[Salmonella osteomyelitis - a rare differential diagnosis of bone tumors]. / Salmonellenosteomyelitis ­ eine seltene Differenzialdiagnose eines Knochentumors.

This case describes a rare salmonella infection suspected to be an osseous lymphoma. A 27-year-old female presented herself with painful swelling of her knee, with prednisolone-treated Crohn's disease as her only pre-existing condition. Salmonella species group C were detected in the osseous material derived from an extraction. The disease was treated with intravenous ceftriaxone, oral cotrimoxazole as well as multiple debridements. The working diagnosis should thus always be questioned and bone pain in patients who are immunosuppressed should be further investigated.

[Periprosthetic Infection of the Knee Megaprosthesis following a Resection of Malignant Tumours around the Knee]. / Periprotetické infekce megaprotéz po resekcích kostních nádoru oblasti kolene.

PURPOSE OF THE STUDY The study presents the monocentric retrospective study of a group of patients with malignant tumours around the knee, treated by a wide resection and a reconstruction with megaprosthesis due to infectious complications. Provided is a detailed analysis of each operative treatment due to the manifestation and process of periprostethic infection of the knee megaprosthesis and the use of external fixator during a two-stage revision. MATERIAL AND METHODS Between 01/1993 and 12/2013, a total of 67 cemented megaprostheses were assessed, with a detailed analysis of 12 patients with periprosthetic infection. The Kaplan-Meier method and MSTS for lower extremity clinical assessment were used and a range of motion was evaluated. RESULTS The endoprosthesis failed due to all kinds of complications (mechanical, biological, infection) in 27 (40.3%) patients. The estimated one-year survival rate from the surgery was 94%, the five-year survival rate was 72%, and the ten-year survival rate was 46%. Based on the statistical analysis of the implant survival due to infection, the one-year survival rate was 94%, the five-year survival rate was 75%, and the ten-year survival rate was 57%. Three patients were treated with radical surgical debridement. Five patients were treated with a two-stage revision with a cement spacer and external fixator, and three patients underwent nail fixation. Clinical values before and two years after the revision surgery for periprosthetic infection using MSTS were assessed. The mean of the difference of clinical values was 1.91 and the p value of paired t-test was 0.24, therefore there was no prove of the clinical result difference using MSTS before and after the revision surgery. DISCUSSION The acute radical debridement and lavage is preferred, if the surgery can be done up to three weeks after the first clinical signs of infection under the condition of good retention of the implant. In case of extensive infectious damage, when abscess, fistula and loosening of the implant are present and when the patient has a good oncological prognosis, we prefer a twostage revision with a cement spacer stabilized by an external fixator. In patients with mitigated infection or uncertain oncological prognosis we prefer a two-stage revision with the combination of a cement spacer and intramedullary nail fixation. CONCLUSIONS The study presents the results of operative treatment of periprosthetic infection of megaprosthesis and the modification of the two-stage replantation of infected MP with the use of external fixation for stabilisation of a non-articulated cement spacer allowing the patient to remain active during the time before the second stage. Key words: periprosthetic infection, megaprosthesis, bone tumour, external fixator, two-stage revision.

A novel co-culture model of murine K12 osteosarcoma cells and S. aureus on common orthopedic implant materials: 'the race to the surface' studied in vitro.

Infection is a major cause of orthopedic implant failure. There are few studies assessing both tissue cell and bacterial adherence on common orthopedic implant materials in a co-culture environment. An in vitro co-culture model was created using K12 osteosarcoma cells and Staphylococcus aureus in a medium incubated over metal disks for 48 h. The results showed that, in the presence of S. aureus, there were fewer osteosarcoma cells attached to the disks for all substrata tested. There were significantly more osteosarcoma cells adhering to the cobalt chrome than the stainless steel and titanium disks. Overall, in the presence of osteosarcoma cells, there were more bacteria adhering to the disks for all the substrata tested, with significantly more bacteria adhering to the stainless steel disks compared to cobalt chrome and titanium disks. Scanning electron microscopy verified that osteosarcoma cells and bacteria were adherent to the metal disks after incubation for 48 h. Furthermore, the observation that more bacteria were in the co-culture than in the control sample suggests that the osteosarcoma cells serve as a nutrient source for the bacteria. Future models assessing the interaction of osteogenic cells with bacteria on a substratum would be improved if the model accounted for the role of the immune system in secondary bone healing.

Oral microbiota distinguishes patients with osteosarcoma from healthy controls.

Objective: The human microbiota plays a key role in cancer diagnosis, pathogenesis, and treatment. However, osteosarcoma-associated oral microbiota alterations have not yet been unraveled. The aim of this study was to explore the characteristics of oral microbiota in osteosarcoma patients compared to healthy controls, and to identify potential microbiota as a diagnostic tool for osteosarcoma. Methods: The oral microbiota was analyzed in osteosarcoma patients (n = 45) and matched healthy controls (n = 90) using 16S rRNA MiSeq sequencing technology. Results: The microbial richness and diversity of the tongue coat were increased in osteosarcoma patients as estimated by the abundance-based coverage estimator indices, the Chao, and observed operational taxonomy units (OTUs). Principal component analysis delineated that the oral microbial community was significant differences between osteosarcoma patients and healthy controls. 14 genera including Rothia, Halomonas, Rhodococcus, and Granulicatella were remarkably reduced, whereas Alloprevotella, Prevotella, Selenomonas, and Campylobacter were enriched in osteosarcoma. Eventually, the optimal four OTUs were identified to construct a microbial classifier by the random forest model via a fivefold cross-validation, which achieved an area under the curve of 99.44% in the training group (30 osteosarcoma patients versus 60 healthy controls) and 87.33% in the test group (15 osteosarcoma patients versus 30 healthy controls), respectively. Notably, oral microbial markers validated strong diagnostic potential distinguishing osteosarcoma patients from healthy controls. Conclusion: This study comprehensively characterizes the oral microbiota in osteosarcoma and reveals the potential efficacy of oral microbiota-targeted biomarkers as a noninvasive biological diagnostic tool for osteosarcoma.

Elucidating the Intricate Roles of Gut and Breast Microbiomes in Breast Cancer Metastasis to the Bone.

BACKGROUND: Breast cancer is the most predominant and heterogeneous cancer in women. Moreover, breast cancer has a high prevalence to metastasize to distant organs, such as the brain, lungs, and bones. Patients with breast cancer metastasis to the bones have poor overall and relapse-free survival. Moreover, treatment using chemotherapy and immunotherapy is ineffective in preventing or reducing cancer metastasis. RECENT FINDINGS: Microorganisms residing in the gut and breast, termed as the resident microbiome, have a significant influence on the formation and progression of breast cancer. Recent studies have identified some microorganisms that induce breast cancer metastasis to the bone. These organisms utilize multiple mechanisms, including induction of epithelial-mesenchymal transition, steroid hormone metabolism, immune modification, bone remodeling, and secretion of microbial products that alter tumor microenvironment, and enhance propensity of breast cancer cells to metastasize. However, their involvement makes these microorganisms suitable as novel therapeutic targets. Thus, studies are underway to prevent and reduce breast cancer metastasis to distant organs, including the bone, using chemotherapeutic or immunotherapeutic drugs, along with probiotics, antibiotics or fecal microbiota transplantation. CONCLUSIONS: The present review describes association of gut and breast microbiomes with bone metastases. We have elaborated on the mechanisms utilized by breast and gut microbiomes that induce breast cancer metastasis, especially to the bone. The review also highlights the current treatment options that may target both the microbiomes for preventing or reducing breast cancer metastases. Finally, we have specified the necessity of maintaining a diverse gut microbiome to prevent dysbiosis, which otherwise may induce breast carcinogenesis and metastasis especially to the bone. The review may facilitate more detailed investigations of the causal associations between these microbiomes and bone metastases. Moreover, the potential treatment options described in the review may promote discussions and research on the modes to improve survival of patients with breast cancer by targeting the gut and breast microbiomes.

Osteomyelitis of the femur mimicking bone tumors: a review of 10 cases.

BACKGROUND: The clinical symptoms and radiographic appearance of osteomyelitis can mimic those of bone tumors. METHODS: We reviewed 10 patients with osteomyelitis of the femur who were initially diagnosed as having bone tumors and were subsequently transferred to our institution. RESULTS: Nocturnal pain of moderate intensity occurred in seven patients, and all 10 patients had elevated C-reactive protein levels. The radiographic findings included the following: a permeative, moth-eaten osteolytic lesion in six patients, an osteolytic lesion with sclerotic borders in three patients, and cortical destruction with pathological fracture in one patient. Magnetic resonance imaging was performed for eight patients, and only one had a positive penumbra sign. All patients underwent a surgical biopsy to confirm the final diagnosis for histological analysis and cultures. Klebsiella pneumoniae was detected in six patients and Staphylococcus aureus, the most common organism in osteomyelitis, was detected in three. Recurrence of infection occurred in five patients following debridement surgery; of these three had a Klebsiella pneumoniae infection. All patients received antibiotic treatment for an average of 20.4 weeks (range, 4 to 44) and surgical treatment an average of 1.8 times (range, 1 to 4). At the final follow-up, all patients were fully recovered with no signs of infection. CONCLUSIONS: When used in combination, clinical examinations, laboratory data, and radiographic findings can reliably distinguishing osteomyelitis from bone tumors.

High hydrostatic pressure, a novel approach in orthopedic surgical oncology to disinfect bone, tendons and cartilage.

High hydrostatic pressure (HHP) is widely used in the food processing industry, for example to inactivate vegetative microorganisms in meat products, milk and juice, thereby avoiding the addition of any chemical preservatives. Besides this, HHP is also an attractive novel approach to effectively kill vegetative microorganisms or tumor cells in bone, cartilage and tendon ex vivo while leaving the tissues' mechanical properties unimpaired, thus allowing reimplantation of the resected tissue explants. In contrast, sterilization by gamma irradiation and thermal or chemical inactivation of potentially infected autografts, allografts and other biomaterials considered for tissue regeneration and reconstruction is often associated with deterioration of the mechanical, physical and biological properties of the implant. HHP technology is now in preclinical testing with the aim of disinfecting/devitalizing grafts in order to inactivate both vegetative microorganisms and tumor cells in resected bone tissue segments, eventually allowing reimplantation of resected bone segments initially afflicted with osteomyelitis or tumors. The technical advantages, state-of-the-art, and potential application of HHP in orthopedic surgery are reviewed.

Tumor-targeting Salmonella typhimurium A1-R regresses an osteosarcoma in a patient-derived xenograft model resistant to a molecular-targeting drug.

Osteosarcoma occurs mostly in children and young adults, who are treated with multiple agents in combination with limb-salvage surgery. However, the overall 5-year survival rate for patients with recurrent or metastatic osteosarcoma is 20-30% which has not improved significantly over 30 years. Refractory patients would benefit from precise individualized therapy. We report here that a patient-derived osteosarcoma growing in a subcutaneous nude-mouse model was regressed by tumor-targeting Salmonella typhimurium A1-R (S. typhimurium A1-R, p<0.001 compared to untreated control). The osteosarcoma was only partially sensitive to the molecular-targeting drug sorafenib, which did not arrest its growth. S. typhimurium A1-R was significantly more effective than sorafenib (P <0.001). S. typhimurium grew in the treated tumors and caused extensive necrosis of the tumor tissue. These data show that S. typhimurium A1-R is powerful therapy for an osteosarcoma patient-derived xenograft model.

Identification of type A and type C virus particles in BF murine osteosarcoma.

Two types of virus particles, intracisternal type A and extracellular type C with budding, were detected in the same cells of BF osteosarcoma, its cultured cell lines, and their BFO tumors in CBA mice. The type C particles were approximately 100 microns in diameter. The buoyant density of the virions was 1.16g/ml in sucrose and 1.07 g/ml in Ficoll. A 72S RNA was demonstrated by gel electrophoresis, but no DNA was detected. Reverse transcriptase activity was also demonstrated in detergent-treated virions. Thus, the particles seem to be RNA virus. Cellular transformation and focus formation were observed after rat and mouse embryo cell monolayers were infected with the virus. The same kind of osteosarcoma was produced by inoculation of cloned transformed cells (BFOSV) of CBA embryo cells into CBA mice. Thus, the virus seems to be an oncornavirus.

Sarcoma-negative leukemia-positive transformed cell culture established from a murine sarcoma virus-induced rat bone tumor.

Inoculation of the Soehner-Dmochowski isolate of the Moloney strain of murine sarcoma virus (MSV), designated MSV-SD, consistently leads to the development of bone tumors in the susceptible New Zealand black (NB) rats. Two separate cell cultures have been established from 2 individual MSV-SD-induced NB rat bone tumors. Cells of 1 bone tumor culture, designated RBT-E, are in early in vitro passages. These cells form colonies in agar medium and take up 2-deoxy-D-[3H]glucose at a greatly enhanced rate, 5 times that of normal nontransformed rat embryo cells. Cells of the RBT-E culture release both MSV and murine leukemia virus (MuLV) and therefore contain sarcoma-positive leukemia-positive transformed cells. The other rat bone tumor culture, designated RBT-L, produced MSV at early passages. RBT-L culture has been passaged over 130 times in vitro. Cells of the RBT-L culture form colonies in agar medium and take up 2-deoxy-D-[3H]glucose at an enhanced rate (3 times that of rat embryo cells), indicating the presence of transformed cells within the RBT-L culture. However, cells of the RBT-L culture at late passages (Passage 130 or more) produce only MuLV and no detectable MSV activity (as shown by the lack of tumor-inducing activity and the lack of focus-forming activities by direct assay or by infectious center assay). Attempts to rescue MSV activity from RBT-L cells by cocultivation with MuLV-producing mouse cells were not successful. The MuLV found in the RBT-L cells, however, is a competent helper virus capable of rescuing the MSV genome from MSV-SD-induced hamster bone tumor cells. All the available evidence supports the notion that late passages of the RBT-L culture contain transformed cells that do not produce conventionally detectable MSV. These cells are referred to as sarcoma-negative leukemia-positive cells. The sarcoma-negative leukemia-positive cells represent a different kind of MSV-induced transformed cells and provide a unique system for studies in search of MSV markers such as MSV-specific antigens and MSV-specific nucleotide sequences.

Dexamethasone effects on induction of neoplastic transformation by Fujinami sarcoma virus in an in vitro chick embryo periosteal model for osteosarcoma.

Recently we have developed a model in vitro system for the study of factors regulating the histogenesis of osteosarcoma. In this system, Fujinami sarcoma virus (FSV) induces osteosarcomatous changes such as increased cell proliferation and altered patterns of bone and nonmineralized matrix (osteoid) formation. Such changes can be quantitated at the individual cell level, by computer-assisted morphometry. Here we report on the effects of dexamethasone (DEX) on FSV-induced neoplastic transformation and osteogenesis in chick embryonic periosteum cultures, as reflected by a series of histopathological parameters. Most significantly, it was found that compared to 10(-9) M DEX treated cultures, in 10(-7) M DEX pretreated cultures, the bone/osteoid ratio was increased due to a relative increase in the area of bone and a decrease in the area of osteoid. The number of [3H]thymidine-labeled cells decreased significantly, while the proportion of alkaline phosphatase positive cells increased. Double-label immunohistochemistry (with anti-P140gag-fps) and histochemistry for alkaline phosphatase activity was performed, to demonstrate production of the oncogene-encoded protein, and osteoblastic differentiation, respectively. In an in vitro transformation assay single cells derived from 10(-9) M DEX treated cultures formed a significantly higher number of colonies than those obtained from 10(-7) M DEX pretreated cultures. Taken together, the data indicate that in the chick embryonic periosteum culture system, pretreatment with 10(-7) M DEX inhibits the ability of FSV to induce neoplastic transformation. This effect is probably the result of DEX-induced cell differentiation, prior to infection with FSV.

Retroviruses that express different ras mutants cause different types of tumors in chickens.

We have used replication-competent retroviral vectors to express avian and murine ras genes in cultured chick embryo fibroblasts (CEF) and in chickens. Since the viral vectors are identical, it is possible to compare the oncogenic potential of the ras genes directly. The normal (12 gly) form of chicken c-Ha-ras is not oncogenic in vivo, nor does high-level expression transform CEF. Expression of murine v-ras or modified forms of chicken c-Ha-ras with either lysine or glutamine at position 12 transforms CEF and causes tumors in birds. However, the oncogenic potential of the transforming ras genes is different; the viruses that express the genes with lysine and glutamine at position 12 cause a distinct spectrum of tumors.

Myeloid leukaemogenicity and transmission of the HPRS-103 strain of avian leukosis virus.

The HPRS-103 strain of avian leukosis virus (ALV) was isolated recently from meat-type chickens and represents a new envelope subgroup. Its oncogenicity has been studied in three meat-type and five Leghorn strains of chickens. In the meat-type strains, the virus, following embryonal inoculation, induced an overall incidence of 27% myelocytic myeloid leukosis (myelocytomatosis) and 12% renal adenomas, with long median latent periods. Amongst the Leghorn lines, these tumors occurred with similar incidence in line 0, but with lower or zero incidences in the other lines. A variety of other tumours occurred with low incidence. Embryonal infection resulted in a permanently tolerant viraemic state with shedding of ALV group specific (gs)-antigen to egg albumen; contact infection resulted mainly in the development of non-shedder birds with serum virus-neutralising antibodies. Contact infection in a meat-type line was associated with the development of transient or permanent viraemia in some birds, and a low tumour incidence. A viraemic phase was not detected following contact infection in a Leghorn line and no tumours developed. The long latent period between embryo infection and tumour mortality, apparently differing from the consequences of infection with acutely transforming ALVs, and the inability of HPRS-103 ALV to transform cultured bone marrow cells, suggests that this virus may lack a viral oncogene and exert its oncogenic properties by some other mechanism such as promoter insertion activation of a cellular oncogene.

Regulation of an H-ras-related transcript by parathyroid hormone in rat osteosarcoma cells.

The rat osteosarcoma cell line UMR 106-01 is a commonly used model system for the study of osteoblast function. However, it also expresses a phenotype characteristic of transformed cells. To test whether the latter could be accounted for by aberrant oncogene expression, we probed Northern blots of UMR and other osteoblastic cells with a panel of oncogene probes. These blots, when probed with a cDNA specific for v-H-ras, revealed a 7.0-kilobase (kb) H-ras-related transcript (designated HRRT) in UMR 106-01 cells that was not expressed in other osteoblastic cells. Osteoblast-enriched calvarial cells expressed the typical 1.1-kb H-ras mRNA, which was absent in UMR cells. Additionally, Western blots of lysates of UMR cells documented the presence of three proteins immunologically related to H-rasp21. To determine whether HRRT represented a recombinant retrovirus product, Northern blots were probed with a cDNA specific for the highly conserved gag-pol region of Moloney murine leukemia virus. These blots showed parallel cross-reactivity with an apparently identical transcript of 7.0 kb. The 7.0-kb transcripts detected by both v-H-ras and gag-pol probes declined to the same extent after treatment with concentrations of PTH known to inhibit proliferation of these cells. PTH regulated the abundance of HRRT in a time- and dose-dependent manner, with greatest repression of the transcript after 8 h of treatment with 10(-8) M PTH. The decrease in HRRT could not be completely accounted for by changes in transcriptional activity, as determined by nuclear run-on assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor-targeting Salmonella typhimurium A1-R inhibits human prostate cancer experimental bone metastasis in mouse models.

Bone metastasis is a frequent occurrence in prostate cancer patients and often is lethal. Zoledronic acid (ZOL) is often used for bone metastasis with limited efficacy. More effective models and treatment methods are required to improve the outcome of prostate cancer patients. In the present study, the effects of tumor-targeting Salmonella typhimurium A1-R were analyzed in vitro and in vivo on prostate cancer cells and experimental bone metastasis. Both ZOL and S. typhimurium A1-R inhibited the growth of PC-3 cells expressing red fluorescent protien in vitro. To investigate the efficacy of S. typhimurium A1-R on prostate cancer experimental bone metastasis, we established models of both early and advanced stage bone metastasis. The mice were treated with ZOL, S. typhimurium A1-R, and combination therapy of both ZOL and S. typhimurium A1-R. ZOL and S. typhimurium A1-R inhibited the growth of solitary bone metastases. S. typhimurium A1-R treatment significantly decreased bone metastasis and delayed the appearance of PC-3 bone metastases of multiple mouse models. Additionally, S. typhimurium A1-R treatment significantly improved the overall survival of the mice with multiple bone metastases. The results of the present study indicate that S. typhimurium A1-R is useful to prevent and inhibit prostate cancer bone metastasis and has potential for future clinical use in the adjuvant setting.

Structure of endogenous retroviruses expressed in radiation-induced and spontaneous murine bone tumours.

The molecular structure of murine retroviruses expressed in spontaneous and radiation-induced bone tumours was studied. These viruses induce osteomas, lymphomas and osteopetrosis in mice of the NMRI strain. RNase T1 fingerprint analysis indicates the presence of mixed virus populations in the tumours, with major components showing close relationship to Akv MuLV. Cloned viruses, closely related to Akv MuLV, have the same oncogenic properties as the original mixtures. In its nucleotide sequence of the repeat segments of the transcriptional enhancer in the LTR, one cloned virus analysed was distinct from Akv MuLV, but closely related to a spontaneous bone tumour virus isolate, FBJ MuLV.

Endogenous murine leukemia viruses: frequency of radiation-activation and novel pathogenic effects of viral isolates.

Female C57BL/6 and BALB/c mice were injected i.p. with 0.06 microCi/kg or 0.5 microCi/kg of the short-lived alpha-emitting radionuclide 224radium at 3-day intervals. Infectious N-ecotropic XC+, and xenotropic C-type retroviruses were activated in several tissues in both strains. In C57BL/6 mice the activation of ecotropic and xenotropic virus was dose-dependent as observed 4 weeks after the start of irradiation. In BALB/c mice a few animals showed activation of ecotropic virus after four weeks of irradiation. The expression of xenotropic virus was similar in irradiated mice and controls. Viral antigen, indicative for viraemia, was not detected in irradiated or control animals. Antiviral antibodies were found in both control and irradiated mice but higher titers were found in the irradiated mice. Bone tissue-derived N-tropic XC+ virus isolates were found to be non-oncogenic in newborn mice of the parental strain. In contrast, the same virus isolates induced a novel pattern of disease, such as osteopetrosis and osteomas together with malignant lymphomas in NMRI mice. The data indicate that the pattern of endogenous murine leukemia virus activation by internal alpha-irradiation is dependent on the dose rate, and on the genetics of the mouse strain.

Activation and biological properties of endogenous retroviruses in radiation osteosarcomagenesis.

The activation of endogenous retroviruses (MuLV) by internal irradiation and the presence of activated retroviruses in radiation-induced murine osteosarcomas as well as their biological properties in vivo and in vitro were studied. Ecotropic and xenotropic MuLV were expressed dependent on the radiation dose in spleen, bone marrow and bone tissues of C57Bl/6 mice after 224Ra treatment. Radiation-induced osteosarcomas of BALB/c, C57Bl/6 and C3H X 101/F1 mice harboured infectious ecotropic and/or xenotropic viruses whereas in osteosarcomas of NMRI mice predominantly virus protein could be detected. In about 50% of the radiation-induced osteosarcomas of BALB/c mice an amplification of ecotropic proviruses could be detected. This was not found in clonally grown cells from non-tumorous tissues. MuLV from radiation-induced osteosarcomas induced osteopetrosis, osteomas and lymphomas after infection of newborn NMRI mice. In differentiating bone tissue the viruses were found to infect predominantly osteoblast precursor cells suggesting that virus infection results in increased growth and metabolic activity of these cells, which may be a possible mechanism for their pathogenic action in bone tissues.

Verrucous carcinoma of the leg positive for human papillomavirus DNA 11 and 18: a case report.

Human papillomavirus (HPV) types 6 and/or 11 have been associated with benign lesions, while types 16, 18, 31, and 33 are prevalent in malignant lesions. This case report describes the findings in a verrucous carcinoma of the leg, which was examined for HPV types 11, 16, and 18 by in situ DNA hybridization. The lesion gave positive results for HPV subtypes 11 and 18, a combination that, to our knowledge, has not been previously reported in this neoplasm.

Morphological, biological, immunological and biochemical studies on bone tumors of animals and man.

Biological studies on FBJ osteosarcoma virus in tissue cultures have led to the isolation of murine sarcoma virus. Characteristic type C-MuLV particles were observed in bone tumors induced by the SD-MSV-M-virus in vitro and in vivo. The SD-MSV-M virus also induced bone tumors in rats of all strains tested, and it has a similar tumor-inducing property in hamsters. Immunoelectronmicroscopic studies showed that envelope antigens of MSV-SD virus in rat bone tumors can be distinguished from those found in hamster bone tumor cells. In tissue cultures of MSV-SD rat bone tumors, two separate cell lines have been established: one of them releases both MSV and MuLV and the other produces MuL virus only. The MuLV in this cell line acts as helper. The different interactions appear to support the concept of control mechanisms for the partial expression of genes which are responsible for neoplastic properties, virus replication, and synthesis of gs-antigens. Biochemical studies on structural rearrangement and subunit composition of RNA released from MSV-SD virus, have shown that there are two forms of the native genome RNA differing in their sedimentation coeffiiecients and in subunit composition. In human osteosarcoma tissue culture, type-C viruslike particles are found. In cocultures derived from human osteosarcoma with cells taken from the bone marrow or peripheral blood of patients with different types of leukemia, certain morphological changes are observed which resemble those induced in animal cells by RNA tumor viruses. In osteosarcomas where no cytoplasmic antigen could be proved by an immunofluorescence test, the antigen could be produced by cocultivation with antigen-positive leukemic bone marrow cells. Whole human embryo cells treated with fluid from leukemia bone marrow cultures showed the presence of the cytoplasmic antigen when tested with positive sera, but they showed no morphologic changes. In high molecular weight RNA species, sedimentation coefficients ranging from 62S to 68S are demonstrated by molecular hybridization techniques. In cross-hybridization experiments, annealing values were observed only with complementary DNA products synthesized from sarcoma viruses. Three particularly high molecular weight RNA species released from human sarcoma cell cultures showed no cross-hybridization with either the DNA product of Rauscher leukemia virus or that of Gross leukemia virus.