Recombination between an expressed immunoglobulin heavy-chain gene and a germline variable gene segment in a Ly 1+ B-cell lymphoma

The human T-cell rearranging gamma (TRG) genes and the gamma T-cell receptor

The human T-cell Rearranging Gamma genes or T-cell Receptor Gamma (TRG) chain genes, like those encoding the T-cell Receptor (TcR) alpha and beta polypeptides, undergo rearrangements specifically in T-cells. The human TRG locus which has been mapped to chromosome 7 (7p15) is composed of 2 constant region genes (TRGC), 5 joining segments (TRGJ) and at least 14 variable gamma genes (TRGV). 8 variable genes are functional and belong to 4 different subgroups. Based on restriction fragments, the TRG rearrangements can be assigned to given V and J segments, in normal T-cells, T leukemias and lymphomas. The product of the rearranged TRG gene is the gamma chain which is expressed at the surface of a subset of CD3+4-8- T lymphocytes lacking the conventional receptor alpha beta. Structural differences exist between the different 'gamma T-cell receptors', the gamma and delta polypeptides being disulfide or non-disulfide linked. Although the TRG+ cells display a cytolytic activity, their precise function remains to be elucidated.

Rearrangement and expression of T cell receptor and immunoglobulin loci in immortalized CD4-CD8- T cell lines

Injection of newborn mice with mixtures of wild-type moloney murine leukemia (Mo-MuLV) virus and other recombinant retroviruses harboring the myc oncogene alone or in combination with the H-ras oncogene resulted in a 100% incidence of lymphatic leukemias from which permanent cell lines could be established in vitro. These cells are immunoglobulin (Ig)-, Thy-1+BP- and CD8-CD4- indicating that they are early thymocytes. Such transformed pre-T lines lack retroviral myc and ras genes but occasionally possess proviral insertion near to their endogenous myc and pim genes. We show that both Ig heavy chain (Igh) and T cell receptor (TcR) genes are rearranged in most of these lines. In some cases, a primary recombination was followed by a secondary rearrangement at the same locus. We show that VT gamma genes can rearrange outside of their known cluster suggesting that TcR gamma diversification in such pre-T cells may be different to that in more mature T cells. Ig D-JH recombinations may precede TcR gene recombination in these early T cell lines, and some but not all express sterile Cmu transcripts. Some of these lines express surface heterodimers that appear composed of alpha and beta chains that can be immunoprecipitated with a monoclonal anti-T3 antibody but not with the anti-V beta 8 monoclonal antibody F23.1. This established pre-T cell line represents novel biological material for the dissection of T cell development and function analogous to A-MuLV transformed pre-B cells.

Complex rearrangements within the human J delta-C delta/J alpha-C alpha locus and aberrant recombination between J alpha segments

We have examined DNA rearrangements within a 120 kb cloned region of the human T cell receptor J delta-C delta/J alpha-C alpha locus. Three types of pattern emerge from an analysis of T cell lines and clones. Firstly, cells with two rearrangements within J delta-C delta; secondly, cells with one rearrangement within J delta-C delta and one or more J alpha rearrangements, and finally, cells with rearrangements within J alpha and consequential deletion of the delta locus. Further analysis by cloning of rearrangements within the J alpha locus show that, in addition to V alpha-J alpha joins, J alpha-J alpha aberrant recombinations occur and rearrangement data indicate that such events are frequent. A model is presented to account for such recombinations.

Comparison of T cell receptor alpha, beta, and gamma gene rearrangement and expression in T cell acute lymphoblastic leukemia

We have analyzed the configuration of the T cell receptor (TCR) alpha gene using newly developed genomic joining region (J alpha) probes, which cover approximately 80 kb of the J alpha region upstream from the constant region in 19 patients with T cell acute lymphoblastic leukemia (T-ALL) and in three CD3- leukemic T cell lines (HSB2, CEM, and MOLT4). In parallel, transcription of the TCR-alpha, beta, and gamma genes was examined in 11 of these patients and in the T cell lines. All T-ALL and the three T cell lines exhibited both TCR-gamma and beta gene rearrangements. 8 of 10 T-ALL and all T cell lines expressed TCR-gamma transcripts. All samples tested expressed both TCR-beta and CD3-gamma transcripts. TCR alpha transcripts were only observed in CD3+ T-ALL but not in CD3- T-ALL or the CD3- cell lines. Among the CD3+ T-ALL, eight had TCR-alpha gene rearrangements. In addition, TCR-alpha gene rearrangements were detected in one CD3- T-ALL and all three T cell lines. These leukemic cells may represent a transient stage between rearrangement and expression and provide an opportunity for analyzing the mechanism regulating the expression of the TCR-alpha gene.

Point mutations cause the somatic diversification of IgM and IgG2a antiphosphorylcholine antibodies

The genetic mechanism responsible for the somatic diversification of two mAbs was determined. The two PC-binding hybridomas were representative of events early and late in the immune response. The P28 cell line that produces an IgM antibody and thus represents events early in the immune response, was found to have 3 bp changes in its heavy chain variable (VH) region, with some changes in antibody affinity or specificity. The RP93 cell line that produces an IgG2a antibody and thus represents later events in the immune response, was found to have 9 bp changes in its VH region resulting in decreased affinity for PC and altered specificity. Oligonucleotides specific for linked base changes in the second hypervariable regions of both of these antibodies were used to look for previously undescribed V regions or other donor sequences that could have been responsible for these base changes. Since no donor sequences were found, we have concluded that somatic point mutation rather than gene conversion, V region replacement or the expression of an unidentified germline VH region gene is truly responsible for at least some of the somatic diversification of these antibodies.

Single cell origin of bigenotypic and biphenotypic B cell proliferations in human follicular lymphomas

To investigate the possible relatedness of the subpopulations that make up so-called biclonal lymphomas, we examined five bigenotypic and biphenotypic follicular lymphomas using DNA probes specific for the t(14;18) chromosomal translocation, which is a characteristic feature of these neoplasms. On Southern blot analysis, both subpopulations from four of five lymphomas contained comigrating t(14;18) DNA rearrangements, confirming the single cell origins for these neoplasms. No comigrating t(14;18) DNA rearrangements were observed in the fifth lymphoma, but nucleotide sequence analysis of cloned, breakpoint DNA showed identical t(14;18) crossovers in the two subpopulations. The migration differences of both the Ig and chromosome 18 DNA rearrangements were shown to result from somatically acquired mutations of the Ig genes from the fifth lymphoma. These studies indicate that Ig gene rearrangements and idiotope expression are not consistently stable clonal markers since they are subject to variability as a result of somatic mutation. Although translocated chromosome 18 DNA rearrangements are more reliable, they may also vary among cells of some tumors since somatic mutation can affect, as well, DNA of translocated alleles in follicular lymphomas.

Nonrandom TRG gamma variable gene rearrangement in normal human T cells and T cell leukemias

To estimate the extent of the TRG gamma variable (V) gene repertoire used in human T cell ontogeny, we have analyzed the variety of V gamma gene rearrangements in a large series of T and non-T acute and chronic leukemias. A limited heterogeneity of rearranged fragments was observed: only 13 types of differently rearranged fragments, four of which occurred only once, were found among 80 rearranged chromosomes. Furthermore, in the leukemic population as a whole, the frequency distribution of the most common types of rearranged V gamma gene-containing fragments appeared to be nonrandom (p less than 0.01). Of interest is the clear preference for functional vs. nonfunctional V gamma genes (nonfunctional genes being those which carry frameshifts or nonsense mutations but which presumably can still rearrange due to their conserved signal sequences). We discuss the possibilities that this preference may result either from selection of the TRG gamma product at some stage during T cell development or, alternatively, from an intrinsic, antigen-independent polarity in V gamma gene activation.

The CD5+ B cell: a B cell lineage with a central role in autoimmune disease?

It is apparent that B cells are heterogeneous with respect to, for example, the antigens they express on their surface, and the stimuli to which they can respond. It is still unclear to what extent these differences relate to the stage of differentiation (eg. virgin B cells differing from activated B cells or memory cells), or whether distinct developmental lineages might exist. It has been proposed by some authors that, in the mouse, B cells expressing the ly-1 antigen constitute a separate lineage. In man also, a minor population of B cells expresses detectable levels of the CD5 antigen, but far less information is available about these cells. Interest in the CD5+ and ly-1+ B cell subpopulations has been further stimulated by the suggestion that these cells might play a special role in autoimmune disease. Although, in mouse, ly-1+ B cells differ in several respects from ly-1- B cells, the main evidence that they form a separate lineage derives from experiments in which ly-1+ B cells could not be reconstituted with adult bone marrow. It should be borne in mind that the situation is quite different in humans where, following bone marrow transplantation, CD5+ B cells are rapidly restored. Moreover, in the irradiated mice, at least in some of the experiments ly-1+ B cells were in fact reconstituted by adult bone marrow. Furthermore, at least in humans, expression of CD5 can sometimes be induced. There is, as yet, no good evidence that human CD5+ B cells form a distinct lineage, and it is possible that CD5 expression depends upon microenvironmental influences acting on the B cell during its differentiation. Several interesting properties have been attributed to ly-1+ B cells, including the ability to provide help to other B cells, and the secretion of autocrine factors. However there is also evidence that these features are not exclusive to B cells expressing ly-1. It has also been suggested that ly-1+ B cells might be long-lived. It is not yet known whether some of the properties of ly-1+ B cells might be a direct result of their expressing this antigen; this may become more clear when the function of CD5 is elucidated. The suggestion that the repertoire of ly-1+ B cells might be biased towards the expression of certain V genes is very interesting. Many of the hybridomas from neonatal mice produce antibodies which are multi-specific, and therefore well suited to form a first line of defence against potential pathogens.(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of CD5-positive B cells in blood and synovial fluid of patients with rheumatic diseases

CD5 (OKT1, Leu-1) is an antigen originally associated only with T cells. This antigen has recently been detected on a population of B cells that have been implicated in autoimmune diseases, particularly in rheumatoid arthritis (RA). We determined the percentage of these cells in the peripheral blood (PB) and synovial fluid (SF) of patients with RA and other joint diseases (OJD) using flow cytometry and two-colour fluorescence. No significant difference was observed between the percentages of CD5-positive B cells in the PB of these two patient groups or healthy individuals. In comparison with PB, significantly higher percentages of these cells were observed in the SF of patients with RA, but not in SF of OJD patients. Higher percentages of B cells were also noted in RA SF. However, when B-cell percentages were accounted for, no significant difference was observed between the numbers of B cells expressing CD5 in SF. No correlation was observed between the percentages of CD5-positive B cells and the levels of rheumatoid factor (RF) or C-reactive protein (CRP). We conclude that CD5-positive B cells are an integral part of the B-cell pool of PB and that there is increased representation of B cells in SF. The increased percentages of B cells in RA SF, compared with OJD, may reflect the autoimmune phenomenon occurring in the rheumatoid joint.

Development of the primary antibody repertoire

The ability to generate a diverse immune response depends on the somatic assembly of genes that encode the antigen-binding portions of immunoglobulin molecules. In this article, we discuss the mechanism and control of these genomic rearrangement events and how aspects of this process are involved in generating the primary antibody repertoire.

Early restriction of the human antibody repertoire

Diversification of the antibody repertoire in mammals results from a series of apparently random somatically propagated gene rearrangement and mutational events. Nevertheless, it is well known that the adult repertoire of antibody specificities is acquired in a developmentally programmed fashion. As previously shown, rearrangement of the gene segments encoding the heavy-chain variable regions (VH) of mouse antibodies is also developmentally ordered: the number of VH gene segments rearranged in B lymphocytes of fetal mice is small but increased progressively after birth. In this report, human fetal B-lineage cells were also shown to rearrange a highly restricted set of VH gene segments. In a sample of heavy-chain transcripts from a 130-day human fetus the most frequently expressed human VH element proved to be closely related to the VH element most frequently expressed in murine fetal B-lineage cells. These observations are important in understanding the development of immunocompetence.

T-cell gamma gene is allelically but not isotypically excluded and is not required in known functional T-cell subsets

The T-cell gamma genes, structurally related to immunoglobulin genes and the T-cell antigen-receptor alpha- and beta-chain genes, undergo somatic rearrangement in T-lineage cells. However, the role of the T-cell gamma genes has not yet been determined. To determine the potential for gamma gene expression in a set of well-characterized, cloned T-cell lines, we cloned all of the rearranged gamma genes from each cell line. The genes were sequenced to determine if the junction of the variable and joining regions maintained the proper translational reading frame. We then attempted to correlate the presence of an in-frame gamma gene with a T-cell subset. We were unable to establish such a correlation. We found evidence, however, that allelic exclusion influences the rearrangement of the gamma gene. This is consistent with the idea that the gamma gene product participates in establishing a clonally diverse population of T cells recognizing a polymorphic ligand. Isotypic exclusion does not apply to the gamma gene, however, suggesting different roles for the different gamma gene isotypes.

T cell receptor gamma chain variable gene rearrangements in acute lymphoblastic leukemias of T and B lineage

The status of immunoglobulin and T cell receptor genes in acute lymphoblastic leukemia (ALL) of T and B lineage has been studied. Our data indicate that illegitimate gene rearrangements at immunoglobulin heavy chain (in T cell ALL), and T cell receptor beta chain (in pre-B ALL) genes are only rarely found (2 out of 30 patients). In contrast, T cell receptor gamma chain gene rearrangements, characteristically found in T-ALL, are also present in 7 of 18 patients with pre-B ALL. Several features distinguish these illegitimate T cell receptor gamma chain gene rearrangements from those in normal and leukemic T cells. V gamma genes located far upstream of the J gamma/C gamma complexes (V gamma 2, V gamma 3, V gamma 4, V gamma 5) appear to be preferentially used in normal adult peripheral blood T cells. In contrast, V gamma genes located immediately 5' to the J gamma/C gamma complexes (V gamma 8, V gamma 9, V gamma 10, V gamma 11) predominate in V gamma -J gamma recombinations observed in T-ALL and pre-B ALL. Whereas the J gamma 2 region is primarily used in T cell receptor gamma gene rearrangements observed in T-ALL, those in pre-B ALL are confined mostly to the J gamma 1 region. These data suggest a limited accessibility of the T cell receptor gamma chain gene locus for recombination processes in early stages of B cell differentiation.

Developmental stage specificity of the lymphoid V(D)J recombination activity

We have examined the level of immunoglobulin gene V(D)J recombination activity in a number of cell lines derived from lymphoid or nonlymphoid lineages. The assay we employed uses extrachromosomal DNA as substrate and thereby avoids difficulties associated with the use of chromosomally integrated substrates. The recombination activity decreases during B-lymphoid development. It is highest at the earliest stages of committed B-cell differentiation and then falls progressively, reaching undetectable levels at the mature B-cell stage. The activity is also present in multipotential progenitors of myeloid cells and in pre-T cells but not mature T cells. No activity was found in several nonhematopoietic cell lines. Recombination was seen only among substrate molecules which had replicated in the eukaryotic cells. Several possible interpretations of this result are discussed.

In vitro differentiation of a null-acute leukemia: T-lymphoid surface antigen expression associated with rearrangement in T-cell receptor beta chain variable genes

We describe a human acute unclassified leukemia with a unique t(4;17) translocation that coexpresses T-lymphoid and myeloid surface antigens after in vitro culture in the presence of the tumor promoter, TPA. Under these conditions, the joining regions of the immunoglobulin heavy chain and T-cell receptor gamma and beta chain complexes remained in germ line configuration. A T-cell receptor beta chain variable gene probe, however, revealed the presence of rearrangements in the V beta M3-2 gene region after bilineage differentiation. These results may be pertinent to the interrelationship of T-cell receptor gene rearrangements and the control of T-cell antigen surface expression.

Identification of a DNA binding protein that recognizes the nonamer recombinational signal sequence of immunoglobulin genes

Extracts of nuclei from B- and T-lymphoid cells contain a protein that binds specifically to the conserved nonamer DNA sequence within the recombinational signals of immunoglobulin genes. Complexes with DNA fragments from four kappa light-chain joining (J) segments have the same electrophoretic mobility. Nonamer-containing DNA fragments from heavy-chain and light-chain genes compete for binding. Within the 5'-flanking DNA of the J kappa 4 gene segment, the binding site has been localized to a 27-base-pair interval spanning the nonamer region. The binding activity is recovered as a single peak after ion-exchange chromatography. The site of binding of the protein and its presence in nuclei of lymphoid cells suggest that it may function in the assembly of immunoglobulin genes.

Recent research in organization and expression of immunoglobulin V region genes

The first Jacques Monod Conference was held in Roscoff, Brittany on 1-5 June 1987 and dealt with the topic of 'Selection of Lymphocyte Repertoires' (organizers F. W. Alt, Columbia University, New York. P.-A. Cazenave, Institut Pasteur, Paris and A. Coutinho, Institut Pasteur, Paris). Much of the meeting was concerned with the recent developments in immunoglobulin and T-cell receptor V region organization and expression. This review is based on the contributions and discussions on Ig V genes, in particular their organization, rearrangements, allelic exclusion and somatic mutation. (Names without references indicate the conference speaker on that topic.)

Circulating lymphoma cells in patients with B & T non-Hodgkin's lymphoma detected by immunoglobulin and T-cell receptor gene rearrangement

We studied peripheral blood mononuclear cells from 50 patients with active B- and T-cell non-Hodgkin's lymphoma by DNA hybridisation. Nineteen patients (38%) had circulating clones of cells detected by immunoglobulin gene rearrangement (17 patients) or T-cell receptor gene rearrangement (2 patients) with JH and J beta 2 probes. Lymphoma tissue and peripheral blood were studied simultaneously in 22 patients, 9 of which had a circulating clone of cells in peripheral blood. In 7 patients the gene rearrangement in lymphoma tissue and peripheral blood mononuclear cells was identical. However, in 2 patients both heavy chain and light chain gene rearrangements were different in tissue and peripheral blood. The incidence of peripheral blood involvement was commonest in advanced CSIII & IV disease (54%) compared to CSI & II disease (18%) (P less than 0.05), and in low grade (45%) compared to intermediate and high grade lymphoma (31%) (difference not statistically significant). Only 4 patients had definite lymphoma cells seen on peripheral blood smear. The presence of circulating lymphoma cells correlated with conventional assessment of bone marrow involvement although circulating clones were detected in 30% (12/40) of patients with apparently normal bone marrow.

Immunoglobulin heavy chain gene diversification in the long-term bone marrow culture of normal mice and mice with severe combined immunodeficiency

The change of immunoglobulin heavy (H) chain gene configuration during the differentiation of B cells from their early precursors was investigated in long-term cultures of bone marrow cells (LTBC). Hemopoietic stem cells are maintained in LTBC described by Dexter et al. (J. Cell. Physiol. 1977. 91: 335; LTBC-D), which supports the differentiation of myeloid lineage cells but not B lineage cells. By simply shifting the culture condition to that devised by Whitlock and Witte (Proc. Natl. Acad. Sci. USA 1982. 79: 3608; LTBC-B) to support the development of B lineage cells, surface IgM-bearing (sIgM+) B cells became detectable by the 2nd week after the shift and the number quickly increased thereafter, while the number of polymorphonuclear cells and granulocyte-macrophage colony-forming cell (CFU-c) decreased rapidly. H chain gene configuration of the developing cells in the culture was examined by Southern blot analysis of Eco RI-digested DNA with a JH probe. Whereas rearranged JH gene configuration was not detectable in the DNA from LTBC-D cells, it first appeared 2 weeks after the shift, and the level of the rearrangement rapidly increased thereafter as the intensity of JH band of germ-line configuration decreased. Almost all the cells in the culture had undergone H chain gene rearrangement in both chromosomes by the 6th week after the shift. During 2 to 4 weeks after the shift, a cluster of bands spanning around 4.5-5.5 kb appeared dominant among the rearranged configurations of JH gene and then it decreased in intensity as the pattern of JH band became a more homogeneous smear. The distribution of rearranged JH bands observed during 3-4 weeks after the shift was strikingly similar to that observed in normal spleen B cells. By semi-quantitative analysis of the intensity of JH and DSP2 bands remaining in germ-line configuration, it was found that the loss of germ-line JH band was far more rapid than that of germ-line DSP2 bands in the developing B cells in vitro. This result is consistent with the conclusion obtained in B cell tumor lines that D to J assembly occurred first and was followed by V to DJ assembly in this culture system. Taken together, it is likely that the process of H chain gene diversification in this culture system may represent the actual process during B cell differentiation in vivo. Differentiative capacity of bone marrow stem cells from mouse with severe combined immunodeficiency (SCID) was also analyzed in the same culture system.(ABSTRACT TRUNCATED AT 400 WORDS)

Single germline VH and V kappa genes encode predominating antibody variable regions elicited in strain A mice by immunization with p-azophenylarsonate

We have cloned and sequenced the predominant germline V kappa gene segment expressed by B cells of strain A origin that synthesize antibodies with specificity for Ars. In hybridomas synthesizing anti-Ars antibodies, this V kappa gene segment (V kappa IdCR) has been found exclusively associated with the J kappa 1 gene segment without exhibiting junctional sequence variation. Sequence comparisons of the germline V kappa IdCR gene with expressed derivatives reveals that the latter frequently contain somatically introduced amino acid replacements. Taken together with results of previous structural analyses, these results show that the predominant population of IdCR+ V regions elicited in the secondary immune response is encoded by one or two combinations of V gene segments, has little junctional diversity, and is extensively diversified by somatic mutation in both heavy and light chains.

N segment insertion and region-directed somatic hypermutation in a kappa gene of a t(2;8) chromosomal translocation

A detailed molecular analysis of both reciprocal recombination products of the variant t(2;8) chromosomal translocation of the Burkitt lymphoma derived cell line JI and their germline counterparts was carried out. The breakpoint on chromosome 8 is localized 28 kb to the 3' side of the c-myc protooncogene, the breakpoint on chromosome 2 was found to be within an aberrantly rearranged VK gene (abbreviations ref. 1). Novel features of the immunoglobulin moiety involved in this process include insertion of extra nucleotides in the V-J junction which have the characteristics of a N segment as it has been found up to now only in heavy chain and T cell receptor genes; the occurrence of somatic mutations in 8q+ and not in 2p-. These data allow a reconstruction of the course of events in the cell line JI; remarkable sequence regularities at the chromosomal breakpoints consisting of symmetrically placed dinucleotides and elements related to the hepta- and nonanucleotide recombinase recognition sequences are discussed in the context of the translocation mechanism.

Active lambda and kappa antibody gene rearrangement in Abelson murine leukemia virus-transformed pre-B cell lines

The two Abelson murine leukemia virus (A-MuLV)-transformed cell lines, BM18-4 and ABC-1, undergo immunoglobulin L-chain gene recombination during passage in tissue culture. BM18-4 cells are capable of kappa gene recombination, whereas ABC-1 cells are capable of both kappa and lambda gene recombination. The expression of H chains is apparently not necessary for continuing L chain gene recombination in either of these cells, although H-chain expression may have been involved in the initiation of L-chain gene recombination. All ABC-1 cells that have lambda gene rearrangements also display recombined kappa alleles, supporting the hypothesis that kappa and lambda gene recombination are initiated in an ordered, developmentally regulated manner in maturing B cells. However, analyses of the ABC-1 line indicate that pre-B cells that have initiated lambda gene recombination do not terminate kappa gene rearrangement. The lambda gene recombinations that occur in the ABC-1 cell line indicate that the germline order of lambda gene segments is: 5' ... V lambda 2 ... J lambda 2C lambda 2-J lambda 4C lambda 4 ... V lambda 1 ... J lambda 3C lambda 3-J lambda 1C lambda 1 ... 3'. In addition, the frequencies of lambda 1, lambda 2, and lambda 3 gene recombinations among ABC-1 cells are quite different than the frequencies of B cells producing lambda 1, lambda 2, and lambda 3 L-chains in the mouse. RS DNA recombinations also occur in the BM18-4 and ABC-1 cell lines, supporting the notion that Ig gene recombinases are involved in RS rearrangement. Recombined RS segments are infrequent among BM 18-4 cells but common among ABC-1 cells, suggesting that RS recombinational events often occur in maturing pre-B cells just before initiation of lambda gene rearrangements. This developmental timing is consistent with the hypothesis that RS recombination may be involved in the initiation of lambda gene assembly.

Somatic diversification of S107 from an antiphosphocholine to an anti-DNA autoantibody is due to a single base change in its heavy chain variable region

The S107 myeloma cell line expresses the germ-line sequence of the T15 antiphosphocholine (P-Cho) antibody, which is the major antibody made by BALB/c mice in response to P-Cho, either on a variety of bacterial polysaccharides or when attached to a protein carrier. We have previously reported that a somatic mutant of the S107 cell line produces an antibody that has lost the ability to bind P-Cho and has acquired binding for double-stranded DNA. This antibody has a substitution of an alanine for a glutamic acid at residue 35 in the heavy chain variable region. We now show that this amino acid substitution is due to a single A-C transversion, which is the only nucleotide change in the heavy and light chain variable regions. Further, it appears that this change is due to somatic mutation rather than to gene conversion.

MYC oncogene involved in a t(8;22) chromosome translocation is not altered in its putative regulatory regions

We have cloned the translocation-associated MYC gene from the Burkitt lymphoma cell line (BL2) with a t(8;22) chromosomal translocation and have determined the nucleotide sequence of the first exon and of the 3' and 5' flanking regions, where sequences with putative regulatory functions have been identified. The nucleotide sequence of the 5' flanking region, which contains regions of DNase hypersensitivity and binding sites for putative regulatory proteins, is the same as that of the normal MYC. Accordingly, mutations in these regulatory regions are not required for the transcriptional deregulation of MYC in the BL2 cell line. The nucleotide sequence of the first exon is similar to that of the normal MYC [Gazin, C., Dupont de Direchin, S., Hampe, A., Masson, J. M., Martin, P., Stehelin, D. & Galibert, F. (1984) EMBO J. 3, 383-387] and has the coding capacity for a 188-residue polypeptide. However, six nucleotide changes that occur in the middle of this reading frame could result in amino acid substitutions. We also have cloned and sequenced the t(8;22) chromosomal breakpoint that is located 10 kilobases 3' of the MYC exon 3 and near the C lambda 3 gene on chromosome 22. Sequences with homology to immunoglobulin joining signals occur close to the breakpoint both on chromosome 8 and 22, providing further evidence that the immunoglobulin joining enzymes may be involved in the recombinations associated with a variety of chromosomal translocations in B and T cells.

A new V gene expressed in lambda-2 light chains of the mouse

We have partially sequenced the light chain variable regions expressed in three IgM-producing hybridomas generated from newborn mice or from manipulated animals suppressed for IgM production. In these lines a new V gene (V-lambda-X), exhibiting less than 60% homology to any known lambda or kappa V gene, is rearranged to J-lambda-2. The light chains produced by these cells contain the lambda-2 constant domain, but are not recognized by goat antisera raised against conventional mouse lambda light chains.

Constitutive functional heterogeneity without detectable somatic mutation of antigen receptor genes in helper T cell clones: possible regulation by novel HLA class II "DY" determinants

The majority of interleukin 2-dependent HLA class II alloreactive human CD4-positive helper T-cell clones (TCC) presented the phenomenon of constitutive intraclonal heterogeneity, as reflected by limiting dilution analysis of changing frequencies of autonomously proliferative cells within the monoclonal population. Moreover, at 30-35 population doublings, these TCC lost their allospecific proliferative and helper capacity (phase I) and instead acquired strong antigen-non-specific suppressive activity (phase II). The TCR was still expressed at the same level on the cell surface. As shown by stable and identical rearrangement profiles of their T-cell receptor beta- and gamma-chain genes in both phases I and II, this constitutive change of function was probably not due to somatic mutation of the genes coding for the antigen-specific receptor. Moreover, antigen specific reactivity was retained in phase II TCC by the criterion of specifically stimulated secretion of granulocyte/macrophage colony stimulating factor. The preprogrammed intra-clonal functional flexibility is explained here by invoking a novel regulatory mechanism mediated by a fourth group of HLA class II determinants. When TCC were used as stimulators with the appropriate primed responders, it could be demonstrated that phase I autonomously proliferative non-suppressive T-helper lines failed to express certain novel lymphocyte activating determinants (LADs), whereas after their acquisition of suppressive function (phase II) these LADs were present. These stimulatory moieties appeared to represent a novel class II-like structure as established by serology, immunochemistry and functional characterization employing monoclonal antibodies to block stimulation. These operationally designated "DY" determinants are primarily and thus far exclusively involved in the induction of antigen non-specific suppressor cells. It is proposed that the intra-clonal changes of T-cell function described here are mediated by a switch in the utilization of qualitatively distinct class II-like restriction elements. The functional status of the phase I TCC can be altered by a switching over to the engagement of "DY" determinants in phase II. Thus, an autostimulatory and self-maintaining suppressive network may operate in extended inductive phases of human HLA restricted T-cell responses.

Studies on the somatic instability of immunoglobulin genes in vivo and in cultured cells

We have examined the molecular mechanism and impact of somatic diversification on the T15 heavy chain variable region gene in vivo and in vitro. Somatic point mutation appears to be responsible for the changes we have observed in both hybridomas from early and late in the immune response and in the S107 myeloma cell line in culture. By identifying S107 mutants with decreases in antigen binding, we have shown that a single point mutation can cause the loss of binding to the eliciting antigen and the acquisition of binding to another antigen. Furthermore, in this case a point mutation of the T15 heavy chain variable region gene caused the conversion of an important protective antibody to an autoantibody. While the S107 cell line frequently generates both constant and variable region mutants, hybridomas appear to have relatively stable variable region genes and unstable constant region genes which in some cases result in mutants with increased binding.

Adult B-cell repertoire is biased toward two heavy-chain variable-region genes that rearrange frequently in fetal pre-B cells

Fetal pre-B cells rearrange a very restricted set of immunoglobulin variable genes for the heavy chain (VH). To determine whether the adult B-cell repertoire is similarly skewed, we first identified the genes that rearrange in pre-B cells from BALB/c mice and then determined their frequency of rearrangement in adult B cells. In fetal pre-B cell lines, two genes, VH81X from the 7183 subfamily and VHOx2 from the Q52 subfamily, comprise 75% of the rearranged alleles of an estimated 1000 genes (P less than 0.001). Sequencing analyses revealed that rearrangements involving the two genes were both productive and nonproductive. The biased rearrangement of these two VH genes persists in B-cell hybridomas from adult mice at a frequency of 22%, as determined by Southern gel analysis and RNA sequencing. The sequence of one VHOx2 rearrangement from a hybridoma shows that the rearrangement is productive, suggesting that the gene encodes an antibody that could participate in the immune response. The data indicate that the adult B-cell repertoire is not random concerning usage of individual VH genes, and it may be shaped by the unknown mechanisms that cause preferential rearrangement of certain genes early in ontogeny.

A hyperconversion mechanism generates the chicken light chain preimmune repertoire

The chicken immunoglobulin light chain repertoire has been shown to be entirely derived from a single V lambda 1-J rearranged combination. The complete coding information of the lambda locus was determined: it comprises 25 V-hybridizing elements, all of which are pseudogenes, clustered in both orientations within 19 kb of DNA, starting 2.4 kb upstream of the V lambda 1 gene. Sequences of somatically rearranged V lambda 1 genes from embryonic and posthatching bursal cells show that diversification of light chain sequences occurs during ontogeny by a segmental gene conversion mechanism which takes place at a frequency of 0.05-0.1 per cell generation between the pseudogene pool and the unique rearranged functional V gene.

Allelic inclusion in a pre-B-cell line that generates immunoglobulin heavy chain genes in vitro

In a pre-B-cell line that rearranges its heavy chain gene segments in vitro, we found that the rate of productive rearrangement on one allele was not influenced by the presence of heavy chain protein encoded by the other allele. This shows that allelic exclusion of heavy chain genes is not regulated at the genetic level.

Characterization of T cell receptor gamma chain expression in a subset of murine thymocytes

While much information exists about the structure and function of the clonally distributed T cell receptor (TCR) alpha beta heterodimer, little is known about the gamma protein, the product of a third rearranging TCR gene. An antiserum to a carboxyl-terminal peptide common to several of the murine gamma chain constant regions and a monoclonal antibody to the murine T3 complex were used to identify products of this TCR gene family in a subpopulation of Lyt2-, L3T4- thymocytes. This subpopulation does not express TCR alpha or full-length TCR beta messenger RNA. The gamma chain is a 35-kilodalton (kD) protein that is disulfide-bonded to a 45-kD partner and is associated with the T3 complex. Analysis of the glycosylation pattern of this thymic gamma chain revealed that the major variable region gamma (V gamma) gene transcribed in activated peripheral T cells is absent from this subpopulation. The cells that bear this second T cell receptor may therefore represent a distinct lineage differentiating within the thymus.

A common mechanism of chromosomal translocation in T- and B-cell neoplasia

The chromosomal breakpoint involved in the t(8;14)(q24;q11) chromosome translocation in the SKW-3 cell line, which directly involves the 3' flanking region of the c-myc gene, was cloned and sequenced. The breakpoint on chromosome 8 mapped to a position 3 kb 3' of c-myc while the chromosome 14 breakpoint occurred 36 kb 5' of the gene for the constant region of the alpha chain of the T-cell receptor (TCR). The translocation resulted in a precise rearrangement of sequences on chromosome 8 and what appears to be a functional J alpha segment on chromosome 14. Signal sequences for V-J joining occurred at the breakpoint positions on both chromosomes 14 and 8, suggesting that the translocation occurs during TCR gene rearrangement and that it is catalyzed by the enzymatic systems involved in V-J joining reactions. The involvement of c-myc in the translocation and the association of joining signals at the breakpoints provides a parallel to the situation observed in the translocations involving c-myc and the immunoglobulin loci in B-cell neoplasms and suggests that common mechanisms of translocation and oncogene deregulation are involved in B- and T-cell malignancies.

The t(8; 14) chromosomal translocation occurring in B-cell malignancies results from mistakes in V-D-J joining

The reciprocal chromosome translocation, t(8;14), involving the heavy chain locus on chromosome 14 and the c-myc oncogene on chromosome 8 is a characteristic of the B-cell malignancies Burkitt's lymphoma and acute lymphoblastic leukaemia (ALL). We have cloned and sequenced the t(8; 14) breakpoints of an African Burkitt's lymphoma cell line, P3HR-1, and a pre-B cell ALL cell line, 380. In each case the region of chromosome 8 involved has recombined with a JH region on chromosome 14. The two sites of breakage on chromosome 8 lie within 70 base pairs (bp) of one another. At each joining site, sequences homologous to the signal sequences thought to be recognized by the V-D-J recombinase were identified, as were N regions. In B-cell chronic lymphocytic leukaemias (B-CLL) carrying the t(11; 14) chromosome translocation and in follicular lymphomas carrying the t(14; 18) translocation, the V-D-J recombinase is implicated in the mechanism of chromosomal translocations. We speculate that the same enzymatic mechanism is responsible for the t(8; 14) translocations in African Burkitt's lymphoma and pre-B cell ALL.