Staphylococcal Enterotoxin is a Bovine T Cell Superantigen

Different isoforms of soluble staphylococcal enterotoxins (SE): SEB, SEC-1 and SEC-2, were shown to stimulate bovine T cell proliferation, expression of cytokine messages, and IgG production. Intact metabolic function of APC was not required since peripheral blood mononuclear cells (PBMC), UV-irradiated prior to or following incubation with SE, were both capable of presenting SE, while PBMC treated with MAbs against MHC II lost the ability to stimulate T cell proliferation. SE caused approximately two fold increase of CD4⁺, and CD8⁺ T cells, but not MHC II⁺ APC or B cells. This model system suggests that SE transduces not only T cell activation signal, but also a non-proliferative signal for primary B cells to produce polyclonal IgG. We hypothesize that enterotoxin virulence may be in part due to its effect on activating the immune system.     

“Nk-Like” T Cytotoxicity Against B Lymphocytes in a Hypogammaglobulinemic Patient

Physiologically, cells with NK activity appear to exert a negative control on immunoglobulin production. The clinical association of large granular lymphocyte (LGL) proliferation with hypogammaglobulinemia suggests that these functional NK cells could also be involved in pathological situations.

We studied in vitro lymphocyte functions in a patient presenting LGL proliferation associated with hypogammaglobulinemia. The CD3⁺ CD8⁺ CD57⁺ CD16^- phenotype lymphocytes expressed a high NK type cytotoxicity towards K562 targets, suggesting that they may be considered as “NK-like” T cells. We cultured the patient peripheral blood mononuclear cells (PBMC) with control subject PBMC and with PBMC from two other subjects with B chronic lymphocytic leukemia (B- CLL) of the CD20⁺ CD21^- CD10^- phenotype. Patient PBMC exhibited a lytic activity on control PBMC and on the B lymphocytes of one of the two B- CLL but only in the presence of PWM. This activity was not exerted by the culture supernatant and required a cell - to - cell contact. We suggest that the hypogammaglobulinemia observed in this patient may be related to a cytotoxic effect exerted on B lymphocytes by a CD3⁺ CD8⁺ CD57⁺ CD16^- LGL proliferation.     

Human B cell differentiation induced by microbial superantigens: unselected peripheral blood lymphocytes secrete polyclonal immunoglobulin in response to Mycoplasma arthritidis mitogen.

Microbial superantigens (SA) activate a significant portion of the T cell repertoire based on their dual avidity for MHC class II antigens and T cell receptor (TCR) epitopes common to products of one or several TCR beta chain variable gene families. While SA that induce massive T cell proliferation and cytokine secretion have been implicated in clinical syndromes characterized by shock and generalized immunosuppression, SA activation of a more restricted T cell response may also have significant, perhaps immunostimulatory, effects on the immune system. To investigate this issue, we measured 3H-thymidine incorporation and polyclonal IgM and IgG secretion by normal human peripheral blood mononuclear cells (PBMC) cultured with a panel of microbial SA, including the Staphylococcus aureus-derived SA, SEA, SEB, SEC-1, SEC-2, SEC-3, SEE, TSST-1, and the Mycoplasma arthritidis-derived SA, MAM. The S. aureus-derived SA induce vigorous proliferation by PBMC, while optimal MAM-induced proliferation is significantly lower in magnitude. In all 12 subjects tested, mitogenic concentrations of MAM reproducibly stimulate unselected PBMC to secrete polyclonal IgM and IgG. In contrast, the S. aureus-derived SA induce Ig production only in cultures containing isolated B cell populations and either very low numbers of untreated autologous T cells, larger numbers of X-irradiated autologous T cells, or very low concentrations of the SA. No difference in the activation of helper (CD4) versus suppressor/cytotoxic (CD8) T cells by MAM and the S. aureus-derived SA was noted. Taken together, these data suggest that MAM's capacity to induce B cell differentiation correlates with its induction of a relatively weak proliferative response by unselected human T cells. MAM-like SA, when encountered in vivo, may result in a significant perturbation of the human immune system and potentially contribute to clinical syndromes characterized by immunostimulation and hypergammaglobulinemia.     

T Helper-Independent Activation of Human CD8+ Cells: the Role of CD28 Costimulation

The concept that activation of MHC class I-restricted CD8⁺ cells entirely depends on help from MHC class II-restricted CD4⁺ T cells has recently been supplemented with an alternative model in which CD8⁺ cells can directly be activated by MHC class I-expressing professional antigen-presenting cells (APC), which are able to deliver an accessory signal. The authors analysed the role of CD28-mediated costimulation for T helper cell-independent activation of purified human CD8⁺ T cells in two different in vitro models. Freshly isolated CD8⁺ cells could be activated (proliferation, IL-2 production and cytotoxic activity) by anti-CD3-presenting FcγR⁺ mouse cells transfected with the human CD28 ligand, CD80, as the only accessory signal. On the other hand, activation of CD8⁺ cells by allogeneic MHC class I on EBV-transformed B cells, which express two different CD28 ligands, CD80 and CD86, also proceeded very efficiently (proliferation, cytotoxic activity and CD25 expression), but was either not, or only partially, blocked by anti-CD80 and anti-CD86 MoAb or CTLA-4Ig. This indicates that other costimulatory signals are also effective, and that CD28 triggering is not absolutely required for initial T-cell activation. CsA and CD80/CD86-blocking agents were synergistic in completely inhibiting activation of CD8⁺ cells in the MLR with allogeneic B-cell lines. This combination also induced non-responsiveness of CD8⁺ cells upon restimulation in the absence of blocking agents. Therefore, although professional APC can apparently provide multiple costimulatory signals for direct activation of CD8⁺ T cells, the signal derived from CD80/CD86 is unique in providing CsA-resistance.     

A new clinically relevant approach to expand myelin specific T cells

Human self-reactive T cells are potentially involved in many autoimmune diseases. Although ex vivo detection of self-reactive T cells is possible, exhaustive functional characterization of these cells is impeded by their low frequency. In vitro expansion of antigen (Ag) specific T cells is typically achieved by using autologous (fresh or frozen) irradiated peripheral blood mononuclear cells (PBMCs), EBV-immortalized B cells or dendritic cells in the presence of Ag. These approaches require a large blood volume. We explored a method successfully applied for tumor specific T cells using in vitro expanded autologous B cells. PBMCs were stimulated with irradiated CD40L-expressing fibroblasts and IL-4, resulting in an enriched population of B cell that expressed high levels of MHC and co-stimulatory molecules, essential hallmarks of antigen presenting cells (APCs). Expanded B cells were loaded with Ag, irradiated and then used as APCs to stimulate T cells. The specificity of T cell lines was assessed by comparing their proliferation and IFN-γ secretion when cultured with antigen-loaded B cells vs. unloaded B cells. T cell lines exhibiting antigen-specific proliferation and/or IFN-γ secretion were expanded. Using this method, MBP and MOG specific CD4⁺ and CD8⁺ T cell lines were obtained from multiple donors in comparable numbers to those obtained using the traditional approach (i.e. fresh PBMCs as APCs) and were kept in culture for many weeks. We have shown that myelin specific CD4⁺ and CD8⁺ T cells can be expanded from a relatively small volume of blood (50–100 ml) from multiple donors using expanded B cells as APCs.     

胚胎骨髓来源间充质干细胞对人Th17细胞的免疫调节

背景：众多研究表明间充质干细胞能发挥免疫调节功能,抑制T细胞增殖。 目的：观察胚胎骨髓来源间充质干细胞对人Th17细胞的调节作用。 方法：将人胚胎骨髓间充质干细胞与正常人外周血单个核细胞或CD4⁺ T细胞以1∶10比例共培养4 d,以单个核细胞或CD4⁺T细胞单独培养为对照。应用实时定量PCR检测细胞白细胞介素17 mRNA表达,酶联免疫吸附试验检测细胞上清中白细胞介素17蛋白水平,流式细胞术检测Th17细胞数量。 结果与结论：胚胎骨髓来源间充质干细胞与单个核细胞共培养组白细胞介素17 mRNA表达水平明显高于单个核细胞组(P < 0.01)。与此一致的是,胚胎骨髓来源间充质干细胞与单个核细胞或CD4⁺T细胞共培养组细胞上清中白细胞介素17蛋白水平明显高于单个核细胞组、CD4⁺ T细胞组(P < 0.05,P < 0.01)。胚胎骨髓来源间充质干细胞与CD4⁺ T细胞共培养组Th17细胞数量明显高于CD4⁺ T细胞组(P < 0.01),但胚胎骨髓来源间充质干细胞本身并不表达白细胞介素17。表明胚胎骨髓来源间充质干细胞可促进人Th17细胞增殖。     

Induction of antigen-presenting capacity in tumor cells upon infection with non-replicating recombinant vaccinia virus encoding murine MHC class II and costimulatory molecules

The possibility of inducing antigen-presenting capacity in cells normally lacking such capacity, currently represents a major goal in vaccine research. To address this issue we attempted to generate ‘artificial’ APC able to stimulate CD4⁺ T cell responses when tumor cells were infected with a single, recombinant, vaccinia virus (rVV) containing the two genes encoding murine MHC class II I-A^k and a third gene encoding the murine B7-1 (mB7-1) costimulatory molecule. To minimize the cytopathic effect and to improve safety, in view of possible in vivo applications, we made this rVV replication incompetent by Psoralen and long wave UV treatment. Tumor cells infected with rVV encoding I-A^k alone, pulsed with hen egg white lysozyme peptide (HEL_46–61), induced IL-2 secretion by an antigen-specific T hybridoma. Tumor cells infected with the rVV encoding mB7-1 provided costimulation for activating resting CD4⁺ T cells in the presence of ConA. Tumor cells infected with the rVV encoding I-A^k and mB7-1, and pulsed with chicken ovotransferrin peptide (conalbumin_133–145), induced a significantly higher response in a specific Th₂ cell clone (D10.G4.1) as compared to cells infected with rVV encoding I-A^k molecules only. Thus, this replication incompetent rVV represents a safe, multiple gene, vector system able to confer in one single infection step effective APC capacity to non-professional APCs.     

Ethanol-induced CD3 and CD2 hyporesponsiveness of peripheral blood T lymphocytes

The functional relevance of a direct ethanol effect on the membrane structure of T lymphocytes and accessory cells (APC), as well as on signal transduction systems was studied in ten normal subjects. Ethanol incubation (80 mM for 24h) of highly purified T cells increased the number of CD4⁺/CD45RA⁺ lymphocytes. In contrast, ethanol exposure induced a drop in CD14⁺/LFA-3⁺ APC values. These changes were accompanied by faulty T-cell proliferation in response to anti-CD3 and anti-CD2 mAb and inhibition of CD3- and CD2-mediated rises in intracellular calcium and, to a lesser extent, inositol 1,4,5-triphosphate levels.

These data clearly indicate that a membrane-specific ethanol interaction both modifies surface glycoproteic and/or glycolipidic structures and alters transmembrane transduction of the activation signals.     

Human suppressor T cells: Induction, differentiation, and regulatory functions

T-cell-mediated suppression of human immune responses involves a complex interaction between distinct lymphocyte subsets with suppressor-inducer and suppressor-effector functions. Recent studies with subset-specific monoclonal antibodies have defined a characteristic phenotype of suppressor-inducer cells (CD4⁺ Leu8⁺ 2H4⁺ 4B4⁻) that can be distinguished from that of helper cells for antibody synthesis (CD4⁺ Leu8⁻ 2H4⁻ 4B4⁺). Similarly, suppressor-effector cells (CD8⁺ CD11⁺ Tp44⁻ can typically be defined as a subset separable from cytotoxic T cells (CD8⁺ CD11⁻ Tp44⁺). Both antigen-specific and nonspecific interactions are important in suppressor T-cell activation and function. Soluble signals required for differentiation of CD8⁺ suppressor cells include an indomethacin-sensitive monocyte product and interferon gamma. In contrast, proliferation of the CD8⁺ suppressor cell subset depends on stimulations first by a product of CD4⁺ Leu8⁺ cells, T suppressor cell growth factor, and second by interleukin 2. Although the molecular basis of antigen-specific interactions between CD4⁺ and CD8⁺ cells in suppressor cell generation has not been defined, it may involve both conventional, presumably MHC-restricted, interactions between antigen and antigen receptors, as well as anti-idiotypic interactions of suppressor-effectors with determinants on suppressor-inducer receptors. Progress in elucidating requirements for activation, growth, and differentiation of suppressor cells should facilitate long-term culture of such cells and lead to clearer understanding of mechanism of suppressor-cell mediated immunoregulation.     

Inclusion of Brefeldin A during dendritic cell isolation allows in vitro detection of cross-presented self-antigens

The mechanism of cross-presentation enables dendritic cells (DC) to induce immunity against intracellular pathogens and to tolerize autoreactive CD8 T cells. The antigen-presenting cells (APCs) responsible for cross-presentation of self-antigens have been identified as CD8⁺ CD11c⁺ DC. Isolation of these cells has been notoriously difficult, and the resulting responses of T cell hybridomas were too low to permit further studies. Here, we demonstrate that inclusion of Brefeldin A (BfA), an agent reported to block MHC class I–peptide complex turnover on the cell surface, during DC isolation from transgenic RIP-mOVA mice facilitated activation and proliferation of naïve OVA-specific CD8⁺ T cells in vitro. CD8⁺ DC were more efficient than CD8⁻ CD11c⁺. BfA also reversibly preserved expression of costimulatory molecules by DC, as evidenced by their expression of costimulatory markers and by an increased stimulatory capacity of DC matured in vivo by LPS. We conclude that the use of BfA notably improves sensitivity of detection of cross-presented self-antigens.     

Pregnancy-induced expansion of regulatory T-lymphocytes may mediate protection to multiple sclerosis activity

The role of activated CD8⁺ T cells in shaping the dynamics of in vivo antigen presentation and immune responses is a subject receiving more attention. We studied whether cytotoxic T lymphocyte (CTL) would limit antibody responses by targeting antigen-specific B cells. A modified in vivo CTL assay was developed and used herein to demonstrate cytotoxicity in vivo, and to show that antigen-specific B cells that process exogenous antigen and present peptide in association with MHC class I can be the targets of CD8⁺ T cells. B cells from C57BL/6 mice immunized with ovalbumin (OVA)/alum were pulsed with OVA in vitro, and transferred into C57BL/6 recipient mice that had been immunized with vaccinia virus expressing SIINFEKL minigene to generate CD8⁺ CTL against K^b/SIINFEKL. OVA-pulsed B220⁺ B cells from OVA-immunized mice were killed to a greater extent than B220⁺ B cells from naïve mice (28 ± 20% versus 12 ± 16%, p = 0.0042). However, mice receiving vaccinia-SIINFEKL and generating CTL, did not appear to target endogenous B cells, since both primary and secondary antibody responses to OVA were unaffected. Our findings indicate that CTL responses to the protein antigen do not interfere with endogenous B cell responses, even though exogenous B cells expressing the CTL epitope can be efficiently lysed.     

Responses of Human T Cells to Dominant Discrete Protein Antigens of Escherichia coli and Pseudomonas aeruginosa

Normal human beings have circulating T lymphocytes that proliferate in response to Escherichia coli and Pseudomonas aeruginosa . We performed the present study to characterize the nature of the responding T cells and to determine whether distinct or shared conventional antigens, superantigens or polylonal activators account for T cell proliferation. Long term antigen-specific T cell lines were generated by repeated stimulation of PBMC from four donors with soluble antigen preparations of E. coli or P. aeruginosa . This resulted in the emergence of distinct T cell populations, which responded to strains of either E. coli or P. aeruginosa , but not to both. Trypsin treatment of the bacterial preparations largely eliminated their ability to stimulate the T cells. The T cell lines were predominantly CD4⁺ and their proliferation to bacterial antigens was optimal using autologous APC. E. coli T cell lines proliferated not only in response to the E. coli strain with which they were initially selected, but also to four different strains of E. coli , as well as to several related Gram-negative species. P. aeruginosa selected T cells exhibited proliferative responses to six different P. aeruginosa strains, but not to the other Gram-negative species. The finding that repeated stimulation of PBMC with E. coli or P. aeruginosa leads to CD4⁺ T cells highly reactive with conventional protein antigens specific either for E. coli or P. aeruginosa indicates that these bacteria possess separate dominant protein antigens that drive the proliferation of peripheral blood T cells.     

Non-MHC-restricted CD4+ T lymphocytes are regulated by HLA-Cw7-mediated inhibition

Natural killer cells (NK cells) represent an important component of innate immunity with the capacity to kill many tumor and virus-infected cells. The discovery of several classes of killer cell inhibitory receptors expressed by NK cells that bind specific MHC class I ligands on target cells provides detailed insight into the regulation of NK cells. Inhibitory receptors deliver negative signals following MHC ligand binding that abrogate cytotoxicity and, thus, determine the specificity of NK effector cell function. Here, we describe a novel subset of human memory CD4⁺ T lymphocytes that display an NK-like pattern of regulation. These CD4⁺ T cells display non-MHC-restricted cytotoxicity that is governed by HLA-Cw7 mediated inhibition. In NK cells, such specificity is associated with expression of the inhibitory receptor p58.2. In contrast, neither p58.2 nor other known inhibitory receptors were detected on these non-MHC-restricted CD4⁺ T cells. This suggests that these cells are regulated by a hitherto unknown inhibitory receptor. The finding that interactions with MHC molecules downregulate the function of these CD4⁺ T cells suggests that these non-MHC-restricted T cells may function to detect and eliminate cells with aberrant MHC expression.     

Kinectin-麦芽糖结合蛋白融合蛋白致敏树突状细胞对T细胞分化格局的改变

背景：Kinectin作为树突状细胞瘤苗可运用于肝癌临床免疫治疗。 目的：检测kinectin-麦芽糖结合蛋白融合蛋白致敏的树突状细胞刺激T细胞亚群的分化情况。 方法：运用免疫组化法检测kinectin-麦芽糖结合蛋白孵育的树突状细胞刺激增殖的T细胞中CD4⁺、CD8⁺ T细胞亚群活化情况,同时设立麦芽糖结合蛋白组、非致敏树突状细胞组及普通培养T细胞组作为比较。 结果与结论：Kinectin-麦芽糖结合蛋白致敏树突状细胞刺激的T细胞组CD8⁺T细胞明显高于麦芽糖结合蛋白孵育树突状细胞刺激的T细胞组、非致敏树突状细胞刺激组及普通培养T细胞组(P < 0.05);各组CD4值之间、CD4/CD8值之间比较,差异无显著性意义(P > 0.05)。经Kinectin-麦芽糖结合蛋白融合蛋白致敏的树突状细胞能有效刺激自体CD8⁺ T淋巴细胞的增殖,Kinectin-麦芽糖结合蛋白作为肝癌相关抗原可通过致敏树突状细胞发挥较明显的抗肿瘤功能。     

肝移植后他克莫司血药浓度对外周血单个核细胞内HBV DNA的影响

背景：肝移植后他克莫司等免疫抑制剂的长期应用导致机体细胞免疫功能降低,并有可能影响机体对乙肝病毒的清除。 目的：分析乙肝相关肝移植患者后不同浓度他克莫司对外周血单个核细胞中的HBV DNA含量的影响。 方法：纳入乙肝相关终末期肝病肝移植受者23例,根据移植后12周清晨空腹他克莫司血药浓度,分为高浓度组(≥ 10 μg/L) 9例和低浓度组(< 10 μg/L)14例,同时用荧光标记单克隆抗体结合流式细胞技术检测外周血T细胞亚群的百分比,用实时荧光定量PCR检测外周血单个核细胞内的HBV DNA。 结果与结论：用多元线性回归分析外周血单个核细胞内的HBV DNA含量与CD8⁺CD152⁺呈正相关,与CD8⁺CD28⁺呈负相关。高血药浓度他克莫司的患者外周血单个核细胞内的HBV DNA高于低浓度组,其改变与反映细胞免疫功能的指标CD8⁺CD152⁺和CD8⁺CD28⁺的变化有关。     

Human purified CD8+ T cells: Ex vivo expansion model to generate a maximum yield of functional cytotoxic cells

CD8⁺ T cells are a critical component of the cellular immune response. They play an important role in the control of viral infection and eliminating cells with malignant potential. However, attempts to generate and expand human CD8⁺ T cells in vitro for an adoptive immunotherapy have been conducted with limitation of the very low frequency of CD8⁺ T cells in blood. Therefore, several expansion protocols have been developed to obtain large and efficient numbers of human CD8⁺ T cells for use in adoptive immunotherapies. In this study various common culture conditions using different cytokines IL-2, IL-4, IL-7, IL-10, IL-12 and IL-15 and autologous feeders and sera were investigated to expand human purified CD8⁺ T cells. The importance and the influence of these factors on the growth and phenotype of CD8⁺ T cell were assessed by serially sampling cultures using flow cytometry. We demonstrated that combination of IL-2 (50U/ml) and autologous feeders induced maximal CD8⁺ T cell proliferation (40-50 folds) compared to other cytokines. Immunophenotypic analysis of cultured cells showed that expanded CD8⁺ T cells were activated and differentiated. Furthermore our expansion model also demonstrated that expanded CD8⁺ T cells are functionally cytotoxic active by killing Allogeneic LCLs cells. In conclusion, we have developed a reliable, simple method that uses minimal cell numbers to generate a high yield of functional cytotoxic CD8⁺ T cells, which can be used for the development of cellular immunotherapies.     

恶性肿瘤干细胞标记物CD34在鼻咽癌细胞系的表达

BACKGROUND:Previous research have confirmed that CD34 is closely related to oncogenesis, progress, recurrence, metastasis and drug-resistance of various cancers, but its role in nasopharyngeal carcinoma remains unclear. OBJECTIVE:To sort cells positive and negative for CD34 in nasopharyngeal carcinoma cell lines and to detect cell proliferation and migration. METHODS:Expressions of CD34 in nasopharyngeal carcinoma cell lines 5-8F, 6-10B, CNE1 and CNE2 were detected by flow cytometry. And CD34+ and CD34^- cells were sorted based on cell surface markers for purity identification. Afterwards, proliferation and migration of CD34⁺ and CD34^- cells were detected by MTT assay, colony-formation assay and scratch assay. RESULTS AND CONCLUSION:All four nasopharyngeal carcinoma cell lines expressed CD34 in 0.1%-0.2%, and the level of CD34 was closely related to the cell growth density. The purity of CD34⁺ cell was more than 98% in the sorted CD34⁺ cell populations, but no CD34⁺ cells were found in the sorted CD34^- cell populations. At 1, 3, 5 and 7 days the proliferation rate of CD34⁺ cell, populations was significantly higher than that of CD34^- cells (P < 0.05). Consistently, the colony-formation efficiency of CD34⁺ cell was significantly higher than that of CD34^- cells (P < 0.05). Moreover, CD34⁺ cells migrated significantly faster than CD34^- cells by scratch assay (P < 0.05). In conclusion, CD34⁺ cells cultured in vitro display higher proliferation and migration capacities, indicating that CD34⁺ cells have the potential of nasopharyngeal carcinoma stem cells.     

Amyl Nitrite Alters Human in Vitro Immune Function

Effects on the human immune system of volatile nitrite inhalation were studied in 18 male volunteers. While nitrite inhalation decreased the absolute number of CD3⁺ T lymphocytes during the period of inhalation, cell numbers returned to pre-treatment levels within one week after cessation of the drug. Nitrite inhalation did not alter the percentage of CD3⁺, CD4⁺, CD8⁺ or CD19⁺ lymphocytes. Natural killer (NK) cell activity against K562 target cells was depressed by nitrite administration but returned to pre-inhalation or greater levels after nitrite discontinuation. Cell proliferation following cell activation by PHA, ConA and PWM was unaffected by amyl nitrite inhalation. We conclude that in humans inhalation of volatile nitrites causes cycles of modest immunosuppression, particularly in NK activity, followed by gradual recovery when the drug is not inhaled for several days.     

Cell mediated immunity changes in ageing, relative importance of cell subpopulation switches and of nutritional factors

Decreased T-cell functions with ageing have been extensively described. This review focuses on recent data on changes in T-cell subpopulations related to ageing and their consequences on T-cell proliferation. Increase of immature T cells CD2⁺ CD3⁻ is an ageing phenomenon related to T-cell declining proliferation. Recently it was shown that increase of immature T cells was due to an increase in different subtypes of the CD2⁺ CD3⁻ population, double-negative CD2⁺ CD4⁻ CD8⁻ and double-positive CD2⁺ CD4⁺ CD8⁺ subpopulations, the former being associated with nutritional deficit, the latter with associated diseases. Other authors have focused on decreases of naive T cells with parallel increase of memory T cells; such a switch is also relevant to declining T-cell proliferation. This review focuses on two major factors which influence immune ageing: nutritional parameters and antigen exposure.     

Cultures derived from peripheral blood CD34+ progenitor cells of head and neck cancer patients and from cord blood are functionally different

Patients with head and neck squamous cell carcinoma (HNSCC) have profound immune defects mediated, in part, by an increased number of immune suppressive CD34⁺ progenitor cells in their peripheral blood and tumor. One means of overcoming this immune suppression is to stimulate the CD34⁺ cells to differentiate into more mature, nonsuppressive progeny such as dendritic cells or monocytes. This study determined that CD34⁺ cells from the peripheral blood of HNSCC patients have the same potential to differentiate into dendritic cells as do human umbilical cord blood CD34⁺ cells following 12–16 days of culture with a cytokine cocktail. When compared functionally, the cultures that developed from CD34⁺ cells of cord blood were able to induce an allostimulatory response in naive T-cells, while the cultures that developed from patient CD34⁺ cells lacked allostimulatory ability. Both cultures expressed class II MHC (HLA-DR), but the proportion of cells expressing the costimulatory molecules CD80 and CD86 was significantly less in cultures that developed from HNSCC-patient CD34⁺ cells. Therefore, although the CD34⁺ cells from the peripheral blood of HNSCC patients can differentiate into dendritic cells, their allostimulatory capabilities are impaired, raising the question of their potential effectiveness in stimulating antitumor immune responses.