Production and properties of monoclonal antibodies to guinea pig Ia antigens

Production and characterization of alloantisera specific for bovine class II major histocompatibility complex antigens

Ten alloantisera defining five major histocompatibility complex (MHC) class II specificities of the bovine lymphocyte antigen (BoLA) complex were produced and characterized. Eight antisera defining four of the specificities were generated by immunizing cattle with class I compatible-class II incompatible lymphocytes. The alloantiserum defining the fifth class II specificity was produced by skin implant immunization. A pregnancy serum specific for one of the class II specificities was also identified. The class II antigens recognized by these antisera were designated 'Dx' antigens to indicate that they are BoLA-D region antigens encoded by one or more undetermined class II loci. The molecules identified by the alloantisera are heterodimers composed of a 34-kd alpha and a 26- to 28-kd beta chain, and are expressed on B-lymphocytes but not on resting T-lymphocytes. In family studies the BoLA-Dx antigens segregated in linkage with the BoLA-A locus alleles. Most of the BoLA-A alleles present in the Cornell Holstein herd at a high frequency were found to exist in gametic association with two or more serologically defined class II haplotypes. On the basis of a population study it was determined that three pairs of class I and class II alleles (w10-Dx4, w31-Dx5, and c3-Dx2) were present in the Cornell herd at significantly increased frequencies.

Targeting Melanoma Cells with Human High Molecular Weight-Melanoma Associated Antigen-Specific Antibodies Elicited by a Peptide Mimotope: Functional Effects

Human high molecular weight-melanoma associated Ag (HMW-MAA) mimics have been shown to elicit HMW-MAA-specific humoral immune responses that appear to be clinically beneficial. This finding has stimulated interest in characterizing the mechanism(s) underlying the ability of the elicited Abs to exert an anti-tumor effect. To address this question, in the present study, we have generated HMW-MAA-specific Abs by sequentially immunizing rabbits with the peptide P763.74, which mimics the HMW-MAA determinant recognized by mAb 763.74, and with HMW-MAA(+) melanoma cells. HMW-MAA-specific Abs isolated from immunized rabbits mediated cell-dependent cytotoxicity but did not mediate complement-dependent cytotoxicity of HMW-MAA(+) melanoma cells. These Abs also effectively inhibited spreading, migration and Matrigel invasion of HMW-MAA(+) melanoma cells. Besides contributing to our understanding of the role of HMW-MAA in the biology of melanoma cells, these results suggest that both immunological and nonimmunological mechanisms underlie the beneficial clinical effects associated with the induction of HMW-MAA-specific Abs in melanoma patients immunized with a HMW-MAA mimic.

Differential Immunogenicity of Two Peptides Isolated by High Molecular Weight-Melanoma-Associated Antigen-Specific Monoclonal Antibodies with Different Affinities

Peptide mimics isolated from phage display peptide libraries by panning with self-tumor-associated Ag (TAA)-specific mAbs are being evaluated as immunogens to implement active specific immunotherapy. Although TAA-specific mAb are commonly used to isolate peptide mimics, no information is available regarding the Ab characteristics required to isolate immunogenic TAA peptide mimics. To address this question, we have used mAb 763.74 and mAb GH786, which recognize the same or spatially close antigenic determinant(s) of the human high m.w.-melanoma-associated Ag (HMW-MAA), although with different affinity. mAb 763.74 affinity is higher than that of mAb GH786. Panning of phage display peptide libraries with mAb 763.74 and mAb GH786 resulted in the isolation of peptides P763.74 and PGH786, respectively. When compared for their ability to induce HMW-MAA-specific immune responses in BALB/c mice, HMW-MAA-specific Ab titers were significantly higher in mice immunized with P763.74 than in those immunized with PGH786. The HMW-MAA-specific Ab titers were markedly increased by a booster with HMW-MAA-bearing melanoma cells, an effect that was significantly higher in mice primed with P763.74 than in those primed with PGH786. Lastly, P763.74, but not PGH786, induced a delayed-type hypersensitivity response to HMW-MAA-bearing melanoma cells. These findings suggest that affinity for TAA is a variable to take into account when selecting mAb to isolate peptide mimics from a phage display peptide library.

Structural relatedness of distinct determinants recognized by monoclonal antibody TP25.99 on beta 2-microglobulin-associated and beta 2-microglobulin-free HLA class I heavy chains

The association of HLA class I heavy chains with beta2-microglobulin (beta2m) changes their antigenic profile. As a result, Abs react with either beta2m-free or beta2m-associated HLA class I heavy chains. An exception to this rule is the mAb TP25.99, which reacts with both beta2m-associated and beta2m-free HLA class I heavy chains. The reactivity with beta2m-associated HLA class I heavy chains is mediated by a conformational determinant expressed on all HLA-A, -B, and -C Ags. This determinant has been mapped to amino acid residues 194-198 in the alpha3 domain. The reactivity with beta2m-free HLA class I heavy chains is mediated by a linear determinant expressed on all HLA-B Ags except the HLA-B73 allospecificity and on <50% of HLA-A allospecificities. The latter determinant has been mapped to amino acid residues 239-242, 245, and 246 in the alpha3 domain. The conformational and the linear determinants share several structural features, but have no homology in their amino acid sequence. mAb TP25.99 represents the first example of a mAb recognizing two distinct and spatially distant determinants on a protein. The structural homology of a linear and a conformational determinant on an antigenic entity provides a molecular mechanism for the sharing of specificity by B and TCRs.

Limited Diversity of Human scFv Fragments Isolated by Panning a Synthetic Phage-Display scFv Library with Cultured Human Melanoma Cells

To broaden the specificity of the Abs recognizing human melanoma-associated Ags (MAAs), we have isolated human single-chain fragment of the V region (scFv) fragments by panning the synthetic phage Ab library (#1) with the human melanoma cell lines S5 and SK-MEL-28. All of the isolated scFv fragments reacted with the mouse mAb defined high molecular weight melanoma-associated Ag (HMW-MAA). scFv #70 immunoprecipitates the two characteristic subunits of HMW-MAA, while scFv #28 only immunoprecipitates its large subunit. These results challenge the current view regarding the structure of HMW-MAA and indicate that it consists of two independent subunits. The human scFv fragments share some similarities with the mouse anti-HMW-MAA mAb. Like mAb 149.53 and 225.28, scFv #28 reacts with rat B49 neural cells that express a homologue of HMW-MAA. scFv #70 reacts with a determinant that is spatially close to the one identified by mAbs 149.53, VT68.2, and VT86. Besides suggesting similarities in the recognition of human melanoma cells by the mouse and human Ab repertoire, these results indicate that the Abs isolated from synthetic Ab libraries resemble those that are found in natural Ab repertoires. The restricted diversity of the scFv fragments that were isolated by panning synthetic Ab libraries with different melanoma cell lines suggests that certain Ags, like HMW-MAA, are immunodominant in vitro. This phenomenon, which parallels the in vivo immunodominance of certain Ags, implies that the antigenic profile of the cells used for panning determines the specificity of the preponderant population of isolated Abs.

Induction and functional characterization of beta2-microglobulin (beta2-mu)-free HLA class I heavy chains expressed by beta2-mu-deficient human FO-1 melanoma cells

The frequent loss of beta2-microglobulin (beta2-mu) in malignant cells has stimulated interest in the functional characteristics of beta2-mu-free HLA class I heavy chains, since this information contributes to assess the impact of beta2-mu abnormalities on the interaction of malignant cells with immune cells. Therefore, the present study has investigated the ability of beta2-mu-free HLA class I heavy chains to modulate NK cell-mediated lysis of melanoma cells and to present melanoma-associated antigen (MAA)-derived peptides to HLA class I-restricted, MAA-specific cytotoxic T lymphocytes (CTL). Beta2-mu-free HLA class I heavy chains were induced on beta2m null FO-1 cells by sequential incubation with IFN-alpha for 48 h at 37 degrees C and for 24 h at 26 degrees C. Transfection of cells with a wild-type H-2Ld gene (FO-1Ld) enhanced the induction of beta2-mu-free HLA class I heavy chains under such experimental conditions. Beta2-mu-free HLA class I heavy chains expressed on the cell membrane did not protect the B2m null FO-1 cells from NK cell-mediated lysis. Furthermore, FO-1 cells which express beta2-mu-free HLA-A2 heavy chains following transfection with a wild-type HLA-A2 gene were not lysed by HLA-A2-restricted, MAA-specific CTL lines and clones. These results indicate that association with beta2-mu is required for interaction of HLA class I molecules with NK inhibitory receptors and for peptide presentation to CTL.

Characterization of pigs transgenic for human decay-accelerating factor

BACKGROUND

To prevent the central role played by complement activation in the hyperacute rejection of pig organs transplanted into primates, pigs transgenic for human decay-accelerating factor (HDAF) have recently been produced. The data presented here extend previous immunohistochemical findings by documenting the immunological characterization and the levels of expression of HDAF in these transgenic pigs.

METHODS

Animals from 30 independently derived lines were included in this study. HDAF expression was characterized by immunoprecipitation and epitope mapping. Quantitative analysis was performed by radiometric assays followed by Scatchard analysis and by double-determinant radioimmunoassay. Deposition of iC3b on porcine aortic endothelial cells was determined by radioimmunoassay. DNA slot-blot analysis and densitometric scanning were used to evaluate HDAF transgene copy number.

RESULTS

The integrity of HDAF expressed by these transgenic pigs could be demonstrated. HDAF was present in 72% of the organs analyzed, although considerable variation in expression occurred, both between animals and within the same pig. High levels of HDAF on porcine aortic endothelial cells resulted in iC3b deposition at levels as low as that detected on human endothelial cells. Twenty-six organs expressed levels of HDAF greater than those observed in the equivalent human tissue. HDAF expression did not correlate with the number of copies of the transgene incorporated into the porcine genome.

CONCLUSIONS

Transgenic pigs, which express levels of functional HDAF even greater than those observed in humans, have successfully been produced. Pigs transgenic for human complement inhibiting molecules could represent a source of organs for future clinical xenotransplantation.

Expression and structural features of endoglin (CD105), a transforming growth factor beta1 and beta3 binding protein, in human melanoma

Human endoglin (CD105) is a member of the transforming growth factor beta (TGF-beta) receptor family that binds TGF-beta1 and -beta3, but not TGF-beta2, on human endothelial cells. Immunohistochemical analyses demonstrated that CD105 is expressed on normal and neoplastic cells of the melanocytic lineage. The anti-CD105 MAb, MAEND3, stained 50, 25 and 34% of intradermal naevi, primary and metastatic melanomas investigated, respectively, and nine out of 12 melanoma cell lines. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed that CD105 expressed by melanoma cells consists of a homodimeric protein with an apparent molecular weight of 180 and 95 kDa under non-reducing and reducing conditions. Cross-linking of 125I-labelled TGF-beta1 to melanoma cells, Mel 97, by disuccinimidyl suberate (DSS) demonstrated that CD105 expressed on pigmented cells binds TGF-beta1; the pattern of binding of TGF-beta1 to melanoma cells was found to be similar to that of human umbilical vein endothelial cells. The addition of exogenous, bioactive TGF-beta1 significantly (P<0.05) inhibited the growth of CD105-positive melanoma cells, Mel 97, but did not affect that of CD105-negative melanoma cells, F0-1. These data, altogether, demonstrate that CD105 is expressed on pigmented cells and might play a functionally relevant role in the biology of human melanoma cells by regulating their sensitivity to TGF-betas.

Characterization of anti-HLA class II monoclonal antibody LGII-612.14 reacting with formalin fixed tissues

mAb LGII-612.14 derived from a BALB/c mouse immunized with interferon-gamma (IFN-gamma) treated cultured human B lymphoid cells LG-2 has been shown with serological and immunochemical assays to recognize a monomorphic determinant expressed on the beta chain of HLA-DR, -DQ and -DP antigens. The linear nature of the determinant, which is likely to be formed by residues 19-25, is indicated by the reactivity of mAb LGII-612.14 with HLA-DR, -DQ and -DP beta chains purified by electrophoresis in presence of SDS. An unusual characteristic of mAb LGII-612.14 is its reactivity with fixed tissue sections. The intensity of staining is affected by the incubation temperature, the incubation time and the fixative used. Maximal intensity of staining of formalin fixed, paraffin embedded tissue sections required an incubation time of 16 h. The intensity of staining of paraffin embedded tissues initially fixed with Bouin's solution, formalin or ethanol was similar to that of frozen tissue sections and stronger than that of tissues fixed with B5 solution. No staining was detected of paraffin embedded tissues fixed with glutaraldehyde or Zenker's solution. Comparison of the staining patterns with mAb LGII-612.14 of frozen and fixed tissue sections showed that the latter substrates provide a superior detail of tissue architecture and cellular morphology without significant loss of sensitivity. Furthermore, comparison of the characteristics of mAb LGII-612.14 with the few previously published anti-HLA class II mAb reacting with fixed tissues indicates that mAb LGII-612.14 stains formalin fixed, paraffin embedded tissues, while mAb 910D7 and TAL-1B5 stain tissues fixed with less commonly used fixatives. Furthermore, mAb LGII-612.14 is likely to yield more sensitive staining results than anti-HLA-DR, -DQ and -DP mAb KUL/05. The present results indicate that mAb LGII-612.14 represents a useful probe to apply immunohistochemical techniques to the analysis of the distribution of HLA class II antigens in fixed tissues. This will greatly facilitate the use of readily available collections of fixed tissue specimens in retrospective studies to assess the clinical significance of changes in HLA class II antigen expression which occur in various disease states.

Anti-histone autoantibodies react specifically with the B cell surface

In an attempt to induce an immune response against Mls-1a antigens by immunizing C57B1/6 mouse (Mls-1b) with purified B cells from DBA/2 mouse (Mls-1a), we generated a panel of monoclonal antibodies from which the 5B9.6 mAb, taken as a representative antibody, was thoroughly investigated. This antibody specifically reacts with B cells from all mouse strains studied including C57Bl/6 mice as shown by FACS analysis of double-antibody labelled spleen cells. Using enzyme immunoassays and immunoprecipitation techniques, 5B9.6 mAb was found to be specific for histones. Amino acid sequence analysis of a peptide derived from a 5B9.6-immunoprecipitated polypeptide from DBA/2 B cells showed a 100% homology with a sequence within H2B histones. Furthermore, 5B9.6 mAb was able to interact with the cell surface of 7OZ/3 cell line, known as a typical pre-B cell line. The presence of histones can be modulated on the surface of 7OZ/3 cells since this antigen was upregulated after exposure of these cells to a cocktail of IL-1 and cAMP. Finally, 5B9.6 mAb was shown to interact with freshly isolated B cells from human peripheral blood.

Lack of HLA class I antigen expression by melanoma cells SK-MEL-33 caused by a reading frameshift in beta 2-microglobulin messenger RNA

The lack of HLA class I antigen expression by the melanoma cell line SK-MEL-33 is caused by a unique lesion in beta 2-microglobulin (beta 2-mu). Sequencing of beta 2-mu mRNA detected a guanosine deletion at position 323 in codon 76 that causes a frameshift with a subsequent introduction of a stop codon at a position 54 base upstream of the normal position of the stop codon in the message. The loss of 18 amino acids and the change of 6 amino acids, including a cysteine at position 80 in the carboxy terminus of beta 2-mu, are likely to cause marked changes in the structure of the polypeptide. The latter may account for the inability of beta 2-mu to associate with HLA class I heavy chains and for its lack of reactivity with the anti-beta 2-mu mAb tested. HLA class I antigen expression on SK-MEL-33 cells was reconstituted after transfection with a wild-type B2m gene, therefore indicating that the abnormality of endogenous B2m gene is the only mechanism underlying lack of HLA class I antigen expression by SK-MEL-33 cells. The guanosine deletion in B2m gene was detected also in the melanoma tissue from which SK-MEL-33 cells had originated. Therefore, the molecular lesion identified in the SK-MEL-33 melanoma cell line is not caused by a mutation acquired during growth in vitro but is likely to reflect a somatic mutation during tumor progression.

Lack of HLA class I antigen expression by cultured melanoma cells FO-1 due to a defect in B2m gene expression

The melanoma cell line FO-1 does not express HLA class I antigens and does not acquire them on the cell surface after incubation with IFN-gamma. Immunochemical studies showed that FO-1 cells synthesize HLA class I heavy chain, but do not synthesize beta 2-microglobulin (beta 2-mu). The latter abnormality is associated with lack of beta 2-mu mRNA which remains undetectable in FO-1 cells incubated with IFN-gamma. The defect was identified as a genetic lesion in the B2m gene, since DNA hybridization analysis detected a deletion of the first exon of the 5'-flanking region, and of a segment of the first intron of the B2m gene. HLA class I antigen expression was reconstituted on melanoma cells FO-1 after transfection with the wild-type mouse B2m gene, thereby confirming the abnormality of the endogenous B2m gene. The defect identified in FO-1 cells is distinct from that underlying the lack of HLA class I antigen expression by lymphoblastoid cells Daudi, but is remarkably similar to that causing lack of H-2 class I antigen expression by mouse lymphoblastoid cells R1 (TL-). These results suggest that genetic recombination in the 5' region of the B2m gene is a recurrent mechanism in B2m gene defects. In addition to contributing to our understanding of molecular abnormalities in HLA class I antigen expression by melanoma cells, FO-1 cells represent a useful model for analyzing the role of HLA class I antigens in the biology of melanoma cells and in their interaction with cells of the immune system.

Active specific immunotherapy in patients with melanoma. A clinical trial with mouse antiidiotypic monoclonal antibodies elicited with syngeneic anti-high-molecular-weight-melanoma-associated antigen monoclonal antibodies

In two clinical trials the mouse antiidiotypic monoclonal antibody (MAb) MF11-30, which bears the internal image of human high-molecular-weight-melanoma-associated antigen (HMW-MAA) was administered by subcutaneous route without adjuvants to patients with stage IV malignant melanoma on day 0, 7, and 28. Additional injections were administered if anti-antiidiotypic antibodies were not found or their titer decreased. In the first phase I trial with 16 patients the initial dose was 0.5 mg per injection and escalated to 4 mg per injection. Neither toxicity nor allergic reactions were observed despite the development of anti-mouse Ig antibodies. Minor responses were observed in three patients. In a second clinical trial MAb MF11-30 was administered to 21 patients at a dose of 2 mg per injection, since this dose had been shown in the initial study to be effective in inducing anti-antiidiotypic antibodies. Two patients were inevaluable; in the remaining 19 patients, the average duration of treatment was 34 wk. In this trial as well, neither toxicity nor allergic reactions were observed. 17 of the 19 immunized patients increased the levels of anti-mouse Ig antibodies and 16 developed antibodies that inhibit the binding of antiidiotypic MAb MF11-30 to the immunizing anti-HMW-MAA MAb 225.28. One patient increased the level of anti-HMW-MAA antibodies. One patient achieved a complete remission with disappearance of multiple abdominal lymph nodes for a duration of 95 wk. Minor responses were observed in three patients. These results suggest that mouse antiidiotypic MAb that bear the internal image of HMW-MAA may be useful reagents to implement active specific immunotherapy in patients with melanoma.

Murine antiidiotypic monoclonal antibodies that bear the internal image of HLA-DR allospecificities

Hybridization of murine myeloma cells P3-X63-Ag8.653 with splenocytes from a BALB/c mouse immunized with the syngeneic anti HLA-DR1,4,w6,w8,w9 MAb AC1.59 resulted in the development of 108 hybridomas secreting antiidiotypic antibodies. 100 of them inhibited the binding of MAb AC1.59 to target cells. Detailed analysis of the antiidiotypic MAb F5-444, F5-830, F5-963, F5-1126, F5-1336, and F5-1419 showed that all of them recognize idiotopes within or spatially close to the antigen combining site of MAb AC1.59. In cross-blocking experiments, the six antiidiotypic MAbs cross-blocked each other. It is likely that the six MAbs recognize spatially close, but not identical idiotopes because they elicited antiantiidiotypic antibodies of different or similar, but not identical specificity and differ in their ability to elicit anti-HLA class II antibodies. The latter, which were found only in sera from BALB/c mice immunized with antiidiotypic MAb F5-444 and F5-830, mimic the specificity of MAb AC1.59 and express the idiotope defined by the immunizing antiidiotypic MAb. These results indicate that the MAb F5-444 and F5-830 are antiidiotypes beta and the remaining four are antiidiotypes gamma.

Analysis of autoreactive I region-restricted T cell colonies isolated from the guinea pig syngeneic mixed leukocyte reaction and from immune responses to conventional foreign antigens

Guinea pig proliferating T cell colonies were isolated from T cell populations stimulated during the syngeneic mixed leukocyte reaction (SMLR) or following positive selection of immune T lymphocytes specific for pork insulin (PI) or the copolymer of L-glutamic acid, L-lysine (GL). SMLR-responding T cell colonies could be isolated in the absence of any extrinsic antigen and were strictly restricted to the recognition of Ia molecules on stimulator peritoneal exudate cells (PEC) and required both stimulator cells and interleukin 2-enriched fluids for optimal proliferative responses. Blocking of T cell colony proliferation with a panel of monoclonal anti-Ia antibodies showed that SMLR T cell colonies were restricted by discrete and distinct self-Ia epitopes. Analysis of individual T cell colonies generated against PI and GL revealed three types of colonies: (a) antigen specific, I region-restricted; (b) autoreactive, I region-restricted; and (c) antigen specific, but also autoreactive. These doubly reactive colonies were restricted to the same Ia epitope when stimulated with self-PEC alone or when stimulated with self-PEC in the presence of the relevant exogenous antigen. These results substantiate the hypothesis that both the SMLR and antigen-specific responses are mediated by a common set of precursor T lymphocytes and that the guinea pig SMLR is at least in part the result of the polyclonal proliferative responses of several distinct antigen-reactive T cell clones in the absence of exogenous antigen.