Selective usage of VH genes in adult human B lymphocyte repertoires

Antibody Surface Profiling Identifies Glycoforms in Multiple Myeloma as Targets for Immunotherapy: From Antibody Derivatives to Mimetic Peptides for Killing Tumor Cells

Despite therapeutic advances in recent years, there are still unmet medical needs for patients with multiple myeloma (MM). Hence, new therapeutic strategies are needed. Using phage display for screening a large repertoire of single chain variable fragments (scFvs), we isolated several candidates that recognize a heavily sulfated MM-specific glycoform of the surface antigen syndecan-1 (CD138). One of the engineered scFv-Fc antibodies, named MM1, activated NK cells and induced antibody-dependent cellular cytotoxicity against MM cells. Analysis of the binding specificity by competitive binding assays with various glycan ligands identified N-sulfation of glucosamine units as essential for binding. Additionally, site-directed mutagenesis revealed that the amino acids arginine and histidine in the complementarily determining regions (CDRs) 2 and 3 of the heavy chain are important for binding. Based on this observation, a heavy-chain antibody, known as a nanobody, and a peptide mimicking the CDR loop sequences were designed. Both variants exhibited high affinity and specificity to MM cells as compared to blood lymphocytes. Specific killing of MM cells was achieved by conjugating the CDR2/3 mimic peptide to a pro-apoptotic peptide (KLAKLAK)_2. In a co-culture model, the fusion peptide killed MM cells, while leaving normal peripheral blood mononuclear cells unaffected. Collectively, the development of antibodies and peptides that detect tumor-specific glycoforms of therapeutic targets holds promise for improving targeted therapies and tumor imaging.

Feasibility of polyelectrolyte-driven Fab fragment separation

The use of antigen-binding fragments (Fabs) as biotherapeutic agents is gaining interest and thus requires development of adequate purification strategies aimed at separating Fabs from other proteins. Thus, the feasibility of using a copolymer for separation of Fabs from monoclonal antibodies (mAbs) and fragment constant regions (Fcs) was evaluated, employing a blend of purified solutions of these proteins. The use of a copolymer exerting both hydrophobic as well as anionic properties resulted in high precipitation yields for both the mAb and Fc fragment, even at ionic strength of 150 mM NaCl. On the contrary, Fabs exhibited reduced precipitation yields upon copolymer addition. These observations are attributed to differences in protein physicochemical parameters, allowing mAbs and Fcs to be precipitated via conjoint electrostatic and hydrophobic interactions. In contrast, Fabs were mainly precipitated via electrostatic interactions, being reduced at higher ionic strength. This finding was corroborated by hydrophobicity analysis using 2-p-toluidinonaphthalene-6-sulfonate, showing enhanced hydrophobicity of Fcs compared to mAbs alone, while Fabs exhibited the lowest hydrophobicity. Within the context of increasing demand for Fabs as therapeutic proteins, these results may open up a simpler purification strategy for this protein class, potentially also to be implemented within the context of polymer-driven protein purification during fermentation.

An efficient method for variable region assembly in the construction of scFv phage display libraries using independent strand amplification

Phage display library technology is a common method to produce human antibodies. In this technique, the immunoglobulin variable regions are displayed in a bacteriophage in a way that each filamentous virus displays the product of a single antibody gene on its surface. From the collection of different phages, it is possible to isolate the virus that recognizes specific targets. The most common form in which to display antibody variable regions in the phage is the single chain variable fragment format (scFv), which requires assembly of the heavy and light immunoglobulin variable regions in a single gene. In this work, we describe a simple and efficient method for the assembly of immunoglobulin heavy and light chain variable regions in a scFv format. This procedure involves a two-step reaction: (1) DNA amplification to produce the single strand form of the heavy or light chain gene required for the fusion; and (2) mixture of both single strand products followed by an assembly reaction to construct a complete scFv gene. Using this method, we produced 6-fold more scFv encoding DNA than the commonly used splicing by overlap extension PCR (SOE-PCR) approach. The scFv gene produced by this method also proved to be efficient in generating a diverse scFv phage display library. From this scFv library, we obtained phages that bound several non-related antigens, including recombinant proteins and rotavirus particles.

Isolation and characterization of a human antibody fragment specific for Ts1 toxin from Tityus serrulatus scorpion

Scorpion stings are a common event that occurs in tropical and subtropical areas of the world, being a public health problem in certain countries. In most places, medical treatment relays on antivenoms obtained from the sera of hyper-immunized horses, however some efforts are being made to prepare specific antibodies of human origin, using phage display methodology. This communication describes the strategy followed for obtaining a protective human single chain antibody (scFv) capable of partially neutralizing the effect of Ts1, the major toxin isolated from the venom of the Brazilian scorpion Tityus serrulatus. Phage display technique allowed the isolation of scFv 15e from a human library of antibodies, after four rounds of selection against Ts1. This clone codes for 124 amino acids belonging to the family VH6 and 114 amino acids of family VK4. This scFv also recognizes toxins from the scorpions Tityus packyurus and Tityus cambridgei from the Amazonian region. Mice challenged with a LD(50) of Ts1 in the presence of this scFv were substantially resistant to intoxication. ScFv 15e is a leading compound for the development of better anti-scorpion antidotes.

Analysis of the expressed heavy chain variable-region genes of Macaca fascicularis and isolation of monoclonal antibodies specific for the Ebola virus' soluble glycoprotein

The cynomolgus macaque, Macaca fascicularis, is frequently used in immunological and other biomedical research as a model for man; understanding it's antibody repertoire is, therefore, of fundamental interest. The expressed variable-region gene repertoire of a single M. fascicularis, which was immune to the Ebola virus, was studied. Using 5' rapid amplification of cDNA ends with immunoglobulin (Ig)G-specific primers, we obtained 30 clones encoding full-length variable, diversity, and joining domains. Similar to the human V(H) repertoire, the M. fascicularis repertoire utilized numerous immunoglobulin heavy variable (IGHV) gene fragments, with the V(H)3 (41%), V(H)4 (39%), and V(H)1 (14%) subgroups used more frequently than the V(H)5 (3.9%) or V(H)7 (1.7%) subgroups. Diverse immunoglobulin heavy joining (IGHJ) fragments also appeared to be utilized, including a putative homolog of JH5beta gene segment identified in the related species Macaca mulatta, Rhesus macaque, but not in humans. Although the diverse V region genes in the IgG antibody repertoire of M. fascicularis had likely undergone somatic hypermutations (SHMs), they nevertheless showed high nucleotide identity with the corresponding human germline genes, 80-89% for IGHV and 72-92% for IGHJ. M. fascicularis and human V(H) genes were also similar in other aspects: length of complementarity-determining regions and framework regions, and distribution of consensus sites for SHMs. Finally, we demonstrated that monoclonal antibodies (mAbs) specific for an Ebola protein could be obtained from M. fascicularis tissue samples by phage display technology. In summary, the study provides new insight into the M. fascicularis V region gene repertoire and further supports the idea that macaque-derived mAbs may be of therapeutic value to humans.

Protective and nonprotective human immunoglobulin M monoclonal antibodies to Cryptococcus neoformans glucuronoxylomannan manifest different specificities and gene use profiles

The features of protective murine antibodies to the Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM) have been rigorously investigated; however, the characteristics of protective human antibodies to GXM have not been defined. We produced monoclonal antibodies (MAbs) from XenoMouse mice (transgenic mice that express human immunoglobulin M [IgM], IgG2, and kappa) which were immunized with a C. neoformans serotype D strain 24067 GXM-diphtheria toxoid conjugate. This study reports the specificity and efficacy of three human IgM MAbs, G14, G15, and G19, generated from these mice. Each MAb was specific for GXM, but G14 and G19 had different specificity based on their binding to serotype A strain H99 and SB4 GXMs, to which G15 did not bind. Nucleic acid sequence analysis revealed that G15 uses V(H)3-64 in the germ line configuration. G14 and G19 use V(H)6-1, which has somatic mutations. All of the MAbs use V kappa DPK22/A27. Studies of MAb efficacy in BALB/c mice showed that administration of 0.1 mg, but not 1 or 0.01 mg, of G15 prolonged survival against lethal C. neoformans strain 24067 challenge, whereas G14 and G19 were not protective at any dose. This panel of MAbs illustrates that serotype D GXM has epitopes that elicit human antibodies that can be either protective or nonprotective. Our findings suggest that V(H) gene use may influence GXM specificity and efficacy, and they provide insights into the possible contribution that V(H) gene use may have in resistance and susceptibility to cryptococcosis.

Long-term kinetics of adult human antibody repertoires

In healthy humans, antibody repertoires change during ontogeny and senescence. The dynamics of antibody repertoires among adults over a longer period of time in one and the same individual has, however, not been extensively studied. In this study we analysed peripheral blood samples from five healthy adults, taken over a period of 10 weeks and once 9 years later. A competitive, quantitative polymerase chain reaction (PCR) was developed to investigate short and long-term variations in VH gene family repertoires. Serum antibody levels to common self and non-self antigens were determined in samples taken at the same time-points as the cell samples to analyse possible correlations between molecular and serological expression profiles. We found a high degree of stability in the VH gene family repertoire over time as well as between individuals with a Caucasian background. A specific change in the usage of primarily the VH3 and VH5 gene families was observed in one individual at one time-point. The deviating pattern resembled the VH gene family utilization pattern observed in naturally activated B lymphocytes. The fluctuations in VH3 and VH5 gene family expression correlated with the presence of rheumatoid factor in serum. We discuss the possible influence of polyclonal, transient stimulation of B cells on VH gene repertoires, as measured in circulating B cells.

Spectrotype analysis and clonal characteristics of human anti-Gal alpha1-3Gal antibodies

Galalpha1-3Gal (anti-Gal), a polyclonal so-called natural antibody (Ab), is present in large amounts in human serum not only as IgG-, but also as IgM- and IgA-isotypes. It has gained a particular interest in the context of xenotransplantation, because the endothelial pig cells express the terminal Galalpha1-3Gal determinant on several adhesion molecules. Little is known of it's function and direct examination of the structure of the Ig genes responsible for coding anti-Gal is lacking. We used the technique of isoelectric focussing (IEF)/affinity immunoblotting for direct analysis of the clonal distribution and spectrotype analysis of IgM- and IgG anti-Gal. By single cell analysis of magnetic bead and fluorescent-activated cell sorter (FACS) isolated mature anti-Gal bearing human B cells from whole blood we analyzed the VH gene families involved in anti-Gal production. Oligoclonal and individually distinct IgG banding patterns were found with isoelectric points between 4 and 9. IgM spectrotypes revealed to be more uniform with a polyclonal banding pattern of more than 12 bands at a pH between 4.7 and 7. IgG- and IgM-banding patterns over a period of 6 months remained unchanged. Single cell polymerase chain reaction (PCR), with all family specific primers, revealed the use of the VH2f gene family for the IgG2 isoptype. The differences found in the spectrotype banding patterns of IgG and IgM could be explained by the suggestion that anti-Gal IgM were produced by the use of unmutated germline genes and the possibility of the absence of somatic mutations. The greater clonal heterogeneity in the IgG population could be explained by somatic hypermutations during the switch from IgM to IgG. The use of this VH2f gene family, which is also involved in the generation of Abs against bacterial pathogens, could mean that this is a predominant region used for the generation of such natural occurring antibodies.

Immunoglobulin heavy-chain gene rearrangement in adult acute lymphoblastic leukemia reveals preferential usage of J(H)-proximal variable gene segments

The aim of this study was to characterize individual-segment and overall patterns of V(H) gene usage in adult B-lineage acute lymphoblastic leukemia (ALL). Theoretical values of V(H) segment usage were calculated with the assumption that all V(H) segments capable of undergoing rearrangement have an equal probability of selection for recombination. Leukemic clones from 127 patients with adult B-lineage acute leukemias were studied by fingerprinting by means of primers for the framework 1 and joining segments. Clones from early preimmune B cells (245 alleles identified) show a predominance of V(H)6 family rearrangements and, consequently, do not conform to this hypothesis. However, profiles of V(H) gene family usage in mature B cells, as investigated in peripheral blood (6 samples), B-cell lymphomas (36 clones) and chronic lymphocytic leukemia (56 clones), are in agreement with this theoretical profile. Sequence analyses of 64 V(H) clones in adult ALL revealed that the rate of V(H) usage is proportional to the proximity of the V(H) gene to the J(H) locus and that the relationship can be mathematically defined. Except for V(H)6, no other V(H) gene is excessively used in adult ALL. V(H) pseudogenes are rarely used (n = 2), which implies the existence of early mechanisms in the pathway to B-cell maturation to reduce wasteful V(H)-(D(H))-J(H) recombination. Finally, similar to early immunoglobulin-H rearrangement patterns in the mouse, B cells of ALL derive from a pool of cells more immature than the cells in chronic lymphoid B-cell malignancies.

Molecular dissection of the tissue transglutaminase autoantibody response in celiac disease

Celiac disease (CD) is an intestinal malabsorption characterized by intolerance to cereal proteins accompanied by immunological responses to dietary gliadins and tissue transglutaminase, an autoantigen located in the endomysium. Tissue transglutaminase belongs to the family of enzymes that catalyze protein cross-linking reactions and is constitutively expressed in many tissues as well as being activated during apoptosis. The role of gliadins in eliciting the immune response in CD and how transglutaminase is linked to the primary reaction are still unclear. In this work, we report the production and analysis of six phage Ab libraries from the peripheral and intestinal lymphocytes of three CD patients. We were able to isolate Abs to transglutaminase from all intestinal lymphocytes libraries but not from those obtained from peripheral lymphocytes. This is in contrast to Abs against gliadin, which could be obtained from all libraries, indicating that the humoral response against transglutaminase occurs at the local level, whereas that against gliadin occurs both peripherally and centrally. Abs from all three patients recognized the same transglutaminase epitopes with a bias toward the use of the V(H)5 Ab variable region family. The possible role of these anti-transglutaminase Abs in the onset of CD and associated autoimmune pathologies is discussed.

Ig heavy chain CDR3 size diversities are similar after conventional peripheral blood and ex vivo expanded hematopoietic cell transplants

It is largely unknown whether the immune repertoire can be reconstituted successfully after high-dose chemotherapy and transplantation using ex vivo expanded hematopoietic stem cell (HSC) grafts. It is critically important for the transplant outcome that immune repertoire reconstitution progresses after ex vivo expanded HSC graft transplants at least as efficiently as that seen after conventional HSC transplants. Previously, we showed that the T cell receptor V beta (TCRVB) third complementarity determining region (CDR3) diversification after ex vivo expanded bone marrow (BM) HSC graft transplants was similar to that seen after conventional peripheral blood stem cell transplants (PBSCTs). In the present study, the CDR3 diversity of the six immunoglobulin (Ig) heavy chain variable region gene (V(H)) families was examined in five breast cancer patients who were transplanted with ex vivo expanded BM HSCs as the only source of stem cells. For comparison, 12 healthy adults and four conventional PBSCT recipients were also studied. Using both CDR3 fingerprinting and single strand conformation polymorphism (SSCP) methodologies, it is shown that the contribution of the V(H) families to the overall repertoire among healthy adults is highly variable and not always proportional to V(H) family member size. After both ex vivo expanded HSC transplants and conventional PBSCTs, the V(H) CDR3 repertoires were limited in size diversity at 6 weeks post transplant. By 6 months, however, V(H) families displayed a repertoire diversity that was as complex as that seen in healthy adults. No difference was seen between ex vivo expanded HSC graft transplant recipients and conventional PBSCT recipients in V(H) repertoire diversity. In one patient there was a follow-up analysis 12 months after ex vivo expanded graft transplant, and the diversity of the V(H) families was maintained. In all patients, the amino acid size of the CDR3 regions fell within adult limits at all time points post transplant. These results indicate that B cell repertoire regeneration after ex vivo expanded hematopoietic cell graft transplants is similar to that seen after conventional PBSCT.

A High Frequency of Circulating B Cells Share Clonotypic Ig Heavy-Chain VDJ Rearrangements With Autologous Bone Marrow Plasma Cells in Multiple Myeloma, as Measured by Single-Cell and In Situ Reverse Transcriptase-Polymerase Chain Reaction

In multiple myeloma (MM), the VDJ rearrangement of the immunoglobulin heavy chain expressed by MM plasma cells provides a unique clonotypic marker. Although clonotypic MM cells have been found in the circulation, their number has been controversial. Our objective was to provide direct evidence, using single-cell assays, for the frequency of clonotypic cells in blood of 18 MM patients, and to confirm their identity as B cells. The clonotypic Ig heavy-chain (IgH) VDJ was determined from single plasma cells using consensus reverse transcriptase-polymerase chain reaction (RT-PCR), subcloning, and sequencing. For all patients, using patient-specific primers, clonotypic transcripts were amplified from 10 or more individual plasma cells. Using in situ RT-PCR, for all patients greater than 80% of plasma cells were found to be clonotypic. Three separate methods, RT-PCR, single-cell RT-PCR, and in situ RT-PCR, were used to analyze clonotypic cells in peripheral blood mononuclear cells (PBMC) from MM patients. Sequencing of the IgH transcripts expressed by individual cells obtained by limiting dilution of freshly isolated PBMC from a MM patient showed that all B cells expressed an identical CDR3. This intraclonal homogeneity indicates an escape from antigenic-selection, characteristic of malignant B cells. For this patient, the frequency of clonotypic PBMC, about 25%, was comparable to the number of PBMC B cells (34%). Because the PBMC included less than 1% plasma cells, virtually all clonotypic PBMC must be B cells. Using single-cell RT-PCR, clonotypic IgH transcripts were identified in individual sorted B cells from blood. To accurately quantify the number of clonotypic B cells, sorted B cells derived from 18 MM patients (36 samples) and 18 healthy donors (53 samples) were analyzed using in situ RT-PCR with patient-specific primers. Clonotypic transcripts were not detectable among normal B cells. For the 18 MM patients, a mean of 66% ± 4% (SE) of blood B cells were clonotypic (range, 9% to 95%), with mean absolute number of 0.15 ± .02 × 109/L blood. Over time in individual patients, conventional chemotherapy transiently decreased circulating clonotypic B cells. Their numbers were increased in granulocyte colony-stimulating factor (G-CSF)– mobilized blood of one patient. However, clonotypic B cells of a one patient became undetectable after allogeneic transplant, correlating with complete remission. Although contributions to MM spread and progression is likely, their malignant status and impact has yet to be clarified. Their high frequency in the blood, and their resistence to conventional chemotherapy suggests that the number of circulating clonotypic cells should be clinically monitored, and that therapeutic targeting of these B cells may benefit myeloma patients.

© 1998 by The American Society of Hematology.

A High Frequency of Circulating B Cells Share Clonotypic Ig Heavy-Chain VDJ Rearrangements With Autologous Bone Marrow Plasma Cells in Multiple Myeloma, as Measured by Single-Cell and In Situ Reverse Transcriptase-Polymerase Chain Reaction

In multiple myeloma (MM), the VDJ rearrangement of the immunoglobulin heavy chain expressed by MM plasma cells provides a unique clonotypic marker. Although clonotypic MM cells have been found in the circulation, their number has been controversial. Our objective was to provide direct evidence, using single-cell assays, for the frequency of clonotypic cells in blood of 18 MM patients, and to confirm their identity as B cells. The clonotypic Ig heavy-chain (IgH) VDJ was determined from single plasma cells using consensus reverse transcriptase-polymerase chain reaction (RT-PCR), subcloning, and sequencing. For all patients, using patient-specific primers, clonotypic transcripts were amplified from 10 or more individual plasma cells. Using in situ RT-PCR, for all patients greater than 80% of plasma cells were found to be clonotypic. Three separate methods, RT-PCR, single-cell RT-PCR, and in situ RT-PCR, were used to analyze clonotypic cells in peripheral blood mononuclear cells (PBMC) from MM patients. Sequencing of the IgH transcripts expressed by individual cells obtained by limiting dilution of freshly isolated PBMC from a MM patient showed that all B cells expressed an identical CDR3. This intraclonal homogeneity indicates an escape from antigenic-selection, characteristic of malignant B cells. For this patient, the frequency of clonotypic PBMC, about 25%, was comparable to the number of PBMC B cells (34%). Because the PBMC included less than 1% plasma cells, virtually all clonotypic PBMC must be B cells. Using single-cell RT-PCR, clonotypic IgH transcripts were identified in individual sorted B cells from blood. To accurately quantify the number of clonotypic B cells, sorted B cells derived from 18 MM patients (36 samples) and 18 healthy donors (53 samples) were analyzed using in situ RT-PCR with patient-specific primers. Clonotypic transcripts were not detectable among normal B cells. For the 18 MM patients, a mean of 66% ± 4% (SE) of blood B cells were clonotypic (range, 9% to 95%), with mean absolute number of 0.15 ± .02 × 109/L blood. Over time in individual patients, conventional chemotherapy transiently decreased circulating clonotypic B cells. Their numbers were increased in granulocyte colony-stimulating factor (G-CSF)– mobilized blood of one patient. However, clonotypic B cells of a one patient became undetectable after allogeneic transplant, correlating with complete remission. Although contributions to MM spread and progression is likely, their malignant status and impact has yet to be clarified. Their high frequency in the blood, and their resistence to conventional chemotherapy suggests that the number of circulating clonotypic cells should be clinically monitored, and that therapeutic targeting of these B cells may benefit myeloma patients.

© 1998 by The American Society of Hematology.

Somatic mutation of immunoglobulin V(H)6 genes in human infants

Infants respond to antigen by making antibody that is generally of low affinity for antigen. Somatic hypermutation of immunoglobulin genes, and selection of cells expressing mutations with improved affinity for antigen, are the molecular and cellular processes underlying the maturation of antibody affinity. We have reported previously that neonates and infants up to 2 months of age, including individuals undergoing strong immunological challenge, show very few mutated V(H)6 sequences, with low mutation frequencies in mutated sequences, and little evidence of selection. We have now examined immunoglobulin genes from healthy infants between 2 and 10 months old for mutation and evidence of selection. In this age group, the proportion of V(H)6 sequences which are mutated and the mutation frequency in mutated sequences increase with age. There is evidence of selection from 6 months old. These results indicate that the process of affinity maturation, which depends on cognate T-B cell interaction and functional germinal centres, is approaching maturity from 6 months old.

Efficient construction of a large nonimmune phage antibody library: the production of high-affinity human single-chain antibodies to protein antigens

A large library of phage-displayed human single-chain Fv antibodies (scFv), containing 6.7 x 10(9) members, was generated by improving the steps of library construction. Fourteen different protein antigens were used to affinity select antibodies from this library. A panel of specific antibodies was isolated with each antigen, and each panel contained an average of 8.7 different scFv. Measurements of antibody-antigen interactions revealed several affinities below 1 nM, comparable to affinities observed during the secondary murine immune response. In particular, four different scFv recognizing the ErbB2 protein had affinities ranging from 220 pM to 4 nM. Antibodies derived from the library proved to be useful reagents for immunoassays. For example, antibodies generated to the Chlamydia trachomatis elementary bodies stained Chlamydia-infected cells, but not uninfected cells. These results demonstrate that phage antibody libraries are ideally suited for the rapid production of panels of high-affinity mAbs to a wide variety of protein antigens. Such libraries should prove especially useful for generating reagents to study the function of gene products identified by genome projects.

A definitive set of oligonucleotide primers for amplifying human V regions

BACKGROUND

The creation of large diverse phage antibody libraries from natural sources relies on primers which are able to amplify as many V genes as possible. All functional germline V genes have recently been catalogued in a database, V BASE [1]. Previously published primer sets are unable to recognise all these V genes.

OBJECTIVES

The design of a human primer set able to recognise all functional human V genes which can be used to create diverse phage antibody libraries.

STUDY DESIGN

A new set of primers able to recognise all functional V genes were designed using the following criteria: at least 16 bp homology of the 3' end of the primer to the V gene, no more than 8-fold total degeneracy and minimum primer dimer formation. These primers were tested in all possible combinations in PCR using cDNA from human peripheral blood lymphocytes or from human cord blood lymphocytes.

RESULTS

By computer analysis, all V genes in V BASE could be amplified using this primer set. This theoretical result was tested practically by PCR and all primer pairs were shown to be functional, producing PCR products of the expected size. The intensity of the PCR products reflected information available on the expression of the different V gene families recognised and their expression in these two different V gene sources.

CONCLUSIONS

This new primer set will facilitate the creation of more diverse phage antibody libraries than has been hitherto possible using presently available primer sets.

Age-related impaired affinity maturation and differential D-JH gene usage in human VH6-expressing B lymphocytes from healthy individuals

To elucidate the basic molecular events underlying humoral immunity during ontogeny and senescence, we analyzed a panel of 179 polymerase chain reaction-derived VH6-D-JH rearrangements from cord blood, peripheral blood, and spleen. Nucleotide sequence analysis of the CDR3 region shows that there is a difference in D and JH gene usage in functional rearrangements between lymphocytes from peripheral blood and spleen. Analysis of the VH6 gene shows that the mutational frequencies rise from 0.81% in cord blood to 1.96% in peripheral blood lymphocytes derived from young adults, and decrease to 0.80% in samples from individuals older than 50 years. The number of rearrangements carrying mutations follows a similar pattern: 22% in cord blood, 73% in the age group 20-49 years, and 57% in the age group over 50 years. The mutational frequencies among the mutated genes are, however, similar for cord blood and young adults, 2.76% and 2.51%, respectively, and 1.3% in older adults. These data show an age-related impaired affinity maturation which might relate to the decrease in immunological responsiveness among the elderly.