Production and persistence of specific antibodies in COVID-19 patients with hematologic malignancies: role of rituximab

The ability of patients with hematologic malignancies (HM) to develop an effective humoral immune response after COVID-19 is unknown. A prospective study was performed to monitor the immune response to SARS-CoV-2 of patients with follicular lymphoma (FL), diffuse large B-cell lymphoma (DLBCL), chronic lymphoproliferative disorders (CLD), multiple myeloma (MM), or myelodysplastic/myeloproliferative syndromes (MDS/MPN). Antibody (Ab) levels to the SARS-CoV-2 nucleocapsid (N) and spike (S) protein were measured at +1, +3, +6 months after nasal swabs became PCR-negative. Forty-five patients (9 FL, 8 DLBCL, 8 CLD, 10 MM, 10 MDS/MPS) and 18 controls were studied. Mean anti-N and anti-S-Ab levels were similar between HM patients and controls, and shared the same behavior, with anti-N Ab levels declining at +6 months and anti-S-Ab remaining stable. Seroconversion rates were lower in HM patients than in controls. In lymphoma patients mean Ab levels and seroconversion rates were lower than in other HM patients, primarily because all nine patients who had received rituximab within 6 months before COVID-19 failed to produce anti-N and anti-S-Ab. Only one patient requiring hematological treatment after COVID-19 lost seropositivity after 6 months. No reinfections were observed. These results may inform vaccination policies and clinical management of HM patients.

Lymphocyte homeostasis is maintained in perinatally HIV-infected patients after three decades of life

Background

While immunosenescence, defined as reduced production of new lymphocytes, restriction of T-cell receptor repertoire and telomeres shortening, has been extensively evaluated in HIV-infected children and adults, no data about these parameters are available in perinatally-infected patients with very long-lasting HIV infection.

Methods

We compared thymic and bone marrow output, telomere length (measured by Real-Time PCR) and T-cell receptor repertoire (determined by spectratyping) of 21 perinatally HIV-infected subjects (with a median of 27 years of infection) with those of 19 age-matched non-perinatally HIV-infected patients and 40 healthy controls. All patients received a combined antiretroviral therapy.

Results

While thymic and bone marrow output were not different among the analyzed groups, telomere length in peripheral blood cells and T-cell receptor diversity were significantly lower in HIV-perinatally and non-perinatally infected individuals compared to healthy controls.

Conclusions

In HIV-infected subjects, a normal thymic output together with a reduced telomere length and a restricted T-cell receptor repertoire could be explained by the shift of newly produced cells into memory subsets. This phenomenon may allow to control viral infection and maintain peripheral homeostasis.

Peripheral loss of regulatory T cells and polyautoimmunity in an HIV-infected patient

We report a case of a human immunodeficiency virus (HIV)/hepatitis C virus-co-infected patient with an optimal virological status but with a poor CD4+ cell profile, followed up in the University Department of Infectious and Tropical Diseases of Brescia, Italy. He presented several autoimmune diseases (ADs) over the years concomitant with CD4+ cell increase episodes following severe immune depression of unknown cause. We studied T- and B-cell subsets and found low levels of K-deleting Recombination Excision Circles, T-cell Receptor Excision Circles and B and T memory subpopulations, which indicated that the bone marrow and thymic outputs were lower than in healthy controls. The most relevant phenotypic alteration was in the regulatory T-cell (Treg) population, because total Tregs as well as naïve, central memory and effector memory cells were detected at very low levels. This was the first case of polyautoimmunity defined as the presence of more than one AD in the same individual, occurring in an HIV patient. Several factors may be implicated, including genetic susceptibility, environmental factors, concomitant therapies and dysregulation of immune system cells. The extremely low number of Tregs found in our patient may play a major role in the regulation of the immune response and the development of all ADs.

Newly produced T and B lymphocytes and T-cell receptor repertoire diversity are reduced in peripheral blood of fingolimod-treated multiple sclerosis patients

BACKGROUND

Fingolimod inhibits lymphocyte egress from lymphoid tissues, thus altering the composition of the peripheral lymphocyte pool of multiple sclerosis patients.

OBJECTIVE

The objective of this paper is to evaluate whether fingolimod determines a decrease of newly produced T- and B-lymphocytes in the blood and a reduction in the T-cell receptor repertoire diversity that may affect immune surveillance.

METHODS

Blood samples were obtained from multiple sclerosis patients before fingolimod therapy initiation and then after six and 12 months. Newly produced T and B lymphocytes were measured by quantifying T-cell receptor excision circles and K-deleting recombination excision circles by real-time PCR, while recent thymic emigrants, naive CD8(+) lymphocytes, immature and naive B cells were determined by immune phenotyping. T-cell receptor repertoire was analyzed by complementarity determining region 3 spectratyping.

RESULTS

Newly produced T and B lymphocytes were significantly reduced in peripheral blood of fingolimod-treated patients. The decrease was particularly evident in the T-cell compartment. T-cell repertoire restrictions, already present before therapy, significantly increased after 12 months of treatment.

CONCLUSIONS

These results do not have direct clinical implications but they may be useful for further understanding the mode of action of this immunotherapy for multiple sclerosis patients.

Adult-type hypolactasia genotyping in Northern Italy: prevalence of C/T-13910 polymorphism and questions after comparison with existing data

A genotyping assay was setup to assess the prevalence, in the population of a Northern Italian city, of the C/T-13910 single nucleotide polymorphism, closely associated to lactose malabsorption in many world areas including Sardinia. The results were compared to published Italian data, in order to evaluate the worth of a future validation of the assay for use in routine practice. DNA was extracted from blood samples of 123 randomly chosen healthy blood donors coming from the same city area, and was analyzed by a real-time polymerase chain reaction (PCR) genotyping assay; the frequency of the hypolactasia-associated CC-genotype was compared to the weighted average of results extracted from studies reporting the frequency of hypolactasic phenotype or genotype in nearby or distant Italian regions. Sixty-five percent of donors carried the CC-genotype, a percentage similar to other northern Italian cities, but significantly higher than what previously determined in surrounding Italian regions at the phenotype level, i.e. by breath test. This discrepancy parallels recent reports of non concordance between results of genotyping and hypolactasic phenotype in some world areas, including a neighbouring Northern Italian city. A north-south gradient of CC-prevalence was also observed. These results reinforce the notion of wide inter-regional variations in the frequency of C/T-13910 polymorphism and of incostant concordance with hypolactasic phenotype, even in subjects from the same country. Given the unsatisfactory results recently obtained from validation of a related assay in a neighbouring city, the authors decided not to proceed further and keep the assay only as a diagnostic aid in special situations.

Renewal of the T-cell compartment in multiple sclerosis patients treated with glatiramer acetate

The immunomodulating activity of glatiramer acetate on T-cells of multiple sclerosis patients has only been partially clarified. The objective of this work was to investigate whether glatiramer acetate modifies thymic release of newly produced T-cells and the peripheral composition of the T-cell repertoire. T-cell receptor excision circles, (thymic) naive (CD4(+)CD45RA(+)CCR7(+)CD31(+)) T helper cells, and central (CD4(+)CD45RA(-)CCR7(+)) and effector (CD4(+)CD45RA(-)CCR7(-)) memory T-cells were evaluated in 89 untreated patients, 84 patients treated for at least 1 year, and 31 patients beginning treatment at the time of inclusion in the study and then followed-up for 12 months; controls were 81 healthy donors. The T-cell repertoire was analysed in selected samples. The percentage of (thymic)naive T helper cells was diminished in untreated patients, but rose to control values in treated subjects; a decrease in central memory T-cells was also observed in treated patients. Follow-up patients could be divided into two subgroups, one showing unmodified (thymic)naive T helper cells and T-cell diversity, the other in which the increased release of new T-cells was accompanied by modifications of the T-cell repertoire. Glatiramer acetate modifies the peripheral T-cell pool by activating a thymopoietic pathway of T-cell release that leads to a different setting of T-cell diversity and, likely, to a dilution of autoreactive T-cells.

SEN virus infection and its relationship to transfusion-associated hepatitis

SEN virus (SEN-V) is a recently identified single-stranded, circular DNA virus. Two SEN-V variants (SENV-D and SENV-H) were assayed by polymerase chain reaction (PCR) to investigate their role in the causation of transfusion-associated non-A to E hepatitis. The incidence of SEN-V infection after transfusion was 30% (86 of 286) compared with 3% (3 of 97) among nontransfused controls (P < .001). Transfusion risk increased with the number of units transfused (P < .0001) and donor-recipient linkage for SEN-V was shown by sequence homology. The prevalence of SEN-V in 436 volunteer donors was 1.8%. Among patients with transfusion-associated non-A to E hepatitis, 11 of 12 (92%) were infected with SEN-V at the time of transfusion compared with 55 of 225 (24%) identically followed recipients who did not develop hepatitis (P < .001). No effect of SEN-V on the severity or persistence of coexistent hepatitis C virus (HCV) infection was observed. In 31 infected recipients, SEN-V persisted for greater than 1 year in 45% and for up to 12 years in 13%. SEN-V-specific RNA (a possible replicative intermediate) was recovered from liver tissue. In summary, SENV-D and -H were present in nearly 2% of US donors, and were unequivocally transmitted by transfusion and frequently persisted. The strong association of SEN-V with transfusion-associated non-A to E hepatitis compared with controls raises the possibility, but does not establish that SEN-V might be a causative agent of posttransfusion hepatitis. The vast majority of SEN-V-infected recipients did not develop hepatitis.

Detection of identical T-cell clonotype expansions in both the donor and recipient after allogeneic bone marrow transplantation

Using phenotypic, functional and molecular techniques, this study was performed to compare the complexity of the T-cell receptor repertoire of a bone marrow transplanted patient with that of his HLA-matched related donor, both of whom developed a chronic lymphocytosis sustained by CD3+CD8+CD57+CD16-CD56- granular lymphocytes 3 years after transplantation. Although Southern blot analysis revealed the presence of extra bands in both subjects, thus indicating the presence of at least one clonal T-cell population, the study of the different T-cell receptor Vbeta (TCRBV) usage did not demonstrate discrete overexpression of any TCRBV segments. On the contrary, heteroduplex analysis of TCRBV transcripts suggested the presence of oligoclonal T-cell expansions in the two subjects. Cloning and sequencing studies demonstrated that T-cell clones expressing identical TCRBV chains were expanded both in the donor and in the recipient. Furthermore, clones with similar, but not identical, junctional regions were also found in the two subjects. These data indicate that, at the time of the graft, a few cells with a monoclonal/oligoclonal pattern that were present in the donor were transferred to the recipient, where they may have found the same environmental in vivo conditions and/or the antigenic pressure favouring their abnormal expansion.

Detection of skewed T-cell receptor V-beta gene usage in the peripheral blood of patients with multiple sclerosis

The ex vivo analysis of the T-cell receptor V-beta (TCRBV) gene usage by circulating T lymphocytes in Multiple Sclerosis (MS) patients may contribute to understanding disease pathogenesis. In the present study, TCRBV gene usage was analyzed in freshly collected unstimulated peripheral blood mononuclear cells (PBMC) isolated from 40 MS patients and 20 healthy controls. Nine patients presented abnormal repertoires, with expansion of one or more TCRBV segments. Among these patients, six presented expansion of TCRBV9 chain expression, three also having an expansion of TCRBV1, TCRBV11 and TCRBV22 segments. The most frequently observed TCRBV chain expansion, TCRBV9, was further analyzed and identified as polyclonal. Evaluation of clinical variables showed that median disease duration was shorter in patients with TCRBV gene expression abnormalities. Longitudinal evaluation of five patients with a skewed repertoire showed regression of expanded TCRBV chains expression to normal values. These data indicate that certain MS patients have abnormal TCRBV gene expression. Such abnormalities are caused by polyclonal expansions of T lymphocyte subpopulations that use the same TCRBV gene families, are unstable and preferentially observed early in the course of the disease.

Development of autologous, oligoclonal, poorly functioning T lymphocytes in a patient with autosomal recessive severe combined immunodeficiency caused by defects of the Jak3 tyrosine kinase

Defects of the common gamma chain subunit of the cytokine receptors (gamma c) or of Jak3, a tyrosine kinase required for gamma c signal transduction, result in T-B+ severe combined immunodeficiency (SCID). However, atypical cases, characterized by progressive development of T lymphocytes, have been also reported. We describe a child with SCID caused by Jak3 gene defects, which strongly but not completely affect Jak3 protein expression and function, who developed a substantial number (> 3,000/microL) of autologous CD3+CD4+ T cells. These cells showed a primed/activated phenotype (CD45R0+ Fas+ HLA-DR+ CD62L(lo)), defective secretion of T-helper 1 and T-helper 2 cytokines, reduced proliferation to mitogens, and a high in vitro susceptibility to spontaneous (caused by downregulation of bcl-2 expression) as well as activation-induced cell death. A restricted T-cell receptor repertoire was observed, with oligoclonal expansion within each of the dominant segments. These features resemble those observed in gamma c-/y and in Jak3-/- mice, in which a population of activated, anergic T cells (predominantly CD4+) also develops with age. These results suggest that residual Jak3 expression and function or other Jak3-independent signals may also permit the generation of CD4+ T cells that undergo in vivo clonal expansion in humans; however, these mechanisms do not allow development of CD8+ T cells, nor do they fully restore the functional properties of CD4+ T lymphocytes.

Oligoclonal CD4+ CD57+ T-cell expansions contribute to the imbalanced T-cell receptor repertoire of rheumatoid arthritis patients

A peculiar feature of rheumatoid arthritis patients is that they carry clonally expanded CD4+ and CD8+ cells in the peripheral blood. While the distortion of the repertoire of CD8+ cells has been ascribed to the increase of CD8+ CD57+ large granular lymphocytes, often detected in these patients, the mechanism responsible for the clonal expansion of CD4+ cells remains unexplained. Here, we report that CD4+ CD57+ cells, that in healthy individuals represent a small subset of peripheral CD4+ lymphocytes, are significantly expanded in the peripheral blood of a considerable percentage of rheumatoid arthritis patients. Furthermore, the expansion of these lymphocytes appears to correlate with the presence of rheumatoid factor. The molecular analysis of the T-cell receptor variable beta segments expressed by the CD4+ CD57+ cells enriched in rheumatoid arthritis patients showed that they use restricted repertoires, that partially overlap with those of their CD4- CD57+ counterpart. The structural feature of the receptor ligand expressed by these cells revealed that their expansion is most likely mediated by strong antigenic pressures. However, since we also found that CD4+ CD57+ and CD4- CD57+ cells can share the same clonal specificity, it is likely that their selection is not mediated by conventional major histocompatibility complex restricted mechanisms. Thus, while our data demonstrate that CD4+ CD57+ cells play an important role in establishing the imbalance of the CD4+ cell repertoire observed in rheumatoid arthritis patients, they also suggest that these cells have common features with mouse CD4+ CD8- NK1.1+/T cells.

Detection of clonal T cell populations with closely related T cell receptor junctional sequences in persons at high risk for human immunodeficiency virus (HIV) infection and in patients acutely infected with HIV

The T cell repertoires were characterized for CD4+ and CD4 lymphocytes derived from 2 patients with acute human immunodeficiency virus (HIV) infection and from 25 HIV-seronegative persons at high risk for acquiring HIV. Oligoclonal expansions of CD4 cells were detected in the HIV-infected patients and in 2 of 3 uninfected high-risk subjects with a reduced number of CD4+ lymphocytes. Furthermore, nucleotide sequencing revealed that some of the T cell receptor (TCR) beta variable segments (TCRBV), which were highly selected in the high-risk subjects, shared closely related junctional sequences, with the TCRBV predominantly expanded in the HIV-infected patients. Since the likelihood that these similarities occurred by chance is extremely low, these data provide direct molecular evidence in support of several cellular and serologic studies suggesting that some persons remain uninfected despite exposure to HIV.

The T-cell receptor repertoires expressed by CD4+ and CD4- large granular lymphocytes derived from the same patients suggest the persistent action of an immune-mediated selection process

The lymphoproliferative syndrome with large granular lymphocytes (LGL) is an heterogeneous disorder of unknown etiology. The analysis of T-cell receptor (TCR) genes rearrangements has shown that, in most cases, the disease is associated with clonal proliferation of CD8+CD57+ LGL. However, the putative neoplastic nature of these expansions remains questionable because clonal proliferations of CD8+ cells have recently been found also in physiologic conditions. To obtain more precise information on the mechanisms responsible for LGL expansions, we decided to compare the molecular characteristics of TCRBV chains expressed by LGL with different phenotype and function, but derived from the same patients. To this end, we characterized, at the molecular level, the TCR repertoires of fractionated T-cell populations of two unusual patients with concurrent expansions of CD4+CD57+ and CD4-CD57+ LGL. Our results show that the dominant TCRBV chains expressed by the different CD4+ and CD4- LGL populations were strictly oligoclonal. However, the molecular characteristics of the dominant V-D-J rearrangements also imply that the selection of these clones was not due to a neoplastic event. Rather, our data suggest that these particular LGL proliferations can be ascribed to a chronic T-cell-mediated immune response that involves recognition by the engaged TCR of antigens that are not necessarily presented to immune system in the classical major histocompatibility complex-restricted pathway.

Assessment of T-cell receptor beta-chain diversity by heteroduplex analysis

The aim of this work was to search for a simple and alternative approach to the currently used methodologies for the analysis of T-cell receptor repertoire diversity. To this end we studied whether the heteroduplex analysis could be adapted to study the clonality of the T-cell receptor beta chain (TCRBV). We therefore analyzed, by sequencing, the molecular characteristics of the V-D-J junctions of numerous TCRBV chains from a variety of patients and from normal individuals, and compared the results with those obtained with the heteroduplex analysis. The latter procedure involves the amplification of the target TCRBV chains and the denaturation and renaturation of the amplified product to permit the random association of the distinct DNA strands encoding the different junctional regions. Whereas amplified material from polyclonal lymphoid cells migrates on a polyacrylamide gel as a "smear" of bands composed of different-sized polyclonal PCR fragments, the mismatched chains derived from oligoclonal populations migrate as discrete "heteroduplexes" and can be separated from the matched "homoduplex" obtained from homogeneous clonal cells. Our results provide evidence demonstrating that heteroduplex analysis can successfully be applied to the analysis of T-cell clonality in a variety of samples and can be complementary or substitute for the standard approach of TCR cloning and multiple sequencing of junctional regions. Thus, the procedure should facilitate the implementation of the analysis of TCR in diagnostic routine and should find applications in numerous physiologic and pathologic conditions.

Evidence for antigenic selection of large granular lymphocytes in a patient with Wiskott-Aldrich syndrome

It is now recognized that CD3+ large granular lymphocyte (LGL) proliferations may be clonally derived from their normal CD3+LGL+ counterpart, but the nature of the pressure responsible for the proliferation of these cells remains unclear. We approached this problem by analyzing the diversity of the T-cell receptor repertoire of LGL developed in different clinical settings. Two of our patients had typical lymphoproliferative disorders. The third case was much more unusual, as the LGL proliferation was associated with a Wiskott-Aldrich syndrome. Our data relative to the patients with the lymphoproliferative disorders only suggest that these LGL were clonally expanded. The data relative to the patient with Wiskott-Aldrich syndrome were more unexpected, as the T-cell repertoire of the LGL appeared to have common features with that of the other T-cell populations analyzed. These LGL were characterized by the clonal expansion of a few TCRBV segments that shared common amino acid motifs in the junctional region of the T-cell receptor. This common pattern of junctional diversity associated with different TCRBV segments is, therefore, consistent with a strong on-going antigenic selection process, possibly related to the pathogenesis of Wiskott-Aldrich syndrome. Furthermore, the finding that the same TCRBV segments were also highly expanded among other T-cell subpopulations questions the malignant nature of this LGL proliferation.

Engrafted maternal T cells in a severe combined immunodeficiency patient express T-cell receptor variable beta segments characterized by a restricted V-D-J junctional diversity

To better understand the peculiar functional behavior of engrafted maternal T cells in a severe combined immunodeficiency (SCID) patient, we characterized, at the molecular level, the T-cell repertoire of a SCID child with a high number of engrafted, mature, activated lymphocytes. We found that, although these transplacentally acquired T cells express a random set of T-cell receptor variable beta (TCRBV) segments, the TCRBV transcripts are characterized by an extremely restricted V-D-J junctional diversity. Only a few cDNA clones were dominant among the TCRBV4+, TCRBV6+, and TCRBV20+ populations in engrafted cells, whereas the same TCRBV chains expressed by the mother's lymphocytes had the expected junctional hetero-geneity. Highly diverse and polyclonal junctions were also expressed by maternal cells activated in mixed lymphocyte reaction by Epstein-Barr virus (EBV)-transformed B lymphocytes from the patient, indicating that the strong clonal selection that characterizes the engrafted cells repertoire is probably not due to allorecognition. Furthermore, we report that the repertoire of the transplacentally acquired lymphocytes is dynamic over time and is characterized by waves of expression and contraction of selected clones, expressing different TCRBV segments. These results help to explain some of the abnormal functional behaviors of engrafted maternal cells and raise new questions regarding the mechanisms responsible for the restricted clonal diversity.

Different TCRBV genes generate biased patterns of V-D-J diversity in human T cells

The aim of this work was to assess whether each T-cell receptor (TCR) BV segment generates a random pattern of junctional diversity or if, alternatively, biased patterns of V-D-J rearrangements limit the number of available TCR specificities. Detailed molecular analysis of T-cell receptors expressed by lymphocytes was obtained by generating a large number of junctional regions sequences from TCRBV3, TCRBV4, TCRBV5S1, TCRBV12, TCRBV13S2, TCRBV17, TCRBV20, and TCRBV22 variable genes. The > 800 sequences analyzed have allowed the characterization of the recombination frequencies of each germline-encoded V, D, and J segments, as well as of the magnitude of exonucleolytic nibbling and of the number of N nucleotides inserted for each group of TCRB segments. The data obtained indicate that the extent of junctional diversity varies considerably depending on the TCRBV gene implicated in the recombination event, due to the occurrence of skewed patterns of J and D region usage. Furthermore, our results show that "illegitimate" rearrangements occur with unexpectedly high incidence, specifically at the level of TCRBD to TCRBJ joining. These findings provide additional information for a more accurate estimation of the size of the TCRBV repertoire and for understanding the well-established biased pattern of TCRBV expression in humans.

Insertion of a short human immunodeficiency virus (HIV)-2 gp36 sequence into an HIV-1 p24 recombinant protein results in a polypeptide with potent and TCRBV-restricted T cell triggering activity

In the present work we investigate whether artificial alterations of the structure of an inactive retrovirus-encoded protein could transform it in a superantigen. As a model system we used a recombinant human immunodeficiency virus (HIV)-1 p24 protein and two of its variants in which a short peptide corresponding to sequences of gp41 of HIV-1 (HIV-1 p24*) or gp36 of HIV-2 (HIV-1-2 p24*) has been inserted nearby the carboxy-terminal end of HIV-1 p24. As expected both HIV-1 p24 and HIV-1 p24* were inactive, while HIV-1-2 p24* was a potent inducer of human, but not murine, T cell proliferation. The possibility that the observed activity was due to contaminants was ruled out since the proliferative response could be specifically inhibited by a monoclonal anti-p24 antibody and by a peptide encompassing the area of HIV-1 p24/HIV-2 gp36 junction. Furthermore, the data exclude the possibility that the gp36 insertion is per se responsible for the observed proliferative activity. The analysis of the functional, phenotypic and molecular properties of the responding cells demonstrated that the response was class II dependent and that the activated cells were predominantly CD4+CD8- expressing a strongly biased repertoire of TCRBV segments. Collectively, these data strongly suggest that the HIV-1-2 p24* fusion protein shares common functional properties typical of superantigen molecules. Thus, our demonstration that a viral protein can be transformed into a superantigen simply by the insertion of a short peptide at the carboxy-terminal end has important implications for understanding the mode of action of retrovirus-encoded superantigens.

Superantigen-reactive human T cells express a biased repertoire of T-cell receptor V beta joining regions

A major characteristic of superantigens is their ability to stimulate T cells based predominantly on the type of variable segment of the T-cell receptor (TCR) V beta chain. Recently, however, reports from several laboratories have also implied a role for non-V beta elements in superantigen binding. The goal of the present study was to determine whether TCR V beta-D beta-J beta joining sequences may influence the interaction of superantigens with their target cells. To ascertain how the actual TCR repertoire of superantigen-triggered cells deviates from the theoretical one, we generated a large panel of joining region sequences from TCR carrying the TCR V beta 12 and TCR V beta 5,1 regions. The 245 sequences analysed represent transcripts of T cells from the same donor triggered either with an anti-CD3 monoclonal antibody or with the Staphylococcus aureus enterotoxins. Comparison of the joining sequences of these different groups demonstrates a skewed J beta usage in the sequences derived from superantigen-triggered cells and also provides evidence that ascribes to the putative CDR3 region of V beta segments a role in superantigen recognition. Finally, the data presented give some hints of the regions of the putative CDR3 loop that may play a major role in this function.

Selection of T lymphocytes in two rheumatoid arthritis patients defines different T-cell receptor V beta repertoires in CD4+ and CD8+ T-cell subsets

To study the selective pressures responsible for the expansion of T cells in rheumatoid arthritis, we constructed cDNA mini-libraries from purified CD4+ and CD8+ T cells prepared from peripheral blood and from synovial fluids of two rheumatoid arthritis patients. Comparison of these libraries by hybridization with specific probes indicated that V beta 2 and V beta 8 transcripts are selectively enriched in the CD4+ synovial fluid lymphocyte population, while V beta 4 was over-represented among both the CD4+ and CD8+ subsets. The enrichment of V beta 14 and V beta 17 observed in synovial fluid T cells of one patient was, however, selectively confined to the CD8+ T-cell subpopulation. Sequence analysis of several V beta 2, V beta 4 and V beta 8 clones, derived from CD4+ cells, revealed a high degree of heterogeneity in the V beta-D beta-J beta junctions, while a more biased utilization of J segments and a more restricted junctional heterogeneity were observed in V beta 4, V beta 14 and V beta 17 clones derived from CD8+ cells. These data suggest that the disease may be induced by the initial activation of a rather heterogeneous population of T-helper cells that are later responsible for the expansion of a more restricted pool of highly specific effector lymphocytes.

T cell repertoire and autoimmune diseases

Self-reactivity and autoimmunity are processes related to the breakage of self-tolerance that can be distinguished by their different clinical outcome and are widely accepted cornerstones of immunology. The finding that several potentially autoaggressive cells contribute to the repertoire of healthy individuals has stimulated a great deal of experimental work aimed at understanding the mechanisms that prevent autoimmune pathology. In this review we will consider the basic principles, and our present knowledge of the rules that preside over the interplay of the immune system with self-components. One viewpoint stresses the importance of major histocompatibility complex (MHC) and non-MHC genes in determining genetic predisposition to develop autoimmune phenomena. At a different level there is a strong interest in understanding the mechanisms of processing and presentation of self antigens, especially during ontogeny. Another topic of major interest concerns the interaction between MHC genes and the T cell receptor (TcR) complex as well as the identification of TcR V genes that are preferentially expressed by autoimmune T cells. All of these aspects are evaluated in the context of tolerance based on deletion and anergy. Finally we will propose a general model of autoimmunity based on the most recent findings concerning the biological activity of exogenous superantigens.

Expression and combinatorial diversity of germ line-encoded T cell receptor V genes in human peripheral blood T cells

The potential diversity of the T cell receptor (TcR) is defined by the combinational expression of variable segments and by mechanisms that insert or delete nucleotides at the junctional regions. The available repertoire is strongly influenced by negative and positive selection events. To study whether the diversity of the human T cell receptor of peripheral T cells is further restricted by the interaction between the TcR alpha and beta chains, we compared the level of transcription of different V alpha elements in human T cell blasts expressing either restricted or unrestricted sets of V beta genes. Our data establish that in some individuals, but not in others, the transcription of a given V alpha element is independent from the presence of particular V beta transcripts. Furthermore, our data also suggest that, in contrast to mouse, major TcR V gene deletions are absent in humans. Taken collectively, these results indicate that the diversity of the peripheral human TcR repertoire can benefit from the combinatorial expression of all the V elements present in the genome.

Analysis of amplified T cell receptor Vβ transcripts by a non-isotopic immunoassay

We have recently described a new colorimetric DNA enzyme immunoassay (DEIA) for detecting specific hybrids of complementary nucleic acids. This technology is based on an antibody that selectively recognizes double, but not single stranded DNA and therefore reveals the hybridization event independently from the DNA sequences. Most importantly, the test has an ELISA format and is very rapid and convenient for processing large numbers of samples. In the present report we have adapted this method to reveal the specificity of amplified T cell receptor V beta transcripts. V beta genes were amplified by polymerase chain reaction, using family specific primers and the specificity of the amplified products was determined by Southern blot and by DEIA. Our data demonstrate that DEIA had the same degree of sensitivity and specificity of conventional Southern hybridization. The possibility of analyzing amplified products with the simplicity of a conventional immunoassay should greatly facilitate the analysis of complex multigenic systems such as the T cell receptor and the immunoglobulin repertoire.

Selective depletion in HIV infection of T cells that bear specific T cell receptor V beta sequences

The mechanism of T cell depletion during infection with the human immunodeficiency virus (HIV) is unclear. Examination of the repertoire of T cell receptor V (variable) regions in persons infected with HIV revealed the absence of a common set of V beta regions, whereas V alpha usage was normal. The lack of these V beta segments did not appear to correlate with opportunistic infections. The selective elimination of T cells that express a defined set of V beta sequences may indicate the presence of an HIV-encoded superantigen, similar to those encoded by the long terminal repeat of the mouse mammary tumor virus.

Use of variable human V delta genes to create functional T cell receptor alpha chain transcripts

Previous studies of the human T cell receptor delta genes identified five commonly used V delta segments distinct from any of the known V alpha genes. To define better the relationship between the T cell receptor delta and alpha repertoires we amplified cDNA obtained by polyclonally activated lymphocytes with a common 3' antisense C alpha-specific primer and with five different 5' sense V delta family-specific primers. Amplified products were detected in staphylococcal enterotoxin C2, staphylococcal enterotoxin E, phytohemagglutinin, concanavalin A, anti-CD3 and anti-V beta 8-activated cells, although each cell population expressed a selective pattern of V delta genes. Sequence analysis revealed that each of the known V delta genes can productively rearrange to J alpha segments to produce functional V delta-J alpha-C alpha transcripts. These results argue strongly against the notion that the human V delta and V alpha repertoires are distinct. They further suggest that the restricted delta repertoire observed in many gamma/delta clones results from selection rather than from controlled rearrangements at the T cell receptor alpha/delta locus.

Restricted expression of T cell receptor V beta but not V alpha genes in rheumatoid arthritis

Synovial fluids of patients with rheumatoid arthritis contain activated T lymphocytes that may play an important role in the pathogenesis of the disease. Previous studies have suggested that the T cell receptor (TcR) repertoire of these cells is restricted, reflecting in vivo selection of a limited number of T cell specificities at the site of inflammation. To characterize better these T cell populations we used the polymerase chain reaction technology to estimate the proportion of TcR alpha and beta RNA containing any particular V elements from transcripts directly isolated from the synovial fluid cells and from peripheral blood mononuclear cells of three patients with rheumatoid arthritis. Our data show that, in contrast to peripheral blood mononuclear cells, synovial fluid T cells expressed only few V beta transcripts, one of which was overrepresented in two patients. Peripheral and joint fluid T cells, on the other hand, appeared to express the same set of non-restricted V alpha elements. These results suggest that a major antigen associated with the pathogenesis of rheumatoid arthritis may interact selectively with the V beta component of the TcR.

Expression of the human V beta 8 gene product preferentially correlates with class II major histocompatibility complex restriction specificity

We report that, in peripheral blood T cells, the V beta 8 gene product is much more represented on CD4+CD8- than on CD4-CD8+ lymphocytes. This skewing was observed in all individuals tested and with two independent strategies, one of which allows the selection of V beta 8+ T cells independently from their major histocompatibility complex-antigen specificity. Our data imply that the human V beta 8 gene product confers class II restriction specificity and that both the T cell receptor chains and CD4 molecule are involved in the selection of the T cell repertoire.

Positive and negative immunoregulation through CD4 depends on the concentration of the specific ligand and on the state of activation of the responding cells

In order to better define the functional role of the interaction of CD4 polypeptide with the T-cell receptor (TCR) complex, we analysed the effect of an anti-CD4 monoclonal antibody (mAb) on T-cell activation and on the modulation of expression of CD3, CD4 and TCR variable (V) regions. The results presented here demonstrate that both positive and negative modulation of CD3 and TCR V regions can be obtained with different concentrations of the same anti-CD4 mAb and that these effects are functionally directly related to differences in IL2-receptor expression. Moreover, our data show that the dose of anti-CD4 mAb required for modulating CD3- and CD4-molecule expression on activated E+ peripheral blood mononuclear cells is at least 30 times higher than that required to obtain the same effect on resting cells. Thus, our results demonstrate that the interaction of CD4 molecule with its ligand can result in both up and downregulation of TCR and IL2-receptor expression, and that this differential modulation is strictly dependent on the concentration of available ligand as well as on the activation state of the responding cells.