Enhancement of Immunotherapies in Head and Neck Cancers Using Biomaterial-Based Treatment Strategies

Abstract

Head and neck squamous cell carcinoma (HNSCC) is a challenging disease to treat because of typically late-stage diagnoses and tumor formation in difficult-to-treat areas, sensitive to aggressive or invasive treatments. To date, HNSCC treatments have been limited to surgery, radiotherapy, and chemotherapy, which may have significant morbidity and often lead to long-lasting side effects. The development of immunotherapies has revolutionized cancer treatment by providing a promising alternative to standard-of-care therapies. However, single-agent immunotherapy has been only modestly effective in the treatment of various cancers, including HNSCC, with most patients receiving no overall benefit or increased survival. In addition, single-agent immunotherapy's limitations, namely immune-related side effects and the necessity of multidose treatments, must be addressed to further improve treatment efficacy. Biocompatible biomaterials, in combination with cancer immunotherapies, offer numerous advantages in the concentration, localization, and controlled release of drugs, cancer antigens, and immune cells. Biomaterial structures are diverse, and their design can generally be customized to enhance immunotherapy response. In preclinical settings, the use of biomaterials has shown great promise in improving the efficacy of single-agent immunotherapy. Herein, we provide an overview of current immunotherapy treatments for HNSCC and their limitations, as well as the potential applications of biomaterials in enhancing cancer immunotherapies.

Impact Statement

Advances in anticancer immunotherapies for the past 30 years have yielded exciting clinical results and provided alternatives to long-standing standard-of-care treatments, which are associated with significant toxicities and long-term morbidity. However, patients with head and neck squamous cell carcinoma (HNSCC) have not benefited from immunotherapies as much as patients with other cancers. Immunotherapy limitations include systemic side effects, therapeutic resistance, poor delivery kinetics, and limited patient responses. Biomaterial-enhanced immunotherapies, as explored in this review, are a potentially powerful means of achieving localized drug delivery, sustained and controlled drug release, and immunomodulation. They may overcome current treatment limitations and improve patient outcomes and care.

Introduction

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer across the globe and accounts for >90% of all head and neck cancers. In 2020 alone, there were >900,000 new reported cases and almost 500,000 deaths from HNSCC.¹ This cancer type is defined by malignant tumors originating from the mucosal epithelial cells in the oral cavity, pharynx, and larynx. HNSCCs are often associated with carcinogen exposure, namely from tobacco use and alcohol consumption. Increasingly, cases—particularly of the oropharynx—are associated with human papilloma virus (HPV) infection.^2–5

Conventional and new treatments for HNSCC

The standard-of-care treatment for HNSCC generally involves either (1) a combination of surgical resection and adjuvant radiotherapy, with or without chemotherapy, or (2) radiotherapy given concurrently with chemotherapy.⁶ The primary tumor site and stage largely dictate the appropriate treatment. Cancers of the oral cavity, for instance, are primarily treated with resection and radiotherapy, whereas pharyngeal and laryngeal cancers are primarily treated with radiotherapy and concurrent chemotherapy. For locally restricted and early-stage HNSCC, primary treatment with just one of these modalities is often sufficient to not only manage but also cure the disease, and surgery and radiotherapy are generally considered before cytotoxic chemotherapy.^7,8 In addition, surgical advances (e.g., transoral robotic and laser resection), improved reconstructive techniques, and—in patients with occult metastases in the draining cervical lymph node basins—elective neck dissection have improved overall survival in patients with HNSCC.^9–11

The standard-of-care therapies are most effective in treating small primary cancers with the clinical involvement of no more than one lymph node. However, patients with HNSCC are often diagnosed with more advanced disease because of a lack of detection of antecedent premalignant lesions. HPV status has a significant bearing on disease severity, with HPV− status typically resulting in more negative outcomes than HPV+ status.^5,6,12,13 Patients with long histories of carcinogen exposure, HPV− status, and advanced disease tend to have higher instances of recurrence, which in turn reduces their chances for effective treatment.

Despite therapeutic advances, patients with advanced disease and recurrent or metastatic HNSCC generally have poor prognosis and low survivorship. In these patients, surgery, repeated high-dose radiotherapy, and cytotoxic chemotherapy treatments are the primary treatment options.^6,14 Although these treatments can be potentially curative, they are also generally invasive, aggressive, and disfiguring. Treatment, particularly of advanced cancers, comes with a great risk of significant morbidity and a variety of severe acute and chronic side effects. Impairments in voice quality, speech, and swallowing may occur after radiotherapy and persist for years after treatment, negatively impacting patients' quality of life.^15–17

The risks of HNSCC treatment pose a great challenge for patients and those working to develop safe and effective treatment approaches. To reduce risk to patients and optimize functional preservation, treatments must be carefully selected for each patient based on affected anatomical site, disease stage and progression, and curative possibility. The more favorable outcomes in patients with HPV+ versus HPV− disease have increased interest in treatment de-escalation and the individualization of treatments, especially for patients at low risk of distant metastases and disease recurrence. However, poor outcomes in several such de-escalation trials have shown the need for further study.^5,13,18,19

The advent of immunotherapy in the past decade has revolutionized cancer treatment, especially for HNSCC. Using the body's own immune system, this promising new modality seeks to stimulate the host's response to cancer cells to subvert the cancer's ability to evade immune surveillance and destruction.^17,20 Immunotherapies offer the potential for effective treatment with less toxicity than that associated with standard-of-care treatments. However, immunotherapeutic agents have their own toxicities, resulting in immune-related adverse events (irAEs).

In addition, most patients with HNSCC do not respond to single-agent immunotherapy. Multiple approaches, including immunomodulation, the promotion of cancer cell death and antigen presentation, the reduction of side effects and irAEs, and the exploration of alternative treatment modalities and administration routes, can be used to enhance conventional standard-of-care treatments and the currently approved immunotherapies.²¹ Studies investigating this resistance to therapy are ongoing.²² Various trials are also in progress to determine the potential of novel biomarker targets and combination therapies to further improve surgical approaches and reduce radiotherapy doses. Meanwhile, the need to effectively control tumor progression while improving patients' quality of life remains.^6,12,20,23

The case for biomaterial-based systems

Discoveries from the rapidly growing research fields of biomedicine and materials science show promise as a means of enhancing conventional standard-of-care treatments and currently approved immunotherapies. The biomaterials produced in these fields are diverse and dynamic and include lipid carriers, synthetic nanoparticles and microparticles, implantable and injectable scaffolds, hydrogels, and cryogels. These materials have been effectively used in a variety of areas, including device implants, imaging contrast agents, tissue engineering constructs, and drug delivery systems.^24–26 Their use in cancer immunotherapy offers a promising approach to addressing existing treatment limitations and, specifically, mitigating the toxicities associated with the standard-of-care treatments and immunotherapies (Fig. 1).^25–27

FIG. 1.

Summary of immunotherapies used in cancer treatments and the potential use with biomaterials. Various bioactive agents, including small molecules, nucleic acids, proteins, and immune cells, may be loaded into biomaterials. Rationally designed biomaterials allow for localized delivery of treatments and controlled release and presentation around the material, as well as support for growth of exogenous cells. Such approaches move to overcome the adverse and largely systemic effects currently associated with standard deliveries of immunotherapies. CAR, chimeric antigen receptor; CDNs, cyclic dinucleotides; CpG, cytosine phosphodiester guanine; DNA, deoxyribonucleic acid; mRNA, messenger ribonucleic acid; NK, natural killer; TIL, tumor-infiltrating lymphocytes; TLR, toll-like receptor. Created with BioRender.com

Several clinical trials involving nanomedicines and nanoparticles, for example, are ongoing (Table 1).^28–32 A review from Fenton et al.³³ makes a case for the relevance and need for controlled drug delivery in their comprehensive overview of biomaterial advances for use as delivery systems, detailing the chemistry and specific mechanisms of various types of biomaterials outside the scope of this review. Wang and Mooney's 2018 review covers a decade's worth of biomaterials for use in targeted immunomodulation in cancer treatment and thoughtfully discusses the potential and pitfalls of these approaches.³⁴ Similarly, a recent Yang et al.³⁵ review further discusses the latest developments in nanobiomaterials and their promise in combination anticancer treatments.

Table 1.

Cancer Immunotherapy Clinical Trials Involving Nanomedicines and Bioparticles

Treatment	Cancer type	Organization	Trial No.
Albumin-stabilized nanoparticles, paclitaxel	Advanced/metastatic solid tumors, Lymphomas	University of Southern California; Vasgene Therapeutics, Inc.	NCT02495896 (I/II)28
Albumin-stabilized nanoparticles, paclitaxel	Head and neck	Washington University School of Medicine; Celgene	NCT01566435 (II)29
Hafnium(IV) oxide (HfO2) nanoparticle	Head and neck (oral cavity, oropharynx)	Nanobiotix	NCT01946867 (I)30
Lipid nanoparticle capsulation of mRNA (human OX40 ligand, IL-23, IL-34g)	Advanced/metastatic solid tumors, Lymphomas	ModernaTX	NCT03739931 (I)31
Poly(lactic-co-glycolic acid) scaffold-supported autologous vaccine	Melanoma	Dana-Farber Cancer Institute	NCT01753089 (I)32

IL, interleukin; mRNA, messenger ribonucleic acid.

In HNSCC, however, biomaterial use is currently limited to preclinical models, although the development of three-dimensional (3D) in vitro tumoroids that can accurately replicate in vivo tumor characteristics is of growing interest in drug screening.^36,37 This review summarizes several current immunotherapeutic approaches used in the treatment of HNSCC and their limitations. Furthermore, it highlights biomaterial-based strategies for encapsulated, targeted, or localized drug delivery and immunomodulations that have been used to overcome the shortcomings of current treatments and that may have additional potential in the treatment of HNSCC.

Cancer Immunotherapies and Their Limitations

Immune checkpoint inhibitors and targeted antibody-based therapies

Immune checkpoint inhibitors (ICIs), which block key checkpoint ligands from binding with their partner receptors to prevent T cell inhibition, were first approved for use in advanced melanoma.^38,39 They have galvanized the cancer immunotherapy field and have shown substantial efficacy across various cancers. To date, the United States Food and Drug Administration (FDA) has approved two anti–programmed cell death protein 1 (PD-1) therapies—nivolumab and pembrolizumab—for use in HNSCC. Preclinical and clinical studies of anti-PD-1 antibodies have demonstrated their effectiveness in recurrent and metastatic HNSCC. Compared with patients treated with standard-of-care chemotherapy drugs, those treated with anti-PD-1 antibodies have shown improved overall survival.^40–42

Other such treatments, including treatments with cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) antibodies such as ipilimumab and tremelimumab, have been effective in other cancers, although they are not approved for HNSCC.⁴³ Despite the promise of these ICIs, most patients with HNSCC and other cancers do not see durable responses to monotherapies and may experience off-target toxicities.⁴⁴ This has led to the theory that the complexity of anticancer immunity requires combinations of modalities to effectively treat HNSCC.⁴⁵

Cetuximab, a molecular targeted therapy, is another FDA-approved antibody used to treat HNSCC. As a cancer treatment, cetuximab inhibits the epidermal growth factor receptor, which targets tumor angiogenesis, halts tumor cell proliferation, radio-sensitizes tumors, and complements deoxyribonucleic acid (DNA)-damaging cytotoxic agents. It may also cause cellular cytotoxic immune responses.⁴⁶ Researchers are now developing antibody-drug conjugates (e.g., telisotuzumab vedotin, indatuximab ravtansine, and W0101), in which a monoclonal antibody is chemically linked to a drug; bispecific antibodies, which are antibodies capable of binding two targets to induce cellular immunity (e.g., GBR 1372 and ABL001); and cytokine-antibody fusion proteins, or immunocytokines, which increase tumor antigens through the localized and targeted delivery of immune-activating cytokines to tumor cells. However, the success of these antibodies is limited in HNSCC.^47–52

Higher mutation burden in HNSCC generally correlates with a worse prognosis, and patients with a high mutation burden are promising candidates for immunotherapy. However, different HNSCCs associated with carcinogen exposure and those that are HPV+ correlate with increased mutagenesis and immune cell infiltration, respectively. These response differences may account for limited responses to ICIs and other immunotherapies in HNSCC patients and further indicate the need for new therapeutic approaches to enhance patients' immune responses.^53–56

Ongoing trials combining ICIs, therapeutic vaccines, costimulatory agonists, and cytotoxic agents with a number of targeted antibodies are under development (Table 2).^57–123 Phase III trials of treatments combining anti-CTLA-4 and anti-PD-1/programmed death-ligand 1 (PD-L1) antibodies, which have previously been effective in patients with melanoma, are underway for patients with HNSCC to evaluate the combination treatments' synergistic effects and compare the combination treatments to standard-of-care treatments, including standard chemotherapy regimens. Other trials are examining the outcomes of combining ICIs with chemoradiotherapy.^17,146–153

Table 2.

Antibody-Based Immunotherapies for Head and Neck Cancer Treatment

Treatment	Target	Organization	Trial No. (status/phase)
Cetuximab	EGFR	Erbitux	NCT00004227 (Approved, 2006)57
Nivolumab	PD-1	Opdivo	NCT02105636 (Approved, 2016)58
Pembrolizumab	PD-1	Keytruda	NCT02358031, NCT02252042 (Approved, 2017)59,60
PF04518600	OX40 (CD134)	Pfizer	NCT02315066 (I)61
Spartalizumab	PD-1	Novartis	NCT04213404 (I), NCT04000529 (I)62,63
Sym004 (futuximab, modotuximab)	EGFR	Symphogen A/S	NCT01417936 (II)64
Ficlatuzumab	HGF/SF Ligand	AVEO Oncology	NCT03422536 (II)65
Cusatuzumab (ARGX110)	CD70	Argenx SE; Janssen R&D, LLC	NCT02759250 (I)66
Urelumab	CD137 (4-1BB Ligand)	Bristol-Myers Squibb AB	NCT02110082 (I)67
Cemiplimab-rwlc	PD-1	Regeneron; Sonafi	NCT04242173 (II)68
Dalantercept	ALK1	Acceleron Pharma Inc.	NCT01458392 (II)69
Zalutumumab	EGFR	Genmab A/S	NCT00401401 (I/II), NCT00707655 (I/II), NCT01054625 (I/II), NCT00542308 (II), NCT00496652 (III)70–74
Nimotuzumab	EGFR	CIMYM Bioscience; Oncoscience AG	NCT00957086 (III)75
ABL001	VEGF/DLL4	ABL Bio	NCT03292783 (I)76
Panitumumab	EGFR	Abgenix Inc.; Amgen	NCT02415881 (I), NCT03733210 (I), NCT03405142 (I)77–79
Enoblituzumab	CD276 (B7-H3)	MacroGenics	NCT04129320 (II/III), NCT02475213 (I)80,81
Bavituximab	Phosphatidylserine	Peregrine Pharmaceuticals	NCT04150900 (I)82
Budigalimab (ABBV-181)	PD-L1	AbbVie	NCT04196283 (I), NCT03000257 (I)83,84
Cosibelimab	PD-L1	Checkpoint Therapeutics	NCT03212404 (I)85
CPI-006	CD73	Corvus Pharmaceuticals	NCT03454451 (I)86
Hu5F9-G4	CD47	Forty-Seven, Inc.	NCT02953782 (I)87
W0101	IGF-1R	Pierre Fabre	NCT03316638 (I/II)88
Tislelizumab (BGB-A317)	PD-1	BeiGene	NCT03430843 (III), NCT03783442 (III), NCT03957590 (III), NCT03924986 (III)89–92
ISU104	HER3	ISU ABXIS Co.	NCT03552406 (I)93
GA201 (RG7160)	EGFR	Roche	NCT00721266 (I)94
LJM716	HER3	Novartis AG	NCT01598077 (I), NCT01822613 (I)95,96
Siltuximab	IL-6	Centocor, Inc. (Janssen Biotech)	NCT00841191 (I/II)97
Vopratelimab (JTX-2011)	ICOS	Jounce Therapeutics, Inc.	NCT04319224 (I/II), NCT02904226 (I/II)98,99
Ipilimumab	CTLA-4	Bristol-Myers Squibb	NCT02812524 (I), NCT02919683 (II), NCT02741570 (III), NCT02823574 (II), NCT04080804 (II), NCT03690986 (I), NCT03700905 (III), NCT03162731 (I), NCT01935921 (I), NCT03003637 (I/II), NCT03406247 (II), NCT03620123 (II)100–111
Trastuzumab	HER2	Genentech (Roche)	NCT00004163 (II), NCT02627274 (I)112,113
Pertuzumab	HER2	Genentech (Roche)	NCT02465060 (II)114
Lirilumab (IPH2102)	KIR2DL1/2/3	Innate Pharma SA; Bristol-Myers Squibb AB	CA223-001 (EU, I/II)115
Bevacizumab	VEGF	Genentech, Inc.	NCT01262859 (II), NCT01588431 (II), NCT00409565 (II), NCT00703976 (II)116–119
MN-14	CEA		NCT00004048 (I/II)120
anti-CD45 mAb	CD45	Baylor College of Medicine	NCT00078546 (I)121
Onartuzumab	c-Met	Genentech (Roche)	Preclinical47,122,123
GBR 1372	EGFR, CD3	Glenmark Pharmaceuticals	Preclinical47,122,123
Indatuximab ravtansine (BT-062)	CD138 (Syndecan-1)	ImmunoGen	Preclinical47,122,123
Telisotuzumab vedotin (ABV-399)	c-Met	AbbVie	Preclinical47,122,123
Daromun	ED-B of L19 and L19-TNFa	Philogen SpA	Preclinical47,122,123
FRMD4A Ab	FERMD4A		Preclinical47,122,123

Only three such treatments are approved for HNSCC, demonstrating the need for more effective treatment options. Various clinical trials and preclinical studies are ongoing.

ALK1, activin receptor-like kinase 1; CEA, carcinoembryonic antigen; c-Met, tyrosine-protein kinase Met; CTLA-4, cytotoxic T-lymphocyte-associated antigen 4; DLL4, delta-like canonical notch ligand 4; ED-B, extra-domain B; EGFR, epidermal growth factor receptor; FERMD4A, FERM domain containing 4A; HER3, human epidermal growth factor receptor 3; HGF, human hepatocyte growth factor; HNSCC, head and neck squamous cell carcinoma; ICOS, inducible T cell costimulatory; IGF-1R, insulin-like growth factor 1 receptor; KIR2DL1/2/3, killer cell immunoglobulin-like receptor two IgG domains and long cytoplasmic tail 1/2/3; L19, fibronectin; L19-TNFα, fibromun; PD-1, programmed cell death protein 1; PD-L1, programmed death-ligand 1; SF, scatter factor; VEGF, vascular endothelial growth factor.

Thus far, these combination treatments have achieved long-term remissions with fewer toxicities in patients with HNSCC but have not prolonged overall survival. Some patients, particularly those with HPV− status and recurrent disease, experience irAEs (e.g., pneumonitis, colitis, and organ injury) and accelerated disease progression, although it has been observed that the response to chemotherapy may improve in these cases and lead to durable responses.^154–156

Another concern besides the clinical limitations of ICI treatments is that antibody availability and access for patients are limited by the antibodies' high production costs. In addition, polymorphisms in Fc gamma receptors, regulatory T cell activity, and tumor escape result in poor antibody performance.¹⁵⁷ Finally, poor pharmacokinetic qualities, such as ineffective tumor penetration due to large antibody sizes and limited routes of administration, are also practical disadvantages to these therapies.¹⁵⁸ Several other clinical trials are exploring novel immunotherapy options for patients with metastatic or recurrent HNSCC, as well as combinations of ICIs with antiangiogenic agents.^22,153,159

Biomaterial-based strategies can counter these limitations of such conventional immunotherapies. The specificity of ICIs and antibodies can be increased and the potential for irAEs can be reduced through the use of biomaterial-based delivery method encapsulation of an albumin-based complex, loading into controlled-release, injectable hydrogels, conjugation to gold-silica nanoparticles, and use of engineered exosomes.^47,160–167 Galstyan et al.¹⁶⁵ recently showed that use of targeted nano immunoconjugate drugs in a poly(β-l-malic acid) scaffold carried covalently attached ICIs across the blood–brain barrier and elicited immune responses in a GL261 glioblastoma model.

In another study, gold nanoparticles (GNPs) conjugated to anti-PD-L1 antibodies in a colon cancer model were used to locally deliver ICIs to tumors; computed tomography imaging allowed for the visualization of GNP accumulation in the tumor and, therefore, predictions of response.^168–171 Furthermore, conjugated GNPs may enhance the killing capacity of the immune response by converting light into heat, which can ultimately destroy cancer cells and potentially treat HNSCC.^47,167 These select biomaterial formulations and strategies are just some of the many that can potentially be applied to HNSCC.

Small-molecule immune adjuvants and agonists

Small molecules—natural or synthetic compounds acting as agonists, antagonists, or inhibitors—are another class of promising cancer immunotherapeutics. These compounds can be diverse in function, and they target immunosuppressive mechanisms or trigger various innate or adaptive immune pathways, which also implies that they may have large numbers of molecular targets.^172–175 They also may cross cell membranes and penetrate solid tumors more efficiently than larger proteins (i.e., antibodies) or molecules to better access targets. Their systemic (oral) bioavailability and amenability to controlled release make them good alternatives to other therapies that result in irAEs.

In addition, small molecules are less expensive to produce than antibodies, which increases their availability and patient access.^176–179 Small molecule treatments also allow for improved mechanism-guided therapeutic targeting and can be used in combination with ICIs to improve specificity. One study demonstrated the use of small-molecule inhibitors in targeting PD-1/PD-L1 interaction, resulting in in vivo cytotoxic T cell recruitment to solid tumors in a colorectal cancer animal model.¹⁸⁰

One class of small molecule increasingly used in cancer immunotherapy is the stimulator of interferon genes (STING) class of agonists (Table 3).^124,125 The STING pathway is critical for the detection of and response to pathogen-associated molecular patterns. The accumulation of cytoplasmic DNA—originating from damaged mitochondria or leaky nuclei, viral or bacterial infection, or phagocytosed DNA from dead cells—serves as a danger signal to the immune system. Cyclic guanosine monophosphate–adenosine monophosphate (GMP–AMP) synthase detects cytoplasmic DNA, resulting in the synthesis of 2′3′-cyclic GMP-AMP, and ultimately directs the binding and activation of STING. 2′3′-cyclic GMP-AMP and other cyclic dinucleotides (CDNs) are potent agonists of the STING pathway and, in turn, activators of innate immunity because of their generation of type I interferons.^{174,181–183}

Table 3.

Clinical Trials of Immunotherapies, Including STING Agonists, Cell-Mediated Therapies, and Vaccine-Based Treatments for Head and Neck Cancer

Immunotherapy type	Treatment	Organization	Trial No. (status/phase)
STING agonists	M1W815 (ADUS100) ± pembrolizumab	Aduro Biotech	NCT03937141 (II)124
	MK-1454 ± pembrolizumab	Merck Sharp & Dohme	NCT04220866 (II)125
Cytokines	Interferon-α (IFNα)	Northwestern University; Eastern Cooperative Oncology Group	NCT00004897 (II), NCT00054561 (III)126,127
	Pegylated IFNα-2b	M.D. Anderson Cancer Center	NCT00276523 (II)128
	IL-2	H. Lee Moffitt Cancer Center and Research Institute; European Institute of Oncology	NCT00006033 (II), NCT00002702 (III)129,130
	IL-12	Dana-Farber Cancer Institute	NCT00004070 (I/II)131
	ALT-801 (recombinant fusion protein with IL-2 component)	Altor BioScience	NCT00496860 (I)132
	IRX-2	Brooklyn ImmunoTherapeutics, LLC	NCT00210470 (II)133
Vaccines	ALVAC-CEA	Georgetown University	NCT00003125 (II)134
	Anti-CEA RNA-pulsed DC	Duke University	NCT00004604 (I)135
	EBV LMP-2 peptide	National Institutes of Health Clinical Center	NCT00078494 (I)136
	HPV-16 E7/E6 peptide	National Cancer Institute	NCT00019110 (I)137
	JAX-594 (thymidine kinase-deleted vaccinia virus plus GM-CSF)	Jennerex Biotherapeutics	NCT00625456 (I)138
	MAGE-A3/HPV-16	University of Maryland, Baltimore	NCT00257738 (I)139
	Multiple-peptide (LY6K, VEGFR1, VEGFR2)	Japanese Foundation for Cancer Research	NCT00561275 (I)140
	p53-pulsed DC	University of Pittsburgh	NCT00404339 (I)141
	Ras peptide	National Cancer Institute	NCT00019331 (II)142
	Fowlpox-CEA-TRICOM (fCEA-TRI)	National Cancer Institute; National Institute on Deafness and Other Communication Disorders; Duke University	NCT00028496 (I), NCT00021424 (I), NCT00027534 (I)143–145

DC, dendritic cell; HPV, human papilloma virus; STING, stimulator of interferon genes.

Various analogs of STING agonists have been developed, and they have been efficacious in preclinical trials as monotherapy treatments and in combination treatments with anti-PD-1 and DNA-damaging agents. However, recent clinical trials of ADU-S100/MIW815, a higher-affinity analog of c-di-AMP (cyclic diadenylate monophosphate), with anti-PD-1 ICIs did not result in substantially enhanced antitumor activity in HNSCC.^{124,181,184,185} In addition, as with other potent immunostimulatory agents, systemic administration could result in severe toxicities.^181,186,187 These toxicities may occur because negatively charged CDNs have limited cellular permeability.

Similar to other small molecules, their rapid diffusion upon administration can limit drug exposure in the tumor or other target tissue and result in off-target toxicities, including those affecting cytotoxic CD8⁺ T cell responses.¹⁸¹ An ongoing phase I clinical trial is testing a novel systemically delivered anti-HER2-STING agonist antibody-drug conjugate (XMT-2056) in advanced or recurrent HER2+ solid tumors.¹⁸⁸ Early in vitro and in vivo applications, which resulted in FDA orphan drug designation for gastric cancers in 2022, demonstrated a significant increase in potency compared with free STING agonist in both tumor-resident immune cells and tumor cells.^189,190 The current trial, however, was recently suspended due to severe adverse effects observed in at least two reported patients and is currently under investigation, further indicating the need for greater understanding of such immunomodulatory agents.^188,191

A variety of small molecules are used in anticancer immunotherapies, but CDN STING agonists are especially notable here because of the biomaterial-based immunotherapy research that has tested these molecules in HNSCC preclinical models. The delivery of STING agonists through various hydrogel and nanoparticle systems continues to be explored.^192–200 A recent study from Park et al.¹⁹⁵ showed that delivering the STING agonist 2′3′-c-di-AM(PS)2 (Rp,Rp) through perioperative hydrogel delivery to tumor resection sites prevented local tumor recurrence and induced systemic antitumor immunity in breast cancer, lung carcinoma, and melanoma models.

In 2018, our research group described the use of “STINGel,” a cationic, lysine-based K2(SL)6K2 multidomain peptide (MDP) that mimics an extracellular matrix by self-assembling into a local nanofibrous network upon injection.^200,201 Charged-small molecule drugs, such as CDN, can be loaded into the hydrogel, allowing for gradual controlled drug release. A durable acquired immune response and increased overall survival were observed in an HNSCC tumor model after a single intratumoral STINGel injection loaded with CDN ML RR-S2 CDA.²⁰⁰ In a subsequent publication, we built upon this initial study with the use of “SynerGel.” This hydrogel iteration is a bioactive drug-mimicking MDP that incorporates L-NIL [N⁶-(1-iminoethyl)-l-lysine] loaded with CDN (Fig. 2).

FIG. 2.

Design and structure of a drug-mimicking self-assembling MDP hydrogel. (A) The chemical structure of the small-molecule drug L-NIL. (B) The structure of the L-NIL-MDP, in which the small molecule L-NIL is incorporated into the MDP design. (C) Graphical depiction of the formation of antiparallel β-sheets that comprise the nanofibers of the MDP hydrogel upon self-assembly. (D) Image of L-NIL-MDP hydrogel material, formed at 1 wt% in a phosphate-containing buffer. This gel can be loaded with other bioactive agents (i.e., CDN) for additional therapeutic targeting. L-NIL, N⁶-(1-iminoethyl)-l-lysine; MDP, multidomain peptide. Figure reproduced with permission from ACS Biomaterials Science & Engineering (2019).²⁰²

L-NIL is a potent small-molecule inhibitor of inducible nitric oxide synthase, and it effectively targets myeloid-derived immunosuppressive cells.^201–205 Thus, “SynerGel” is designed to reverse the immunosuppressive environment facilitated by myeloid-derived suppressor cells while triggering an antitumor immune response. Our preclinical results showed modest success in HNSCC tumor regression (4–5 mm) and improved overall survival after a single intratumoral injection of SynerGel, demonstrating the potential of L-NIL-MDP hydrogel as an effective bioactive material for drug delivery.²⁰¹

Cytokines and bioactive proteins

Cytokines are small bioactive proteins produced largely by immune cells. They are key signaling molecules that direct cell growth and activity, most importantly in the regulation of the immune response. The secretion of primarily interferons, interleukins (ILs), and growth factors by immune cells is critical for signaling and immunomodulation. Cytokine-based immunotherapeutic treatments take advantage of the robust and critical functions of these chemical messengers. Thus far, only two cytokines have been approved by the FDA as monotherapies for anticancer treatment: IL-2 for metastatic renal cell carcinoma and metastatic melanoma, and interferon alpha for hairy cell leukemia.^206,207

The antitumor response is induced by the locoregional or systemic delivery of proinflammatory cytokines. Cytokines actively explored for use in HNSCC include granulocyte-macrophage colony-stimulating factor, IL-2, interferon gamma, IL-12, and IRX-2 (a multicytokine biologic) (Table 3).^{126–133,208} Critical to the use of cytokines as therapies is an understanding of their mechanisms and toxicities. For example, high doses of systemically delivered cytokines can lead to production of antidrug antibodies, as well as severely toxic cytokine storms, which are usually caused by the downstream release of other cytokines and by vascular leak syndrome resulting from microvascular permeability.^209,210 The key to minimizing the adverse effects of cytokine therapy is to minimize plasma exposure (circulating cytokines) while maintaining treatment efficacy.

Protein engineering and biomaterial-based approaches are among the strategies used to mitigate these negative effects of cytokine immunotherapies. Cytokines such as IL-12, which have robust antitumor activity but are rarely used because they cause severe systemic toxicity, have proven effective in the treatment of HNSCC when they are delivered locally by intratumoral injection and in multiple doses.^211–214 Microspheres, chitosan (bioadhesive polysaccharide) coformulations, liposomes, and nanoparticles have been used in various cancer models for effective localized IL-12 delivery.^{213,215–221}

Barberio et al.²²¹ used a “layer-by-layer” nanoparticle system, in which polymer materials are layered on the particle surface electrostatically, to optimize cytokine delivery to tumors. The study showed that, in models of MC38 colon cancer (immunologically “hot,” meaning immune-infiltrated) and HM-1 ovarian cancer (immunologically “cold”), the layer-by-layer nanoparticles effectively localized to the surfaces of tumor cells, reduced systemic IL-12 exposure (because the layers served as a barrier), and slowly released IL-12 over time as the particle surface eroded.²²¹ Kim et al.²²² recently showed that “BALLkine-2,” a formulation of unmodified recombinant IL-2 loaded into a biodegradable porous silica nanoparticle, induced an immune response while reducing toxic irAEs when peritumorally injected into B16F10 melanoma models and combined with anti-PD-1 treatment.

In a recent publication, Nash et al.²²³ demonstrated another cytokine-biomaterial approach: the use of alginate spheres that encapsulate cytokine-producing ARPE-19 cells and serve as “cytokine factories.” A phase II clinical trial in patients with ovarian cancer previously showed that intraperitoneal IL-2 administration resulted in more tolerable toxicity levels and more stable concentrations of IL-2 at the site of injection for an extended period of time.²²⁴ Coinciding with these clinical data, the implantable IL-2-secreting alginate spheres were therapeutically efficacious in tumors of ovarian and colorectal cancer preclinical animal models, eliminating tumors and producing a robust immune response and highly controlled predictable IL-2 local release.

Adoptive cell-based therapies

Cell-based therapy, or adoptive cell transfer (ACT), is most frequently done using T cells and generally involves the ex vivo amplification and adoptive transfer of a patient's own immune cells back into the patient to enhance the immune response. This type of immunotherapy is promising for personalized medicine across various disease contexts, including cancer.^225–232 The ACT of T cells, however, can result in graft-versus-host disease because of T cell receptor specificities, as well as cytokine release syndrome and other neurotoxicities.

To circumvent these limitations, researchers have explored and shown the efficacy of tumor-infiltrating lymphocytes and gene-engineered T cell receptor T cells in ACT applications, including in cases of HPV-associated cancers, demonstrating their potential use in advanced epithelial cancers such as HNSCC.²²⁶ A recent publication by Wei et al.²³¹ showed the exciting potential of ACT. Specifically, the researchers used HLA-restricted neoantigen-specific T cell receptor-engineered T (TCR-T) cells to allow for greater specificity in ACT treatment of HNSCC.

However, limited efficacy and systemic toxicity remain common failings for ACT because of dysfunction in reintroduced immune cells or in their ability to expand.^228,233 Alternatively, chimeric antigen receptor (CAR) T cell therapy enhances T cell activity and the binding of tumor antigens without the MHC/HLA restrictions of the TCR, but durable responses remain poor in solid tumors because of their environments, which are generally highly immunosuppressive. Another drawback of CAR T cell therapy is that the generation of these T cells is costly and inefficient.^{27,227,228,234}

In the context of ACT applications, biomaterials have been largely explored as a means of preserving T cell viability and quality during periods of exogenous activation. For any ACT using biomaterials, the degradation, toxicity, and immunogenicity of these materials must be evaluated before their reintroduction into patients. Studies of various biomaterials engineered to promote T cell expansion indicate that they may be useful for purposes other than drug delivery.^{226,235–237} In ACT, natural killer (NK) cells can be used as alternatives to CAR T cells because they can generate a robust innate immune response against infected or exogenous cells without the same limitations or toxicities induced by T cells.

NK cells are an increasingly explored and promising option for immunotherapy, and researchers are currently investigating biomaterial- and NK cell–based approaches to cancer immunotherapy, including use of an implantable scaffold that facilitates cell homing and continued proliferation and activation upon reintroduction into patients.^{236,238–240} As with T cells, biomaterials such as cell-permeable scaffolds may release cytokines promoting NK cell growth and activation.

In a 2022 study, Ahn et al.²⁴⁰ demonstrated the use of 3D-ENHANCE, their 3D, hyaluronic acid–based, and macroporous polymer scaffold for cell expansion. Not only were NK cells able to expand ex vivo on this scaffold, but controlled degradation of the engineered material also allowed the scaffold to be effectively implanted in resection sites as an in vivo cell reservoir in an MDA-MB-231 breast cancer model. This scaffold offered a potentially game-changing method of expanding NK cells without conventionally used feeder cells, which facilitate very slow cell growth with little cell yield and can potentially contaminate the final ACT products, endangering patients.^{236,238–240}

Cancer vaccines

Vaccines against HPV, which is known to cause cervical cancer and HNSCC, are perhaps the best known prophylactic vaccines in the context of cancer prevention. Therapeutic cancer vaccines stimulate and strengthen a patient's adaptive immune system, thereby enhancing the antitumor immune response and sparing healthy cells (Table 3).^134–145 For example, the therapeutic vaccine sipuleucel-T was approved by the FDA in 2010 for the treatment of hormone-resistant prostate cancer.²⁴¹ Perhaps the biggest challenges in the development of therapeutic cancer vaccines are efficient vaccine delivery and the selection of an appropriate antigen to generate a robust and broad T cell response for cytotoxic activity throughout the heterogeneous tumor microenvironment.^242–244

Neoantigens, which result from somatic mutations introduced into tumor cell DNA, are highly immunogenic antigens expressed specifically in tumor cells and are increasingly looked to as tumor-specific therapeutic targets.⁵³ The loss of tumor antigen expression may occur upon encountering an initially effective antitumor immune response. This mechanism of tumor cell immune escape is a well-studied result of immunoediting and has been shown to operate in numerous preclinical cancer models.²⁴⁵ Our group recently reported supporting data in MOC2-E6E7, a murine oral cancer cell line expressing HPV-16 oncoproteins E6 and E7. MOC2-E6E7 tumors not only displayed an “inflamed” immune microenvironment, but also exhibited decreased expression of E6 and E7 genes in immunocompetent MOC2-E6E7 tumor-bearing mice over time (which was not observed in vitro).²⁴⁶ Therefore, overcoming immune escape using vaccines that target “driver” oncogenes is essential.

Personalized cancer vaccines targeting tumor-associated or tumor-specific antigens are an increasingly promising approach. Recent technological advances in next-generation genomic sequencing have improved the efficiency of neoantigen identification.⁵⁴ A recent phase I clinical trial evaluated the mutation-associated TG4050 vaccine in patients with either ovarian cancer or HNSCC. Vaccines were generated for each patient after genomic characterization, and patients were given multiple vaccine doses with boosters. Of the four patients with HNSCC who were in the trial at the cutoff point, three were in complete remission and one had relapsed. This trial showed that the patients developed a T cell immune response after the administration of the vaccine, regardless of their human leukocyte antigen haplotype, and that the vaccine was safe and well tolerated.²⁴⁴

Biomaterials may provide useful systems for localized and slow-release vaccine delivery.²⁴⁷ In acute myeloid leukemia (AML), standard-of-care chemotherapy induces remission, but relapse often follows soon after. However, the use of a macroporous cryogel-based vaccine allows for the sustained release of the toll-like receptor agonist cytosine phosphodiester guanine (CpG)-oligodeoxynucleotides, dendritic cell (DC)-recruiting granulocyte-macrophage colony-stimulating factor, and leukemia antigens. Studies in mice have shown that prophylactic vaccination confers potent durable anti-AML immunity that is transferable from vaccinated mice through bone marrow transplantation.²⁴⁸

The vaccination of tumor-bearing mice, when combined with chemotherapy, increased long-term survival. In addition, increases in the apoptotic markers in the vaccination site and draining lymph nodes were noted, and the apoptotic markers appeared to colocalize with activated DCs.²⁴⁸ These results demonstrate the capacity of a biomaterial-based vaccine to induce potent immune responses depleting AML and preventing relapse, even without defined antigen targets. In HNSCC specifically, our group has also demonstrated the importance of both driver antigen-targeting and immunogenicity using a mesoporous silica rod-based cancer vaccine against E7. We observed increased infiltration of antigen-specific CD8⁺ T cells, delayed tumor growth, as well as modest increased overall survival in MOC2-E6E7 tumors and more so in the E7-driven mEER HNSCC model.²⁴⁶ Such vaccines have been shown to form a local structure promoting immunomodulation for adaptive immune response and antitumor immunity.^249,250

DCs, which facilitate antigen presentation and regulate T cell immunity, are of interest in the development of cancer vaccines and ACTs.²⁴⁷ However, transplanted DCs have a short lifespan upon activation, and this potentially compromises their downstream tumor-specific immune response. Moreover, the extracorporeal time-consuming cell-manipulation process is expensive, and the effectiveness of the modified DCs may be low or unpredictable.

In a lymphoma model, Yang et al.²⁵¹ generated a DC vaccine by encapsulating DCs and tumor antigens into a nanofibrous RADA16 peptide hydrogel (Fig. 3). This injectable self-assembling hydrogel served as a 3D matrix scaffold to support the survival, potentiation, and biological uptake (antigen uptake) of the encapsulated DCs. The addition of anti-PD-1 antibody further enhanced these immune functions. Studies have shown that administering DCs directly to the tumor site may reduce systemic exposure and improve treatment efficacy.^247,251 Again, these uses of biomaterials in cancer vaccines demonstrate their potential application in the treatment of other cancers, including HNSCC.

FIG. 3.

Summary of the assembly and immunological mechanism of an exogenous DC vaccine delivered by a RADA16 nanofibrous peptide hydrogel. Antigen release from the hydrogel recruits and activates endogenous DCs, which migrate to draining lymph nodes to potentiate antigen-specific T cell immune response. DC, dendritic cell. Figure reproduced with permission from Nano Letters (2018).²⁵¹

Conclusion

Together, immunotherapies and biomaterials represent a powerful and exciting area of anticancer research. This brief review gives a glimpse as to what the future might look like for the field of HNSCC, as well as for the patients affected by this disease, most of whom receive no substantial benefit from the current treatments. Several of the biomaterial-based approaches described earlier have not published findings in the context of HNSCC, but their use in other cancer types lays the groundwork for HNSCC-specific studies and offers hope that similar strategies will be successful in the treatment of that disease. Furthermore, new thoughtfully selected therapeutic targets and rationally designed biomaterials are being discovered and studied together, and the benefits of doing so are being increasingly realized.

Notably, a common aspect of the studies included in this overview is the use of multimodal combination treatments. Indeed, many active clinical trials are evaluating some combination of existing therapies, and biomaterials have been shown to be another tool with which to further address the complexities of effective anticancer treatment and immunotherapy development. It is increasingly clear that HNSCC is a complex disease that cannot easily be cured with a single treatment approach. Thus, it is crucial to consider multipronged approaches to disrupt tumor cell immunosuppression and evasion, expand effector T cells, and sustain T cell activation to achieve true complete responses to therapy.²⁵² Finding appropriate materials for biomaterial-based treatment approaches and evaluating what balance of therapeutic combinations will lead to efficient and durable responses, increased survival, and preserved quality of life for patients with HNSCC is key.

Authors' Contributions

S.Y., G.S., and A.G.S. structured the review, and G.S. wrote the initial article draft. S.Y., A.G.S., and J.H. corrected and edited the article. All authors contributed to the article and approved the submitted version.

Disclosure Statement

The authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.

Funding Information

G.S. is a PhD graduate student at The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences. This study was supported by the NIH-NIDCR grant R01DE030140.