Identification of a novel cell type in peripheral lymphoid organs of mice. V. Purification of spleen dendritic cells, new surface markers, and maintenance in vitro

Dendritic cells (DCs; 1) have been purified from mouse spleen in good yield. Spleen cell suspensions were floated on dense bovine plasma albumin (BPA) columns, and the low density fraction was adhered to glass (2). The adherent cells consisted of DCs and immature macrophages most of which eluted in a viable state from the culture dish after overnight incubation. The macrophages were then removed by selective rosetting with opsonized erythrocytes and recentrifugation on dense BPA. This protocol resulted in a purified DC fraction, containing 1--3 X 10(5) DCs/spleen, which was homogeneous and distinctive in its properties. All cells exhibited the phase contrast and transmission electron microscopy (EM) cytologic features that were previously described for freshly isolated adherent DCs. By scanning EM, most purified DCs exhibited a remarkable array of bulbous protrusions of varying length and shape, unlike any other lymphoid cell. All DCs expressed surface Ia and other major histocompatibility complex (MHC)-linked alloantigens. DCs, however, lacked surface Ig and T-cell antigens, and did not bind or interiorize opsonized erythrocytes. Purified DCs have been maintined in vitro for 3 days. Recovery of cultured purified cells was 70% or more of starting cell numbers. When [3H]uridine-tagged DCs were mixed with nonlabeled heterogeneous spleen cells, 70--80% of the labeled DCs were recovered as viable cells 2--3 days later. Purified DCs did not readhere to tissue culture surfaces and did not proliferate, even when cultured with mitogenic doses of concanavalin A and lipopolysaccharide. Finally, DCs did not change their cytologic or surface properties after 3 days of culture. These observations extend the evidence that DCs are a novel cell type and provide useful properties and techniques for their further study.

HLA-C is the inhibitory ligand that determines dominant resistance to lysis by NK1- and NK2-specific natural killer cells

Natural killer (NK) cells recognize alloantigens on normal cells. One of these alloantigens correlates with homozygosity for a dimorphism of HLA-C at positions 77-80, which is shared by a number of HLA-C alleles. A second allelic alloantigen correlates with homozygosity for the alternative HLA-C dimorphism, which is shared by the remaining HLA-C alleles. Moreover, NK1- and NK2-specific NK cell lines can be generated by mixed leukocyte cultures in which donor and stimulator are homozygous for the alternative dimorphisms at positions 77-80 of HLA-C. In the present work, the role of HLA-C in NK cell-mediated allorecognition was directly investigated by analyzing the effects produced by transfection of several HLA-C alleles on NK sensitivity of class I-deleted mutant cell lines. Transfection of cells with HLA-C alleles encoding Asn-77-Lys-80 (including HLA-Cw4, -Cw5, and -Cw6) inhibited the lysis of the targets by NK1-specific NK cells, whereas HLA-C alleles encoding Ser-77-Asn-80 (including HLA-Cw1, -Cw7, and -Cw13) protected the targets from NK2-specific NK cells. Thus, HLA-C alleles are the dominant inhibitory ligands that protect targets from lysis by these allospecific NK cells.

The human platelet alloantigens, PlA1 and PlA2, are associated with a leucine33/proline33 amino acid polymorphism in membrane glycoprotein IIIa, and are distinguishable by DNA typing

The human platelet alloantigens, PlA1 and PlA2, comprise a diallelic antigen system located on a component of the platelet fibrinogen receptor, membrane glycoprotein (GP) IIIa. Of the known platelet alloantigens, PlA1, which is carried by 98% of the caucasian population, appears to be the alloantigen that most often provokes neonatal alloimmune thrombocytopenic purpura and posttransfusion purpura. The structural features of the GPIIIa molecule responsible for its antigenicity are as yet unknown. Using the polymerase chain reaction (PcR), we amplified the NH2-terminal region of platelet GPIIIa mRNA derived from PlA1 and PlA2 homozygous individuals. Nucleotide sequence analysis of selected amplified cDNA products revealed a C in equilibrium T polymorphism at base 196 that created a unique Nci I restriction enzyme cleavage site in the PlA2, but not the PlA1 form of GPIIIa cDNA. Subsequent restriction enzyme analysis of cDNAs generated by PcR from 10 PlA1/A1, 5 PlA2/A2, and 3 PlA1/A2 individuals showed that Nci I digestion permitted clear discrimination between the PlA1 and PlA2 alleles of GPIIIa. All PlA2/A2 individuals studied contain a C at base 196, whereas PlA1 homozygotes have a T at this position. This single base change results in a leucine/proline polymorphism at amino acid 33 from the NH2-terminus, and is likely to impart significant differences in the secondary structures of these two allelic forms of the GPIIIa molecule. The ability to perform DNA-typing analysis for PlA phenotype may have a number of useful clinical applications, including fetal testing and determination of the phenotype of severely thrombocytopenic individuals.

Alloantigen-specific regulatory T cells generated with a chimeric antigen receptor

Adoptive immunotherapy with regulatory T cells (Tregs) is a promising treatment for allograft rejection and graft-versus-host disease (GVHD). Emerging data indicate that, compared with polyclonal Tregs, disease-relevant antigen-specific Tregs may have numerous advantages, such as a need for fewer cells and reduced risk of nonspecific immune suppression. Current methods to generate alloantigen-specific Tregs rely on expansion with allogeneic antigen-presenting cells, which requires access to donor and recipient cells and multiple MHC mismatches. The successful use of chimeric antigen receptors (CARs) for the generation of antigen-specific effector T cells suggests that a similar approach could be used to generate alloantigen-specific Tregs. Here, we have described the creation of an HLA-A2-specific CAR (A2-CAR) and its application in the generation of alloantigen-specific human Tregs. In vitro, A2-CAR-expressing Tregs maintained their expected phenotype and suppressive function before, during, and after A2-CAR-mediated stimulation. In mouse models, human A2-CAR-expressing Tregs were superior to Tregs expressing an irrelevant CAR at preventing xenogeneic GVHD caused by HLA-A2+ T cells. Together, our results demonstrate that use of CAR technology to generate potent, functional, and stable alloantigen-specific human Tregs markedly enhances their therapeutic potential in transplantation and sets the stage for using this approach for making antigen-specific Tregs for therapy of multiple diseases.

Evidence for a new segregant series of B cell antigens that are encoded in the HLA-D region and that stimulate secondary allogenic proliferative and cytotoxic responses

Five new histocompatibility antigens, designated secondary B cell or (SB) antigens, have been identified by secondary allogeneic proliferative and cytotoxic responses. The reagents used to define the SB antigents are lymphocytes primed between donors matched for all known HLA antigens. The SB antigens stimulate weak primary allogeneic proliferative responses (a mean relative response of 8%) but strong secondary proliferative responses. Strong secondary cell-mediated cytotoxicity is generated against target antigens that are distinguishable from the SB antigens defined by proliferation. Studies by direct lysis and by cold-target inhibition indicate that these target antigens are preferentially expressed on B cells relative to T cells. The SB antigens segregate with HLA, and the gene(s) encoding the SB1, 3, and 4 antigens maps centromeric to HLA-B. The SB antigens are major histocompatibility antigens not only because they are encoded by major histocompatibility complex (MHC) genes, but also by the functional criteria that the proliferative and cytotoxic responses to SB antigens are not restricted by HLA-DR or HLA-A,-B. Parallel studies of the SB antigens and the DR antigens with respect to: (a) their preferential expression on B cells, (b) their function in secondary allogeneic proliferative and cytotoxic respones, and (c) the location of their structural gene within the MHC. However, the SB antigens and the DR antigens are clearly distinct antigens, because population studies indicate that they can occur independently, and family studies indicate that specific SB antigens segregate with HLA haplotypes having different D and DR specificities. Our data are consistent with the hypotheses that the SB antigens are a new segregant series of B cell alloantigens, and that the SB gene and the DR gene derive from a duplicated ancestral gene.

Peripheral human T cells sensitized in mixed leukocyte culture synthesize and express Ia-like antigens

We have studied the modulation of Ia-like antigens on the surface membrane of human T cells responding in a one-way mixed leukocyte culture. A heterologous antiserum, (anti-p23,30), which is specific to HLA-D-related antigens and which is unreactive with normal peripheral T cells or thymocytes, was found to bind significantly to all T cells transformed in mixed leukocyte culture (MLC) as determined by indirect immunofluorescence on a fluorescence-activated cell sorter 1. Furthermore, cytotoxic T cells responsible for cell-mediated lympholysis were shown to react with anti-p23,30, whereas their unactivated progenitors did not. Immunoprecipitation and sodium dodecyl sulfate polyacrylamide gel electrophoresis of a radioactive 29,000 and 34,000 dalton complex from MLC-primed T cells labeled with [35S]methionine indicated that allosensitized T cells synthesized these HLA-D-related antigens.

T-T-cell interactions during the vitro cytotoxic allograft responses. I. Soluble products from activated Lyl+ T cells trigger autonomously antigen-primed Ly23+ T cells to cell proliferation and cytolytic activity

Secondary murine cytotoxic T lymphocyte responses from alloantigen-primed T cells can be induced in vitro by apparently unrelated regimens, such as addition of either concanavalin A (Con A), conditioned medium from Con A stimulated lymphocyte cultures, conditioned medium from secondary mixed lymphocyte cultures (MLC), or stimulator cells sharing only the I-region with the stimulating cells used for primary sensitization. We now report that upon polyclonal (Con A), or antigen-specific (MLC) stimulation, Lyl+ T cells release a factor, which in turn triggers alloantigen primed Ly23+ T cells to proliferation and cytolytic activity. The secondary cytotoxic T lymphocyte inducing factor (SCIF) is produced within 24 h. For its production, an intact protein metabolism, not DNA metabolism, is required. Once induced, the functional activity of SCIF is nonspecific and not H-2 restricted. SCIF allows exponential growth and long-term propagation of cytolytic Ly23+ T cells with specificity to alloantigens used for primary sensitization. SCIF induced activation of alloantigen primed Ly23+ T cells does not require the presence of alloantigens. The results therefore reveal a process by which Lyl+ T-cell-derived nonspecific factor(s) induce autonomously Ly23+ T-cell-mediated, antigen-specific, cytotoxic T lymphocyte responses.

Genetics of ABO, H, Lewis, X and related antigens

The present knowledge on chemical, enzymatic, serologic and genetic aspects of ABH antigens is reviewed in an effort to produce a simple and coherent genetic model for the biosynthesis of these antigens and chemically related structures. The genetic control of type 1 (Le(a), Le(b), Le(c) and Le(d)), type 2 (X, Y, I, and H), type 3 and type 4 ABH and related antigens in different animal and human tissues is analyzed, taking into account the properties of the glycosyltransferases which are involved in their synthesis and considering possible competition for common acceptor and donor substrates. The phylogeny of ABH determinants shows that they appeared as tissular antigens much earlier than as red cell antigens. The ontogeny of ABH antigens suggests that they behave as differentiation antigens, and an effort is made to correlate their tissular distribution in the adult with the embryological origin of each tissue.

Two distinct types of helper T cells involved in the secondary antibody response: independent and synergistic effects of Ia- and Ia+ helper T cells

We have described here two distinct types of carrier-specific helper T cells which act independently and synergistically to augment the B-cell response to a hapten. They are separable by passage through a nylon wool column. The first type of helper T cell, which we designate as Th1, is nylon nonadherent, and can help the response of hapten-primed B cells only if the haptenic and carrier determinants are present on a single molecule (cognate interaction). The second type of helper T cell, Th2, adheres to the nylon wool column, and can help the B-cell response to a hapten coupled to a heterologous carrier upon stimulation with unconjugated relevant carrier (polyclonal interaction). The addition of a small number of Th2 to the mixture of Th1 and B cells significantly augmented the net response to the hapten carrier conjugate. Both Th1 and Th2 cells belong to the Lyt-1+,2-,3- subclass. Th1 has no detectable Ia antigen, whereas Th2 is killed by certain anti-Ia antisera and complement. The Ia antigen detected on Th2 was found to be controlled by a locus in the I-J subregion. The results clearly established the fact that there are two distinct pathways in the T- and B-cell collaboration, which involves two different subsets of carrier-specific helper T cells.

Autoreactive B cells in the marginal zone that express dual receptors

Allotype and isotype exclusion is a property of most lymphocytes. The reason for this property is not known but it guarantees a high concentration of a single receptor, and threshold numbers of receptors may be required for efficient positive and negative selection. Receptor editing compromises exclusion by sustaining recombination even after a functional receptor is formed. Consequently, B cells expressing multiple receptors arise. We have studied such B cells in which one of the two receptors is anti-self, and find that these partially autoreactive B cells accumulate in the marginal zone. The restriction of these cells in this location may help to prevent them from undergoing diversification and developing into fully autoreactive B cells.

A DNA-RFLP typing system that positively identifies serologically well-defined and ill-defined HLA-DR and DQ alleles, including DRw10

A single enzyme/multiple probe system of HLA-DR and DQ typing using restriction fragment-length polymorphism (RFLP) analysis is presented. TaqI-digested genomic DNAs are hybridized sequentially with short DR beta, DQ beta, and DQ alpha cDNA probes. The DR beta probe discriminates between the DR allelic specificities DR1 to DRw14, with the two exceptions of some DR3/DRw13 and some DR7/DRw9 combinations. We describe the positive identification of a DRw10-specific RFLP and demonstrate its segregation in families. The DQ beta probe defines an allelic system that identifies the alleles DQw1, DQw2, and DQw3. This permits the resolution of DR3/DRw13 and DR7/DRw9 alleles by defining the DR/DQ association caused by linkage disequilibrium. The DQ alpha probe defines another allelic series interrelated with, but independent from, the DQ beta series. Specific DQ beta/DQ alpha RFLP combinations correlate with known Dw splits of DR2, DRw6, and DR7. Combined use of the three probes permits the identification of HLA-DR, DQ, and certain Dw specificities and provides an effective and easily interpretable system for major histocompatibility complex class II allogenotyping.

A T-cell epitope encoded by a subset of HLA-DPB1 alleles determines nonpermissive mismatches for hematologic stem cell transplantation

The importance of HLA-DPB1 matching for the outcome of allogeneic hematologic stem cell (HSC) transplantation is controversial. We have previously identified HLA-DPB1*0901 as a target of cytotoxic T cells mediating in vivo rejection of an HSC allograft. Here we show that HLA-DPB1*0901 encodes a T-cell epitope shared by a subset of DPB1 alleles that determines nonpermissive mismatches for HSC transplantation. Several T-cell clones obtained from the patient at the time of rejection showed HLA-DP restricted recognition of allogeneic targets expressing HLA-DPB1*0901, *1001, *1701, *0301, *1401, and *4501, but not other alleles. Based on these findings, we developed an algorithm for prediction of nonpermissive HLA-DPB1 mismatches. Retrospective evaluation of 118 transplantations showed that the presence of nonpermissive HLA-DPB1 mismatches was correlated with significantly increased hazards of acute grade II to IV graft-versus-host disease (HR = 1.87, P =.046) and transplantation-related mortality (HR = 2.69, P =.027) but not relapse (HR = 0.98, P =.939), as compared with the permissive group. There was also a marked but statistically not significant increase in the hazards of overall mortality (HR = 1.64, P =.1). These data suggest that biologic characterization of in vivo alloreactivity can be a tool for definition of clinically relevant nonpermissive HLA mismatches for unrelated HSC transplantation.

Fc gamma receptor III on human neutrophils. Allelic variants have functionally distinct capacities

As a model system to explore the functional consequences of structural variants of human Fc gamma receptors (Fc gamma R), we have investigated Fc gamma R-mediated phagocytosis in relation to the NA1-NA2 polymorphism of Fc gamma RIII (CD16) on neutrophils (Fc gamma RIIIPMN). The neutrophil-specific NA antigen system is a biallelic polymorphism with codominant expression demonstrating a gene dose effect with the anti-NA1 MAb CLB-gran 11 in a large donor population. To explore the impact of this allelic variation of Fc gamma RIIIPMN on phagocytosis, we used two Fc gamma RIII-dependent probes, IgG-sensitized erythrocytes (EA) and concanavalin. A-treated erythrocytes (E-ConA). Comparison of Fc gamma R-mediated phagocytosis by PMN from NA1 subjects and from NA2 subjects showed lower levels of phagocytosis of both probes by the NA2 individuals. The difference was most pronounced with lightly opsonized EA: at the lowest level of sensitization the phagocytic index was 72% lower for NA2 donors, whereas at the highest level of sensitization it was 21% lower (P less than 0.003). Blockade of Fc gamma RII with MAb IV.3 Fab amplified by threefold the difference between NA1 and NA2 donors. NA1 and NA2 individuals had identical phagocytic capacities for the non-Fc gamma RIII probes, serum-treated and heat-treated zymosan. These individuals did not show differential quantitative cell surface expression of Fc gamma RIIIPMN measured by a panel of anti-CD16 MAb (3G8, CLB FcR-gran 1, VEP13, BW209/2) and by Scatchard analysis of 125I-IgG dimer binding. The difference in Fc gamma R-mediated phagocytosis was not explicable on the basis of differential collaboration of Fc gamma RIIIPMN alleles with Fc gamma RII, since (a) the difference in phagocytic capacity between NA1 and NA2 individuals was readily apparent with the E-ConA probe (which is independent of Fc gamma RII) and (b) the difference in phagocytosis of EA was magnified by Fc gamma RII blockade. The demonstration that allelic polymorphisms in Fc gamma R can have significant consequences for physiological functions implies that within the structural complexity of human Fc gamma Rs, including both allelic forms and cell type-specific isoforms, there will be differences in quantitative, and perhaps qualitative, function with potential importance for disease processes.

Ia-bearing T lymphocytes in man. Their identification and role in the generation of allogeneic helper activity

The presence of Ia-like antigens was demonstrated on a small population (2-6%) of highly purified human circulating T lymphocytes by immunofluorescence with a rabbit anti-Ia serum raised against the isolated bimolecular Ia structure. The Ia+ T lymphocytes have no surface or intracellular immunoglobulins. The expansion of this Ia+ T-cell population was encountered in certain patients. Ia antigens were also found on T blasts grown in long-term cultures with conditioned medium generated by phytohemagglutinin-stimulated lymphocytes. In addition, leukemia blasts which stained for Ia antigens and formed E rosettes were identified in the peripheral blood of two leukemic patients. This evidence further supports the existence of Ia-bearing T cells in man. The Ia+ T-lymphocyte population was shown to contain cells responsible for the generation of allogeneic helper activity. Elimination of Ia+ lymphocytes from a purified T-cell population by the anti-Ia antiserum and complement abolished its ability to help an allogeneic B-cell preparation to generate plaque-forming cells against sheep erythrocytes in vitro in the presence of the antigen.

Ia antigen-bearing B cell tumor lines can present protein antigen and alloantigen in a major histocompatibility complex-restricted fashion to antigen-reactive T cells

Several Ia-positive BALB/c B cell tumor lines were screened for their ability to present alloantigen and protein antigens to alloreactive and antigen-reactive T cells. Of six Ia-positive tumor lines studied, three were found to be effective as antigen presenting cells (APC). Indeed, on a per cell basis, one of the stimulatory lines, A20.3, was substantially more effective than whole spleen cells. The other three lines, although Ia-positive, were nonstimulatory. A20.3 was chosen for further study. This tumor appeared to behave like the conventional APC because (a) the tumor cells presented alloantigen, (b) they presented protein antigen in an MHC-restricted fashion to both primed donor T cells and to long-term continuous T cell lines, (c) alloantigen presentation was blocked by the inclusion of an anti-Ia antibody in the culture system, and (d) A20.3 cells could be effectively pulsed with antigen, although the continuous presence of antigen in the culture system resulted in a superior response. The addition of an exogenous source of interleukin 1 proved necessary to obtain an alloreactive but not an antigen-specific T cell response, although its inclusion did enhance the magnitude of antigen-stimulated proliferation. These tumor cells should prove useful in studying the biochemical events that occur during antigen processing and the requirements for T cell triggering by processed antigen in association with Ia molecules.

KIR ligands and prediction of relapse after unrelated donor hematopoietic cell transplantation for hematologic malignancy

Recurrent malignancy remains a significant complication after allogeneic hematopoietic cell transplantation (HCT). Efforts to decrease relapse have included donor lymphocyte infusion to stimulate donor anti-recipient T-cell allorecognition of major and minor histocompatibility differences. Recently, alloreactive effects of donor natural killer cell-mediated inhibitory killer immunoglobulin-like receptor (KIR) recognition of recipient HLA-C and -B ligands have been described. We examined KIR ligand effects on risk of relapse in 1770 patients undergoing myeloablative T-replete HCT from HLA-matched or -mismatched unrelated donors for the treatment of myeloid and lymphoid leukemias. KIR ligands defined by HLA-B and -C genotypes were used to determine donor-recipient ligand incompatibility or recipient lack of KIR ligand. Among HLA-mismatched transplantations, recipient homozygosity for HLA-B or -C KIR epitopes predicted lack of KIR ligand and was associated with a decreased hazard of relapse (hazard ratio, 0.61; 95% confidence interval, .043-0.85; P = .004). Absence of HLA-C group 2 or HLA-Bw4 KIR ligands was associated with lower hazards of relapse (hazard ratio, 0.47; 95% confidence interval, 0.28-0.79, P = .004; hazard ratio, 0.56; 95% confidence interval, 0.33-0.97; P = .04, respectively). The decrease in hazard of relapse in patients with acute myelogenous leukemia was similar to that in patients with chronic myelogenous leukemia and acute lymphoblastic leukemia (P = .95). Recipient homozygosity for HLA-B or -C epitopes that define KIR ligands is likely to be a predictive factor for leukemia relapse after myeloablative HCT from HLA-mismatched unrelated donors. This effect was not observed in HLA-identical unrelated transplants.

Qat-4 and Qat-5, new murine T-cell antigens governed by the Tla region and identified by monoclonal antibodies

Two new lymphocyte antigens, provisionally designated Qat-4 and Qat-5 have been identified with two different hybridoma-derived, monoclonal AKR antiC57BL/6 antibodies. These antigens are governed by genes located to the right (distal) end of the H-2 complex, within the Qa-2,3 region. Qat-4 and Qat-5 antigens which do not seem to be identical with Qa-2,3 or TL antigens are absent from Ig/ lymphocytes and thymocytes. They are only present on a fraction of peripheral T cells. Thus, Qat-4 is expressed on 70%, and Qat-5 on 30% of splenic and lymph node T cells, Qat-4 is also found on the majority of Ig- cells from athymic nude mice. These findings illustrate the complexity of the chromosome segment between the H-2D and Tla loci and they emphasize the role of major histocompatibility complex-associated genes for the differentiation of T cells into different subpopulations with possibly distinct immunologic functions.

Large scale identification of human hepatocellular carcinoma-associated antigens by autoantibodies

Autoantibodies are often detected in hepatocellular carcinoma (HCC), and these responses may represent recognition of tumor Ags that are associated with transformation events. The identities of these Ags, however, are less well known. Using serological analysis of recombinant cDNA expression libraries (SEREX) from four HCC patients, we identified 55 independent cDNA sequences potentially encoding HCC tumor Ags. Of these genes, 15 are novel. Two such proteins, HCA587 and HCA661, were predominantly detected in testis, but not in other normal tissues, except for a weak expression in normal pancreas. In addition to HCC, these two Ags can be found in cancers of other histological types. Therefore, they can be categorized as cancer-testis (CT) Ags. Two other Ags (HCA519 and HCA90) were highly overexpressed in HCC and also expressed in cancer cell lines of lung, prostate, and pancreas, but not in the respective normal tissues. Four other Ags were identified to be expressed in particular types of cancer cell lines (HCA520 in an ovarian cancer cell line, HCA59 and HCA67 in a colon cancer cell line, HCA58 in colon and ovarian cancer cell lines), but not in the normal tissue counterpart(s). In addition, abundant expression of complement inactivation factors was found in HCC. These results indicate a broad range expression of autoantigens in HCC patients. Our findings open an avenue for the study of autoantigens in the transformation, metastasis, and immune evasion in HCC.

HLA-DRw52a is involved in alloimmunization against PL-A1 antigen

The alloimmunization against the platelet PL-A1 antigen is strongly associated with a HLA class II structure in mothers of thrombocytopenic neonates. Most of the immunized women have first been shown to possess the DR3 specificity and subsequently the DRw52 allele. The 18 immunized mothers studied here by restriction fragment length polymorphism analysis had the DRw52a specificity at the DRB3 locus whatever their HLA-DRB1 gene product. This finding strongly suggests that the DRB3 chain is directly involved in the presentation of the PL-A1 antigen to the specific T cell. In addition, the similarities between DR3 and DRw52 structures due to a hypothetical gene conversion event should be considered in order to understand the high frequency of DR3 among the DRw52a-responding women. Alternatively, the high frequency of DR3 among the DRw52-responding mothers might be due to the high responder status associated with the former specificity.

Carcinoembryonic antigens: alternative splicing accounts for the multiple mRNAs that code for novel members of the carcinoembryonic antigen family

The recent cloning of complete cDNAs encoding carcinoembryonic antigen (CEA) and non-specific cross-reacting antigen has revealed the existence of a new gene family belonging to the immunoglobulin gene superfamily. We have reported the isolation of a partial CEA cDNA and of L-cell transfectant cell lines that express human antigens cross-reactive with commercial antibodies directed to native CEA (Kamarck, M., J. Elting, J. Hart, S. Goebel, P. M. M. Rae, J. Nedwin, and T. Barnett. 1987. Proc. Natl. Acad. Sci. USA. 84:5350-5354). In this study, we describe the identification and cloning of 3.9-, 3.7-, 2.2-, and 1.8-kb cDNAs and a 23-kb genomic transcription unit, which code for new members of the CEA gene family. DNA sequence analysis of these cloned DNAs establishes the existence of a set of four alternatively spliced mRNAs which are expressed in several tumor cell lines, in human fetal liver, and in L-cell transfectants. Deduced amino acid sequences of the encoded isoantigens show extensive similarity to CEA and nonspecific cross-reacting antigens, but in addition demonstrate transmembrane and cytoplasmic domains. We designate members of this antigen family transmembrane CEAs. The transmembrane CEA isoantigens share general structural characteristics with members of the immunoglobulin gene superfamily and can be specifically compared to the cell adhesion molecules, N-CAM (neural cell adhesion molecule) and MAG (myelin-associated glycoprotein).

Expression of the developmental I antigen by a cloned human cDNA encoding a member of a beta-1,6-N-acetylglucosaminyltransferase gene family

The blood group i/I antigens were the first identified alloantigens that display a dramatic change during human development. The i and I antigens are determined by linear and branched poly-N-acetyllactosaminoglycans, respectively. In human erythrocytes during embryonic development, the fetal (i) antigen is replaced by the adult (I) antigen as a result of the appearance of a beta-1,6-N-acetylglucosaminyltransferase, the I-branching enzyme. Here, we report the cDNA cloning and expression of this branching enzyme that converts linear into branched poly-N-acetyllactosaminoglycans, thus introducing the I antigen in transfected cells. The cDNA sequence predicts a protein with type II membrane topology as has been found for all other mammalian glycosyltransferases cloned to date. The Chinese hamster ovary cells that stably express the isolated cDNA acquire I-branched structures as evidenced by the structural analysis of glycopeptides from these cells. Comparison of the amino acid sequence with those of other glycosyltransferases revealed that this I-branching enzyme and another beta-1,6-N-acetylglucosaminyltransferase that forms a branch in O-glycans are strongly homologous in the center of their putative catalytic domains. Moreover, the genes encoding these two beta-1,6-N-acetylglucosaminyltransferases were found to be located at the same locus on chromosome 9, band q21. These results indicate that the I-branching enzyme represents a member of a beta-1,6-N-acetylglucosaminyltransferase gene family of which expression is controlled by developmental programs.