Cytotoxic T-lymphocyte Precursor Frequencies Research Articles

Correlation of circulating EBV-targeted cytotoxic T lymphocyte precursors (EBV-CTLp) and clinical response following tabelecleucel (tab-cel) infusion in patients with EBV-driven disease.

2532 Background: EBV is implicated in a variety of diseases. Tab-cel is an investigational off-the-shelf, allogeneic T-cell immunotherapy utilizing endogenous T cell receptors targeting EBV antigens. We hypothesized the clinical activity of tab-cel is mediated by expansion and persistence of EBV-specific T cells. Therefore, we quantified circulating EBV- CTLp after tab-cel administration and examined the correlation between expansion and clinical response. Methods: Samples from 10 patients with EBV+ post-transplant lymphoproliferative disease (PTLD) and other EBV-associated diseases enrolled in an multicenter expanded access protocol (EAP) study ( NCT02822495 ) were analyzed. To evaluate CTLp frequencies, limited dilution analysis was performed on samples taken at baseline and day 34 post first tab-cel dose (end cycle 1). The day 34 persistence of circulating EBV-CTLp from best overall response to initial tab-cel product was tested using the two-tailed Mann-Whitney test. Changes in inflammatory cytokines were also measured. Results: Responders represented in this sampling (n=6; 2 PR and 4 CR) showed a median 5.8-fold increase in circulating CTLp between baseline and day 34 (range: 0.8 to 133-fold). Five of 6 responders showed an increase in EBV-CTLp at day 34 of ≥ 3.8-fold while 1 pt showed no change in CTLp (0.8-fold change). In contrast, the 4 non-responders (3 SD; 1 PD) showed a median 0.3-fold decrease in EBV-CTLp from baseline (range: 1.2 to 0.02-fold; ns). Cumulative analyses revealed a statistically significant correlation between the fold-change of circulating CTLp at day 34 and clinical response (p=0.038) which did not appear to correlate with the type of the EBV-associated disease. Inflammatory cytokines showed no meaningful change from baseline. The safety profile remains consistent with previously reported data. Conclusions: These data support the correlation of clinical activity of tab-cel with the expansion and persistence of EBV-specific T-cells at day 34 post-treatment, as well as the use of circulating CTLp as a biomarker for response in clinical studies. Clinical trial information: NCT02822495.

LBOR03: ASSOCIATION BETWEEN CTL PRECURSOR FREQUENCY TO HLA-C MISMATCHES AND HLA-C ANTIGEN CELL SURFACE EXPRESSION

Aim Previous studies showed the relevance of the cytotoxic T cell precursor frequency assay (CTLp) for prediction of the outcome of HLA mismatched hematopoietic cell transplantation (HCT). Recently it has been shown that HLA-C cell surface expression is correlated with virus specific cytotoxic T cell responses and viremia control in HIV patients. The aim of the current study was to investigate the association between HLA-C antigen expression and the CTLp frequency to the mismatched HLA-C antigen. Methods In total 115 recipient–donor pairs, for whom a successful CTLp assay was performed, were evaluated in this pilot study. All donor–recipient pairs were matched at 9/10 alleles with a single mismatch at the HLA-C locus. Antigen expression level of the mismatched HLA-C allele for each recipient and donor was based on the MFI values as described by Apps et al. (Science, 2013). Results The cell surface expression of recipient’s mismatched C antigen was significantly lower among CTLp negative ( n = 59) compared to CTLp positive ( n = 56) pairs (154 and 193 MFI units, respectively; p = 0.0031). This difference was more pronounced in donor–recipient pairs that were mismatched for residue-116 located in the groove of the HLA-C antigen, suggesting the importance of peptide binding in the allo-recognition. Furthermore, in the case of low expression of the recipient mismatched HLA-C antigen (MFI n = 26), while in CTLp positive cases ( n = 15) the median MFI of donor’s HLA-C antigen was 193. ( P = 0.0093). Conclusion We conclude that the expression level of the donor and recipient mismatched HLA-C antigens affect CTLp outcome. HLA-C antigen expression levels in combination with the CTLp assay may prove useful for the prediction of the clinical outcome of HLA-C mismatched HCT.

Association between CTL Precursor Frequency to HLA-C Mismatches and HLA-C Antigen Cell Surface Expression.

Previous studies showed the relevance of the cytotoxic T-cell precursor (CTLp) frequency assay for prediction of the outcome of HLA mismatched hematopoietic cell transplantation (HCT). Recently, it has been shown that HLA-C cell surface expression is correlated with virus specific cytotoxic T-cell responses and viremia control in HIV patients. The aim of the current study was to investigate the association between HLA-C antigen expression and the CTLp frequency to the mismatched HLA-C antigen. In total 115 recipient–donor pairs, for whom a successful CTLp assay was performed, were evaluated for this pilot study. All donor–recipient pairs were matched at 9/10 alleles with a single mismatch at the HLA-C locus. Antigen expression level of the mismatched HLA-C allele for each recipient and donor was based on the mean fluorescence intensity (MFI) values as described by Apps et al. (1). The cell surface expression of recipient’s mismatched HLA-C antigen was significantly lower among CTLp negative (n = 59) compared to CTLp positive (n = 56) pairs (154 and 193 MFI units, respectively, p = 0.0031). This difference was more pronounced in donor–recipient pairs that were mismatched for amino-acid residue-116 located in the groove of the HLA-C antigen, suggesting that the importance of peptide binding in the allo-recognition. Furthermore, in the particular case of low expression of the recipient mismatched HLA-C antigen (MFI < 115), CTLp reactivity depended on HLA-C expression level in the donor, the median MFI of donor’s mismatched HLA-C antigen was 114 in CTLp negative cases (n = 26), while in CTLp positive cases (n = 15) the median MFI of donor’s HLA-C antigen was 193 (p = 0.0093). We conclude that the expression level of the donor and recipient mismatched HLA-C antigens affect CTLp outcome. HLA-C antigen expression levels in combination with the CTLp assay may prove useful for the prediction of the clinical outcome of HLA-C mismatched HCT.

The Influenza Virus–Specific CTL Immunodominance Hierarchy in Mice Is Determined by the Relative Frequency of High-Avidity T Cells

Virus-specific CTL responses typically fall into reproducible hierarchies with particular epitopes eliciting either immunodominant or subdominant responses after viral challenge. The recently acquired capacity to directly enumerate naive CTL precursors (CTLps) in both mice and humans has implicated CTLp frequency as a key predictor of immune response magnitude after Ag challenge. However, recent studies have indicated that naive CTLp frequencies do not necessarily predict the size of the Ag-driven response, indicating an important role for differential CTLp recruitment and/or expansion. This study characterizes the early emergence of various influenza epitope-specific CTL responses at multiple sites in C57BL/6 mice, and probes the role of Ag dose and TCR avidity in dictating immune response hierarchies. Despite large naive CTLp numbers, subdominance was found to arise largely as a consequence of the abrupt and premature cessation of CTL proliferation, at least for one epitope specificity. Investigation into the possible drivers of the poor proliferation observed for subdominant specificities showed that the immunodominance hierarchy endured irrespective of epitope abundance, and correlated with the prevalence of high-avidity T cells in both the naive and immune compartments. Our study strongly indicates that the quality, and not simply the quantity, of antiviral CTLs dictate response magnitude.

An Immunological Basis for Chronic Histiocytic Intervillositis in Recurrent Fetal Loss

Chronic histiocytic intervillositis (CHIV) is a rare type of placental pathology that is associated with reproductive loss at all gestational ages. The aim of the study was to investigate the relationship between the severity of CHIV and the outcome of pregnancy and to compare the immune response between CHIV patients and controls to explore an immunological origin of CHIV. Microscopic slides were reviewed and scored according to a previously published grading system in 30 pregnancies of 22 CHIV patients. Partner-specific mixed lymphocyte reactions, cytotoxic T-lymphocyte precursor frequencies (CTLpf), and anti-HLA antibodies were determined in four patients and seven controls. Higher CHIV scores are associated with worse pregnancy outcome. CHIV patients demonstrated a higher CTLpf against their partner compared to non-complicated pregnancies (P=0.03). The CTLpf was extremely high in 75% of the patients. Antipaternal HLA antibodies were only present in 75% of the CHIV patients compared to none of the controls (P=0.02). CHIV scores seem to be associated with the severity of adverse pregnancy outcome. High antipaternal cellular (T-cell) and humoral (B-cell) response to partner-specific CTLpf and the presence of anti-HLA antibodies directed to the partner suggest an immunologic origin of CHIV.

Third Party Donor Derived EBV Specific T Cells for the Treatment of Refractory EBV-Related Malignancies in Immunodeficient Recipients

AbstractAbstract ▪577▪This icon denotes a clinically relevant abstractAdoptive immunotherapy is an effective strategy for the treatment of EBV+ lymphoproliferative diseases (EBV-LPD) arising after an allogeneic hematopoietic stem cell (HSCT) or solid organ transplant (SOT). This approach is, however, often limited by an inability to generate donor derived in vitro expanded EBV-specific cytotoxic T-lymphocyte (EBV-CTL) lines in a timely manner and/or the fact that EBV CTL lines derived from HLA non-identical donors may be restricted by non-shared HLA alleles.To date, we have treated 25 consecutive patients with an EBV LPD (N=20) or EBV Leiomyosarcoma (LMS) (N=5) with in vitro expanded EBV-CTLs derived from a donor other than the patient or their transplant (HSCT or SOT) donor. EBV CTLS were selected from a bank of 345 lines generated under GMP conditions from normal HSCT donors. Each donor was specifically consented for use of their T cells in patients other than their designated transplant recipient. Patients were recipients of unmodified (n=4), T cell depleted (n=5) or unrelated cord blood (n=5) HSCT, a solid organ transplant (n=6), a combined SOT and HSCT (n=1), or were non-transplanted patients with a primary immunodeficiency disease (n=4).EBV disease in transplanted patients was of host origin in 5 of 10 evaluable HSCT recipients, in 3 of 4 evaluable solid organ recipients, and in the one patient who underwent a combined HSCT/solid organ transplant. Third party EBV-CTLs were selected on the basis of HLA matching at a minimum of 2/8 recipient alleles. Where possible EBV-CTLs were selected that were restricted through HLA alleles present on the EBV+ tumor. HLA restriction was evaluated in vitro in 20 EBV-CTL donor lines. The restriction was at a single HLA allele (n=12), at two alleles (n=6) and at >than two alleles (n=2).Patients received infusions of 3rd party EBV-CTLs after failing a median of 2 prior therapies including rituximab in all but one case of EBV LPD. Four patients failed prior infusions with EBV-CTLs which were autologous (n=1), derived from their original HSCT (n=2) or from their solid organ donor (n=1). In two patients who progressed after treatment with EBV CTLs generated from their HSCT or organ donor, it was demonstrated that the donor derived EBV CTLs were restricted by a non-shared HLA allele.Patients received a median of 5 infusions most at 1×106 EBV-CTL/kg/infusion. Four patients received EBV-CTLs from >1 3rd party donor. Nine patients achieved a completed response. Nine patients died of progressive disease, 6 shortly after the first infusion (17–29 days). Two patients with LMS achieved long term stable disease (46 and 8 months); 5 achieved partial remissions which have been sustained in 4 (11- 68 months), and 1 patient progressed after 10 months in a partial remission. Response to EBV CTL therapy did not correlate with the degree of HLA matching between donor and recipient or donor and tumor. Radiographic and clinical responses correlated with detectable increases in the frequency of CTL precursors in the blood. However durable EBV CTL engraftment was not seen.One patient developed mild skin GvHD after infusion with 3rd party EBV-CTLs, but tolerated subsequent infusion of EBV-CTLs from an alternate 3rd party donor. Although no SOT recipient developed anti-HLA antibodies, one developed and episode of steroid responsive renal transplant rejection more than 6 months after infusion of EBV CTLs without evidence of donor (by STR analysis) in biopsied tissue.This study demonstrates a high response rate among patients with otherwise refractory EBV malignancy treated with EBV specific 3rd party CTLs restricted by HLA alleles shared by the tumor. Treatment failures correlated with the use of EBV CTLs restricted by HLA alleles not shared by the tumor. In addition two patients with a primary immunodeficiency disease who were unable to mount an endogenous EBV T cell response had transient but not durable responses to 3rd party cells. EBV CTLs can be effective when selected based on restriction to shared alleles despite significant HLA disparity. The bank of EBV specific T cells can provide an immediate source of HLA partially matched appropriately restricted T cells for adoptive immunotherapy to treat EBV associated malignancy. This enables treatment early in the course of disease and the use of EBV-CTL lines previously prepared and characterized in terms of HLA restriction. This is anticipated to maximize the response rate. Disclosures:No relevant conflicts of interest to declare.

Immune responses against islet allografts during tapering of immunosuppression – a pilot study in 5 subjects

Transplantation of isolated islet of Langerhans cells has great potential as a cure for type 1 diabetes but continuous immune suppressive therapy often causes considerable side effects. Tapering of immunosuppression in successfully transplanted patients would lower patients' health risk. To identify immune biomarkers that may prove informative in monitoring tapering, we studied the effect of tapering on islet auto- and alloimmune reactivity in a pilot study in five transplant recipients in vitro. Cytokine responses to the graft were measured using Luminex technology. Avidity of alloreactive cytotoxic T Lymphocytes (CTL) was determined by CD8 blockade. The influence of immunosuppression was mimicked by in vitro replenishment of tacrolimus and MPA, the active metabolite of mycophenolate mofetil. Tapering of tacrolimus was generally followed by decreased C-peptide production. T-cell autoreactivity increased in four out of five patients during tapering. Overall alloreactive CTL precursor frequencies did not change, but their avidity to donor mismatches increased significantly after tapering (P = 0·035). In vitro addition of tacrolimus but not MPA strongly inhibited CTL alloreactivity during tapering and led to a significant shift to anti-inflammatory graft-specific cytokine production. Tapering of immunosuppression is characterized by diverse immune profiles that appear to relate inversely to plasma C-peptide levels. Highly avid allospecific CTLs that are known to associate with rejection increased during tapering, but could be countered by restoring immune suppression in vitro. Immune monitoring studies may help guiding tapering of immunosuppression after islet cell transplantation, even though we do not have formal prove yet that the observed changes reflect direct effects of immune suppression on immunity.

Adoptive immunotherapy with unselected or EBV-specific T cells for biopsy-proven EBV+ lymphomas after allogeneic hematopoietic cell transplantation

AbstractWe evaluated HLA-compatible donor leukocyte infusions (DLIs) and HLA-compatible or HLA-disparate EBV-specific T cells (EBV-CTLs) in 49 hematopoietic cell transplantation recipients with biopsy-proven EBV-lymphoproliferative disease (EBV-LPD). DLIs and EBV-CTLs each induced durable complete or partial remissions in 73% and 68% of treated patients including 74% and 72% of patients surviving ≥ 8 days after infusion, respectively. Reversible acute GVHD occurred in recipients of DLIs (17%) but not EBV-CTLs. The probability of complete response was significantly lower among patients with multiorgan involvement. In responders, DLIs and EBV-CTLs regularly induced exponential increases in EBV-specific CTL precursor (EBV-CTLp) frequencies within 7-14 days, with subsequent clearance of EBV viremia and resolution of disease. In nonresponders, EBV-CTLps did not increase and EBV viremia persisted. Treatment failures were correlated with impaired T-cell recognition of tumor targets. Either donor-derived EBV-CTLs that had been sensitized with autologous BLCLs transformed by EBV strain B95.8 could not lyse spontaneous donor-derived EBV-transformed BLCLs expanded from the patient's blood or biopsied tumor or they failed to lyse their targets because they were selectively restricted by HLA alleles not shared by the EBV-LPD. Therefore, either unselected DLIs or EBV-specific CTLs can eradicate both untreated and Rituxan-resistant lymphomatous EBV-LPD, with failures ascribable to impaired T-cell recognition of tumor-associated viral antigens or their presenting HLA alleles.

A Proposed Algorithm Predictive for Cytotoxic T Cell Alloreactivity

Previously, we showed that with an increasing number of amino acid differences in single HLA class I-mismatched molecules, the probability of T cell alloreactivity decreases. It is unlikely that every amino acid difference will affect T cell alloreactivity in a similar way; we hypothesized that the effect of an amino acid difference may be dependent on its position and/or physicochemical properties. We selected 131 patient/donor pairs with either a single HLA-A or -C mismatch in the graft-versus-host direction and that were compatible for HLA-B, -DRB1, and -DQB1. The alloreactive CTL precursor (CTLp) frequency was determined and associated with the amino acid differences between the single HLA class I mismatches. In the β sheet, only amino acids that are noncompatible in their physicochemical properties affect T cell alloreactivity, whereas in the α helices, both compatible and noncompatible amino acids affect CTLp outcome. Positions 62, 63, 73, 76, 77, 80, 99, 116, 138, 144, 147, and 163 were bivariately associated with CTLp outcome, irrespective of the total number of amino acid differences. In multivariate analysis, positions 62, 63, 73, 80, 116, 138, 144, and 163 were found to be most predictive for negative CTLp outcome. These results formed the basis for a weighted predictive mismatch score; pairs with the highest mismatch scores are estimated to be 13 times more likely to have a negative CTLp. This new algorithm may be a tool in donor selection for hematopoietic stem cell transplantation.

Discontinuation of calcineurin inhibitors treatment allows the development of FOXP3+ regulatory T-cells in patients after kidney transplantation

This study investigated specific gene expression profiles in patients with donor-specific cytotoxic-hyporesponsiveness, reflected by cytotoxic T-lymphocyte precursor frequency (CTLpf). The effect of calcineurin inhibitor (CNI) withdrawal was studied on markers for cytotoxicity (perforin, granzyme B), apoptosis (Fas,FasL), Th1 and Th2 cytokines (IL-2, IL-10), Th1 and Th2 transcription factors (T-bet, GATA 3), Th17 transcription factor and cytokine (RORγt, IL-17), and for immune regulation/activation (CD25, FOXP3). Peripheral blood samples from renal allograft recipients (n = 18) more than two yr after transplantation with stable renal function were analyzed before and four months after CNI withdrawal. Additionally, systolic and diastolic blood pressure, cholesterol, serum creatinine and proteinuria were evaluated, and no significant differences were measured before and after CNI withdrawal. However, CNIs' discontinuation influenced peripheral gene expression profiles. After CNI withdrawal, the mRNA expression of Granzyme B, Perforin, Fas, FasL, T-bet, GATA3 and CD25 were significantly lower than during CNI treatment. After CNI discontinuation, donor-specific CTLpf decreased, while FOXP3 expression discriminated between detectable and non-detectable donor-specific cytolysis reactivity; FOXP3 transcript values were highest in absence of donor-specific cytotoxicity (p < 0.01). Our study shows CNI withdrawal in stable kidney transplant recipients two yr after transplantation is safe. Moreover, discontinuation of CNIs' treatment allows FOXP3+ regulatory T-cells development, resulting in a significant decrease of anti-donor immune reactivity.

Preeclampsia is associated with increased cytotoxic T-cell capacity to paternal antigens

During an uncomplicated pregnancy the conceptus is a semiallogeneic entity in which rejection is prevented by suppression of the maternal immune system. We hypothesized that this suppression is disturbed in patients with preeclampsia and that a maternal immune response to fetal (foreign/paternal) antigens in the fetal-maternal interface may be responsible for local inflammation, with subsequent endothelial dysfunction and systemic disease. Blood samples were obtained from 14 women with preeclampsia (cases), 14 gestational-age and parity-matched women with uncomplicated pregnancies (controls), and their partners. We determined the partner-specific cytotoxic T-lymphocyte precursor frequency (CTLpf) and the CTLpf directed to unrelated partners with uncomplicated pregnancies. We measured the CTLpf in peripheral blood mononuclear cells (PBMCs) from cases and controls using limited-dilution assays. In addition, proliferation was tested in a mixed-lymphocyte culture (MLR). The partner-specific CTLpf was significantly higher in cases compared with controls (median, 183 [15-338] vs 67 [9-232] per million PBMCs, P = .02). In contrast, in women with uncomplicated pregnancies, the partner-specific CTLpf was down-regulated compared with the CTLpf directed to an unrelated partner who fathered uncomplicated pregnancies (P = .02). No difference was found in partner-specific MLR response between cases and controls. These results suggest that women with preeclampsia have a higher cytotoxic T-cell response to paternal antigens compared with pregnant controls. This insufficiently suppressed immune response may eventually lead to the development of preeclampsia.

Methods to measure vaccine immunity

The biggest triumph in vaccination is the eradication of smallpox. Ironically, no methods to measure vaccine immunity were set in place. Protection and immunity was achieved without detailed analysis nor knowledge of cellular or humoral immunity induction. Today, owing to strict health and safety issues of vaccine manufacturing, vaccines must meet higher standards of safety and biochemical characterization than they did in the past. This has led to the production of highly purified vaccines, and the identification and isolation of the antigens responsible for protection. A vaccine cannot move forward without the demonstration of effective immunity induced by the regime. Moreover, contrary to the vaccination strategy that eradicated smallpox and other acute viral infections, several modern vaccines aim at the eradication of established chronic diseases such as chronic viral infections or cancer. As the pathogens or cancer antigens are generally intracellular, modern vaccines can rely less effectively on the neutralizing properties of antibody responses that cannot cross the cell membrane, and depend predominantly on T-cell-based recognition of affected cells for their elimination. Thus, new technologies have to be developed to measure vaccine immunity. Are we going round and round in circles? Are we making it harder for ourselves? Is vaccine development getting too hard? Why do we have to demonstrate immunity, if we can show protection? No regulatory agency will take a vaccine forward that is not highly purified and can demonstrate immunity induction. Several methods of measuring humoral and cellular immunity have been required to be developed to meet this criteria. Some methods include ELISA, cytotoxic T-lymphocyte (CTL) assay, CTL precursor frequency assay, T-cell proliferation assays, carboxyfluorescein diacetate succinimidyl ester assays, intracellular and extracellular cytokine production by cells in culture using either ELISA or multiplex and flow cytometry, polyfunctional T-cell assays, ELISpot and MHC class I/II tetramers. Thus, there is an enormous amount of information and reagents available for guiding vaccine and immunotherapeutics development. This special issue on ‘Methods to measure vaccine immunity’ focuses on a number of recent and promising approaches used to measure immunity induced following vaccination. Topics included in this special focus issue are as follows: Gene-expression profiling in vaccine therapy and immunotherapy for cancer [1]. The use of microarrays is described in order to understand the mechanism by which tumors are rejected; Antibody-profiling technologies for studying humoral responses to infectious agents [2]. Protein microarrays are used to evaluate antibody responses to thousands of antigens at one time. The luciferase immunoprecipitation system overcomes some drawbacks of the conventional protein microarray assay. These new technologies offer a new tool for understanding humoral immunity induction to proteins; Vaccine-induced antibody responses in patients with carcinoma [3]. A nice overview of current methods utilized for measuring antibody responses and for assessing their antitumor efficacy in the context of clinical trials; Methods to measure T-cell responses [4]. A mini review on recent methods used to measure T-cell immunity, such as the use of CTL, CTL precursor frequency assays, carboxyfluorescein diacetate succinimidyl ester, flow cytometric approaches, spectrophotometric approaches and use of ovalbumin-specific CD8+ T cells from OTI and OTII T-cell receptor tansgenic mice; New flow cytometric assays for monitoring cell-mediated cytotoxicity [5]. A comparison of IFN-γ ELISpot, granzyme B ELISpot and conventional 51Cr-release assays is given. A detailed analysis of the use of flow cytometric methods to measure T-cell immunity induction is demonstrated; Evaluation of cellular immune responses in cancer vaccine recipients [6]. Measurement of cellular immunity is addressed using NY-ESO-1 as an example and techniques such as delayed-type hypersensitivity, measurement of T cells from peripheral blood, use of overlapping peptides to measure CD4 and CD8 T cells, and the role of Treg cells in vaccine immunity induction are described; Development and application of phosphoflow as a tool for immunomonitoring [7]. This article describes the new flow cytometry technology, phosphoflow for measuring multiple intracellular signaling molecules in the immune system at a single-cell level for lymphocyte immune monitoring; Surface plasmon resonance for vaccine design and efficacy studies [8]. An outline of how surface plasmon resonance biosensors are emerging to understand how serum is used to monitor antibody immunity; The challenges of assessing infant vaccine responses in resource-poor settings [9]. A very nice and comprehensive article on methods to measure vaccine immune responses where only poor settings are available. There is a vast amount of information already available to promote a greater understanding into the role of specific immune induction to a vaccination regime. The use of newer immune monitoring tools as described in this special focus issue will serve to improve immune monitoring and determine the effectiveness of vaccine strategies for the treatment or immunotherapeutic approaches to diseases.

Detection and ex vivo expansion of dormant anti-viral CTL precursors isolated from recipients of unrelated umbilical cord blood transplant (UCBT). (145.31)

Abstract Two potentially fatal viruses ,CMV and adenovirus can be detected 2-4 weeks after UCBT. Infection may trigger in vivo priming of the infused na ve T cells despite immunosuppressive (IS)medications. We hypothesized that 1) threshold numbers of CTL precursors can be identified that may influence outcome 2) CTL precursors may reside below the level of detection during IS. Methods: Monocytes infected with an adenovirus vector encoding CMV pp65 (Ad5f35pp65) were used as APC in the presence of IL7. Antiviral CTLp was quantitated by IFNg ELISPOT among 1x10e5 responders after overlapping peptide pool stimulation. Results: 8 infected patients at a median age of 9.9 years have been studied before day 100 . Only 1/3 patients with adenovirus exhibited viremia while all 5 patients with CMV had viremia. In freshly drawn blood, 1/8 patients had any detectable reactivity. However, after 9-12 days of stimulation we could enumerate CTLp in 7/8 patients. For adenovirus, the median hexon-specific response was 52 SFC, and the penton-specific CTLp frequency was 13 SFC. CMV pp65-specific response was 6.7 SFC. No responses were found against CMV EI-1 demonstrating critical role for antigenic restimulation. All patients survive beyond 6 months. Conclusion: To our knowledge these are the first data demonstrating that dormant virus-specific CTLp are present already in the first 3 months in infected UCBT recipients. Although these rare events are below detection ex vivo expansion permits quantitation.

Relapse of Leukemia with Loss of Mismatched HLA Due to Uniparentaldisomy Follwing Haploidentical Hematopoietic Transplantation.

Abstract 2457Poster Board II-434 Introduction:Down-regulation or loss of human leukocyte antigen (HLA) expression can lead to impaired T-cell recognition and a blunted immune response to malignant tumors. We investigated HLA expression on leukemic cells derived from patients at the time of diagnosis and relapse after HLA haploidentical hematopoietic stem cell transplantation (HSCT) using flow cytometry with locus-specific antibodies. We hypothesized that the loss of HLA haplotype caused leukemic cells to escape immunosurveillance and consequently led to relapse of the disease. Materials and methods:The CD13+/34+ leukemic blasts were sorted by flow cytometry from bone marrow cells at the time of diagnosis and at the time of relapse. Genomic DNA was extracted from leukemic cells by fluorescence-activated cell-sorter as well as phytohemagglutinin-stimulated patient-derived T cells and subjected to single-nucleotide polymorphism (SNP) array analysis using GeneChip NspI arrays (Affymetrix, Tokyo, Japan). Allele-specific copy number was detected using Copy Number Analyser for GeneChip® software. The frequencies of cytotoxic T lymphocyte precursor (CTLp) specific for the recipient mismatched HLA molecules were analyzed using a standard limiting dilution assay. Allo-HLA-restricted CTL clones were isolated by standard limiting dilution and expanded for cytotoxicity assay against mismatched HLA transduced HLA class I-deficient 721.221 B-LCLs. Results:Two of three relapsed patients after HLA haploidentical HSCT demonstrated loss of HLA alleles on leukemic cells at the time of relapse and this loss was limited to the mismatched alleles in both patients. However, none of seven relapsed patients experienced haplotype loss following HLA matched HSCT. SNP array analyses of sorted leukemic cells at the time of diagnosis and at the time of relapse further revealed the copy number-neutral loss of heterozygosity, namely acquired uniparental disomy (UPD) on the short arm of chromosome 6, resulting in the total loss of the mismatched HLA haplotype. Recipient alloantigen-specific cytotoxic T-cell clones were generated from the donor that did not recognize the leukemic cells at the time of relapse, whereas those cells taken at diagnosis were recognized and efficiently killed. In one of the patients, we sought to determine if the number of CTLp had changed during the post-transplant course. A limiting dilution analysis with a split-well 51Cr-release assay was carried out to compare the CTLp frequencies specific for the mismatched antigens between the recipient and donor. Surprisingly, the CTLp frequencies reactive with recipient T cell blasts in CD8+ T cells obtained around Days 100, 180, and 300 (4 months before relapse) were undetectable, while the CTLp frequency obtained at Day 520 (1 month after the third DLI or 2 weeks after remission confirmed by bone marrow aspirate) was 8.6 × 10-5 [95% confidence interval (CI), 1.49 × 10-6 – 5.0 × 10-5]. The CTLp frequency in the donor CD8+ cells was 4.3 × 10-5 (95%CI, 7.2 × 10-5 – 2.5 × 10-5), which was close to that obtained after DLI in the recipient. Conclusions:These results suggest that the cytotoxic T lymphocyte response to mismatched HLA alleles can eradicate leukemic cells; however, escape from immunosurveillance by the loss of mismatched HLA alleles using UPD may be involved in relapse after haploidentical HSCT. Disclosures:No relevant conflicts of interest to declare.

Detection and Ex Vivo Expansion of Anti-Viral T Cells Isolated From Recipients of Unrelated Umbilical Cord Blood Transplant.

Abstract 2245Poster Board II-222 Background:Viral infection is commonly detected within the first weeks after umbilical cord blood transplant (UCBT), likely triggering T cell activation and in vivo priming of infused naïve T cells. This hypothesis is supported by the observation that despite the continuous exposure to immunosuppressive (IS) drugs, viremia may resolve even in the absence of antiviral agents. However, IS may delay or even prevent effective T cell priming and the development of protective immunity, therefore causing significant morbidity and mortality. Hypothesis and Objective:Our laboratory has a long standing interest in defining pre-requisites of protective immunity after UCBT. In this study we focused on two of the most common potentially fatal viruses, CMV and Adenovirus to assess antigen-specific immune reconstitution. We hypothesized that 1) threshold numbers of CTL precursors can be identified for each virus that will impact clinical outcome 2) there may be circulating CTL precursors even if below the level of detection in lymphopenic patients that receive IS drugs, however, ex vivo restimulation could lead to expansion and subsequent quantitation. Methods:We have established in vitro assays to test the impact of cytokines and new culture techniques to promote anti-viral precursor survival and expansion. Monocytes in bulk cultures, infected with replication incompetent adenovirus vectors encoding the pp65 CMV matrix protein (Ad5f35pp65), served as APC. Antiviral responses were quantitated by ELISPOT, utilizing computerized enumeration of interferon gamma (IFNg) producing spot forming cells (SFC) in response to overlapping peptide spanning immunodominant viral antigens. Hexon and penton for adenovirus, and pp65 and EI-1 for CMV. Results:There were 8 patients enrolled on this IRB approved study transplanted at a median age of 9.9 years (range 2-17). Blood samples was obtained at a median of 70 days (range 34-470). Only 1 of 3 patients with adenovirus infection ( stool x1, urine x1, respiratory tract x 1) had previous viremia while all five (5) patients with CMV had viremia. Only 1 of the 3 adeno patients had detectable SFC from freshly drawn peripheral blood, 11 SFC/1×10e5 cells against hexon and penton respectively. None of the 5 CMV+ patients had detectable pp65 or EI-1-specific T cell responses from freshly drawn blood. However, after 9-12 days of ex vivo culture, in the presence of IL7 (10ng/ml), we were able to enumerate significantly amplified CTL responses in 7 of the 8 patients, with one CMV viremic the exception. In the remaining patients the median adenovirus hexon-specific response was 52 SFC/1×10e5 cells (range 20-90). the median penton-specific CTLp frequency was 13 SFC/1×10e5 (range 1 - 25). The median CMV pp65-specific response was 6.7 SFC/1×10e5 (range 0-14) while no responses were recorded against EI-1 demonstrating the critical role of antigenic restimulation provided by the Ad5f35pp65 construct lacking IE. The amplified immune responses were highly restricted; in the CMV+ patients (all adeno-) we were able to detect SFC only against pp65 and to neither IE or penton/hexon, while in the adenovirus+/CMV- patients (n=-3) we were able to detect SFC solely in those wells that were stimulated by hexon and penton peptides. All patients have survived at a median of 220 days after transplant (range 81-532). Conclusion:To our knowledge these ongoing experiments are the first to demonstrate that dormant virus-specific immune responses are present already in the first 100 days in most UCBT recipients (7/8 in this dataset) if infected with either adenovirus or CMV despite failure to detect these extremely rare events by standard ELISPOT assays from freshly isolated blood. Moreover, these data suggests that anti-viral CTLp can be expanded ex vivo by antigen specific restimulation that lends support to further efforts aimed at developing adoptive anti-viral T cell therapies. Disclosures:No relevant conflicts of interest to declare.

Pretransplant Immune Parameters Associate With Islet Allograft Outcome

Extensive and informative immunological assessments of islet transplant recipients have been limited due, in part, to the smaller numbers of patients transplanted compared with solid organ trials. Limitations related to blood volume and the logistical challenges of collecting multiple posttransplant samples for drug levels as well as clinical and metabolic parameters also pose challenges. Several variables affect islet allograft outcome, including allo- and autoimmune responses to transplanted islets, β-cell mass and islet quality, efficacy of the immunosuppressive regimen and its effect on islet function, as well as glycemic control. In fact, much debate has centered on whether or not islet attrition is due to immune-mediated loss, death of overworked cells caused by insufficient mass, and/or diabetogenic effect of various immune intervention agents. In addition, many of these parameters may have differing effects based on the transplanted mass, with marginal mass transplants being more susceptible to immune-mediated or stress-induced loss. Recently, several studies have demonstrated immunological alterations in islet allograft patients. Posttransplant changes in lymphocytes and lymphocyte subsets were reported to be variable depending on the immune suppression used but have not yet been associated with graft status or specific clinical outcomes (1–4). Higher posttransplant cytotoxic T-cell precursor frequency against donor antigens was associated with poorer outcome at 6 months in recipients treated with sirolimus-based maintenance therapy but not tacrolimus–mycophenolate mofetil (5). In one study, cytokine production in allogeneic mixed lymphocyte reactions (MLRs) was skewed toward …

Deficient TNF-α and IFN-γ Production Correlates With Nondetectable Donor-Specific Cytotoxicity After Clinical Kidney Transplantation

We previously reported that no cytotoxic T-lymphocyte precursor frequencies (CTLpf) were found in 60% of patients on azathioprine or mycophenolate mofetil+Pred long after kidney transplantation. We questioned whether the absence of donor-specific CTLpf was associated with low levels of stimulatory Th1 (tumor necrosis factor [TNF]-alpha, interferon [IFN]-gamma) or high levels of regulatory Th2 (interleukin [IL]-4, IL-6, IL-10) cytokines. In this study, peripheral blood monocyte cells (PBMC) were stimulated with irradiated donor cells. After 7 days, cytokine production was determined by cytokine bead array, and CTLpf by limiting dilution assay. Patients with detectable CTLpf (> or =10/10(6) PBMC) had significantly higher levels of TNF-alpha (P=0.04) and IFN-gamma (P=0.02) than patients with nondetectable CTLpf (<10/10(6) PBMC). Donor-reactive IL-4, IL-6, and IL-10 production was comparable in both patient groups. Additionally, CTLpf was positively correlated with TNF-alpha (rs=0.54, P=0.0003) and IFN-gamma (rs=0.64, P<0.0001) production. The absence of donor-specific CTLp after transplantation correlates with low levels of stimulatory cytokines, not with elevated levels of regulatory cytokines.

Induction of human tumor‐associated differentially expressed gene‐12 (TADG‐12/TMPRSS3)‐specific cytotoxic T lymphocytes in human lymphocyte antigen‐A2.1–positive healthy donors and patients with advanced ovarian cancer

Tumor-associated differentially expressed gene-12 (TADG-12) is a serine protease recently found highly differentially expressed in epithelial ovarian cancer. The goal of this study was to identify potential immunogenic peptides derived from TADG-12 for immunotherapy of ovarian carcinoma. A bioinformatics approach (ie, the BIMAS algorithm, National Institutes of Health, http://bimas.dcrt.nih.gov/molbio/hla_bind) was used to identify multiple immunogenic peptides derived from TADG-12 that bind to human leukocyte antigen-A2.1 and elicit peptide-specific human cytotoxic T lymphocyte (CTL) responses in healthy individuals and in patients with advanced stage ovarian cancer. CD8+ CTL populations generated against 5 TADG-12-derived peptides were consistently able to induce lysis of autologous peptide-loaded target cells above background. Importantly, TADG-12 YLPKSWTIQV peptide-specific CTLs from healthy donors and ovarian cancer patients were found to effectively kill ovarian cancer cells naturally expressing TADG-12. Cytotoxicity was significantly inhibited by anti-human lymphocyte antigen (HLA)-A2.1 (BB7-2) and anti-HLA class I (W6 of 32) monoclonal antibodies, whereas natural killer-sensitive K562 cells were not lysed. TADG-12 YLPKSWTIQV peptide-specific CTL precursor frequency was low in peripheral blood leukocytes of normal donors and ovarian cancer patients, as determined by interferon-gamma production in enzyme-linked immunosorbent spot-forming cell assays. Intracellular cytokine expression measured by flow cytometry after OKT-3 monoclonal antibody stimulation showed a type 1 cytokine profile in YLPKSWTIQV peptide-specific CTLs. The TADG-12 YLPKSWTIQV peptide is an immunogenic epitope in ovarian tumors and may represent an attractive target for immunotherapy of ovarian cancer. These data may pave the way for TADG-12 peptide-derived cell-based therapy, including dendritic cell immunotherapy, for the vaccination of ovarian cancer patients harboring chemotherapy-resistant or residual disease.

T‐cell precursor frequencies and long‐term outcome following unrelated hematopoietic stem cell transplantation

Functional assays measuring alloreactivity of donor cells are desired to detect either cryptic epitopes inducing graft-vs.-host disease (GvHD) after human leukocyte antigen (HLA)-identical hematopoietic stem cell transplantation (HSCT) or permissible HLA mismatches. However, their value in predicting GvHD and survival is still limited. We determined the cytotoxic and helper T-cell precursor (CTLp and HTLp) frequencies by limiting dilution analysis (LDA) in 40 unrelated recipient/donor combinations. The median observation period at the time of this writing was 4.44 years (range from 0.1 to 11.28). Better overall survival was observed in patients with rather low host-specific CTLp and HTLp frequencies, whereas a trend toward high CTLp frequencies was seen in patients with higher incidence of acute GvHD, especially in patients mismatched in HLA-C. CTLp and HTLp frequencies did not correlate with the incidence of chronic GvHD and relapse. In conclusion, we detected a trend toward better overall survival of patient/donor pairs with low CTLp and HTLp frequencies, however, recommend to use LDA as an additional tool for identifying the most suitable donor when more than one fully HLA-matched stem cell donor is available.

Limiting dilution analysis of the allo-MHC anti-paternal cytotoxic T cell response. I: Normal primigravid and multiparous pregnancies.

Anti-paternal cytotoxic T lymphocyte precursor frequencies (CTLpF) were determined by limiting dilution analysis (LDA) in the peripheral blood of eight primigravid and seven multiparous women during the three trimesters of pregnancy. In five of these women the responses to cord blood lymphocytes (CBL) and paternal lymphocytes were also determined at the time of delivery and at 6 weeks post delivery. As controls, CTLpF against unrelated third party donors were determined. A wide range of CTLpF against all three groups of targets was found in both the primigravid and multiparous women, reflecting the wide range of frequencies found in random populations. These frequencies remained fairly constant during and 6 weeks after the pregnancy. Splitwell analysis demonstrated that the responses generated in our culture system were specific to the stimulator. The LDA data conform to single-hit kinetics, indicating that only cytotoxic T cells were limiting in the assay. Proliferative responses of maternal lymphocytes to paternal, cord blood and third party MHC antigens also remained unchanged as determined by time-course mixed lymphocyte reactions (MLR). Our data suggest that there is no significant allo-stimulation or suppression of the maternal immune system during normal pregnancy. The mother remains immunocompetent and is capable of both cytotoxic and proliferative responses to paternally-derived fetal MHC antigens. Our findings confirm that in normal pregnancy the trophoblast, which is devoid of classical MHC antigens, forms an effective immune barrier which prevents interaction of the maternal and fetal immune systems.