Humanized C3 Mouse: A Novel Accelerated Model of C3 Glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is characterized by the alternative-pathway (AP) hyperactivation induced by nephritic factors or complement gene mutations. Mice deficient in complement factor H (CFH) are a classic C3G model, with kidney disease that requires several months to progress to renal failure. Novel C3G models can further contribute to understanding the mechanism behind this disease and developing therapeutic approaches.

METHODS

A novel, rapidly progressing, severe, murine model of C3G was developed by replacing the mouse C3 gene with the human C3 homolog using VelociGene technology. Functional, histologic, molecular, and pharmacologic assays characterize the presentation of renal disease and enable useful pharmacologic interventions in the humanized C3 (C3^hu/hu) mice.

RESULTS

The C3^hu/hu mice exhibit increased morbidity early in life and die by about 5-6 months of age. The C3^hu/hu mice display elevated biomarkers of kidney dysfunction, glomerulosclerosis, C3/C5b-9 deposition, and reduced circulating C3 compared with wild-type mice. Administration of a C5-blocking mAb improved survival rate and offered functional and histopathologic benefits. Blockade of AP activation by anti-C3b or CFB mAbs also extended survival and preserved kidney function.

CONCLUSIONS

The C3^hu/hu mice are a useful model for C3G because they share many pathologic features consistent with the human disease. The C3G phenotype in C3^hu/hu mice may originate from a dysregulated interaction of human C3 protein with multiple mouse complement proteins, leading to unregulated C3 activation via AP. The accelerated disease course in C3^hu/hu mice may further enable preclinical studies to assess and validate new therapeutics for C3G.

Selection of anti-cancer antibodies from combinatorial libraries by whole-cell panning and stringent subtraction with human blood cells

Traditional strategies for the identification of cell-surface cancer targets often fall short of their objective. For example, whole-cell panning of antibody libraries to isolate a diverse panel of antibodies directed against targets on cancer cells often identifies all immunogenic and/or abundant cell-surface antigens, not simply tumor-specific or tumor-associated antigens. Here we describe the use of stringent negative selection in combination with positive panning to increase tumor specificity and clinical relevance of selected antibodies. Sera from cancer cell-immunized mice showed strong binding to immunizing cancer cell lines but also cross-reacted strongly with human blood cells. Antisera blood cell binding was considerably decreased after stringent subtraction with human red blood cells (RBCs) and white blood cells (WBCs), yet cancer cell specificity was retained. In order to select for a higher percentage of clinically relevant antibodies for potential therapeutic use, stringent negative selection by RBC subtraction was employed in whole-cell panning of a disease-specific phage displayed antibody library on the prostate cancer cell line, PC-3. Isolated antibodies were found to bind to target antigens implicated in tumorigenicity and cancer cell migration and/or invasion, and included CD26, CDCP1, and the integrin complexes alpha2/beta1, alpha3/beta1, alpha5/beta1, and alpha6/beta4. Compared with traditional cell panning, this method considerably increased the selectivity of antibodies to tumor-associated antigens.

CD200 expression on tumor cells suppresses antitumor immunity: new approaches to cancer immunotherapy

Although the immune system is capable of mounting a response against many cancers, that response is insufficient for tumor eradication in most patients due to factors in the tumor microenvironment that defeat tumor immunity. We previously identified the immune-suppressive molecule CD200 as up-regulated on primary B cell chronic lymphocytic leukemia (B-CLL) cells and demonstrated negative immune regulation by B-CLL and other tumor cells overexpressing CD200 in vitro. In this study we developed a novel animal model that incorporates human immune cells and human tumor cells to address the effects of CD200 overexpression on tumor cells in vivo and to assess the effect of targeting Abs in the presence of human immune cells. Although human mononuclear cells prevented tumor growth when tumor cells did not express CD200, tumor-expressed CD200 inhibited the ability of lymphocytes to eradicate tumor cells. Anti-CD200 Ab administration to mice bearing CD200-expressing tumors resulted in nearly complete tumor growth inhibition even in the context of established receptor-ligand interactions. Evaluation of an anti-CD200 Ab with abrogated effector function provided evidence that blocking of the receptor-ligand interaction was sufficient for control of CD200-mediated immune modulation and tumor growth inhibition in this model. Our data indicate that CD200 expression by tumor cells suppresses antitumor responses and suggest that anti-CD200 treatment might be therapeutically beneficial for treating CD200-expressing cancers.

Immune evasion by CD200: New approaches to targeted therapies for chronic lymphocytic leukemia (CLL)

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Background: Although the human immune system is capable of raising an immune response against many cancer types, that response is insufficient to eradicate the cancer in most patients, possibly due to immune evasion through negative regulation of the immune system by the tumor. We identified the immune-suppressive molecule CD200 to be upregulated 1.5–5.4-fold on CLL cells in all 80 patients examined. Interaction of CD200 with its receptor alters cytokine profiles from Th1 to Th2 in mixed lymphocyte reactions, and results in the induction of regulatory T cells, which are thought to hamper tumor-specific effector T cell immunity. We addressed whether CD200 expression on tumor cells plays a role in immune evasion, thereby preventing elimination of tumor cells by the immune system in a xenograft hu/SCID mouse model, and whether treatment with an antagonistic anti-CD200 antibody affects tumor growth. Methods: The human non-Hodgkins lymphoma cell lines RAJI and Namalwa were transduced with human CD200 and injected subcutaneously together with human peripheral blood lymphocytes (PBL) into NOD/SCID mice. Tumor growth over time was compared among mice that either received CD200-expressing tumor cells or received tumor cells lacking CD200 expression. In subsequent experiments, mice were treated with chimeric or humanized anti-CD200 antibodies (doses ranged from 1 to 20 mg/kg) by intravenous injection. Treatment was either started immediately or 7 days after tumor cell injection. Results: As expected, PBLs reduced CD200-negative RAJI or Namalwa tumor growth by up to 75%. In contrast, growth of RAJI or Namalwa tumors expressing CD200 at levels comparable to that of CLL was not reduced by PBLs. Administration of anti-CD200 antibodies at 5 mg/kg resulted in nearly complete tumor growth inhibition (1/10 mice developed a small tumor) over the course of the study even when treatment was started 7 days after tumor cell injection. Conclusions: CD200 expression on tumor cells inhibits the ability of human lymphocytes to eradicate tumor cells. Treatment of CD200-expressing tumors with antagonistic anti-CD200 antibodies inhibits tumor growth, indicating the potential for anti-CD200 therapy as a promising approach for CLL.

No significant financial relationships to disclose.

A controlled trial of a school-based intervention to improve asthma management

The present study investigated schools as an appropriate context for an intervention designed to produce clinical and psychological benefits for children with asthma. A total of 193 out of 219 (88.1%) children with asthma (aged 7-9 yrs) from 23 out of 24 (95.8%) schools completed the study. Intervention schools received a staff asthma-training session, advice on asthma policy, an emergency beta2-agonist inhaler with spacer and whole-class asthma workshops. Nonintervention schools received no asthma-related input. Intervention children required less general practitioner-prescribed preventer medication despite no differences in symptom control compared with the nonintervention asthmatic group. Increased peer knowledge of asthma may have mediated improved active quality of life in the intervention group, together with increased self-esteem in young females. Those females not receiving the intervention, but identified as being asthmatic within the classroom, and thus possibly stigmatised, reported decreased self-esteem. Lower self-esteem in young males was associated with pet ownership. No change was found in staff knowledge, the establishment of asthma policies or school absences which were low even before intervention. In conclusion, a whole-school intervention can improve the health of children with asthma when followed with support for all children but effects are likely to be modified by sex and the home environment.

Mouse FGF15 is the ortholog of human and chick FGF19, but is not uniquely required for otic induction

The inner ear develops from an ectodermal placode that is specified by inductive signals from the adjacent neurectoderm and underlying mesoderm. In chick, fibroblast growth factor (Fgf)-19 is expressed in mesoderm underlying the presumptive otic placode, and human FGF19 induces expression of otic markers in a tissue explant containing neural plate and surface ectoderm. We show here that mouse Fgf15 is the sequence homolog of chick and human Fgf19/FGF19. In addition, we show that FGF15, like FGF19, is sufficient to induce expression of otic markers in a chick explant assay, suggesting that these FGFs are orthologs. Mouse embryos lacking Fgf15, however, do not have otic abnormalities at E9.5-E10.5, suggesting that Fgf15 is not uniquely required for otic induction or early patterning of the otocyst. To compare FGF15 and FGF19 signaling components and assess where signals potentially redundant with FGF15 might function, we determined the expression patterns of Fgf15 and Fgf19. Unlike Fgf19, Fgf15 is not expressed in mesoderm underlying the presumptive otic placode, but is expressed in the adjacent neurectoderm. Fgfr4, which encodes the likely receptor for both FGF19 and FGF15, is expressed in the neurectoderm of both species, and is also expressed in the mesoderm only in chick. These results suggest the hypotheses that during otic induction, FGF19 signals in either an autocrine fashion to the mesoderm or a paracrine fashion to the neurectoderm, whereas FGF15 signals in an autocrine fashion to the neurectoderm. Thus, the FGFs that signal to the neurectoderm are the best potential candidates for redundancy with FGF15 during mouse otic development.

Nucleotides in 16S rRNA protected by the association of 30S and 50S ribosomal subunits

We have studied the interaction of 16S rRNA in 30S subunits with 50S subunits using a series of chemical probes that monitor the accessibility of the RNA bases and backbone. The probes include 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluene sulfonate (CMCT; to probe U at N-3 and G at N-1), diethylpyrocarbonate (DEPC; to probe A at N-7), dimethyl sulfate (DMS; to probe A at N-1, and C at N-3), kethoxal (to probe G at N-1 and N-2), hydroxyl radicals generated by free Fe(II)-EDTA (to probe the backbone ribose groups) and Pb(II). The sites of reaction were identified by primer extension of the probed RNA. Association of the subunits protects the bases of 11 nucleotides and the ribose groups of over 90 nucleotides of 16S rRNA. The nucleotides protected from the base-specific probes are often adjacent to one another and surrounded by sugar-phosphate backbone protections; thus, the results obtained with the different probes confirmed each other. Most of the protected nucleotides occur in five extended-stem-loop structures around positions 250, 700, 790, 900, and 1408-1495. These regions are located in the platform and bottom of the subunit in the general vicinity of inter-subunit bridges that are visible in reconstructed electron micrographs. Our results provide an extensive map of the nucleotides in 16S rRNA that are likely to be involved in subunit-subunit interactions.

Audit of nutritional support provided to surgical patients by a nutrition team

An audit was carried out over a 24 month period to assess the practice, safety and efficacy of nutritional support provided to surgical patients by a designated team. 135 patients received nutritional support: 51% were fed parenterally, 32% enterally and 17% via combined nutritional support. The duration of feeding ranged from 1-177 days with 23% being supported for < 7 days. The line infection rate for patients receiving intravenous nutrition was 6.5%. Nutritional outcome was assessed using weight, anthropometry and bioelectrical impedance analysis. Pre-and post-feeding results were available for 67% of patients. These patients were classified as either oedematous (n = 21), normally nourished (n = 23) or nutritionally depleted (n = 46). Overall, the oedematous patients lost water, the protein status of the normally nourished group deteriorated slightly and the nutritional status of the nutritionally depleted patients was maintained. Audit is a valuable means of defining the efficacy of a nutrition support service and has identified areas which require review.

Binding of dansyl propranolol to the (Ca2+ + Mg2+)-ATPase

We have studied the binding of dansyl propranolol to lipid bilayers and to the (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum. The fluorescence emission spectra for dansyl propranolol bound to the ATPase system can be fitted to the sum of three peaks, characteristic of probe bound to lipid and to protein and free in solution, respectively. Titrations show that binding to the lipid component of the ATPase system is comparable to binding to simple lipid bilayers. Binding constants obtained using fluorescence spectroscopy for binding to lipid bilayers agree with constants obtained from microelectrophoresis measurements. Binding to sites on the ATPase can be described either in terms of the aqueous concentration of dansyl propranolol or in terms of the mole fraction of dansyl propranolol in the lipid phase of the membrane. Both descriptions suggest extensive binding to annular sites at the lipid/protein interface of the ATPase. Binding at other sites on the ATPase might also be present. Binding of dansyl propranolol to the ATPase results in a marked inhibition of activity. At high Ca2+ concentrations, inhibition fits to a non-competitive model of inhibition, described by a Ki of 5 microM. We attribute this effect to binding at annular sites. At lower Ca2+ concentration, a decrease is observed in the apparent affinity of the ATPase for Ca2+ which can be attributed to a build-up of positive charge on the membrane as a result of binding.

Annular and non-annular binding sites on the (Ca2+ + Mg2+)-ATPase

Quenching of the fluorescence of the (Ca2+ + Mg2+)-ATPase purified from muscle sarcoplasmic reticulum can be used to measure relative binding constants of hydrophobic compounds to the phospholipid-protein interface. We show that the binding constant for cholesterol is considerably less than that for phosphatidylcholine, so that cholesterol is effectively excluded from the phospholipid annulus around the ATPase. However, dibromocholestan-3 beta-ol causes quenching of the fluorescence of the ATPase, and so has access to other, non-annular sites. We suggest that these non-annular sites could be at protein/protein interfaces in ATPase oligomers. Oleic acid can bind at the phospholipid/protein interface, although its binding constant is less than that for a phosphatidylcholine, and it can also bind at the postulated non-annular sites. The effects of these compounds on the activity of the ATPase depend on the structure of the phospholipid present in the systems.

Interaction of fatty acids with the calcium-magnesium ion dependent adenosinetriphosphatase from sarcoplasmic reticulum

The fluorescence emission spectrum of dansylundecanoic acid is sensitive to the environment and appears at a lower wavelength when the fatty acid is bound to protein than when it is bound to phospholipid. When bound to the (Ca2+-Mg2+)-ATPase of sarcoplasmic reticulum, the emission spectrum can be resolved into separate components assigned to fatty acid bound to protein and to lipid. Efficiency of energy transfer from the tryptophan residues of the ATPase to dansylundecanoic is higher for protein-bound probe than for lipid-bound probe. Fluorescence titrations are consistent with three fatty acid binding sites per ATPase with a Kd of 7 microM, and these sites are postulated to occur at the protein-protein interface in ATPase oligomers. Fatty acid incorporated into the lipid component of the membrane appears to be bound outside the lipid annulus around the protein.