Use of hu-IgG-SCID mice to evaluate the in vivo stability of human monoclonal IgG antibodies.

Human and in vitro modified mAbs such as humanized rodent mAbs and immunotoxins are now considered for a variety of applications in humans. The adequate in vivo stability of these Ig preparations is not easily predicted from in vitro studies and may be essential for many therapeutic applications. In this study, we report the development and characterization of an in vivo model for testing this parameter using SCID mice containing a physiological concentration of human IgG (hu-IgG-SCID). The model was tested with several IgG1 and IgG3 human mAbs reacting with the human Rh(D) red cell antigen. It is known that human IgG have a shorter half-life in SCID mice than in humans. However, our results showed that the half-life of IgG3 mAbs (1.5 +/- 0.5 days) was much shorter than the one of IgG1 mAbs (5.8 +/- 1.4 days), indicating that the relative stability of IgG1 and IgG3 human mAbs in hu-IgG-SCID mice is similar to the one previously reported in humans (21 days vs. 7 days respectively). The IgG catabolism rate in humans is known to be inversely proportional to serum IgG concentrations. Accordingly, the dilution of the mAbs in a large excess (200-fold) of human IgG was found to be an important parameter of the hu-IgG-SCID mouse model since much longer (3-4-fold) mAb half-lives were obtained in the presence of a lower dose or in the absence of co-injected human IgG. This study show the usefulness of this animal model for the evaluation of human antibody stability in an in vivo environment.

Use of human keratinocytes cultured on fibrin glue in the treatment of burn wounds.

Keratinocytes isolated from a small skin biopsy and cultured according to the method of Rheinwald and Green (Cell 1975, 6: 331) are able to undergo rapid expansion in vitro and have been used successfully in the treatment of burn wounds. One of the inconveniences of this method involves the transfer of the epidermal sheet from the culture flask onto the wound bed. One way to facilitate this process is to use fibrin glue (Biocol) as a culture bed for the keratinocytes. Burns are then grafted by simply placing the sheet of fibrin glue and keratinocytes onto the wound bed. This process has been successful in two patients, permanently covering areas of 720 cm2 and 5342 cm2. The newly formed epidermis was fully differentiated and histologically normal after 1 year. The efficiency of this improved, faster procedure could lead to a new approach in the treatment of extensive burn wounds.

Influenza virus host response of C57Bl/6 mice treated with TACI-Ig.

TACI-Ig is a soluble glycoprotein comprised of a human IgG1-Fc fused with the extracellular domain of the human TACI receptor. Chronic exposure to TACI-Ig is associated with reduced circulating B cells in mouse and non-human primates, and a concomitant decrease in circulating immunoglobulin. Because of these activities, TACI-Ig is in clinical evaluation for treatment of various autoimmune diseases and B cell malignancies. In this study, the effect of TACI-Ig treatment on the ability of C57Bl/6 mice to clear influenza virus was evaluated. C57Bl/6 mice were exposed to vehicle (negative control), dexamethasone (positive control), or TACI-Ig (0.05, 0.50, or 5.0 mg/kg, SC, thrice weekly) from within one week prior to viral exposure through 21 days thereafter. Dexamethasone treatment of influenza-infected mice prolonged the infection, and decreased survival, body weight, lymphoid organ weight, influenza-specific IgM and IgG, and viral clearance relative to control animals, consistent with its expected immunosuppressive activity. Animals treated with TACI-Ig (0.05, 0.50, and 5.0 mg/kg) demonstrated a dose-dependent decrease in spleen weight and influenza-specific IgG and IgM in both lung and serum relative to control animals. In addition, flow cytometric analyses showed a decrease in B cells, but not T cells, in peripheral blood in animals treated with TACI-Ig. However, neither viral clearance nor survival was affected by TACI-Ig treatment. These data demonstrate the expected B cell-specific pharmacological effects of TACI-Ig in influenza-challenged C57Bl/6 mice without apparent effect on influenza virus clearance. It is concluded that non-B cell related antiviral competence remains intact during TACI-Ig treatment.

[Characterization and validation of a human anti-C monoclonal antibody]. / Caractérisation et validation d'un anticorps monoclonal humain anti-C.

Peripheral lymphocytes were obtained from an immunized woman against C and Ce antigens. Punction was realized 14 days after childbirth. After hetero-hybridization, a unique cell line continued secreting a monoclonal IgM antibody. Serological characterization of this antibody was determined by direct agglutination tests against 150 native and enzyme treated red blood cells including some rare phenotypes. This antibody was specific of C determinant of the Rh system. It showed strong reactions by saline and enzymatic technics, against C positive cells from Ce positive and Ce negative patients. The validation was performed by a manual direct agglutination test in saline (tube) and by an automated-hemagglutination test (in microplate) against 2,500 patients samples. No discrepancy was observed. This monoclonal IgM anti-C could be used as a potent reagent and since one year, about 30,000 patients and pregnant women have been phenotyped in our laboratory successfully.

Restricted use of cationic germline V(H) gene segments in human Rh(D) red cell antibodies.

The human red cell Rh(D) antigen elicits the production of high-affinity IgG antibodies, which can prevent blood transfusion and cause hemolytic disease of the newborn. It has been known for 20 years that Rh(D) antibodies are among the most positively charged human serum IgGs. Analysis by IEF of 9 human anti-Rh(D) monoclonal antibodies showed that their isoelectric points (pI) (8.3 to 8.6) were also significantly higher than the average pI of serum IgGs (7.0 to 8.5). Sequencing of the anti-Rh(D) H and L chains cDNAs showed a preferential use of V(H)1, V(H)3, J(H)6, and V(kappa)1 gene segments. The high pIs in IEF were correlated with a higher number of cationic amino acid residues in the H chain V regions without clustering in the complementary determining region. Computer analysis indicated that the germline V(H) used in anti-Rh(D) was selected among the most cationic segments available in the human V(H) repertoire or expressed in normal B cells. These results indicate that the selection of cationic V(H) segments may be an important early step in the formation of clinically relevant anti-Rh(D) and other red cell antibodies, possibly to facilitate epitope binding in the negatively charged red cell membrane environment.

Direct agglutination of weak D red cells by tetramolecular complexes containing monoclonal IgG anti-D.

The capacity of blood group antibodies to agglutinate red cells suspended in saline is largely dependent on the antibody isotype. The immunological cross-linking of IgG antibodies has previously been described as a means to increase the reactivity of IgG in many situations. We have prepared anti-D-containing complexes by blending a human IgG anti-D monoclonal antibody (mAb) and a murine anti-human IgG mAb. In standard red cell serology assays, the anti-D complexes exhibited a very high avidity and could agglutinate weak D-positive red cells in direct saline testing. These results indicate that potent saline hem-agglutinating reagents of RhD and eventually of other blood group specificities can be prepared from IgG mAbs.

Characterization and large production of human monoclonal antibodies against the HIV-1 envelope.

Peripheral blood lymphocytes from a volunteer immunized with a recombinant vaccinia virus VSC-25 expressing the gp160 env protein of HTLV-IIIB strain and from an asymptomatic HIV-infected individual were immortalized by Epstein-Barr (EBV). Clones which secrete human monoclonal antibodies from the two individuals (DZ, IgG1, lambda and C31, IgG1, kappa) were obtained and were stable for more than 2 years. The two monoclonals were directed against the gp160 env protein of HIV, DZ directed against the gp41 and C31 directed against the gp120. C31 was group-specific, whereas DZ was directed against the HTLV-IIIB and HTLV-RF strains. The epitope recognized by DZ was mapped to the carboxy terminus of the gp41, by expression of HIV DNA fragments in a yeast system and peptide analysis. The C31 epitope was not expressed by the yeast library and not present among the peptides which were tested. Monoclonal antibodies had no inhibitory effect in an HIV-induced cell fusion assay, but DZ showed a weak neutralizing activity against the HTLV-IIIB strain. Cloned EBV-transformed cell lines were fused to a murine myeloma, which allowed the heteromyeloma to be cultivated in serum-free medium. The monoclonal antibodies were produced in large quantity in a hollow-fibre reactor at defined culture conditions and purification procedures.

Detection of HIV-1 infections by PCR: evaluation in a seropositive subject population.

To study the polymerase chain reaction (PCR) performance in detecting human immunodeficiency virus (HIV) infections, we tested 53 HIV-1 seropositive patients and 29 HIV-1 seronegative subjects for four different HIV-1 DNA regions. Fifty-one seropositive patients were found positive by PCR with at least one primer pair, but two were repeatedly negative for all primers. Weekly blood samples from 12 seropositive subjects all detected positive for at least one primer pair, but for three patients an irregular primer detection pattern was found. One additional HIV-1 seropositive sample, found negative for HIV DNA, was also negative for the beta-globin PCR control. The 29 seronegative specimens were HIV-1 DNA negative, as was a HIV-2 seropositive patient. This study demonstrates that PCR is almost as good as serological tests for detecting HIV infections, with a specificity of 100% and a sensitivity of 96% and that resampling the patients may improve detection performance.

Survival of human monoclonal anti-Rho (D) antibodies in the rhesus monkey.

In vivo half-life of a 125I-labeled human anti-D monoclonal antibody (mAb) and that of 131I-labeled Rho-GAM was assessed in a rhesus monkey injected simultaneously with both reagents. The half-life of the mAb was 7.9 days, compared to 17 days of Rho-GAM. Survival of the second dose of mAb, given 34 days after the first injection, was identical to that of the first dose, thus showing that the human mAb did not elicit an immune response. The in vitro produced human mAbs appear to be an alternative, unlimited source of anti-D antibodies for possible use in prevention of feto-maternal Rh immunization.

Polyreactivity of human monoclonal antibodies: human anti-Rh monoclonal antibodies of IgM isotype are frequently polyreactive.

The specific aim of this study was to characterize human anti-Rh monoclonal antibodies cross-reacting with self-antigens. We studied supernatants from man-mouse hybridomas and from lymphoblastoid cell lines. Man-mouse hybridomas were established by fusion of peripheral blood lymphocytes from healthy individuals recently immunized against Rh alloantigens, with mouse myeloma (or man-mouse heteromyeloma) cell lines. Lymphoblastoid cell lines were produced by Epstein-Barr virus induction of lymphocytes from identical sources. Of the 55 monoclonal alloantibodies studied, 11 also reacted with intracellular self-antigens as demonstrated by immunofluorescence assay on cryostat sections of human tissues. This cross-reactivity was mainly a property of monoclonal alloantibodies belonging to the IgM isotype (among the 11 cross-reacting mAbs 10 were IgM). The cross-reactivities of these monoclonal antibodies were ascertained by absorption of alloreacting antibodies with red blood cells. Similar results were obtained on a panel of purified cellular antigens by ELISA. The results confirm that during an immune response against a foreign antigen (alloantigen), B cells that produce polyreactive antibodies are not excluded from the pool of responding cells. Therefore, polyreactive autoantibodies present in sera from healthy individuals may be the result of an immune response against foreign antigens.

Human monoclonal anti-D-induced clearance of human D-positive red cells in a chimpanzee model.

Two human monoclonal anti-Rh0(D) antibodies, one IgG1, and one IgG3, were tested for their ability to clear human D-positive red blood cells (RBCs) from chimpanzee circulation. Human RBCs (phenotype A1, R1r) from 1 donor were radiolabelled with chromium 51 and injected into 4 chimpanzees. One day later the control animal received isotonic saline whereas 2 animals received 400 micrograms of purified human monoclonal anti-D, either IgG1 or IgG3. The remaining animal received both antibodies together (200 micrograms of IgG1 and 200 micrograms of IgG3). Both individual antibody-mediated clearance of human D-positive cells and synergy was not observed when both antibodies were used in combination. IgG1 was slightly more effective than IgG3. This animal model is a suitable alternative for conducting in vivo experiments in human beings, especially at the preclinical study phase of monoclonal anti-D antibodies.