Dendritic cells and their emerging clinical applications

Dendritic cells (DC) are now recognised as a unique leukocyte type, consisting of two or more subsets. The origins and functional inter-relationships of these cells are the subject of intense basic scientific investigation. They play important roles in initiating and directing immune responses, defending the host from pathogens and maintaining self tolerance. Fundamental studies are defining new molecules and mechanisms associated with DC function. The first methods for counting these rare blood cell populations are already providing interesting new clinical data. Indeed, abnormal DC function may contribute to deficiencies in the immune response against malignancies. Phase I trial data suggests that DC-based cancer vaccination protocols may contribute an important new biological approach to cancer therapy. Manipulation of DC to facilitate allogeneic transplantation and even to manage autoimmune disease are likely developments.

CD40 and CD86 upregulation with divergent CMRF44 expression on blood dendritic cells in inflammatory bowel diseases

OBJECTIVE

Dendritic cells (DC) are the only antigen-presenting cells that can activate naïve T lymphocytes and initiate a primary immune response. They are also thought to have a role in immune tolerance. DC traffic from the blood to peripheral tissue where they become activated. They then present antigen and the costimulating signals necessary to initiate an immune response. In this study, we investigated the number, subsets, and activation pattern of circulating and intestinal DC from patients with clinically mild ulcerative colitis (UC) or Crohn's disease.

METHODS

Patients were recruited, if they were not taking immunosuppressive therapy, and were assessed for clinical severity of their disease using for UC, the Clinical Activity Index, and for Crohn's disease, the Crohn's Disease Activity Index. Blood CD11c+ and CD11c- DC subsets, expression of costimulatory antigens, CD86 and CD40, and the early differentiation/activation antigen, CMRF44, were enumerated by multicolor flow cytometry of lineage negative (lin- = CD3-, CD19-, CD14-, CD16-) HLA-DR+ DC. These data were compared with age-matched healthy and the disease control groups of chronic noninflammatory GI diseases (cGI), acute noninflammatory GI diseases (aGI), and chronic non-GI inflammation (non-GI). In addition, cryostat sections of colonoscopic biopsies from healthy control patients and inflamed versus noninflamed gut mucosa of inflammatory bowel disease (IBD) patients were examined for CD86+ and CD40+ lin- cells.

RESULTS

Twenty-one Crohn's disease and 25 UC patients, with mean Crohn's Disease Activity Index of 98 and Clinical Activity Index of 3.1, and 56 healthy controls, five cGI, five aGI, and six non-GI were studied. CD11c+ and CD11c- DC subsets did not differ significantly between Crohn's, UC, and healthy control groups. Expression of CD86 and CD40 on freshly isolated blood DC from Crohn's patients appeared higher (16.6%, 31%) and was significantly higher in UC (26.6%, 46.3%) versus healthy controls (5.5%, 25%) (p = 0.004, p = 0.012) and non-GI controls (10.2%, 22.8%) (p = 0.012, p = 0.008), but not versus cGI or aGI controls. CD86+ and CD40+ DC were also present in inflamed colonic and ileal mucosa from UC and Crohn's patients but not in noninflamed IBD mucosa or normal mucosa. Expression of the CMRF44 antigen was low on freshly isolated DC, but it was upregulated after 24-h culture on DC from all groups, although significantly less so on DC from UC versus Crohn's or healthy controls (p = 0.024). The CMRF44+ antigen was mainly associated with CD11c+ DC, and in UC was inversely related to the Clinical Activity Index (r = -0.69, p = 0.0002).

CONCLUSIONS

There is upregulation of costimulatory molecules on blood DC even in very mild IBD but surprisingly, there is divergent expression of the differentiation/activation CMRF44 antigen. Upregulation of costimulatory molecules and divergent expression of CMRF44 in blood DC was also apparent in cGI and aGI but not in non-GI or healthy controls, whereas intestinal CD86+ and CD40+ DC were found only in inflamed mucosa from IBD patients. Persistent or distorted activation of blood DC or divergent regulation of costimulatory and activation antigens may have important implications for gut mucosal immunity and inflammation.

Surgical and physical stress increases circulating blood dendritic cell counts independently of monocyte counts

Dendritic cells (DCs) are specialized antigen-presenting cells that have the unique ability to initiate a primary immune response. The effect of physiologic stress on circulating blood DCs has thus far not been studied. In this study, we applied a recently developed method of counting blood DCs to test the hypothesis that significant stress to the body such as surgery and exercise might induce measurable changes in the DC numbers, subsets, phenotype, and function. Twenty-six patients scheduled for elective laparoscopic cholecystectomy, 4 for elective hysterectomy, 56 controls, and 5 volunteers who underwent a stress exercise test were enrolled in the study. Absolute DC counts increased acutely (71.7% +/- 11% [SEM], P =.0001) in response to the stress of surgery and dropped below preoperative levels (-25% +/- 14% [SEM], P =.05) on days 2-3. The perioperative DC subset balance remained constant. Interestingly, DC counts changed independently of monocyte counts. Exercise also induced a rise in DC counts but coincidentally with monocyte counts. Surprisingly, no phenotypic or functional activation of DCs was seen in either stress situations in vivo. DCs are rapidly mobilized into the circulation in response to surgical and exercise stress, which may serve to prepare the host's immune defenses against trauma. The independent regulation of the DC and monocyte counts reinforces the distinction between these 2 cell populations.

Phenotypic characterization of five dendritic cell subsets in human tonsils

Heterogeneous expression of several antigens on the three currently defined tonsil dendritic cell (DC) subsets encouraged us to re-examine tonsil DCs using a new method that minimized DC differentiation and activation during their preparation. Three-color flow cytometry and dual-color immunohistology was used in conjunction with an extensive panel of antibodies to relevant DC-related antigens to analyze lin(-) HLA-DR(+) tonsil DCs. Here we identify, quantify, and locate five tonsil DC subsets based on their relative expression of the HLA-DR, CD11c, CD13, and CD123 antigens. In situ localization identified four of these DC subsets as distinct interdigitating DC populations. These included three new interdigitating DC subsets defined as HLA-DR(hi) CD11c(+) DCs, HLA-DR(mod) CD11c(+) CD13(+) DCs, and HLA-DR(mod) CD11c(-) CD123(-) DCs, as well as the plasmacytoid DCs (HLA-DR(mod) CD11c(-) CD123(+)). These subsets differed in their expression of DC-associated differentiation/activation antigens and co-stimulator molecules including CD83, CMRF-44, CMRF-56, 2-7, CD86, and 4-1BB ligand. The fifth HLA-DR(mod) CD11c(+) DC subset was identified as germinal center DCs, but contrary to previous reports they are redefined as lacking the CD13 antigen. The definition and extensive phenotypic analysis of these five DC subsets in human tonsil extends our understanding of the complexity of DC biology.

A soluble form of CD83 is released from activated dendritic cells and B lymphocytes, and is detectable in normal human sera

CD83 is an inducible glycoprotein expressed predominantly by dendritic cells (DC) and B lymphocytes. Expression of membrane CD83 (mCD83) is widely used as a marker of differentiated/activated DC but its function and ligand(s) are presently unknown. We report the existence of a soluble form of CD83 (sCD83). Using both a sCD83-specific ELISA and Western blotting, we could demonstrate the release of sCD83 by mCD83(+) B cell and Hodgkin's disease-derived cell lines, but not mCD83(-) cells. Inhibition of de novo protein synthesis did not affect the release of sCD83 during short-term (2 h) culture of cell lines although mCD83 expression was significantly reduced, suggesting sCD83 is generated by the release of mCD83. Isolated tonsillar B lymphocytes and monocyte-derived DC, which are mCD83(low), released only low levels of sCD83 during culture. However, the differentiation/activation of these populations both up-regulated mCD83 and increased sCD83 release significantly. Analysis of sera from normal donors demonstrated the presence of low levels (121 +/- 3.6 pg/ml) of circulating sCD83. Further studies utilizing purified sCD83 and the analysis of sCD83 levels in disease may provide clues to the function and ligand(s) of CD83.

The gene encoding the immunoregulatory signaling molecule CMRF-35A localized to human chromosome 17 in close proximity to other members of the CMRF-35 family

The immunoregulatory signaling (IRS) family includes several molecules, which play major roles in the regulation of the immune response. The CMRF-35A and CMRF-35H molecules are two new members of the IRS family of molecules, that are found on a wide variety of haemopoietic lineages. The extracellular functional interactions of these molecules is presently unknown, although CMRF-35H can initiate an inhibitory signal and is internalized when cross-linked. In this paper, we described the gene structure for the CMRF-35A gene and its localization to human chromosome 17. The gene consists of four exons spanning approximately 4.5 kb. Exon 1 encodes the 5' untranslated region and leader sequence, exon 2 encodes the immunoglobulin (Ig)-like domain, exon 3 encodes the membrane proximal region and exon 4 encodes the transmembrane region, the cytoplasmic tail and the 3' untranslated region. A region in the 5' flanking sequence of the CMRF-35A gene, that promoted expression of a reporter gene was identified. The genes for the CMRF-35A and CMRF-35H molecules are closely linked on chromosome 17. Similarity between the Ig-like exons and the preceding intron of the two genes suggests exon duplication was involved in their evolution. We also identified a further member of the CMRF-35 family, the CMRF-35J pseudogene. This gene appears to have arisen by gene duplication of the CMRF-35A gene. These three loci - the CMRF-35A, CMRF-35J and CMRF-35H genes-form a new complex of IRS genes on chromosome 17.

Expression of multilectin receptors and comparative FITC-dextran uptake by human dendritic cells

Dendritic cells (DC) are potent antigen-presenting cells and understanding their mechanisms of antigen uptake is important for loading DC with antigen for immunotherapy. The multilectin receptors, DEC-205 and macrophage mannose receptor (MMR), are potential antigen-uptake receptors; therefore, we examined their expression and FITC-dextran uptake by various human DC preparations. The RT-PCR analysis detected low levels of DEC-205 mRNA in immature blood DC, Langerhans cells (LC) and immature monocyte-derived DC (Mo-DC). Its mRNA expression increased markedly upon activation, indicating that DEC-205 is an activation-associated molecule. In Mo-DC, the expression of cell-surface DEC-205 increased markedly during maturation. In blood DC, however, the cell-surface expression of DEC-205 did not change during activation, suggesting the presence of a large intracellular pool of DEC-205 or post-transcriptional regulation. Immature Mo-DC expressed abundant MMR, but its expression diminished upon maturation. Blood DC and LC did not express detectable levels of the MMR. FITC-dextran uptake by both immature and activated blood DC was 30- to 70-fold less than that of LC, immature Mo-DC and macrophages. In contrast to immature Mo-DC, the FITC-dextran uptake by LC was not inhibited effectively by mannose, an inhibitor for MMR-mediated FITC-dextran uptake. Thus, unlike Mo-DC, blood DC and LC do not use the MMR for carbohydrate-conjugated antigen uptake and alternative receptors may yet be defined on these DC. Therefore, DEC-205 may have a different specificity as an antigen uptake receptor or contribute to an alternative DC function.

Assessment of cardiotoxicity during haemopoietic stem cell transplantation with plasma brain natriuretic peptide

Cardiac failure is a known complication of haemopoietic stem cell transplantation (HSCT) and is often difficult to diagnose as patients may have multiple medical problems. Since brain natriuretic peptide (BNP) is largely a hormone of cardiac ventricular origin and is released early in the course of ventricular dysfunction, we have examined the value of serial plasma BNP levels for detecting cardiac failure in patients undergoing cytotoxic conditioning for HSCT. Fifteen patients undergoing HSCT were evaluated (10 undergoing autologous HSCT; five undergoing allogeneic HSCT). BNP was measured by radioimmunoassay prior to therapy and weekly for 5 weeks. Seven patients had a significant rise in BNP level (above a previously established threshold of 43 pmol/l associated with cardiac failure), occurring 1-4 weeks post commencement of conditioning. In three of these patients, cardiac failure was subsequently diagnosed clinically 3, 9 and 23 days after a BNP level of 43 pmol/l had been detected. These three patients had the highest peak BNP levels for the group and in each case elevation in BNP level occurred for a period exceeding 1 week. Although numbers were relatively small, a BNP >43 pmol/l was significantly associated with the inclusion of high-dose cyclophosphamide in the preparative regimen (P = 0.02). BNP levels showed no relationship to febrile episodes. In conclusion, these results show that plasma BNP may be used as a marker for early detection of cardiac dysfunction in patients undergoing HSCT, particularly if levels are increased for periods exceeding 1 week. Measurement of BNP during HSCT may be helpful in patients at risk of cardiac failure, in complex clinical situations and in monitoring the cardiotoxicity of preparative regimens.

Successful high dose therapy for relapsed mediastinal large B cell lymphoma following surgical repair of anterior chest wall defect

We describe a man with relapsed large B cell mediastinal lymphoma and associated infected large anterior chest wall defect who required high dose salvage therapy for his underlying disease. An initial mediastinotomy wound, associated with recurrent sepsis, had developed into an abscess, then fistula and eventually a large anterior chest wall defect. Safe use of salvage chemotherapy required reconstructive surgery consisting of a pedicled muscle flap. The subsequent high dose chemotherapy was carried out without complications and 15 months later the patient is alive and well.

The role of dendritic cells in the innate immune system

Dendritic cells (DCs) are bone-marrow-derived leucocytes that are specialised antigen-presenting cells capable of stimulating a primary T-lymphocyte response to specific antigen. In this chapter we discuss the role DCs play in the innate response acting as a critical link with the adaptive response and the influence of the innate response on dendritic cells.

Lectin ligands on human dendritic cells and identification of a peanut agglutinin positive subset in blood

As only a few cell surface markers for dendritic cells (DC) have been identified to date, this study examined the expression of ligands for lectin on different human DC populations. The ability of Concanavalin A (Con A), Wheat Germ Agglutinin (WGA), peanut agglutinin (PNA), and Helix pomatia (HPA) to bind to cell lines and PBMC and DC populations was analyzed by flow cytometry and specificity of binding confirmed using inhibitory and noninhibitory sugars. The cell lines showed non-lineage-restricted binding with Con A and WGA, independent of sialidase treatment. HPA and PNA bound to a restricted number of lines, but showed broad reactivity after sialidase treatment. The peripheral blood mononuclear cells (PBMC) and directly isolated blood DC, activated CD83(+) blood DC, epidermal Langerhans cells (LC), and monocyte-derived DC (Mo-DC) showed strong binding of Con A and WGA, both before and after sialidase treatment. No HPA binding ligands were detected on PBMC populations, including directly isolated blood DC. Following sialidase treatment CD3(+), CD16(+), and a subset of CD19(+) lymphocytes bound HPA. The lectin PNA bound weakly to CD14(+) monocytes and a subpopulation of circulating DC that were HLA-DR(hi)CDw123 Dr(hi)CDw123(dim)/(neg)CD11c(+). The HLA-DR(mod)CDw123(hi)CD11c(neg) subpopulation did not bind PNA. Without sialidase treatment LC expressed both HPA and PNA ligands, but these were either absent on activated CD83(+) blood DC or weakly expressed on Mo-DC. Following sialidase treatment PBMC populations, activated CD83(+) blood DC, and Mo-DC became PNA positive. Thus human DC express several lectin ligands and PNA binding identifies a subset of blood DC. That may reflect discrete changes associated with stages of DC development or functional maturation.

The CMRF-35H gene structure predicts for an independently expressed member of an ITIM/ITAM pair of molecules localized to human chromosome 17

The CMRF-35 monoclonal antibody recognizes an epitope found on at least two cell surface molecules, differentially expressed by many leukocytes. These molecules, the CMRF-35H (9) and CMRF-35A (CMRF-35) antigens are both members of the immunoglobulin (Ig) superfamily with a single V-like Ig domain. The function of these molecules is unknown, however the presence of putative immunoreceptor tyrosine-based inhibitory motifs (ITIM) in the cytoplasmic domain of the CMRF-35H molecule suggests that this molecule may play a regulatory role in leukocyte function. The CMRF-35H and CMRF-35A molecules show several similarities to the family of molecules containing ITIM or immunoreceptor tyrosine-based activatory motifs (ITAM) suggesting that CMRF-35H/CMRF-35A may be new members of this family. This would further indicate that, like other ITIM/ITAM containing molecules, CMRF-35H/CMRF-35A will also play an important role in the immune response. To further characterize these molecules, we have isolated genomic clones for the CMRF-35H gene and determined its intron-exon organization. The gene spans approximately 12 kb and consists of seven exons. Furthermore, this gene has been mapped to chromosome 17 and thus is not linked to the known human ITIM containing genes which map to human chromosome 19 or the recently characterized molecule, NKp44, localized to human chromosome 6.

Cells expressing dendritic cell markers are present in the rheumatoid nodule

OBJECTIVE

To determine if dendritic antigen-presenting cells (DC) are present in rheumatoid nodules, as has been reported in the synovial lesions of rheumatoid arthritis.

METHODS

Nodules (n = 14) were examined with monoclonal antibodies (Mab) recognizing the DC differentiation/activation markers CD83, CMRF44, and CMRF56 and an antibody recognizing the CD1a antigen present on epithelial tissue associated DC. Results. Cells expressing CMRF44 were common in rheumatoid nodules, comprising 22% of nucleated cells versus 13% in synovial membranes (n = 10). Cells positive for CD1a (5%) and CD83 (2%) were less common. A majority (86%) of CMRF44 positive cells were also positive for the macrophage marker CD14. This left a significant minority of putative DC that were single stained with CMRF44.

CONCLUSION

Cells bearing DC markers are as frequent in the rheumatoid nodule as in the synovial lesions. A majority are "indeterminate" cells that are CD14 positive but a proportion are single stained putative DC. The lack of lymphoid collections containing DC and T and B lymphocytes in the nodule suggests that local presentation of antigen may not occur in the rheumatoid nodule, as is thought to be the case in synovial membranes containing lymphoid follicles. This difference could potentially be explained by different states of activation, and differentiation of DC within the 2 lesions.

Induction of dendritic cell costimulator molecule expression is suppressed by T cells in the absence of antigen-specific signalling: role of cluster formation, CD40 and HLA-class II for dendritic cell activation

Full activation of T lymphocytes by dendritic cells (DC) during antigen presentation is known to require the interaction of several inducible receptor-ligand pairs. We have postulated that the reciprocal activation of DC by T lymphocytes is also important. Potential signalling molecules that might increase the stimulatory capacity of DC during antigen presentation to T lymphocytes were tested using an in vitro model. Fresh human blood DC were cocultured with CD4+ and CD8+ allogeneic or with autologous T lymphocytes plus Staphylococcus superantigen A (SEA). Surprisingly, costimulator expression on DC cocultured with T lymphocytes was reduced in comparison to DC cultured alone. However, the minority (10-30%) of DC clustering with T lymphocytes showed antigen-specific up-regulation of the CD40, CD80 and CD86 costimulator molecules, whereas the non-clustered DC (70-90%) had less up-regulation than control DC cultured alone and did not respond to antigen-specific triggering. Monoclonal antibodies (mAb) to CD40 ligand (CD40L) and human leucocyte antigen (HLA)-DR, but not lymphocyte function-associated antigen-1 (LFA-1), LFA-3 or HLA-class I, significantly inhibited the T-lymphocyte induction of DC costimulator expression. Since HLA-class II, but not HLA-class I mAb, inhibited allogeneic T-lymphocyte-mediated activation of DC, CD4 T lymphocytes appear to be the main subset activating DC in the mixed lymphocyte reaction. Cross-linking of CD40, but not HLA-class II, up-regulated DC or B-cell costimulator expression. Although direct class II signalling does not appear to play a role in DC activation, antigen-specific T-cell recognition contributes via other mechanisms to regulate DC activation.

Expression of the RelB transcription factor correlates with the activation of human dendritic cells

The RelB gene product is a member of the nuclear factor (NF)-kappaB family of transcription factors. It has been identified recently within mouse antigen-presenting cells and human monocyte-derived dendritic cells (DC). Disruption of the mouse RelB gene is accompanied, amongst other phenotypes, by abnormalities in the antigen-presenting cell lineages. In order to define RelB expression during human DC differentiation, we have analysed RelB mRNA by reverse transcriptase-polymerase chain reaction and RelB protein by intracellular staining in CD34+ precursors and different types of DC preparations. RelB mRNA was not detected in CD34+ precursor populations. Fresh blood DC (lineage-human leucocyte antigen-DR+ (lin-HLA-DR+)) lacked RelB mRNA and cytoplasmic RelB protein but a period of in vitro culture induced RelB expression in blood DC. Purified Langerhans' cells (LC) (CD1a+ HLA-DR+) failed to express RelB mRNA. Immunocytochemical staining identified RelB protein in human skin epithelium. RelB protein was expressed in a very few CD1a+, CD83+ or CMRF-44+ dermal DC but was not present in CD1a+ LC. Tonsil DC (lin-HLA-DR+ CMRF-44+) were positive for RelB mRNA and RelB protein. Intestinal DC (HLA-DR+) also lacked immunoreactive RelB protein. The majority of interdigitating CD83+, CMRF-44+, CMRF-56+ or p55+ DC located in paracortical T-lymphocyte areas of lymph node and tonsil contained RelB protein. The expression of RelB mRNA and RelB protein correlates with the activated phase of blood DC and the postmigration cell (activated) stage of tissue DC development.

Dendritic cell immunotherapy for cancer: application to low-grade lymphoma and multiple myeloma

The confirmation that most cancers express one or more molecular changes, which may act as tumour-associated antigens (TAA), combined with the knowledge that T lymphocytes recognize even single amino acid differences in MHC presented peptides has stimulated renewed clinical interest in immunotherapeutic strategies. Dendritic cells (DC) are now recognized as specialist antigen-presenting cells, which initiate, direct and regulate immune responses. Recent data suggest that DC are not recruited into, or activated by, cancers and that other abnormalities in DC function are associated with malignancy, including multiple myeloma. This provides a rationale for designing immunotherapeutic strategies, which exploit DC as nature's adjuvant either in vivo or in vitro. Low-grade lymphoma and multiple myeloma are slowly progressive malignancies, which generally express a unique immunoglobulin idiotype as a potential TAA. Data from animal models and clinical studies suggest that DC-based immunotherapy strategies, applied when the patient has minimal residual disease, may improve the long-term prognosis in these diseases.

CD1a dendritic cells predominate in transitional cell carcinoma of bladder and kidney but are minimally activated

PURPOSE

In this study, we employed similar techniques to detail dendritic cell subsets within bladder transitional cell carcinoma and kidney transitional cell carcinoma.

MATERIALS AND METHODS

To identify both the CD1a+ and CD1a- antigen-expressing dendritic cell populations we employed a double labeling technique to identify non-lineage-expressing leukocytes similar to that employed to isolate blood dendritic cells.

RESULTS

Dendritic cells were found in significant numbers within both bladder and kidney derived transitional cell carcinoma. Almost all the dendritic cells among the tumor cells belonged to the CD1a+ subset of epithelial dendritic cells. Similar numbers of dendritic cells were observed in the lamina propria adjacent to the tumor. These dendritic cells belonged predominantly to the CD1a- subset. These differences appear to reflect the different dendritic cell phenotypes reported for the epidermis and dermis.

CONCLUSIONS

The number of dendritic cells increased as the grade of the tumor increased, reflecting an overall higher leukocyte density in higher grade tumors. However, a possible trend for less dendritic cell activation in higher grade cancers was noted, raising the intriguing possibility that this might be a relevant prognostic factor, to be confirmed in a larger study.

Dendritic cells in chronic myelomonocytic leukaemia

Blood dendritic cells (DC) differentiate in vitro via two separate pathways: either directly from blood DC precursors (DCp) or from CD14+ monocytes. In chronic myelomonocytic leukaemia (CMML) abnormal bone marrow precursors contribute to blood monocyte development but DC development has not been studied previously. Monocytes comprised 60% of blood MNC in 15 CMML patients studied, compared with 20% in 16 age-matched controls. The increase in blood monocytes was accompanied by a reciprocal decrease in mean blood DC percentage (from 0.42% of MNC in normal individuals to 0.16% of MNC in CMML patients). Absolute blood DC numbers showed a minimal (non-significant) reduction from 9.8 x 10(6)/l in normal individuals to 7.5 x 10(6)/l in CMML patients. The CD14(low) WCD16+ monocyte subpopulation was not found in CMML patients. After culture in GM-CSF/IL-4, CMML CD14+ monocytes acquired the phenotype of immature monocyte derived DC (Mo-DC) with similar yields to normal blood Mo-DC generation. Addition of TNF-alpha or LPS induced both normal and CMML Mo-DC to express prominent dendritic processes, the CMRF44+ and CD83+ antigens and high levels of HLA-DR, CD80 and CD86. Treatment either with TNF-alpha or LPS increased the allostimulatory activity of normal Mo-DC, but had little effect on the allostimulatory activity of CMML Mo-DC, perhaps reflecting the underlying neoplastic changes in monocyte precursors. We conclude that the blood DC numbers are relatively unaffected in CMML, suggesting discrete regulation of monocyte and DC production.

Human dendritic cells express a 95 kDa activation/differentiation antigen defined by CMRF-56

Despite the unique functions of dendritic cells (DC), only two cell surface antigens (CMRF-44 and CD83) with relatively restricted expression on human DC have been described to date. We describe a third mAb, CMRF-56, which recognizes another DC early activation/differentiation antigen with limited expression on other haemopoietic cell populations. Circulating blood leukocytes did not express the CMRF-56 antigen and, following either in vitro culture or activation of PBMC populations, CMRF-56 antigen expression was detected only on DC and a subpopulation of CD19+ lymphocytes. Circulating blood DC were CMRF-56 but induced expression within 6 h of in vitro culture. This, together with the finding that tonsil and synovial fluid DC upregulate the antigen following short-term in vitro culture, confirmed that CMRF-56 recognizes an early activation antigen on DC. Isolated Langerhan's cells, dermal DC, migratory dermal DC and monocyte derived DC (GM-CSF/IL-4/TNFalpha) also express the CMIRF-56 antigen. Antigen modulation studies demonstrated that the amount of cell surface bound CMRF-56 and CMRF-44 (but not CD83) mAb was dramatically reduced by short-term incubation at 37 degrees C. This effect was not due to internalization and the reduction in CMRF-56 binding was a reversible, temperature-dependent process. In contrast, the decrease in CMRF-44 binding was irreversible, suggesting that following ligation the CMRF-44 antigen undergoes an irreversible conformational change or shedding at 37 degrees C. Western blotting confirmed that CMRF-56 recognizes a previously undescribed 95 kDa activation antigen whose cellular distribution and expression kinetics overlaps with, but is clearly distinguishable from, that of the CD83 and CMRF-44 antigens. CMRF-56 therefore provides a useful additional marker for studies on human DC.

Synovial fluid transforming growth factor beta inhibits dendritic cell-T lymphocyte interactions in patients with chronic arthritis

OBJECTIVE

To examine whether rheumatoid synovial fluid (SF) inhibits dendritic cell (DC) expression of the CD80 and CD86 costimulator molecules and contributes to SF T lymphocyte hyporesponsiveness.

METHODS

Cell-free rheumatoid SF was tested for its effect on DC-stimulated autologous/allogeneic mixed lymphocyte reactions and for its effect on DC surface antigen expression, as assessed by flow cytometry. Blocking monoclonal antibodies were used to identify the SF cytokines that inhibited DC-T lymphocyte interactions.

RESULTS

Low concentrations of SF (2.5%) could inhibit DC-mediated autologous and allogeneic T lymphocyte proliferation. This inhibitory effect could be reversed by neutralizing transforming growth factor beta (TGFbeta) and interleukin-2 (IL-2), but not by IL-12, in the SF. Hyaluronic acid, IL-6, IL-10, and tumor necrosis factor alpha were not associated with SF inhibition. In vitro culture alone and crosslinking with the CD40 ligand up-regulated DC CD80/CD86 expression and costimulator function, and this was not affected by inclusion of SF. In the presence of SF, DC clustered with autologous T lymphocytes showed decreased CD80 and CD86 expression, and variable CD80/CD86 decreases were observed on DC clustered with allogeneic T lymphocytes.

CONCLUSIONS

TGFbeta in SF appears to suppress T lymphocyte function, which may affect both signaling to DC and the induction of DC costimulator function.

Monitoring human blood dendritic cell numbers in normal individuals and in stem cell transplantation

Dendritic cells (DC) originate from a bone marrow (BM) precursor and circulate via the blood to most body tissues where they fulfill a role in antigen surveillance. Little is known about DC numbers in disease, although the reported increase in tissue DC turnover due to inflammatory stimuli suggests that blood DC numbers may be altered in some clinical situations. The lack of a defined method for counting DC has limited patient studies. We therefore developed a method suitable for routine monitoring of blood DC numbers, using the CMRF44 monoclonal antibody (MoAb) and flow cytometry to identify DC. A normal range was determined from samples drawn from 103 healthy adults. The mean percentage of DC present in blood mononuclear cells (MNC) was 0.42%, and the mean absolute DC count was 10 x 10(6) DC/L blood. The normal ranges for DC (mean +/- 1.96 standard deviation [SD]) were 0.15% to 0.70% MNC or 3 to 17 x 10(6) DC/L blood. This method has applications for monitoring attempts to mobilize DC into the blood to facilitate their collection for immunotherapeutic purposes and for counting blood DC in other patients. In preliminary studies, we have found a statistically significant decrease in the blood DC counts in individuals at the time of blood stem cell harvest and in patients with acute illnesses, including allogeneic bone marrow transplant (BMT) recipients with acute graft-versus-host disease (aGVHD).

Presentation of tumor antigens

Dendritic cells, with their extraordinary capacity for initiating primary and secondary T-lymphocyte responses, may be pivotal in the development of immunotherapeutic strategies for multiple myeloma. Although host lymphocytes are able to recognize tumor-associated antigens (TAAs), many tumors are able to avoid dendritic cell-mediated immune surveillance. One reason may be that the tumor environment inhibits the maturation and activation of dendritic cells. A recently developed strategy to use dendritic cells in immunotherapy involves removing them from the tumor, pulsing them in vitro with antigen, and reinfusing them into the patient to generate responding T cells in vivo. Methods for reliably obtaining dendritic cells for therapeutic use are currently being investigated. Among other efforts to induce T-cell-mediated immunity against cancer, the presentation of tumor antigens by the tumor cells themselves is being investigated. Issues to be resolved include defects of antigen presentation by tumor cells and whether all cells present the same set of peptides. Moreover, as long as all the tumor antigens have not been identified, the tumor cell itself remains the primary source of unknown antigens and, therefore, is a worthwhile subject for study. Phase I trials of immunotherapy using adenovirus-infected autologous plasma cells have recently been undertaken. The adenoviral vectors carry genes with therapeutic potential, including interleukin-2 (IL-2), interleukin-12, and B7-1. Initial results showed that the vector can be readily detected in tumor cells at 13 days postinjection, and IL-2 expression was evident at 7 days. The chief side effect reported was inflammation.

Generation of CMRF-44+ monocyte-derived dendritic cells: insights into phenotype and function

The CMRF-44 monoclonal antibody (MoAb) recognizes an intermediate stage of blood dendritic cell (DC) differentiation as well as mature CD83+ blood DC. Here we describe the use of the CMRF-44 MoAb to monitor the in vitro development of DC-like cells from peripheral blood mononuclear cells. Neither granulocyte-macrophage colony-stimulating factor (GM-CSF) nor GM-CSF plus tumor necrosis factor-alpha (TNF-alpha) supported the development of CMRF-44+ cells. However, GM-CSF plus interleukin (IL)-4 generated a substantial number of CMRF-44+ cells among the heterogeneous CD14- myeloid cell population, produced after 7 or 10 days of culture. The addition of TNF-alpha to GM-CSF+IL-4 on the fifth day of culture enhanced the generation of CMRF-44+ cells from days 7 to 14. A concentration of 50 U/mL of IL-4 was sufficient to allow the development of CMRF-44+ cells. The presence of GM-CSF was essential, but a wide range of concentrations (50-800 U/mL) was effective for supporting IL-4-induced generation of CMRF-44+ cells. TNF-alpha at concentrations of 20 or 50 ng/mL induced a maximal increase in the number of CMRF-44+ cells. The CMRF-44+ DCs generated in the presence of GM-CSF+IL-4 were large, irregularly shaped cells with variable CD1a expression and have CD83 transcripts but no CD83 surface expression. Additional TNF-alpha treatment induced prominent dendritic processes and surface expression of CD83 on CMRF-44+ DCs. The CMRF-44+ DCs generated in GM-CSF+IL-4 showed higher allostimulatory activity than CMRF-44 cells but were less efficient at processing and presenting soluble antigen to T-lymphocyte lines. TNF-alpha treatment reduced antigen uptake but increased the allostimulatory activity of CMRF-44+ DCs. CMRF-44+ DC differentiation from blood CD14+ monocytes was not radiosensitive and thus does not involve cell division. We conclude that the MoAb CMRF-44 identifies both intermediate and fully mature stages of monocyte-DC differentiation and may be a useful marker in establishing the optimal timing for antigen loading of in vitro-generated monocyte-derived DCs.

Dermal dendritic cells associated with T lymphocytes in normal human skin display an activated phenotype

The CMRF-44 and CD83 (HB15) antigens are associated with functional maturation and activation of blood dendritic cells (DC). We describe the expression of these antigens on freshly isolated epidermal Langerhans cells and dermal DC as well as the distribution of CD83+/ CMRF-44++-activated DC within sections of normal human skin. Fresh Langerhans cells were prepared by standard techniques and large numbers of enriched (25%-55%), viable dermal DC were obtained using an improved collagenase treatment protocol with density gradient enrichment. Freshly isolated Langerhans cells and dermal DC had similar costimulator and activation antigen expression, and both stimulated moderate levels of allogeneic T lymphocyte proliferation as determined in the 7 d mixed leukocyte reaction. In situ labeling of DC within skin sections revealed a population of CD83 and CMRF-44 positive dermal cells of which most (approximately 75%) were in intimate contact with CD3+ T lymphocytes, especially in the adnexal regions. In contrast, only 25%-30% of the more numerous CD1a++ dermal DC population were directly apposed to T lymphocytes. The CMRF-44++ dermal DC population stimulated an allogeneic mixed leukocyte reaction, confirming their identity as DC. These data, plus comparative data obtained for migratory dermal DC, suggest that only a small proportion of dermal DC have been triggered to a more advanced state of differentiation or activation. The striking association of the activated dermal DC population with T lymphocytes suggests that communication between these two cell types in situ may occur early in the immune response to cutaneous antigen.

Optimisation of the conditions for generating human DC initiated antigen specific T lymphocyte lines in vitro

Naive T lymphocytes specific for a given primary antigen occur in low frequencies and require the relevant antigen to be presented by specialist antigen presenting cells (APC), i.e., dendritic cells (DC). For these reasons, the in vitro induction of primary T lymphocyte responses remains a significant technical challenge. We have attempted to improve current strategies for generating in vitro responses by optimising (i) isolation and concomitant activation of DC from peripheral blood, (ii) uptake, processing and presentation of antigen by DC and (iii) antigen driven T lymphocyte proliferation. We established that RPMI 1640 media supplemented with 10% autologous serum resulted in the best yield of CMRF-44+, CD14-, CD19- DC after enrichment over a Nycodenz gradient. Optimal presentation of whole protein and peptide antigen was achieved by addition after the purification of the APC, i.e., at the start of the T lymphocyte proliferation assay. RPMI 1640 supplemented with 10% autologous serum or plasma supported the best antigen driven specific T lymphocyte responses. Using these optimised conditions, we compared the efficacy of PBMC and purified blood DC for priming T lymphocyte responses to the chronic myeloid leukaemia (CML) specific bcr-abl (b3a2) peptide. Peptide specific T lymphocyte responses were generated with both purified DC and whole PBMC, suggesting that T lymphocyte precursor frequency was the limiting factor in these experiments. These results will aid in the generation of human T lymphocyte lines to primary antigens, for in vitro and therapeutic applications.

Molecular cloning and functional analysis of the CD33 promoter

CD33 is a leucocyte differentiation antigen restricted to myeloid cells in blood and bone marrow. Two mRNA transcripts encoding CD33 are observed in leukaemic cell lines. The smaller transcript of 1.5 kb is comparable in size to the isolated CD33 cDNA but the origin of the larger 1.8 kb transcript is unknown. To study the regulation of human CD33 expression, a 5' genomic clone from the CD33 gene was isolated and studied for promoter activity. The clone, although lacking a TATAA box, exhibits other sequences characteristic of a promoter. Two transcriptional start sites were identified, 414 and 527 nucleotides 5' of the ATG initiation codon, suggesting that these sites are used to generate the 1.8 kb transcript observed in CD33+ cell lines. The CD33 genomic sequence directed high expression of a luciferase reporter gene in myeloid cell lines. Using deletion mutants of the promoter sequence, maximal expression was localized to the first 220 bp 5' of the ATG initiation codon. Site-directed mutagenesis of an Sp-1 and PU.1 binding site within this region showed that the PU.1, but not Sp-1, was critical for CD33 expression in myeloid lines. Given the restricted expression of CD33 on haemopoietic cells, the identification of the CD33 promoter may be useful for the study of transcription factors that regulate gene expression during early myeloid differentiation.

A long-lasting interferon-gamma response is induced to a single inoculation of antigen-pulsed dendritic cells

Vaccines against infectious organisms must produce not only long-lasting immunity but also the appropriate immune response to clear the infection. Obligate intracellular parasites, such as mycobacteria, require a predominantly cell-mediated immune response rather than antibody. Presentation of antigen by dendritic cells (DC) has been associated with the development of strong cell-mediated responses generating the production of interferon-gamma (IFN-gamma). This cytokine has an essential role in the elimination of mycobacteria. Therefore, we investigated both the duration and the nature of the immune response after priming with DC pulsed with mycobacterial antigen and compared this with priming using a conventional adjuvant. We used two strains of mice: C57BL/6, which inherently produces a T-helper 1 (Th1)-type response to mycobacterial antigen, and BALB/c, which does not. DC-enriched cell suspensions, purified DC or cultured bone marrow cells resembling DC (BMAPC) were prepared, pulsed overnight with PPD and injected intravenously (i.v.) into naive mice. Six and 12 weeks later, splenic T lymphocytes from these mice were challenged in vitro with antigen and their proliferative response and cytokine production was determined. Significant antigen-specific proliferation was observed in all assays on rechallenge with antigen in vitro 6 and 12 weeks after the initial priming with DC. IFN-gamma was detected in both strains but was only antigen specific in the C57BL/6 strain. Purified protein derivative (PPD)-pulsed BMAPC generated similar responses 6 weeks after priming. Thus, long-term T-lymphocyte responses and the production of IFN-gamma can be generated using a single inoculation of PPD-pulsed DC.

Type I IFNs enhance the terminal differentiation of dendritic cells

This study identifies type I IFNs as activating cytokines in a serum-free system in which human dendritic cells (DC) were generated from CD34+ progenitor cells. After 14 days of culture in GM-CSF, TNF-alpha, and IL-4, CD34+ progenitors gave rise to a population of large, immature DC expressing CD1a and CD11b but lacking CD14, CD80, CD83, CD86, and CMRF44. During the next 2 wk, this population spontaneously matured into nonadherent, CD1a(low/-), CD11b(low/-), CD14-, CD80+, CD83+, CD86+, CMRF44+ DC with high allostimulatory activity in the MLR. To examine which factors influenced this maturation, 25 different cytokines or factors were added to the immature DC culture. Only type I IFNs (alpha or beta) accelerated this maturation in a dose-dependent manner, so that after only 3 days the majority of large cells acquired the morphology, phenotype, and function characteristics of mature DC. Furthermore, supernatants from cultures containing spontaneously maturing DC revealed low levels of endogenous IFN production. Because of the similarity of the activation of DC in our culture system with the phenotypic and functional changes observed during Langerhans cells activation and migration in vivo, we investigated the effect of IFN-alpha on human Langerhans cell migration. IFN-alpha also activated the migration of human split skin-derived DC, demonstrating that this effect was not limited to DC derived in vitro from hemopoietic progenitor cells. DC activation by type I IFNs represents a novel mechanism of immunomodulation by these cytokines, which could be important during antiviral responses and autoimmune reactions.

The CMRF-35 mAb recognizes a second leukocyte membrane molecule with a domain similar to the poly Ig receptor

The CMRF-35 mAb recognizes an antigen found on most leukocytes including monocytes, neutrophils, macrophages, dendritic cells, and subpopulations of lymphocytes and bone marrow cells. A cDNA expressing the CMRF-35 epitope was isolated by expression cloning and this predicts for a type I cell surface glycoprotein belonging to the Ig superfamily. Here we demonstrate that the CMRF-35 mAb recognizes an epitope more widely distributed on hemopoietic cells and cell lines than suggested by expression analysis of the CMRF-35 mRNA. Furthermore, we have isolated a novel cDNA (CMRF-35-H9) that encodes a protein product also recognized by the CMRF-35 mAb. This cDNA product is a type I cell surface glycoprotein with a single Ig V-like domain. Although the sequences of the extracellular V-like domains of the two molecules are very similar, there is little similarity between the remainder of their sequences. The two transcripts are expressed independently of each other, and their presence accounts for the discrepancy between CMRF-35 mAb binding and mRNA analysis. The cytoplasmic tail of CMRF-35-H9 contains motifs similar to the inhibitory motifs found in some leukocyte surface receptors. Their expression in hemopoietic cells suggests that these two molecules may play distinct but related roles in the regulation of leukocyte function.

cDNA cloning of human DEC-205, a putative antigen-uptake receptor on dendritic cells

Dendritic cells (DC) are specialist antigen presenting cells which capture antigens in the periphery, migrate centrally, and present the processed antigens in the context of major histocompatibility complex and appropriate co-stimulatory molecules to T lymphocytes for the initiation of an immune response. DEC-205 has been identified as a putative antigen-uptake receptor, which is expressed abundantly on mouse DC. The recently cloned mouse DEC-205 cDNA predicts a molecular structure which has a marked similarity to the macrophage mannose receptor. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA library screening, we obtained the full coding region of human DEC-205 cDNA from the Hodgkin's disease-derived L428 cell line. The predicted protein structure is a type I transmembrane protein of 1722 amino acids consisting of a signal peptide, cysteine-rich domain, fibronectin type II domain, ten carbohydrate recognition-like domains, transmembrane domain, and a cytoplasmic tail. Human DEC-205 is 77% identical to the mouse protein with completely conserved cysteines. The DEC-205 gene (LY75) was mapped to chromosome band 2q24 by somatic cell hybrid panel analysis and fluorescent in situ hybridization. Northern blot analysis detected 7.8 and 9.5 kilobase DEC-205 transcripts in myeloid, B lymphoid, and Hodgkin's disease-derived cell lines. RT-PCR analysis indicated that immature blood DC contain a barely detectable amount of DEC-205 transcripts but these were markedly increased upon differentiation/activation.

Blockade of B7-2, not B7-1, inhibits purified protein derivative-primed T-lymphocyte responses but fails to influence the proportion of Th1 versus Th2 subsets

The ability to select for a cell-mediated response rather than antibody production following infection with intracellular mycobacteria, would be an advantage in preventing the occurrence of disease. Recent work suggests that the two members of the B7 family of costimulatory molecules, B7-1 and B7-2, may differentially influence the nature of primary immune responses but little is known of their role in this capacity in secondary responses. We have used an in vitro model to investigate whether blocking B7-1 and B7-2 affects changes in the cytokine profiles of Th lymphocytes previously primed to purified protein derivative (PPD) from Mycobacterium bovis. In C57BL/6 and BALB/c mice we found that the proliferative responses of a component of recently activated T lymphocytes, and those returning to the resting state, were inhibited by B7-2 blockade. B7-1 blockade had no distinguishable effect. However, in cultures containing anti-B7-2 antibody, the production of both interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), indicative of cell-mediated and antibody responses, respectively, were reduced. This suggests that intervention in a recall response to mycobacterial antigen by blocking B7-1 or B7-2 molecules, is unlikely to alter the nature of the immune response.

Minimal recruitment and activation of dendritic cells within renal cell carcinoma

Dendritic cells (DCs) are predicted to participate in natural tumor immunity by migrating into tumors, where they acquire antigen, undergo activation, and migrate to lymph nodes to initiate a T-lymphocyte response against tumor-associated antigens. The presence of DCs using defined lineage markers and their function in human tumors has not been assessed previously. The monoclonal antibodies against CMRF-44 and CD83, which are differentiation/activation antigens on DCs, were used in immunohistological and flow cytometry studies to analyze the DC subtypes infiltrating 14 cases of human renal cell carcinoma (RCC). The functional immunocompetence of the DCs isolated from RCC was assessed by testing their ability to stimulate an allogeneic mixed leukocyte reaction. The majority of leukocytes present within the RCC were macrophages (62% +/- 14.7) or T lymphocytes (19% +/- 9.5), with CD45+ HLA-DR+ lineage-negative putative DCs accounting for less than 10% of the leukocytes present. Of these, a subset, comprising less than 1% of total leukocytes, had an activated CMRF-44+ or CD83+ DC phenotype. Activated CMRF-44+ and CD83+ DCs were more evident outside the tumor in association with T-lymphocyte clusters. The number of CMRF-44+ DCs correlated closely with the number of S-100-positive DCs. Isolation of DCs from eight RCCs was achieved, and flow cytometry studies confirmed the small proportion of activated CMRF-44+ DCs. The CMRF-44+ DCs stimulated an allogeneic mixed leukocyte reaction, but the CMRF-44- DCs (normal tissue DC precursors and other cells) failed to do so. These results suggest that RCCs recruit few DCs into the tumor substance, and the tumor environment fails to initiate the expected protective activation of DCs. These two mechanisms, amongst others, may contribute to tumor escape from immunosurveillance. In vitro loading of DCs with tumor-associated antigens may be a useful therapeutic maneuver.

Human dendritic cells express functional interleukin-7

Interleukin-7 (IL-7) supports the proliferation of mature T lymphocytes, however, the cellular source of IL-7 for T lymphocyte activation has not been well established. We therefore investigated whether human peripheral blood dendritic cells (DC) produce IL-7 as a contribution towards T lymphocyte activation. Human CMRF-44+/CD14-/CD19- low density DC, purified after overnight tissue culture, contained IL-7 transcripts, detected by direct cell reverse transcription-polymerase chain reaction. Intracytoplasmic staining confirmed IL-7 protein in at least a subpopulation of cultured low density DC. In contrast, resting/immature DC, isolated directly by immunodepletion of lineage marker positive cells, contained no IL-7 mRNA. Thus, the expression of IL-7 by DC follows the pattern described previously for CD80, CD86 and CD40. However, tissue culture of purified resting/immature DC, in contrast to CD80, CD86 and CD40, failed to induce IL-7 transcripts. The functional importance of DC IL-7 expression was demonstrated in an allogeneic mixed leukocyte reaction (MLR). Neutralising mAb to IL-7 significantly inhibited T lymphocyte proliferation when low DC numbers were used, but at higher stimulator numbers, anti-IL-7 mAb failed to inhibit an allogeneic MLR. This suggests, that when DC are in excess, other co-stimulatory pathways can compensate for the lack of IL-7. Addition of IL-7 to a MLR caused a significant increase in the proliferative response stimulated by monocytes and B lymphocytes but not by DC. These data support the concept of an initial phase of antigen uptake by DC followed by the optimisation of DC co-stimulatory potential. The co-stimulatory repertoire expressed, including IL-7, may be regulated by exogenous stimuli, thereby ensuring DC flexibility in mounting a response appropriate to the environmental changes.

Invasive aspergillosis in severely neutropenic patients over 18 years: impact of intranasal amphotericin B and HEPA filtration

The impact of intranasal amphotericin B and high-efficiency particulate air (HEPA) filtration on the incidence of invasive aspergillosis was reviewed in patients from 1977 to 1994 undergoing intensive chemotherapy. Overall, the incidence of proven invasive aspergillosis was reduced from 24.4% (1977-1984) to 7.1% (1985-1991) (P < 0.001) following the introduction of intranasal prophylaxis, but when probable cases of aspergillosis were included and lymphoma cases excluded, there was no change in incidence. Following the introduction of HEPA filtration, patient exposure to aspergillus spores as measured by air sampling was markedly reduced and there were no new cases of invasive aspergillosis. HEPA filtration proved effective in reducing invasive aspergillosis and has allowed increasingly aggressive treatment regimens to be introduced.

Hodgkin's cells express CD83, a dendritic cell lineage associated antigen

Hodgkin's cells (HC) are considered to be the malignant cells of Hodgkin's disease (HD), but despite extensive studies, no conclusive evidence has emerged regarding their non-malignant counterpart and the ontogeny of these cells remains controversial. The analysis of a possible dendritic cell (DC) origin of HC has been hampered to date by the lack of a DC lineage specific marker. The expression of the two DC-associated antigens CD83 and CMRF-44, the B lymphocyte restricted molecule CD79, and the costimulator molecule CD86, was examined in lymph nodes from 23 HD patients using immunohistological techniques. The majority of HC expressed the CD83 (22/23) and CD86 antigens (20/23), whereas expression of the CMRF-44 antigen was variable (10/23) and usually only a subpopulation of HC stained. In contrast, the CD79 antigen was absent from most HC (17/23). The presence of the CD83 antigen on HC in the absence of the CD79 antigen supports a possible DC lineage origin for some HC. Regardless of its role in lineage assignment, CD83 may become a useful immunohistological marker for HD as the CD83 antigen was present on most HC.

HLA-DR1-restricted bcr-abl (b3a2)-specific CD4+ T lymphocytes respond to dendritic cells pulsed with b3a2 peptide and antigen-presenting cells exposed to b3a2 containing cell lysates

Chronic myeloid leukemia (CML) is characterized by a specific translocation of the c-abl oncogene on chromosome 9 to the break point cluster region (bcr) on chromosome 22, t(9;22) (q34;q11). This translocation results in the expression of a 210-kD bcr-abl protein fusion gene product. The juxtaposition of the bcr and abl genes produces a novel junctional amino acid sequence, which may be presented by antigen-presenting cells and recognized specifically by human T lymphocytes. We have generated a CD4+ T lymphocyte line (NG-1) which recognizes the peptide epitope (GFKQSSKALQR) in association with HLA-DRbeta1*0101-02. A comparison of antigen-presenting cells showed that CMRF-44+ blood dendritic cell presented a 12mer b3a2 peptide effectively. The b3a2 peptide was able to generate specific primary T-lymphocyte responses in other HLA-DR1 donors. We also show that bcr-abl, b3a2 peptide-specific T-lymphocyte lines proliferate in response to bcr-abl b3a2 containing cell lysates (K562 or CML PBMC derived) but not control (including b2a2 CML PBMC) lysates.

Priming to mycobacterial antigen in vivo using antigen-pulsed antigen presenting cells generated in vitro is influenced by the dose and presence of IL-4 in APC cultures

Antigen presenting cells (APC) similar to immature dendritic cells can be generated in vitro from bone marrow precursors. The authors have compared the yield, the phenotype and the function of murine bone marrow cells cultured for 7 or 11 days in either granulocyte macrophage colony stimulating factor alone (GM BMAPC) or in combination with interleukin-4 (GM/IL-4 BMAPC). The results showed that GM/IL-4 BMAPC expressed the highest levels of MHC Class 2 molecules, CD86/B7-2 and CD80/B7-1 co-stimulatory molecules and the lowest levels of F4/80 macrophage marker. However, when these APC were pulsed with BCG culture filtrate antigen or PPD they were not correspondingly more effective at stimulating activated T lymphocytes in vitro or priming naive T lymphocytes in vivo. Also, in contrast to GM BMAPC, high backgrounds recorded following injections of GM/IL-4 BMAPC without antigen were not consistently reduced by lowering the dose and irradiating the cells prior to administration. The authors conclude that the degree of maturity of BMAPC varies with culture conditions and that this may be an important consideration where BMAPC are to be used in vivo in immunotherapeutic regimens.

Prolonged remission of longstanding systemic lupus erythematosus after autologous bone marrow transplant for non-Hodgkin's lymphoma

We describe a patient with longstanding steroid-dependent systemic lupus erythematosus (SLE) in whom clinical and serological remission was achieved following high-dose therapy and autologous bone marrow rescue for high-grade non-Hodgkin's lymphoma. However, 3 years later, autoimmune disease re-presented in the form of immune thrombocytopenia (ITP), which had not previously been a feature of the SLE, necessitating reintroduction of steroid immunosuppression. Relapse of SLE is most likely, although de novo ITP post-BMT is also a possibility. The case suggests that severe long-standing autoimmune disease may be controlled by high-dose therapy and autologous stem cell reconstitution. However, further studies are required to determine the mechanism of re-emergence of autoimmunity and to evaluate optimal regimens and the potential value of such therapy in severe autoimmune diseases.

Isolation of human blood dendritic cells using the CMRF-44 monoclonal antibody: implications for studies on antigen-presenting cell function and immunotherapy

Dendritic cells (DC) are potent antigen-presenting cells (APC) with the capacity to stimulate a primary T lymphocyte immune response and are therefore of interest for potential immunotherapeutic applications. Freshly isolated DC or DC precursors may be preferable for studies of antigen uptake and the potential control of APC costimulator activity. In this report, we report that the monoclonal antibody CMRF-44 can be used to detect early DC differentiation. The majority of DC circulating in blood do not express any known DC lineage specific markers, but can be identified by CMRF-44 labeling after a brief period of in vitro culture. The sequential acquisition of DC activation antigens allows the identification of two stages of DC maturation/activation. Cytokines, especially granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF)alpha, enhance both phases of this process, whereas CD40-ligand trimer preferentially enhances the final DC maturation to a fully mature, activated phenotype. DC positively selected using CMRF-44 possess potent allostimulatory activity and are efficient at the uptake, processing, and presentation of soluble antigens for both primary and secondary immune responses. CMRF-44+ DC are also more potent than other APC types at restimulation of a chronic myeloid leukemia peptide specific T-cell clone. The use of a purified population of freshly isolated DC may be advantageous in attempts to initiate, maintain, and direct immune responses for immunotherapeutic applications.

Human T lymphocytes and hematopoietic cell lines express CD24-associated carbohydrate epitopes in the absence of CD24 mRNA or protein

The CD24 surface antigen is a small glycophosphatidylinositol (GPI)-anchored glycoprotein found on human granulocytes and most B lymphocytes. Many CD24 monoclonal antibodies (MoAbs) have been described that identify several epitopes, with the majority of them related to carbohydrate structures associated with the CD24 molecule. Considerable variation has been observed in the apparent tissue distribution of the CD24 antigen depending on the MoAb used, and hence the CD24 epitope studied. In this study, CD24 expression by human cell lines and normal hematopoietic call populations was assessed using a panel of carbohydrate and protein core-specific CD24 MoAbs and reverse transcriptase polymerase chain reaction (RT-PCR) analysis. A number of CD24 carbohydrate epitope-reactive MoAbs bound to both T lymphocytes and several hematopoietic cell lines, despite the absence of concomitant CD24 mRNA or detectable surface CD24 core protein in the same cells. This additional CD24 MoAb reactivity on T lymphocytes was, in common with that observed on granulocytes (CD24 protein+), specifically inhibited by the presence of both sialyllactose and mucin. Similarly, the binding of carbohydrate epitops-reactive CD24 MoAb was reduced on both T lymphocytes and granulocytes by pretreatment with phospholipase C, pronase, or neuraminidase. Together, the data indicate that a number of CD24-associated carbohydrate epitopes have a broader tissue distribution than the CD24 protein and are expressed on additional GPI-linked molecule(s). These findings have immediate implications for both leukemia phenotyping and attempts to examine CD24 function with CD24 MoAb.

Identification of a novel dendritic cell surface antigen defined by carbohydrate specific CD24 antibody cross-reactivity

Dendritic cells (DC) are characterized as leucocytes that lack mature lineage specific markers and stimulate naive T-lymphocyte proliferation in vitro and in vivo. The mouse heat stable antigen (HSA) participates in T lymphocyte co-stimulation and is expressed by DC isolated from thymus, skin and spleen. The human HSA homologue, CD24, is predominantly expressed by B lymphocytes and granulocytes, but its expression on DC has not been studied in detail. CD24 clearly participates in B-lymphocyte signalling but co-stimulatory activity for T lymphocytes has not yet been described. We have examined the expression of CD24 on human peripheral blood DC populations isolated directly or following in vitro culture. The CD24 antigen was absent from blood DC however, cross-reactive sialylated carbohydrate epitopes were detected on DC with some CD24 monoclonal antibodies (mAb). These CD24 mAb define a protein surface antigen, which is expressed by an immature or resting subpopulation of peripheral blood DC and is down-regulated following activation differentiation in vitro.

Expression and function of CD80 and CD86 costimulator molecules on synovial dendritic cells in chronic arthritis

OBJECTIVE

To examine CD86 expression on dendritic cells isolated from the synovial fluid (SFDC) of patients with chronic arthritis, and to determine the importance of both CD80 and CD86 molecules in SFDC-T lymphocyte interactions.

METHODS

CD86 messenger RNA (mRNA) and surface expression were analyzed in SFDC using reverse transcriptase-polymerase chain reaction and flow cytometry, respectively. The costimulator activity of the SFDC CD80 and CD86 molecules was determined by allogeneic mixed lymphocyte reaction (MLR). CD80 and CD86 induction on SFDC during in vitro culture was also examined.

RESULTS

Fresh SFDC either lacked or showed very weak surface expression of CD86 molecules (as shown previously for CD80), yet contained CD86 mRNA. CD80 antibodies minimally inhibited an allogeneic MLR, whereas CD86 antibodies and CTLA-4 Ig showed significant inhibition. Both CD80 and CD86 molecules were inconsistently induced on SFDC following culture in either media, interferon-gamma, or granulocyte-macrophage colony-stimulating factor.

CONCLUSION

SFDC may be defective antigen-presenting cells in vivo. The ability of CD80 and CD86 molecules to be induced and become functional on SFDC in vitro implies the presence of a negative regulatory compound(s) in the synovial environment.

Human dendritic cells activate T lymphocytes via a CD40: CD40 ligand-dependent pathway

The CD40:CD40 ligand (CD40L) interaction provides T lymphocyte-mediated help for B lymphocyte and monocyte function but has also been shown to serve as a co-stimulus for T lymphocyte activation. In this report, we studied the regulation of CD40 expression and its functional relevance for the human dendritic cell (DC) stimulation of T lymphocytes. Only a small subpopulation of directly isolated blood DC expressed CD40. However, CD40 was rapidly up-regulated by culture, and its expression was further enhanced by interleukin (IL)-1 alpha, IL-1 beta, IL-3, tumor necrosis factor-alpha and granulocyte/macrophage-colony-stimulating factor. Expression of CD40L on DC was not detected. The proliferation of T lymphocytes in an allogeneic mixed leukocyte reaction, stimulated by blood DC or epidermal Langerhans cells, was significantly reduced in the presence of the CD40 immunoglobulin (CD40Ig) fusion protein or CD40L monoclonal antibodies. Cross-linking of CD40 on directly isolated DC with mouse CD40L trimer (mCD40LT) markedly augmented CD80 and CD86 up-regulation. Nevertheless, the same cross-linking mCD40LT inhibited DC stimulated T lymphocyte proliferation. When CD40Ig was added simultaneously with CTLA-4Ig, only minimal and variable additional inhibition of DC-stimulated allogeneic T lymphocyte proliferation and IL-2 secretion was observed, compared to each fusion protein alone. These results suggest that both CD80/CD86-dependent and -independent components of DC-T lymphocyte CD40:CD40L co-stimulation exist and further emphasize that the majority of blood DC have to differentiate or be activated to express co-stimulatory molecules.