Antiapoptotic function of NF-kappaB in T lymphocytes is influenced by their differentiation status: roles of Fas, c-FLIP, and Bcl-xL

Inducible protection from apoptosis in vivo controls the size of cell populations. An important question in this respect is how differentiation affects mechanisms of apoptosis regulation. Among mature T lymphocytes, the NF-kappaB/Rel transcription factors are coupled to receptors that control cell population sizes by concurrently regulating survival and multiplication. In the present study, we used a transgenic inhibitor of NF-kappaB/Rel signaling to investigate the role of this pathway in proliferation and death of mature T cells in vivo. The results indicate that NF-kappaB integrates two critical yet distinct molecular pathways preventing apoptosis affected by the death receptor Fas, coordinately regulating levels of FLIP and Bcl-x(L) in primary T cells. Surprisingly, NF-kappaB blockade preferentially impacted naive as compared to memory T cells. The Fas/FasL pathway was linked to these findings by evidence that the abnormalities imposed by NF-kappaB inhibition were ameliorated by Fas deficiency, particularly for the CD4(+) lineage. Moreover, levels of an inhibitor of Fas-mediated apoptosis, c-FLIP, were diminished in cells expressing the transgenic inhibitor. NF-kappaB was also linked to T cell survival in vivo by mediating induction of Bcl-x(L): restoration of Bcl-x(L) levels reversed the preferential deficit of naive T cells, differentially impacting the CD4 and CD8 subsets. These results show that promoting survival and effective multiplication are central roles for NF-kappaB in T lymphoid homeostasis in vivo, but this effect and its underlying mechanisms are influenced by the developmental state of the lymphocyte.

Lymphokine-dependent proliferation of T-lymphoid cells: regulated responsiveness and role in vivo

The discovery of lymphokines stemmed from their ability to promote T-lymphocyte proliferation in vitro. Even after 20 years of intensive investigation, crucial aspects remain to be clarified about the role of specific lymphokines in T-cell proliferation and the biochemical mechanisms by which they play these roles, particularly in vivo. The present review focuses on conventional populations of TCR(alpha)beta T cells. Older findings and new insights into the function of specific lymphokines in T-lymphocyte proliferation in vivo are summarized along with unanswered questions raised by these observations. Vital contributions of lymphokines to clonal proliferation arise from two processes: the protection of cells against apoptosis and the activation of cell cycling. Findings are underscored indicating that the activity of a particular lymphokine depends on the subset of T cells (CD4 vs. CD8; naive vs. memory) to which it binds, and that point to potential pitfalls of extrapolating from tissue culture-adapted models to the regulation of T cells in vivo. After summaries of signaling mechanisms related to the proliferative activity of lymphokines, recent findings are highlighted suggesting that such signaling is a regulated and plastic process rather than one fixed schema of action.

IL-4 signaling, gene transcription regulation, and the control of effector T cells

The central goal of our laboratory is to understand the regulation of lymphoid cells through molecular mechanisms of signal transduction and transcriptional control. A long-standing focus has been on changes that influence the effector function of mature lymphocytes. Work in the laboratory is oriented toward the identification of new regulatory mechanisms using cell lines and primary cells, and the validation of these in vitro findings in mouse models of immune responses and diseases. In this review, we summarize key insights into the regulation of T helper cell function during the phase of immunity where effector responses arise de novo. Particular interest has been centered on cytokine gene regulation as part of T cell differentiation into the Th1 and Th2 subsets. Information on IL-4 receptor signaling and the role of NF-kappaB transcription factors is reviewed. Our more recent work is designed to understand how regulation at the Th1/2 effector stages is related to the control of memory T cell survival, immune recall responses, and the role of these responses in immune-mediated disease.

NF-kappa B activation plays an important role in the IL-4-induced protection from apoptosis

IL-4 alone protects cells from apoptosis by insulin receptor substrate (IRS)-dependent and -independent mechanisms. However, in vivo cells are typically exposed to a number of signals at the same time. To determine the contribution of co-stimulatory signals to the regulation of apoptosis by IL-4, we first analyzed whether tumor necrosis factor (TNF)-alpha, which has been shown to inhibit the activation of IRS-1 by insulin, could modify IL-4 signaling and protection from apoptosis. We found that TNF-alpha cooperates with IL-4 in protecting 32D cells from factor withdrawal-induced apoptosis. This effect was independent of the expression of IRS-1, indicating that this cooperation is via an alternative anti-apoptotic pathway. Moreover, TNF-alpha had no effect on the activation of IRS-1 induced by IL-4. IL-4 enhanced TNF-alpha-induced activation of the transcription factor NF-kappaB. Interestingly, pharmacologic inhibition of NF-kappaB activation or protein synthesis resulted in the induction of cell death that could not be inhibited by IL-4, suggesting that IL-4 cooperates with NF-kappaB to signal protection from apoptosis. Supporting this hypothesis, IL-4 also increased NF-kappaB activation induced by anti-CD3 antibodies in primary T cells and protected them from apoptosis induced by receptor engagement. However, IL-4 was not able to inhibit apoptosis induced by anti-CD3 in T lymphocytes isolated from transgenic mice expressing a dominant-negative form of IkappaBalpha that prevents NF-kappaB activation. Thus, in addition to the previously identified IRS-1 pathway, IL-4-induced protection from apoptosis may also be mediated through cooperation with the NF-kappaB family of transcription factors.

Inefficient ZAP-70 phosphorylation and decreased thymic selection in vivo result from inhibition of NF-kappaB/Rel

Signaling from the TCR regulates T lymphoid survival, deletion by apoptosis, and selective clonal expansion. One set of signaling pathways activated during thymic selection leads to degradation of a cytosolic retention protein, the inhibitor of kappaB (IkappaB)alpha, followed by nuclear translocation of the NF-kappaB/Rel family of transcription factors. It has been found previously that NF-kappaB proteins mediate a pathway signaling the survival of mature T cells and protection of thymocytes against TNF-induced apoptosis. In contrast, we show in this study that a transgenic inhibitor of NF-kappaB/Rel signaling interferes with the negative selection of immature thymocytes by endogenous MHC ligands in vivo. Positive selection of the H-Y TCR also was diminished. This attenuation of thymic selection efficiency was associated with decreased ZAP-70 phosphorylation and TCR signaling of CD69 induction. These findings demonstrate that the NF-kappaB transcriptional pathway plays an important role in normal processes of clonal deletion and they indicate that the NF-kappaB/IkappaB axis can regulate the efficiency of TCR signaling.

Preferential role for NF-kappa B/Rel signaling in the type 1 but not type 2 T cell-dependent immune response in vivo

T cell function is a critical determinant of immune responses as well as susceptibility to allergic diseases. Activated T cells can differentiate into effectors whose cytokine profile is limited to type 1 (IFN-gamma-dominant) or type 2 (IL-4-, IL-5-dominant) patterns. To investigate mechanisms that connect extracellular stimuli with the regulation of effector T cell function, we have measured immune responses of transgenic mice whose NF-kappa B/Rel signaling pathway is inhibited in T cells. Surprisingly, these mice developed type 2 T cell-dependent responses (IgE and eosinophil recruitment) in a model of allergic pulmonary inflammation. In contrast, type 1 T cell responses were severely impaired, as evidenced by markedly diminished delayed-type hypersensitivity responses, IFN-gamma production, and Ag-specific IgG2a levels. Taken together, these data indicate that inhibition of NF-kappa B can lead to preferential impairment of type 1 as compared with type 2 T cell-dependent responses.

Lineage-specific differences among CD8+ T cells in their dependence of NF-kappa B/Rel signaling

Whereas most CD8+ T cells in lymph nodes and spleen express the CD8alpha beta heterodimer and depend absolutely on thymic competence for their development, a substantial population of T cells expressing CD8alpha alpha matures extrathymically. Although the existence of these CD8 sublineages is well established, relatively little is known about differences that might exist among CD8 cells in their requirement for particular transcriptional pathways during the development and maintenance of normal populations. Transgenic mice whose T lineage expresses an IkappaBalpha mutant exhibited decreased NF-kappaB signaling and a diminution in mature CD8 T cells. We now have determined that although TCR-dependent CD69 induction by CD8alpha alpha and CD8alpha beta T cells was unaffected by inhibition of NF-kappaB, TCRalpha beta CD8alpha beta T cells were preferentially reduced compared to their TCRalpha beta CD8alpha alpha or TCRgamma delta counterparts. This finding was most prominent in spleen, but was also apparent in Peyer's patches of transgenic mice. In addition, diminished antiviral cytotoxic responses of CD8alpha beta intraepithelial lymphocytes were observed after enteric reovirus infection. Taken together, these results indicate that NF-kappaB signaling is more important for the thymus-dependent TCRalpha beta CD8alpha beta population than for other CD8 lineages, and thus regulates the number, function, and normal balance of CD8 subsets in the periphery.

Essential role of T cell NF-kappa B activation in collagen-induced arthritis

NF-kappa B/Rel proteins are ubiquitous transcription factors that are activated by proinflammatory signals or engagement of Ag receptors. To study the role of NF-kappa B/Rel signaling in T lymphocytes during autoimmune disease, we investigated type II collagen-induced arthritis (CIA) in transgenic mice expressing a constitutive inhibitor of NF-kappa B/Rel (I kappa B alpha(Delta N)) in the T lineage. Expression of the I kappa B alpha(Delta N) transgene was persistently high in adult peripheral lymphoid organs and undetectable in T cell-depleted splenocytes, suggesting the expression of the transgene is restricted to the T lineage. The incidence and severity of CIA were decreased significantly in these I kappa B alpha(Delta N) transgenic mice compared with nontransgenic littermates. Inhibition of CIA was not due solely to a decrease in their CD8+ population because transfer of wild-type CD8+ cells into transgenic mice failed to restore disease susceptibility. Protection against disease was associated with a moderate decrease in clonal expansion and a profound and persistent decrease in Ag-induced IFN-gamma production in vivo. Consistent with decreased level of anti-type II collagen-specific Abs and IFN-gamma, serum levels of IgG2a anti-CII Abs were significantly reduced. However, anti-CII-specific IgG1 levels were normal, indicating that some aspects of T cell help were unaffected. Taken together, these results suggest that inhibition of NF-kappa B in T cells impairs CIA development in vivo through decreases in type 1 T cell-dependent responses.

Costimulation reverses the defect in IL-2 but not effector cytokine production by T cells with impaired IkappaBalpha degradation

Although the transcriptional basis for states of unresponsiveness in primary T cells is unclear, tolerant B lymphocytes exhibit inhibition of both c-Jun N-terminal kinase induction and IkappaBalpha (inhibitor of NF-kappaBalpha) degradation, leading to lower levels of both nuclear AP-1 and NF-kappaB. Expression of an IkappaBalpha mutant resistant to signal-induced degradation in transgenic T cells caused markedly deficient effector cytokine (IL-4, IFN-gamma) production after primary TCR stimulation despite a detectable level of nuclear NF-kappaB. A TCR response element from the IFN-gamma promoter, despite lacking detectable NF-kappaB/Rel sites, was also unresponsive to TCR ligation. Nuclear induction of AP-1 proteins in response to T cell activation was diminished in transgenic T cells. Costimulation induced by anti-CD28 mAb increased IL-2 production, but failed to reverse the defects in effector cytokine production. Taken together, these data indicate that impaired NF-kappaB/Rel signaling in T cells interferes with the signal transduction pathways required for efficient induction of effector cytokine production.

In vivo function of an interleukin 2 receptor beta chain (IL-2Rbeta)/IL-4Ralpha cytokine receptor chimera potentiates allergic airway disease

Strength of T cell receptor (TCR) signaling, coreceptors, costimulation, antigen-presenting cell type, and cytokines all play crucial roles in determining the efficiency with which type 2 T lymphocytes (Th2, Tc2) develop from uncommitted precursors. To investigate in vivo regulatory mechanisms that control the population of type 2 T cells and disease susceptibility, we have created lines of transgenic mice in which expression of a chimeric cytokine receptor (the mouse interleukin 2 receptor beta chain [IL-2Rbeta] extracellular domain fused to the cytoplasmic tail of IL-4Ralpha) is targeted to the T lymphoid lineage using the proximal lck promoter. This chimera transduced IL-4-specific signals in response to IL-2 binding and dramatically enhanced type 2 responses (IL-4, IL-5, and immunoglobulin E production) upon in vitro TCR stimulation or in vivo antigen challenge. Thus, type 2 effector function was augmented by IL-4 signals transduced through a chimeric receptor expressed in a T cell-specific manner. This influence was sufficient for establishment of antigen-induced allergic airway hyperresponsiveness on a disease-resistant background (C57BL/6).

Stimulus-dependent synergism of the antiapoptotic tumor necrosis factor receptor-associated factor 2 (TRAF2) and nuclear factor kappaB pathways

Tumor necrosis factor (TNF) signaling leads to pleiotropic responses in a wide range of cell types, in part by activating antiapoptotic and proapoptotic signaling pathways. Thus, although TNF can cause apoptosis and may prove useful in the treatment of malignancies, most cells are resistant to TNF-induced cell death unless de novo protein synthesis is inhibited. Previous studies suggested that TNF activation of the nuclear factor (NF)-kappaB transcription factor family antagonizes the proapoptotic signals initiated by TNF-alpha. TNF receptor-associated factor (TRAF)2 has also been shown to mediate crucial antiapoptotic signals during TNF stimulation, yet is not essential in activation of NF-kappaB under physiologic conditions, thus raising questions about the relationship between these antiapoptotic pathways. We report here that inhibition of TRAF2 and NF-kappaB function in primary cells, by coexpression of a constitutive repressor of multiple NF-kappaB/Rel proteins (IkappaBalpha.DN) and a dominant negative form of TRAF2 (TRAF2.DN), synergistically enhanced TNF-induced apoptosis. The effects were stimulus dependent, such that neither inhibitory molecule affected Fas- and daunorubicin-induced apoptosis to the same degree as TNF-induced death. These findings indicate that the NF-kappaB and TRAF2 pathways activate independent antiapoptotic mechanisms which act in concert to suppress the proapoptotic signals induced by TNF-alpha.

Controlled lipidation and encapsulation of peptides as a useful approach to mucosal immunizations

To generate a useful strategy for mucosal immunization, we have developed an approach of lipidating a multiple Ag peptide (MAP) containing part of the V3 loop from HIV-1 gp120IIIB. In this work, we compare two delivery systems, lipidated MAP in PBS and encapsulation in poly(DL-lactide-co-glycolide) microparticles. Subcutaneous immunization, followed by intragastric administration of MAP peptide entrapped or not entrapped in microparticles, induced mucosal and systemic immune responses at local and distant sites, including mucosal IgA in saliva, vaginal secretions and feces, and IgG in blood. However, lipidated Ag delivered in microparticles induced higher levels of mucosal Abs, particularly of intestinal IgA, and generated CTL responses. In contrast, lipidated MAP delivered by nasal route microparticles was less effective in inducing CTL responses. These results demonstrate the feasibility of using a lipidated multimeric peptide for mucosal immunization to stimulate both systemic and mucosal immune systems, including the genital tract, irrespective of the route or method of delivery and without requiring the use of a carrier or an extraneous adjuvant.

Lipidation as a novel approach to mucosal immunization

We describe the design and development of a novel peptide-based approach for mucosal immunization. The design contains an amplified peptide chain as multiple antigen peptide (MAP) with a cluster of lipids. Such a design would confer on lipidated MAP the ability to self-assemble in water, mimicking enveloped viral particles. The importance of lipidation for mucosal immunization was confirmed by oral immunization with lipidated MAP in phosphate-buffered saline (PBS), which induced mucosal and systemic immune responses at local and distant sites, including sera and vaginal IgG as well as secretory IgA in saliva, vaginal secretions and fecal matter. T-cell proliferative responses were found in spleen, Peyer's patches and genital lymph nodes. In addition, significant splenic cytotoxic T-cell responses were also observed. No significant immune responses were observed with non-lipidated MAPs by oral delivery in PBS. Furthermore, these responses were selectively enhanced by different regimens, systemic priming and microparticle delivery. These results demonstrate the effectiveness of lipidated MAP for mucosal immunization to evoke both systemic and mucosal immune responses without the use of carrier or extraneous adjuvant.

Perturbation of the T lymphocyte lineage in transgenic mice expressing a constitutive repressor of nuclear factor (NF)-kappaB

Members of the nuclear factor (NF)-kappaB/Rel family transcription factors are induced during thymic selection and in mature T lymphocytes after ligation of the T cell antigen receptor (TCR). Despite these findings, disruption of individual NF-kappaB/Rel genes has revealed no intrinsic defect in the development of mature T cells, perhaps reflecting functional redundancy. To circumvent this possibility, the T cell lineage was targeted to express a trans-dominant form of IkappaBalpha that constitutively represses the activity of multiple NF-kappaB/Rel proteins. Transgenic cells expressing this inhibitor exhibit a significant proliferative defect, which is not reversed by the addition of exogenous interleukin-2. Moreover, mitogenic stimulation of splenocytes leads to increased apoptosis of transgenic T cells as compared with controls. In addition to deregulated T cell growth and survival, transgene expression impairs the development of normal T cell populations as evidenced by diminished numbers of TCRhi CD8 single-positive thymocytes. This defect was significantly amplified in the periphery and was accompanied by a decrease in CD4(+) T cells. Taken together, these in vivo findings indicate that the NF-kappaB/Rel signaling pathway contains compensatory components that are essential for the establishment of normal T cell subsets.

Vaccination with SPf66, a chemically synthesised vaccine, against Plasmodium falciparum malaria in Colombia

Preclinical and clinical studies have established the safety and immunogenicity of the chemically synthesised SPf66 malaria vaccine. The present study is a phase III randomised, double-blind, placebo-controlled, efficacy trial completed in La Tola, Colombia. 1548 volunteers over one year of age received three doses of either the vaccine (n = 738) or placebo (n = 810). Active and passive case detection methods were used to document clinical episodes of malaria among the study population. The follow-up period began one month after the third dose and lasted for one year. 168 and 297 episodes of Plasmodium falciparum malaria were documented in the SPf66 group and the placebo group, respectively; this corresponds to a crude protective efficacy of 38.8%. Incidence rates for first or only P falciparum malarial episodes were 22.3% per annum among the vaccinee group and 33.5% among the placebo group (RR = 1.5; 95% Cl 1.23, 1.84). Therefore, the protective efficacy of SPf66 against first or only episodes was 33.6% (95% Cl 18.8, 45.7), being highest in children aged 1-4 years (77%) and adults older than 45 years (67%). The estimated protective efficacy against second episodes was 50.5% (95% Cl 12.9-71.9). Our study shows that the chemically synthesised SPf66 malaria vaccine is safe, immunogenic, and protective against P falciparum malaria in semi-immune populations subject to natural challenge.

Safety and immunogenicity of the synthetic malaria vaccine SPf66 in a large field trial

In the first field trial with synthetic malaria vaccine SPf66 in a large population naturally exposed to malaria, 9957 persons greater than 1 year old and residing on the Colombian Pacific coast received three doses of the vaccine. To evaluate vaccine safety, clinical observations were made 30 min and 48 h after each immunization. There were no adverse reactions in 95.7% of cases. In the 4.3% of cases with adverse reactions, local induration and erythema were the most frequent. In a randomly selected group of vaccinees, anti-SPf66 antibody titers were measured after the third dose: 93% of the vaccinees raised antibodies to SPf66. Among these, 55% had titers greater than 1:1600. These results demonstrate the safety and immunogenicity of the SPf66 vaccine in a large field trial.

Determination of the immunization schedule for field trials with the synthetic malaria vaccine SPf 66

The synthetic malaria vaccine SPf 66 has been shown to be safe, immunogenic and effective in trials performed with controlled groups naturally and experimentally exposed to the disease. In order to continue the trials in open populations, it was necessary to standardize the vaccination characteristics. We have performed four field trials with soldier volunteers with the aim, among others, of defining the number of doses required, the intervals between applications, the protein concentration, and the adjuvant to be used. In these trials, the vaccinated individuals' immune responses were evaluated by assaying anti-SPf 66 antibody titres, in vitro growth inhibition of the P. falciparum parasite, and the vaccinees' capacity to recognize P. falciparum native proteins. From these results we conclude that the best vaccination schedule, for adults, is three doses administered subcutaneously on days 0, 30 and 180, each containing 2 mg of the synthetic polymerized petide SPf 66 adsorbed to alum hydroxide.

The first field trials of the chemically synthesized malaria vaccine SPf66: safety, immunogenicity and protectivity

This paper reports the results of the first field study performed to assess the safety, immunogenicity and protectivity of the synthetic malaria vaccine SPf66 directed against the asexual blood stages of Plasmodium falciparum. Clinical and laboratory tests were performed on all volunteers prior to and after each immunization, demonstrating that no detectable alteration was induced by the immunization process. The vaccines were grouped as high, intermediate or low responders according to their antibody titres directed against the SPf66 molecule. Two of the 185 (1.08%) SPf66-vaccinated and nine of the 214 (4.20%) placebo-vaccinated volunteers developed P. falciparum malaria. The efficacy of the vaccine was calculated as 82.3% against P. falciparum and 60.6% against Plasmodium vivax.

Genetic control of the immune response to a synthetic vaccine against Plasmodium falciparum

Two independent vaccination trials using a hybrid synthetic polypeptide containing epitopes from four proteins of Plasmodium falciparum were performed. In the first trial 63 and in the second 122 volunteers were vaccinated, using different immunization schedules. The analysis of the humoral response to the vaccine, measured by IgG antibody titres to the polypeptide showed a bimodal distribution in both cases suggesting genetic control of the immune response to this protein. There was a small group of low or non-responders and a large group of good responders. HLA phenotyping of the two groups disclosed an association of the low responders to HLA-DR4 antigens with chi-square P value of 0.00039 when compared with the good responders group. These findings provide evidence for the genetic control of the immune response to the synthetic vaccine by the association of this response with particular alleles of the HLA class II antigens; such findings may lead to an explanation of the mechanism involved in disease susceptibility and need to be used in the design of a totally effective vaccine.

Molecular analysis of HLA DR4-beta 1 gene in malaria vaccinees. Typing and subtyping by PCR technique and oligonucleotides

The combination of the PCR technique and the synthetic oligonucleotides has proved to be a useful tool in the molecular analysis of HLA class II genes, allowing recognition of as little as a single nucleotide modification in the sequence of the gene. The molecules encoded by these genes have been associated with genetic control of the immune response and with susceptibility to certain diseases. Studies carried out in our laboratory have shown three patterns of humoral immune response in the human volunteers vaccinated with the synthetic protein SPf 66; high, intermediate and low responders. Approximately 73.3% of the low responders were serologically typed as HLA DR4 and 42% as DQw6. These results moved us to look for a subtype (Dw) correlation between the DR4 positive individuals and the different humoral immune response patterns. Using oligo-typing methods after previous amplification of the DR4 B1 exon, we subtyped 20 DR4 volunteers, classified as high, intermediate and low responders. We did not find any direct association between the HLA DR4 Dw special subtype in the high or low responders immunized with the SPf 66 vaccine.