Regenerative Medicine

Slide 1 · Regenerative Medicine

Stem cells · tissue renewal · reprogramming · clinical translation

Foundations and translational barriers

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain how stem cells support tissue homeostasis and repair.

Compare embryonic, adult, and induced pluripotent stem cells.

Describe clinically used and proposed cell-based strategies.

Analyze graft rejection and functional-integration barriers.

Explain how patient-derived iPS cells enable disease modeling.

Slide 3 · Why tissue regeneration is difficult

Replacing lost cells is not equivalent to restoring the function of an injured organ.

New cells must reach the damaged site, survive, differentiate appropriately, and become functionally integrated.

Slide 4 · Cell population homeostasis

Mature cells are continually lost or removed.

Stem-cell input and proliferation replenish the pool.

Differentiation supplies specialized parenchymal cells.

Homeostasis reflects the balance among these processes.

Population balance

Stem-cell input

Mature tissue pool

Cell loss / apoptosis

Equilibrium requires matching supply and loss

Slide 5 · What changes the size of a cell population?

Rate of stem-cell input into a tissue.

Rate of proliferation within the cell population.

Rate of differentiation into specialized cell types.

Rate of mature-cell death, including apoptosis.

Regenerative interventions aim to restore a useful cell supply and function.

Slide 6 · The defining stem-cell properties

Self-renewal preserves the stem-cell compartment.

Differentiation generates specialized progeny.

The balance between them maintains tissue architecture.

Stem cell

Self-renewal

Specialized cell

Slide 7 · Asymmetric stem-cell division

One daughter retains stem-cell identity.

The other daughter begins differentiation.

Stem-cell pool size can be maintained while tissue output continues.

Parent stem cell

Stem daughter

Committed daughter

Slide 8 · Symmetric stem-cell division

Both daughters retain self-renewal capacity.

The stem-cell compartment can expand.

Early development and marrow recovery after ablative therapy.

Stem daughter

Stem daughter

Slide 9 · Asymmetric versus symmetric division

Feature

Asymmetric division

Symmetric self-renewal

Daughter identities

One stem + one committed

Two stem cells

Immediate effect

Maintains the reserve

Expands the reserve

Physiologic context

Balanced cell replacement

Development or stress response

Relevance to repair

Sustains ongoing output

Can enlarge stem-cell pool

Slide 10 · Stem-cell differentiation hierarchy

Differentiation potential becomes restricted along lineage progression.

Early developmental cells have broad lineage capacity.

Committed progenitors lead to specialized mature cells.

Zygote / earliest embryo

Pluripotent stem cells

Restricted progenitors

Differentiated cells

Slide 11 · Potency: Use the terms precisely

Totipotency

Totipotent: Includes embryonic and extraembryonic developmental potential.

Zygote and earliest cleavage-stage cells are the usual examples.

Pluripotency

Pluripotent: Generates derivatives of all three embryonic germ layers.

Embryonic stem cells and iPS cells are described as pluripotent in standard usage.

Terminology note: Robbins text sometimes labels ES cells “totipotent”; Its Fig. 1.22 calls them pluripotent.

Slide 12 · Embryonic stem cells: Developmental source

Embryonic stem cells arise from the inner cell mass of the blastocyst.

They exhibit extensive capacity for self-renewal in culture.

Appropriate conditions can direct differentiation toward multiple tissues.

Inner cell mass

Schematic blastocyst

Slide 13 · Embryonic lineages from pluripotent cells

The three embryonic germ layers define broad developmental trajectories.

Controlled differentiation seeks a specified mature lineage.

Pluripotency does not itself guarantee a functional graft.

Pluripotent stem cell

Ectoderm

Mesoderm

Endoderm

Slide 14 · Adult stem cells: Tissue-restricted renewal

Present in mature tissues, near their differentiated progeny.

Maintain local cell populations and replace damaged cells.

Differentiation repertoire is usually limited to that tissue.

Specialized microenvironments regulate their behavior.

Restricted lineage capacity is a central transplantation consideration.

Slide 15 · Embryonic versus tissue stem cells

Characteristic

Embryonic stem cells

Adult tissue stem cells

Location

Blastocyst inner cell mass

Resident tissue niche

Lineage breadth

Pluripotent

Usually restricted

Self-renewal

Extensive in culture

Supports local tissue maintenance

Principal issue

Allogeneic HLA recognition

Tissue-specific lineage range

Conceptual role

Broad differentiation source

Physiologic turnover and repair

Slide 16 · A niche is an active regulatory environment

Stem cells are housed in specialized microenvironments.

Nearby supporting cells and soluble factors influence their fate.

Signals balance quiescence, expansion, and differentiation.

Tissue microenvironment

Stem cell

Supporting cells and soluble signals

Slide 17 · Skin: Basal-layer renewal

Epidermal stem cells reside within the basal layer.

Progeny differentiate as they move toward the surface.

Mature cells are ultimately shed and replaced.

Basal stem-cell layer

Upward migration and differentiation

Slide 18 · Skin renewal as a homeostatic sequence

Basal stem cell

Cell division

Upward movement

Differentiation

Surface loss

Why it matters

Continuous replacement depends on a persisting basal stem-cell reservoir.

Slide 19 · Intestinal crypt: Location matters

Epithelial stem cells occur at the base of intestinal crypts.

Crypt-base columnar cells are interspersed with Paneth cells.

Their progeny populate the renewing intestinal epithelium.

Crypt stem

Paneth cell

Crypt base → transit-amplifying cells

Slide 20 · Bone marrow: A perivascular niche

Hematopoietic stem cells cluster near marrow vessels.

Their niche regulates residence and cell fate.

Mobilization can permit collection from peripheral blood.

Blood vessel

HSC

Perivascular niche

Slide 21 · Hair-follicle bulge as a stem-cell site

Stem cells occur in the bulge region of hair follicles.

Other skin stem-cell compartments include epidermal basal cells.

Anatomic localization is a defining feature of tissue stem cells.

Bulge region

Schematic hair follicle

Slide 22 · Other tissue stem-cell niches

Corneal limbus

A tissue-associated stem-cell site listed by Robbins.

Brain subventricular zone

Example of a specialized stem-cell microenvironment.

Liver canals of Hering

Illustrated site of oval-cell progenitors.

Slide 23 · Tissue turnover shapes regenerative demand

Tissue context

Baseline renewal

Regenerative teaching implication

Epidermis / gut epithelium

Ongoing rapid renewal

Endogenous stem-cell output sustains tissue

Bone marrow

Continuous replacement

HSCs maintain circulating blood elements

Liver

Quiescent / inducible proliferation

Many mature cells can re-enter the cycle

Neurons / myocardium

Very limited mature-cell proliferation

Replacement may require new cell sources

Slide 24 · Hematopoietic stem-cell function

HSCs replenish circulating blood elements.

Daughter lineages produce mature erythroid and myeloid cells and platelets.

A small pool supports extensive ongoing hematopoiesis.

Hematopoietic stem cell

Erythrocytes

Leukocytes

Platelets

Schematic lineage overview

Slide 25 · Where transplantable HSCs are obtained

Marrow collection

Bone marrow can be sampled directly.

The stem-cell population can be purified using cell-surface markers.

Mobilized peripheral blood

Peripheral blood can supply HSCs after mobilization.

Certain colony-stimulating factors induce marrow release.

Slide 26 · Marrow rescue after chemotherapy

Cytotoxic treatment can deplete hematopoietic marrow.

Transplanted HSCs can repopulate the depleted compartment.

Marrow reconstitution is an established use in the source.

Stem-cell source

Collection / selection

Marrow repopulation

After marrow-depleting therapy

Slide 27 · Replacement of a defective blood-cell system

HSC collection

Functional precursors

Marrow engraftment

Blood-cell output

Clinical benefit

Why it matters

Sickle cell disease among disorders in which normal precursors may correct blood-cell defects.

Slide 28 · Why hematopoietic therapy is a useful model

The normal stem-cell compartment is anatomically identifiable.

Stem cells can be collected and enriched.

Repopulation has a measurable physiological output: Blood-cell production.

The marrow provides a native niche for functional replacement.

Success in blood does not establish feasibility in other organs.

Slide 29 · Mesenchymal stem cells: Source and scope

Mesenchymal stem-cell populations occur in bone marrow and adipose tissue.

These cells exhibit multipotent stromal differentiation.

They can be expanded substantially under culture conditions.

Potential roles include manufacturing stromal components for regeneration.

Slide 30 · Mesenchymal stem-cell lineages

Chondrogenic differentiation generates cartilage-forming cells.

Osteogenic differentiation generates bone-forming cells.

Adipogenic differentiation generates adipocytes.

Robbins additionally mentions myogenic differentiation.

Mesenchymal stem cell

Cartilage

Bone

Fat

Slide 31 · Stromal scaffolding is not a complete organ

Potential contribution

Cells can generate components of tissue support.

Extracellular or stromal framework may aid tissue construction.

Remaining requirement

Organ function also requires correct architecture.

Replacement cells must integrate at the recipient site.

Slide 32 · The regenerative-medicine workflow

Identify a stem-cell population.

Isolate and expand a suitable cell source.

Deliver replacement cells or differentiated progeny.

Achieve functional integration in injured tissue.

Identify

Isolate

Expand

Deliver

Functional integration remains critical

Slide 33 · The cell source determines possibilities

Embryonic stem cells: Broad developmental potential.

Adult stem cells: Familiar tissue-restricted progeny.

Mesenchymal stem cells: Stromal differentiation potential.

IPS cells: Differentiated cells reprogrammed to pluripotency.

Choice of cell source also alters immune compatibility.

Slide 34 · Purification does not guarantee a treatment

What laboratory preparation can achieve

Improved ability to purify stem cells.

Expanded cells provide material for further differentiation or grafting.

What it cannot ensure

Cells must still arrive at appropriate anatomical sites.

Long-term survival and functional incorporation remain hurdles.

Slide 35 · Directed differentiation is a distinct step

Pluripotent cells have broad potential, not one preset function.

Culture conditions can induce specified differentiation.

The resulting cell lineage must match the therapeutic target.

Pluripotent stem cell

Ectoderm

Mesoderm

Endoderm

Slide 36 · Delivery and integration are separate hurdles

A graft may reach an injured tissue without restoring function.

Functional incorporation is a stated limitation of cell-replacement efforts.

Regeneration must be judged by recovered tissue function, not cell counts alone.

Delivered cells

Survival

Functional coupling

Presence ≠ restored organ function

Slide 37 · Myocardial infarction: Proposed tissue repair

Cardiac myocytes have little intrinsic proliferative capacity.

Regenerative approaches seek functional cardiac replacement.

Unresolved delivery and integration hurdles.

Tissue injury

Candidate cell graft

Target organ function?

Restoration is a biological endpoint, not simply cell delivery

Slide 38 · Stroke: Potential neural replacement

Mature neurons ordinarily do not proliferate.

Restoring neural tissue after stroke is an area of interest.

Transplanted progeny must incorporate into functional neural tissue.

Tissue injury

Candidate cell graft

Target organ function?

Restoration is a biological endpoint, not simply cell delivery

Slide 39 · Blood, heart, and brain are not equivalent targets

Target

Regenerative context

Main lesson

Hematopoietic marrow

Continual stem-cell-driven turnover

Established capacity for clinical repopulation

Myocardium

Low intrinsic mature-cell proliferation

Cell delivery and integration remain difficult

Neural tissue

Low intrinsic mature-neuron proliferation

Functional restoration remains challenging

Slide 40 · Transplant immunology enters the problem

Most adult stem cells and ES cells express HLA molecules.

Donor-recipient incompatibility can provoke immune rejection.

Immune recognition limits transplant persistence.

Donor / ES-derived cells

Recipient immune recognition

Potential graft rejection

HLA disparity can be relevant

Slide 41 · Autologous versus allogeneic cell sources

Autologous: Derived from the intended recipient.

Allogeneic: Derived from another individual.

Patient-specific reprogramming aims to reduce HLA-mediated rejection risk.

Cell source

Autologous

Allogeneic

Recipient-derived

Donor-derived

Slide 42 · Immunologic privilege: A qualified claim

Mesenchymal stem cells may be relatively less immunogenic; This does not establish universal graft acceptance.

A potentially locally immunosuppressive microenvironment and partial immune privilege—not immunity from rejection.

Slide 43 · Somatic-cell reprogramming changes the source

Differentiated cells such as fibroblasts may be collected from a patient.

Introduction of reprogramming genes induces a pluripotent state.

The resulting cells are induced pluripotent stem cells (iPSCs).

Patient fibroblast

Reprogramming genes

IPS cell

Directed differentiation

Slide 44 · The iPS-cell generation sequence

Patient cell

Reprogram genes

IPS population

In vitro culture

Chosen lineage

Why it matters

The workflow yields pluripotent cells and then differentiates them toward a selected lineage.

Slide 45 · Reprogramming and differentiation are distinct

Reprogramming

Reprogramming reverses a differentiated somatic phenotype toward pluripotency.

IPS cells acquire stem-cell-like developmental potential.

Directed differentiation

Directed differentiation specifies desired specialized progeny.

Lineage identity is necessary but not sufficient for clinical function.

Slide 46 · Potential iPS-derived target lineages

Ectodermal, mesodermal, and endodermal fates.

Cell products can be designed for disease models or replacement.

Each use requires lineage-specific biological validation.

Pluripotent stem cell

Ectoderm

Mesoderm

Endoderm

Slide 47 · Patient-derived iPS cells as disease avatars

Patient cells can retain disease-associated genetic variants.

Reprogrammed derivatives enable cellular disease models in vitro.

Models may reveal mechanisms not directly accessible in patients.

Patient with disease variant

Patient-derived iPS cells

Differentiated disease-relevant cells

Mechanism study / drug testing

Slide 48 · Therapeutic screening in a cell-based model

Generate disease-relevant patient-derived cells.

Expose the model to candidate therapeutic compounds.

Evaluate cellular outcomes before considering clinical translation.

Disease model

Candidate compounds

Cellular response

In vitro screening ≠ proven clinical efficacy

Slide 49 · Model validity: What should be questioned?

Do differentiated model cells represent the affected tissue?

Does the disease-relevant cellular phenotype appear?

Can a drug-induced change be interpreted as meaningful?

Would a cell-culture response translate to an intact organ?

The textbook establishes the use of avatars, not universal model validity.

Slide 50 · β-cell replacement: A conceptual example

The source proposes iPS-derived insulin-secreting β cells.

The intended target is impaired endogenous insulin production.

This as a future therapeutic possibility, not established routine practice.

Patient-derived iPS cells

Insulin-secreting β cells

Potential cell-replacement strategy

Proposed example, not presented as an established cure

Slide 51 · Can stem cells manufacture a whole organ?

Therapeutic aspiration

Differentiated progeny might repopulate damaged parenchyma.

Theoretical interest extends to entire replacement organs.

Biological obstacle

Organs need organized cell types and tissue architecture.

Graft positioning and functional integration remain unresolved.

“Theoretically” is central to the source’s claim; Do not mistake an aspiration for a standard therapy.

Slide 52 · Three cell-source strategies compared

Property

Embryonic

Tissue stem cell

Induced pluripotent

Origin

Blastocyst inner cell mass

Resident tissue niche

Reprogrammed somatic cell

Potency

Pluripotent

Usually restricted

Pluripotent

Potential use

Broad derivative lineages

Native tissue replacement

Disease models and proposed grafts

Core constraint

HLA mismatch for donor cells

Restricted differentiation

Derivation, specification, integration

Slide 53 · What is demonstrated versus proposed?

Application

Presentation in source

Teaching status

HSC marrow repopulation

Can repopulate marrow after therapy

Clinical application

HSCs for blood disorders

May supply normal precursors

Clinical application

Patient-derived iPS disease models

Increasingly used for studies and screening

Research application

IPS-derived β-cell replacement

May be a therapeutic strategy

Prospective application

Myocardial / neural graft restoration

Active therapeutic interest

Major translational hurdles

These labels describe the textbook’s narrative; They are not a review of post-publication trial or regulatory status.

Slide 54 · Five bottlenecks to evaluate in a graft

Cell selection

Does the source have an appropriate lineage repertoire?

Cell production

Can a useful population be isolated and expanded?

Immune fit

Will recipient immunity recognize foreign HLA?

Delivery

Can the cells be introduced at the intended site?

Integration

Will they make a functional contribution to the tissue?

Translation

Is the use established, experimental, or only theoretical?

Slide 55 · Application case: Depleted bone marrow

After myeloablative treatment, which cell source fits the source’s established repopulation example?

A. Hematopoietic stem cells

B. Patient-derived neuronal cells

C. Blastocyst-derived cardiomyocytes

D. Epidermal keratinocytes

Slide 56 · Application case: Infarcted myocardium

Which barrier is explicitly stressed for attempts to replace infarcted heart tissue?

A. Poor cell expansion alone

B. Integration of graft cells into cardiac function

C. Absence of embryonic cell types

D. Normal rapid mitosis of cardiac myocytes

Slide 57 · Application case: Patient-specific disease model

What is the clearest cellular starting point for an individual’s iPS-derived disease avatar?

A. Embryonic stem cells from an unrelated donor

B. Patient fibroblasts reprogrammed to iPS cells

C. Only fully differentiated mature neurons

D. A sample of extracellular matrix alone

Slide 58 · Application case: Immune compatibility

What is the main rationale for developing patient-specific replacement cells?

A. Donor HLA can trigger recipient rejection

B. Any stem-cell population is universally immune privileged

C. Pluripotency always prevents rejection

D. Cell expansion eliminates immune recognition

Slide 59 · Integrative take-home messages

Stem cells couple self-renewal with lineage-specific tissue production.

Normal regeneration depends on niches and controlled differentiation.

HSC transplantation demonstrates that functional cell replacement is possible.

IPS technology enables patient-derived pluripotent disease models.

Immune compatibility, delivery, and integration constrain broader cell therapies.

Slide 60 · Primary textbook and figure provenance

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th ed. (2026).

Chapter 1: “The Cell as a Unit of Health and Disease,” pp. 25–28.

Sections: “Stem Cells” and “Regenerative Medicine.”

Conceptual context: textbook Figs. 1.21–1.24; figures are not reproduced.

All diagrams in this presentation are original editable schematics.