Producer T cells: Using genetically engineered T cells as vehicles to generate and deliver therapeutics to tumors

Figures & data

Figure 1. Schematic of possible T cell vehicle biologics and their therapeutic targets. (A) TIL are isolated from tumors, expanded, and can be genetically engineered using a wide variety of transgenes. (B) Immunosuppressive cells generate a tumor microenvironment conducive to tumor cell growth which limits T cell function. (C) Immunosuppressive cytokines and bioactive molecules suppress T cell function. (D) Immune checkpoints are activated by interactions between T cells, tumor cells, and other cells of the tumor microenvironment and suppress effector cell function. (E) Transgenes can be designed with promotors allowing antigen-dependent expression. (F) A wide variety of transgene products can be selected for various purposes. Abbreviations: APC, antigen presenting cell; BiTE, bi-specific T-cell engager; CAR, chimeric antigen receptor; CTL, cytotoxic T lymphocyte; MDSC, myeloid-derived suppressive cell; NFAT, nuclear factor of activated T-cells; NK, natural killer; PD-1, programmed death-1; PD-L1, programmed death ligand 1; pNFAT, NFAT-responsive promoter; PTD, protein transduction domain; TAM, tumor-associated macrophage; TCR, T cell receptor; TGF-β, transforming growth factor β; TIL, tumor infiltrating lymphocyte; Treg, regulatory T cell; VEGF, vascular endothelial growth factor;.

Table 1. Advantages of producer T cells.

Challenges With Systemic Drug Delivery	Advantages of T Cell Vehicles
Drug is systemic. Affects cancerous and non-cancerous tissues.	T cells home and accumulate in tumor. Local drug secretion.
Cannot preferentially localize drugs to tumor site.	T cells home and accumulate in tumor. Local drug secretion. Inducible expression of biological after T cells reach tumor site.
Require multiple rounds of treatment.	T cells proliferate and continually produce biological.
Cannot effectively penetrate certain anatomical sites.	T cells can infiltrate virtually all anatomical sites and can efficiently penetrate and accumulate in tumors.
Must account for pharmacokinetics and pharmacodynamics.	Localized drug secretion results in limited metabolic pressures within the tumor but not systemically.
Therapeutics may limit or reduce T cell antitumor activity.	Biologicals can be selected to enhance T cell efficacy.
	Easily interchange what molecule is expressed. A wide variety of molecules can be selected.

Table 2. Literature review on producer T cells.

TransgeneProduct	Organism	Cell Type(s)	Disease Model	Reference
IL-2	Human	Primary T cell / PBMC / CD8^+ T cell clone	Melanoma	Liu and Rosenberg, 2001
IL-2	Human	TIL	Melanoma	Liu and Rosenberg, 2003
IL-2/IL-15	Human	PBMC	N/A	Quintarelli et al., 2007
IL-2	Human	TIL	Melanoma (Clinical trial)	Heemskerk et al., 2008
IL-15	Murine	Tumor reactive T cells	Melanoma	Hsu et al., 2005
IL-15	Human	Sup T1 (human T lymphocyte)	N/A	Klebanoff et al., 2005
IL-15	Human	PBL	N/A	Hsu et al., 2007
IL-15	Human	PBMC	Lymphoma / Leukemia	Hoyos, et al., 2010
IL-12	Human	CD8^+ CTL	Hodgkin's lymphoma	Wagner et al., 2004
IL-12	Murine	Tumor reactive T cells	Melanoma	Kerkar et al., 2010
IL-12	Murine	T cells	Melanoma / Sarcoma / Colon carcinoma	Chinnasamy et al., 2012
IL-12	Murine/Human	Murine tumor reactive T cells / Human PBL	Melanoma	Zhang et al., 2011
IL-12	Human	PBMC / PBL / TIL	N/A	Zhang et al., 2012
IL-12	Murine	T cells	B cell malignancies	Pegram et al., 2012
IL-12	Human	PBMC	Ovarian cancer	Koneru et al., 2015
IL-12	Human	Umblical cord blood	B-cell acute lymphoblastic leukemia	Pegram et al., 2015
IL-12	Human	TIL	Melanoma (Clinical trial)	Zhang et al., 2015
IL-2/IL-7/IL-15/IL-21	Human	PBL	CD19^+malignancies	Markley and Sadelain, 2010
Anti-CD3/CEA BiTE	Human	PBMC	Colon carcinoma	Compte et al., 2007
Anti-CD3/EphA2 BiTE	Human	PBMC	Glioma / Lung cancer	Iwahori et al., 2015

Abbreviations: CTL, cytotoxic T lymphocyte; PBMC, peripheral blood mononuclear cell; TIL, tumor-infiltrating lymphocyte; PBL, peripheral blood leukocyte; BiTE, bi-specific T-cell engager; N/A, not applicable.

Table 3. Limitations and challenges of producer T cells.

Challenges/Limitations	Potential Solutions
Potential for malignant transformation due to genetic engineering.	Low risk of this occurring. Use of selection markers or “kill switches.”
Limited biologic output, particularly when using NFAT antigen-inducible system.	Use of highly potent biologics. Development of stronger antigen-inducible promoter systems.
Therapeutic must be encoded by DNA and product must be a nucleic acid or protein.	None.
Therapeutics that require internalization may necessitate modifications, potentially reducing efficacy.	Use of molecules naturally internalized by target cells. Development of highly efficient internalization signals.
Autoreactive T cells modified with NFAT-driven systems would constitutively express transgenes.	Use of thoroughly investigated CARs or TCRs.
When using antigen-inducible systems, transgene expression would be activated upon endogenous TCR engagement on receptor-modified T cells.	None.
In a clinical trial using NFAT-driven IL-12, remarkably high levels of circulating IL-12 were observed in some patients.	Refinement of the NFAT system or development of new antigen-inducible promoter systems.
Unexpected consequences of genetically engineering T cells (e.g., IL-12 reduces T cell proliferation; IL-15 potentially generates transformed T cells).	Thoughtful selection and thorough investigation of transgenes in preclinical models before clinical use.