Detection of mutations by cleavage of DNA heteroduplexes with bacteriophage resolvases.

We have explored the application of the bacteriophage resolvases T4 endonuclease VII and T7 endonuclease I for detecting mutations in genomic DNA. Heteroduplex DNA fragments prepared by amplification from DNA containing known mutations were cleaved by one or both enzymes at nucleotide mismatches created by 3 of 3 short deletions and 13 of 14 point mutations in fragments as large as 940 basepairs. Heteroduplexes representing all four classes of possible single nucleotide mismatches were cleaved, and the sizes of the cleavage products generated correlated with the location of the mutation. We conclude that bacteriophage resolvases may be useful reagents for the rapid screening of DNA for mutations.

Interallelic V(D)J trans-rearrangement within the beta T cell receptor gene is infrequent and occurs preferentially during attempted D beta to J beta joining.

Previous work has demonstrated that intergenic V(D)J rearrangement, a process referred to as trans-rearrangement, occurs at an unexpectedly high frequency. These rearrangements generate novel V(D)J combinations which could conceivably have some role in the normal immune system, and since they probably arise through chromosomal rearrangements akin to those associated with lymphoid neoplasia, they may also serve as a model for investigating recombinational events which underlie oncogenesis. In view of the existence of a mechanism that permits relatively frequent intergenic trans-rearrangements, it seems reasonable that interallelic trans-rearrangements involving segments belonging to each of the two alleles of a single antigen receptor gene might also occur. To determine the frequency of such rearrangements, we examined thymocytes of F1 progeny of a cross between SWR mice, which have a deletion spanning 10 of the known V beta segments, and NZW mice, which have a deletion involving all J beta 2 segments. Rearranged TCR-beta genes containing V beta segments from the NZW chromosome and J beta segments from the SWR chromosome were amplified from the DNA of F1 thymocytes with the polymerase chain reaction. Using this approach, we found that such rearrangements are relatively uncommon, being present in about 1 in 10(5) thymocytes, a frequency lower than that of V gamma/J beta intergenic trans-rearrangements. The ratio of conventional cis-rearrangement to interallelic trans-rearrangement for any particular V beta segment appears to be about 10(4):1. The structure of the junctions in all trans-rearrangements analyzed closely resembles conventional cis-rearrangements, indicating involvement of V(D)J recombinase in the ultimate joining event. However, in contrast to cis-rearrangements, a strong bias for inclusion of D beta 1 segments over D beta 2 segments was noted, suggesting that interallelic trans-rearrangement may occur preferentially during attempted D-J joining. J beta 2 segment usage in trans-rearrangements also appeared to differ from that expected from previously studied cis-rearrangements. The results have implications with respect to the events and timing of conventional cis-rearrangement during thymocyte differentiation, and the prevalence of various types of trans-rearrangements.

Augmented expression of a human gene for 8-oxoguanine DNA glycosylase (MutM) in B lymphocytes of the dark zone in lymph node germinal centers.

B cells that mediate normal, T cell-dependent, humoral immune responses must first pass through germinal centers (GCs) within the cortex of antigenically stimulated lymph nodes. As they move through the dark zone and then the light zone in the GC, B cells are subjected to somatic hypermutation and switch recombination within their rearranged immunoglobulin genes and also participate in a number of other processes that control development into memory cells or cells specialized for antibody secretion. To investigate the molecular mechanisms that contribute to B cell development within GCs, we constructed a recombinant DNA library enriched for cDNAs derived from human genes expressed in B cells at this site. This library was found to contain a cDNA structurally and functionally related to genes in bacteria and yeast for the DNA repair enzyme 8-oxoguanine DNA glycosylase. Northern blot analysis indicated that the human gene is expressed as two alternatively spliced messenger RNAs within GC B cells at levels greatly exceeding that found in other tissues. In situ hybridization studies revealed that expression of this gene is most abundant within the dark zones of GCs. Both the function and localized expression of this gene suggest that it may play a role in somatic hypermutation of immunoglobulin genes.

Chromosomal translocations joining LCK and TCRB loci in human T cell leukemia.

A case of T lymphoblastic leukemia (T-ALL) showing t(1;7)(p34;q34) as the sole karyotypic abnormality was investigated at the molecular level. Screening of a phage library of tumor DNA with a probe for the beta T cell receptor gene (TCRB), which maps to chromosomal band 7q34, resulted in the isolation of a clone containing DNA spanning the translocation breakpoint of the der(1) chromosome. This clone contained chromosome 1 DNA juxtaposed upstream of a D beta-J beta joint. Cloning of the corresponding germline region of chromosome 1 resulted in the isolation of a phage containing the breakpoint from the reciprocal, der(7), product, which showed chromosome 1 DNA joined downstream to a V beta segment. Comparison of germline and translocation clones demonstrated that breakage of chromosome 1 had occurred at the border of a tandem repeat of Alu sequences. To search for transcripts from DNA near the breakpoint, a chromosomal walk was initiated along chromosome 1. A probe consisting of chromosome 1 DNA from 24-30 kb upstream of the breakpoint hybridized to a transcript derived from the gene encoding the lymphocyte-specific tyrosine kinase p56lck, previously mapped to chromosomal band 1p34. The nonrandom nature of the breakpoints in this case was confirmed by the analysis of a second independent case of T-ALL containing a t(1;7) translocation, which was also found to show breakage within the LCK locus. The chromosomal breakpoint in the first case was localized 2 kb upstream of the lck upstream promoter and first nontranslated exon, while the breakpoint of the second case lay between the two alternative lck promoters, upstream of the second exon. Relative to normal thymus and activated T cells, levels of lck mRNA were greatly elevated in the first case and moderately elevated in the second. The existence of these translocations raises the possibility that alterations in the promoter region of the LCK locus may play a role in human cancer.

Detection of a second t(14;18) breakpoint cluster region in human follicular lymphomas.

Our results indicate that there are two major breakpoint cluster regions in chromosome 18 DNA for t(14;18) translocations in follicular lymphomas. The absence of a pFL-1 homologous transcript in a cell line containing a pFL-2-detectable translocation suggests that there may be two different pathogenetic consequences of t(14;18) translocations. One possibility is that, despite the distances between them (greater than 20 kb), breakpoints in the two cluster regions in some way affect transcription of the same gene product, which has not yet been identified. Alternatively, two separate transcriptional units may be involved. The availability of DNA probes for each of the two t(14;18) breakpoint cluster regions will allow further studies regarding the biologic significance of these two genetically distinct classes of t(14;18) translocations.

Continuing rearrangement but absence of somatic hypermutation in immunoglobulin genes of human B cell precursor leukemia.

Southern blot analyses revealed that cells from nearly 30% of childhood B cell precursor acute lymphoblastic leukemias (ALLs) contained more than two rearranged, nongermline bands for Ig heavy chain genes. DNA corresponding to these bands was molecularly cloned from two cases which showed three and seven rearranged bands, respectively. Nucleotide sequence analysis of the cloned DNA demonstrated that each band represented different VDJ or DJ rearrangements. While the same DJ joints were shared by several rearrangements, different DJ joints were found in the majority of rearrangements, precluding V region substitution as an explanation for the multiplicity of heavy chain rearrangements in these leukemias. Most of the V region segments involved in these rearrangements were restricted to VH region families that have been shown previously to be preferentially rearranged in human fetal B lineage cells. Sequence analysis of multiple copies of the same VDJ rearrangements from different cells revealed no somatic mutation, a mechanism responsible for detection of extra rearranged Ig DNA bands in certain other B lineage tumors. The data suggest that in some cases of ALL Ig heavy chain genes begin and continue to rearrange de novo within the neoplastic B cell precursor populations derived from an original malignant cell transformed at a stem cell stage of differentiation.

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.

Frequent biclonality and Ig gene alterations among B cell lymphomas that show multiple histologic forms.

Configurations of Ig gene DNA were examined in multiple biopsy specimens from seven cases of human B cell lymphoma that showed histologic differences among the specimens within each case. Analysis by Southern blot hybridizations with DNA probes for each of the three Ig loci revealed that the configurations of DNA within these loci were identical among the specimens in two of the cases. This result indicated the monoclonality of these lymphomas, despite differences in histology between biopsy specimens. In contrast, no common nongermline configurations of Ig gene DNA were detected among multiple biopsies in each of three other cases. Therefore, different histologies correlated with separate clones of proliferating B cells in these cases. In the last two cases, the configurations of light chain gene DNA were the same among biopsies in each case, consistent with a monoclonal origin in both lymphomas. However, differences were detected in the configuration of the heavy chain gene DNA. Analysis with a series of DNA probes of the mu heavy chain region indicated that the differences in the DNA configurations of the heavy chain genes from the biopsies probably arose from postrearrangement deletions of either the switch or constant regions of the mu gene. These studies indicate that, contrary to the conventional belief, individual tumors that contain different histologic types of lymphoma within the same patient frequently arise from separate clones of neoplastic cells. Furthermore, the heavy chain genes of monoclonal tumors may show postrearrangement deletions, often resulting from instability of DNA sequences within or around the mu switch region.

Consistent breakage between consensus recombinase heptamers of chromosome 9 DNA in a recurrent chromosomal translocation of human T cell leukemia.

Chromosomal translocations in lymphoid tumors frequently result from recombination between a normally rearranging antigen receptor gene and a normally non-rearranging second locus. The possibility that the lymphocyte recombinase apparatus plays a role in determining the position of breakage at the second locus has been a matter of controversy because of the inconsistent presence of heptamer-like recognition sequences adjoining breakpoints at this site. To further investigate this issue, sites of DNA recombination were analyzed in both the der(9) and der(7) products of t(7;9)(q34;q32), a recurrent translocation of human acute lymphoblastic leukemias (T-ALL). In each of three separate cases, the translocation has divided the TCR-beta locus, juxtaposing chromosome 9 DNA 5' to a J-region in the der(9) product and 3' to a D-region in the der(7) product, with variably sized N-insertions and small deletions detectable at the junctions. All three cases contain breakpoints in chromosome 9 DNA tightly clustered between two closely spaced, and oppositely oriented heptamer sequences, CAC(A/T)GTG, which perfectly match the consensus heptamer sequence recognized by the lymphocyte recombinase apparatus in normal antigen receptor gene rearrangement. In no case was there evidence of directly duplicated sequences in the two reciprocal products, as is often associated with recombination involving random staggered breakage of DNA. Taken together, these results support a mechanism for this particular translocation proceeding by recombinase-mediated breakage of both participating chromosomes.

Exclusive development of T cell neoplasms in mice transplanted with bone marrow expressing activated Notch alleles.

Notch is a highly conserved transmembrane protein that is involved in cell fate decisions and is found in organisms ranging from Drosophila to humans. A human homologue of Notch, TAN1, was initially identified at the chromosomal breakpoint of a subset of T-cell lymphoblastic leukemias/lymphomas containing a t(7;9) chromosomal translocation; however, its role in oncogenesis has been unclear. Using a bone marrow reconstitution assay with cells containing retrovirally transduced TAN1 alleles, we analyzed the oncogenic potential of both nuclear and extranuclear forms of truncated TAN1 in hematopoietic cells. Although the Moloney leukemia virus long terminal repeat drives expression in most hematopoietic cell types, retroviruses encoding either form of the TAN1 protein induced clonal leukemias of exclusively immature T cell phenotypes in approximately 50% of transplanted animals. All tumors overexpressed truncated TAN1 of the size and subcellular localization predicted from the structure of the gene. These results show that TAN1 is an oncoprotein and suggest that truncation and overexpression are important determinants of transforming activity. Moreover, the murine tumors caused by TAN1 in the bone marrow transplant model are very similar to the TAN1-associated human tumors and suggest that TAN1 may be specifically oncotropic for T cells.

HIV-associated gut dysbiosis is independent of sexual practice and correlates with noncommunicable diseases.

Loss of gut mucosal integrity and an aberrant gut microbiota are proposed mechanisms contributing to chronic inflammation and increased morbidity and mortality during antiretroviral-treated HIV disease. Sexual practice has recently been uncovered as a major source of microbiota variation, potentially confounding prior observations of gut microbiota alterations among persons with HIV (PWH). To overcome this and other confounding factors, we examine a well-powered subset of AGEhIV Cohort participants comprising antiretroviral-treated PWH and seronegative controls matched for age, body-mass index, sex, and sexual practice. We report significant gut microbiota differences in PWH regardless of sex and sexual practice including Gammaproteobacteria enrichment, Lachnospiraceae and Ruminococcaceae depletion, and decreased alpha diversity. Men who have sex with men (MSM) exhibit a distinct microbiota signature characterized by Prevotella enrichment and increased alpha diversity, which is linked with receptive anal intercourse in both males and females. Finally, the HIV-associated microbiota signature correlates with inflammatory markers including suPAR, nadir CD4 count, and prevalence of age-associated noncommunicable comorbidities.

Abortion, illegitimacy, and the American birth rate.

In sum, it appears that legal abortion depressed overall fertility, but particularly illegitimate fertility, by giving women an opportunity to terminate their pregnancies when other means of birth control either had not been used or had failed. If legalized abortion had not been available, an estimated additional 39,000 illegitimate babies and 28,000 legitimate babies would have been born in 1971 in the United States. While this makes up a small part of total births (3,500,000), the illegitimate births prevented represent almost onetenth of all out-of-wedlock children born in the country in that year. In addition to preventing these births the legalization of abortion appears to have reduced the incidence of pregnancy-related marriages and thereby may have helped to limit subsequent marital disruption. Finally, legal abortion prevented large numbers of illegal abortions from occurring. Our data indicate that well over half-most likely between two-thirds and three-fourths-of all legal abortions in the United States in 1971 were replacements for illegal abortions. Further declines in illegitimate birth rates for the country as a whole will depend, in considerable part, on the extent to which legal abortion becomes more readily available and more widely used. Theoretically, greater use of efficient contraception could also cause illegitimate fertility to decline. But there are many reasons why women do not use efficient contraception even when they know about it and have access to the materials (25). Even though the use of abortion throughout the nation is now legalized by the Supreme Court decision, this does not necessarily mean that services will in fact be everywhere more readily available. Our interstate analysis suggests that should the liberalization of abortion laws be reversed, not only would there be an upturn in illegal abortions and pregnancy-related marriages, but also a marked rise in illegitimacy, particularly among women who do not have the means to obtain an illegal abortion.

T cell receptor gene trans-rearrangements: chimeric gamma-delta genes in normal lymphoid tissues.

Joining of V-, D-, and J-region gene segments during DNA rearrangements within all antigen receptor genes involves recognition of the same highly conserved heptamernonamer sequences flanking each segment. In order to investigate the possibility that recognition of these conserved sequences may sometimes permit intergenic joining of segments among different antigen receptor genes, DNA of normal human lymphoid tissues was examined by polymerase chain reaction amplification for the presence of chimeric gamma-delta T cell receptor gene rearrangements. These studies detected V gamma-(D delta)-J delta and V delta-(D delta)-J gamma rearrangements in thymus, peripheral blood, and tonsil. Analysis of thymus RNA indicated that many of these rearrangements are expressed as V gamma-(D delta)-J delta-C delta and V delta-(D delta)-J gamma-C gamma transcripts. Most transcripts (19 of 20 complementary DNA clones studied) are appropriately spliced and show correct open translational reading frames across the V-(D)-J junctions. Thus, chimeric antigen receptor genes are generated in a subset of normal lymphoid cells, probably as a result of chromosomal translocations, and such genes may possibly contribute to increased diversity within the antigen receptor repertoire.

Individual tumors of multifocal EB virus-induced malignant lymphomas in tamarins arise from different B-cell clones.

Cotton-top tamarins were inoculated with sufficient Epstein-Barr virus to induce multiple tumors in each animal within 14 to 21 days. The tumors consisted of large-cell lymphomas that contained multiple copies of the Epstein-Barr virus genome and generated Epstein-Barr virus-carrying cell lines showing no detectable consistent chromosomal abnormality. Hybridization of tumor DNA with immunoglobulin gene probes revealed that each lymphoma was oligo- or monoclonal in origin and that individual tumors from the same animal arose from different B-cell clones. Thus the virus induced multiple transformation events in tamarins in vivo to cause malignant tumors resembling the Epstein-Barr virus-associated lymphomas of patients with organ transplants.

Practical methods of mutation detection.

The past few years have seen a marked increase in the demand for practical methods of mutation detection. Over this period of time, both the development of new methods and improvements in existing methods have made mutation detection in the research setting a less cumbersome task. Nevertheless, all of the commonly used approaches to this problem are labor intensive, and truly practical mutation detection methods in the clinical setting will depend on the development of more fully automated technology.

Protoporphyrin hepatopathy. Effects of cholic acid ingestion in murine griseofulvin-induced protoporphyria.

Short-term effects of cholic acid ingestion on hepatic accumulation, fecal excretion, and blood levels of protoporphyrin were studied in vivo in griseofulvin-induced protoporphyric mice. Experimental mice that received feed with 2% griseofulvin and 0.5% cholic acid were compared with control mice that received feed with 2% griseofulvin for 4 wk. Five mice from each group were assessed each week for liver and blood porphyrin levels. Fecal protoporphyrin was compared weekly in the total pooled output of each population. Mean protoporphyrin levels were significantly lower for liver (P less than 0.0001), erythrocytes (P less than 0.05), and plasma (P less than 0.05), and higher for feces (P less than 0.001) for the mice that were fed cholic acid. Microscopic protoporphyrin deposits, inflammation, necrosis, and dysplasia were more severe in livers of control mice. A second experimental design compared four regimens in the feed given to all mice after 1-wk induction with 2% griseofulvin: (a) 0.5% cholic acid, (b) no adulterant, (c) 2% griseofulvin and 0.5% cholic acid, and (d) 2% griseofulvin. No difference in protoporphyrin removal from livers of mice in groups 1 and 2 was observed after 1 and 2 wk of these regimens. The apparent reduction in hepatic protoporphyrin content in mice of group 3 as compared with group 4 at weeks 2 and 3 was not significant at P less than 0.05. These data suggest that in selected circumstances, hepatic protoporphyrin secretion may be enhanced in protoporphyric disease states by bile salt supplementation.

Isolation and functional analysis of a cDNA for human Jagged2, a gene encoding a ligand for the Notch1 receptor.

Signaling through Notch receptors has been implicated in the control of cellular differentiation in animals ranging from nematodes to humans. Starting from a human expressed sequence tag-containing sequence resembling that of Serrate, the gene for a ligand of Drosophila melanogaster Notch, we assembled a full-length cDNA, now called human Jagged2, from overlapping cDNA clones. The full-length cDNA encodes a polypeptide having extensive sequence homology to Serrate (40.6% identity and 58.7% similarity) and even greater homology to several putative mammalian Notch ligands that have subsequently been described. When in situ hybridization was performed, expression of the murine Jagged2 homolog was found to be highest in fetal thymus, epidermis, foregut, dorsal root ganglia, and inner ear. In Northern blot analysis of RNA from tissues of 2-week-old mice, the 5.0-kb Jagged2 transcript was most abundant in heart, lung, thymus, skeletal muscle, brain, and testis. Immunohistochemistry revealed coexpression of Jagged2 and Notch1 within thymus and other fetal murine tissues, consistent with interaction of the two proteins in vivo. Coculture of fibroblasts expressing human Jagged2 with murine C2C12 myoblasts inhibited myogenic differentiation, accompanied by increased Notch1 and the appearance of a novel 115-kDa Notch1 fragment. Exposure of C2C12 cells to Jagged2 led to increased amounts of Notch mRNA as well as mRNAs for a second Notch receptor, Notch3, and a second Notch ligand, Jagged1. Constitutively active forms of Notchl in C2C12 cells also induced increased levels of the same set of mRNAs, suggesting positive feedback control of these genes initiated by binding of Jagged2 to Notch1. This feedback control may function in vivo to coordinate differentiation across certain groups of progenitor cells adopting identical cell fates.

Calcium depletion dissociates and activates heterodimeric notch receptors.

Notch receptors participate in a highly conserved signaling pathway that regulates morphogenesis in multicellular animals. Maturation of Notch receptors requires the proteolytic cleavage of a single precursor polypeptide to produce a heterodimer composed of a ligand-binding extracellular domain (N(EC)) and a single-pass transmembrane signaling domain (N(TM)). Notch signaling has been correlated with additional ligand-induced proteolytic cleavages, as well as with nuclear translocation of the intracellular portion of N(TM) (N(ICD)). In the current work, we show that the N(EC) and N(TM) subunits of Drosophila Notch and human Notch1 (hN1) interact noncovalently. N(EC)-N(TM) interaction was disrupted by 0.1% sodium dodecyl sulfate or divalent cation chelators such as EDTA, and stabilized by millimolar Ca(2+). Deletion of the Ca(2+)-binding Lin12-Notch (LN) repeats from the N(EC) subunit resulted in spontaneous shedding of N(EC) into conditioned medium, implying that the LN repeats are important in maintaining the interaction of N(EC) and N(TM). The functional consequences of EDTA-induced N(EC) dissociation were studied by using hN1-expressing NIH 3T3 cells. Treatment of these cells for 10 to 15 min with 0.5 to 10 mM EDTA resulted in the rapid shedding of N(EC), the transient appearance of a polypeptide of the expected size of N(ICD), increased intranuclear anti-Notch1 staining, and the transient activation of an Notch-sensitive reporter gene. EDTA treatment of HeLa cells expressing endogenous Notch1 also stimulated reporter gene activity to a degree equivalent to that resulting from exposure of the cells to the ligand Delta1. These findings indicate that receptor activation can occur as a consequence of N(EC) dissociation, which relieves inhibition of the intrinsically active N(TM) subunit.

Clonal analysis by study of X chromosome inactivation in formalin-fixed paraffin-embedded tissue.

Analysis of clonality by X chromosome inactivation has proven to be a powerful strategy in the study of neoplastic and preneoplastic disorders (P. J. Fialkow, Biochim. Biophys. Acta, 458: 283-321, 1976; B. Vogelstein et al., Cancer Res., 47: 4806-4813, 1987). Recently, the gene for the androgen receptor has been shown to be a highly polymorphic locus in which methylation of DNA correlates with inactivation of one or the other X homologue (R. C. Allen et al., Am. J. Hum. Genet., 51: 1229-1239, 1992). Unlike other loci used for analysis of X inactivation, the methylation sites within the androgen receptor gene lie close to the region of DNA containing the polymorphism. Consequently, it should be possible to use methylation-sensitive restriction enzymes and polymerase chain reaction to study differential methylation among alleles of this gene in formalin-fixed and paraffin-embedded archival tissue specimens. To investigate this question, we performed clonal analysis on a variety of randomly selected, formalin-fixed, paraffin-embedded tumor tissues from 15 women. Thirteen of the women were found to be heterozygous for polymorphisms at the androgen receptor locus. Among these women, 11 tumors were clearly clonal in assays of methylation of the androgen receptor gene. Interpretation of results for the remaining two cases was complicated because of a skewed pattern of X chromosome inactivation found in normal control tissues. We conclude that analysis of methylation in the androgen receptor gene should allow study of clonality in most formalin-fixed, paraffin-embedded tissue specimens from women, including small preneoplastic lesions or rare conditions for which sufficient material is not available for analysis by other techniques.

Establishment and characterization of a common acute lymphoblastic leukemia cell line with a deletion of chromosome 3 band q26.

This paper describes the establishment and characterization of a new cell line (SUP-B7) which was established from a child with "common" acute lymphoblastic leukemia. The SUP-B7 cells (and the patient's tumor) have been characterized by cytochemical staining, monoclonal antibodies, enzyme analyses, gene rearrangement studies, and karyotype analysis. The SUP-B7 cells are periodic acid-Schiff positive, common acute lymphoblastic leukemia antigen positive, and terminal deoxynucleotidyl transferase positive, and they lack the Epstein-Barr virus genome. In addition, the SUP-B7 cells lack cytoplasmic and surface immunoglobulins, and the immunoglobulin gene rearrangement studies showed rearranged heavy chain genes with germ line light chain genes. Concordance between the cell line and the patient's tumor was established by the immunoglobulin gene rearrangement studies. Using Southern blot analysis of the DNA from the patient's tumor and the SUP-B7 cells, there was comigration of the bands representing the rearranged immunoglobulin heavy chain gene. In addition, the SUP-B7 cells possess a single chromosome abnormality: del(3)(q26q28), with the chromosome breakpoint at or near the transferrin receptor gene. Since the SUP-B7 cell line is concordant with the patient's malignancy and since these cells possess a single chromosomal abnormality, the SUP-B7 cell line may be a useful tool in determining the biological significance of the chromosome deletion: del(3)(q26q28).