HyStem®: A Unique Clinical Grade Hydrogel for Present and Future Medical Applications

Medicine needs targeted, minimally-invasive delivery of protein-based and cell-based therapeutics to increase efficacy and reduce occurrence and severity of side effects. Local delivery requires a matrix to sequester and protect the medicine until its effect can be realized. The problem is, unlike stable small molecule drugs, proteins and cells cannot be co-packaged with a matrix in a prefilled syringe—they must be mixed with their matrix at the point of care. HyStem hydrogels fix this problem: They are arguably the first commercially available, GMP-qualified biodegradable hydrogels both with the ability to formulate with either proteins or cells in the hospital/surgical suite and with a history of safe use in humans. HyStem is designed to be protein, cell-friendly and in situ crosslinkable, permitting homogeneous mixing of therapeutics. One HyStem formulation is 510(k) cleared and another the subject of two European clinical trials. Key applications include localized delivery of therapeutic growth factors, antibodies, and cells. In the future, we envision HyStem’s flexibility and clinical use history forming the basis for a new generation of therapeutics. Two examples described here include HyStem’s use for patient-derived organoid culture to develop new drugs as well as for bioprinting to manufacture new organs

The effect of mesenchymal stromal cell sheets on the inflammatory stage of flexor tendon healing

BACKGROUND: The clinical outcomes following intrasynovial flexor tendon repair are highly variable. Excessive inflammation is a principal factor underlying the formation of adhesions at the repair surface and affecting matrix regeneration at the repair center that limit tendon excursion and impair tendon healing. A previous in-vitro study revealed that adipose-derived mesenchymal stromal cells (ASCs) modulate tendon fibroblast response to macrophage-induced inflammation. The goal of the current study was therefore to explore the effectiveness of autologous ASCs on the inflammatory stage of intrasynovial tendon healing in vivo using a clinically relevant animal model. METHODS: Zone II flexor tendon transections and suture repairs were performed in a canine model. Autologous ASC sheets were delivered to the surface of repaired tendons. Seven days after repair, the effects of ASCs on tendon healing, with a focus on the inflammatory response, were evaluated using gene expression assays, immunostaining, and histological assessments. RESULTS: ASCs delivered via the cell sheet infiltrated the host tendon, including the repair surface and the space between the tendon ends, as viewed histologically by tracking GFP-expressing ASCs. Gene expression results demonstrated that ASCs promoted a regenerative/anti-inflammatory M2 macrophage phenotype and regulated tendon matrix remodeling. Specifically, there were significant increases in M2-stimulator (IL-4), marker (CD163 and MRC1), and effector (VEGF) gene expression in ASC-sheet treated tendons compared with nontreated tendons. When examining changes in extracellular matrix expression, tendon injury caused a significant increase in scar-associated COL3A1 expression and reductions in COL2A1 and ACAN expression. The ASC treatment effectively counteracted these changes, returning the expression levels of these genes closer to normal. Immunostaining further confirmed that ASC treatment increased CD163(+) M2 cells in the repaired tendons and suppressed cell apoptosis at the repair site. CONCLUSIONS: This study provides a novel approach for delivering ASCs with outcomes indicating potential for substantial modulation of the inflammatory environment and enhancement of tendon healing after flexor tendon repair

Peri-tumor administration of controlled release anti-CTLA-4 synergizes with systemic anti-PD-1 to induce systemic antitumor immunity while sparing autoimmune toxicity.

Combination immunotherapy targeting the PD-1 and CTLA-4 checkpoint inhibitor pathways provides substantial clinical benefit in patients with advanced-stage cancer but at the risk of dose-limiting inflammatory and autoimmune toxicity. The delicate balance that exists between unleashing tumor killing and promoting systemic autoimmune toxicity represents a major clinical challenge. We hypothesized that targeting anti-CTLA-4 so that it perfuses tumor-draining lymph nodes would provide a significant therapeutic advantage and developed an injectable hydrogel with controlled antibody release characteristics for this purpose. Injection of hydrogel-encapsulated anti-CTLA-4 at a peri-tumor location (MC-38 tumor model) produced dose-dependent antitumor responses and survival that exceeded those by anti-CTLA-4 alone (p < 0.05). Responses to 100 µg of targeted anti-CTLA-4 also equaled or exceeded those observed with a series of systemic injections delivering 600 µg (p < 0.05). While preserving antitumor activity, this approach resulted in serum anti-CTLA-4 exposure (area under the curve) that averaged only 1/16th of that measured with systemic therapy. Consistent with the marked differences in systemic exposure, systemic anti-CTLA-4 stimulated the onset of autoimmune thyroiditis in iodide-exposed NOD.H-2h4 mice, as measured by anti-thyroglobulin antibody titer, while hydrogel-encapsulated anti-CTLA-4 had a minimal effect (p ≤ 0.01). At the same time, this targeted low-dose anti-CTLA-4 approach synergized well with systemic anti-PD-1 to control tumor growth and resulted in a high frequency of complete responders that were immune to tumor re-challenge at a distant site. We conclude that targeted and controlled delivery of low-dose anti-CTLA-4 has the potential to improve the benefit-risk ratio associated with combination checkpoint inhibitor therapy

Hydrogel-delivered brain-derived neurotrophic factor promotes tissue repair and recovery after stroke

Stroke is the leading cause of adult disability. Systemic delivery of candidate neural repair therapies is limited by the blood-brain barrier and off-target effects. We tested a bioengineering approach for local depot release of BDNF from the infarct cavity for neural repair in chronic periods after stroke. The brain release levels of a hyaluronic acid hydrogel + BDNF were tested in several stroke models in mouse (strains C57Bl/6, DBA) and non-human primate ( Macaca fascicularis) and tracked with MRI. The behavioral recovery effects of hydrogel + BDNF and the effects on tissue repair outcomes were determined. Hydrogel-delivered BDNF diffuses from the stroke cavity into peri-infarct tissue over 3 weeks in two mouse stroke models, compared with 1 week for direct BDNF injection. Hydrogel delivery of BDNF promotes recovery of motor function. Mapping of motor system connections indicates that hydrogel-BDNF induces axonal sprouting within existing cortical and cortico-striatal systems. Pharmacogenetic studies show that hydrogel-BDNF induces the initial migration of immature neurons into the peri-infarct cortex and their long-term survival. In chronic stroke in the non-human primate, hydrogel-released BDNF can be detected up to 2 cm from the infarct, a distance relevant to human functional recovery in stroke. The hydrogel can be tracked by MRI in mouse and primate

Intracerebral Delivery of Brain-Derived Neurotrophic Factor Using HyStem^®-C Hydrogel Implants Improves Functional Recovery and Reduces Neuroinflammation in a Rat Model of Ischemic Stroke

Ischemic stroke is a leading cause of death and disability worldwide. Potential therapeutics aimed at neural repair and functional recovery are limited in their blood-brain barrier permeability and may exert systemic or off-target effects. We examined the effects of brain-derived neurotrophic factor (BDNF), delivered via an extended release HyStem®-C hydrogel implant or vehicle, on sensorimotor function, infarct volume, and neuroinflammation, following permanent distal middle cerebral artery occlusion (dMCAo) in rats. Eight days following dMCAo or sham surgery, treatments were implanted directly into the infarction site. Rats received either vehicle, BDNF-only (0.167 µg/µL), hydrogel-only, hydrogel impregnated with 0.057 µg/µL of BDNF (hydrogel + BDNFLOW), or hydrogel impregnated with 0.167 µg/µL of BDNF (hydrogel + BDNFHIGH). The adhesive removal test (ART) and 28-point Neuroscore (28-PN) were used to evaluate sensorimotor function up to two months post-ischemia. The hydrogel + BDNFHIGH group showed significant improvements on the ART six to eight weeks following treatment and their behavioral performance was consistently greater on the 28-PN. Infarct volume was reduced in rats treated with hydrogel + BDNFHIGH as were levels of microglial, phagocyte, and astrocyte marker immunoexpression in the corpus striatum. These data suggest that targeted intracerebral delivery of BDNF using hydrogels may mitigate ischemic brain injury and restore functional deficits by reducing neuroinflammation