Use ofUse ofMesenchymal Stem Cells Mesenchymal Stem Cells

In In Myocardial Infarction TreatmentMyocardial Infarction Treatment

4/5/06Snehal Patel

Advisor: Dr. Bettye Hollins

Challenging the DogmaChallenging the Dogma

It has always been believed that the heart is composed of terminally It has always been believed that the heart is composed of terminally differentiated cardiac myocytes but research has shown that stem cells are differentiated cardiac myocytes but research has shown that stem cells are capable of myocardial regeneration and they can prevent and even reverse capable of myocardial regeneration and they can prevent and even reverse necrosis and scarring of cardiac tissue.necrosis and scarring of cardiac tissue.

865,000 cases of MI are reported annually in USA and 180, 000 deaths occur865,000 cases of MI are reported annually in USA and 180, 000 deaths occurannually.annually.

Stem CellsStem Cells

Totipotent: capable of developing Totipotent: capable of developing into any cell of an organism into any cell of an organism

eg: zygoteeg: zygote

Pluripotent: capable of developing Pluripotent: capable of developing into most tissues except the into most tissues except the placentaplacenta

eg: embryonic stem cellseg: embryonic stem cells

Multipotent: capable of developing Multipotent: capable of developing into a limited number of tissuesinto a limited number of tissues

eg: adult stem cellseg: adult stem cells

http://www.bcm.edu/fromthelab/vol03/is10/images/StemCellHierarchy.jpg

Embryonic stem cells are derived from embryonic and fetal tissue while adult stem cells are undifferentiated cells harvested from adults.

Adult Stem CellsAdult Stem Cells

Different types of adult Different types of adult stem cells:stem cells:

Hematopoietic stem Hematopoietic stem cellscells

Mesenchymal stem cells Mesenchymal stem cells (MSCs)(MSCs)

Skeletal myoblastsSkeletal myoblasts Resident cardiac stem Resident cardiac stem

cellscells

http://stemcells.nih.gov/StaticResources/images/figure3_sm.jpg

Steps in Stem Cell TreatmentSteps in Stem Cell Treatment

Extraction of MSCs:Extraction of MSCs: They are extracted from the bone marrow They are extracted from the bone marrow of the donor.of the donor.

Expansion of MSCs in culture medium :Expansion of MSCs in culture medium : This is done using off This is done using off the shelf products like enrichment cocktails and growth the shelf products like enrichment cocktails and growth mediums.mediums.

Delivery Delivery of the MSCs to the site of the infarct.of the MSCs to the site of the infarct.

Homing and differentiation of MSCs:Homing and differentiation of MSCs: Once in the system the Once in the system the MSCs migrate to the site of the infarct and differentiate into MSCs migrate to the site of the infarct and differentiate into myocytes under the influence of cytokines and paracrine myocytes under the influence of cytokines and paracrine

agentsagents..

Routes of DeliveryRoutes of Delivery

Two main routes of deliveryTwo main routes of delivery

Transvascular:Transvascular: This includes intravenous infusion This includes intravenous infusion and intracoronary infusion. Intracoronary infusion is and intracoronary infusion. Intracoronary infusion is done using percutaneous coronary intervention (PCI). done using percutaneous coronary intervention (PCI).

Direct injection into the myocardium:Direct injection into the myocardium: In this In this approach the MSCs are directly injected into the approach the MSCs are directly injected into the myocardium at the borders of the site of the infarct myocardium at the borders of the site of the infarct (endocardial) using a needle catheter during a PCI or (endocardial) using a needle catheter during a PCI or (intramyocardial) as an adjunct to a coronary bypass (intramyocardial) as an adjunct to a coronary bypass graft (CABG)graft (CABG)

Routes of DeliveryRoutes of Delivery

IntravenousIntravenous Least invasiveLeast invasive More effective in acute settingsMore effective in acute settings More systemic exposureMore systemic exposure

IntracoronaryIntracoronary IntermediateIntermediate More effective in acute settingsMore effective in acute settings Less systemic exposureLess systemic exposure High rate of engraftement at the site of High rate of engraftement at the site of

infarctinfarct

Direct Myocardial injectionDirect Myocardial injection Most invasiveMost invasive Can be used later as compared to Can be used later as compared to

intravascular approachesintravascular approaches Least systemic exposureLeast systemic exposure High rate of engraftment at the rite of High rate of engraftment at the rite of

infarctinfarct

Homing and DifferentiationHoming and Differentiation

Myocardial necrosis causes Myocardial necrosis causes release of inflammatory signals release of inflammatory signals which induce mobilization and which induce mobilization and homing of MSCs to the site of the homing of MSCs to the site of the infarct. Some of these includeinfarct. Some of these include

Stem cell factor (SCF) and c-kitStem cell factor (SCF) and c-kit CXCR4 and stromal cell derived CXCR4 and stromal cell derived

factor-1(SDF-1)factor-1(SDF-1) Vascular endothelial growth Vascular endothelial growth

factor (VEGF) and VEGF factor (VEGF) and VEGF receptor-2.receptor-2.

Allogenic vs. AutologousAllogenic vs. Autologous

MSCs are considered to be MSCs are considered to be immune privilegedimmune privileged since they evade allorejection. This is the since they evade allorejection. This is the result of three mechanismsresult of three mechanisms

Hypoimmunogenicity:Hypoimmunogenicity: MSCs lack MHC-MSCs lack MHC-II protein and thus evade recognition by T cells II protein and thus evade recognition by T cells and they also lack co stimulatory factors CD40, and they also lack co stimulatory factors CD40, CD40L,CD80 and CD86 required for T cell CD40L,CD80 and CD86 required for T cell activationactivation

Affect dendritic cells and natural Affect dendritic cells and natural killer cells:killer cells: MSCs prevent maturation and MSCs prevent maturation and migration to the lymph nodes of dendritic cells migration to the lymph nodes of dendritic cells and natural killer cells. They also decrease and natural killer cells. They also decrease secretion of TNF-secretion of TNF-αα by dendritic cells and IFN- by dendritic cells and IFN-γγ by natural killer cells and increase secretion of by natural killer cells and increase secretion of IL-10 by dendritic cells.IL-10 by dendritic cells.

Suppress T cell proliferation and Suppress T cell proliferation and generate a local immunosuppressive generate a local immunosuppressive milieu:milieu: MSCs produce nitric oxide which MSCs produce nitric oxide which inhibits stat5 phosphorylation which is essential inhibits stat5 phosphorylation which is essential for T cell proliferation. MSCs also produce for T cell proliferation. MSCs also produce hepatocyte growth factor (HGF), PGE2 and hepatocyte growth factor (HGF), PGE2 and transforming growth factor-transforming growth factor-ββ1(TGF-1(TGF-ββ1) which 1) which create a local immunosuppressive environment.create a local immunosuppressive environment.

ConductionConduction

After the MSCs undergo differentiation it is essential that they also acquire the After the MSCs undergo differentiation it is essential that they also acquire the electrical properties of cardiac myocytes. Electrical conduction through the electrical properties of cardiac myocytes. Electrical conduction through the differentiated MSCs is attributed to the development of gap junctions, which are differentiated MSCs is attributed to the development of gap junctions, which are seen at the interfaces between the MSCs themselves and between the MSCs and seen at the interfaces between the MSCs themselves and between the MSCs and cardiac myocytes.cardiac myocytes.

MSCs have a resting potential of -30 to -40mV.They express a small fraction of L-MSCs have a resting potential of -30 to -40mV.They express a small fraction of L-type Ca channels and they are considered inexcitable which results in slower type Ca channels and they are considered inexcitable which results in slower conduction velocity in-vitro, in a co-culture of MSCs and myocytes as compared to conduction velocity in-vitro, in a co-culture of MSCs and myocytes as compared to only myocytes. But the conduction velocity in a co-culture of MSCs and myocytes only myocytes. But the conduction velocity in a co-culture of MSCs and myocytes is still faster than that observed in a co-culture of fibroblasts and myocytes, which is still faster than that observed in a co-culture of fibroblasts and myocytes, which would be seen in the case of an MI. would be seen in the case of an MI.

Resynchronization of two separately beating fields has been seen within 24 to 48 Resynchronization of two separately beating fields has been seen within 24 to 48 hours of transplantation.hours of transplantation.

Risks vs. BenefitsRisks vs. Benefits

Benefits:Benefits:Clinical trials have shown improvement of both systolic Clinical trials have shown improvement of both systolic

and diastolic function after transplant of MSCand diastolic function after transplant of MSC

Increase in left ventricular ejection fraction (LVEF)Increase in left ventricular ejection fraction (LVEF) Decrease in the area of functional defectDecrease in the area of functional defect Increase in the wall movement velocity of the Increase in the wall movement velocity of the

infarcted areainfarcted area No significant changes in the left ventricular dystolic No significant changes in the left ventricular dystolic

diameter (LVDd)diameter (LVDd) No significant changes in E/A ratioNo significant changes in E/A ratio Small increase in isovolumic relaxation time (IVRT)Small increase in isovolumic relaxation time (IVRT)

Risks:Risks: Highly invasive procedures except for IV infusionHighly invasive procedures except for IV infusion Susceptible to re-entrant arrhythmiasSusceptible to re-entrant arrhythmias Risk of propagating genetic defectsRisk of propagating genetic defects TumorsTumors

ProvacelProvacel

FDA has approved Phase I clinical FDA has approved Phase I clinical trial for Provacel an interventional trial for Provacel an interventional therapy using MSCs to prevent heart therapy using MSCs to prevent heart failure resulting from an acute failure resulting from an acute myocardial infarction, sponsored by myocardial infarction, sponsored by Osiris Therauptics Inc. 53 patients Osiris Therauptics Inc. 53 patients were admitted in this double-blind, were admitted in this double-blind, placebo-controlled, dose escalating, placebo-controlled, dose escalating, multicenter, randomized trial and multicenter, randomized trial and were treated using allogenic MSCs were treated using allogenic MSCs which were delivered through a which were delivered through a standard IV line within 7 days of standard IV line within 7 days of suffering from a first MI. These suffering from a first MI. These patients are going to be followed for a patients are going to be followed for a period of two years to demonstrate period of two years to demonstrate the safety of the product and to the safety of the product and to evaluate preliminary efficacy data. evaluate preliminary efficacy data.

Control groupControl group

Experimental group treated using ProvacelExperimental group treated using Provacel

ConclusionConclusion

Preclinical and human trials have showed short term benefits of using Preclinical and human trials have showed short term benefits of using MSCs post MI that include improvement in LVEF, reduction of scar tissue, MSCs post MI that include improvement in LVEF, reduction of scar tissue, absence of hypertrophy and improvement in in contractility and conduction absence of hypertrophy and improvement in in contractility and conduction but it is also essential to study long term effects. Further studies are but it is also essential to study long term effects. Further studies are warranted to help design treatments that are best suited to individual needs warranted to help design treatments that are best suited to individual needs depending on the location of the infarct, time elapsed since the MI and depending on the location of the infarct, time elapsed since the MI and hemodynamic stability of the patient.hemodynamic stability of the patient.

Thus although MSC transplants have a long way to go from the Thus although MSC transplants have a long way to go from the laboratory to the patient’s bedside, they do show promise, that their use laboratory to the patient’s bedside, they do show promise, that their use will help improve the quality of life of the patients and reduce progression will help improve the quality of life of the patients and reduce progression to heart failure.to heart failure.

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