H2AX promotes replication fork degradation and chemosensitivity in BRCA-deficient tumours.

Histone H2AX plays a key role in DNA damage signalling in the surrounding regions of DNA double-strand breaks (DSBs). In response to DNA damage, H2AX becomes phosphorylated on serine residue 139 (known as γH2AX), resulting in the recruitment of the DNA repair effectors 53BP1 and BRCA1. Here, by studying resistance to poly(ADP-ribose) polymerase (PARP) inhibitors in BRCA1/2-deficient mammary tumours, we identify a function for γH2AX in orchestrating drug-induced replication fork degradation. Mechanistically, γH2AX-driven replication fork degradation is elicited by suppressing CtIP-mediated fork protection. As a result, H2AX loss restores replication fork stability and increases chemoresistance in BRCA1/2-deficient tumour cells without restoring homology-directed DNA repair, as highlighted by the lack of DNA damage-induced RAD51 foci. Furthermore, in the attempt to discover acquired genetic vulnerabilities, we find that ATM but not ATR inhibition overcomes PARP inhibitor (PARPi) resistance in H2AX-deficient tumours by interfering with CtIP-mediated fork protection. In summary, our results demonstrate a role for H2AX in replication fork biology in BRCA-deficient tumours and establish a function of H2AX separable from its classical role in DNA damage signalling and DSB repair.

Self-inflicted DNA breaks in cell differentiation and cancer.

Self-inflicted DNA strand breaks are canonically linked with cell death pathways and the establishment of genetic diversity in immune and germline cells. Moreover, this form of DNA damage is an established source of genome instability in cancer development. However, recent studies indicate that nonlethal self-inflicted DNA strand breaks play an indispensable but underappreciated role in a variety of cell processes, including differentiation and cancer therapy responses. Mechanistically, these physiological DNA breaks originate from the activation of nucleases, which are best characterized for inducing DNA fragmentation in apoptotic cell death. In this review, we outline the emerging biology of one critical nuclease, caspase-activated DNase (CAD), and how directed activation or deployment of this enzyme can lead to divergent cell fate outcomes.

DNA binding and RAD51 engagement by the BRCA2 C-terminus orchestrate DNA repair and replication fork preservation.

The tumor suppressor BRCA2 participates in DNA double-strand break repair by RAD51-dependent homologous recombination and protects stressed DNA replication forks from nucleolytic attack. We demonstrate that the C-terminal Recombinase Binding (CTRB) region of BRCA2, encoded by gene exon 27, harbors a DNA binding activity. CTRB alone stimulates the DNA strand exchange activity of RAD51 and permits the utilization of RPA-coated ssDNA by RAD51 for strand exchange. Moreover, CTRB functionally synergizes with the Oligonucleotide Binding fold containing DNA binding domain and BRC4 repeat of BRCA2 in RPA-RAD51 exchange on ssDNA. Importantly, we show that the DNA binding and RAD51 interaction attributes of the CTRB are crucial for homologous recombination and protection of replication forks against MRE11-mediated attrition. Our findings shed light on the role of the CTRB region in genome repair, reveal remarkable functional plasticity of BRCA2, and help explain why deletion of Brca2 exon 27 impacts upon embryonic lethality.

Cancer cells use self-inflicted DNA breaks to evade growth limits imposed by genotoxic stress.

Genotoxic therapy such as radiation serves as a frontline cancer treatment, yet acquired resistance that leads to tumor reoccurrence is frequent. We found that cancer cells maintain viability during irradiation by reversibly increasing genome-wide DNA breaks, thereby limiting premature mitotic progression. We identify caspase-activated DNase (CAD) as the nuclease inflicting these de novo DNA lesions at defined loci, which are in proximity to chromatin-modifying CCCTC-binding factor (CTCF) sites. CAD nuclease activity is governed through phosphorylation by DNA damage response kinases, independent of caspase activity. In turn, loss of CAD activity impairs cell fate decisions, rendering cancer cells vulnerable to radiation-induced DNA double-strand breaks. Our observations highlight a cancer-selective survival adaptation, whereby tumor cells deploy regulated DNA breaks to delimit the detrimental effects of therapy-evoked DNA damage.

Intermediate-term survival of robot-assisted versus open radical cystectomy for muscle-invasive and high-risk non-muscle invasive bladder cancer in The Netherlands.

BACKGROUND: Radical cystectomy with pelvic lymph node dissection is the recommended treatment in non-metastatic muscle-invasive bladder cancer (MIBC). In randomised trials, robot-assisted radical cystectomy (RARC) showed non-inferior short-term oncological outcomes compared with open radical cystectomy (ORC). Data on intermediate and long-term oncological outcomes of RARC are limited. OBJECTIVE: To assess the intermediate-term overall survival (OS) and recurrence-free survival (RFS) of patients with MIBC and high-risk non-MIBC (NMIBC) who underwent ORC versus RARC in clinical practice. METHODS AND MATERIALS: A nationwide retrospective study in 19 Dutch hospitals including patients with MIBC and high-risk NMIBC treated by ORC (n = 1086) or RARC (n = 386) between January 1, 2012 and December 31, 2015. Primary and secondary outcome measures were median OS and RFS, respectively. Survival outcomes were estimated using Kaplan-Meier curves. A multivariable Cox regression model was developed to adjust for possible confounders and to assess prognostic factors for survival including clinical variables, clinical and pathological disease stage, neoadjuvant therapy and surgical margin status. RESULTS: The median follow-up was 5.1 years (95% confidence interval ([95%CI] 5.0-5.2). The median OS after ORC was 5.0 years (95%CI 4.3-5.6) versus 5.8 years after RARC (95%CI 5.1-6.5). The median RFS was 3.8 years (95%CI 3.1-4.5) after ORC versus 5.0 years after RARC (95%CI 3.9-6.0). After multivariable adjustment, the hazard ratio for OS was 1.00 (95%CI 0.84-1.20) and for RFS 1.08 (95%CI 0.91-1.27) of ORC versus RARC. Patients who underwent ORC were older, had higher preoperative serum creatinine levels and more advanced clinical and pathological disease stage. CONCLUSION: ORC and RARC resulted in similar intermediate-term OS and RFS in a cohort of almost 1500 MIBC and high-risk NMIBC.

Serological assessment of collagen fragments and tumor fibrosis may guide immune checkpoint inhibitor therapy.

Despite the overall clinical success of immune checkpoint inhibitors (ICIs) for treating patients with solid tumors, a large number of patients do not benefit from this approach. Consequently, there is a need for predictive biomarkers. The most prevalent biomarkers such as PD-L1 expression and tumor mutational burden (TMB) do not reliably predict response to ICIs across different solid tumor types suggesting that a broader view of regulating factors in the tumor microenvironment is needed. Emerging evidence indicates that one central common denominator of resistance to ICIs may be fibrotic activity characterized by extracellular matrix (ECM) and collagen production by cancer-associated fibroblasts (CAFs). A fibroblast-and collagen-rich stroma attenuates immunotherapy response by contributing to inhibition and exclusion of T cells. Here we review opportunities and limitations in the utilization of the most prevalent biomarkers for ICIs and elaborate on the unique opportunities with biomarkers originating from the activated fibroblasts producing an impermeable ECM. We propose that ECM and collagen biomarkers measured non-invasively may be a novel and practical approach to optimize treatment strategies and improve patient selection for ICI therapy.

Preoperative cryoablation of a hypervascular bone metastasis: A case of effective devascularization before preoperative embolization.

Image-guided cryoablation has become a common approach for the palliative treatment of painful metastatic bone lesions, and indications for this procedure have expanded to include local control of bone metastases. We report a case in which cryoablation was performed on a large hypervascular renal cell carcinoma bone metastasis before surgical fixation of an impending fracture. In this case, cryoablation reduced the patient's pain but also appeared to result in devascularization of the tumor, thus obviating the need for preoperative embolization. This case raises the possibility that image-guided cryoablation may represent an alternative to preoperative embolization for vascular tumors while also serving a palliative function.

Germline RBBP8 variants associated with early-onset breast cancer compromise replication fork stability.

Haploinsufficiency of factors governing genome stability underlies hereditary breast and ovarian cancer. One significant pathway that is disabled as a result is homologous recombination repair (HRR). With the aim of identifying new candidate genes, we examined early-onset breast cancer patients negative for BRCA1 and BRCA2 pathogenic variants. Here, we focused on CtIP (RBBP8 gene), which mediates HRR through the end resection of DNA double-strand breaks (DSBs). Notably, these patients exhibited a number of rare germline RBBP8 variants. Functional analysis revealed that these variants did not affect DNA DSB end resection efficiency. However, expression of a subset of variants led to deleterious nucleolytic degradation of stalled DNA replication forks in a manner similar to that of cells lacking BRCA1 or BRCA2. In contrast to BRCA1 and BRCA2, CtIP deficiency promoted the helicase-driven destabilization of RAD51 nucleofilaments at damaged DNA replication forks. Taken together, our work identifies CtIP as a critical regulator of DNA replication fork integrity, which, when compromised, may predispose to the development of early-onset breast cancer.

WEE1 kinase limits CDK activities to safeguard DNA replication and mitotic entry.

Precise execution of the cell division cycle is vital for all organisms. The Cyclin dependent kinases (CDKs) are the main cell cycle drivers, however, their activities must be precisely fine-tuned to ensure orderly cell cycle progression. A major regulatory axis is guarded by WEE1 kinase, which directly phosphorylates and inhibits CDK1 and CDK2. The role of WEE1 in the G2/M cell-cycle phase has been thoroughly investigated, and it is a focal point of multiple clinical trials targeting a variety of cancers in combination with DNA-damaging chemotherapeutic agents. However, the emerging role of WEE1 in S phase has so far largely been neglected. Here, we review how WEE1 regulates cell-cycle progression highlighting the importance of this kinase for proper S phase. We discuss how its function is modulated throughout different cell-cycle stages and provide an overview of how WEE1 levels are regulated. Furthermore, we outline recent clinical trials targeting WEE1 and elaborate on the mechanisms behind the anticancer efficacy of WEE1 inhibition. Finally, we consider novel biomarkers that may benefit WEE1-inhibition approaches in the clinic.

Update on spinal epidural abscess.

PURPOSE OF REVIEW: Spinal epidural abscess (SEA) is still a rare but potentially very morbid infection of the spine. In recent years, the incidence has risen sharply but the condition remains a medical conundrum wrought with unacceptably long diagnostic delays. The outcome depends on timely diagnosis and missed opportunities can be associated with catastrophic consequences. Management and outcomes have improved over the past decade. This review focuses on risk factors and markers that can aid in establishing the diagnosis, the radiological characteristics of SEA on MRI and their clinical implications, as well as the importance of establishing clear indications for surgical decompression. RECENT FINDINGS: This once exclusively surgically managed entity is increasingly treated conservatively with antimicrobial therapy. Patients diagnosed in a timely fashion, prior to cord involvement and the onset of neurologic deficits can safely be managed without decompressive surgery with targeted antimicrobial therapy. Patients with acute cord compression and gross neurologic deficits promptly undergo decompression. The greatest therapeutic dilemma remains the group with mild neurological deficits. As failure rates of delayed surgery approach 40%, recent research is focused on predictive models for failure of conservative SEA management. In addition, protocols are being implemented with some success, to shorten the diagnostic delay of SEA on initial presentation. SUMMARY: SEA is a potentially devastating condition that is frequently missed. Protocols are put in place to facilitate early evaluation of back pain in patients with red flags with appropriate cross-sectional imaging, namely contrast-enhanced MRI. Efforts for establishing clear-cut indications for surgical decompression of SEA are underway.

PALB2 connects BRCA1 and BRCA2 in the G2/M checkpoint response.

The G2/M checkpoint inhibits mitotic entry upon DNA damage, thereby preventing segregation of broken chromosomes and preserving genome stability. The tumor suppressor proteins BRCA1, PALB2 and BRCA2 constitute a BRCA1-PALB2-BRCA2 axis that is essential for homologous recombination (HR)-based DNA doublestrand break repair. Besides HR, BRCA1 has been implicated in both the initial activation and the maintenance of the G2/M checkpoint, while BRCA2 and PALB2 have been shown to be critical for its maintenance. Here we show that all three proteins can play a significant role in both checkpoint activation and checkpoint maintenance, depending on cell type and context, and that PALB2 links BRCA1 and BRCA2 in the checkpoint response. The BRCA1-PALB2 interaction can be important for checkpoint activation, whereas the PALB2-BRCA2 complex formation appears to be more critical for checkpoint maintenance. Interestingly, the function of PALB2 in checkpoint response appears to be independent of CHK1 and CHK2 phosphorylation. Following ionizing radiation, cells with disengaged BRCA1-PALB2 interaction show greatly increased chromosomal abnormalities due apparently to combined defects in HR and checkpoint control. These findings provide new insights into DNA damage checkpoint control and further underscore the critical importance of the proper cooperation of the BRCA and PALB2 proteins in genome maintenance.

Histone H4K20 methylation mediated chromatin compaction threshold ensures genome integrity by limiting DNA replication licensing.

The decompaction and re-establishment of chromatin organization immediately after mitosis is essential for genome regulation. Mechanisms underlying chromatin structure control in daughter cells are not fully understood. Here we show that a chromatin compaction threshold in cells exiting mitosis ensures genome integrity by limiting replication licensing in G1 phase. Upon mitotic exit, chromatin relaxation is controlled by SET8-dependent methylation of histone H4 on lysine 20. In the absence of either SET8 or H4K20 residue, substantial genome-wide chromatin decompaction occurs allowing excessive loading of the origin recognition complex (ORC) in the daughter cells. ORC overloading stimulates aberrant recruitment of the MCM2-7 complex that promotes single-stranded DNA formation and DNA damage. Restoring chromatin compaction restrains excess replication licensing and loss of genome integrity. Our findings identify a cell cycle-specific mechanism whereby fine-tuned chromatin relaxation suppresses excessive detrimental replication licensing and maintains genome integrity at the cellular transition from mitosis to G1 phase.

Amino acid-based Poly(ester urea) copolymer films for hernia-repair applications.

The use of degradable materials is required to address current performance and functionality shortcomings from biologically-derived tissues and non-resorbable synthetic materials used for hernia mesh repair applications. Herein a series of degradable l-valine-co-l-phenylalanine poly(ester urea) (PEU) copolymers were investigated for soft-tissue repair. Poly[(1-VAL-8)0.7-co-(1-PHE-6)0.3] showed the highest uniaxial mechanical properties (332.5 ±â€¯3.5 MPa). Additionally, l-valine-co-l-phenylalanine poly(ester urea)s were blade coated on small intestine submucosa extracellular matrix (SIS-ECM) and found to enhance the burst test mechanical properties of SIS-ECM in composite films (force at break between 102.6 ±â€¯6.5-151.4 ±â€¯11.3 N). Free standing films of l-valine-co-l-phenylalanine PEUs were found to have superior extension at break when compared to SIS-ECM (averages between 1.2 and 1.9 cm and 1.2 cm respectively). Fibroblast (L-929) spreading, proliferation, and improved attachment over control were observed without toxicity in vitro, while a reduced inflammatory response at both 7 and 14 days post-implant was observed for poly[(1-VAL-8)⁠0.7-co-(1-PHE-6)⁠0.3] when compared to polypropylene in an in vivo rat hernia model. These results support the use of PEU copolymers as free-standing films or as composite materials in soft-tissue applications for hernia-repair.

Preclinical in Vitro and in Vivo Assessment of Linear and Branched l-Valine-Based Poly(ester urea)s for Soft Tissue Applications.

New polymers are needed to address the shortcomings of commercially available materials for soft tissue repair. Herein, we investigated a series of l-valine-based poly(ester urea)s (PEUs) that vary in monomer composition and the extent of branching as candidate materials for soft tissue repair. The preimplantation Young's moduli (105 ± 30 to 269 ± 12 MPa) for all the PEUs are comparable to those of polypropylene (165 ± 5 MPa) materials currently employed in hernia-mesh repair. The 2% branched poly(1-VAL-8) maintained the highest Young's modulus following 3 months of in vivo implantation (78 ± 34 MPa) when compared to other PEU analogues (20 ± 6-45 ± 5 MPa). Neither the linear or branched PEUs elicited a significant inflammatory response in vivo as noted by less fibrous capsule formation after 3 months of implantation (80 ± 38 to 103 ± 33 µm) relative to polypropylene controls (126 ± 34 µm). Mechanical degradation in vivo over three months, coupled with limited inflammatory response, suggests that l-valine-based PEUs are translationally relevant materials for soft tissue applications.

Septic Arthritis of an Atlantoaxial Facet Joint with Normal Inflammatory Markers: Case Report and Literature Review.

BACKGROUND: Septic arthritis of the atlantoaxial facet joint is extremely rare. Contiguous spread to the median atlantoaxial joints with subsequent dens erosion can lead to atlantoaxial instability. Misleading normal inflammatory markers can result in delayed diagnosis and catastrophic consequences. CASE DESCRIPTION: A 56-year-old man presented with right-sided neck pain that had lasted for 2 days. He did not have fever or chills, and his serum C-reactive protein and erythrocyte sedimentation rate were normal. The patient was diagnosed with acute neck strain and treated conservatively. The pain continued for the next 3 weeks; cervical spine radiographs demonstrated normal findings with the exception of degenerative changes. The patient was treated with physical rehabilitation for the presumed neck strain and degenerative changes of the cervical vertebrae. Worsening neck pain and stiffness prompted a magnetic resonance imaging study obtained 5 weeks after the initial presentation, which showed an epidural collection with septic arthritis of the right facet and median atlantoaxial joints. Computed tomography demonstrated severe dens erosion. Surgical evacuation of the abscess and occipitocervical fusion were performed. Pathologic evaluation of tissue obtained during surgery demonstrated the presence of an infection, and Streptococcus anginosus grew from cultures. CONCLUSIONS: Infection must be considered in the differential diagnosis for neck pain when imaging findings are suggestive of an infectious process, even in an afebrile patient with normal C-reactive protein and erythrocyte sedimentation rate levels. Magnetic resonance imaging and computed tomography can play a critical role in such cases, potentially leading to a more timely diagnosis.

The caspase-activated DNase: apoptosis and beyond.

Organismal development and function requires multiple and accurate signal transduction pathways to ensure that proper balance between cell proliferation, differentiation, inactivation, and death is achieved. Cell death via apoptotic caspase signal transduction is extensively characterized and integral to this balance. Importantly, the view of apoptotic signal transduction has expanded over the previous decades. Subapoptotic caspase signaling has surfaced as mechanism that can promote the adoption of a range of cellular fates. An emerging mechanism of subapoptotic caspase signaling is the activation of the caspase-activated DNase (CAD) through controlled cleavage of the inhibitor of CAD (ICAD). CAD-induced DNA breaks incite a DNA damage response, frequently invoking p53 signaling, that transduces a change in cell fate. Cell differentiation and senescence are fates demonstrated to arise from CAD-induced DNA breaks. Furthermore, an apparent consequence of CAD activity is also emerging, as a potential source of oncogenic mutations. This review will discuss the mechanisms underlying CAD-induced DNA breaks and highlight how CAD activity promotes diverse cell fates.

Mesenchymal Stem Cell Seeding of Porcine Small Intestinal Submucosal Extracellular Matrix for Cardiovascular Applications.

In this study, we investigate the translational potential of a novel combined construct using an FDA-approved decellularized porcine small intestinal submucosa extracellular matrix (SIS-ECM) seeded with human or porcine mesenchymal stem cells (MSCs) for cardiovascular indications. With the emerging success of individual component in various clinical applications, the combination of SIS-ECM with MSCs could provide additional therapeutic potential compared to individual components alone for cardiovascular repair. We tested the in vitro effects of MSC-seeding on SIS-ECM on resultant construct structure/function properties and MSC phenotypes. Additionally, we evaluated the ability of porcine MSCs to modulate recipient graft-specific response towards SIS-ECM in a porcine cardiac patch in vivo model. Specifically, we determined: 1) in vitro loading-capacity of human MSCs on SIS-ECM, 2) effect of cell seeding on SIS-ECM structure, compositions and mechanical properties, 3) effect of SIS-ECM seeding on human MSC phenotypes and differentiation potential, and 4) optimal orientation and dose of porcine MSCs seeded SIS-ECM for an in vivo cardiac application. In this study, histological structure, biochemical compositions and mechanical properties of the FDA-approved SIS-ECM biomaterial were retained following MSCs repopulation in vitro. Similarly, the cellular phenotypes and differentiation potential of MSCs were preserved following seeding on SIS-ECM. In a porcine in vivo patch study, the presence of porcine MSCs on SIS-ECM significantly reduced adaptive T cell response regardless of cell dose and orientation compared to SIS-ECM alone. These findings substantiate the clinical translational potential of combined SIS-ECM seeded with MSCs as a promising therapeutic candidate for cardiac applications.

ATM/ATR-mediated phosphorylation of PALB2 promotes RAD51 function.

DNA damage activates the ATM and ATR kinases that coordinate checkpoint and DNA repair pathways. An essential step in homology-directed repair (HDR) of DNA breaks is the formation of RAD51 nucleofilaments mediated by PALB2-BRCA2; however, roles of ATM and ATR in this critical step of HDR are poorly understood. Here, we show that PALB2 is markedly phosphorylated in response to genotoxic stresses such as ionizing radiation and hydroxyurea. This response is mediated by the ATM and ATR kinases through three N-terminal S/Q-sites in PALB2, the consensus target sites for ATM and ATR Importantly, a phospho-deficient PALB2 mutant is unable to support proper RAD51 foci formation, a key PALB2 regulated repair event, whereas a phospho-mimicking PALB2 version supports RAD51 foci formation. Moreover, phospho-deficient PALB2 is less potent in HDR than wild-type PALB2. Further, this mutation reveals a separation in PALB2 function, as the PALB2-dependent checkpoint response is normal in cells expressing the phospho-deficient PALB2 mutant. Collectively, our findings highlight a critical importance of PALB2 phosphorylation as a novel regulatory step in genome maintenance after genotoxic stress.

Lysophosphatidic acid enhances stromal cell-directed angiogenesis.

Ischemic diseases such as peripheral vascular disease (PVD) affect more than 15% of the general population and in severe cases result in ulcers, necrosis, and limb loss. While the therapeutic delivery of growth factors to promote angiogenesis has been widely investigated, large-scale implementation is limited by strategies to effectively deliver costly recombinant proteins. Multipotent adipose-derived stromal cells (ASC) and progenitor cells from other tissue compartments secrete bioactive concentrations of angiogenic molecules, making cell-based strategies for in situ delivery of angiogenic cytokines an exciting alternative to the use of recombinant proteins. Here, we show that the phospholipid lysophosphatidic acid (LPA) synergistically improves the proangiogenic effects of ASC in ischemia. We found that LPA upregulates angiogenic growth factor production by ASC under two- and three-dimensional in vitro models of serum deprivation and hypoxia (SD/H), and that these factors significantly enhance endothelial cell migration. The concurrent delivery of LPA and ASC in fibrin gels significantly improves vascularization in a murine critical hindlimb ischemia model compared to LPA or ASC alone, thus exhibiting the translational potential of this method. Furthermore, these results are achieved using an inexpensive lipid molecule, which is orders-of-magnitude less costly than recombinant growth factors that are under investigation for similar use. Our results demonstrate a novel strategy for enhancing cell-based strategies for therapeutic angiogenesis, with significant applications for treating ischemic diseases.

Effects on proliferation and differentiation of multipotent bone marrow stromal cells engineered to express growth factors for combined cell and gene therapy.

A key mechanism for mesenchymal stem cells/bone marrow stromal cells (MSCs) to promote tissue repair is by secretion of soluble growth factors (GFs). Therefore, clinical application could be optimized by a combination of cell and gene therapies, where MSCs are genetically modified to express higher levels of a specific factor. However, it remains unknown how this overexpression may alter the fate of the MSCs. Here, we show effects of overexpressing the growth factors, such as basic fibroblast growth factor (bFGF), platelet derived growth factor B (PDGF-BB), transforming growth factor ß(1) (TGF-ß(1) ), and vascular endothelial growth factor (VEGF), in human bone marrow-derived MSCs. Ectopic expression of bFGF or PDGF-B lead to highly proliferating MSCs and lead to a robust increase in osteogenesis. In contrast, adipogenesis was strongly inhibited in MSCs overexpressing PDGF-B and only mildly affected in MSCs overexpressing bFGF. Overexpression of TGF-ß(1) blocked both osteogenic and adipogenic differentiation while inducing the formation of stress fibers and increasing the expression of the smooth muscle marker calponin-1 and the chondrogenic marker collagen type II. In contrast, MSCs overexpressing VEGF did not vary from control MSCs in any parameters, likely due to the lack of VEGF receptor expression on MSCs. MSCs engineered to overexpress VEGF strongly induced the migration of endothelial cells and enhanced blood flow restoration in a xenograft model of hind limb ischemia. These data support the rationale for genetically modifying MSCs to enhance their therapeutically relevant trophic signals, when safety and efficacy can be demonstrated, and when it can be shown that there are no unwanted effects on their proliferation and differentiation.