 12 μιη membrane results in the highest viability both with serum- containing and serum-free media. The fraction of live cells recovered is highest with serum- free media and a 12 μm membrane. With serum-containing medium, the fraction of live cells recovered is highest with the 10 μm membranes.

Example 4

The presence of stealth liposomes in the filtration mixture

increases cell survival after filtration

[0070] HeLa cells growing in culture were trypsinized, washed, and resuspended in 4 ml DMEM complete medium. Stealth liposomes with 0.2 mol% lipid-Rhodamine prepared as in Example 1 were added to 4 ml of the cell suspension for a final lipid concentration of 1.25 mM. Three 1 ml aliquots of the suspension were passed through a 12 μm-thick membrane with a pore size of 8, 10, or 12 μm, using an extruder at 10 psi of pressure. One 1 ml aliquot served as a no filtering control. An additional 1 ml of cell free DMEM complete medium was passed through each membrane to flush any retained cells. The cells were incubated for 20 hours and then fixed in 4% paraformaldehyde for 10 minutes, washed in 1% PBS, and stained with DAPI at 5 μg/ml for 10 min. The cells were rinsed in PBS, and DAPI and rhodamine fluorescence were observed under a microscope. The percent viability before and after filtration was and percentage of alive cells recovered were determined as in Example 3. The viability results are set forth in Table 3 and Table 4.

TABLE 3

TABLE 4

[0071] Compared to the results for complete DMEM cell suspensions without liposomes in Table 1, the cell suspension with liposomes shows higher percentages for viability and proportion of alive cells recovered for all membranes.

[0072] FIG. 4 shows substantially higher proportions of cells with rhodamine fluorescence for cells that were passed through the membranes (top right— 8 μm, bottom left— 10 μm, and bottom right— 12 μm) than for control cells that were not passed through a membrane (top left panel). This was confirmed by measuring the intensity of GFP fluorescence for individual cells in the filtered and control samples by imaging cytometry. FIG. 5 shows that cells passed through both membranes exhibited greater GFP fluorescence than the unfiltered control. The loading of rhodamine into cells is not obviously dependent on the pore size, but the recovered cell viability is much higher at the 12 μm pore size.

Example 5

Transfection with gene editing construct

[0073] Cultured NGP and SY5Y cells were trypsinized and resuspended in 4 ml of

Opti-MEM media (ThermoFisher Scientific). 20 μg of the GFP-encoding plasmid pCas9 GFP 10kd was added to the suspension. This plasmid contains a CRISPR-Cas9 gene editing construct that causes the GFP DNA sequence to be inserted at a target sequence. At the same time, 15 μg of an mCherry 5067 bp was added to the suspension. This plasmid contains a target sequence for the CRISPR-Cas9 gene editing construct. The cell suspension was then passed through a hydrophilic polycarbonate membrane with 5 μm pore size using an extruder with 10 psi. The cells were incubated for 68 hours, then fixed in 4% paraformaldehyde for 10 minutes, washed in lx PBS, and stained with 5 μg/ml DAPI for 10 minutes. The cells were washed in PBS, and DAPI, GFP, and mCherry fluorescence were observed under a microscope. The percent viability before and after filtration and percent of alive cells recovered were determined by trypan blue exclusion assays. The viability results are set forth in Table 5 and Table 6.

TABLE 5

TABLE 6

[0074] Although recovery of cells was low, SY5Y cells expressing both GFP and mCherry were recovered, as shown by FIG. 6. The arrow heads in the right panel point to cells co-expressing GFP (green) and mCherry (red), demonstrating that both plasmids were taken up by the cells and the GFP construct was inserted.

Example 6 Transfecting K562 leukemia cells

[0075] K562 leukemia cells are notoriously difficult to transfect. However, the inventors were able to achieve transfection of these cells by passing them through a membrane. Cultured K562 leukemia cells were trypsinized, washed, and resuspended in RPMI media. 50 μΐ of 100 mM lipid concentration of stealth liposomes with 0.2 mol% lipid- Rhodamine prepared as described in Example 1 was added to 4 ml of cell suspension for a final lipid concentration of 1.25 mM. 20 μg of MIGR 1 6056 bp GFP plasmid (Addgene) was added to 4 ml of cell suspension. The cell suspensions were passed through a polycarbonate membrane having 10 μm pores using an extruder at 10 psi. The cells filtered with the plasmid were incubated for 72 hours and the cells filtered with the rhodamine liposomes were incubated for -20 hours. After incubation, the cells were fixed in 4% paraformaldehyde for 10 minutes, washed in lx PBS, and stained with 5 μg/ml DAPI for 10 minutes. The cells were washed in PBS, and rhodamine (FIG. 7) and GFP fluorescence (FIG. 8) were observed under a microscope. The percent viability before and after filtration and percent of alive cells recovered were determined by trypan blue exclusion assays. The viability results are set forth in Table 7 and Table 8.

TABLE 7

TABLE 8

[0076] FIG. 7 shows that passing the K562 cell suspension through the membrane caused the cells to uptake rhodamine (bottom right panel) substantially more than control cells that were not passed through the membrane (top right panel).

[0077] FIG. 8 shows that passing the K562 cell suspension through the membrane caused the cells to uptake and express the GFP plasmid (right panel) substantially more than control cells that were not passed through the membrane (left panel). Example 7 Effect of membrane surface properties [0078] K562 leukemia cells were trypsinized, washed, and resuspended in RPMI media. SO μl of 100 mM lipid concentration of stealth liposomes with 0.2 mol% lipid- Rhodamine prepared as in Example 1 was added to the cell suspension for a final lipid concentration of 1.25 mM. Four aliquots of cell suspension were passed through membranes as follows: one aliquot was passed through a 12 μm-thick hydrophilic polycarbonate membrane having 10 μm pores using a gas pressure extruder with approximately 10 psi of applied pressure; one aliquot was passed through a 12 μm-thick hydrophobic polycarbonate membrane having 10 μm pores using a gas pressure extruder; one aliquot was passed through a 12 μm-thick hydrophilic polycarbonate membrane having 10 μm pores using an infusion pump at a flow rate of 25 ml/min; and one aliquot was passed through a 12 μm-thick hydrophobic polycarbonate membrane having 10 μm pores using an infusion pump at the same flow rate. The cells filtered with the plasmid were incubated for 72 hours, and the cells filtered with the rhodamine liposomes were incubated for -20 hours. After incubation, the cells were fixed in 4% paraformaldehyde for 10 minutes, washed in lx PBS, and stained with 5 μg/ml DAPI for 10 minutes. The cells were washed in PBS, and rhodamine fluorescence was observed under a microscope. Viability and percentage of alive cells recovered were calculated as described above. Tables 9 and 10 set forth the viability results for the gas pressure extruded suspensions. Tables 11 and 12 set forth the viability results for the infusion pumped suspensions.

TABLE 9

TABLE 10

TABLE ll—Pre-filtration

[0079] These results show that the hydrophilic membrane better preserves the viability of cells that pass through it than the hydrophobic membrane. FIG. 9 shows that the hydrophilic membrane also promoted uptake of rhodamine more efficiently than the hydrophobic membrane. Cells that were forced through the membrane using both the gas pressure extruder and infusion pump were able to take up rhodamine. This was confirmed by measuring the intensity of rhodamine fluorescence for individual cells in the filtered and control samples by imaging cytometry. FIG. 10 and FIG. 11 show the quantification of fluorescence in filtered and control cells for the extruder and infusion pump, respectively, and confirm the conclusion that passing cells through the hydrophilic membrane promoted uptake of rhodamine more efficiently than through the hydrophobic membrane. Example 8

Successful transfection using membranes having a pore size larger than cell size [0080] Cultured NKT cells, which have diameters of approximately 10 μm and below, were washed and suspended in RPMI. 20 μg of a GFP-encoding plasmid was added to 4 ml of cells. The cell suspension was passed through a hydrophilic polycarbonate membrane having 12 μm pores and a thickness of 12 μm. After 72 hours of incubation, the cells were fixed in 4% paraformaldehyde for 10 minutes, washed in 1% PBS, and stained with S μg/ml DAPI for 10 minutes. DAPI and GFP fluorescence were observed under a microscope. FIG. 12 shows that cells passed through the membrane took up GFP (panel A and bottom two panels), but control cells (panel B) did not. Thus, surprisingly, passing cells through a membrane can induce cells to take up DNA even when the pores are larger than the cells.

Example 9

Successful transfection when payload is added after cells are passed through a

membrane

[0081] To test the effect of adding payload after the filtration, liposomal Rhodamine at a total lipid concentration of 0.625 mM was incubated with NKT cells under the following three conditions: (1) co-incubation with no filtration, (2) co-incubation followed by co- filtration, and (3) filtration of the cells followed by incubation with the payload. The membranes used were hydrophilic polycarbonate membranes having 8 μιη pores and 12 μm thickness. FIG. 13 shows that co-filtration (middle panel) and post-incubation (right panel) both result in high levels of transduction, whereas co-incubation with no filtration showed minimal transduction.

[0082] To test how long cells remain capable of taking up payload after passing through the membrane, the above experiment was repeated, but instead of immediately adding the lipid rhodamine payload to the cell suspension passed through the membrane in the absence of payload, the filtered cell suspension was split into 6 aliquots, and liposomes with lipid rhodamine payload were added (total lipid concentration: 0.625 mM) 1 min., 30 min., 1 nr., 2 nr., 3 hr., or 4 hr. after filtration. FIG. 14 shows that the cells remained capable of taking up the rhodamine payload at the 1 min., 30 min., and 1 hour time points, after which uptake was indistinguishable from the unfiltered control (top left panel). Example 10

Membranes having a net-like structure do not efficiently pass cells through [0083] The ability of nylon and polypropylene membranes having net-like structures, as shown in FIG. IS, and 10 μm pore sizes to allow cells to pass through was tested using a suspension of NKT cells. Aliquots of the cell suspension were passed through the membranes using an extruder. After cell suspensions were passed through the net-like membranes, the membranes were stained with DAPI to visualize any adherent cells. FIG. 16 shows that both membranes captured numerous cells despite the pore sizes of the membranes being 10 μm.

Prophetic Example 11

Low pressure filtration with high payload delivery efficiency [0084] The efficiency of payload delivery into cells achieved by passing the cells through a porous membrane will be tested at a variety of different applied pressures. Aliquots of cell suspensions with payload added will be passed through porous membranes like those in the Examples above using a gas pressure extruder or infusion pump at a range of applied pressures. The efficiency of payload delivery at the various pressures will be determined by detecting the presence of the payload in the filtered cells and calculating the proportion of filtered cells that take up the payload. It is expected that cell filtration performed according to embodiments disclosed herein will effectively deliver payload into cells even at low applied pressures, i.e., lower than 0.S atm, with efficiencies greater than 20%.

Claims

1. A method of delivering a substance into cells, the method comprising:

(a) providing cells in a suspension;

(b) passing the suspension through a porous membrane; and

(c) exposing the cells to a substance intended to be delivered into the cells.

2. The method of claim 1, wherein the substance is present with the cells in the suspension as the cells are passed through the porous membrane.

3. The method of claim 1, wherein the cells are exposed to the substance only after the cells are passed through the porous membrane.

4. The method of any one of claims 1 to 3, wherein exposing the cells to the substance comprises adding a predetermined amount of the substance to the cell suspension.

5. The method of any one of claims 1 to 4, further comprising detecting the substance in the cells after passing the suspension through the porous membrane.

6. The method of claim 5, wherein detecting the substance in the cells comprises detecting expression of a nucleic acid.

7. The method of claim 5 or 6, wherein detecting the substance in the cells comprising detecting fluorescence of a molecule delivered into the cells.

8. The method of any one of claims 5 to 7, wherein detecting the substance in the cells comprises detecting an effect of the substance on the function of the cells.

9. The method of any one of claims 1 to S, wherein passing the suspension through the porous membrane causes the substance to be delivered into the cells.

10. The method of any one of claims 1 to 9, wherein the substance comprises a nucleic acid molecule.

11. The method of claim 10, wherein exposing the cells to the substance comprises adding the nucleic acid molecule to the cell suspension to a final concentration of at least 1 μg/ml.

12. The method of claim 10 or 11, wherein, after the nucleic acid molecule is delivered into the cells, the cells express a protein encoded by the nucleic acid molecule.

13. The method of claim 10 or 11, wherein the nucleic acid molecule comprises a gene editing construct.

14. The method of any one of claims 1 to 13, wherein the membrane is made of a thermoplastic polymer.

15. The method of claim 14, wherein the thermoplastic polymer is polycarbonate.

16. The method of any one of claims 1 to 15, wherein the membrane is hydrophilic.

17. The method of any one of claims 1 to 16, wherein the membrane is made from a material having a Moh's hardness below 4.

18. The method of any one of claims 1 to 17, wherein the membrane comprises pores having a circular cross-section.

19. The method of claim 18, wherein the pores have diameters between 4 μm and 12 μm.

20. The method of claim 18 or 19, wherein the membrane pores have an average diameter larger than the average diameter of the cells.

21. The method of any one of claims 1 to 20, wherein the flow rate of the suspension through the membrane is between 0.04 ml/s-cm² and 0.7 ml/s-cm².

22. The method of any one of claims 1 to 21, further comprising applying a pressure differential across the membrane to accelerate flow of the cell suspension through the porous membrane.

23. The method of claim 22, wherein the absolute value of the pressure differential is less than 1 atm.

24. The method of any one of claims 1 to 21, wherein no pressure differential is applied across the membrane.

25. The method of any one of claims 1 to 24, wherein the membrane has a thickness of about 12 μm.

26. The method of any one of claims 1 to 25, wherein, after passing the cell suspension through the porous membrane, the proportion of cells that remain viable is greater than 90%.

27. The method of any one of claims 1 to 26, wherein the substance is delivered into at least 90% of the cells that are viable after having passed through the membrane.

28. The method of any one of claims 1 to 27, wherein the suspension further comprises liposomal particles.

29. The method of claim 28, wherein the liposomal particles enhance the survival rate of cells present in the suspension after the suspension is passed through the membrane.

30. The method of claim 28 or 29, wherein the liposomal particles comprise

(a) a matrix lipid selected from L-a-phosphatidlycholine, hydrogenated; dipalmitoylphosphatidylcholine; and l,2-distearoyl-s7i-glycero-3- phophocholine;

(b) a lipid-PEG conjugate; and

(c) cholesterol.

31. The method of any one of claims 28 to 30, wherein the liposomal particles are approximately 80 to 500 nm in diameter.

32. The method of any one of claims 28 to 31, wherein the liposomal particles are present in a concentration yielding a lipid concentration between about 0.5 and 2 mM.

33. The method of any one of claims 1 to 32, wherein the cells are mammalian cells.

34. The method of claim 33, wherein the cells are K562 leukemia cells.

35. A method of delivering a nucleic acid molecule into a cell, the method comprising:

(a) providing a suspension comprising the cell and the nucleic acid molecule; and

(b) passing the suspension through a polycarbonate porous membrane;

wherein passing the suspension through the membrane causes the nucleic acid molecule to be delivered into the cell.

36. A method of delivering a substance into a cell, the method comprising:

(a) providing a suspension comprising cells;

(b) adding to the suspension a substance intended to be delivered into the cells;

(c) passing the suspension through a porous membrane; and

(d) detecting the substance in the cells after the suspension has been passed through the porous membrane.