Omar A. Ali

Harnessing traction-mediated manipulation of the cell/matrix interface to control stem-cell fate

Stem cells sense and respond to the mechanical properties of the extracellular matrix. However, both the extent to which extracellular matrix mechanics affect stem cell fate in 3D micro-environments and the underlying biophysical mechanisms are unclear. We demonstrate that the commitment of mesenchymal stem cell (MSC) populations changes in response to the rigidity of 3D micro-environments, with osteogenesis occurring predominantly at 11–30 kPa. In contrast to previous 2D work, however, cell fate was not correlated with morphology. Instead, matrix stiffness regulated integrin binding as well as reorganization of adhesion ligands on the nanoscale, both of which were traction-dependent and correlated with osteogenic commitment of MSC populations. These findings suggest that cells interpret changes in the physical properties of adhesion substrates as changes in adhesion ligand presentation, and that cells themselves can be harnessed as tools to mechanically process materials into structures that feedback to manipulate their fate.

Infection-mimicking materials to program dendritic cells in situ

Cancer vaccines typically depend on cumbersome and expensive manipulation of cells in the laboratory, and subsequent cell transplantation leads to poor lymph node homing and limited efficacy. We propose that materials mimicking key aspects of bacterial infection may instead be used to directly control immune cell trafficking and activation in the body. It is demonstrated that polymers can be designed to first release a cytokine to recruit and house host dendritic cells (DCs), and subsequently present cancer antigens and danger signals to activate the resident DCs and dramatically enhance their homing to lymph nodes. Specific and protective anti-tumor immunity was generated with these materials, as 90% survival was achieved in animals that otherwise die from cancer within 25 days. These materials show promise as cancer vaccines, and more broadly suggest that polymers may be designed to program and control the trafficking of a variety of cell types in the body.

In Situ Regulation of DC Subsets and T Cells Mediates Tumor Regression in Mice

An implanted copolymer matrix that incorporates inflammatory cytokines, an immune danger signal, and tumor antigens elicits an immune response network that can eradicate established tumors in mice. Forcing Cancer to Retreat It was a momentous moment in medical history when the English doctor Edward Jenner inoculated a young boy with cowpox, thus preventing him from catching smallpox and heralding the arrival of an era in which many infectious diseases are routinely prevented by vaccination. Today, scientists are striving to design vaccines to treat cancer—a much more complex biological challenge—by enhancing the body’s immune response against tumor cells. One critical problem is that tumors actively inhibit the immune response: They secrete factors that suppress the immune system and induce regulatory T cells that restrain the activity of tumor-fighting immune cells. Now, Mooney and colleagues describe an anticancer vaccine that triggers a sustained antitumor immune response and inhibits regulatory T cell activity—and shows promising results in mice with cancer. Key to many immune-based approaches to cancer therapy, dendritic cells survey the body for pathogens and activate immune responses against them. When immature dendritic cells recognize the molecular features characteristic of some pathogens, like DNA rich in guanosine and cytosine, the cells mature, migrate to lymph nodes, and activate T cells that recognize antigens presented on the dendritic cell surface. One approach to cancer vaccine production is to isolate dendritic precursor cells from the patient’s blood, to use in vitro treatments to convert them to dendritic cells, and then to expose them to tumor antigens. The cells are then infused back into the patient so that they will induce tumor-directed immune attack. Although responses occur, in general the vaccines do not increase the patients’ survival time relative to standard treatments or cause solid tumors to regress. A more effective cancer vaccine might require the induction of more than one class of dendritic cells, because different dendritic cell populations have different specialties, such as antigen presentation and the production of cytokines that control regulatory T cell activity. Mooney’s group aimed to generate a varied population of dendritic cells by creating a device that imitates an infection site in the host itself. Previously, they developed an implantable polymer matrix that releases an inflammatory cytokine to recruit dendritic cells and displays short strands of pathogen-like DNA and tumor antigens to activate those cells. In the present work, these researchers showed that implanting this system in mice leads to the activation of multiple dendritic cell types and the generation of tumor-fighting cytotoxic T cells, as well as to the inhibition of regulatory T cell activity. The multiple components of the system have different and synergistic effects on the host’s immune system. Notably, when used as a vaccine in mice with established melanoma, it caused complete remission of tumors and long-term survival of a substantial portion of the population. This system, which has practical advantages over approaches in which the patient’s cells are cultured, may serve as a paradigm for the design of human vaccines. Vaccines are largely ineffective for patients with established cancer, as advanced disease requires potent and sustained activation of CD8+ cytotoxic T lymphocytes (CTLs) to kill tumor cells and clear the disease. Recent studies have found that subsets of dendritic cells (DCs) specialize in antigen cross-presentation and in the production of cytokines, which regulate both CTLs and T regulatory (Treg) cells that shut down effector T cell responses. Here, we addressed the hypothesis that coordinated regulation of a DC network, and plasmacytoid DCs (pDCs) and CD8+ DCs in particular, could enhance host immunity in mice. We used functionalized biomaterials incorporating various combinations of an inflammatory cytokine, immune danger signal, and tumor lysates to control the activation and localization of host DC populations in situ. The numbers of pDCs and CD8+ DCs, and the endogenous production of interleukin-12, all correlated strongly with the magnitude of protective antitumor immunity and the generation of potent CD8+ CTLs. Vaccination by this method maintained local and systemic CTL responses for extended periods while inhibiting FoxP3 Treg activity during antigen clearance, resulting in complete regression of distant and established melanoma tumors. The efficacy of this vaccine as a monotherapy against large invasive tumors may be a result of the local activity of pDCs and CD8+ DCs induced by persistent danger and antigen signaling at the vaccine site. These results indicate that a critical pattern of DC subsets correlates with the evolution of therapeutic antitumor responses and provide a template for future vaccine design.

Injectable cryogel-based whole-cell cancer vaccines

A biomaterial-based vaccination system that uses minimal extracorporeal manipulation could provide in situ enhancement of dendritic cell (DC) numbers, a physical space where DCs interface with transplanted tumour cells, and an immunogenic context. Here we encapsulate GM-CSF, serving as a DC enhancement factor, and CpG ODN, serving as a DC activating factor, into sponge-like macroporous cryogels. These cryogels are injected subcutaneously into mice to localize transplanted tumour cells and deliver immunomodulatory factors in a controlled spatio-temporal manner. These vaccines elicit local infiltrates composed of conventional and plasmacytoid DCs, with the subsequent induction of potent, durable and specific anti-tumour T-cell responses in a melanoma model. These cryogels can be delivered in a minimally invasive manner, bypass the need for genetic modification of transplanted cancer cells and provide sustained release of immunomodulators. Altogether, these findings indicate the potential for cryogels to serve as a platform for cancer cell vaccinations.

Injectable VEGF Hydrogels Produce Near Complete Neurological and Anatomical Protection Following Cerebral Ischemia in Rats

Vascular endothelial growth factor (VEGF) is a potent proangiogenic peptide and its administration has been considered as a potential neuroprotective strategy following cerebral stroke. Because VEGF has a short half-life and limited access to the brain parenchyma following systemic administration, approaches are being developed to deliver it directly to the site of infarction. In the present study, VEGF was incorporated into a sustained release hydrogel delivery system to examine its potential benefits in a rat model of cerebral ischemia. The hydrogel loaded with VEGF (1 μg) was stereotaxically injected into the striatum of adult rats 15 min prior to a 1-h occlusion of the middle cerebral artery. Two days after surgery, animals were tested for motor function using the elevated bias swing test (EBST) and Bederson neurological battery. Control animals received either stroke alone, stroke plus injections of a blank gel, or a single bolus injection of VEGF (1 μg). Behavioral testing confirmed that the MCA occlusion resulted in significant deficits in the the EBST and Bederson tests. In contrast, the performance of animals receiving VEGF gels was significantly improved relative to controls, with only modest impairments observed. Cerebral infarction analyzed using 2,3,5-triphenyl-tetrazolium chloride staining confirmed that the VEGF gels significantly and potently reduced the lesion volume. No neurological or histological benefits were conferred by either blank gel or bolus VEGF injections. These data demonstrate that VEGF, delivered from a hydrogel directly to the brain, can induce significant functional and structural protection from ischemic damage in a rat model of stroke.

Identification of Immune Factors Regulating Antitumor Immunity Using Polymeric Vaccines with Multiple Adjuvants

The innate cellular and molecular components required to mediate effective vaccination against weak tumor-associated antigens remain unclear. In this study, we used polymeric cancer vaccines incorporating different classes of adjuvants to induce tumor protection, to identify dendritic cell (DC) subsets and cytokines critical to this efficacy. Three-dimensional, porous polymer matrices loaded with tumor lysates and presenting distinct combinations of granulocyte macrophage colony-stimulating factor (GM-CSF) and various Toll-like receptor (TLR) agonists affected 70% to 90% prophylactic tumor protection in B16-F10 melanoma models. In aggressive, therapeutic B16 models, the vaccine systems incorporating GM-CSF in combination with P(I:C) or CpG-ODN induced the complete regression of solid tumors (≤40 mm(2)), resulting in 33% long-term survival. Regression analysis revealed that the numbers of vaccine-resident CD8(+) DCs, plasmacytoid DCs (pDC), along with local interleukin (IL)-12, and granulocyte colony-stimulating factor (G-CSF) concentrations correlated strongly to vaccine efficacy regardless of adjuvant type. Furthermore, vaccine studies in Batf3(-/-) mice revealed that CD8(+) DCs are required to affect tumor protection, as vaccines in these mice were deficient in cytotoxic T lymphocytes priming and IL-12 induction in comparison with wild-type. These studies broadly demonstrate that three-dimensional polymeric vaccines provide a potent platform for prophylactic and therapeutic protection, and can be used as a tool to identify critical components of a desired immune response. Specifically, these results suggest that CD8(+) DCs, pDCs, IL-12, and G-CSF play important roles in priming effective antitumor responses with these vaccines.

Vaccines Combined with Immune Checkpoint Antibodies Promote Cytotoxic T-cell Activity and Tumor Eradication

Despite dramatic clinical successes for cancer vaccines and immune checkpoint blockade, disease usually progresses. In a mouse model that combined vaccines with checkpoint blockade, significant CTL activation, tumor eradication, and long-term survival was achieved. We demonstrate that a poly(lactide-co-glycolide) (PLG) cancer vaccine can be used in combination with immune checkpoint antibodies, anti–CTLA-4 or anti–PD-1, to enhance cytotoxic T-cell (CTL) activity and induce the regression of solid B16 tumors in mice. Combination therapy obviated the need for vaccine boosting and significantly skewed intratumoral reactions toward CTL activity, resulting in the regression of B16 tumors up to 50 mm2 in size and 75% survival rates. These data suggest that combining material-based cancer vaccines with checkpoint antibodies has the potential to mediate tumor regression in humans. Cancer Immunol Res; 4(2); 95–100. ©2015 AACR.

Sustained GM-CSF and PEI condensed pDNA presentation increases the level and duration of gene expression in dendritic cells

Current techniques to educate dendritic cells (DCs) ex vivo for immunotherapy are plagued by inefficient protocols and DC modifications are often transient and lost upon transplantation. This study investigated the role of sustained presentation of GM-CSF and PEI condensed pDNA (PEI-DNA) on gene transfer and long-term gene expression. Appropriate GM-CSF signaling during DC transfection promoted PEI-DNA uptake, although high cytokine concentrations induced intercellular DNA degradation, indicating the need for controlled presentation. Poly(lactide-co-glycolide) scaffolds that continuously stimulated DCs with both GM-CSF and PEI-DNA led to a 20-fold increase in gene expression, and high levels of expression persisted for a period of 10 days, in vitro. These results encourage the exploitation of biomaterials and GM-CSF to develop novel delivery vectors for genetically modified DCs or to genetically program host DCs in situ for vaccination and the treatment of autoimmunity.

Highly cited research articles in Journal of Controlled Release: Commentaries and perspectives by authors

Abstract To celebrate the success of the Journal of Controlled Release and the research covered in the journal, here we highlight some of the most cited research articles in the history of the journal. Based on the literature search in Google Scholar in July 2013, we identified ~30 research articles that have received most number of citations. Authors of these articles were invited to provide a commentary on these articles. This compilation of commentaries gives a historical perspective and current status of research covered in these articles.

Immunologically Active Biomaterials for Cancer Therapy

Our understanding of immunological regulation has progressed tremendously alongside the development of materials science, and at their intersection emerges the possibility to employ immunologically active biomaterials for cancer immunotherapy. Strong and sustained anticancer, immune responses are required to clear large tumor burdens in patients, but current approaches for immunotherapy are formulated as products for delivery in bolus, which may be indiscriminate and/or shortlived. Multifunctional biomaterial particles are now being developed to target and sustain antigen and adjuvant delivery to dendritic cells in vivo, and these have the potential to direct and prolong antigen-specific T cell responses. Three-dimensional immune cell niches are also being developed to regulate the recruitment, activation and deployment of immune cells in situ to promote potent antitumor responses. Recent studies demonstrate that materials with immune targeting and stimulatory capabilities can enhance the magnitude and duration of immune responses to cancer antigens, and preclinical results utilizing material-based immunotherapy in tumor models show a strong therapeutic benefit, justifying translation to and future testing in the clinic.