Patent Publication Number: US-2007100323-A1

Title: Facilitation of endothelialization by in situ surface modification

Description:
BACKGROUND  
      1. Field of the Invention  
      Inhibiting intravascular thrombosis, vascular smooth muscle cell proliferation or restenosis.  
      2. Background  
      Balloon angioplasty is utilized as an alternative to bypass surgery for treatment early in the development of stenosis or occlusion of blood vessels due to the abnormal build-up of plaque on the endothelial wall of a blood vessel. Angioplasty typically involves guiding a catheter that is usually fitted with a balloon through an artery to the region of stenosis or occlusion, followed by brief inflation of the balloon to push the obstructing intravascular material or plaque against the endothelial wall of the vessel, thereby compressing and/or breaking apart the plaque and reestablishing blood flow. In some cases, particularly where a blood vessel may be perceived to be weakened, a stent may be deployed.  
      Balloon angioplasty and stent deployment may result in injury to a wall of a blood vessel and its endothelial lining. For example, undesirable results such as denudation (removal) of the endothelial cell layer in the region of the angioplasty, dissection of part of the inner vessel wall from the remainder of the vessel wall with the accompanying occlusion of the vessel, or rupture of the tunica intima layer of the vessel. A functioning endothelial reduces or mitigates thrombogenicity, inflammatory response, and neointimal proliferation.  
     SUMMARY  
      According to one embodiment of the invention that may be used to reduce the risk of intravascular thrombosis formation, and/or it may be used to inhibit vascular smooth muscle cell proliferation or restenosis following, for example, vascular intervention or injury, or in denuded or incompletely endothelialized areas of vasculature. One way the method achieves this is by accelerating recovery of endothelial coverage by delivering to a treatment site within a lumen of a blood vessel, a cellular component including either or both of endothelial cells and endothelial progenitor cells. The cellular component may be modified (e.g., genetically modified) to increase expression of molecules capable of attaching to a wall of a blood vessel. Alternatively, it may be encapsulated in a lipid or biodegradable polymer membrane capable of lodging in openings or fissures at the injury site, or modified at its surface to attach to a wall of a blood vessel. Still further, the cellular component may be modified to express or release a treatment agent such as a growth factor or a cytokine. In still another embodiment, the cellular component may be modified, for example, at its surface, to include a molecule or molecular moiety that either or in conjunction with a compatible molecule is capable of attaching the cellular component to a wall of a blood vessel.  
      In addition to accelerating endothelial coverage area, the functionality of the endothelial cells may also be facilitated. As endothelial density up to confluence and inter-cellular communication influences endothelial function, improved or accelerated recovery of endothelial function may also be achieved by increasing the rate of recovering endothelial coverage. While a confluent coverage of a functionally competent endothelium is a desired outcome, the method may be deemed successful in any instance where vascular healing mediated by facilitation of re-endothelialization is improved.  
      According to another embodiment, the method includes delivering to an injury site within a lumen or a blood vessel, a treatment agent having a first site capable of adhering with a wall of a blood vessel and a second site capable of bonding or conjugating with a cellular component. By utilizing a treatment agent having a second site having an affinity for endothelial progenitor cells, the conjugates may attract circulating cells (e.g., endothelial progenitor cells) from the blood stream, either those cells naturally present or cells introduced (infused locally or systemically) in or after a procedure.  
      According to another embodiment, a method is also described. The method includes coating an injury site within a lumen of a blood vessel with a polymeric biomaterial. The biomaterial may contain molecular moieties with affinity to cells and/or a treatment agent. For example, a coating may present molecular moieties at its luminal surface with affinity to the surface of circulating progenitor cells or cells locally infused after coating the blood vessel wall. The coating may be loaded with a treatment agent, such as a cytokine and/or growth factor to stimulate migration of neighboring cells to the injury site or impede proliferation of target cells (e.g., smooth muscle cells). Additionally the coating may also be loaded with cytokines or growth factors such as, for example, vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF) to stimulate recovery of endothelial coverage and/or function. Alternatively or in addition, the composition from the culture expanded media for endothelial coverage may be added to the coating. This will include an array of cytokines, growth factors to elicit a synergistic effect. In another embodiment, a treatment agent may be embedded in the coating through the use of carriers such as polymer particles, liposomes and polymer vesicles. Alternatively, a coating may incorporate a treatment agent by providing attachment site for the treatment agent. The treatment agent, in such case, may disassociate from the attachment site with a certain dissolution rate or may be chemically conjugated to the biomaterial through a degradable bond, releasing the treatment agent upon degradation.  
      One property of a polymeric biomaterial coating of a blood vessel is that it may insulate a vessel wall from platelets deposition and monocyte/neutrophil adhesion. In order to increase a thrombo-resistant property of the biomaterial coating, drugs such heparin may be incorporated into the coating.  
      According to still another embodiment, a composition is described that may include an amount of a cellular component suitable for delivery to a blood vessel. The cellular component may include endothelial cells or progenitor cells (e.g., endothelial progenitor cells) that have been modified to increase the potential for retention at a treatment site within the blood vessel. Modifications include but are not limited to, genetic or molecular modifications to increase the retention of molecules at a treatment site (e.g., affinity for a blood vessel wall), encapsulation in lipid or polymer membranes or shells with affinity to the vessel wall, expressing or releasing agents that stimulate migration of neighboring cells to a treatment site or impede proliferation of target cells. In another embodiment, a composition is disclosed that is suitable for being introduced at a treatment site and has a property capable of capturing or recruiting circulating cells, such as circulating progenitor cells.  
      In a further embodiment, a composition including a polymeric biomaterial is described. The polymeric biomaterial is suitable for delivery into a blood vessel possibly to form an in situ coating on a wall of the blood vessel. The biomaterial may include moieties with affinity to circulating cells and/or treatment agents such as cytokines, growth factors or drugs. The embodiment includes but is not limited to the following coating configurations: a) Hydrogel materials containing bioactive agent, that are packaged in nanoparticle or nanovesicular form; b) a blend of hydrophilic and hydrophobic polymers such as polyethylene glycol (PEG) and d,l-polylactic acid (d,l-PLA) such that the blend contains and allows the transport of bioactive agents into the tissue and prevents platelet activation by virtue of, for example, a PEG rich surface. The blend ratio may be optimized based on four parameters: transport of bioactive, surface hydrophilicity without any polyion, interfacial adhesion to the tissue, and the kinetics of dissolution or disintegration of the coating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features, aspects, and advantages of the invention will become more thoroughly apparent from the following detailed description, appended claims, and accompanying drawings in which:  
       FIG. 1  shows a schematic side and sectional view of a blood vessel.  
       FIG. 2  shows a cross-sectional side view of a distal portion of a catheter assembly in a blood vessel during an angioplasty procedure.  
       FIG. 3  shows the blood vessel of  FIG. 2  following the removal of the catheter assembly.  
       FIG. 4  schematically illustrates a cellular component of a treatment agent modified to express a moiety to binding sites on a blood vessel.  
       FIG. 5  schematically illustrates a vessel wall modified to recruit circulating cells.  
       FIG. 6  schematically illustrates a bioconjugation between two conjugates on a cellular component and a blood vessel wall, respectively.  
       FIG. 7  shows a representation of a cross-linking event involving multifunctional molecular moieties.  
       FIG. 8  shows the blood vessel of  FIG. 3  and a first embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 9  shows the blood vessel of  FIG. 3  and a second embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 10  shows the blood vessel of  FIG. 3  and a third embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 11  shows the blood vessel of  FIG. 3  and a fourth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 12  shows the blood vessel of  FIG. 3  and a fifth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 13  shows a sixth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 14  shows a seventh embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 15  shows an eighth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 16  shows a ninth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 17  shows a tenth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 18  shows the blood vessel of  FIG. 3  and a eleventh embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 19  shows the blood vessel of  FIG. 3  and a twelfth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel.  
       FIG. 20  shows the blood vessel of  FIG. 3  and a thirteenth embodiment of a catheter assembly to deliver a treatment agent introduced into the blood vessel. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIG. 1 , a non-diseased artery is illustrated as a representative blood vessel. Blood vessel  100  includes an arterial wall having a number of layers. Inner most layer  110  is generally referred as to the intimal layer. that includes the endothelium, the subendothelial layer, and the internal elastic lamina. Medial layer  120  is concentrically outward from inner most layer  110  and bounded by external elastic lamina. There is no external elastic lamina in a vein. Medial layer  120  (in either an artery or vein) primarily consists of smooth muscle fibers and collagen. Adventitial layer  130  is concentrically outward from medial layer  120 . The arterial wall (including inner most layer  110 , medial layer  120  and adventitial layer  130 ) defines lumen  140  of blood vessel  100 .  
      Stenosis or occlusion of a blood vessel such as blood vessel  100  occurs by the build-up of plaque on inner most layer  110 . The stenosis or occlusion can result in decreased blood flow through lumen  140 . One technique to address this is angioplasty.  FIG. 2  shows a portion of artery of blood vessel  100  including stenosis or occlusion referenced herein as injury site or treatment site  210 . To minimize or remove the stenosis or occlusion, catheter assembly  220  including balloon  225 , may be advanced over guidewire  215  to the injury site (treatment site). Balloon  225  may be briefly inflated one or more times to dilate the vessel and/or minimize the size of the stenosis or occlusion.  FIG. 2  shows balloon  225  in an expanded state contacting and exerting pressure on treatment site  210 . The dilating of a vessel or minimizing of a stenosis or occlusion may restore blood flow in blood vessel  100  to levels approaching those prior to the formation of the stenosis or occlusion.  
       FIG. 3  shows blood vessel  100  following an angioplasty procedure. Representatively, the stenosis or occlusion at treatment site  210  is minimized and portions of plaque contributing to the stenosis or occlusion may have been removed.  FIG. 3  also shows the optional deployment of a structural supporting device or stent  300  over stenosis or occlusion of treatment site  210 .  
      Balloon angioplasty and stent deployment may result in injury to blood vessel  100  and its endothelial lining, resulting in a potential formation of thrombus or neointimal proliferation. A functioning endothelial reduces or mitigates thrombogenecity, inflammatory response, neointimal proliferation. Therefore, it is desirable to accelerate re-endothelialization.  
      One technique for accelerating re-endothelialization at an injury site within a blood vessel is to infuse a cellular component that promotes the growth of endothelial cells or a restoration of an endothelial layer. In one embodiment, the technique includes introducing endothelial cells or progenitor cells (e.g., endothelial progenitor cells) as, for example, a fluid local to the target site to repopulate an injured vessel wall and/or stent (or other blood contacting implant) surface. The cell source may be autologous, meaning perhaps that it was previously harvested from the blood stream of the patient undergoing a procedure. In such case, the endothelial cells or endothelial progenitor cells (EPC) harvested from the blood stream may be concentrated and then fused locally to an injury site. Alternatively, the cell source may be an exogenous cell line, such as an allogenic (human) cell line not from the patient.  
      Treatment Agents  
      In one embodiment, a treatment agent may include suitable cellular components such as but not limited to endothelial cells or progenitor cells (e.g., endothelial progenitor cells) or bone marrow derived stem cells or other stem cells that may have a property or function that modifies (e.g., improves) a blood vessel wall following an injury to the vessel wall such as may occur in the context of a treatment of a stenosis or occlusion, or in the context of naturally occurring incompletely endothelialized vasculature. In another embodiment, these cells may be pre-conditioned to increase the expression of attachment molecules, where such attachment molecules have, for example, affinity to a subendothelium. For example, cells may be genetically modified to express integrins or other moieties that have an affinity to binding sites of the subendothelium such as proteins present therein, e.g. laminin, collagen or fibrin, or the arginine-glycine-aspartic acid (RGD) sequence found in these proteins.  FIG. 4  schematically illustrates a cellular component of a treatment agent modified to express a moiety to binding sites on a blood vessel.  FIG. 4  shows cell  410  expressing moiety  420 . Moiety  420  has an affinity for a protein or amino acid sequence  440  (e.g., an RGD sequence) of vessel wall  430 .  
      In another embodiment, the cells may be packaged or encapsulated. in a liposome or stealth liposome or other outer shell such as, for example, lipid or polymer membranes, or polymer shells, or other lipid-philic shells. This embodiment recognizes that an atheromatous plaque tends to have a number of micro-cracks in its surface. These micro-cracks can act as secondary reservoirs for cell component treatment agents. Accordingly, an embodiment where a cell component treatment agent is packaged or encapsulated in liposomes or other outer shell such as lipid or polymer membranes, or polymer shells, or other lipid-philic shells, allows the treatment agent to be lodged into the micro-cracks of the atheromatous plaque. In order to accommodate endothelial progenitor cells, these cell-loaded capsules are, for example, of a size of 10 to 20 micrometers (μm).  
      In another embodiment, cells such as endothelial cells or endothelial progenitor cells may be genetically modified to express and/or release a therapeutic in situ. For example, a cell may be modified to express and/or release a cytokine capable of stimulating migration toward a particular site or a growth factor (e.g., VEGF) having a tendency to make cells proliferate. Such cytokines or growth factors may help to induce migration and/or proliferation of neighboring endothelial cells to an injured (e.g., denuded) vessel wall surface or help to recruit circulating endothelial progenitor cells to the target site. A modification of cells to express and/or release a therapeutic may be done in conjunction with a modification to the cell to increase the expression of attachment molecules or the packaging of cells in liposomes or other membrane capsules with a surface having affinity to the subendothelium of a vessel wall.  
      In another embodiment, cells may be modified, for example, at their surface, by bi- or multifunctional linker molecules where at least one functionality of the linker molecule has affinity to the cell surface of molecular components thereof, and at least one other functionality has affinity to the surface of the target site, e.g., the subendothelium. For example, a molecule having two linked antibodies, where one antibody has affinity to a receptor on a cell surface and the other antibody has affinity to proteins of the subendothelium may be used to modify the cells. Alternatively, antibody fragments, affibodies (a library of proteins with recognition capabilities similar to antibodies), peptides or other molecules with the desired affinity may be used. For example, an anti-CD34 antibody linked to an affibody with affinity to an RGD sequence via a short organic spacer may be used to modify the surface of endothelial progenitor cells. When modifying progenitor cells in this fashion, the CD34 antibody will adhere to CD34 receptors at the cell surface and the cell surface will present molecules (affibodies) with affinity to proteins of the subendothelium (e.g., RGD sequences present in proteins of the subendothelium). In another example, anti-laminin-anti-CD34 may be used to modify the cell surface. Alternatively, suitable linker molecules, having an affinity to the subendothelium, may be chemically conjugated to a cell surface, such as to amine groups using reactive esters, epoxides, aldehydes; to sulfhydryl groups using maleimides, vinyl sulfones; to carboxyl groups using dimethylaminopropylcarbodiimide (EDC) chemistry. A molecular moiety having affinity for a target area such as a lumen surface may be separated from the attachment site on the cell surface by a spacer. Representative spacers include hydrophilic polymers such as polyethylene glycol (PEG) of molecular weight from about, but are not intended to be limited to, 500 to 40,000, preferably from about 2,000 to 10,000, and more preferably, from about 2,000 to 5,000.  
      In a situation where a stent is deployed at a target site, it may be desirable to deliver a treatment agent including a cellular component to the stent surface. Delivery to a stent surface may be enhanced by using a stent the surface of which is coated with cell adhesion molecules, such as laminin, fibronectin, or an adhesion peptide such as RGD peptide. The treatment agent may be modified in a manner specified above to enhance adhesion or improve the therapeutic activity of the treatment agent. Alternatively, a stent surface may be modified to include morphological features to provide a means of cell adhesion enhancement.  
      Modification of Blood Vessel  
      In the above embodiments, compositions and devices for introducing compositions are described, where the compositions may be introduced as a treatment agent into a blood vessel or to a stent in a blood vessel to, for example, promote endothelial cell migration or proliferation at a target site. In another embodiment, a treatment agent may be introduced that has a capability to recruit cells to a target site such as a luminal surface of the blood vessel. These treatment agents may include properties capable of recruiting circulating endothelial progenitor cells, either those naturally present or those cells infused to a target site. One technique to recruit cells to a target site is to modify a vessel wall to retain such cells.  FIG. 5  schematically illustrates a vessel wall modified to recruit circulating cells.  FIG. 5  shows vessel wall  530  having a surface modified to contain molecule or moiety  540  that has a property that makes it capable of attracting cell  510 .  
      Bi- or multifunctional linkers or molecules have at least one functionality having affinity to a surface of the lumen surface of the target site, such as an affinity for proteins of the subendothelium (e.g., laminin, fibronectin, collagen, tissue factor) and at least one other functionality having affinity to the surface of endothelial cells or progenitor cells, or molecular components present at the respective cell surface. One example of a molecule having affinity to a surface of circulating endothelial cells is a CD34 antibody. An example of a bi-functional molecule is an anti-CD34 -anti-RGD molecule. When infused into a target area, the anti-RGD moiety of this molecule can attach to proteins (e.g., laminin, fibrin) present at a denuded lumen surface, thereby presenting the anti-CD34 moiety to the vessel lumen. When circulating endothelial progenitor cells come in contact with the modified lumen surface, the CD34 receptor of the cell can attach to the CD34 antibody, thereby effectively retaining the cell at the modified target surface. An additional example would be the fab-fragment of an anti-CD133 antibody conjugated to an anti-laminin antibody. Alternatively, a vessel wall may be coated with an anti-laminin-anti-CD34 or an anti-laminin-anti-CD133 molecule by inducing either of these molecules local to a target site.  
      Molecules or molecular moieties possessing affinity to a surface of endothelial progenitor cells may be chemically conjugated through a luminal surface of a target site. The molecule or molecular moiety may be conjugated to the lumen surface via a spacer molecule, such as a hydrophilic polymer (e.g., PEG) to enhance accessibility. In one embodiment, the molecular moiety may possess more than one molecular moiety with affinity to a cell surface wherein a spacer may be, for example, branched.  
      Alternatively, attachment molecules may be chemically conjugated to the luminal surface of a blood vessel, through, for example: (i) amine groups using reactive esters, epoxides, aldehydes, or isocyanates (NCO); (ii) sulfhydryl groups using maleimides, vinyl sulfones; (iii) carboxyl groups using dimethylaminopropylcarbodiimide chemistry; (iv) hydroxyl groups using isocyanates (NCO) or epoxides. In this embodiment, one of the functionalities of the bi-functional molecule consists of a chemically reactive group while the other functionality of the molecule has affinity, for example, to the surface of endothelial or endothelial progenitor cells. Alternatively, photo-reactive chemistry may be used for conjugation. An example of a photo-reactive conjugation involves activating a photo-reactive moiety of a molecule by a catheter-based light or ultraviolet (UV) radiation after infusion of the molecular into a target lumen.  
      One example of modifying a vessel wall with an agent capable of recruiting cells at a target site is modifying a lumen surface of a blood vessel with antibodies to receptors present on endothelial progenitor cells (e.g., CD34, CD133, KDR). This may be done by conjugating a vinyl sulfone(VS)-PEG-antibody molecule to sulfhydryl groups present at a lumen surface. VS-PEG-antibody molecule may be locally infused or circulated in a lumen volume isolated by proximal and distal occlusion balloon (e.g., see  FIG. 9 ) to modify the lumen surface. A VS-PEG-antibody molecular construct may be made in the following way. A cystein residue may be inserted at a C terminus of an antibody (e.g., CD34, CD133), or an antibody fragment by genetic engineering. Genetic code of antibodies may be obtained from clonol selection through phage display. The genetic code of a mono-clonol antibody may be modified to include a cystein residue at the C terminus and expressed in a bacterial or mammalian expression system as described in, for example, Harma, et al., Clinical Chemistry (2000), 46:1755-61. These engineered antibodies may be incubated with a molar excess of VS-PEG-VS to yield a sulfhydryl reactive, via-PEG-antibody.  
      In another example, a maleimide-anti-CD133 molecule may be used to conjugate the CD133 antibody to sulfhydryl groups present in the vessel lumen surface. Alternatively, an NHS-PEG-biotin may be conjugated to the subendothelium at a target site and avidin may be subsequently infused into the target area. In a final step, VEGF-biotin may be bound to the vessel wall by infusing it into the avidin-modified target area. VEGF has affinity to the KDR receptor found on the surface of endothelial progenitor cells. Alternatively, biotinylated anti-CD34 may be used in the last step.  
      In yet another example, cyclic RGD (cRGD) molecules may be infused to the treatment site, where the cRGD non-specifically adheres to the subendothelial matrix, thereby providing attachment sites for endothelial cells or endothelial progenitor cells.  
      Modification of Blood Vessel Wall and Cellular Component  
      In the above embodiments, compositions may, for example, be introduced into a blood vessel as treatment agents to promote endothelial cell migration or proliferation at a target site. For example, treatment agents including cellular components that have been modified to increase affinity for a luminal wall of a blood vessel or treatment agent that has affinity to a cell surface (e.g., endothelial progenitor cells) may be introduced into a blood vessel. In a further embodiment, a treatment agent (first treatment agent) may be introduced into a blood vessel that has affinity for a cell surface without affinity for a luminal surface of the blood vessel at approximately the same time, after or prior to the introduction of a treatment agent (second treatment agent) with no affinity for a cell surface, but with affinity to the luminal surface of the blood vessel. In such case, the first treatment agent, in addition to being modified to have an affinity for a wall surface may be modified to present a conjugate and the second treatment agent may have a corresponding conjugate so that the first treatment agent and the second treatment agent may be conjugated through a bioconjugate of a conjugate on the first treatment agent and the conjugate on the second treatment agent.  FIG. 6  schematically illustrates the bioconjugation. Representatively, first treatment agent  610  of an endothelial progenitor cell may be modified to present conjugate  642  such as avidin chemically conjugated to treatment agent  610  such as through amine groups, sulfhydryl groups, or carboxyl groups. Second treatment agent  620  may be modified to have affinity for a luminal surface of blood vessel wall  630 , such as an affinity to binding sites of the sub-endothelium such as RGD sequences found in laminin, collagen or fibrin. Second treatment agent  620  also has conjugate  644  chemically connected thereto that has an affinity for conjugate  642  of first treatment agent  610 . A suitable conjugate in this example is, for example, biotin.  
      Blood Vessel Wall Modification  
      In another embodiment, a luminal surface of a vessel wall may be modified at a treatment site by forming a coating on the luminal surface of, for example, a hydrogel. In one embodiment, this modification or coating may be formed in situ. Suitable hydrogels include, but are not limited to, cross-linked PEG hydrogels or hydrogels formed from biopolymers. One example of a hydrogel that may be formed in situ (e.g., within a lumen of a blood vessel) is the combination of tri- or more functional PEG-amine with bi- or more functional PEG-reactive ester at a slightly basic pH (e.g., on the order of 7.6 to 9.0). Another example of a suitable hydrogel is a hydrophilic polymer such as PEG or a biopolymer such as chitosan mixed with a photoreactive crosslinker. A suitable photoreactive crosslinker is, for example, is a bi- or multifunctional acrylate where site specific photo-irradiation will locally activate the crosslinker to form a localized hydrogel.  
       FIG. 7  shows a representation of a cross-linking event involving a multifunctional PEG-amine with a multifunctional PEG-reactive ester.  FIG. 7  shows multifunctional PEG-ester moiety  710  having reactive ester groups  720  at ends of two chains. Those reactive esters are available for bonding to reactive amines of multifunctional PEG-amine moiety  730 .  FIG. 7  shows esters (NHS ester groups) of multifunctional PEG-ester moiety  710  aligned with amine groups of multifunctional PEG-amine moiety  730 . In addition to forming a hydrogel in situ, the hydrogel may present molecular moieties at a luminal surface of the blood vessel having affinity for constituents of the vessel wall (e.g., peptides or fractions of subendothelial proteins such as RGD sequences).  FIG. 7  shows multifunctional PEG-ester moiety  710  having molecular moiety  750  with an affinity for a luminal surface of a blood vessel. Alternatively, or in addition, a hydrogel may present molecular moieties at a luminal surface of the gel with an affinity for circulating cellular components, such as circulating progenitor cells.  FIG. 7  shows multifunctional PEG-ester moiety  710  having molecular moiety  760  (e.g., CD34, CD133, KDR) with affinity for circulating progenitor cells  770 .  
      In addition to having molecular moieties to promote the adhesion of the hydrogel to a vessel wall or a hydrogel with an affinity for circulating progenitor cells, a hydrogel may be loaded with a therapeutic agent, such as a cytokine and/or growth factor to stimulate migration of neighboring endothelial cells to the target area, or a therapeutic agent to impede proliferation of target cells, e.g., smooth muscle cells. Drug carriers such as polymer particles, liposomes, or polymer vesicles may be embedded in the hydrogel. Alternatively, the hydrogel may incorporate the therapeutic by providing attachment sites for the therapeutic, for example, where the therapeutic disassociates from these attachment sites with a certain disassociation rate. Or, the therapeutic may be chemically conjugate to the polymers of the hydrogel where the chemical bond is degradable, releasing the therapeutic upon degradation.  FIG. 7  may be illustrative of this concept with molecular moiety  760 , for example, being substituted with an attachment site for a therapeutic agent.  
      In one embodiment, a hydrogel formed in situ on a vessel wall, such as a denuded vessel wall may insulate the vessel wall from platelet deposition and monocyte/neutrophil adhesion. In order to increase a thrombo-resistant property of the hydrogel, an inhibitor such as heparin may be incorporated into the coating. A hydrogel coating may also contain a cocktail of acellular components of culture expansion in order to induce controlled healing.  
      Cellular components may be delivered as described above after a vessel wall has been modified, such as by a hydrogel coating. Cellular components may include mature endothelial cells or progenitor cells (e.g., endothelial progenitor cells). The affinity of a hydrogel for a particular cell may be modified using techniques described above (e.g., presenting moieties in the hydrogel that have an affinity for a particular cell).  
      In addition to combining surface modification of a wall coating such as a hydrogel with affinity for cellular components and cell delivery, a vessel coating modification and cell surface modification may be used as a complement. For example, a surface of a wall coating (e.g., a hydrogel) may be modified to present a conjugate and a separate cellular component may be modified at its surface or genetically modified to express surface receptors to present a conjugate or molecular moiety having an affinity for the conjugate presented by the wall coating. The conjugation of a conjugate on the wall coating and a conjugate or other molecular moiety on the surface of the cell will form a bioconjugate. An alternative to a chemical conjugation or binding, these conjugates or conjugate and molecular moieties may be in the form of magnetically responsive materials.  
      One example of the above description is modifying the surface of endothelial progenitor cells by incubation with NHS-PEG-biotin and subsequent incubation in avidin. At the same time, a surface of a wall coating is modified by NHS-PEG-biotin alone. Thus, avidin is attached to the cell surface, or biotin is presented at the lumen surface. When the avidin-modified cells are infused into a target area and the cell surface bound avidin is brought into contact with the lumen-bound biotin, the avidin will bind the biogen and thereby retain the cells at the lumen surface.  
      Devices  
      In the above embodiments, treatment agents including a cellular component and modified treatment agents are described that may be used to modify (e.g., improve) a target site such as luminal surface of a blood vessel. Also described are treatment agents having a capability to recruit cells to a target site or to modify a target site such as by coating a luminal surface of a blood vessel. The following paragraphs describe representative devices that may be used to introduce the contemplated treatment agents.  
      To increase delivery and engraftment efficiency of a treatment agent including, for example, modified or unmodified cells, blood flow may be temporarily reduced or a stopped through balloon occlusion of the target vessel prior to the introduction.  FIG. 8  shows blood vessel  100  having catheter assembly  800  disposed therein. Catheter assembly  800  includes proximal portion  805  and distal portion  810 . Proximal portion  805  may be external to blood vessel  100  and to the patient. Representatively, catheter assembly  800  may be inserted through a femoral artery and through, for example, a guide catheter and with the aid of a guidewire to a location in the vasculature of a patient. That location may be, for example, a coronary artery.  FIG. 8  shows distal portion  810  of catheter assembly  800  positioned proximal or upstream from treatment site  210 .  
      In one embodiment, catheter assembly  800  includes primary cannula  815  having a length that extends from proximal portion  805  (e.g., located external through a patient during a procedure) to connect with a proximal end or skirt of balloon  825 . Primary cannula  815  has a lumen therethrough that includes inflation cannula and delivery cannula  840 . Each of inflation cannula  830  and delivery cannula  840  extends from proximal portion  805  of catheter assembly  800  to distal portion  810 . Inflation cannula  830  has a distal end that terminates within balloon  825 . Delivery cannula  840  extends through balloon  825 .  
      Catheter assembly  800  also includes guidewire cannula  820  extending, in this embodiment, through balloon  825  through a distal end of catheter assembly  800 . Guidewire cannula  820  has a lumen sized to accommodate guidewire  822 . Catheter assembly  800  may be an over the wire (OTW) configuration where guidewire cannula  820  extends from a proximal end (external to a patient during a procedure) to a distal end of catheter assembly  800 . Guidewire cannula  820  may also be used for delivery of a treatment agent such as a cellular component or other vessel wall modifying agent when guidewire  822  is removed with catheter assembly  800  in place. In such case, separate delivery cannula (delivery cannula  840 ) is unnecessary or a delivery cannula may be used to delivery one treatment agent while guidewire cannula  820  is used to delivery another treatment agent.  
      In another embodiment, catheter assembly  800  is a rapid exchange (RX) type catheter assembly and only a portion of catheter assembly  800  (a distal portion including balloon  825 ) is advanced over guidewire  822 . In an RX type of catheter assembly, typically, the guidewire cannula/lumen extends from the distal end of the catheter to a proximal guidewire port spaced distally from the proximal end of the catheter assembly. The proximal guidewire port is typically spaced a substantial distance from the proximal end of the catheter assembly.  FIG. 8  shows an RX type catheter assembly.  
      In one embodiment, catheter assembly  800  is introduced into blood vessel  100  and balloon  825  is inflated (e.g., with a suitable liquid through inflation cannula  830 ) to occlude the blood vessel. Following occlusion, a solution (fluid) including a cellular component that promotes the growth of endothelial cells or a restoration of an endothelial layer is introduced through delivery cannula  840 . A suitable solution of endothelial cells or progenitor cells is a saline solution with a concentration of endothelial cells or progenitor cells on the order of 10 2  to 10 5  per milliliter (ml), more specifically 10 3  to 10 5  per milliliter. By introducing the cellular component in this manner, the endothelial cells or progenitor cells can re-populate the vessel wall at treatment site  210  or stent  300 .  
      In an effort to improve the target area of a cellular component to a treatment site, such as treatment site  210 , the injury site may be isolated prior to delivery.  FIG. 9  shows an embodiment of a catheter assembly having two balloons where one balloon is located proximal to treatment site  210  and a second balloon is located distal to treatment site  210 .  FIG. 9  shows catheter assembly  900  disposed within blood vessel  100 . Catheter assembly  900  has a tandom balloon configuration including proximal balloon  925  and distal balloon  935  aligned in series at a distal portion of the catheter assembly. Catheter assembly  900  also includes primary cannula  915  having a length that extends from a proximal end of catheter assembly  900  (e.g., located external to a patient during a procedure) to connect with a proximal end or skirt of balloon  925 . Primary cannula  915  has a lumen therethrough that includes inflation cannula  930  and inflation cannula  950 . Inflation cannula  930  extends from a proximal end of catheter assembly  900  to a point within balloon  925 . Inflation cannula  930  has a lumen therethrough allowing balloon  925  to be inflated through inflation cannula  930 . In this embodiment, balloon  925  is inflated through an inflation lumen separate from the inflation lumen that inflates balloon  935 . Inflation cannula  950  has a lumen therethrough allowing fluid to be introduced in the balloon  935  to inflate the balloon. In this manner, balloon  925  and balloon  935  may be separately inflated. Each of inflation cannula  930  and inflation cannula  950  extends from, in one embodiment, the proximal end of catheter assembly  900  through a point within balloon  925  and balloon  935 , respectively.  
      Catheter assembly  900  also includes guidewire cannula  920  extending, in this embodiment, through each of balloon  925  and balloon  935  through a distal end of catheter assembly. Guidewire cannula  920  has a lumen therethrough sized to accommodate a guidewire. No guidewire is shown within guidewire cannula  920 . Catheter assembly  900  may be an over the wire (OTW) configuration or a rapid exchange (RX) type catheter assembly.  FIG. 9  illustrates an RX type catheter assembly.  
      Catheter assembly  900  also includes delivery cannula  940 . In this embodiment, delivery cannula extends from a proximal end of catheter assembly  900  through a location between balloon  925  and balloon  935 . Secondary cannula  945  extends between balloon  925  and balloon  935 . A proximal portion or skirt of balloon  935  connects to a distal end of secondary cannula  945 . A distal end or skirt of balloon  925  is connected to a proximal end of secondary cannula  945 . Delivery cannula  940  terminates at opening  960  through secondary cannula  945 . In this manner, a treatment agent may be introduced between balloon  925  and balloon  935  positioned between treatment site  210 .  
       FIG. 9  shows balloon  925  and balloon  935  each inflated to occlude a lumen of blood vessel  100  and isolate treatment site  210 . In one embodiment, each of balloon  925  and balloon  935  are inflated to a point sufficient to occlude blood vessel  100  prior to the introduction of a treatment agent. A treatment agent containing a cellular component of, for example, endothelial cells or progenitor cells (e.g., endothelial progenitor cells) is then introduced.  
      In the above embodiment, separate balloons having separate inflation lumens are described. It is appreciated, however, that a single inflation lumen may be used to inflate each of balloon  925  and balloon  935 . Alternatively, in another embodiment, balloon  935  may be a guidewire balloon configuration such as a PERCUSURG™ catheter assembly where catheter assembly  900  including only balloon  925  is inserted over a guidewire including balloon  935 .  
       FIG. 10  shows catheter assembly  1000  disposed within a lumen of blood vessel  100 . Catheter assembly  1000  has a tandom balloon configuration similar to the configuration described with respect to catheter assembly  900  of  FIG. 9 . In this case, the secondary cannula between the tandom balloons is also inflatable.  FIG. 10  shows catheter assembly  1000  includes primary cannula or tubular member  1015 . In one embodiment, primary cannula  1010  extends from a proximal end of the catheter assembly (proximal portion  1005 ) intended to be external to a patient during a procedure, to a point proximal to a region of interest or treatment site within a patient, in this case, proximal to treatment site  210 . Representatively, catheter assembly  1000  may be percutaneously inserted via femoral artery or a radial artery and advanced into a coronary artery.  
      Primary cannula  1015  is connected in one embodiment to a proximal end (proximal skirt) of balloon  1025 . A distal end (distal skirt) of balloon  1025  is connected to secondary cannula  1045 . Secondary cannula  1045  has a length dimension, in one embodiment, suitable to extend from a distal end of a balloon located proximal to a treatment site beyond a treatment site. In this embodiment, secondary cannula  1045  has a property such that it may be inflated to a greater than outside diameter than its outside diameter when it is introduced (in other words, secondary cannula  1045  is made of an expandable material). A distal end of secondary cannula  1045  is connected to a proximal end (proximal skirt of balloon  1035 ). In one embodiment, each of balloon  1025 , balloon  1035 , and secondary cannula  1045  are inflatable. Thus, in one embodiment, each of balloon  1025 , balloon  1035 , and secondary cannula  1045  are inflated with a separate inflation cannula.  FIG. 10  shows catheter assembly having inflation cannula  1030  extending from a proximal end of catheter assembly  1000  to a point within balloon  1025 ; inflation cannula  1050  extending from a proximal end of catheter assembly  1000  to a point within balloon  1035 ; and inflation cannula  1070  extending from a proximal end of catheter assembly  1000  to a point within secondary cannula  1045 . In another embodiment, the catheter assembly may have a balloon configured in a dog-bone arrangement such that inflation of the balloon through a single inflation lumen inflates each of what are described in the figures as separated balloon  1025 , balloon  1035  and secondary cannula  1045 .  
      By using an expandable structure such as secondary cannula  1045  adjacent a treatment site, the expandable structure may be expanded to a point such that a treatment agent may be dispensed very near or at the treatment site.  FIG. 10  shows catheter assembly  1000  including delivery cannula  1040  extending from a proximal end of catheter assembly  1000  through primary cannula  1015 , through balloon  1025  and into secondary cannula  1045 . Delivery cannula  1040  terminates at dispensing port  1060  within secondary cannula  1045 . As viewed, secondary cannula  1045  is expandable to an outside diameter less than an expanded outside diameter of balloon  1025  or balloon  1035  (e.g., secondary cannula  1045  has an inflated diameter less than an inner diameter of blood vessel  100  at a treatment site).  
       FIG. 11  shows another embodiment of a catheter assembly. Catheter assembly  1100 , in this embodiment, includes a porous balloon through a treatment agent, such as endothelial cells or progenitor cells (e.g., endothelial progenitor cells) may be introduced.  FIG. 11  shows catheter assembly  1100  disposed within blood vessel  100 . Catheter assembly  1100  has a porous balloon configuration positioned at treatment site  210 . Catheter assembly  1100  includes primary cannula  1115  having a length that extends from a proximal end of catheter assembly  1100  (e.g., located external to a patient during a procedure) to connect with a proximal end or skirt of balloon  1125 . Primary cannula  1115  has a lumen therethrough that includes inflation cannula  1130 . Inflation cannula  1130  extends from a proximal end of catheter assembly  1100  to a point within balloon  1125 . Inflation cannula  1130  has a lumen therethrough allowing balloon  1125  to be inflated through inflation cannula  1130 .  
      Catheter assembly  1100  also includes guidewire cannula  1120  extending, in this embodiment, through balloon  1125 . Guidewire cannula  1120  has a lumen therethrough sized to accommodate a guidewire. No guidewire is shown within guidewire cannula  1120 . Catheter assembly  1100  may be an over-the-wire (OTW) configuration or rapid exchange (RX) type catheter assembly.  FIG. 11  illustrates an OTW type catheter assembly.  
      Catheter assembly  1100  also includes delivery cannula  1140 . In this embodiment, delivery cannula  1140  extends from a proximal end of catheter assembly  1100  to proximal end or skirt of balloon  1125 . Balloon  1125  is a double layer balloon. Balloon  1125  includes inner layer  11250  that is a non-porous material, such as PEBAX, Nylon or PET. Balloon  1125  also includes outer layer  11255 . Outer layer  11255  is a porous material, such as extended polytetrafluoroethylene (ePTFE). In one embodiment, delivery cannula  1140  is connected to between inner layer  11250  and outer layer  11255  so that a treatment agent can be introduced between the layers and permeate through pores in balloon  1125  into a lumen of blood vessel  100 .  
      As illustrated in  FIG. 11 , in one embodiment, catheter assembly is inserted into blood vessel  100  so that balloon  1125  is aligned with treatment site  210 . Following alignment of balloon  1125  of catheter assembly  1100 , balloon  1125  may be inflated by introducing an inflation medium (e.g., liquid through inflation cannula  1130 ). In one embodiment, balloon  1125  is only partially inflated or has an inflated diameter less than an inner diameter of blood vessel  100  at treatment site  210 . In this manner, balloon  1125  does not contact or only minimally contacts the blood vessel wall. A suitable expanded diameter of balloon  1125  is on the order of 2.0 to 5.0 mm for coronary vessels. It is appreciated that the expanded diameter may be different for peripheral vasculature. Following the expansion of balloon  1125 , a treatment agent, such as a cellular component of endothelial cells or progenitor cells (e.g., endothelial progenitor cells) is introduced into delivery cannula  1140 . The treatment agent flows through delivery cannula  1140  into a volume between inner layer  11250  and outer layer  11255  of balloon  1125 . At a relatively low pressure (e.g., on the order of two to four atmospheres (atm)), the treatment agent then permeates through the porous of outer layer  11255  into blood vessel  100 .  
       FIG. 12  shows another embodiment of a catheter assembly suitable for introducing a treatment agent into a blood vessel.  FIG. 12  shows catheter assembly  1200  disposed within blood vessel  100 . Catheter assembly  1200  includes primary cannula  1215  having a length that extends from a proximal end of catheter assembly  1200  (e.g., located external to a patient during a procedure) to connect with a proximal and/or skirt of balloon  1225 . Balloon  1225 , in this embodiment, is located at a position aligned with treatment site  210  in blood vessel  100 .  
      Disposed within primary cannula  1215  is guidewire cannula  1220  and inflation cannula  1230 . Guidewire cannula  1220  extends from a proximal end of catheter assembly  1200  through balloon  1225 . A distal end or skirt of balloon  1225  is connected to a distal portion of guidewire cannula  1220 .  
      Inflation cannula  1230  extends from a proximal end of catheter assembly  1200  to a point within balloon  1225 . In one embodiment, balloon  1225  is made of a porous material such as ePTFE. A suitable pore size for an ePTFE balloon material is on the order of one micron (μm) to 60 μms. The porosity of ePTFE material can be controlled to accommodate a treatment agent flow rate or particle size by changing a microstructure of an ePTFE tape used to form a balloon, for example, by wrapping around a mandrel. Alternatively, pore size may be controlled by controlling the compaction process of the balloon, or by creating pores (e.g., micropores) using a laser.  
      ePTFE as a balloon material is a relatively soft material and tends to be more flexible and conformable with tortuous coronary vessels than conventional balloons. ePTFE also does not need to be folded which will lower its profile and allow for smooth deliverability to distal lesions and the ability to provide therapy to targeted or regional sites post angioplasty and/or stent deployment.  
      A size of balloon  1225  can also vary. A suitable balloon diameter is, for example, in the range of two to five millimeters (mm). A balloon length may be on the order of eight to 60 mm. A suitable balloon profile range is, for example, approximately 0.030 inches to 0.040 inches.  
      In one embodiment, a porous balloon may be masked in certain areas along its working length to enable more targeted delivery of a treatment agent.  FIG. 13  shows an embodiment of porous balloon masked in certain areas. Catheter assembly  1300  includes balloon  1325  connected to primary cannula  1315 . Balloon  1325  is a porous material such as ePTFE with masks  1335  of a nonporous material (e.g., Nylon) positioned along a working length of balloon  1325 .  
      In another embodiment, a sheath may be advanced over a porous balloon (or the balloon withdrawn into a sheath) to allow tailoring of a treatment agent distribution.  FIG. 14  shows catheter assembly  1400  including balloon  1425  connected to primary cannula  1415 . Sheath  1435  is located over a portion of balloon  1425  (a proximal portion of the working length).  
      In another embodiment, a sheath may have a window for targeting delivery of the treatment agent through a porous balloon.  FIG. 15  shows catheter assembly  1500  including balloon  1525  connected to primary cannula  1515 . Sheath  1535  is extended over a working length of balloon  1525 . Sheath  1535  has window  1545  that provides an opening between the sheath and balloon  1525 .  
      In another embodiment, a liner inside a porous balloon may be used to target preferential treatment agent delivery. For example, the liner may have a window through which a treatment agent is delivered, e.g., on one side of a liner for delivery to one side of a vessel wall. This type of configuration may be used to address eccentric lesions.  FIG. 16  shows catheter assembly  1600  including balloon  1625  of a porous material connected to primary cannula  1610 . Disposed within (e.g., connected to an inner wall of) balloon  1625  is liner  1635  of a non-porous material such as Nylon.  FIG. 16  also shows opening or window  1245  between liner portions that allow a material to exit pores in balloon  1625 . Alternatively, a liner may have a tailored distribution of pores along the liner. The orientation of the balloon liner may be visualized through radio-opaque markers or through indicators on the external portion of catheter assembly  1600 .  
      In an alternative embodiment, rather than using a porous material like ePTFE for forming a porous balloon (e.g., balloon  1225  in  FIG. 12 ), a conventional balloon material such as PEBAX, Nylon or PET may be used that has tens or hundreds of micropores around its circumference for treatment agent diffusion. A suitable pore size may range, for example, from approximately five to  100  microns. Pores may be created by mechanical means or by laser perforation. Pore distribution along a balloon surface may be inhomogeneous to tailor distribution of treatment agent delivery. For example,  FIG. 17  shows catheter assembly  1700  including balloon  1725  connected to primary cannula  1715 . Balloon  1725  has a number of openings or pores  1755  extending in a lengthwise direction along the working length of balloon  1725 . The pores get gradually larger along its length (proximal to distal).  FIG. 17  shows two rows of pores  1755  as an example of a pore distribution. In other examples, pores  1755  may be created only on one side of balloon  1725  to deliver a treatment agent preferentially to one side of a blood vessel (e.g., to address eccentric lesions). The orientation of balloon  1725  in this situation may be visualized through radio-opaque markers, or through indicators on an external portion of catheter assembly  1700 . Balloon  1725  may also be retractable into optional sheath  1735  to tailor a length of treatment agent delivery. In an alternative embodiment, sheath  1735  may have an opening on one side to preferentially deliver a treatment agent to one side of the vessel.  
      According to any of the embodiments described with reference to  FIGS. 12-17  and the accompanying text, a treatment agent such as a cellular component including endothelial cells or progenitor cells (e.g., endothelial progenitor cells) may be introduced through the inflation cannula (e.g., inflation cannula  1230 ) to expand the balloon (e.g., balloon  1225 ). In the example of a balloon of a porous material, such as balloon  1225 , the treatment agent will expand balloon  1225  and at relatively low pressure (e.g., 2-4 atm) diffuse through pores in the porous balloon material to treatment site  210  within a lumen of blood vessel  100 .  FIG. 12  shows treatment agent  1280  diffusing through balloon  1225  into a lumen of blood vessel  100 . Since balloon  1225  is positioned at treatment site  210 , treatment agent  1280  is diffused at or adjacent (e.g., proximal or distal) to treatment site  210 .  
       FIG. 18  shows another embodiment of a catheter assembly suitable for introducing a treatment agent at a treatment site.  FIG. 18  shows catheter assembly  1800  disposed within blood vessel  100 . In this embodiment, catheter assembly  1800  utilizes an absorbent possibly porous device such as a sponge or a brush, connected to a catheter to dispense a treatment agent.  
      In one embodiment, catheter assembly  1800  includes guidewire cannula  1820  extending from a proximal end of catheter assembly  1800  (e.g., external to a patient during a procedure) to a point in blood vessel  100  beyond treatment site  210 . Overlying guidewire cannula  1820  is primary cannula  1840 . In one embodiment, primary cannula  1840  has a lumen therethrough of a diameter sufficient to accommodate guidewire cannula  1820  and to allow a treatment agent to be introduced through primary cannula  1840  from a proximal end to a treatment site. In one embodiment, catheter assembly  1800  includes a brush or sponge material connected at a distal portion of primary cannula  1840 . A sponge is representatively shown. Sponge  1890  has an exterior diameter that, when connected to an exterior surface of primary cannula  1840  will fit within a lumen of blood vessel  100 . Catheter assembly  1800  also includes retractable sheath  1818  overlying primary cannula  1840 . During insertion of catheter assembly  1800  into a blood vessel to a treatment site, sponge  1890  may be disposed within sheath  1818 . Once catheter assembly  1800  at a distal portion disposed at a treatment site, sheath  1818  may be retracted to expose sponge  1890 .  FIG. 18  shows sheath  1818  retracted, such as by pulling the sheet in a proximal direction.  
      In one embodiment, prior to insertion of catheter assembly  1800 , sponge  1890  may be loaded with a treatment agent. Representatively, sponge  1890  may be loaded with a cellular component including endothelial cells and progenitor cells (e.g., endothelial progenitor cells).  
      In one embodiment, catheter assembly  1800  may provide for additional introduction of a treatment agent through primary cannula  1840 .  FIG. 18  shows primary cannula  1840  having a number of dispensing ports  1845  disposed in series along a distal portion of primary cannula  1840  coinciding with a location of sponge  1890 . In this manner, once sponge  1890  is placed at treatment site  210  within blood vessel  100 , additional treatment agent may be introduced through primary cannula  1840  if desired.  
       FIG. 19  shows another embodiment of a catheter assembly suitable for introducing a treatment agent into a blood vessel.  FIG. 19  shows catheter assembly  1900  disposed within blood vessel  100 . Catheter assembly  1900  includes primary cannula  1915  having a length that extends from a proximal end of catheter assembly  1900  (e.g., located external to a patient during a procedure) to connect with a proximal end or skirt of balloon  1925 . Balloon  1925 , in this embodiment, is located at a position aligned with treatment site  210  in blood vessel  100 .  
      In one embodiment, catheter assembly  1900  has a configuration similar to a dilation catheter, including guidewire cannula  1920  and inflation cannula  1940  disposed within primary cannula  1915 . Guidewire cannula  1920  extends through balloon  1925  and balloon  1925  is connected to a distal end or skirt of guidewire cannula  1920 . Inflation cannula  1940  extends to a point within balloon  1925 .  
      In one embodiment, catheter assembly  1900  includes sleeve  1990  around a medial working length of balloon  1925 . Balloon  1925 , including a medial working length of balloon  1925 , may be made of a non-porous material (e.g., a non-porous polymer). In one embodiment, sleeve  1990  is a porous material that may contain a treatment agent such as a cellular component as described above. A representative material for sleeve  1990  is a silastic material. Sleeve  1990  may be loaded with or soaked (e.g., saturated) in a treatment agent before inserting catheter assembly  1900  into a blood vessel. Representatively, the pores of the porous sleeve may be filled with agent beforehand. The pores can also expand upon balloon inflation to deliver payload.  
       FIG. 20  shows another embodiment of a catheter assembly suitable for dispensing a treatment agent into a blood vessel. The catheter assembly of  FIG. 20  relies on a flexible polymeric or metal hollow coil with microporous perfusion holes to deliver a treatment agent into a blood vessel.  FIG. 20  shows catheter assembly  2000  including coil  2090  disposed from a proximal end of the catheter assembly (e.g., intended to be external to a patient during a procedure) to a point within a blood vessel, such as treatment site  210  of blood vessel  100 . In one embodiment, coil  2090  is formed from a material that has a hollow cross-section, such as a hypo-tube or extrusion. In the embodiment shown, only a distal portion of coil  2090  is coiled, with the remaining portion being linear. A representative length of a distal portion of coil  2090  is on the order of one to 15 centimeters (cm). In addition, coil may be tapered from proximal to distal having (e.g., a reduced diameter at a distal end) to accommodate narrowing of blood vessels towards distal portion. Alternatively, coil may be in linear configuration in sheath (during delivery before deployment and during catheter retraction after deployment). This may be achieved by using a shape memory material such as Nitinol.  
      At a distal portion of coil  2090  (e.g., the coiled portion), a number (e.g., hundreds) of perfusion holes or micropores  2095  are formed to release a treatment agent therethrough. A suitable hole or micropore diameter is on the order of five to 100 microns formed, for example, around a circumference of a distal portion of coil  2090  using a laser. A proximal end of coil  2090  is connected to delivery hub  2098 . A treatment agent, such as a treatment agent including a cellular component, can be injected through delivery hub  2098  and exit through holes or micropores  2095 .  
      Catheter assembly  2000  includes sheath  2035 . Sheath  2035  may be used to deliver coil  2090  to a treatment site and then retracted to expose at least a portion of the distal portion of coil  2090  including holes or micropores  2095 . For delivery to a treatment site, a distal end of coil  2090  is tightly wound in either a clockwise or counterclockwise configuration. For delivery of a treatment agent, a distal portion of coil  2090  may be unwound, either by inflation through pressurization or through re-expansion into a previously memorized shape (e.g., where coil is a shape-memory material such as a nickel-titanium alloy). After a treatment agent has been introduced through pores  2095 , a distal portion of coil  2090  may be withdrawn, either by deflation or by withdrawal into sheath  2035 .  
      To minimize potential trauma to a vessel wall by shearing of the coil and against the vessel wall, a distal end of coil  2090  may be rounded or have a small sphere. Alternatively, two coils of opposite helisity may be joined at their distal end but not at overlaps in between. In another embodiment, the delivery system may consist of joined “Vs” which are rolled into a cylindrical configuration around an axis orthogonal to a plane of the Vs. Tightly wound in this configuration, a catheter assembly may be delivered to a treatment site where it is unwound to deliver a treatment agent through pores incorporated into the system.  
      In any of the embodiments of utilizing a coil to deliver a treatment agent, a pore distribution along a distal portion of the coil may be non-uniform to deliver the treatment agent preferentially to specific sites within a treatment area (e.g., to one side of a blood vessel). Techniques for forming coil  2090  include extruding tubing where certain treatment agents such as drugs can be mixed with extrusion resin and then herically slitting the tubing to form a coil. Alternatively, coil  2090  may be made from a hollow ripen.  
      A flexibility and profile of coil  2090  allows for regional treatment agent delivery in one embodiment up to approximately 15 centimeters long in a coronary vessel. An outer diameter of a hollow coil can range from 0.005 inches to 0.010 inches, and a wall thickness may range from 0.0005 inches to 0.003 inches. Treatment agent distribution may be controlled by pitch length of coil  2090 .  
      The above delivery devices and systems are representation of devices that may be used to deliver a treatment agent including, but not limited to, a modified or unmodified cellular component or treatment agents to modify a luminal surface of a blood vessel. For example, treatment agents suitable to form an in situ layer for wall modification described above with reference to  FIG. 7  may be introduced at a treatment site with a variety of delivery devices. These devices include delivery through pores of a porous balloon, see  FIGS. 11-12  and the accompanying text, or through a saturated sponge mounted on a distal end of a delivery system, see, for example,  FIG. 13 . In addition, the vessel may be balloon occluded proximal and distal to the target site as shown in  FIG. 9  and  FIG. 10  (e.g., a dog-bone shape balloon). Additional treatment agents that might be added subsequently to an in situ formed layer may be deposited through the same deposition devices that are used to introduce the hydrogel coating or through a second devices.  
      In the preceding detailed description, reference is made to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the following claims. The specification and drawings are, accordingly, to be regarded, in an illustrative rather than a restrictive sense.