Cytokine responsiveness of mitogen-activated T cells derived from acute leukemia patients with chemotherapy-induced leukopenia.

The aim of the study was to characterize effects of exogenous cytokines on T lymphocytes derived from acute leukemia patients with chemotherapy-induced leukopenia. We investigated the cytokine responsiveness of long-term expanded CD4+ and CD8+ T cell clones and the effects of exogenous cytokines on anti-CD3-stimulated polyclonal T cell responses. After mitogenic activation in the presence of acute myelogenous leukemia (AML) blasts, most CD4+ and CD8+ clones proliferated in response to interleukin-2 (IL-2). Although a majority of the IL-2-responsive clones could also proliferate in the presence of exogenous IL-4, IL-7, IL-9, IL-10, IL-12, and IL-15, only IL-15 responses were equal to or exceeded the corresponding IL-2 responses. Exogenous cytokines were also added during T cell activation with phytohemagglutinin (PHA) + accessory leukemia cells derived from different AML patients, and all the cytokines then had divergent effects that depended on both differences between clones and differences between AML patients. However, for most of these T cell clone/AML blast combinations, IL-2 and IL-15 caused enhanced T cell proliferation. IL-2 and IL-15 also enhanced anti-CD3-stimulated polyclonal responses of nonexpanded T cells derived from cytopenic patients, whereas other cytokines had only minor effects. Our results demonstrate that cytokine-responsive T cells remain in the circulation during chemotherapy-induced cytopenia, and combination therapy including intensive chemotherapy and T cell-targeting cytokine therapy should, therefore, be possible in AML.     

IL-35 is a novel cytokine with therapeutic effects against collagen-induced arthritis through the expansion of regulatory T cells and suppression of Th17 cells

Epstein-Barr virus-induced gene 3 (EBI3) and the p35 subunit of IL-12 have been reported to form a heterodimeric hematopoietin in human and mouse. We have constructed a heterodimeric protein covalently linking EBI3 and p35, to form a novel cytokine which we now call IL-35. The Fc fusion protein of IL-35 induced proliferation of murine CD4(+)CD25(+) and CD4(+)CD25(-) T cells when stimulated with immobilized anti-CD3 and anti-CD28 antibodies in vitro. The IL-35-expanded CD4(+)CD25(+) T cell population expressed Foxp3 and produced elevated levels of IL-10, whereas the IL-35-induced CD4(+)CD25(-) T cells produced IFN-gamma but not IL-4. The in vitro expanded CD4(+)CD25(+) T cells retained their suppressive functions against CD4(+)CD25(-) effector cells. Furthermore, when cultured with soluble anti-CD3 antibody and antigen-presenting cells, IL-35 suppressed the proliferation of CD4(+)CD25(-) effector cells. Moreover, IL-35 inhibited the differentiation of Th17 cells in vitro. In vivo, IL-35 effectively attenuated established collagen-induced arthritis in mice, with concomitant suppression of IL-17 production but enhanced IFN-gamma synthesis. Thus, IL-35 is a novel anti-inflammatory cytokine suppressing the immune response through the expansion of regulatory T cells and suppression of Th17 cell development.     

IL-12 enhances the generation of tumour antigen-specific Th1 CD4 T cells during ex vivo expansion

CD4+ T cells are essential for the immune response against cancer. Vaccination against cancer will likely only be effective at preventing growth of micrometastatic disease while adoptive T cell therapy will be better suited for eradication of bulky pre-existing disease (Knutson et al. Expert Opin Biol Ther 2002; 2:55-66). Problems with the use of adoptive T cell therapy include lack of CD4+ T cell help, low frequency of antigen-specific T cells, and lack of effective ex vivo expansion techniques. In this study, we focused on improving ex vivo expansion of CD4+ T helper cells. The effects of IL-12, along with IL-2, on the ex vivo generation of HER-2/neu antigen-specific T cells were examined. Patients were immunized with a peptide-based vaccine that contained a helper epitope, p776-790, derived from the intracellular domain of HER-2/neu. While T cell immunity to p776-790, assessed by proliferation assays, could be readily measured in short-term cultures, cell line generation by multiple in vitro stimulation with peptide and IL-2 as the only added cytokine resulted in loss of antigen-specific proliferation. The inclusion of IL-12, along with IL-2, restored antigen-specific proliferation in a dose-dependent fashion. The resulting p776-790-specific T cells responded readily to antigen by proliferating and producing type I cytokines (IFN-gamma and TNF-alpha). The increased proliferative response of the cultures was due in part to an increase in the number of HER-2/neu-specific T cells. These results suggest that IL-12 is an important cytokine for ex vivo recovery and maintenance of antigen-specific CD4+ T lymphocytes that would otherwise be lost by using IL-2 alone in combination with antigen. Furthermore, these results have important implications for ex vivo expansion of CD4+ T cell for use in anti-tumour adoptive immunotherapy.     

Acute myeloid leukaemia cells secrete a soluble factor that inhibits T and NK cell proliferation but not cytolytic function--implications for the adoptive immunotherapy of leukaemia.

Evidence of an immune mediated graft-versus-leukaemia effect has led to the belief that T and NK cell based adoptive immunotherapy can constitute effective treatment for relapsed leukaemias. However, work on solid tumours has shown this strategy may be hampered, by an immune escape mechanism in which tumour secreted immunosuppressive factors compromise T and NK cell function. Indeed, acute myeloid leukaemia (AML) cells secrete immunosuppressive factors that block the synthesis of Th1 type cytokines in T cells. We demonstrate here that this immunosuppression, mediated by both HL60 AML cell line and primary AML blasts, inhibits T and NK cell proliferation but not cytolytic activity. Supernatants from HL60 cell line and primary AML blasts inhibited T cell proliferation to mitogenic and alloantigen stimulation but had no effect on cytolytic function. Similarly, the proliferation of NK cells to IL-2 and IL-15 stimulation was inhibited whilst their cytolytic function, shown by lysis of AML blasts, K562 and Daudi cells remained unaffected. The failure of T and NK cells to proliferate was not due to effector cell apoptosis. Indeed, removal of lymphocytes from the immunosuppressive environment partially restored their capacity to respond to mitogenic stimulation. T cells exposed to immunosuppressive supernatants did not increase expression of mitotic inhibitory proteins that arrest cell division, thereby ruling this out as a mechanism of operation for this immunosuppression. T cell expansion requires antigen stimulation, usually provided in the form of AML blasts, therefore our data suggest that NK cells may be more practical for the immunotherapy of AML.     

Activation requirements for the induction of CD4+CD25+ T cell suppressor function

The in vivo differentiation/survival of CD4(+)CD25(+) T suppressor cells is dependent on IL-2 and CD28-mediated costimulatory signals. To determine the cytokine and costimulatory requirements for CD25(+) T cells in vitro, we established a two-stage culture system where CD25(+) T cells were activated in a primary culture. In the subsequent culture, activated CD4(+)CD25(+) cells were then mixed with responders in order to assess their suppressor function. Pre-culture of CD25(+) T cells with anti-CD3 alone resulted in poor survival and minimal induction of suppressor activity. Pre-culture in the presence of anti-CD3 and IL-2 or IL-4, but not IL-6, IL-7, IL-9, IL-10 or IL-15, resulted in proliferation of the CD25(+) cells and induction of potent suppressor function. Inhibition of the interaction of CD28 or cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) with CD80/CD86 in the pre-culture of CD4(+)CD25(+) cells did not prevent the induction of suppressor function. Furthermore, the inhibition of costimulatory signals did not inhibit the ability of fresh CD25(+) T cells to inhibit CD8(+) responders under conditions where activation of the responders was independent of CD80/CD86. These studies support the view that activation of CD25(+) T cells requires IL-2/IL-4 for their survival/differentiation into effector cells, but is independent of CD28/CTLA-4-mediated costimulation.     

Differential expression of the cytokine receptors for human interleukin (IL)-12 and IL-18 on lymphocytes of both CD45RA and CD45RO phenotype from tonsils, cord and adult peripheral blood

The objective of this study was to demonstrate the variable expression of cytokine receptors on naive versus memory human CD4+ T cell subpopulations in tonsillar tissue, cord blood and adult blood. We prove that the receptors for both interleukin (IL)-12 and IL-18 are expressed exclusively on memory T cells. This observation was seen not only on the CD45RO+ memory T cells but also on a significant percentage of the CD45RA+, CD62L-, CD27- and CCR7- populations. Furthermore, CD45RA+ CD62L+, CD27+ or CCR7+ CD4+ T cells that expressed IL-12Rbeta1 and IL-18Ralpha did not express CD31, a marker for recent thymic emigrants. We reveal that cord blood lymphocytes do not express IL-12Rbeta1 whereas IL-18Ralpha expression was detected at low levels. Importantly, the IL-12Rbeta2 signalling chain, which is absent in all resting T cells, was up-regulated in both CD45RA+ and CD45RO+ T cells as a result of stimulation with anti-CD3 and anti-CD28 in vitro. This observed up-regulation was, however, restricted to 80% of the total CD4+ population. Finally, a very small proportion of the CD4+ CD45RO+ tonsillar T cells expressed the IL-12 and IL-18 receptors, thereby establishing the differential expression of these receptors between peripheral and tonsillar memory T cell subpopulations.     

Effect of CD80 and CD86 on T Cell Cytokine Production

Conjugation of the T cell receptor (TCR) with antigen/MHC proteins must be accompanied by conjugation of T cell counterreceptors (CD28 or CTLA-4) with costimulatory molecules CD80 or CD86 (B7-1 or B7-2) on antigen presenting cells (APC) to avert T cell anergy, and to provide essential signals for T cell activation and cytokine production. However, T cells and APC express changing patterns of counterreceptors and costimulatory molecules during the immune response. To determine the involvement of CD80 and CD86 in costimulation of T cell cytokine production, T cells were incubated with peritoneal exudate macrophages, which express CD80 and CD86, and stimulated in vitro for 48 or 72 hrs with anti-CD3 in the presence or absence of blocking antibody to CD80 or CD86. Alternatively, enriched anti-CD3 stimulated T cells were costimulated with antibody to CD28 and CTLA-4. Production of T cell IL-2, IL-4, and IL-5 was depressed in the presence of anti-CD86 but not anti-CD80. Production of IFN-γ was significantly blocked by either anti-CD80 and anti-CD86. Anti-CD28 was a potent costimulator of IFN-γ and IL-2 production, but a less potent costimulator of IL-4 and IL-5 production. The data suggest that T cell counterreceptors and APC costimulatory molecules act with varying efficacies at stimulating production of T cell cytokines.     

Effect of CD80 and CD86 on T Cell Cytokine Production

Conjugation of the T cell receptor (TCR) with antigen/MHC proteins must be accompanied by conjugation of T cell counterreceptors (CD28 or CTLA-4) with costimulatory molecules CD80 or CD86 (B7-1 or B7-2) on antigen presenting cells (APC) to avert T cell anergy, and to provide essential signals for T cell activation and cytokine production. However, T cells and APC express changing patterns of counterreceptors and costimulatory molecules during the immune response. To determine the involvement of CD80 and CD86 in costimulation of T cell cytokine production, T cells were incubated with peritoneal exudate macrophages, which express CD80 and CD86, and stimulated in vitro for 48 or 72 hrs with anti-CD3 in the presence or absence of blocking antibody to CD80 or CD86. Alternatively, enriched anti-CD3 stimulated T cells were costimulated with antibody to CD28 and CTLA-4. Production of T cell IL-2, IL-4, and IL-5 was depressed in the presence of anti-CD86 but not anti-CD80. Production of IFN-γ was significantly blocked by either anti-CD80 and anti-CD86. Anti-CD28 was a potent costimulator of IFN-γ and IL-2 production, but a less potent costimulator of IL-4 and IL-5 production. The data suggest that T cell counterreceptors and APC costimulatory molecules act with varying efficacies at stimulating production of T cell cytokines.     

Ex vivo expansion of dendritic-cell-activated antigen-specific CD4+ T cells with anti-CD3/CD28, interleukin-7, and interleukin-15: potential for adoptive T cell immunotherapy

There is an increasing realization that the failure of adoptive therapy with cytotoxic T lymphocytes in the autologous setting, at least in part, results from the lack of help from antigen-specific CD4+ T cells. To incorporate these cells into this treatment strategy, it is not known whether currently used ex vivo culture conditions are adequate for expanding and charting these T cells with the desired qualities for optimal in vivo activity. In this study, we show that stimulation with agonistic antibodies to CD3 plus CD28 (anti-CD3/CD28), a commonly used method for CD4+ T cell expansion, is unable to expand dendritic-cell-activated hepatitis B virus (HBV)-specific CD4+ T cells to clinical relevant numbers. Whereas, in combination with interleukin(IL)-7 and IL-15, it leads to a 4000-fold expansion of HBV-specific CD4+ T cells in 2 weeks. This outcome is correlated with the anti-apoptosis effect of IL-7 and IL-15. Importantly, antigen specificity is preserved during expansion. Although a late addition of IL-2 to the anti-CD3/CD28-expanding cultures also results in robust expansion, this expansion condition renders HBV-specific CD4+ T cells more sensitive to cytokine withdrawal-, activation-, and transforming growth factor-beta-induced cell death compared to those expanded in IL-7 and IL-15. Moreover, NKG2D rather than 4-1BB, whose ligands are constitutively expressed on tumor cells, is significantly up-regulated on IL-7/IL-15-expanded HBV-specific CD4+ T cells, and its engagement promotes expansion and interferon-gamma production by these cells and thus may serve to provide co-stimulation to T cells once they reach tumor tissues. Collectively, these results may have important therapeutic implications for adoptive T cell therapy.     

Characterization of dendritic-like cells derived from t(9;22) acute lymphoblastic leukemia blasts

We asked herein whether functional dendritic-like cells could be generated from t(9;22) acute lymphoblastic leukemia (ALL) blasts. We first determined that the combination of interleukin (IL)-1beta, IL-3, IL-7, tumor necrosis factor-alpha, stem cell factor and CD40 ligand was optimal for generating dendritic-like cells from t(9;22) ALL cell lines. Following 6 days in culture, four of five cell lines demonstrated dendrite-like morphology, upregulation of CCR7, CD54, CD80 and CD86, uptake of extracellular proteins and activation of T cells, and similar results were obtained with blasts from three t(9;22) ALL patients. The dendritic-like cells appeared to be composed of populations resembling both immature and mature dendritic cells (DCs), distinguished by CD80 expression. CD80-CD86+ cells were classified as immature DCs, demonstrating high endocytic capability and inducing minimal allogeneic T cell proliferation, while CD80+CD86+ cells were classified as mature DCs, exhibiting negligible endocytic capability and inducing robust allogeneic T cell proliferation. These mature dendritic-like cells induced autologous cytotoxic T cell responses against the unmodified blasts in a patient who achieved prolonged remission. In summary, CD80+CD86+ cells generated from t(9;22) ALL blasts may be useful in adoptive immunotherapy for t(9;22) ALL.     

Comparison of cytokines and CD80 for enhancement of immunogenicity of cervical cancer cells

Tumor cells fail to activate specific cytotoxic T lymphocytes due to lack of costimulatory molecules e.g. CD80 (B7.1). We were able to render cervical carcinoma cells immunogenic by introduction of the CD80 gene into the tumor cells. In order to enhance the efficiency of T cell activation we investigated whether addition of interleukins would augment immunostimulation by CD80. To this end, allogeneic T cells were stimulated with CD80-expressing HeLa cells or CaSki cells in the absence or presence of IL-2, IL-7, IL-12, or combinations thereof. The proliferative response of the T cells was determined. CD80-transduced HeLa or CaSki cells induced a stronger proliferative response in allogeneic T cells than parental or mock transfected control cells. All three interleukins enhanced the proliferative response of allogeneic T cells to CD80-expressing tumor cells. IL-2 or IL-7 had stronger effects in expanding the T cells than IL-12. Combination of IL-2 and IL-7 resulted in best T cell expansion. The proliferating T cells were mainly CD8+ cells with MHC class I restricted and unrestricted cytotoxic activity. Stimulation with CD80 alone or in combination with IL-7 induced mainly cytotoxic T lymphocytes. IL-2, IL-12 or the combination of IL-2 and IL-7 induced natural killer cell-like activity and specific cytolytic activity against parental and CD80-positive tumor cells. Our data suggest that the expression of both CD80 and IL-2 plus IL-7 can enhance the efficacy of tumor vaccines.     

Acute myeloid leukemia impairs natural killer cells through the formation of a deficient cytotoxic immunological synapse

Acute myeloid leukemia (AML) cells are killed by allogeneic NK cells. However, autologous NK cells from AML patients express decreased levels of activating receptors, and show reduced cytotoxicity. Here, we investigated how interactions between NK and AML cells might cause loss of NK‐cell activity in patients. Our results show that AML cell lines and primary blasts alter the NK‐cell phenotype, reducing their cytotoxic potential upon prolonged contact. Downregulation of NK‐cell‐activating receptors was contact‐dependent and correlated with conjugate formation. Time‐lapse imaging of HL60 AML cell line and NK‐cell interactions showed a high proportion of noncytolytic contacts. Studies of NK‐cell immunological synapses revealed a defect in lytic synapse formation. Namely, despite correct F‐actin and LFA‐1 recruitment, polarization of lytic granules toward primary blasts or AML cell lines was reduced. The NK–AML cell line synapses showed impairment of CD3ζ recruitment. Attempts to correct these synapse defects by cytokine stimulation of NK cells improved conjugate formation, but not granule polarization. Pretreatment of AML cell lines with the immunomodulating molecule lenalidomide significantly enhanced granule polarization. We speculate that combining immunomodulatory drugs and cytokines could increase AML cell sensitivity to autologous NK cells and reinforce the activity of allogeneic NK cells in adoptive immunotherapy.     

The generation of dendritic-like cells with increased allostimulatory function from acute myeloid leukemia cells of various FAB subclasses

To increase the immunogenicity of leukemic cells, attempts were made to generate dendritic-like antigen presenting cells (DC) from AML blasts from 14 patients with AML FAB classifications M0-M5. Leukemic cells were cultured in the presence or absence of various cytokines including GM-CSF, SCF, TNF-alpha, IL-4, and gamma-interferon. After various intervals recovery of viable cells was measured and expression of CD80, CD86, CD40, CD54, CD58, and CD11a was analyzed by flow cytometry. Functionally, DC derived from six AML samples were tested in a mixed lymphocyte response (MLR) using HLA-DR mismatched donor T cells as responder cells. Proliferation (5/14) or increased survival (7/14) of AML cells was observed in the presence of GM-CSF, SCF, and TNF-alpha. Only in the AML M2, M3, and M4 FAB subtypes proliferation was found. GM-CSF, SCF, and TNF-alpha induced morphologic changes typical for DC and increased the expression of costimulatory and adhesion molecules. No significant effect of IL-4 or gamma-interferon was observed. The day of maximal expression of these molecules varied. In cases with minor upregulation of CD80 or CD86, no further stimulation using CD40-L activation was observed. In the three cases tested, the DC-like cells retained the chromosomal abnormalities present in the original AML cells. In five out of six cases tested an increase in allostimulatory capacity was found at the day of maximal expression of costimulatory and adhesion molecules. In two patients a decrease in stimulatory capacity was found at day 7 compared with day 2 correlating with a decreased expression of these molecules. In conclusion, AML cells can be induced to increase their stimulatory capacity by upregulating costimulatory and adhesion molecules.     

IL-27, a heterodimeric cytokine composed of EBI3 and p28 protein,induces proliferation of naive CD4+ T cells

An efficient Th1-driven adaptive immune response requires activation of the T cell receptor and secretion of the T cell stimulatory cytokine IL-12 by activated antigen-presenting cells. IL-12 triggers Th1 polarization of naive CD4(+) T cells and secretion of IFN-gamma. We describe a new heterodimeric cytokine termed IL-27 that consists of EBI3, an IL-12p40-related protein, and p28, a newly discovered IL-12p35-related polypeptide. IL-27 is an early product of activated antigen-presenting cells and drives rapid clonal expansion of naive but not memory CD4(+) T cells. It also strongly synergizes with IL-12 to trigger IFN-gamma production of naive CD4(+) T cells. IL-27 mediates its biologic effects through the orphan cytokine receptor WSX-1/TCCR.     

Dietary n-3 polyunsaturated fatty acids suppress splenic CD4(+) T cell function in interleukin (IL)-10(-/-) mice

Our laboratory has demonstrated that down-regulation of proliferation and cytokine synthesis by CD4(+) T cells in mice fed diets rich in n-3 polyunsaturated fatty acids (PUFA) is highly dependent on the involvement of the co-stimulatory molecule, CD28. It has been reported that the inhibitory cytokine interleukin (IL)-10 acts directly on T cells which up-regulate IL-10 receptor (IL-10R) expression following stimulation via CD28 by efficiently blocking proliferation and cytokine production. Thus, it was hypothesized that dietary n-3 PUFA would suppress T cell function through the effects of IL-10. The proliferation of purified splenic CD4(+) T cells activated in vitro with anti-CD3 and anti-CD28 (alphaCD3/CD28) from conventional mice (C57BL/6) fed either a control corn oil (CO)-enriched diet devoid of n-3 PUFA, docosahexaenoic acid (DHA; 22 : 6) or eicosapentaenoic acid (EPA; 20 : 5) for 14 days was suppressed by dietary DHA and EPA. Surprisingly, a similar trend was seen in IL-10 gene knock-out (IL-10(-/-)) mice fed dietary n-3 PUFA. IL-10R cell surface expression was also significantly down-regulated on CD4(+) T cells from both the C57BL/6 and IL-10(-/-) mice fed dietary n-3 PUFA after 72 h of in vitro stimulation with alphaCD3/CD28. Enzyme-linked immunosorbent assay (ELISA) measurements revealed that C57BL/6 mice fed DHA had significantly reduced interferon (IFN)-gamma and IL-10 levels 48 h post-activation. However, CD4(+) T cells from IL-10(-/-) mice fed dietary n-3 PUFA produced significantly greater levels of IFN-gamma than the CO-fed group. Our data suggest that in the absence of IL-10, CD4(+) T cells from n-3 PUFA-fed mice may up-regulate IFN-gamma. Suppressed CD4(+) T cells from n-3 PUFA-fed C57BL/6 mice may use mechanisms other than IL-10 to down-regulate T cell function.     

Viral dsRNA-activated human dendritic cells produce IL-27, which selectively promotes cytotoxicity in naive CD8+ T cells

Viral recognition programs DCs to express Signal 3 molecules that promote the differentiation of effector CD8(+) T cells. Besides IL-12, another DC-derived IL-12 family member, IL-27, has been reported to contribute herein, but its specific role is not well understood. Here, we show that whereas IL-12 potently induces inflammatory cytokines (i.e., IFN-γ and TNF-α, but not IL-2), IL-27 excels in inducing proliferation and a cytotoxic profile (GrB, cytotoxicity of target cells) in human na?ve CD8(+) T cells. Compared with bacterial cell-wall peptidoglycan, viral dsRNA-mimic poly (I:C) is superior in priming human BDCA1(+) peripheral blood DCs to produce IL-12 and IL-27, which promote inflammatory cytokines and a cytotoxic profile in differentiating CD8(+) T cells, respectively. These data support the concept that viral dsRNA-activated human DCs produce IL-27 to act as a specialized procytotoxic, antiviral cytokine in the development of effector CD8(+) T cells.     

Regulation of CD80/B7-1 and CD86/B7-2 molecule expression in human primary acute myeloid leukemia and their role in allogenic immune recognition

Clinical data and animal models afford evidence for anti-leukemia immunity in humans, but the interactions critical for blast cell recognition are unresolved. Expression of B7 molecules by antigen-presenting cells (APC) provides co-stimulatory signals to T lymphocytes via CD28 and CTLA-4 which prevent the induction of alloantigen-specific tolerance. Conversely, expression of CD40 ligand by stimulated T cells activates APC via CD40. In human hematological B cell malignancies (follicular lymphoma and chronic lymphocytic leukemia), the defect in alloantigen presentation of tumoral cells can be repaired by up-regulation of B7 and other co-stimulatory molecules via CD40. We studied the role of B7 molecules in alloimmune recognition and the various ways to improve the antitumoral response on peripheral blood leukemic cells from 20 patients with a diagnosis of primary acute myeloid leukemia (AML). We focused on myelo/monocytic M4/M5 French-American-British classification subtypes which are considered as the neoplastic counterpart of normal monocytes, a prototypic APC. In one-way mixed lymphocyte reaction of CD4+ T cells against leukemic cells, differences in B7-1, B7-2 or CD40 expression by AML cells did not induce specific cytokine secretion; interleukin (IL)-2 and interferon (IFN)-γ were detected but not IL-4, corresponding to a Th1 pattern. Blockade experiments showed that proliferation and IFN-γ secretion only partially depended on B7 molecules, which in contrast had a pivotal role in IL-2 synthesis. In contrast with murine models which suggest a pivotal role for CD80/B7-1 in the immune response against AML, our data support a greater role for CD86/B7-2, in line with the baseline expression of CD86/B7-2 and lack of CD80/B7-1 on most M4/M5 AML cells. AML cell stimulation via CD40: (1) significantly improved IL-2 secretion but not proliferation of responding T lymphocytes, (2) increased CD54/ICAM-1 expression in three quarters of cases, (3) failed in most cases to induce CD40-specific CD80/B7-1 up-regulation and (4) had a weak effect on CD86/B7-2 expression. These data contrast with the very efficient up-regulation of both B7 co-stimulatory molecule expression and tumoral cell alloimmune recognition following CD40 stimulation in B cell malignancy models. The role of the defective B7 molecule up-regulation by the CD40 pathway in inefficient tumor immunogenicity of primary AML cells has to be further investigated, in particular using transfection experiments of CD80/B7-1-deficient AML cell lines. From our in vitro data we conclude that B7 molecules play an important role in the alloimmune surveillance of AML as suggested by the high B7 molecule dependency of IL-2 secretion. Nonetheless, the contribution of B7 molecules to alloimmune T cell proliferation against primary AML cells in human and the way to improve it – regulation via CD40 in particular – differ from B cell malignancies and murine models, suggesting the requirement for specific strategies in the development of antitumor immunity.     

IL-1 acts on antigen-presenting cells to enhance the in vivo proliferation of antigen-stimulated naive CD4 T cells via a CD28-dependent mechanism that does not involve increased expression of CD28 ligands

The basis of the adjuvant effect of IL-1 on the clonal expansion of Ag-specific CD4 T cells was measured in vivo using the TCR transgenic T cell adoptive transfer method. Injection of Ag plus IL-1 caused naive CD4 T cells to proliferate to a greater extent than did injection of Ag alone. The T cells had to express CD28 to experience the beneficial effect of IL-1 whereas the host had to express the type I IL-1R, raising the possibility that IL-1's adjuvant properties were related to induction of CD28 ligands on APC. Surprisingly, however, expression of CD28 ligands on DC and B cells was not affected by IL-1. Therefore, the adjuvant properties of IL-1 depend on a basal level of CD28 signaling but cannot be explained by enhanced CD28 signaling due to CD28 ligand induction.     

Enhanced apoptosis of T cells in common variable immunodeficiency (CVID): role of defective CD28 co-stimulation

CVID is a primary immune disorder in which hypogammaglobulinaemia may be associated with a number of T cell defects including lymphopenia, anergy, impaired lymphocyte proliferation and deficient cytokine secretion. In this study we show that T cells of CVID subjects, in comparison with control T cells, undergo spontaneous apoptosis in culture and markedly accelerated apoptosis after gamma-irradiation. Although costimulation of the CD28 receptor following engagement of the TCR/CD3 receptor normally provides a second signal necessary for IL-2 secretion, CD28 costimulation in CVID does not significantly increase IL-2 production, nor does this combination of activators enhance the survival of irradiated CVID T cells, as it does for cultured normal T cells. Addition of IL-2 enhances CVID T cell survival, suggesting that the IL-2 signalling pathways are normal. CVID T cells have similar expression of Bcl-2 to control T cells. CD3 stimulation up-regulates T cell expression of bcl-xL mRNA for normal T cells, but anti-CD28 does not augment bcl-xL expression for CVID subjects with accelerated apoptosis. Defects of the CD28 receptor pathway, leading to cytokine deprivation and dysregulation of bcl-xL, could lead to poor T cell viability and some of the cellular defects observed in CVID.     

Involvement of CD80 in the generation of CD4+ cytotoxic T cells

CD4+ T cells can exert different effector functions, which are partly distinguishable by the secretion of different cytokines, namely by either IFN-γ, IL-2 and lymphotoxins for Th1-like or IL-4, IL-5, IL-10 and IL-13 for Th2-like T cells. Th1-like T cells can exert cytotoxic functions, too. The cytokinetic phenotype of an activated T cell clone (TCC) is mainly influenced by the cytokinetic pattern of the microenvironment where it was activated. However, the interaction between certain adhesion molecules (i.e. CD28-CD80 and CD28-CD86) may also have an influence on the functionality of the reactive T cell. On the contrary, the requirements for the induction of CD4+ cytotoxic T cells (CD4+CTLs) are not well understood. We have focused this review on studies investigating the development of CD4+ T cells with cytotoxic effector functions. In particular, we discuss here whether the type of antigen-presenting cells (APCs) and the distinct expression of important adhesion molecules like CD80 and CD86 may influence the generation of CD4+ CTLs. Among a large panel of APCs only dendritic cells and TCCs are able to induce cytotoxicity. The level of CD80, but not of CD86, present on the APCs appears to be crucial for the induction of CD4+ CTLs.