Cartilage Regeneration Using Pluripotent Stem Cell‐Derived Chondroprogenitors: Promise and Challenges

The cartilage of joints is long‐lasting (i.e., permanent) cartilage and is not spontaneously repaired after injury in humans. There has been considerable interest in the clinical application of stem cells to the repair of damaged cartilage; however, current cell therapies using adult chondrocytes and mesenchymal stromal cells face problems associated with the low yield of such cells. The expansion culture, needed before transplantation, leads to the formation of fibrocartilage or growth plate-like (i.e., bone‐forming) cartilage in vivo. Both types of cartilage are unsuitable for the repair of joint cartilage such as meniscus and articular cartilage. Joints are formed during embryogenesis. Therefore, we hypothesize that embryonic progenitor cells responsible for the development of joint cartilage would be the best for regenerating joint cartilage in the adult. Pluripotent stem cells (PSCs) are expected to differentiate in culture into any somatic cell types through processes that mimic embryogenesis, making human (h)PSCs a promising source of embryonic cells for regenerative medicine. However, regardless of the cell system used, the major research goals leading to clinical application to cartilage regeneration are to (1) expand chondrogenic cells (chondroprogenitors) to sufficient numbers without loss of their chondrogenic activity, and (2) direct the differentiation of such cells in vivo or in vitro toward articular or other types of chondrocytes of interest. The overall aim of the current review was to provide the basis of a strategy for meeting the goals for cartilage regeneration by the use of hPSC‐derived chondroprogenitor cells. We provide an overview on signaling mechanisms that are known to affect the expandability and chondrogenic activity of adult and embryonic chondroprogenitors, as well as their differentiation in vivo or in vitro toward a particular type of chondrocyte. We then discuss alternative types of progenitor cells that might replace or combine with the hPSC‐derived chondroprogenitors to regenerate permanent cartilage. We also include our recent achievement of successfully expanding hPSC‐derived neural crest to generate ectomesenchymal chondroprogenitors that can be maintained for a long term in culture without loss of chondrogenic activity. Finally, we provide information on the challenges that hPSC progeny‐based regenerative medicine will face, and discuss the implications for such challenges for the future use of PSC progeny to regenerate cartilage

Oncogenic FGFR1 mutation and amplification in common cellular origin in a composite tumor with neuroblastoma and pheochromocytoma

Neuroblastoma (NB) and pheochromocytoma (PCC) are derived from neural crest cells (NCCs); however, composite tumors with NB and PCC are rare, and their underlying molecular mechanisms remain unknown. To address this issue, we performed exome and transcriptome sequencing with formalin-fixed paraffin-embedded (FFPE) samples from the NB, PCC, and mixed lesions in a patient with a composite tumor. Whole-exome sequencing revealed that most mutations (80%) were shared by all samples, indicating that NB and PCC evolved from the same clone. Notably, all samples harbored both mutation and focal amplification in the FGFR1 oncogene, resulting in an extraordinarily high expression, likely to be the main driver of this tumor. Transcriptome sequencing revealed undifferentiated expression profiles for the NB lesions. Considering that a metastatic lesion was also composite, most likely, the primitive founding lesions should differentiate into both NB and PCC. This is the first reported case with composite-NB and PCC genetically proven to harbor an oncogenic FGFR1 alteration of a common cellular origin

A Novel Serum-Free Monolayer Culture for Orderly Hematopoietic Differentiation of Human Pluripotent Cells via Mesodermal Progenitors

Elucidating the in vitro differentiation of human embryonic stem (ES) and induced pluripotent stem (iPS) cells is important for understanding both normal and pathological hematopoietic development in vivo. For this purpose, a robust and simple hematopoietic differentiation system that can faithfully trace in vivo hematopoiesis is necessary. In this study, we established a novel serum-free monolayer culture that can trace the in vivo hematopoietic pathway from ES/iPS cells to functional definitive blood cells via mesodermal progenitors. Stepwise tuning of exogenous cytokine cocktails induced the hematopoietic mesodermal progenitors via primitive streak cells. These progenitors were then differentiated into various cell lineages depending on the hematopoietic cytokines present. Moreover, single cell deposition assay revealed that common bipotential hemoangiogenic progenitors were induced in our culture. Our system provides a new, robust, and simple method for investigating the mechanisms of mesodermal and hematopoietic differentiation

Mixed germ cell tumor infiltrating the pineal gland without elevated tumor markers: illustrative case

BACKGROUND: Tumors in the pineal region consist of various histological types, and correct diagnosis from biopsy specimens is sometimes difficult. The authors report the case of a patient with a mixed germ cell tumor infiltrating into the pineal gland despite showing no elevation of tumor markers. OBSERVATIONS: An 18-year-old man complained of headache and nausea and showed disturbance of consciousness. Magnetic resonance imaging showed hydrocephalus associated with a cystic pineal tumor. The patient underwent tumor biopsy followed by endoscopic third ventriculostomy for hydrocephalus in a local hospital. A pineocytoma was diagnosed, and the patient was referred to the authors' hospital for treatment. Concentrations of placental alkaline phosphatase, alpha-fetoprotein (AFP), and beta-human chorionic gonadotropin in cerebrospinal fluid were not elevated. However, the authors' review of the tumor specimen revealed some immature cells infiltrating the pineal gland. These cells were positive for AFP, Sal-like protein 4, and octamer-binding transcription factor 3/4; and the diagnosis was changed to mixed germ cell tumor. Chemoradiotherapy was initiated, followed by surgical removal of the residual tumor. LESSONS: Careful examination of all tumor specimens and immunohistochemical analyses are important for accurate diagnosis of pineal tumors

Long-term efficacy of bevacizumab and irinotecan in recurrent pediatric glioblastoma.

A 5-year-old boy with glioblastoma relapsed soon after postoperative irradiation in combination with temozolomide. Second-line chemotherapy was also ineffective; therefore, the bevacizumab and irinotecan were given after a third gross-total resection of the tumor. Treatment was interrupted for 1 month due to development of posterior reversible encephalopathy syndrome, but was re-initiated at a lower dose of bevacizumab with prolonged intervals between treatments. The patient was alive and disease free 2 years after initial diagnosis. Bevacizumab and irinotecan are a promising regimen for pediatric cases of recurrent glioblastoma after gross-total resection, although the optimal treatment schedule must be determined on a patient-by-patient basis

Rituximab-combination chemotherapy achieves a 10th cycle of remission for Burkitt's lymphoma.

A 14-year-old girl with multiple intra-abdominal tumors was diagnosed with stage III Burkitt's lymphoma. She achieved complete remission after multi-drug chemotherapy, but she relapsed after six courses. Autologous peripheral blood stem cells (PBSC) or allogeneic PBSC harvested from an HLA-identical sibling were insufficient, and her family did not agree to bone marrow collection from the sibling. Although the patient relapsed nine times (the relapses involved intra-abdominal organs or bone) during the following 4 years 7 months, treatment with rituximab monotherapy or in combination with ifosphamide, carboplastin, and etoposide, or local irradiation (33.8-40.0 Gy) to treat the bone metastases, proved effective, resulting in complete or partial remission. At the time of writing, the patient was in a 10th cycle of remission lasting 1 year 6 months and had not required transplantation. Thus, a chemotherapy regimen including rituximab might be effective for Burkitt's lymphoma in patients experiencing multiple relapse