3D ultrasound biomicroscopy for assessment of cartilage repair tissue: volumetric characterisation and correlation to established classification systems.

Objective and sensitive assessment of cartilage repair outcomes lacks suitable methods. This study investigated the feasibility of 3D ultrasound biomicroscopy (UBM) to quantify cartilage repair outcomes volumetrically and their correlation with established classification systems. 32 sheep underwent bilateral treatment of a focal cartilage defect. One or two years post-operatively the repair outcomes were assessed and scored macroscopically (Outerbridge, ICRS-CRA), by magnetic resonance imaging (MRI, MOCART), and histopathology (O'Driscoll, ICRS-I and ICRS-II). The UBM data were acquired after MRI and used to reconstruct the shape of the initial cartilage layer, enabling the estimation of the initial cartilage thickness and defect volume as well as volumetric parameters for defect filling, repair tissue, bone loss and bone overgrowth. The quantification of the repair outcomes revealed high variations in the initial thickness of the cartilage layer, indicating the need for cartilage thickness estimation before creating a defect. Furthermore, highly significant correlations were found for the defect filling estimated from UBM to the established classification systems. 3D visualisation of the repair regions showed highly variable morphology within single samples. This raises the question as to whether macroscopic, MRI and histopathological scoring provide sufficient reliability. The biases of the individual methods will be discussed within this context. UBM was shown to be a feasible tool to evaluate cartilage repair outcomes, whereby the most important objective parameter is the defect filling. Translation of UBM into arthroscopic or transcutaneous ultrasound examinations would allow non-destructive and objective follow-up of individual patients and better comparison between the results of clinical trials.

Transplantation of activated nucleus pulposus cells after cryopreservation: efficacy study in a canine disc degeneration model.

Transplantation of activated nucleus pulposus (NP) cells obtained by coculturing NP cells and bone marrow mesenchymal stromal cells having cell-to-cell contact has been shown to be effective in animal models and, more recently, in human clinical trials. If the NP cells can be cryopreserved, then autologous cell transplantation could be offered to patients as and when required. In a previous study, we confirmed that activated NP cells can be obtained by coculturing with mesenchymal cells after cryopreservation. However, the in vivo effects of cell transplantation therapy using activated NP cells prepared from cryopreserved cells are not known. In this in vivo canine model, we compared indicators of disc degeneration in animals that received transplanted activated normal NP cells, transplanted cryopreserved NP cells, and no cell transplantation after induction of disc degeneration. The intervertebral disc height on radiographs and T2-weighted magnetic resonance imaging were significantly higher in both cell transplantation groups compared with the degenerated disc group. Macroscopic and histological findings demonstrated attenuated disc degeneration in the two transplanted groups. Intense staining of proteoglycan and collagen type II was seen in green fluorescent protein-labelled transplanted cells, which suggested that the cells had survived and were functioning after transplantation. No significant differences were observed between the two transplanted groups. Transplanted activated cryopreserved NP cells induced a similar attenuation of intervertebral disc degeneration as that of conventionally activated NP cells. These findings suggest that the use of cryopreserved cells specific to a patient's condition has potential in transplantation therapy.

Intervertebral disc repair with activated nucleus pulposus cell transplantation: a three-year, prospective clinical study of its safety.

Degeneration of the lumbar intervertebral discs is irreversible, with no treatment currently available. Building upon experimental studies that demonstrated the importance of the nucleus pulposus (NP) in preserving disc structure, we demonstrated that reinsertion of NP cells slowed further disc degeneration and that direct cell-to-cell contact co-culture with mesenchymal stromal cells (MSCs) significantly upregulated the viability of NP cells in basic and pre-clinical studies in vitro and in vivo using animal models and human cells. Here, we report a 3-year result of a prospective clinical study, aimed to assess the safety and efficacy of activated NP cell transplantation in the degenerate lumbar intervertebral disc. Candidates were 9 patients aged 20-29 years who had Pfirrmann's grade III disc degeneration at the level adjacent to the level scheduled for posterior lumbar intervertebral fusion. Viable NP cells from the fused disc were co-cultured in direct contact with autologous bone marrow-derived MSCs. One million activated NP cells were transplanted into the degenerated disc adjacent to the fused level at 7 d after the first fusion surgery. No adverse effects were observed during the 3-year follow-up period. Magnetic resonance imaging did not show any detrimental effects to the transplanted discs and revealed a mild improvement in 1 case. No cases reported any low back pain. Our clinical study confirmed the safety of activated NP cell transplantation, and the findings suggest the minimal efficacy of this treatment to slow the further degeneration of human intervertebral discs.

Studies of the humoral factors produced by layered chondrocyte sheets.

The authors aimed to repair and regenerate articular cartilage with layered chondrocyte sheets, produced using temperature-responsive culture dishes. The purpose of this study was to investigate the humoral factors produced by layered chondrocyte sheets. Articular chondrocytes and synovial cells were harvested during total knee arthroplasty. After co-culture, the samples were divided into three groups: a monolayer, 7 day culture sheet group (group M); a triple-layered, 7 day culture sheet group (group L); and a monolayer culture group with a cell count identical to that of group L (group C). The secretion of collagen type 1 (COL1), collagen type 2 (COL2), matrix metalloproteinase-13 (MMP13), transforming growth factor-ß (TGFß), melanoma inhibitory activity (MIA) and prostaglandin E2 (PGE2) were measured by enzyme-linked immunosorbent assay (ELISA). Layered chondrocyte sheets produced the most humoral factors. PGE2 expression declined over time in group C but was significantly higher in groups M and L. TGFß expression was low in group C but was significantly higher in groups M and L (p<0.05). Our results suggest that the humoral factors produced by layered chondrocyte sheets may contribute to cartilaginous tissue repair and regeneration.

CCL5/RANTES is a key chemoattractant released by degenerative intervertebral discs in organ culture.

Release of chemotactic factors in response to tissue damage has been described for different musculoskeletal tissues, including the intervertebral disc (IVD). This study investigated the chemoattractants that are released by induced degenerative IVDs and may be involved in recruiting mesenchymal stem cells (MSCs). Bovine caudal discs were cultured within a bioreactor and loaded under conditions that mimicked physiological or degenerative settings. Between days 4-6, medium was replaced by PBS, which was subsequently used for proteomic, ELISA and immunoprecipitation analyses of secreted chemokines and cytokines. A Boyden chamber assay was used to observe human MSC migration towards native and chemokine depleted media. Gene expression levels of chemokine receptors in human MSCs were analysed, and CCL5 was localised in bovine and human IVD by immunohistochemistry. Proteomic analysis revealed the presence of CCL5 and CXCL6 within conditioned media. Higher concentrations of CCL5 were found in the degenerative media, and a relationship was found between interleukin-1ß and CCL5 concentration. Chemokine immunoprecipitation showed that MSCs had a significantly reduced chemotactic migration towards CCL5-immunoprecipitated and CCL5/CXCL6 co-immunoprecipitated media, whilst CXCL6 depletion did not change MSC chemotaxis. MSCs showed a significant increase in mRNA expression of the CCL5 receptors, CCR1 and CCR4, upon culture in degenerative media. Furthermore, CCL5 was identified in bovine and human disc tissue by immunohistochemistry. Hence, CCL5 may be a key chemoattractant that is produced and released by the intervertebral disc cells. Therefore, these factors could be used to enhance stem/progenitor cell mobilisation in regenerative therapies for early stages of disc degeneration.

Endoplasmic reticulum stress response in the rat contusive spinal cord injury model-susceptibility in specific cell types.

STUDY DESIGN: Focus group study. OBJECTIVE: To investigate cell-specific endoplasmic reticulum (ER) stress reactions in contusive spinal cord by evaluating the expression of the glucose-regulated protein 78 (GRP78) and C/EBP homologous transcription factor protein (CHOP) using immunohistochemical staining. SETTING: Data were analysed at Tokai University School of Medicine in Japan. METHODS: The authors generated rat spinal cord injury (SCI) models using an IH-Impactor (100 kdyne(LI), 200 kdyne (HI)). Rats were killed at 1, 3, 5, 7 and 14 days post operation (dpo). Spinal cord sections were prepared and the expression ratio of GRP78 and CHOP was evaluated in oligodendrocyte precursor cells (OPCs) (NG2+), oligodendrocytes (OLs) (APC+), neurons (NeuN+) and astrocytes (GFAP+) using double immunohistochemical staining. We examined an area 8 mm distal from SCI-epicenter. RESULTS: Compared with the sham group, both injured groups had higher GRP78 expression ratio in contused spinal cord at 1 dpo. GRP78 expression ratio was highest in GFAP+ cells of both groups, and lowest in NG2+ cells. Although GRP78 was expressed strongly immediately after SCI in the both groups, increased CHOP expression was observed only in the HI group. The CHOP expression in NG2+ cells was significantly higher than that observed in GFAP+ cells at 5 dpo. CONCLUSION: Although the ER stress response contributes to cell survival in the low-stress SCI conditions, the ER stress response induces an apoptotic cascade in high-stress SCI conditions. The ER response varies according to cell type, with the highest observed in astrocytes, and the lowest observed in oligodendrocyte precursor cells.

Transplantatation of scaffold-free spheroids composed of synovium-derived cells and chondrocytes for the treatment of cartilage defects of the knee.

Autologous chondrocyte implantation (ACI) is the treatment of choice for osteoarthritis. However, to regenerate articular cartilage using this method, the procedure paradoxically demands that the cell source of the articular chondrocytes (ACs) for ex vivo expansion be from the patient's own healthy cartilage, which can result in donor site morbidity. Accordingly, it is essential to develop a substitute for AC. In the present study, we investigated whether synovium-derived cells (SYs) could be used as a partial replacement for ACs in ACI. ACs and SYs from the knees of rabbits were isolated and cultured, and the growth rates of the cells were compared. To manufacture the cellular transplants, we developed a high-density suspension-shaking culture method (HDSS), which circulates the cells in culture media, promoting self-assembly of scaffold-free cellular aggregates. ACs and SYs were mixed in various ratios using HDSS. Injectable cellular transplants were harvested and transplanted into full-thickness osteochondral defects. Simultaneously, histological evaluations were conducted with toluidine blue and safranin O, and immunohistochemistry of collagen type I and II was conducted. Gene expression to evaluate chondrocyte-specific differentiation was also performed. We successfully prepared a large quantity of spheroids (spheroidal cell aggregates) in a short time using mixed ACs and SYs, for all cellular composition ratios. Our data showed that the minimal therapeutic unit for the transplants contributed to in situ regeneration of cartilage. In summary, SYs can be used as a replacement for ACs in clinical cases of ACI in patients with broad areas of osteoarthritic lesions.

Transvaginal mesh (TVM) reconstruction with TVT/TOT sling for vaginal prolapse concurrent with stress urinary incontinence.

We evaluated clinical efficacies of transvaginal mesh (TVM) reconstruction alone and those concomitant with a TVT/TOT sling for the treatment of pelvic organ prolapse (POP) and stress urinary incontinence (SUI). Between January 2006 and February 2007, 138 female patients with POP underwent TVM reconstruction. The mean age was 66.6 years (range: 52-84). Fourteen individuals were qualified as grade II in the POP quantification (POP-Q) system, 85 and 39 were grades III and IV, respectively. One hundred and seventeen of 138 (85 %) cases showed SUI. Twenty-one patients without SUI underwent TVM alone, and 117 cases with SUI underwent TVM concomitant with TVT/TOT sling. Mean operation time and intra-operative bleeding was 79 min (range: 25-177) and 74 ml (range: 10-429), respectively. Mean follow-up period is 5.3 months (range: 1-14). The vaginal prolapses were cured (grade 0) in 129 cases (93 %) after the surgery. Total inter-national prostate symptom score (IPSS), its QOL score, International Consultation on Incontinence Questionnaires Short Form (ICIQ-SF) significantly improved (from 12.6 to 3.9; p < 0.0001, from 5.0 to 1.0; p < 0.0001, and from 6.1 to 2.5; p < 0.01, respectively). Six of 21 cases (29%) who underwent TVM alone showed postoperative de-novo SUI. In contrast, 116 cases (99%) who underwent TVM concomitant with TVT/TOT, experienced a cure of SUI. Maximum flow rate did not change postoperatively in the both groups. In conclusion, the short-term efficacies of TVM reconstruction for POP are excellent, and a concomitant TVT/TOT sling prevents postoperative SUI.

Variations in gene and protein expression in human nucleus pulposus in comparison with annulus fibrosus and cartilage cells: potential associations with aging and degeneration.

OBJECTIVE: Regardless of recent progress in the elucidation of intervertebral disc (IVD) degeneration, the basic molecular characteristics that define a healthy human IVD are largely unknown. Although work in different animal species revealed distinct molecules that might be used as characteristic markers for IVD or specifically nucleus pulposus (NP) cells, the validity of these markers for characterization of human IVD cells remains unknown. DESIGN: Eleven potential marker molecules were characterized with respect to their occurrence in human IVD cells. Gene expression levels of NP were compared with annulus fibrosus (AF) and articular cartilage (AC) cells, and potential correlations with aging were assessed. RESULTS: Higher mRNA levels of cytokeratin-19 (KRT19) and of neural cell adhesion molecule-1 were noted in NP compared to AF and AC cells. Compared to NP cytokeratin-18 expression was lower in AC, and alpha-2-macroglobulin and desmocollin-2 lower in AF. Cartilage oligomeric matrix protein (COMP) and glypican-3 expression was higher in AF, while COMP, matrix gla protein (MGP) and pleiotrophin expression was higher in AC cells. Furthermore, an age-related decrease in KRT19 and increase in MGP expression were observed in NP cells. The age-dependent expression pattern of KRT19 was confirmed by immunohistochemistry, showing the most prominent KRT19 immunoreaction in the notochordal-like cells in juvenile NP, whereas MGP immunoreactivity was not restricted to NP cells and was found in all age groups. CONCLUSIONS: The gene expression of KRT19 has the potential to characterize human NP cells, whereas MGP cannot serve as a characteristic marker. KRT19 protein expression was only detected in NP cells of donors younger than 54 years.

Low-intensity pulsed ultrasound stimulates cell proliferation, proteoglycan synthesis and expression of growth factor-related genes in human nucleus pulposus cell line.

Low-intensity pulsed ultrasound (LIPUS) stimulation has been shown to effect differentiation and activation of human chondrocytes. A study involving stimulation of rabbit disc cells with LIPUS revealed upregulation of cell proliferation and proteoglycan (PG) synthesis. However, the effect of LIPUS on human nucleus pulposus cells has not been investigated. In the present study, therefore, we investigated whether LIPUS stimulation of a human nucleus pulposus cell line (HNPSV-1) exerted a positive effect on cellular activity. HNPSV-1 cells were encapsulated in 1.2% sodium alginate solution at 1x10(5) cells/ml and cultured at 10 beads/well in 6-well plates. The cells were stimulated for 20 min each day using a LIPUS generator, and the effects of LIPUS were evaluated by measuring DNA and PG synthesis. Furthermore, mRNA expression was analyzed by cDNA microarray using total RNA extracted from the cultured cells. Our study revealed no significant difference in cell proliferation between the control and the ultrasound treated groups. However, PG production was significantly upregulated in HNPSV cells stimulated at intensities of 15, 30, 60, and 120 mW/cm(2) compared with the control. The results of cDNA array showed that LIPUS significantly stimulated the gene expression of growth factors and their receptors (BMP2, FGF7, TGFbetaR1 EGFRF1, VEGF). These findings suggest that LIPUS stimulation upregulates PG production in human nucleus pulposus cells by the enhancement of several matrix-related genes including growth factor-related genes. Safe and non-invasive stimulation using LIPUS may be a useful treatment for delaying the progression of disc degeneration.

Stem cell applications in intervertebral disc repair.

There is increasing rise of interest in stem cell therapy, as it provides new options for treating a broad range of diseases. Several experimental methods are being explored for the use of stem cells in delaying or reversing the degenerative process of the intervertebral disc, a major cause of low back pain. In this article, we review the current strategies for stem cell applications in intervertebral disc repair and present three novel approaches. These are, first, the activation of nucleus pulposus cells by co-culture with mesenchymal stem cells for autologous disc cell reinsertion; second, the in vitro induction of nucleus pulposus-like or annulus fibrosus-like cells from mesenchymal stem cells; and third, the in vivo induction study by direct transplantation of mesenchymal stem cells to the intervertebral disc induced to degenerate experimentally. Although still untested, stem cell therapy may become a major option in the treatment of intervertebral disc degeneration.

Cross talk between Smad transcription factors and TNF-alpha in intervertebral disc degeneration.

The transforming growth factor-beta (TGF-beta) and the tumor necrosis factor-alpha (TNF-alpha) families are known to play important roles in intervertebral disc degeneration (IVD). However, molecular interactions between the TGF-beta and TNF-alpha signaling pathways have yet to be elucidated. The purpose of this study was to analyze the expression patterns of Smad transcription factor signaling associated with IVDs with aging and to examine the modulation of Smad signaling by TNF-alpha in IVD cells using SD rats. According to these experimental results, BMP signals in the TGF-beta family were more likely to be a key factor in IVD degeneration by aging, and it was predicted that besides the involvement of catabolic factors like MMPs and ADAMS-TS, there may be a decrease in expression of anabolic factors through cross talk of signaling between TNF-alpha and TGF-beta pathway in pathogenesis of disc degeneration.

Cultured articular chondrocytes sheets for partial thickness cartilage defects utilizing temperature-responsive culture dishes.

The extracellular matrix (ECM) of articular cartilage has several functions that are unique to joints. Although a technique for transplanting cultured chondrocytes has already been introduced, it is difficult to collect intact ECM when using enzymes to harvest samples. Temperature-responsive culture dishes have already been clinically applied in the fields of myocardial and corneal transplantation. Earlier studies have shown that a sheet of cultured cells with intact ECM and adhesive factors can be harvested using such culture dishes, which allow the surface properties of the dish to be reversibly altered by changing the temperature. Human chondrocytes were subjected to enzymatic digestion and then were seeded in temperature-responsive culture dishes. A sheet of chondrocytes was harvested by only reducing the temperature after the cultured cells reached confluency. A real-time PCR analysis of the chondrocyte sheets confirmed that type II collagen, aggrecan, and fibronectin were present. These results suggested that, although chondrocytes undergo dedifferentiation in a monolayer culture, multilayer chondrocyte sheets grown in a similar environment to that of three-dimensional culture may be able to maintain a normal phenotype. A histological examination suggested that multilayer chondrocyte sheets could thus prevent the loss of proteoglycans because the area covered by the sheets was well stained by safranin-O. The present experiments suggested that temperature-responsive culture dishes are useful for obtaining cultured chondrocytes, which may then be clinically employed as a substitute for periosteal patches because such sheets can be applied without a scaffold.

Expression of CD90 on keratinocyte stem/progenitor cells.

BACKGROUND: The identification and purification of keratinocyte stem cells (KSCs) that are capable of self-renewal and maintenance of differentiating cell populations could contribute both to our understanding of the biology of these cells, and to significant clinical applications, such as the culturing of keratinocytes for transplantation to severe burn wounds. Here, we report the detection of CD90(+) cells in cultured normal human epidermal keratinocytes and adult skin. OBJECTIVES: To investigate the biological function of CD90(+) and CD90(-) keratinocytes. METHODS: CD90(+) and CD90(-) keratinocytes were purified from adult skin and cultured keratinocytes using fluorescent activated cell sorting, and their biological abilities were analysed using both in vitro and in vivo assays. RESULTS: Flow cytometry (FCM) analysis identified approximately 18% of post-primary neonatal keratinocytes as CD90(+). However, during expansion of the culture, the expression level of CD90 rapidly decreased to about 2.5% at passage 10, while most of the keratinocytes maintained expression of alpha6 integrin. Purified CD90(+) keratinocytes demonstrated a sixfold higher cell growth rate than CD90(-) cells and the ability to form large (over 3 mm in diameter) colonies. We then quantitatively evaluated both populations using a previously described in vivo human epidermal cyst formation assay. Enhanced green fluorescent protein (EGFP)-labelled CD90(+) or CD90(-) keratinocytes were subcutaneously injected into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Six weeks after transplantation, EGFP(+) cell clusters in human epidermal cysts were evaluated using image analysis software. EGFP(+) cell cluster areas in the basal layer, derived from EGFP(+) CD90(+) cells, were eightfold larger than clusters of EGFP(+) CD90(-) cells. Furthermore, immunohistochemical staining and FCM analysis indicated that CD90 was expressed in most of the basal layer of the normal human epidermis. CONCLUSIONS: These results indicated that CD90 is a useful marker for the detection of human KSC-enriched populations in cultured human keratinocytes.

The influence of pedicle screw placement on thoracic trabecular strain.

STUDY DESIGN: Experimental study. INTRODUCTION: Although pedicle screw loosening and fracture are not uncommon, there is little understanding of the loading relationship between the pedicle screw and surrounding bone. There is even less understanding of the trabecular bone mechanics one a pedicle screw has been removed. OBJECTIVES: To investigate and understand the influence of the presence of pedicle screw placement and subsequent removal on vertebral trabecular strain under axial loading. SETTING: Orthopaedic Research Laboratories, University of California, Davis, USA. METHODS: Six cadaver spines were biomechanically loaded and the minimum principal and maximum shear strains were measured using texture correlation. The treatments were divided into three conditions as follows: (1) before screw placement, (2) during screw placement, and (3) after screw removal. The obtained data were statistically analyzed. RESULTS: Trabecular strain adjacent to the pedicle screw was increased following pedicle screw placement and remained high following pedicle screw removal. CONCLUSIONS: The current study demonstrates that pedicle screw placement greatly influences the trabecular bone and introduces weakness in the area following screw removal.

Multiple extradural arachnoid cysts at the spinal cord and cauda equina levels in the young.

STUDY DESIGN: A case report of multiple extradural arachnoid cysts at the spinal cord and cauda equina levels in the young. OBJECTIVE: To report an exceedingly rare case of multiple extradural arachnoid cysts at the spinal cord and cauda equina levels in the young. SETTING: Department of Orthopaedic Surgery, Tokai, Japan. CASE REPORT: An 11-year-old boy was diagnosed with multiple extradural arachnoid cysts at the spinal cord and cauda equina levels extending from the T5 to L5 vertebrae and surgery was performed. At 2 years after surgery, no recurrence was observed and muscle weakness of the lower extremities and sensory disturbance improved. CONCLUSION: Excision of only the arachnoid cysts at the spinal cord level led to a favorable outcome.

Microneurographically recorded Ia discharge from the tibial nerve mainly transmits the angular velocity of the ankle joint in humans.

Investigations of the Ia afferent discharge in clarifying problems in disused and malused skeletal muscles have been carried out mainly in muscles of the upper extremities. However, such problems actually occur more frequently in the antigravity muscles of the lower extremities, such as the triceps surae muscle. An analysis of microneurographically recorded Ia discharges from the tibial nerve innervating the triceps surae muscle during dynamic movement of the ankle joint indicated that they mainly transmitted information on the angular velocity of the joint. However, the information on the position sense of the joint was not as well transmitted through Ia discharges. There was no correlation between the joint angle and the static response. However, the dynamic response of a Ia afferent was well correlated to the angular velocity. It is concluded that the human proprioception of the triceps surae muscle was not dependent on the position of the ankle joint, but largely on its movement by the stretching of the muscle.

Treatment of osteoporotic late collapse of a vertebral body of thoracic and lumbar spine.

Although osteoporotic late collapse of a vertebral body is a common infirmity of old age, it has not been well studied, and no consensus regarding treatment of this condition has been reached. Forty-five patients with osteoporotic late collapse of a vertebral body were classified into six types based on the appearance on the lateral projection of a radiograph and the presence or absence of neurologic symptoms and were evaluated on imaging and clinical outcome. We concluded that the treatment of osteoporotic late collapse of a vertebral body can be individualized based on several factors such as the presentation of the fracture and neurologic condition. Conservative treatment can be selected in patients without neurologic involvement who have the concave type with anterior spur or sclerotic change or flat type with uniform compression of collapse. If the patients in those types of collapse show neurologic involvement, decompression and reconstruction through a posterior approach, including an eggshell procedure and the short segment pedicle screw system, are more suitable. Anterior decompression with anterior strut bone graft and anterior spinal instrumentation should be done for wedged type of collapse regardless of neurologic status.

Nucleus pulposus allograft retards intervertebral disc degeneration.

Autogenous implantation of nucleus pulposus or nucleus pulposus cells that were activated by coculture retards intervertebral disc degeneration, but harvesting such grafts causes disc degeneration at the donor site. This study examined whether nucleus pulposus allografts similarly retard disc degeneration and whether such allografting induces immunologic rejection. Japanese White rabbits served as donors and recipients for allografts. Lumbar disc degeneration was induced by aspirating the nucleus pulposus. Two weeks later, intact nucleus pulposus or nucleus pulposus cells were injected and compared with a sham procedure and normal control. The recipients' discs were examined histologically and immunologically at intervals for 16 weeks. Discs receiving an intact nucleus pulposus showed the least degeneration, followed by discs receiving nucleus pulposus cells, both of which were better than no treatment. These findings correlated directly with the intensity of immunochemical staining for Type II collagen. Allogeneic grafts did not induce any appreciable host-versus-graft response. Injection of nucleus pulposus and nucleus pulposus cells retards intervertebral disc degeneration. However, injection of intact nucleus pulposus is more effective than injection of nucleus pulposus cells alone. The intercellular matrix plays an important, but poorly understood, role in preserving intervertebral discs.