Idiotype-specific T lymphocytes in monoclonal gammopathies: evidence for the presence of CD4+ and CD8+ subsets

Tumour-specific CD4⁺ T helper (Th) and CD8⁺ T cytotoxic (Tc) cells may participate in the control and eradication of tumour cells. In the present study, idiotype-specific stimulation of CD4⁺ and CD8⁺ blood T cells from patients with monoclonal gammopathy of undetermined significance and patients with untreated multiple myeloma stage I was examined. Activation was measured in the CD4⁺ and CD8⁺ subsets enriched by magnetic microbeads as the incorporation of ³H-thymidine and the secretion of interferon (IFN)-γ, interleukin (IL)-2 and IL-4 by single cells using the enzyme-linked immunospot assay. Idiotype-specific T cells were found in four of seven patients. Stimulation was mainly confined to the CD4⁺ subset in three of the four responding patients. This type of response was major histocompatibility complex (MHC) class II restricted as it could be inhibited by monoclonal antibodies against MHC class II (HLA-DR), but not against class I (HLA-ABC) molecules. Idiotype-specific CD8⁺ T cells were also demonstrated in these patients although at a lower frequency. One patient showed a strong and dominating activation of CD8⁺ T cells which could be blocked by antibodies against HLA-ABC but not against HLA-DR. Idiotype-specific CD4⁺ or CD8⁺ T cells were mainly of the type-1 subsets as judged by their secretion of IFN-γ and IL-2. Thus, this study provides evidence for the presence of idiotype-specific and MHC-restricted CD4⁺ and CD8⁺ T cells of the type-1 subsets in patients with monoclonal gammopathies. Such T cells with the potential to control the growth of tumour B cells may be a suitable target for immunotherapeutic interventions in patients.     

Cytokine profile of protective anti-Trichinella spiralis CD4+ OX22− and non-protective CD4+ OX22+ thoracic duct cells in rats: secretion of IL-4 alone does not determine protective capacity

We analysed the cytokine profile of a T cell subset (CD4⁺ CD45 RC⁻) that confers protection against Trichinella spiralis infection in rats. These CD4⁺ cells are generated in the gut and appear in the thoracic duct lymph within 72 h after infection. Cytokine mRNA levels for IL-2, IL-3, IL-4, IL-5, IL-10 and IFN-γ and functional cytokine secretion for IL-4, IL-5, IFN-γ, TNF-α and mast cell differentiation activity were tested in vitro following stimulation with T. spiralis antigens. Compared to a non-protective T cell population (CD4⁺ CD45 RC⁺ or CD8⁺), also isolated from the same thoracic lymph, no significant differences were observed in the levels of mRNA for IL-2, IL-3, IL-4, IL-5, IL-10 or IFN-γ in the protective CD4⁺ CD45 RC⁻ cells. However, analysis of the cytokine activities in culture supernatant of these T cell subsets following 24 h stimulation in vitro with T. spiralis antigens showed that significant IL-4 and IL-5 activity but little IFN-γ or TNF-α was secreted by the protective CD4⁺ CD45 RC⁻ cells. Whereas the non-protective CD4⁺ CD45 RC⁺ cells secreted significant levels of IL-4, IFN-γ, mast cell differentiating activity and TNF-α but little IL-5 activity. Nonprotective CD8⁺ cells were found to secrete IL-4 but not IL-5. Production of IL-4 was essentially equal for both protective and non-protective T cell subsets. These findings suggest that the presence or absence of IFN-γ secretion, rather than IL-4 alone, determines whether a T cell subset has protective activity against T. spiralis infection in rats.     

Induction of CD4+ and CD8+ T cell responses in efferent lymph responding to Toxoplasma gondii infection: analysis of phenotype and function

The kinetics of induction of T cell responses were examined in efferent lymph from a node draining the site of a primary inoculation of Toxoplasma gondii. The numbers of T cells increased after infection, due initially to an expansion of the CD4⁺ T cell population followed by an increase in the number of CD8⁺ T cells which coincided with the peak lymphoblast response. Proliferative responses of CD4⁺ T cells to T. gondii antigen were detectable from day six after infection and immune efferent lymph cells inhibited the intracellular multiplication of T. gondii in vitro. Optimum inhibition was achieved using CD8⁺ T cells restimulated in vitro, and the effector function appeared to be directed preferentially against the autologous rather than the allogeneic infected target cell. The results provide unique information on the induction of immune responses to T. gondii in vivo and provide evidence that both CD4⁺ and CD8⁺ T cells are necessary for the development of protective immunity induced by the S48 strain of T. gondii which is used as a live vaccine in sheep.     

Major role for CD8+ T cells in the protection against Toxoplasma gondii following dendritic cell vaccination

Toxoplasma gondii is the causative agent of toxoplasmosis, a worldwide zoonosis for which an effective vaccine is needed. Vaccination with pulsed dendritic cells is very efficient but their use in a vaccination protocol is unconceivable. Nevertheless, unravelling the induced effector mechanisms is crucial to design new vaccine strategies. We vaccinated CBA/J mice with parasite extract-pulsed dendritic cells, challenged them with T. gondii cysts and carried out in vivo depletion of CD4⁺ or CD8⁺ T lymphocytes to study the subsequent cellular immune response and protective mechanisms. CD4⁺ lymphocytes were poorly implicated either in spleen and mesenteric lymph node (MLN) cytokine secretion or in mice protection. By contrast, the increasing number of intracerebral cysts and depletion of CD8⁺ cells were strongly correlated, revealing a prominent role for CD8⁺ lymphocytes in the protection of mice. Splenic CD8⁺ lymphocytes induce a strong Th1 response controlled by a Th2 response whereas CD8⁺ cells from MLNs inhibit both Th1 and Th2 responses. CD8⁺ cells are the main effectors following dendritic cell vaccination and Toxoplasma infection while CD4⁺ T cells only play a minor role. This contrasts with T. gondii infection which elicits the generation of CD4⁺ and CD8⁺ T cells that provide protective immunity.     

Inhibition of Plasmodium falciparum growth in vitro by CD4+ and CD8+ T cells from non-exposed donors

T cells from most adult non-exposed donors, which express a memory phenotype (CD45RO+), can respond by proliferation to P. falciparum asexual stages in vitro. Such cells may have arisen from exposure to environmental organisms. To address the efficacy of such cells in eliminating parasites and investigate the mechanisms involved, we have used an in vitro assay where parasite growth can be precisely monitored in the presence of different cell preparations. Unfractionated peripheral blood mononuclear cells (PBMC) from both malaria-exposed and non-exposed donors inhibited parasite growth by up to 62% in a two day assay. Purified T cells in the presence of adherent cells had a similar effect, but purified T cells alone or adherent cells alone had minimal effect. Antigens released at the time of schizont rupture were maximally effective in stimulating interferon-γ (IFNγ) production. Neutralizing antibodies to IFNγ showed a partial reduction of growth inhibition in some individuals tested suggesting that different mechanisms may be operative. Neutralizing antibody to TNFα had a partial effect in combination with anti-IFNγ. Antibodies to IL-1 and IL-4 had no effect. T cell fractionation experiments showed that while purified CD4⁺ T cells from some donors produced IFNγ and inhibited parasite growth, purified CD8⁺ T cells could inhibit parasite growth to a greater extent without production of detectable IFNγ. Four parasitised red blood cell clones (CD4⁺, TCRαβ⁺, IFNγ producing) derived from non-exposed donors inhibited parasite growth to comparable levels, but one clone showed low production of IFNγ whilst the other three produced high levels. Our data show that T cells from non-exposed donors have the potential to eliminate malaria parasites via non-IFNγ dependent mechanisms. Such mechanisms may contribute to a degree of innate resistance to malaria in vivo, and may be able to be targeted by malaria vaccine programs.     

Mouse splenic CD4+ and CD8+ T cells undergo extensive apoptosis during a Plasmodium chabaudi chabaudi AS infection

The presence and phenotype of apoptotic lymphocytes was studied in spleen cell suspensions taken from CB6F1 mice infected with Plasmodium chabaudi chabaudi AS. High levels of apoptotic cells were found, associated with high parasitaemias and splenomegaly. This was also accompanied by expansion and disarray of spleen white pulp. Apoptosis levels lowered when parasitaemia was cleared, but were still higher than in normal mice. At this time, the spleen was diminishing in size and the white pulp was contracting and rearranging. When parasitaemia was patent, the cells most affected by apoptosis were CD4+ T cells followed by CD8+ T cells, and to a lesser extent B220+ B cells. When parasitaemia was cleared, CD8+ T cells and B220+ B cells returned to basal levels of apoptosis, while CD4+ T cells still had higher apoptosis levels than normal mice. A similar pattern of lymphocyte subpopulation apoptosis was found in infected BALB/c mice, despite the fact that, for this mouse model, it has been reported that B cells are the cells that are most affected by apoptosis. We consider that the high levels of apoptosis in CD4+ T cells when parasitaemias are still high are not easily explained by a normal mechanism of down regulation of the immune response.     

CD8+/CD57+ cells and apoptosis suppress T-cell functions in multiple myeloma

The aim of this study was to evaluate the role of CD8⁺/CD57⁺ lymphocytes in the immune dysregulation of multiple myeloma (MM). Cytofluorimetry of peripheral blood lymphocytes (PBL) purified from 39 MM patients showed an inverse relationship between the percentage of CD8⁺/CD57⁺ cells and CD4/CD8 ratio. Analysis of their activation antigens revealed that they were prevalently HLA-DR⁺ and Fas⁺. Removal of CD8⁺/CD57⁺ cells from MM PBL significantly improved cell proliferation and pokeweed mitogen (PWM)-induced polyclonal Ig production in vitro, whereas the addition of supernatants from patients' CD8⁺/CD57⁺ cell cultures to normal PBL suppressed both the PWM-driven Ig synthesis and the proliferative rate of stimulated PBL, supporting the contention that CD8⁺/CD57⁺ cells release in vitro an inhibitory factor that is directly involved in T-cell regulatory function. However, since the proliferative recovery of PWM- and phytohaemagglutinin (PHA)-stimulated MM PBL in the absence of CD8⁺/CD57⁺ lymphocytes was only partial, a dysregulated activation-induced apoptosis was anticipated. In fact, patients' PBL displayed an increased susceptibility to apoptosis and this was significantly enhanced after PWM and, even more, after PHA stimulation. Analysis of CD57 antigen expression on apoptotic or viable cells demonstrated a substantial defect of apoptosis in the CD8⁺/CD57⁺ population. Our results indicate that both the immunosuppressive effect of CD8⁺/CD57⁺ cells and the enhanced susceptibility to apoptosis of PBL could be involved in the pathogenesis of the immunodeficiency observed in this disease.     

Activated CD8+ T cells contribute to clearance of gastric Cryptosporidium muris infections

The role of CD4+ and CD8+ T lymphocytes in the development of a protective immune response against Cryptosporidium muris infection was studied by the reconstitution of severe combined immunodeficient (SCID) mice with well-defined populations of either naive or immune CD8+ or CD4+ T lymphocytes. Adoptive transfer of both naive and immune CD4+ T lymphocyte subpopulations protects SCID mice against cryptosporidiosis. Moreover, a significant biological impact of activated CD8+ T cells against gastric cryptosporidiosis was observed. The significant difference in the course and intensity of the infection in reconstituted SCID mice was found to be dependent on the protective function of both the CD4+ and CD8+ T-cell populations transferred. While SCID mice reconstituted with either immune or naive CD4+ or immune CD8+ T-cell subpopulations resolved the infection within 29, 37 and 51 days post-infection, respectively, those reconstituted with naive CD8+ T cells suffered from chronic infection similar to control SCID mice. Reconstitution with CD4+ T cells resulted in suppression of oocyst excretion and shortening of patent period in comparison with SCID mice reconstituted with CD8+ T cells. Thus, although CD4+ T cells are considered important in protective immunity, our results are the first to demonstrate the involvement of activated CD8+ T lymphocytes in the protection of mice against gastric cryptosporidiosis.     

CD4+ T lymphocytes contribute to protective immunity induced in sheep and goats by Haemonchus contortus gut antigens

Immunization with parasite antigens derived from the gut of adult Haemonchus contortus induces significant levels of protection against the parasite in sheep and goats. However, the mechanisms of immunity involved in this protection are not clear. Here, we investigate the requirement for CD4⁺ T lymphocytes in gut antigen-induced immunity against H. contortus. Gut antigen immunized animals were depleted (>98%) of their CD4⁺ T lymphocytes in peripheral blood by intravenous injection of an anti-CD4 MoAb. Depletion in peripheral blood persisted for at least eight days, after which there was gradual recovery of CD4⁺ T lymphocytes. Serum antibody levels in gut antigen-immunized animals correlated significantly with worm parameters, suggesting a contribution by antibody to the immunity observed. By covariate analysis, using ELISA OD as the covariate, CD4⁺ T lymphocyte depletion was shown to partially abrogate immunity induced by gut antigen immunization, against challenge infection with H. contortus. The greatest effect of CD4⁺ T lymphocyte depletion was observed at 14 days post-infection, with differences between CD4⁺ T lymphocyte depleted and intact animals less apparent between days 21 and 25. Collectively, our data indicate that CD4⁺ T lymphocytes contribute to immunity induced by gut antigens. Our results also suggest that antibody works synergistically with CD4⁺ T lymphocytes to confer this immunity.     

Cytokine activity after allogeneic bone marrow transplantation, V. Analysis of IL-2 and IFN production by isolated CD4+ and CD8+ cells

Summary. Previous studies from this laboratory have shown that PBMC from recipients of an HLA-identical sibling bone marrow transplant produce levels of IL-2 which are 10–100-fold lower than those produced by the same number of PBMC from healthy controls, whereas production of IFN-γ is normal. The present study examined IL-2 and IFN production over a range of cell numbers for PBMC and for isolated CD4⁺ and CD8⁺ cells for controls and marrow transplant recipients. There was a 5-fold lower IL-2 production in marrow transplant recipient CD8⁺ cells compared with equivalent numbers of control cells, whereas no difference was found in IL-2 production by CD4⁺ cells. In contrast, IFN production by CD4⁺ cells from marrow transplant recipients was 4-fold higher than in controls, whereas CD8⁺ cells from both populations produced similar amounts of IFN. When the observed production of cytokine by PBMC was compared with the expected production based on the CD4⁺ and CD8⁺ content of the PBMC, control values were similar, but the expected values for both cytokines were approximately 2-fold higher than the observed values for marrow transplant recipients. The results suggest that the capacity of T cells from marrow transplant recipients to produce IL-2 and IFN is not impaired, but that the frequency of cytokine-producing cells may be reduced, and that a negative interaction present in recipient PBMC, eliminated by isolating T-cell subsets, is responsible for the observed low levels of cytokine production.     

Generation and functional characterization of human dendritic cells derived from CD34+ cells mobilized into peripheral blood: comparison with bone marrow CD34+ cells

Dendritic cells (DCs) are the most powerful professional antigen-presenting cells (APC), specializing in capturing antigens and stimulating T-cell-dependent immunity. In this study we report the generation and characterization of functional DCs derived from both steady-state bone marrow (BM) and circulating haemopoietic CD34⁺ cells from 14 individuals undergoing granulocyte colony-stimulating factor (G-CSF) treatment for peripheral blood stem cells (PBSC) mobilization and transplantation. Clonogenic assays in methylcellulose showed an increased frequency and proliferation of colony-forming unit-dendritic cells (CFU-DC) in circulating CD34⁺ cells, compared to that of BM CD34⁺ precursors in response to GM-CSF and TNF-α with or without SCF and FLT-3L. Moreover, peripheral blood (PB) CD34⁺ cells generated a significantly higher number of fully functional DCs, as determined by conventional mixed lymphocyte reactions (MLR), than their BM counterparts upon different culture conditions. DCs derived from mobilized stem cells were also capable of processing and presenting soluble antigens to autologous T cells for both primary and secondary immune response. Replacement of the early-acting growth factors SCF and FLT-3L with IL-4 at day 7 of culture of PB CD34⁺ cells enhanced both the percentage of total CD1a⁺ cells and CD1a⁺CD14^? cells and the yield of DCs after 14 d of incubation. In addition, the alloreactivity of IL-4-stimulated DCs was significantly higher than those generated in the absence of IL-4. Furthermore, autologous serum collected during G-CSF treatment was more efficient than fetal calf serum (FCS) or two different serum-free media for large-scale production of DCs. Thus, our comparative studies indicate that G-CSF mobilizes CD34⁺ DC precursors into PB and circulating CD34⁺ cells represent the optimal source for the massive generation of DCs. The sequential use of early-acting and intermediate-late-acting colony-stimulating factors (CSFs) as well as the use of autologous serum greatly enhanced the growth of DCs. These data may provide new insights for manipulating immunocompetent cells for cancer therapy.     

Induction of CD4+CD8+ double positive T cells and increase in CD5+ B cells in efferent lymph in sheep infected with Trypanosoma evansi

The effects of Trypanosoma evansi on efferent lymphocyte phenotypes draining from a lymph node primed with Pasteurella haemolytica vaccine were studied in sheep. The prefemoral efferent lymphatic ducts of the infected sheep along with those of two uninfected sheep were surgically cannulated. Lymph was collected and lymphocytes recovered from it analysed by two-colour indirect immunofluorescence staining and cytofluoremetry in a fluorescence activated cell analyser (FACSCAN). The study showed the appearance and persistence of T. evansi in the efferent lymph for a long period of time and the appearance of CD4⁺CD8⁺ (double positive, DP) T lymphocytes in the efferent lymph of infected animals. The infection also resulted in increases in CD5⁺ B cells in the prefemoral efferent lymph. In addition, there were decreases in the output of conventional B cells, CD5⁺ and CD4⁺ T cell subsets but large increases in CD8⁺ cells followed by terminal depletion of all cell subsets. In contrast, inoculation of sheep with pasteurella vaccine antigen alone produced little alterations in the proportions, but large increases in the numbers of all T cell subsets except that of CD8⁺ cells which also showed little variation; and there was a concurrent increase in the numbers and proportions of efferent B cells. In addition, the abnormal expression of DP and CD5⁺ B cells did not occur in the uninfected vaccinated sheep. It is concluded that these abnormal changes in the kinetics of efferent lymphocyte phenotypes are likely to play a role in the genesis of the generalized immunosuppression seen in trypanosome-infected hosts.     

Evidence for limited activation of distinct CD4+ T cell subsets in response to the Plasmodium falciparum circumsporozoite protein in Papua New Guinea

Both CD4⁺ and CD8⁺ T cells, as well as antibody, are known to be important in sporozoite immunity. Data from animal studies suggest that cytokines, in particular γ-interferon and interleukin-6, are involved. The interplay of these various factors and their importance in vaccine development has, however, not yet been elucidated. In this study, we have studied cellular and humoral responses of individuals naturally exposed to malaria in a highly endemic region of Papua New Guinea to the circumsporozoite protein of Plasmodium falciparum, a prime vaccine candidate antigen. A paucity of any CD4⁺ lymphoproliferative response to this protein by Papua New Guineans was notable which parallels our recent observation of a paucity of CD8⁺ T cell response and contrasts markedly with the responses of other endemic populations. There was nevertheless a significant antibody response to the central conserved B cell epitope, (NANP)_n, as well as to other critical epitopes. An inverse relationship between γ-interferon production and interleukin-6 production and a positive correlation between γ-interferon production and CS peptide-specific lymphoproliferation was observed. High levels of peptide-specific IL-6 production were associated with high levels of peptide-specific serum antibodies. Our data provide evidence for the limited activation of distinct CD4⁺ T cell subsets and for the existence of functionally distinct subpopulations of human CD4⁺ T cells with respect to cytokines known to be important in sporozoite immunity.     

CD8~+ T细胞在CD4~+ T细胞耗竭小鼠卡氏肺孢子虫肺炎的致病作用

[目的 ]验证参与卡氏肺孢子虫致病过程中 ,宿主炎性反应及其对肺功能的影响。 [方法 ]:将小鼠CD4+ T细胞耗竭或将小鼠CD4+ 和CD8+ T细胞都耗竭后 ,经气管接种卡氏肺孢子虫。观察在CD8+ T细胞缺如或存在的情况下 ,小鼠呼吸机能的改变和肺炎的程度。 [结果 ]耗竭CD4+ 和CD8+ T细胞后 ,小鼠虽发生PCP ,但呼吸频率无明显加快 ,肺组织损伤程度也较轻。相反 ,仅耗竭CD4+ T细胞保留CD8+ T细胞的小鼠的呼吸频率明显加快 ,肺内炎性细胞反应和肺组织损伤程度均较重。支气管肺泡灌洗液 (BALF)中的CD8+ T细胞和嗜中性白细胞的数量明显增多。 [结论 ]PCP的致病过程中 ,宿主的炎性细胞反应对肺功能有直接损伤作用 ,其中CD8+ T细胞似起主要作用。     

Quantitative alterations of CD8+ T cells in juvenile idiopathic arthritis patients in remission

The study was aimed to investigate whether quantities of CD8⁺ T cell subsets are normal in juvenile idiopathic arthritis (JIA) patients with disease remission compared to age-matched healthy donors (HD) and whether chronological age may have an impact on proportions of naive CD8⁺ T cells. CD8⁺ T cell subsets were analyzed in 17 JIA patients and 32 age-matched HD by flow cytometry. JIA patients showed lower CD3⁺CD8⁺ T cells compared to HD. Total counts of CD8⁺CD28⁺ and CD8⁺CD28⁺CD45RA⁺ T cells were inversely correlated to chronological age in JIA patients and HD. In JIA patients, percentages of CD8⁺CD28⁺CD45RA⁺ T cells and of CD62L-expressing CD8⁺CD28⁺CD45RA⁺ T cells showed a negative correlation with age. The trend to lower CD28⁺CD45RA⁺ T cell proportions in aged JIA patients in remission may reflect a disturbed T cell homeostasis independently of disease activity and may be due to an intrinsic effect in reconstitution of the peripheral T cells.     

CD4+ T cells mediate mucosal and systemic immune responses to experimental hookworm infection

Hookworm infection is associated with anaemia and malnutrition in many resource‐limited countries. Ancylostoma hookworms have previously been shown to modulate host cellular immune responses through multiple mechanisms, including reduced mitogen‐mediated lymphocyte proliferation, impaired antigen presentation/processing, and relative reductions in CD4⁺ T cells in the spleen and mesenteric lymph nodes. Syrian hamsters were depleted of CD4⁺ for up to 9 days following intraperitoneal injection (200 μg) of a murine anti‐mouse CD4 monoclonal IgG (clone GK1·5). CD4⁺ T‐cell‐depleted hamsters infected with the hookworm Ancylostoma ceylanicum exhibited a threefold higher mean intestinal worm burden and more severe anaemia than animals that received isotype control IgG. In addition, depletion of CD4⁺ T cells was associated with impaired cellular and humoral (serum and mucosal) immune responses to hookworm antigens. These data demonstrate an effector role for CD4⁺ T cells in hookworm immunity and disease pathogenesis. Ultimately, these studies may yield important insights into the relationship between intestinal nematode infections and diseases that are associated with CD4⁺ T‐cell depletion, including HIV.     

Increased frequency of CD4+PD-1+HLA-DR+ T cells is associated with disease progression in CLL

Chronic lymphocytic leukaemia (CLL) patients often have abnormal expansions of CD4⁺ and CD8⁺ T cells and this can be associated with progressive disease. To characterise the key T-cell populations involved in this phenomenon, we used flow cytometry and 11 phenotypic markers to study 74 CLL patients and 14 controls. T cells of CLL patients were more phenotypically complex than those of healthy controls with significant increases in the frequencies of CD4 and CD8 memory T cells expressing exhaustion-, activation- and senescence-associated markers. Multivariate analysis of 111 different T-cell subsets showed that high frequencies of four subsets (three CD8 and one CD4) were associated with shorter progression-free survival. The most significant association was with CD4⁺HLA-DR⁺PD-1⁺ T cells, and patients could be stratified into high- and low-risk groups based on the frequency of these T cells. The expansion of this CD4⁺ subset could not be accounted for by age, cytomegalovirus infection or increases in Treg cells. Overall, these results highlight two relatively simple biomarkers, percentage CD8⁺ and percentage CD4⁺PD-1⁺HLA-DR⁺ T cells, which can be used to risk-stratify CLL patients, independent of other tumour-associated markers. They also provide further evidence for the pivotal role of T cells in modulating the pathology of CLL.     

Expansion of CD8+CD57+ T cells after allogeneic BMT is related with a low incidence of relapse and with cytomegalovirus infection

Summary. Peripheral blood lymphocytes of 46 recipients of lymphocyte-depleted bone marrow allografts were pheno-typically analysed over a period of 1 year. We investigated the repopulation of lymphocyte subpopulations and their relation with clinical parameters such as graft-versus-host disease (GVHD), graft-versus-leukaemia and cytomegalovirus (CMV) infection. The number of repopulated T cells varied strongly between the blood samples of the recipients. In 45% of the recipients the number of T cells recovered to or above normal levels within 3 months after bone marrow transplantation (BMT), whereas the other recipients remained below normal up to 1 year after BMT. In recipients with a high repopulation, the CD8⁺ T-cell subset contributed more to this high repopulation than the CD4⁺ T-cell subset. We showed that the majority of T cells of these recipients expressed the a/3 T-cell receptor, CD8, CD57 and CDllb. HLA-DR was also highly expressed reflecting the activation stage of T cells in these recipients. BMT recipients with a high repopulation of CD8⁺ T cells showed a lower incidence of leukaemic relapse than recipients with a low repopulation. The 3-year probability of relapse was 19% versus 64% (P=O03), respectively. The relative high number of CD8⁺ T cells at 3 months after BMT was not associated with the incidence of GVHD. In contrast, occurrence of CMV infection after BMT was significantly higher in these recipients. Our results indicate that CD8⁺ T cells, predominantly CD57⁺, of BMT recipients with an expansion of these cells represent an in vivo activated cell population. This CD8⁺ T-cell population may consist partially of cytotoxic cells with anti-leukaemic activity as suggested by a low relapse rate. The signal for the strong expansion of these CD8+CD57+ T cells after BMT is still unclear, but association with CMV infection suggests that viral antigens are involved.     

Long-term decrease of CD4+CD45RA+ T cells and impaired primary immune response after post-traumatic splenectomy

Congenital or acquired absence of the spleen and functional hyposplenism are associated with abnormalities of host defence such as an increased susceptibility to infection with encapsulated bacteria. The effects of the lack of the spleen on cell-mediated immunity are largely unknown. In the present study we have investigated peripheral blood lymphocyte subpopulations in healthy adults who had undergone splenectomy because of severe abdominal trauma > 4 years before the study. The results show a significant reduction in the percentage of CD4+ T cells due to a selective and long-term decrease in the percentage of CD4+CD45RA+ lymphocytes, the CD4+ T-cell subset mainly involved in primary immune responses to newly encountered antigens. Levels of the reciprocal CD45RO+CD4+ T-cell subset were comparable between splenectomized and control individuals, as were lymphoproliferative responses and IFN-gamma production to recall antigens. Decreased levels of CD4+CD45RA+ cells were accompanied by an impairment in primary immune responsiveness, as assessed by investigating T-cell proliferation to stimulation with keyhole limpet haemocyanin and by measuring antibody responses following primary immunization with a clinically relevant T-dependent antigen, hepatitis A vaccine, in vivo. These findings suggest a possible role of the spleen in the generation, maintenance and/or differentiation of naive, unprimed T cells or their precursors, which might have a possible functional relevance for primary immune responses following splenectomy.