Immunoglobulin VH gene replacements in a T-cell lymphoblastic lymphoma

V(H) replacement in rearranged immunoglobulin genes

Examples suggesting that all or part of the V(H) segment of a rearranged V(H)DJ(H) may be replaced by all or part of another V(H) have been appearing since the 1980s. Evidence has been presented of two rather different types of replacement. One of these has gained acceptance and has now been clearly demonstrated to occur. The other, proposed more recently, has not yet gained general acceptance because the same effect can be produced by polymerase chain reaction artefact. We review both types of replacement including a critical examination of evidence for the latter. The first type involves RAG proteins and recombination signal sequences (RSS) and occurs in immature B cells. The second was also thought to be brought about by RAG proteins and RSS. However, it has been reported in hypermutating cells which are not thought to express RAG proteins but in which activation-induced cytidine deaminase (AID) has recently been shown to initiate homologous recombination. Re-examination of the published sequences reveals AID target sites in V(H)-V(H) junction regions and examples that resemble gene conversion.

Receptor revision and systemic lupus

Studies over the past 10 years have shown that B cells can undergo secondary heavy- or light-chain immunoglobulin (Ig) rearrangements at various stages of their normal development, a process termed receptor editing. In the bone marrow, this mechanism is important to maintain tolerance because it can extinguish a self-reactive specificity without having to physically eliminate a potentially autoreactive B cell. In the periphery, secondary rearrangements may also play a role in the diversification and maturation of an immune response, although conclusive evidence for this process is still required. Individuals with systemic autoimmune diseases, such as lupus, show evidence of intricate abnormalities in receptor editing. On the one hand, decreased editing may not eliminate the self-reactive specificities that emerge during B-cell development in the bone marrow. Conversely, excessive secondary rearrangements, especially in the periphery where tolerance mechanisms are less effective, can result in the production of autoantibodies by edited B cells. It will be important to assess whether the complex editing defects observed during lupus are a primary susceptibility factor to this disease or if they are secondary to other abnormalities of lymphocyte development in these autoimmune patients.

Clonal rearrangements in childhood and adult precursor B acute lymphoblastic leukemia: a comparative polymerase chain reaction study using multiple sets of primers

Ig heavy chain (IgH) and T-cell receptor (TCR) gene rearrangements were investigated by polymerase chain reaction (PCR) amplification of diagnostic tumour samples from 91 patients (57 children and 34 adults, with cut-off at age 16) with precursor B acute lymphoblastic leukemia (ALL). Using primers directed to the framework regions (FR) 1, 2 and 3 of the IgH gene, clonal IgH rearrangements were observed in 82, 58 and 58%, respectively, whereas clonality was presented in 45 and 27% using primers hybridising to the TCR delta and gamma genes. A combination of all five primer sets used resulted in 96% positive cases (children 100%, adults 88%). The frequency of clonal IgH rearrangements correlated to patient age with a significantly lower fraction of positive cases in the adult group. The concomitant usage of more than one V(H) family gene was similar for childhood and adult ALL, and an over-representation of V(H)6 rearrangements was found in childhood ALL. Twenty-five out of 91 cases (27%) displayed an oligoclonal pattern for either IgH or TCR gene rearrangements (children 37%, adults 12%). A comparative analysis of samples from different compartments was performed in 23 patients, and differences between two or three compartments were observed in seven cases. Unexpectedly large, clonally appearing PCR products of 540-715 bp were found in three leukemias and sequence analysis verified their clonal nature. In summary, using multiple sets of primers clonal rearrangements of IgH and TCR genes can be detected in a very high frequency, including previously neglected large size PCR products. A common heterogeneity was demonstrated in different compartments reflecting ongoing clonal evolution, which can make detection of minimal residual disease (MRD) in ALL troublesome. Therefore, we suggest that a minimum of three targets should be used to minimise false-negative results.

Unusual immunoglobulin and T-cell receptor gene rearrangement patterns in acute lymphoblastic leukemias

Immunoglobulin (Ig) and T-cell receptor (TCR) genes are rearranged in virtually all acute lymphoblastic leukemia (ALL) cases. However, the recombination patterns display several unusual features as compared to normal lymphoid counterparts. Cross-lineage gene rearrangements occur in more than 90% of precursor-B-ALL and in approximately 20% of T-ALL, whereas they are rare in normal lymphocytes. Approximately 25-30% of the Ig and TCR gene rearrangements at diagnosis are oligoclonal, and can undergo continuing or secondary recombination events during the disease course. Based on our extensive molecular studies we hypothesize that the unusual Ig and TCR gene rearrangements in ALL occur as an early postoncogenic event resulting from the continuing V(D)J recombinase activity on accessible gene loci. This hypothesis is on the one hand supported by the virtual absence of cross-lineage gene rearrangements in normal lymphocytes and mature lymphoid malignancies and on the other hand by the presence of oligoclonality and secondary Ig and TCR gene rearrangements in ALL.

Ig Heavy Chain Gene Rearrangements in T-Cell Acute Lymphoblastic Leukemia Exhibit Predominant Dh6-19 and Dh7-27 Gene Usage, Can Result in Complete V-D-J Rearrangements, and Are Rare in T-Cell Receptor β Lineage

Rearranged IGH genes were detected by Southern blotting in 22% of 118 cases of T-cell acute lymphoblastic leukemia (ALL) and involved monoallelic and biallelic rearrangements in 69% (18/26) and 31% (8/26) of these cases, respectively. IGH gene rearrangements were found in 19% (13/69) of CD3− T-ALL and in 50% of TCRγδ+ T-ALL (12/24), whereas only a single TCRβ+ T-ALL (1/25) displayed a monoallelicIGH gene rearrangement. The association with the T-cell receptor (TCR) phenotype was further supported by the striking relationship between IGH and TCR delta (TCRD) gene rearrangements, ie, 32% of T-ALL (23/72) with monoallelic or biallelicTCRD gene rearrangements had IGH gene rearrangements, whereas only 1 of 26 T-ALL with biallelic TCRD gene deletions contained a monoallelic IGH gene rearrangement. Heteroduplex polymerase chain reaction (PCR) analysis with Vh and Dh family-specific primers in combination with a Jhconsensus primer showed a total of 39 clonal products, representing 7 (18%) Vh-(Dh-)Jh joinings and 32 (82%) Dh-Jh rearrangements. Whereas the usage of Vh gene segments was seemingly random, preferential usage of Dh6-19 (45%) and Dh7-27 (21%) gene segments was observed. Although the Jh4 and Jh6 gene segments were used most frequently (33% and 21%, respectively), a significant proportion of joinings (28%) used the most upstream Jh1 and Jh2 gene segments, which are rarely used in precursor-B-ALL and normal B cells (1% to 4%). In conclusion, the high frequency of incomplete Dh-Jh rearrangements, the frequent usage of the more downstream Dh6-19 and Dh7-27 gene segments, and the most upstream Jh1 and Jh2 gene segments suggests a predominance of immature IGH rearrangements in immature (non-TCRβ+) T-ALL as a result of continuing V(D)J recombinase activity. More mature β-lineage T-ALL with biallelic TCRD gene deletions apparently have switched off their recombination machinery and are less prone to cross-lineageIGH gene rearrangements. The combined results indicate thatIGH gene rearrangements in T-ALL are postoncogenic processes, which are absent in T-ALL with deleted TCRD genes and completed TCR alpha (TCRA) gene rearrangements.

Ig Heavy Chain Gene Rearrangements in T-Cell Acute Lymphoblastic Leukemia Exhibit Predominant Dh6-19 and Dh7-27 Gene Usage, Can Result in Complete V-D-J Rearrangements, and Are Rare in T-Cell Receptor β Lineage

Rearranged IGH genes were detected by Southern blotting in 22% of 118 cases of T-cell acute lymphoblastic leukemia (ALL) and involved monoallelic and biallelic rearrangements in 69% (18/26) and 31% (8/26) of these cases, respectively. IGH gene rearrangements were found in 19% (13/69) of CD3− T-ALL and in 50% of TCRγδ+ T-ALL (12/24), whereas only a single TCRβ+ T-ALL (1/25) displayed a monoallelicIGH gene rearrangement. The association with the T-cell receptor (TCR) phenotype was further supported by the striking relationship between IGH and TCR delta (TCRD) gene rearrangements, ie, 32% of T-ALL (23/72) with monoallelic or biallelicTCRD gene rearrangements had IGH gene rearrangements, whereas only 1 of 26 T-ALL with biallelic TCRD gene deletions contained a monoallelic IGH gene rearrangement. Heteroduplex polymerase chain reaction (PCR) analysis with Vh and Dh family-specific primers in combination with a Jhconsensus primer showed a total of 39 clonal products, representing 7 (18%) Vh-(Dh-)Jh joinings and 32 (82%) Dh-Jh rearrangements. Whereas the usage of Vh gene segments was seemingly random, preferential usage of Dh6-19 (45%) and Dh7-27 (21%) gene segments was observed. Although the Jh4 and Jh6 gene segments were used most frequently (33% and 21%, respectively), a significant proportion of joinings (28%) used the most upstream Jh1 and Jh2 gene segments, which are rarely used in precursor-B-ALL and normal B cells (1% to 4%). In conclusion, the high frequency of incomplete Dh-Jh rearrangements, the frequent usage of the more downstream Dh6-19 and Dh7-27 gene segments, and the most upstream Jh1 and Jh2 gene segments suggests a predominance of immature IGH rearrangements in immature (non-TCRβ+) T-ALL as a result of continuing V(D)J recombinase activity. More mature β-lineage T-ALL with biallelic TCRD gene deletions apparently have switched off their recombination machinery and are less prone to cross-lineageIGH gene rearrangements. The combined results indicate thatIGH gene rearrangements in T-ALL are postoncogenic processes, which are absent in T-ALL with deleted TCRD genes and completed TCR alpha (TCRA) gene rearrangements.

V(H) gene family utilization in different B-cell lymphoma subgroups

V(H) gene family specific polymerase chain reaction (PCR) amplification was performed in 87 B-cell lymphoma samples from 4 different subgroups. No apparent restriction in the VH gene usage was found in follicular lymphomas, lymphoplasmacytoid lymphomas or large B-cell lymphomas, whereas a biased VH1 utilization was shown in patients with chronic lymphocytic leukemia. Eleven of 18 chronic lymphocytic leukemia cases utilized the VH1 gene family, and nucleotide sequencing of the VH1 gene rearrangements revealed that a majority utilized the DP10 (51p1) germline gene, which has been reported to be strongly associated with autoimmune disease. No VH5 or VH6 rearrangements were amplified in the chronic lymphocytic leukemia subgroup, 2 gene families which previously have been found to be over-represented in these patients. In a high proportion (40%) of large B-cell lymphomas, VH gene family-specific PCR failed to amplify any rearrangement. Using primers hybridizing to the framework regions 2 and 3 and Southern blot analysis of the immunoglobulin heavy chain locus, clonal rearrangements were displayed in two-thirds of these PCR negative cases. However, the rearrangement status could not be elucidated in 5 of 35 patients with large B-cell lymphoma.

Low rate of somatic hypermutations characterize progressive B-cell lymphomas

Immunoglobulin heavy (IgH) chain gene rearrangements were characterized in 40 samples from 15 patients with B-cell lymphomas at different time points during tumour progression. Using polymerase chain reaction (PCR) amplification and single strand conformation polymorphism (SSCP) analysis of variable heavy (VH) chain gene segments, we found that 6 cases displayed alterations in their IgH chain rearrangements at relapse. These alterations were mainly observed in follicular or transformed lymphomas, but no association to clinical features was found. Nucleotide sequence analysis revealed a low frequency of mutations in 3 cases, whereas 1 case displayed an extensive mutation rate in a compartment with transformed morphology at relapse. The mutations observed most probably resulted from somatic hypermutations. Further, the mutations were scattered randomly over the VH gene segment and no significant bias favouring amino acid substitutions was observed in 3 cases, suggesting that the tumour cells had not been subjected to antigen-driven selection. In 1 case, however, the mutation pattern indicated that the tumour cells had been affected by an antigen selection process. In the 2 remaining cases, the original V(H)DJ(H) rearrangement could no longer be detected by VH gene family specific PCR at relapse, but using primers specific for the framework region 2 or 3 altered rearrangements were demonstrated, implying that mutations had been introduced in framework region 1. However, the majority of the tumour cell clones analysed were relatively stable during tumour progression, which make them eligible for analysis of minimal residual disease using the VH gene regions as molecular markers.

Alterations of the immunoglobulin heavy chain locus in progressive B-cell lymphomas

Twenty-two patients with relapsed or progressive B-cell lymphomas (BCL) were analysed for alterations in the rearrangement status in the immunoglobulin heavy (IgH) chain gene in samples obtained on different occasions during the course of the disease. The analysis was performed using Southern blot hybridization of the IgH gene and polymerase chain reaction (PCR) amplification of the VH gene families combined with single-strand conformation polymorphism (SSCP) analysis. Using Southern blot analysis, we found that all 22 lymphomas displayed clonal IgH rearrangements, and changes during tumour progression occurred in 8 cases. These alterations were mainly observed in cases with follicular or transformed lymphomas. More than one malignant (sub)clone, indicated by more than two rearranged bands, was detected in one case at diagnosis and in three cases at relapse. Outgrowth of subclones with divergent rearrangement patterns in different compartments was also observed in 2 out of 8 cases. PCR-SSCP analysis indicated that all 15 cases studied displayed clonal rearrangements and in 6 cases altered rearrangement patterns were detected in later samples. Southern blotting and PCR-SCCP analysis gave equivalent results. No association was found between time to relapse or survival time and alterations in rearrangement pattern. The present study illustrates that the neoplastic cell clones in BCL often display alterations in their IgH locus, but the significance of this feature remains to be clarified.