Method for Infusing an Immunotherapy Agent to a Solid Tumor for Treatment

Abstract

A method for delivering an immunotherapy agent to a tumor includes advancing the delivery device into a vessel of a patient, and infusing the agent under pressure into the vessel to penetrate the tumor. The delivery device prevents reflux of the agent toward non-treatment sites.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates devices and methods for administering immunotherapy to a patient, particularly for the treatment of patients with solid tumors.

2. State of the Art

For many years the basic treatment for cancer has consisted of surgery, chemotherapy and radiation therapy. More recently, drugs that target cancer cells, such as imatinib (Gleevac®) and trastuzumab (Herceptin®) by guiding themselves to specific molecular changes seen in the cancer cells have also become standard treatments for a number of cancers.

Now, therapies that take advantage of a patient's immune system to fight their cancers are in clinical use or in development and gaining interest. There are four basic versions of immunotherapy products today, which can be used alone or in combination. These immunotherapy products include immunomodulators, vaccines, modified cells and check-point inhibitors.

Immunomodulators include IL-2, IL-7, IL-12, Interferons, G-CSF, Imiquimod, CCL3, CCL26, CXCL7, cytosine phosphate-guanosine, oligodeoxynucleotides, and glucans, and all operate to systemically increase the patient's immune response. Vaccines comprise an infusion of antigen directly or antigen-activated dendritic cells, which activate the patients white blood cells. Modified cells are blood-derived immune cells from the patient which are engineered and incubated to grow to a large number of modified cells that specifically target a region of tumor. This approach, referred to as adoptive cell transfer (ACT) has generated remarkable responses in the small clinical trials in which it has been investigated. Check-point inhibitors include anti-PD-1, which block the patient's natural suppression of T-cells, thereby effectively increasing the time and number of T-cells that can fight the cancer.

Immunotherapy practice has had success in “liquid” tumors, such as leukemia, where the therapy is easily delivered to the site of the cancer via intravenous injection or infusion. Further, immunotherapy has promise for solid tumors. However, delivery of the therapy with sufficient penetration into the tumors to allow the therapy to interact with the cancer cells remains a challenge.

In current practice, the immunotherapy agents are delivered by oral dosage, venous delivery, or catheter-based delivery to an organ of interest with a traditional microcatheter.

In venous delivery, the agent is generally infused into the patient through a peripherally inserted central catheter (PICC) or a port implanted in the patient. PICCs and ports can remain in place for several weeks or months and are used to reduce the number of times that a patient is subject to needle sticks and to reduce risk of tissue and muscle damage that can occur with a standard IV. While a PICC or port may be suitable for infusion of a chemotherapy treatment agent, which is generally circulated throughout the patient's circulation system, or for a “liquid” tumor, it may not be suitable for delivery of the immunotherapy agent to a solid tumor.

Microcatheters can be delivered to localize delivery of the agent to the vascular system adjacent the organ of interest. However, various issues prevent desirable agent uptake at the tumor.

SUMMARY

In accord with the invention, systems and methods are provided for delivery of immunotherapy agents to a solid tumor.

Solid tumors undergo angiogenesis, which creates unique vascular characteristics compared to healthy tissue. Solid tumors often have regions of high vascular density, a reduced resistance to flow, and a high capacitance for therapy. As a result of the unregulated tumor angiogenic process, a dense branching network of vessels is formed in the tumor. The formed dense network has a different vessel structure than health vessels. A healthy vessel is encased in endothelium, which maintains vascular tone and provides resistance to flow. Tumor vessels have a deteriorated endothelium and lack tone; this results in lower resistance to flow. Also, the dense network of vessels creates a relatively large vascular volume for the relative volume of the tissue, permitting a significantly higher volume of therapy to be deposited in the tumor compared to healthy tissue. Further, solid tumors can exhibit regions of low pressure within their vessels where there is robust flow, and they can have regions of high pressure where the vessels have become leaky and there is poor to no endogenous arterial flow. For these reasons, it is important to have an infusion system that does not rely solely on endogenous arterial flow to control delivery.

In view of these identified factors, it is believed by the inventors that immunotherapy systems and procedures should achieve several goals. Highly targeted delivery to the organ of interest should be obtained without the chance of back-flow into non-target regions. There should be the ability to increase pressure during infusion to overcome regions of high pressure in the tumor. More therapy should be deposited in the tumor than in the healthy tissue. The immunotherapy dose should deliver a maximum amount of intact cells or antibodies (a maximum percentage of healthy immunotherapy dose), and a minimum amount of damaged, destroyed cells, or activated cells during infusion. In addition, it is desirable to have a catheter deliver a homogenous immunotherapy dose across a vessel, including across a vessel branching network.

In accord with these goals, an immunotherapy treatment is delivered through a fully or partially deployed intravascular pressure modulating anti-reflux catheter, such as a catheter with microvalve and filter or a balloon catheter.

Further, the anti-reflux catheter may have one or more additional attributes that are advantageous in the delivery of cancer treatments. By way of example, these attributes can include the following. The catheter has self-centering capability that provides homogeneous distribution of therapy in a downstream branching network of vessels. The catheter includes an anti-reflux capability that blocks the retrograde flow of therapy into proximal non-target vessels proximal to the catheter tip. The system allows forward flow at a reduced pressure when not infusing therapy to target regions of low vascular resistance (tumor) and high capacitance (tumor). The valve and filter or a fully deployed balloon allows the pressure to be increased during infusion, with the pressure being modulated by the physician. An increased pressure allows increased delivery to and penetration into regions of the tumor that are naturally subject to high pressure conditions. According to another aspect of the device, a coating can be provided to the hub and inner lumen of the catheter to inhibit T-cell activation. According to yet another aspect of the device, a coating or construct can be provided to the hub and inner lumen of the catheter that optimize the wall shear during delivery of the therapy. By optimizing the wall shear gradient, the T-cells are subject to reduced trauma and maintain integrity during delivery while preventing clumping of the cells.

In accord with the method described herein, the treatment catheter is used in a method of delivering an immunotherapy agent. The treatment includes infusion of immunotherapy cells, anti-bodies, and/or other biologics into the target organ, including a selected location within the target organ, while maintaining a high integrity of the cells of the immunotherapy dose.

A modified Seldinger technique is used to introduce the catheter into the patient. More particularly, the catheter is introduced into the femoral artery, and then advanced up the aorta to the celiac axis. The catheter is then advanced into the left gastric artery. From the left gastric artery, the distal end of the catheter is advanced to the target artery that feeds the target organ. The catheter is then deployed for organ targeting.

Then, the immunotherapy agent, including immunotherapy T-cells, is infused under pressure through the catheter and to the tumor. Infusion is continued until the prescribed dose of immunotherapy is completely infused. This can occur at sub-stasis, at stasis, or beyond stasis. At stasis, the immunotherapy can be infused without any reflux. Further, by either manually inflating the balloon of a balloon catheter to block flow past the balloon in the vessel, or by use of the dynamically adjustable anti-reflux infusion catheter with valve, the immunotherapy can be infused beyond stasis without concern that the immunotherapy will reflux back toward the vessels of non-target tissues and/or organs.

After the infusion of the immunotherapy agent, the anti-reflux catheter is removed from the patient, and an arterial closure device is used to close the arterial access point for the procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic diagrams of one exemplary embodiment of an apparatus of the invention respectively in an undeployed state, a deployed partially open state with blood passing in the distal direction, and a deployed fully open state where the blood flow is static.

FIGS. 2A-2B are schematic diagrams of an exemplary embodiment of a valve having a braid component that is covered by a filter component in respectively an undeployed state and a deployed state.

FIGS. 3A-3C are schematic diagrams of another exemplary embodiment of an apparatus of the invention respectively in an undeployed state, a deployed partially open state with blood passing in the distal direction, and a deployed fully open state where the blood flow is static.

FIG. 4 is a graph showing the performance of the apparatus of FIGS. 1A-1C compared to the performance of a prior art end-hole catheter in delivering immunotherapy agent under pressure to target tissue.

FIG. 5 is a schematic cross-sectional view across an embodiment of the anti-reflux catheter including oleophobic and/or a hydrophobic surface geometry (shown not to scale).

FIG. 6 is a schematic cross-sectional view across an embodiment of the anti-reflux catheter including a surface geometry that minimizes wall shear (shown not to scale).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the human body and components of the devices and systems described herein which are intended to be hand-operated by a user, the terms “proximal” and “distal” are defined in reference to the user's hand, with the term “proximal” being closer to the user's hand, and the term “distal” being further from the user's hand, unless alternate definitions are specifically provided.

Methods are provided herein for infusing an immunotherapy agent to a tumor site for treatment of cancer. The method includes use of an infusion catheter device. In accord with the method, the infusion catheter device is an infusion microcatheter with valve and filter, or filter valve, (hereinafter “microvalve catheter”) or an infusion microcatheter with a distal balloon (hereinafter “balloon catheter”), with both such devices collectively referred to herein as “anti-reflux infusion catheters”. Whereas the balloon catheter is manually operable between expanded (open) and collapsed (closed) configurations, the microvalve catheter is a dynamic device, automatically moving between open and closed configurations based on local fluid pressure conditions to which the proximal and distal surfaces of the valve and filter are subject.

By way of example, referring to FIGS. 1A through 1C, an embodiment of an anti-reflux catheter 202 includes a flexible microcatheter 204 having a proximal end (not shown) and a distal end 206. A lumen 208 extends through the microcatheter and has a distal orifice 210, preferably coaxial with the axis of the catheter. A filter valve 212 is attached to the distal end 206 of the microcatheter, such that the orifice 210 opens into the proximal end 214 of the filter valve 212. The filter valve 212 comprises a braided polymeric filamentary structure 216 that is adapted to dynamically open and close based on the relatively proximal and distal pressure conditions of the fluid to which the filter valve is subject within a vessel 224. At least a portion of the braided filamentary structure 216 includes a polymeric filter 218 thereon, preferably deposited by electrospinning or electrostatic deposition to bond with the braided filamentary structure (FIGS. 1A and 2B). The filter 218 has a pore size not exceeding 500 μm. With such pore size, the filter 218 construct is semi-porous and allows elevated pressure differentials (greater distal pressure) to dissipate. The microcatheter 204 is adapted for use with an outer delivery catheter 220, with the inner microcatheter 204 extending through the outer delivery catheter 220. Longitudinal displacement of the outer catheter relative to the inner catheter (in the direction of arrow 221) allows the filter valve 212 to move from a non-deployed configuration (FIG. 1A) to a deployed configuration (FIG. 1B). Once deployed, the filter valve 212 is adapted to dynamically move between open and closed configurations (FIG. 1B to FIG. 1C and back) based upon fluid pressure forces 222, 226 applied to the proximal and distal sides of the filter valve when the device 202 is deployed within a vessel 224 (FIG. 1C). Such a microvalve catheter is disclosed in detail in incorporated U.S. Pat. Nos. 8,500,775 and 8,696,698 and in U.S. Pat. No. 9,968,740. In addition, microvalve catheters structurally and functionally similar to that described are sold by Surefire Medical, Inc., Westminster, Colo., as part of the Surefire Infusion System.

Turning now to FIGS. 3A through 3C, as another example, another microvalve catheter 302 includes a catheter 304 having a first lumen 306 for infusing the embolizing agent out of a distal orifice 308, and a second inflation lumen (not shown). An elastic membrane 310 is provided about a distal portion 312 of the catheter 304 and has a lower surface in communication with the inflation lumen to define a fluid inflatable balloon 314. FIG. 3A shows the balloon 314 in a collapsed configuration, FIG. 3B shows the balloon 314 in a partially expanded configuration (i.e., expanded insufficiently to reach across the vessel walls 224), and FIG. 3C shows the balloon 314 in a fully expanded configuration (i.e., expanded fully to the vessel walls 224). It is preferred that the balloon 314 be proximally offset from the distal tip 316 of the catheter 304 and particularly the orifice 308 of the first lumen. The balloon catheter device 302 may additionally include multiple balloons, optionally of different sizes, and either radially or longitudinally offset. The balloon is preferably provided for use with an outer delivery catheter 330, as discussed below.

In accord with one preferred aspect of the anti-reflux infusion catheter used in the method, the anti-reflux infusion catheter is adapted to self-center within a vessel 224. This can be accomplished with the expandable balloon 314 being centered about the balloon catheter, or the expandable valve 212 (FIGS. 1B and 1C) expanding radially symmetrically about the catheter. The self-centering of the anti-reflux infusion catheter is effected to promote homogeneous distribution of immunotherapy in a downstream branching network of vessels. That is, in distinction from a single streamline of delivery from a prior art end-hole catheter, a centrally-positioned anti-reflux infusion catheter creates turbulent flow in a vessel to mix the infused immunotherapy evenly across the cross-sectional area of a vessel.

In accord with another preferred aspect of the anti-reflux infusion catheter, such catheter blocks retrograde flow of immunotherapy into proximal non-target vessels proximal to the catheter tip, or a balloon or a valve on the catheter. In accord with yet another aspect of the anti-reflux infusion catheter, the valve and filter or a partially deployed balloon permit forward flow at a reduced pressure when not infusing the immunotherapy to target regions of low vascular resistance (tumor) and high capacitance (tumor).

In accord with yet another aspect of the anti-reflux infusion catheter, the valve and filter or a fully deployed balloon allows the infusion pressure to be increased during infusion, with the pressure being modulatable by the physician. By increasing the pressure, an increase in delivery and penetration of the immunotherapy into regions of the tumor that are naturally subject to high pressure conditions is effected. Referring to FIG. 4, it is seen that a microvalve anti-reflux catheter of the type available from Surefire Medical, Inc. allows infusion to generate substantially elevated distal pressures relative to a prior art end-hole catheter (with no anti-reflux structure or function). The pressure applied by the Surefire device dissipated after infusion, as fluid was able to diffuse back through the semi-porous membrane of the valve and filter. The end-hole catheter was unable to generate pressure gradients distal to the tip during infusion as fluid was able to reflux, equalizing fluid pressure in the system.

In accord with another aspect of the anti-reflux catheter (with reference to device 202, but equally applicable to device 302), an inner lining of the lumen 208 of the catheter 204 is tailored to minimize surface energy and interaction with T-cells. The inner lining of the lumen 208 is coated with one or more polymers 230 (FIG. 2A) such as silicones and silicone oils, polypropylene, polyethylene and fluoropolymers such as polytetrafluoroethylene, polyvinylidene fluoride, fluorinated ethylene-propylene, and perfluorinated elastomers.

In accord with another aspect of the anti-reflux catheter, as an addition to or alternative to the coating described above, an inner lining surface 232a of the lumen 208a of the catheter 204a is structurally patterned to create an oleophobic and/or a hydrophobic surface geometry (FIGS. 2A and 5). In accord with such aspect, the inner lining surface 232a can be patterned to include micro and/or nano scale ridges, pillars, or other features that generate a rough hydrophobic surface. Such features may be further chemically modified with fluoropolymers 230a (such as perfluoropolyether), silicones, or other chemical entities to enhance the hydrophobic effect and/or to provide oleophobic functionality to the surface features.

In accord with another aspect of the anti-reflux catheter, as an addition to or alternative to the coatings and structure described above, the inner lining surface of the lumen can be modified with hydrogels that can act to inhibit T-cell attachment and/or activation or can be used as protectants against fluid-mechanical cell damage. Such polymers are typically hydrophilic and electrically neutral and hydrogen bond acceptors rather than hydrogen bond donors. Examples include but are not limited to polyvinyl alcohol (PVA) and chemically modified PEO-(X) hybrid gels, poly(ethylene) glycol (PEG) and chemically modified PEG-(X) hybrid gels (PEGylated polymers), polyethylene oxide (PEO) and chemically modified PEO-(X) hybrid gels, Poly(acrylic acid), 2-hydroxyethyl methacrylate (HEMA)-based polymers and zwitterionic hydrogels such as phosphobetaine, sulfobetaine, and carboxybetaine which can display variable surface activity based on environmental pH. Furthermore, natural or artificial protein layers can be provided to the lumen surface or the hydrogel network and can have specific cellular stabilizing activities. Such a protein layer can include cytokines. Such polymers and proteins can be attached in cross-linked networks or in “brushy” layers of polymer strands. Methodology includes self-assembled monolayers of short chain hydrogels or peptides attached to the inner surface of the lumen of the catheter using a variety of covalent or ionic bonding chemistry and layer-by-layer self-assembly of tailored functionality nano-composite gels.

In accord with another aspect of the anti-reflux infusion catheter, an alternative or additional coating or structure can be provided to the hub and/or inner lining of the lumen of the catheter that will reduce the wall shear stress during delivery of the immunotherapy. Such a coating or structure can include a hydrophilic coating, a hydrophobic coating, or a small ‘brushy’ fibrous layer that acts to create a region of low flow or no flow along the wall of the catheter. By way of example, the coating can include glycocalyx or a glycocalyx-mimicking layer. Glycocalyx is a glycoprotein-polysaccharide, including several carbohydrate moieties of membrane glycolipids and glycoproteins. In the vascular endothelial tissue, the glycocalyx is a small, irregularly shaped layer extending approximately 50-100 nm into the lumen of a blood vessel, but can be up to 11 μm thick. The coating in the lumen can mimic such biological structure.

In accord with another aspect of the anti-reflux infusion catheter, wall shear stress along the lumen can be modified by incorporating a surfactant coating 230b into the lining of the lumen of the catheter. By way of another example, the wall shear stress can be modified by extruding the lumen 208b of the catheter 204b with features, including elongate channels 234b formed along length and open to the central lumen 208b (FIG. 6). Such channels 234b are either smaller or bigger than the diameter of a T-cell (e.g., less than 7 microns across or greater than 20 microns across) so as to prevent the channels from engaging and filling with captured T-cells. Thus, the channels will fill with fluid, but no T cells, and the peripheral channel-fluid will guide passage and minimize wall shear stress of the T cells through the lumen.

By way of another example, the catheter is negatively charged. In one manner, this can be effected by providing wires or even a braid about the lumen and applying a negative voltage to the wires (with no/negligible current during use); in another manner, the catheter is constructed with a negatively charged polymer. The immunotherapy agent is naturally negatively charge (as T-cells have negative surface charge). Then, the T-cells in the immunotherapy agent are repelled from the lumen surface to thereby reduce the shear stress upon infusion of the immunotherapy agent.

In accord with another manner of reducing wall shear stress, the wall shear stress can be minimized by incorporating a surfactant into the immunotherapy fluid containing the T cells. The surfactant can be premixed with the immunotherapy agent or mixed at the time of infusion.

In accord with a preferred procedure for delivering immunotherapy, a modified Seldinger technique is utilized. In the Seldinger technique, which is well-known and will not be described in detail herein, access is provided from the thigh to the femoral artery and a guidewire is advanced to the aorta. The delivery catheter is advanced over the guidewire. Once the delivery catheter is at its intended position, and in accord with the method herein, an anti-reflux infusion catheter is advanced through the delivery catheter and over the guidewire.

Then the anti-reflux catheter is displaced relative to the delivery catheter to expose the distal end of the anti-reflux catheter. The anti-reflux catheter is deployed.

Then, the immunotherapy agent, including immunotherapy T-cells, is infused through the catheter and under pressure to the tumor. Infusion is continued until the prescribed dose of immunotherapy is completely infused. This can occur at sub-stasis, at stasis, or beyond stasis. At stasis, the immunotherapy can be infused without any reflux. Further, by either manually inflating the balloon of a balloon catheter to block flow past the balloon in the vessel, or by use of the dynamically adjustable anti-reflux infusion catheter with valve, the immunotherapy can be infused beyond stasis without concern that the immunotherapy will reflux back toward the vessels of non-target tissues and/or organs.

After the infusion of the immunotherapy agent, the anti-reflux catheter is removed from the patient, and an arterial closure device is used to close the arterial access point for the procedure.

There have been described and illustrated herein embodiments of apparatus and methods for delivering immunotherapy agents to target tissue. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Particularly, it is intended that various aspects presented with respect to coated and structurally modifying the lining of the lumen described herein can be used either alone, or in combination with one or multiple other aspects. To such extent, it is anticipated that the lumen can include both structural modification and/or multiple coatings to facilitate passage of the immunotherapy with the least negative effect on the T-cells in the therapy. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.

Claims

1. A method of delivering an immunotherapy agent to a tumor, comprising: a) providing an immunotherapy delivery device including a flexible catheter having a proximal end and a distal end, an expandable fluid pressure modulating structure fixed adjacent the distal end of the catheter, an agent delivery lumen extending through the catheter and opening to an orifice at a distal tip of the catheter;b) providing an immunotherapy agent;c) inserting said device into a vessel in communication with the tumor; andd) infusing the immunotherapy agent through the lumen and out of the orifice of the catheter so that the immunotherapy agent is infused within the vessel at a pressure greater than an endogenous pressure within the vessel.

2. The method of claim 1, wherein the fluid pressure modulating structure prevents reflux of the immunotherapy agent as the immunotherapy agent is infused.

3. The method of claim 1, wherein the fluid pressure modulating structure prevents retrograde flow of the immunotherapy agent into non-target vessels located proximal of the catheter tip.

4. The method of claim 1, wherein the fluid pressure modulating structure is a microvalve.

5. The method of claim 4, wherein the microvalve is a dynamic microvalve that automatically moves between open and closed configurations based on local fluid pressure condition to which relatively proximal and distal surfaces of the microvalve are subject.

6. The method of claim 1, wherein the fluid pressure modulating structure is a balloon.

7. The method of claim 1, wherein the immunotherapy agent includes at least one of immunotherapy cells, anti-bodies, and another biologic.

8. The method of claim 1, wherein the immunotherapy agent includes at least one of immunomodulators, vaccines, modified cells and check-point inhibitors.

9. The method of claim 1, wherein during the infusing the immunotherapy agent is repelled from a wall of the lumen.

10. A method of delivering an agent to a tumor, comprising: a) providing a delivery device including a flexible catheter having a proximal end and a distal end, an expandable fluid pressure modulating structure fixed adjacent the distal end of the catheter, and an agent delivery lumen extending through the catheter and opening to an orifice at a distal tip of the catheter;b) inserting the device into a vessel in communication with the tumor; andc) infusing at least one of immunotherapy cells, anti-bodies, or another biologic through the lumen and out of the orifice of the catheter so that the immunotherapy cells, anti-bodies, or another biologic is infused distal of the distal tip and within the vessel at a pressure greater than an endogenous pressure within the vessel.

11. The method of claim 10, wherein the fluid pressure modulating structure prevents reflux of the at least one of the immunotherapy cells, anti-bodies, or another biologic as the at least one of the immunotherapy cells, anti-bodies, or another biologic is infused.

12. The method of claim 10, wherein the fluid pressure modulating structure prevents retrograde flow of the at least one of immunotherapy cells, anti-bodies, or another biologic into non-target vessels located proximal of the catheter tip.

13. The method of claim 10, wherein the fluid pressure modulating structure is a microvalve.

14. The method of claim 13, wherein the microvalve is a dynamic microvalve that automatically moves between open and closed configurations based on local fluid pressure condition to which relatively proximal and distal surfaces of the microvalve are subject.

15. The method of claim 10, wherein the fluid pressure modulating structure is a balloon.

16. The method of claim 10, wherein during the infusing the at least one of immunotherapy cells, anti-bodies, or another biologic is repelled from a wall defining the lumen.

17. A method of delivering an agent to a tumor, comprising: a) providing a delivery device including a flexible catheter having a proximal end and a distal end, an expandable fluid pressure modulating structure fixed adjacent the distal end of the catheter, an agent delivery lumen extending through the catheter and opening to an orifice at a distal tip of the catheter;b) inserting the device into a vessel in communication with the tumor; andc) infusing at least one of an immunomodulator, a vaccine, modified cells or a check-point inhibitor through the lumen and out of the orifice of the catheter so that the immunomodulator, vaccine, modified cells or check-point inhibitor is infused distal of the distal tip within the vessel at a pressure greater than an endogenous pressure within the vessel.

18. The method of claim 17, wherein the fluid pressure modulating structure prevents reflux of the at least one of an immunomodulator, a vaccine, modified cells or a check-point inhibitor as the at least one of an immunomodulator, a vaccine, modified cells or a check-point inhibitor is infused.

19. The method of claim 17, wherein the fluid pressure modulating structure prevents retrograde flow of the at least one of an immunomodulator, a vaccine, modified cells or a check-point inhibitor into non-target vessels located proximal of the catheter tip.

20. The method of claim 17, wherein the fluid pressure modulating structure is a microvalve.

21. The method of claim 20, wherein the microvalve is a dynamic microvalve that automatically moves between open and closed configurations based on local fluid pressure condition to which relatively proximal and distal surfaces of the microvalve are subject.

22. The method of claim 17, wherein the fluid pressure modulating structure is a balloon.