Intra-operative preparation of autologous bone marrow-derived CD34-enriched cellular products for cardiac therapy

BACKGROUND AND AIMS

With the advent of regenerative therapy, there is renewed interest in the use of bone marrow as a source of adult stem and progenitor cells, including cell subsets prepared by immunomagnetic selection. Cell selection must be rapid, efficient and performed according to current good manufacturing practices. In this report we present a methodology for intra-operative preparation of CD34(+) selected autologous bone marrow for autologous use in patients receiving coronary artery bypass grafts or left ventricular assist devices.

METHODS AND RESULTS

We developed a rapid erythrocyte depletion method using hydroxyethyl starch and low-speed centrifugation to prepare large-scale (mean 359 mL) bone marrow aspirates for separation on a Baxter Isolex 300i immunomagnetic cell separation device. CD34 recovery after erythrocyte depletion was 68.3 ± 20.2%, with an average depletion of 91.2 ± 2.8% and an average CD34 content of 0.58 ± 0.27%. After separation, CD34 purity was 64.1 ± 17.2%, with 44.3 ± 26.1% recovery and an average dose of 5.0 ± 2.7 × 10(6) CD34(+) cells/product. In uncomplicated cases CD34-enriched cellular products could be accessioned, prepared, tested for release and administered within 6 h. Further analysis of CD34(+) bone marrow cells revealed a significant proportion of CD45(-) CD34(+) cells.

CONCLUSIONS

Intra-operative immunomagnetic separation of CD34-enriched bone marrow is feasible using rapid low-speed Hetastarch sedimentation for erythrocyte depletion. The resulting CD34-enriched product contains CD45(-) cells that may represent non-hematopoietic or very early hematopoietic stem cells that participate in tissue regeneration.

Regenerative therapy after cancer: what are the risks?

There is often a pressing need for reconstruction after cancer surgery. Regenerative therapy holds the promise of more natural and esthetic functional tissue. In the case of breast reconstruction postmastectomy, volume retention problems associated with autologous fat transfer could be ameliorated by augmentation with cells capable mediating rapid vascularization of the graft. Intentional placement of regenerating tissue at the site of tumor resection raises questions concerning the possibility of promoting cancer recurrence. Here we review coculture and animal models of tumor/mesenchymal stem cell interactions under regenerating conditions. Available evidence from case reports, cell lines, and clinical isolates favors the interpretation that regenerating tissue promotes the growth of active, high-grade tumor. In contrast, dormant cancer cells do not appear to be activated by the complex signals accompanying wound healing and tissue regeneration, suggesting that engineered tissue reconstruction should be deferred until cancer remission has been firmly established.

Regenerative therapy and cancer: in vitro and in vivo studies of the interaction between adipose-derived stem cells and breast cancer cells from clinical isolates

Adipose-derived stem cells (ASCs) have been proposed to stabilize autologous fat grafts for regenerative therapy, but their safety is unknown in the setting of reconstructive surgery after mastectomy. Both bone marrow mesenchymal stem cells (MSCs) and ASC have been shown to enhance tumorigenesis of established breast cancer cell lines, but primary patient material has not been tested. Here, we ask whether ASC promote the in vitro growth and in vivo tumorigenesis of metastatic breast cancer clinical isolates. Metastatic pleural effusion (MPE) cells were used for coculture experiments. ASC enhanced the proliferation of MPE cells in vitro (5.1-fold). For xenograft experiments (100 sorted cells/injection site), nonhematopoietic MPE cells were sorted into resting and active populations: CD90+ resting (low scatter, 2.1%≥2N DNA), CD90+ active (high scatter, 10.6%≥2N DNA), and CD90-. Resting CD90+ MPE cells were tumorigenic in 4/40 sites but growth was not augmented by ASC. Active CD90+ MPE cells were tumorigenic (17/40 sites) only when coinjected with ASC (p=0.0005, χ2 test). The multilineage potentiality and MSC-like immunophenotype of ASC were confirmed by flow cytometry, differentiation cultures, and immunostaining. The secretome profile of ASC resembled that reported for MSC, but included adipose-associated adipsin and the hormone leptin, shown to promote breast cancer growth. Our data indicate that ASC enhance the growth of active, but not resting tumor cells. Thus, reconstructive therapy utilizing ASC-augmented whole fat should be postponed until there is no evidence of active disease.

Localization of CD44 and CD90 positive cells to the invasive front of breast tumors

BACKGROUND

A variety of markers have been proposed to identify breast cancer stem cells. Here, we used immunohistostaining and flow cytometry to analyze their interrelationships and to sort cells for tumorigenicity studies.

METHODS

Cytokeratin, CD44, and CD90 were localized to primary breast cancer and normal breast (NB) tissue by immunohistostaining and related to CD117 and CD133 expression by flow cytometry. Immunodeficient NOD.CB17-Prkdc(scid) /J and NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl) /SzJ mice were used to test tumorigenicity of sorted CD90+ low-light scatter, CD90+ high-light scatter, and CD90(neg) tumor cells.

RESULTS

NB basal cells coexpressed CD44 and CD90. As cells transited luminally, CD44 was retained and downmodulated, and CD90 was lost and cytokeratin increased. In breast tumors, basal-like CD44+/CD90+ cells were localized to the tumor periphery, adjacent to CD90+ stroma. Like normal luminal cells, interior tumor cells were CD44+/CD90-. Immunophenotyping (CD44/CD90/CD117/CD133) of cytokeratin+ cells revealed no significant difference in expression between tumors and tumor-free breast. In both, CD133 was distributed approximately equally among CD44/CD90 subsets, whereas CD117 expression was highest in the basal-associated CD44+/CD90+ subset. Sorted CD90+ pleural effusion cells with lymphoid light scatter, 49% of which were CD44+, were uniquely tumorigenic in immunodeficient mice (100 cells/injection).

CONCLUSIONS

Our data demonstrate that all tumors contain a small population of CD44+/CD90+ cells, mimicking the phenotype of ductal-basal cells. These are localized to the tumor periphery, adjacent to CD90+ stroma. Among the nonhematopoietic, nonmesothelial cells found in metastatic pleural effusions, low-light scatter CD90+ cells are most potently tumorigenic, compared to high-scatter CD90+ cells and CD90- cells. © 2010 International Clinical Cytometry Society.

Stromal vascular progenitors in adult human adipose tissue

The in vivo progenitor of culture-expanded mesenchymal-like adipose-derived stem cells (ADSC) remains elusive, owing in part to the complex organization of stromal cells surrounding the small vessels, and the rapidity with which adipose stromal vascular cells adopt a mesenchymal phenotype in vitro. Immunohistostaining of intact adipose tissue was used to identify three markers (CD31, CD34, and CD146), which together unambiguously discriminate histologically distinct inner and outer rings of vessel-associated stromal cells, as well as capillary and small vessel endothelial cells. These markers were used in multiparameter flow cytometry in conjunction with stem/progenitor markers (CD90 and CD117) to further characterize stromal vascular fraction (SVF) subpopulations. Two mesenchymal and two endothelial populations were isolated by high speed flow cytometric sorting, expanded in short term culture, and tested for adipogenesis. The inner layer of stromal cells in contact with small vessel endothelium (pericytes) was CD146+/alpha-SMA+/CD90+/-/CD34-/CD31-; the outer adventitial stromal ring (designated supra adventitial-adipose stromal cells, SA-ASC) was CD146-/alpha-SMA-/CD90+/CD34+/CD31-. Capillary endothelial cells were CD31+/CD34+/CD90+ (endothelial progenitor), whereas small vessel endothelium was CD31+/CD34-/CD90- (endothelial mature). Flow cytometry confirmed these expression patterns and revealed a CD146+/CD90+/CD34+/CD31- pericyte subset that may be transitional between pericytes and SA-ASC. Pericytes had the most potent adipogenic potential, followed by the more numerous SA-ASC. Endothelial populations had significantly reduced adipogenic potential compared with unsorted expanded SVF cells. In adipose tissue, perivascular stromal cells are organized in two discrete layers, the innermost consisting of CD146+/CD34- pericytes, and the outermost of CD146-/CD34+ SA-ASC, both of which have adipogenic potential in culture. A CD146+/CD34+ subset detected by flow cytometry at low frequency suggests a population transitional between pericytes and SA-ASC.

Measurement of multiple drug resistance transporter activity in putative cancer stem/progenitor cells

Multiple drug resistance, mediated by the expression and activity of ABC-transporters, is a major obstacle to antineoplastic therapy. Normal tissue stem cells and their malignant counterparts share MDR transporter activity as a major mechanism of self-protection. Although MDR activity is upregulated in response to substrate chemotherapeutic agents, it is also constitutively expressed on both normal tissue stem cells and a subset of tumor cells prior to the initiation of therapy, representing a built-in obstacle to therapeutic ratio. Constitutive and induced MDR activity can be detected in cellular subsets of disaggregated tissues, using the fluorescent substrates Rhodamine 123 and Hoechst 33342 for ABCB1 (also known as P-gp and MDR1) and ABCG2 (BCRP1). In this chapter, we will describe the complete procedure for the detection of MDR activity, including: (1) Preparing single-cell suspensions from tumor and normal tissue specimens; (2) An efficient method to perform cell surface marker staining on large numbers of cells; (3) Flow cytometer setup and controls; (4) Simultaneous measurement of Hoechst 33342 and Rhodamine123 transport; and (5) Data acquisition and analysis.

Identification of human aldehyde dehydrogenase 1 family member A1 as a novel CD8+ T-cell-defined tumor antigen in squamous cell carcinoma of the head and neck

Few epitopes are available for vaccination therapy of patients with squamous cell carcinoma of the head and neck (SCCHN). Using a tumor-specific CTL, aldehyde dehydrogenase 1 family member A1 (ALDH1A1) was identified as a novel tumor antigen in SCCHN. Mass spectral analysis of peptides in tumor-derived lysates was used to determine that the CTL line recognized the HLA-A*0201 (HLA-A2) binding ALDH1A1(88-96) peptide. Expression of ALDH1A1 in established SCCHN cell lines, normal mucosa, and primary keratinocytes was studied by quantitative reverse transcription-PCR and immunostaining. Protein expression was further defined by immunoblot analysis, whereas ALDH1A1 activity was measured using ALDEFLUOR. ALDH1A1(88-96) peptide was identified as an HLA-A2-restricted, naturally presented, CD8(+) T-cell-defined tumor peptide. ALDH1A1(88-96) peptide-specific CD8(+) T cells recognized only HLA-A2(+) SCCHN cell lines, which overexpressed ALDH1A1, as well as targets transfected with ALDH1A1 cDNA. Target recognition was blocked by anti-HLA class I and anti-HLA-A2 antibodies. SCCHN cell lines overexpressing ALDH1 had high enzymatic activity. ALDH1A1 protein was expressed in 12 of 17 SCCHN, and 30 of 40 dysplastic mucosa samples, but not in normal mucosa. ALDH1A1 expression levels in target cells correlated with their recognition by ALDH1A1(88-96) peptide-specific CD8(+) T cells. Our findings identify ALDH1A1, a metabolic antigen, as a potential target for vaccination therapy in the cohort of SCCHN subjects with tumors overexpressing this protein. A smaller cohort of subjects with SCCHN, whose tumors express little to no ALDH1A1, and thus are deficient in conversion of retinal to retinoic acid, could benefit from chemoprevention therapy.

Rare-Event Analysis in Flow Cytometry

Technical aspects of rare-event detection are discussed in this article in a practical context, with two real-life examples. A growing number of flow cytometry-based assays depend on rare-event detection for basic science and clinical applications.

A novel multiparametric flow cytometry-based cytotoxicity assay simultaneously immunophenotypes effector cells: comparisons to a 4 h 51Cr-release assay

Natural killer (NK) cell-or T cell-mediated cytotoxicity traditionally is measured in 4-16 h (51)Cr-release assays (CRA). A new four-color flow cytometry-based cytotoxicity assay (FCC) was developed to simultaneously measure NK cell cytotoxicity and NK cell phenotype (CD3(-)CD16(+)CD56(+)). Target cells, K562 or Daudi, were labeled with Cell Tracker Orange (CTO) prior to the addition of effector cells. Following co-incubation, 7 amino-actinomycin D (7-AAD) was added to measure death of target cells. The phenotype of effectors, viability of targets, the formation of tumor-effector cell conjugates and absolute numbers of all cells were measured based on light scatter (FSC/SSC), double discrimination of the fluorescence peak integral and height, and fluorescence intensity. Kinetic studies (0.5 and 1 to 4 h) at different effector to target (E:T) cell ratios (50, 25, 12, and 6) confirmed that the 3 h incubation was optimal. The FCC assay is more sensitive than the CRA, has a coefficient of variation (CV) 8-13% and reliably measures NK cell-or lymphokine-activated killer (LAK) cell-mediated killing of target cells in normal controls and subjects with cancer. The FCC assay can be used to study a range of phenotypic attributes, in addition to lytic activity of various subsets of effector cells, without radioactive tracers and thus, it is relatively inexpensive. The FCC assay has a potential for providing information about molecular interactions underlying target cell lysis and thus becoming a major tool for studies of disease pathogenesis as well as development of novel immune therapies.

Tumorigenic epithelial stem cells and their normal counterparts

ABC transporters are highly conserved and represent a major protective mechanism for barrier tissues as well as adult tissue stem cells. Emerging data support the existence of a cancer stem cell that shares features of tissue stem cells, including the ability to self-renew and undergo dysregulated differentiation. Here we show that a rare population of cells coexpressing MDR transporters and stem cell markers is a common feature across therapy-naive epithelial cancers as well as normal epithelial tissue. MDR+ and MDR- candidate tumor stem and progenitor populations were all capable of generating highly anaplastic transplantable human tumors in NOD/SCID. The finding that rare cells bearing stem cell markers and having intrinsic MDR expression and activity are already present within the tumorigenic compartment before treatment with cytotoxic agents is of critical importance to cancer therapy. Just as damaged normal epithelial tissues regenerate after chemotherapy by virtue of highly protected resting tissue stem cells, the existence of malignant counterparts in therapy-naive epithelial cancers suggests a common mechanism by which normal and tumor stem cells protect themselves against toxic injury.

Multiple drug resistance in cancer revisited: the cancer stem cell hypothesis

The failure to eradicate cancer may be as fundamental as a misidentification of the target. Current therapies succeed at eliminating bulky disease but often miss a tumor reservoir that is the source of disease recurrence and metastasis. Recent advances in the understanding of tissue development and repair cause us to revisit the process of drug resistance as it applies to oncogenesis and tumor heterogeneity. The cancer stem cell hypothesis states that the cancer-initiating cell is a transformed tissue stem cell, which retains the essential property of self-protection through the activity of multiple drug resistance (MDR) transporters. This resting constitutively drug-resistant cell remains at low frequency among a heterogeneous tumor mass. In the context of this hypothesis, the authors review the discovery of MDR transporters in cancer and normal stem cells and the failure of MDR reversal agents to increase the therapeutic index of substrate antineoplastic agents.

P-GLYCOPROTEIN ACTIVITY IS DECREASED IN CD4+ BUT NOT CD8+ LUNG ALLOGRAFT-INFILTRATING T CELLS DURING ACUTE CELLULAR REJECTION

BACKGROUND

Modulation of P-glycoprotein (P-gp) activity in graft-infiltrating T cells may alter their susceptibility to immunosuppression.

METHODS

P-gp activity was measured by rhodamine efflux in T-cell subsets from bronchoalveolar lavage (BAL) of five healthy volunteers and 27 lung allograft recipients. The effect of T-cell activation on P-gp activity was modeled by stimulation of peripheral blood mononuclear cells with staphylococcal enterotoxin B.

RESULTS

Most BAL T cells expressed memory-effector markers. Patients had a lower proportion of CD4 T cells (P = 0.005), whereas control subjects had CD4-to-CD8 ratios similar to peripheral blood. In controls, basal P-gp activity was greatly increased in both CD4 (35% P-gp active) and CD8 (63%) lung T cells compared with peripheral T cells. Basal P-gp activity was elevated in patient BAL T cells but was lower than control BAL activity (CD4, P = 0.07; CD8, P = 0.03). Lung T cells from transplant patients had modest (CD4) or marked (CD8) increases in substrate-induced P-gp activity compared with normal lung, indicating that P-gp was not irreversibly inhibited. Patients with acute cellular rejection (ACR) had reduced P-gp activity in CD4, but not CD8, BAL T cells compared with patients without ACR (P = 0.004). To determine the relationship between T-cell activation on P-gp modulation, P-gp activity was measured in staphylococcal enterotoxin B-stimulated peripheral blood mononuclear cells. P-gp activity was abrogated in CD71 cycling cells but remained high in a persistent but minor population of resting naive T cells.

CONCLUSIONS

Lung T cells have increased in vivo P-gp activity and therefore may eliminate substrate drugs, resulting in local resistance to immunosuppressive therapy. However, P-gp function is reduced during T-cell activation, providing a window of susceptibility to treatment during ACR.

Measurement of basal, substrate induced and total P-glycoprotein activity in bronchoalveolar lavage T-cell subsets

BACKGROUND

P-glycoprotein (P-gp) is a member of the ABC transporter superfamily. P-gp activity can be detected by measuring efflux of fluorescent substrates such as rhodamine 123 (R123). Our objectives were to evaluate P-gp activity in T cells freshly isolated from bronchoalveolar lavage (BAL) and to develop a strategy to distinguish between basal, in vitro substrate-induced, and total P-gp activities.

METHODS

Cells were obtained from blood (n = 44) and BAL (n = 34), stained for expression of CD3, CD4, CD8, and CD14, and incubated with R123 (0.13 microM) +/- cyclosporine (5 microM), a specific P-gp inhibitor. P-gp activity was detected as median fluorescence intensity (MFI) and percentage of cells falling below a pre-established cutoff.

RESULTS

BAL T cells displayed significant basal P-gp activity, which was most apparent when measured as percentage below the cutoff. Induced activity (difference between P-gp activity measured after load and efflux) was determined equally well when using the MFI or the percentage below cutoff parameter. Total activity was represented by the efflux parameters (MFI or percentage below cutoff) or by the activity-time area under the curve (AUC) method. The two efflux parameters correlated well but were insensitive to the time-dependent nature of dye efflux. In the AUC method, two samples with identical R123 brightness or percentage below cutoff after dye efflux can have very different total activities, depending on their basal activity. The AUC method was also most sensitive in distinguishing between P-gp activity in peripheral blood and resident lung T cells. Application of this methodology to the comparison of P-gp activity in BAL and peripheral CD8+ T cells best revealed the elevated total P-gp activity in BAL T cells.

CONCLUSIONS

We have systematically evaluated several methodologies for analysis of P-gp activity and arrived at a novel and robust strategy amenable to standardization and evaluation of the effects of P-gp modulators in vivo and in vitro.

Dendritic cell subsets in blood and lymphoid tissue of rhesus monkeys and their mobilization with Flt3 ligand

We provide phenotypic and functional evidence of premonocytoid dendritic cells (DCs) and preplasmacytoid DCs in blood and of corresponding DC subsets in secondary lymphoid tissue of rhesus monkeys. Subsets were identified and sorted by 4-color flow cytometry using antihuman monoclonal antibodies cross-reactive with rhesus monkey. To mobilize pre-DC subsets, fms-like tyrosine 3 kinase ligand (Flt3L; 100 microg/kg subcutaneously) was administered for 10 days. Presumptive pre-DC subsets were identified within the lineage- (Lin-) major histocompatibility complex (MHC) class II+ fraction of blood mononuclear cells. Premonocytoid DCs were CD11c+CD123- (interleukin-3Ralpha- [IL-3Ralpha-]). Preplasmacytoid DCs were characterized as CD11c-CD123++ Flt3L increased the CD11c+ pre-DC (7-fold) and CD123++ pre-DC subsets (3-fold) in blood. The freshly isolated CD11c+ pre-DC subset induced modest proliferation of naive allogeneic T cells. After overnight culture with granulocyte macro-phage-colony-stimulating factor (GMCSF) and CD40L, both subsets up-regulated surface costimulatory molecules, and CD11c+ pre-DCs became potent allostimulators. Freshly isolated CD123++ pre-DCs showed typical plasmacytoid morphology and, when cultured with IL-3 and CD40L for 72 hours, developed mature DC morphology. Following stimulation with CD40L, CD11c+ pre-DCs secreted increased levels of IL-12p40. Importantly, herpes simplex virus-stimulated CD123++ pre-DCs, but not CD11c+ pre-DCs, secreted interferon-alpha (IFN-alpha). Corresponding DC subsets were identified by flow analysis and immunohistochemistry in lymph nodes wherein both populations were increased 2- to 3-fold by Flt3L administration. CD123+ pre-DCs produced IFN-alpha in response to in vivo viral infection. Thus, rhesus monkeys exhibit 2 distinct DC precursor populations that closely resemble those of humans. Both are mobilized into blood and lymphoid tissue by Flt3L, offering potential for their further characterization and possible therapeutic application.

Identification, rare-event detection and analysis of dendritic cell subsets in broncho-alveolar lavage fluid and peripheral blood by flow cytometry

Dendritic cells (DCs) and their precursors play important roles, not only as antigen presenting cells, but components of the immunoregulatory network. Depending on their lineage, activation and differentiation state, DCs can promote a strong T-cell response or a state of anergy, and can polarize the T helper response in the direction of TH1 or TH2. The lung comprises one of the major interfaces between the host and the environment and regularly comes into contact with antigens, allergens and pathogens. Inflammation in response to these stimuli must be very carefully regulated in the lung since perturbations, especially of a chronic nature, can result in immunopathology that interferes with the lungs' critical function of gas exchange. Especially in disease states such as chronic obstructive pulmonary disease, which has been associated with a chronic TH1 response, and asthma, which is TH2-driven, the ability to access and characterize DCs and their precursors is critical to the understanding of immune modulation in these processes. In this report we will demonstrate that mature DCs and their monocytoid and plasmacytoid precursors can be sampled in the lung by the minimal invasive procedure of broncho-alveolar lavage (BAL) despite their relative scarcity and can be detected by rare event multiparameter flow cytometry.

Frequencies of tetramer+ T cells specific for the wild-type sequence p53(264-272) peptide in the circulation of patients with head and neck cancer

Immunization with wild-type sequence (wt) p53 epitopes represents a novel therapeutic strategy for cancer patients with tumors accumulating mutant p53. To evaluate usefulness of p53-derived peptides as future cancer vaccines, frequencies of wt p53(264-272) peptide-specific CD8+ T cells were determined in the peripheral circulation of patients with squamous cell carcinoma of the head and neck (SCCHN). T cells of 30 HLA-A2.1+ patients and 31 HLA-A2.1+ healthy individuals were evaluated by multicolor flow cytometry analysis using peptide-HLA-A2.1 complexes (tetramers). T cells specific for an influenza matrix peptide (a model recall antigen) or an HIV reverse transcriptase peptide (a model novel antigen) were studied in parallel. Patients with SCCHN had a significantly higher mean frequency of CD8+ T cells specific for wt p53(264-272) than normal donors (P = 0.0041). Surprisingly, the frequency of epitope-specific T cells in the circulation of patients did not correlate with p53 accumulation in the tumor. In patients whose tumors had normal p53 expression or had p53 gene mutations preventing presentation of this epitope, high frequencies of wt p53(264-272)-specific CD8+ T cells were found, of which many were memory T cells. In contrast, patients whose tumors accumulated p53 had low frequencies of wt p53(264-272)-specific CD8+ T cells, which predominantly had a naive phenotype and were unable to proliferate ex vivo in response to the epitope, as reported by us previously (T. K. Hoffmann, J. Immunol., 165: 5938-5944, 2000). This seemingly contradictory relationship between the high frequency of epitope-specific T cells and wt p53 expression in the tumor suggests that other factors may contribute to the observed anti-p53 responses. Human papillomavirus-16 E6/E7 expression is common in SCCHN, and E6 is known to promote presentation of wt p53 epitopes. Although human papillomavirus-16 E6/E7 expression was detected in 46% of the tumors, it did not correlate with the frequency of wt p53(264-272)-specific CD8+ T cells or with p53 expression in the tumor. These findings emphasize the complexity of interactions between the tumor and the host immune system, and, thus, have particularly important implications for future p53-based immunization strategies.

Rare-event analysis of circulating human dendritic cell subsets and their presumptive mouse counterparts

BACKGROUND

Considerable interest has focused recently on murine CD8alpha- and CD8alpha+ dendritic cell (DC) subsets, because of their roles in initiating and regulating immune responses. Attention has also centered on their presumed human counterparts, DC1 and DC2, respectively, and their precursors. Identification and quantification of these subsets in the blood may be crucial to understanding and monitoring of their immunologic significance, particularly in humans, where blood may be the only tissue readily or routinely available.

METHODS

Leukocytes were isolated from anticoagulated human or mouse (C57BL/10J) blood using conventional procedures. Four-color, rare-event, flow cytometric analysis was used to identify DC1 precursors (pDC1; lineage [lin]- CD4+ CD11c+ HLA-DR+) or DC2 precursors (pDC2; lin- CD4+ CD11c- CD123(hi) [IL-3Ralpha(hi)] HLA-DR+) in normal humans. In mice, CD8alpha+ (CD11b(lo), CD11c+) and CD8alpha- (CD11b(hi), CD11c+) DC subsets were identified both in normal animals and after administration of the potent DC growth factor, fms-like tyrosine kinase 3 ligand (Flt3L).

RESULTS

All human subjects examined had discrete populations of pDC1 and pDC2 comprising approximately 0.6% and 0.1% of blood mononuclear cells. CD8alpha- and CD8alpha+ DC constituted approximately 0.75% and 0.2%, respectively, of blood mononuclear cells in normal mice, and 12% and 0.5%, respectively, in Flt3L-treated animals. Flt3L administration substantially increased the absolute numbers of circulating CD11c+ DC by approximately 200-fold.

CONCLUSIONS

In addition to pDC1 and CD8alpha- DC, pDC2 and CD8alpha+ DC can be identified in normal human or mouse blood, respectively. Monitoring and isolation or characterization of these cells may provide novel insights into their functional significance in transplantation and other clinical conditions.

P-glycoprotein (P-gp) is upregulated in peripheral T-cell subsets from solid organ transplant recipients

Immunosuppressive agents such as cyclosporine, tacrolimus, sirolimus, and corticosteroids are substrates for the transmembrane multidrug resistance pump P-glycoprotein (P-gp). Experience in oncologyhas suggested that chronic exposure to P-gp substrates induces upregulation of P-gp activity, which could result in resistance to immunosuppressive drugs. The authors investigated P-gp function in CD4+ and CD8+ T cells from the peripheral blood of solid organ transplant recipients (SOTX). Subjects included 14 stable SOTX (10 liver, 4 lung) and 16 healthy controls. Four-color flow cytometry was used to simultaneously measure intracellular concentration of the fluorescent P-gp substrate Rhodamine 123 (Rh123) and surface expression of CD45RO (nominal memory/effector), CD45RA (naive), and either CD4 or CD8. P-glycoprotein function was measured by a dye efflux assay in which activity was inferred from a decrease in Rh123 fluorescence. CD4+ and CD8+ T cells from patients and control subjects eliminated Rh123, and this activity was inhibited by verapamil, a known P-gp substrate. CD8+ T cells had greater P-gp activity than CD4+ cells, and naive and transitional T cells displayed greater activity than memory T cells. Activity was bimodal in CD8+ CD45RO+ T cells, with a subset of these cells expressing the greatest P-gp activity. Patient CD8+ naive and transitional T cells had upregulated P-gp activity compared to control subjects. We conclude that (1) P-gp activityis significantly upregulated in specific T-cell subsets (CD8+/CD45RA+) in the peripheral blood of SOTX, and (2) the bimodal nature of P-gp response in CD8+ T cells complicates analysis of the effect of chronic administration of P-gp substrates to SOTX.

Monitoring the patient off immunosuppression. Conceptual framework for a proposed tolerance assay study in liver transplant recipients

The mission of the recently established Immune Tolerance Network includes the development of protocols for the induction of transplant tolerance in organ allograft recipients and the development of assays that correlate with and may be predictive of the tolerant state. The state of clinical organ transplant tolerance seems to already exist in a small minority of conventionally immunosuppressed liver and, more rarely, kidney transplant patients. Immunosuppressive drug therapy has been withdrawn from these patients for a variety of reasons, including protocolized weaning for a uniquely large group of liver patients at the University of Pittsburgh. In this study, we propose to evaluate the validity of a variety of in vitro immunologic and molecular biologic tests that may correlate with, and be predictive of, the state of organ transplant tolerance in stable liver patients off immunosuppression. Only peripheral blood will be available for the execution of these tests. Both adult and pediatric liver graft recipients will be studied, in comparison to appropriate controls. We shall examine circulating dendritic cell (DC) subsets [precursor (p) DC1 and p DC2] including cells of donor origin, and assess both the frequency and function of donor-reactive T cells by ELISPOT and by trans-vivo delayed-type hypersensitivity analysis in a surrogate murine model. Cytokine gene polymorphism and alloantibody titers will also be investigated. It is anticipated that the results obtained may provide physicians with a tolerance assay "profile" that may determine those patients from whom immunosuppressive therapy may be safely withdrawn.

Competition of peptide-MHC class I tetrameric complexes with anti-CD3 provides evidence for specificity of peptide binding to the TCR complex

BACKGROUND

Major histocompatibility complex (MHC)-peptide tetrameric complexes (tetramers) are valuable tools for detecting and characterizing peptide-specific T cells. Because the frequency of these cells is generally very low, it may be difficult to discriminate between nonspecific and specific tetramer binding.

METHODS

A four-color flow cytometric assay that simultaneously measures tetramer, CD3, CD8, and CD14 was used to investigate the sensitivity and specificity of MHC class I tetramer staining. This was accomplished by using the influenza virus matrix protein peptide, GILGFVFTL (FLU), as a model recall antigen and the human immunodeficiency virus (HIV) reverse transcriptase peptide, ILKEPVHGV (HIV), as a model novel antigen. Peripheral blood mononuclear cells (PBMC) from 31 HLA-A2.1(+) and 10 HLA-A2.1(-) healthy individuals were stained with the tetramers.

RESULTS

The lower limit of detection was established at approximately 1/8,000. In HLA-A2(+) PMBC, frequencies of tetramer-positive CD8(+) T cells were log normally distributed and were high for FLU (1/910) but low for HIV (1/6,067). A novel competition assay, in which tetramer binding was shown to diminish subsequent staining with anti-CD3 antibody, was used to confirm the specificity of tetramer binding to the T-cell receptor (TCR) complex. The competition assay was validated by evaluating several anti-CD3 antibodies and showing that in PBMC from HLA-A2(-) subjects, spurious tetramer-positive events (1/20,000) failed to compete with CD3 binding. For the "recall" FLU tetramer, the degree of competition was proportional to the frequency, suggesting a selection of high avidity cells. Although CD3 competition was also highly correlated with the intensity of tetramer staining, competition allowed the identification of false positive cases with relatively high tetramer staining intensity.

CONCLUSION

The data indicate that competition of CD3 binding allows confirmation of the specificity of tetramer binding to the TCR, extending the usefulness of tetramers in the frequency analysis of peptide-specific T lymphocytes.

Clinical significance of cytomegalovirus-specific T helper responses and cytokine production in lung transplant recipients

Cytomegalovirus (CMV) disease continues to be a major problem for lung transplant recipients. In CMV-seropositive individuals, we detected two types of CMV-specific responses: a self-restricted response stimulated by soluble CMV antigen (sCMV-Ag) and a non-self-restricted response induced by CMV-infected cells (cCMV-Ag). Lung transplant recipients who develop the CMV-specific self-restricted T helper response have a low risk of recurrent CMV disease. In contrast, during CMV disease, lung transplant recipients exhibit only the non-self-restricted T helper responses. We characterized the T cell activation and the kinetics of cytokine production of sorted CD4+ and CD8+ T cells from PBLs of CMV seropositive donors. The two types of CMV antigens induced cytokine production in both T cell subsets. We also performed competitive RT-PCR for Granzyme B (GB) in BAL cells of lung transplant recipients prior to, during and following CMV disease. CMV disease was associated with increase in GB gene expression when was accompanied by acute cellular rejection while it remained low in patients with CMV disease that did not have a complicated course. In summary, CMV-activated T cells within the allograft may produce inflammatory cytokines and effector molecules that may promote allograft rejection.

Lymphopoiesis, apoptosis, and immune amnesia

Bone marrow transplant recipients have a functional T-cell deficit long after T-cell counts have returned to normal levels. Early after BMT, T-cell phenotype is predominantly CD45RO+/CD29high/HLA-DR+/CD38high. This profile is associated with activated memory cells in healthy subjects, but also appears on the earliest mature naive T-cells in times of lymphopoietic stress. Most of these cells apoptose in short-term unstimulated culture, suggesting that they would have had a similar fate in vivo. Twelve to 24 months after BMT, CD45RA+/CD29low/HLA-DR-/CD38low T cells increase, apoptosis decreases, and T-cell function normalizes. We hypothesize that in the adult, mature memory T cells regulate their own replacement by rescuing a proportion of newly generated naive cells from apoptosis. Ablation of memory cells consequent to high dose therapy disrupts this process, resulting in a protracted period of high lymphocyte turnover with few cells surviving to make the antigen-driven transition to memory cells. Infection with HIV-1 also eventuates in immune deficiency associated with a loss in CD4+ T cells and dominance of the phenotypic/apoptotic profile which we have associated with lymphopoietic stress. Recent data independently confirm that T-cell turnover is greatly elevated in HIV infection. Catastrophic or chronic depletion of memory T cells due to marrow ablative therapy or HIV-1 infection interferes with memory replacement, substituting short-lived hypofunctional naive T cells which characterize the state of immune amnesia.

Apoptosis parallels lymphopoiesis in bone marrow transplantation and HIV disease

Apoptosis has been implicated in a variety of physiological processes ranging from tissue modeling to deletion of autoreactive T lymphocytes during thymic development. The recent finding that a large proportion of peripheral T cells from HIV-infected subjects (corrected from subjects) apoptose in culture raises an important issue: does this represent a pathologic mechanism by which the virus disrupts the immune system, or a normal physiologic response to virus-mediated T-cell loss? To study the potential relationship between apoptosis and lymphopoiesis, we compared apoptosis rates in unstimulated lymphocyte cultures from healthy subjects, HIV+ gay men, and bone marrow transplant (BMT) recipients undergoing immune reconstruction. BMT recipients were chosen because they undergo massive regeneration of lymphocytes following marrow ablation and graft infusion. The data obtained in BMT recipients suggests that elevated apoptosis accompanies, and is the consequence of, elevated lymphopoiesis. We also found a strong inverse relationship between in vitro T-cell apoptosis rates and peripheral T-cell counts. These results provide new interpretation for elevated apoptosis observed in HIV-infected individuals--that it reflects increased T-cell turnover consequent to virus-mediated destruction of CD4+ T-cells.