PubMed Health⌕ Search

Biomedical subjects

J Xiang

Publications and source records attributed to J Xiang.

159 records · Page 9Linked to original sources
PubMed1992

Genetic engineering of anticolorectal carcinoma Fv molecule in myeloma cells.

The anti-TAG72 Fv molecule composed of a heterodimer of both heavy- and light-chain variable domains was produced by the construction of the expression vector mpSV2neo-EP1-Fv72.3. This vector contained the neo gene as a selection marker, the murine immunoglobulin heavy chain promoter (P1), enhancer (E), the SV40 polyadenylation signal region, and the murine cDNA fragments of VH and VL regions amplified and cloned directly from the B72.3 hybridoma RNA by the polymerase chain reaction technique. Termination codons were introduced into the 3' end of both VH and VL regions. The expression vector was transfected into the SP2/0 cell line. The Fv72.3 molecules were purified by the rabbit anti-B72.3 idiotype antibody affinity column, and retained the binding reactivity for the TAG72 antigen. The small size of Fv72.3 molecule (25 kD) makes it attractive for structural studies and immunodetection of cancers.

Amino Acid Sequence↗
PubMed1992

Regulation of the p58GTA cell division control-related protein kinase during phorbol 12-myristate 13-acetate-induced terminal differentiation of U937 cells.

We describe the regulation of expression, activity and subcellular localization of a cell cycle control-related kinase, p58GTA, during the withdrawal from the cell cycle of U937 human leukemic cells induced by phorbol esters. Our studies indicate that steady-state mRNA, protein levels, transcription and subcellular localization of this kinase are affected in distinctly different manners by phorbol esters (phorbol 12-myristate 13-acetate, PMA). Steady-state mRNA levels increase dramatically within 1 h of PMA treatment, while steady-state protein levels increase only slightly. However, within 24 h of PMA treatment both steady-state p58GTA mRNA and protein levels decrease markedly. Assays of p58GTA protein kinase activity show that, even though steady-state protein levels are relatively constant, protein kinase activity increases within 30 min of PMA treatment, and then peaks at 2 h and 12 h after PMA treatment. Once again, p58GTA protein kinase activity decreases by 48 h to levels similar to unstimulated cells. These results suggest that the expression of the p58GTA protein kinase gene and, quite possibly, its post-translational modification are affected by phorbol esters in a complex manner.

Amino Acid Sequence↗
PubMed1992

Genetic engineering of high affinity anti-human colorectal tumour mouse/human chimeric antibody.

Two amino acids, tyrosine at position 96 and histidine at position 99 in the variable heavy chain (VH) CDR3 region of a mouse/human chimeric anti-TAG72 antibody cB72.3-1-3 were substituted with phenylalanine and asparagine respectively by site-directed mutagenesis technique. The expression vector mpSV2neo-EP1-Vm1-3-C gamma 1 containing mutant VH region fragments (Vm1-3) as well as the immunoglobulin enhancer (E), promoter (P1) and human genomic C gamma 1 region fragments, was transfected into a heavy-chain loss mutant cell line B72.3Mut(k). Mutant chimeric cB72.3m1-3 antibodies were purified from the transfectant supernates and compared based upon their binding affinity for the TAG72 antigen relative to that of the original cB72.3-1-3 antibody. The data show that a single amino acid substitution of histidine with asparagine at position 99 in VH CDR3 region contributes to four times increase in binding affinity for the TAG72 antigen. This suggests that the residue at position 99 in VH CDR3 region may play some role in antibody/antigen (B72.3/TAG72) interaction.

Animals↗
PubMed1991

Correlation of preS antigens and clinical status during chronic hepatitis B virus infection.

The serum kinetics of preS1 and preS2 antigens has been evaluated in 38 serial samples from eight patients with chronic active (CAH) or chronic persistent (CPH) hepatitis, followed for 2-7 years (mean 4.4 years) in whom liver biopsy was performed at intervals, and in 46 samples from ten asymptomatic HBsAg carriers followed for 4-5 years (mean 4.6 years). Four patterns of preS behaviour have been observed: (1) persistently positive preS1 and preS2; (2) disappearance of preS2; (3) disappearance of both preS1 and preS2; and (4) persistently negative preS1 and preS2. Pattern 4 has been observed exclusively among healthy carriers, while seven out of eight chronic patients exhibited either pattern 1 or 2. Among the chronic patients, preS2 disappearance was accompanied or followed by alanine aminotransferase (ALT) normalization. The correlation of preS antigens with conventional viral replication markers showed that 100% of hepatitis B virus (HBV)-DNA-positive and 86.6% of HBeAg-positive sera were preS1/preS2 positive, while 61% of HBV-DNA-negative and 64% of HBeAg-negative sera were preS1/preS2 negative. Our data suggest that continuous monitoring of preS antigens in follow-up sera will allow for an improved prognostic evaluation of chronic HBV infection.

Adolescent↗
PubMed1991

Comparative biodistribution and antibody-dependent cellular cytotoxicity of native and heavy chain chimeric antibody.

We have recently chimerized the heavy chain of the pan-carcinoma monoclonal antibody (mAb) B72.3. Studies were undertaken to compare the IgG1 chimeric antibody, B72.3-1-3 with native murine B72.3 (nB72.3). Using fluorescence-activated cell sorting analysis, B72.3-1-3 demonstrated specific binding to fresh LS174T tumor cells. Biodistribution of 131I B72.3-1-3 was similar to 131I nB72.3 in nude mice bearing LS174T xenografts. Peak radiolocalization indices were noted on day 6 for B72.3-1-3 and day 8 for nB72.3. Both antibodies were capable of imaging LS174T tumors by radioimmunoscintigraphy. Antibody-dependent cellular cytotoxicity of LS174T by human peripheral blood lymphocytes was tested in 8h 51Cr release assays. With either no antibody or nB72.3, lymphocytes were not capable of killing LS174T cells. However, B72.3-1-3 at a concentration of 5 and 50 micrograms/ml mediated significant lysis of tumor cells by human lymphocytes. These results suggest that chimeric antibodies retain their binding properties to tumor cells and display biodistribution patterns similar to their unmodified counterparts. Such modifications may reduce the deleterious human antimouse antibody response to murine mAbs as well as augment antibody-dependent cellular cytotoxicity of tumor cells by human effectors.

Animals↗
PubMedDate not supplied

Pro-apoptotic treatment with an adenovirus encoding Bax enhances the effect of chemotherapy in ovarian cancer.

BACKGROUND: Tumor cell heterogeneity and resistance to chemotherapy-mediated cell death are major obstacles in cancer therapy. It has been reported that expression of the pro-apoptotic molecule Bax can induce cell death or sensitize tumor cells to chemotherapy in stable cell clones derived from tumor cells. However, these studies are limited in that they cannot represent the heterogeneity of cancer cells observed in vivo. In this study, we have further explored the therapeutic potential of Bax. METHODS: Using an inducible recombinant Bax adenovirus, we screened a panel of ovarian cancer cell lines and primary patient-derived ovarian tumor cells for their sensitivity to Bax-mediated cytotoxicity. Apoptotic cell death was evaluated qualitatively with Hoechst staining and quantitatively with MTS and Annexin V-based assays. Endogenous levels of both Bcl-2 and Bax protein and p53 status were evaluated. The potential of bax to sensitize ovarian cancer lines to chemotherapy was also tested. Dose-response curves were generated to evaluate cell death. RESULTS: Overexpression of Bax directly induced apoptosis in both ovarian cancer cell lines and the patient-derived primary cancer cells. However, the sensitivity of these cells to Bax varied and appeared to be independent of both the status of p53 and the endogenous levels of bcl-2 or Bax, critical molecules in the apoptotic pathway. Importantly, overexpression of Bax significantly enhanced chemotherapy-induced cytotoxicity in both established cell lines and primary ovarian carcinoma cells. CONCLUSIONS: These studies suggest that overexpression of Bax alone or in combination with chemotherapy may provide a means to overcome the problems imposed by the heterogeneous nature of tumors, ultimately augmenting the efficacy of chemotherapy in patients suffering from ovarian cancer.

Adenoviridae↗
PubMedDate not supplied

Isolation of metastatic B16 melanoma variants using anti-Met 72 monoclonal antibodies and flow cytometry.

Analysis of a number of B16 melanoma clones has revealed a high correlation between metastatic activity and the quantitative expression of a 72,000 dalton glycoprotein, Met 72. In the present study, metastatic tumor cell variants have been directly isolated from a heterogeneous, poorly metastatic melanoma (B16-F1) by anti-Met 72 monclonal antibodies and cell sorting procedures. These studies provide direct proof that Met-72 antigens are in fact surface markers of B16 melanoma metastatic variants and may provide the means of monitoring their presence, influence and autonomy during tumor progression.

Animals↗
PubMedDate not supplied

The impact of endoscopic technology on gastrointestinal pathology.

Since its introduction in the 1950s, fiberoptic endoscopy has dramatically altered the scope and practice of gastrointestinal (GI) pathology. Whereas examination by rigid instruments was generally restricted to the proximal digestive foregut and distal 25 cm of the large bowel, fiberoptic endoscopy extended these limits considerably, which resulted in a greater volume of biopsies submitted to the pathology laboratory. Furthermore, this technique is associated with a lesser degree of patient discomfort and a lower risk of complications compared to rigid or semiflexible endoscopy. In established endoscopy units, flexible endoscopy is performed increasingly with the videoscope rather than the fiberscope. With the added advantage of direct visualization, flexible endoscopy has eclipsed barium radiology as the premier investigative modality for GI diseases. Although upper GI endoscopy and colonoscopy account for the majority of biopsy material, there are other flexible endoscopic techniques, including endoscopic retrograde cholangiopancreatography and enterostomy. Flexible endoscopy has not only impacted the diagnosis of important disease entities (eg, reflux esophagitis, H. pylori gastritis, celiac disease and GI polyps and neoplasia), but it has also become a key component of surveillance protocols for dysplasia in Barrett's esophagus and idiopathic inflammatory bowel disease. Predicting major trends that may emerge from (GI flexible endoscopy in the future is somewhat difficult, but promising new avenues of investigation include increased use of endoluminal ultrasound and trans-bowel fine needle aspiration. Biopsy material will be submitted with more frequency for genetic molecular studies such as tumor development and progression and identification of infections agents; the priorities for handling biopsy material may have to be re-examined. Gastrointestinal (GI) biopsies constitute a substantial proportion of the surgical pathology load in most tertiary care medical centers. Based on topographic site of origin, the GI tract is the single largest component of the biopsy service in this institution. This relates in part to the high frequency of patients' complaints referable to the digestive tract and is also a result of the advances in GI endoscopy that have led to more widespread application of this technique. To gain a better appreciation of the impact of the changes in endoscopic techniques on gastrointestinal pathology, it is pertinent to examine the historical perspective from which the technology arose.

Digestive System↗
PubMedDate not supplied

Single jejunoileal and right colonic carcinoids as midgut tumors. A study collating immunophenotypes and histogenesis.

The jejunoileum and the right colon, both of which are located in the midgut, have some histologic similarities such as the presence of Paneth cells and intraepithelial endocrine cells (IEECs). Since gastrointestinal (GI) carcinoids arise from the same stem cells as GI endocrine cells, the question was whether or not there might also be similarities in the histogenesis of jejunoileal carcinoids (JICs) and right colonic carcinoids (RCCs). Ten single JICs and 3 RCCs together with their respective controls were stained using various neurohormonal immunoreagents. Our results showed that neither the JICs nor the RCCs appeared to arise from a background of diffuse IEEC hyperplasia. Furthermore, in the jejunoileum, serotonergic progenitor cells appear to have a proclivity for neoplastic transformation, as do cells of the pancreatic polypeptide and glucagon lineage in the right colon.

Carcinoid Tumor↗
PubMedDate not supplied

Inhibition of established tumor growth in syngeneic mice by local inoculation of engineered mouse myeloma cells secreting a recombinant fusion protein RM4/TNF.

Mouse myeloma cell line VKCK/RM4-TNF secreting the recombinant fusion protein RM4/TNF was used to study the relationship between tumor necrosis factor (TNF) secretion of tumor cells and its tumorigenicity, and to study the potential mechanisms responsible for the antitumor immune response. To evaluate tumorigenicity, 5 x 10(5) viable TNF-secreting VKCK/RM4-TNF and non-TNF-secreting VKCK tumor cells were subcutaneously injected into BALB/c mice. Tumor progression or regression was evaluated 2 weeks after tumor inoculation. Our animal studies showed that RM4/TNF secretion by VKCK/RM4-TNF tumor cells curtailed its tumorigenicity in BALB/c mice and induced a long-term, protective immune response against a subsequent challenge of the parental VKCK tumor cells. Our animal studies in T-cell subset-depleted BALB/c mice and in T-cell-deficient nude mice demonstrated that both CD4+ and CD8+ T cells play a major role in the reduction of tumorigenicity. In addition, our results further showed that local inoculation of irradiated VKCK/RM4-TNF cells secreting TNF was able to significantly inhibit the established VKCK tumors in syngeneic mice. This study thus highlights the potential utility of engineered tumor cells secreting RM4/TNF in cancer gene therapy.

Animals↗
PubMedDate not supplied

Cytotoxic CD4+ T cells associated with the expression of major histocompatibility complex class II antigen of mouse myeloma cells secreting interferon-gamma are cytolytic in vitro and tumoricidal in vivo.

Vaccination of mouse myeloma V(K)C(K)-gamma (I) cells secreting interferon (IFN)-gamma and expressing enhanced major histocompatibility complex (MHC) class I antigen (Ag) resulted in protective immunity that was mainly mediated by CD8+ T cells. V(K)C(K)-gamma (I/II) cells expressing both enhanced MHC class I and class II Ags were isolated from V(K)C(K)-gamma (I) cells. These V(K)C(K)-gamma (I/II) cells were used to study the relationship between IFN-gamma secretion of tumor cells, its tumorigenicity, and its induced immunity, as well as to evaluate the cellular immunocomponents mediating this immunity. Our animal studies showed that IFN-gamma secretion by V(K)C(K)-gamma (I/II) cells curtailed its tumorigenicity in syngeneic BALB/c mice and further induced protective immunity against a subsequent graft of parental V(K)C(K) tumor. This immunity is mediated by both CD4+ and CD8+ T cells. The activation of CD4+ T cells is associated with enhanced expression of MHC class II Ag of V(K)C(K)-gamma (I/II) cells. These CD4+ T cells are tumor specific and cytolytic in an MHC-restricted fashion in vitro, and are tumoricidal in a T-cell adoptive transfer experiment in vivo. Our data thus demonstrate that vaccination of genetically modified tumor cells secreting IFN-gamma may provide beneficial antitumor effects by inducing both cytolytic CD4+ and CD8+ cytotoxic T lymphocytes, provided that these tumor cells express both enhanced MHC class I and class II Ags.

Animals↗
PubMedDate not supplied

Intratumoral vaccination of adenoviruses expressing fusion protein RM4/tumor necrosis factor (TNF)-alpha induces significant tumor regression.

Recombinant adenovirus (AdV) vectors are highly efficient at in vitro and in vivo gene delivery. VKCK is a murine myeloma cell line expressing the light chain of the fusion protein RM4/tumor necrosis factor (TNF)-alpha. The in vitro transfection of VKCK cells with the AdV AdV5LacZ, which contains the marker gene beta-galactosidase, can reach a maximal 75% at a multiplicity of infection of 1000. Intratumoral injections of AdV5LacZ (2 x 10(9) plaque-forming units) resulted in substantial gene transfer in nearly 50% of VKCK tumors. The AdV pLpA/M4-TNF-alpha, which contains a fused gene M4-TNF-alpha that codes for the heavy chain of fusion protein RM4/TNF-alpha, was constructed. After the in vitro transfection of pLpA/M4-TNF-alpha at a multiplicity of infection of 1000, transfected VKCK cells showed significant secretion of RM4/TNF-alpha (36 ng/mL/10(6) cells) containing the functional TNF-alpha moiety in tissue culture. The secretion peaks at day 3 and is diminished at day 6 following the viral infection. These transfected VKCK cells also became more immunogenic with enhanced expression of major histocompatibility complex class I antigen. Intratumoral injections of 2 x 10(9) plaque-forming units of pLpA/M4-TNF-alpha virus with a repeated booster resulted in significant VKCK tumor regression in immune-competent mice, but not in athymic nude mice with a mean tumor weight of 0.07 g that were compared with 1.58 g and 1.70 g for tumors injected with AdV5LacZ and phosphate-buffered saline, respectively (P < .01). The tumor regression also results in protective immunity against a second challenge with parental tumor cells, which is mainly mediated by VKCK tumor-specific CD8+ T cells. These results indicate that AdV-mediated cytokine gene therapy may be a useful approach in the clinical management of solid human tumors.

Adenoviridae↗