Synthetic Biology Parts, Devices and Applications

358 17 Synthetic Biology in Immunotherapy and Stem Cell Therapy Engineering

lymphocytes (TILs) and restore T-cell function in cancer patients [83–85]. While

the successes of these treatments have led to US FDA approval of antibodies such

as ipilimumab and pembrolizumab, checkpoint blockade therapies can only be

effective when tumor-reactive T-cell clones already exist in the patient’s system.

To address cancer types that are not naturally immunogenic, researchers have

engineered tumor-targeting T cells to express dominant-negative receptors

(DNRs) that compete with endogenous receptors for binding to tumor-associated

(b)

DNR-expressing

T cell

Tumor cell

Inhibitory cytokine

receptor

(e.g., TGF-βR)

Immunosuppressive

cytokine

(e.g., TGF-β)

DNRs

Checkpoint

receptor

(e.g., PD-1,

CTLA-4, etc.)

Inhibitory-receptor KO

T cell

DNR Receptor

No signaling No signaling

Inhibitory

ligand

(e.g., PD-L1,

CD80, CD86, etc.)

Dysfunction

Exhaustion

Receptor

Costim

Cytokine

Proliferation

Immune-cell

recruitment

Costimulatory

ligand

(e.g., 4-1BBL,

CD40L, etc.)

Cytokine/

chemokine

receptor

(e.g., IL-7R, CCR4,

CXCR2, etc.)

Immunostimulatory

cytokine

(e.g., IL-2, IL-12,

IL-15, etc.)

Autocrine

signaling

Paracrine

signaling

(a) Armored T cell Native immune cell

Persistence

Effector function

Figure 17.3 Synthetic biological constructs and circuits enable controlled enhancement of

T-cell function. (a) “Armored” T cells are engineered to overexpress costimulatory ligands,

cytokine receptors, chemokine receptors, or immunostimulatory cytokines that can boost

T-cell proliferation, persistence, and effector functions in an autocrine manner. Once secreted,

immunostimulatory cytokines (e.g., IL-2, IL-12, IL-15, etc.) can also signal in paracrine fashion

to trigger the recruitment, growth, and antitumor responses of native immune cells. (b) T cells

can be genetically modified to resist inhibitory signals present on tumor cells (e.g., PD-L1) or

within the tumor microenvironment (e.g., TGF-β) by expressing dominant-negative receptors

(DNRs) or knocking out inhibitory receptors. DNRs lack signal transduction domains and

competitively sequester immunosuppressive ligands away from native inhibitory receptors.

Genetic knockout of inhibitory receptor expression abrogates receptor-mediated recognition

of immunosuppressive factors, thus reducing T-cell dysfunction and exhaustion. (c) Inverted

cytokine receptors (ICRs) are fusions between the extracellular ligand binding of an inhibitory

receptor and the intracellular signaling domain of an immunostimulatory receptor. Encounter

with immunosuppressive cytokines (e.g., IL-4) in the tumor microenvironment activates

expression programs that enhance T-cell proliferation, persistence, and effector functions.