Revealing complete complex KIR haplotypes phased by long-read sequencing technology.

The killer cell immunoglobulin-like receptor (KIR) region of human chromosome 19 contains up to 16 genes for natural killer (NK) cell receptors that recognize human leukocyte antigen (HLA)/peptide complexes and other ligands. The KIR proteins fulfill functional roles in infections, pregnancy, autoimmune diseases and transplantation. However, their characterization remains a constant challenge. Not only are the genes highly homologous due to their recent evolution by tandem duplications, but the region is structurally dynamic due to frequent transposon-mediated recombination. A sequencing approach that precisely captures the complexity of KIR haplotypes for functional annotation is desirable. We present a unique approach to haplotype the KIR loci using single-molecule, real-time (SMRT) sequencing. Using this method, we have-for the first time-comprehensively sequenced and phased sixteen KIR haplotypes from eight individuals without imputation. The information revealed four novel haplotype structures, a novel gene-fusion allele, novel and confirmed insertion/deletion events, a homozygous individual, and overall diversity for the structural haplotypes and their alleles. These KIR haplotypes augment our existing knowledge by providing high-quality references, evolutionary informers, and source material for imputation. The haplotype sequences and gene annotations provide alternative loci for the KIR region in the human genome reference GrCh38.p8.

Directionality of non-permissive HLA-DPB1 T-cell epitope group mismatches does not improve clinical risk stratification in 8/8 matched unrelated donor hematopoietic cell transplantation.

In 8/8 HLA-matched unrelated donor (UD) hematopoietic cell transplants (HCT), HLA-DPB1 mismatches between alleles from different T-cell epitope (TCE) groups (non-permissive mismatches) are associated with significantly higher risks of mortality compared with those between alleles from the same TCE group (permissive mismatches); however, the relevance of mismatch directionality, that is (host vs graft (uni-directional HvG), graft vs host (uni-directional GvH) or both (bi-directional) in the non-permissive setting is unknown. We show here significantly higher in vitro relative responses (RR) to bi-directional mismatches compared with uni-directional HvG or GvH mismatches in a total of 420 one-way mixed lymphocyte reactions between 10/10 matched pairs (RR 27.5 vs 7.5 vs 15.5, respectively, P<0.001). However, in 3281 8/8 matched UD HCT for leukemia or myelodysplastic syndrome, the hazards of transplant-related mortality (TRM) were similar for uni-directional HvG or GvH mismatches and bi-directional mismatches (hazard ratio (HR) 1.32, P=0.001 vs HR 1.28, P=0.005 and HR 1.34, P=0.046), compared with permissive mismatches. Similar results were observed for overall survival. No statistical differences between the uni- and the bi-directional non-permissive groups were detected in pairwise comparisons for any of the outcomes tested. We conclude that consideration of directionality does not improve risk stratification by non-permissive HLA-DPB1 TCE mismatches in UD searches.

GvHD after umbilical cord blood transplantation for acute leukemia: an analysis of risk factors and effect on outcomes.

Using the Center for International Blood and Marrow Transplant Research (CIBMTR) registry, we analyzed 1404 umbilical cord blood transplantation (UCBT) patients (single (<18 years)=810, double (⩾18 years)=594) with acute leukemia to define the incidence of acute GvHD (aGvHD) and chronic GvHD (cGvHD), analyze clinical risk factors and investigate outcomes. After single UCBT, 100-day incidence of grade II-IV aGvHD was 39% (95% confidence interval (CI), 36-43%), grade III-IV aGvHD was 18% (95% CI, 15-20%) and 1-year cGvHD was 27% (95% CI, 24-30%). After double UCBT, 100-day incidence of grade II-IV aGvHD was 45% (95% CI, 41-49%), grade III-IV aGvHD was 22% (95% CI, 19-26%) and 1-year cGvHD was 26% (95% CI, 22-29%). For single UCBT, multivariate analysis showed that absence of antithymocyte globulin (ATG) was associated with aGvHD, whereas prior aGvHD was associated with cGvHD. For double UCBT, absence of ATG and myeloablative conditioning were associated with aGvHD, whereas prior aGvHD predicted for cGvHD. Grade III-IV aGvHD led to worse survival, whereas cGvHD had no significant effect on disease-free or overall survival. GvHD is prevalent after UCBT with severe aGvHD leading to higher mortality. Future research in UCBT should prioritize prevention of GvHD.

Limited HLA sequence variation outside of antigen recognition domain exons of 360 10 of 10 matched unrelated hematopoietic stem cell transplant donor-recipient pairs.

Traditional DNA-based typing focuses primarily on interrogating the exons of human leukocyte antigen (HLA) genes that form the antigen recognition domain (ARD). The relevance of mismatching donor and recipient for HLA variation outside the ARD on hematopoietic stem cell transplantation (HSCT) outcomes is unknown. This study was designed to evaluate the frequency of variation outside the ARD in 10 of 10 (HLA-A, -B, -C, -DRB1, -DQB1) matched unrelated donor transplant pairs (n = 360). Next-generation DNA sequencing was used to characterize both HLA exons and introns for HLA-A, -B, -C alleles; exons 2, 3 and the intervening intron for HLA-DRB1 and exons only for HLA-DQA1 and -DQB1. Over 97% of alleles at each locus were matched for their nucleotide sequence outside of the ARD exons. Of the 4320 allele comparisons overall, only 17 allele pairs were mismatched for non-ARD exons, 41 for noncoding regions and 9 for ARD exons. The observed variation between donor and recipient usually involved a single nucleotide difference (88% of mismatches); 88% of the non-ARD exon variants impacted the amino acid sequence. The impact of amino acid sequence variation caused by substitutions in exons outside ARD regions in D-R pairs will be difficult to assess in HSCT outcome studies because these mismatches do not occur very frequently.

Novel HLA-DP region susceptibility loci associated with severe acute GvHD.

Despite HLA allele matching, significant acute GvHD remains a major barrier to successful unrelated donor BMT. We conducted a genome-wide association study (GWAS) to identify recipient and donor genes associated with the risk of acute GvHD. A case-control design (grade III-IV versus no acute GvHD) and pooled GWA approach was used to study European-American recipients with hematological malignancies who received myeloablative conditioning non-T-cell-depleted first transplantation from HLA-A, -B, -C, -DRB1, -DQB1 allele level (10/10) matched unrelated donors. DNA samples were divided into three pools and tested in triplicate using the Affymetrix Genome-wide SNP Array 6.0. We identified three novel susceptibility loci in the HLA-DP region of recipient genomes that were associated with III-IV acute GvHD (rs9277378, P=1.58E-09; rs9277542, P=1.548E-06 and rs9277341, P=7.718E-05). Of these three single nucleotide polymorphisms (SNPs), rs9277378 and rs9277542 are located in non-coding regions of the HLA-DPB1 gene and the two are in strong linkage disequilibrium with two other published SNPs associated with acute GvHD, rs2281389 and rs9277535. Eighteen other recipient SNPs and 3 donor SNPs with a high level of significance (8E-07 or lower) were found. Our report contributes to emerging data showing clinical significance of the HLA-DP region genetic markers beyond structural matching of DPB1 alleles.

YKL-40 in allogeneic hematopoietic cell transplantation after AML and myelodysplastic syndrome.

YKL-40, also called chitinase-3-like-1 protein, is an inflammatory biomarker that has been associated with disease severity in inflammatory and malignant diseases, including AML, multiple myeloma and lymphomas. The objective of the current study was to assess the prognostic value of pretransplant recipient and donor plasma YKL-40 concentrations in patients with AML (n=624) or myelodysplastic syndrome (n=157) treated with allogeneic hematopoietic cell transplantation (HCT). In recipients, the plasma YKL-40 concentrations were increased when the HCT-comorbidity index was ⩾5 (P=0.028). There were no significant associations between plasma YKL-40 concentrations in recipients and any outcome measures. In donors with YKL-40 plasma concentrations above the age-adjusted 95th percentile, a trend toward increased grade II-IV acute GvHD in recipients was observed (adjusted hazard ratio 1.39 (95% confidence interval 1.00-1.94), P=0.050), with no significant associations with overall survival, treatment-related mortality or relapse. In conclusion, our study shows that YKL-40 does not aid risk stratification of patients undergoing allogeneic HCT, but suggests that YKL-40 may aid donor selection when multiple, otherwise equal, donors are available.

Unrelated donor search prognostic score to support early HLA consultation and clinical decisions.

A simple scoring system that can provide a quick search prognosis at the onset of an adult unrelated donor (URD) search could be a useful tool for transplant physicians. We aimed to determine whether patient human leukocyte Ag genotype frequency (GF) could be used as a surrogate measure of whether or not a potential 10/10 and/or 9/10 URD in the Be The Match Registry (BTMR) can be identified for the patient. GF was assigned on a training data set of 2410 patients that searched the BTMR using the reported ethnic group. A proportional odds model was used to correlate GF with defined search productivity categories as follows: 'Good' (>2 10/10), 'Fair' (1-2 10/10 or No 10/10 and >2 9/10) or 'Poor' (No 10/10 and <3 9/10). A second cohort (n=2411) was used to calculate the concordance by the ethnic group in all three categories. In addition, we validated against an independent cohort (n=1344) resolved as having a 10/10 or 9/10 matched URD. Across the ethnic groups, >90% of cases with 'Good' GF prognosis, 20-26% 'Fair' and <10% 'Poor' had a 10/10 URD. Although not a replacement for an actual URD search, GF offers a quick way for transplant physicians to get an indication of the likely search outcome.

Identification of high-risk amino-acid substitutions in hematopoietic cell transplantation: a challenging task.

Allogeneic hematopoietic cell transplantation (HCT) offers the potential to cure hematologic malignancies. In the absence of an HLA-matched donor, HLA mismatched unrelated donors may be used, although risks of GvHD and treatment-related mortality (TRM) are higher. Identification and avoidance of amino-acid substitution and position types (AASPT) conferring higher risks of TRM and GvHD would potentially improve the success of transplantation from single HLA mismatched unrelated donors. Using random forest and logistic regression analyses, we identified 19 AASPT associated with greater risks for at least one adverse transplant outcome: grade III-IV acute GvHD, TRM, lower disease-free survival or worse overall survival relative to HLA-matched unrelated donors and to other AASPT. When tested in an independent validation cohort of 3530 patients, none of the AASPT from the training set were validated as high risk, however. Review of the literature shows that failure to validate original observations is the rule and not the exception in immunobiology and emphasizes the importance of independent validation before clinical application. Our current data do not support avoiding any specific class I AASPT for unrelated donors. Additional studies should be performed to fully understand the role of AASPT in HCT outcomes.

The influence of interleukin-7 receptor α-chain haplotypes on outcome after allogeneic hematopoietic cell transplantation.

We investigated the influence of IL-7 receptor α-chain (IL-7Rα) gene haplotypes in donors on the outcome of haematopoietic cell transplantation (HCT). Unlike the association between single donor SNPs and HCT outcome found previously, only trends towards association were found here, due to 'dilution' of SNPs into haplotypes.

Risk associations between HLA-DPB1 T-cell epitope matching and outcome of unrelated hematopoietic cell transplantation are independent of HLA-DPA1.

HLA-DP antigens are beta-alpha heterodimers encoded by polymorphic HLA-DPB1 and -DPA1 alleles, respectively, in strong linkage disequilibrium (LD) with each other. Non-permissive unrelated donor (UD)-recipient HLA-DPB1 mismatches across three different T-cell epitope (TCE) groups are associated with increased mortality after hematopoietic SCT (HCT), but the role of HLA-DPA1 is unclear. We studied 1281 onco-hematologic patients after 10/10 HLA-matched UD-HCT facilitated by the National Marrow Donor Program. Non-permissive mismatches defined solely by HLA-DPB1 TCE groups were associated with significantly higher risks of TRM compared to permissive mismatches (hazard ratio (HR) 1.30, confidence interval (CI) 1.06-1.53; P=0.009) or allele matches. Moreover, non-permissive HLA-DPB1 TCE group mismatches in the graft versus host (GvH) direction significantly decreased the risk of relapse compared to permissive mismatches (HR 0.55, CI 0.37-0.80; P=0.002) or allele matches. Splitting each group into HLA-DPA1*02:01 positive or negative, in frequent LD with HLA-DPB1 alleles from two of the three TCE groups, or into HLA-DPA1 matched or mismatched, did not significantly alter the observed risk associations. Our findings suggest that the effects of clinically non-permissive HLA-DPB1 TCE group mismatches are independent of HLA-DPA1, and that selection of donors with non-permissive DPB1 TCE mismatches in GvH direction might provide some protection from disease recurrence.

Genotype List String: a grammar for describing HLA and KIR genotyping results in a text string.

Knowledge of an individual's human leukocyte antigen (HLA) genotype is essential for modern medical genetics, and is crucial for hematopoietic stem cell and solid-organ transplantation. However, the high levels of polymorphism known for the HLA genes make it difficult to generate an HLA genotype that unambiguously identifies the alleles that are present at a given HLA locus in an individual. For the last 20 years, the histocompatibility and immunogenetics community has recorded this HLA genotyping ambiguity using allele codes developed by the National Marrow Donor Program (NMDP). While these allele codes may have been effective for recording an HLA genotyping result when initially developed, their use today results in increased ambiguity in an HLA genotype, and they are no longer suitable in the era of rapid allele discovery and ultra-high allele polymorphism. Here, we present a text string format capable of fully representing HLA genotyping results. This Genotype List (GL) String format is an extension of a proposed standard for reporting killer-cell immunoglobulin-like receptor (KIR) genotype data that can be applied to any genetic data that use a standard nomenclature for identifying variants. The GL String format uses a hierarchical set of operators to describe the relationships between alleles, lists of possible alleles, phased alleles, genotypes, lists of possible genotypes, and multilocus unphased genotypes, without losing typing information or increasing typing ambiguity. When used in concert with appropriate tools to create, exchange, and parse these strings, we anticipate that GL Strings will replace NMDP allele codes for reporting HLA genotypes.

Polymorphism in the interleukin-7 receptor-alpha and outcome after allogeneic hematopoietic cell transplantation with matched unrelated donor.

Interleukin-7 (IL-7) is essential for T cell development in the thymus and maintenance of peripheral T cells. The α-chain of the IL-7R is polymorphic with the existence of SNPs that give rise to non-synonymous amino acid substitutions. We previously found an association between donor genotypes and increased treatment-related mortality (TRM) (rs1494555G) and acute graft versus host disease (aGvHD) (rs1494555G and rs1494558T) after hematopoietic cell transplantation (HCT). Some studies have confirmed an association between rs6897932C and multiple sclerosis. In this study, we evaluated the prognostic significance of IL-7Rα SNP genotypes in 590-recipient/donor pairs that received HLA-matched unrelated donor HCT for haematological malignancies. Consistent with the primary studies, the rs1494555GG and rs1494558TT genotypes of the donor were associated with aGvHD and chronic GvHD in the univariate analysis. The Tallele of rs6897932 was suggestive of an association with increased frequency of relapse by univariate analysis (P = 0.017) and multivariate analysis (P = 0.015). In conclusion, this study provides further evidence of a role of the IL-7 pathway and IL-7Rα SNPs in HCT.

16th IHIW: international histocompatibility working group in hematopoietic cell transplantation.

The International Histocompatibility Working Group is a collaborative international effort to understand the HLA and non-HLA genetics of the transplantation barrier. The Working Group is comprised of experts in the fields of histocompatibility and immunogenetics, hematopoietic cell transplantation and outcomes research. Data for 25 855 unrelated donor transplants were submitted in support of research studies for the 16th International Histocompatibility Workshop. Active investigation is in progress in seven key areas: the impact of HLA matching, role of race and ethnicity, identification of permissible HLA mismatches, haplotype-associated determinants, minor histocompatibility antigens, immune response genes and KIR genetics. New hypotheses for the 16th workshop were developed for immunogenetic studies in cord blood and haploidentical-related donor transplantation.

Identification by random forest method of HLA class I amino acid substitutions associated with lower survival at day 100 in unrelated donor hematopoietic cell transplantation.

The identification of important amino acid substitutions associated with low survival in hematopoietic cell transplantation (HCT) is hampered by the large number of observed substitutions compared with the small number of patients available for analysis. Random forest analysis is designed to address these limitations. We studied 2107 HCT recipients with good or intermediate risk hematological malignancies to identify HLA class I amino acid substitutions associated with reduced survival at day 100 post transplant. Random forest analysis and traditional univariate and multivariate analyses were used. Random forest analysis identified amino acid substitutions in 33 positions that were associated with reduced 100 day survival, including HLA-A 9, 43, 62, 63, 76, 77, 95, 97, 114, 116, 152, 156, 166 and 167; HLA-B 97, 109, 116 and 156; and HLA-C 6, 9, 11, 14, 21, 66, 77, 80, 95, 97, 99, 116, 156, 163 and 173. In all 13 had been previously reported by other investigators using classical biostatistical approaches. Using the same data set, traditional multivariate logistic regression identified only five amino acid substitutions associated with lower day 100 survival. Random forest analysis is a novel statistical methodology for analysis of HLA mismatching and outcome studies, capable of identifying important amino acid substitutions missed by other methods.

Evaluating the potential impact of mismatches outside the antigen recognition site in unrelated hematopoietic stem cell transplantation: HLA-DRB1*1454 and DRB1*140101.

DNA sequencing of 268 individuals drawn from four US populations carrying two unresolved DRB1*14 alleles differing only outside the antigen recognition site identified DRB1*1454 in the majority. A database of 4222 human leukocyte antigen (HLA)-matched hematopoietic stem cell transplantation donor-recipient pairs was queried to determine the number likely mismatched for DRB1*140101/DRB1*1454 but matched for class I loci. A power calculation suggests that more than 88,000 transplants among European Americans will be needed to identify sufficient 7/8 allele-matched pairs to evaluate the impact of the DRB1*140101/DRB1*1454 mismatch on transplant outcome. Molecular modeling of the HLA-DR interaction with the T-cell receptor and with CD4 suggests that the amino acid substitution distinguishing the two alleles will have minimal impact on allorecognition.

Effect of level of eicosapentaenoic acid on the transcriptional regulation of Δ-9 desaturase using a novel in vitro bovine intramuscular adipocyte cell culture model.

Ruminant fat is often perceived as having a negative impact on human health; however, the composition of the fat is under complex biochemical control and can be improved through strategic manipulation of the animal's diet. There were two major objectives of this study, namely (i) to develop and validate a primary bovine intramuscular adipocyte cell line and (ii) to examine the effect of eicosapentaenoic acid (EPA) on the transcriptional regulation of Δ-9 desaturase in vitro using the novel cell line. Intramuscular adipose tissue was obtained from the Musculus longissimus thoracis of a beef heifer. Mature adipocytes were isolated and cultured, and subsequently harvested and evaluated for lipid accumulation and the expression of genes regulating key functional adipocyte protein markers at passages 10, 20 and 30. Isolated cells were shown to accumulate lipid in culture over time. Fatty acid analysis by gas chromatography was carried out at passage 30. Thirteen fatty acids ranging from tetradecanoic acid (C14:0) to the polyunsaturated fatty acid, docosahexaenoic acid (C22:6), were easily detected and measured. High-quality total RNA was isolated from adipocytes and the expression of peroxisome proliferator-activated receptor-γ, fatty acid synthase, fatty acid-binding protein-4, adipocyte lipid-binding protein, CD36, Δ-9 desaturase, sterol regulatory element-binding protein (SREBP), microsomal triglyceride transfer protein and leptin genes were identified by reverse transcriptase-PCR and sequence analysis. Expression of the negative control, liver-specific hepatocyte nuclear factor-1alpha, was not detected. Adipocytes were subsequently incubated in medium containing 0, 50 or 100 µM EPA for 24 h. Increasing the EPA concentration of the culture media led to a linear increase in adipocyte EPA concentration (P < 0.01). Expression of Δ-9 desaturase mRNA was decreased five- and seven-fold, respectively, following 50 and 100 µM EPA incubation compared to the control. Gene expression of SREBP-1c was decreased by 6- and 18-fold in cells supplemented with 50 and 100 µM EPA, respectively, compared to the control. Regression analysis showed a negative linear relationship between EPA concentration and the gene expression of both Δ-9 desaturase (P < 0.001) and SREBP-1c (P < 0.001), while a significant positive relationship was observed between Δ-9 desaturase and SREBP-1c gene expression (P < 0.001). This is the first report demonstrating that EPA treatment of bovine intramuscular adipocyte cells decreased gene expression of both Δ-9 desaturase and SREBP-1c in vitro. The bovine adipocyte cell line developed here is an important resource for future studies facilitating less-expensive, rapid screening of research hypotheses and circumventing the limitations associated with the use of experimental animals including cost, inter-animal variation, pre-experimental management and ethics.

KIR2DL5 alleles mark certain combination of activating KIR genes.

Killer cell Ig-like receptors (KIR) control the immune response of NK cells and some T cells to infections and tumors. KIR genes evolve rapidly and are variable between individuals in their number, type and sequence. Here, we determined the nature of KIR2DL5 gene polymorphism in four ethnic groups using direct DNA sequencing method. Nine new sequences were discovered. Within the panel of 248 KIR2DL5-positive individuals, 14 KIR2DL5-sequences differing in coding regions were observed. They differed at only seven amino acid positions, and such limited polymorphism is consistent with its conserved nature throughout the hominoid lineage. Ethnic deviation was seen in the distribution of KIR2DL5A, KIR2DL5B and their alleles. African Americans had more KIR2DL5 alleles than other populations indicating that more polymorphisms are yet to be discovered in Africans. Linkage between KIR2DL5-alleles and certain activating-KIR genes were observed, but frequency of these linked clusters differed substantially between populations. Consequently, KIR2DL5 alleles can be used as markers to predict the activating-KIR gene content. Typing system distinguishing A*001 and B*002 alleles can serve as a powerful screening test to assess the content of most variable activating-KIR genes that have been implicated in human disease and in the outcome of hematopoietic stem cell transplantation.

Strategies and technical challenges in allele level Class II typing in 2578 bone marrow transplantation donor-recipient pairs.

Human leukocyte antigen typing of 2578 donor-recipient pairs whose transplantation was facilitated by the National Marrow Donor Program allowed for an in-depth analysis of the accuracy of high-volume allele level testing data. The methods employed provided allele level typing at DRB1/3/5, DQA1, DQB1, DPA1, and DPB1 using sequence-specific oligonucleotide probe hybridization (SSOPH), polymerase chain reaction (PCR) restriction fragment length polymorphism analysis, sequence specific PCR, and direct sequence-based typing (SBT). Each typing was independently tested by two laboratories in Phase 1, and in subsequent phases targeted samples were typed in duplicate by SBT to monitor typing quality. Comparison with prior transplant center typing was also evaluated. SSOPH detected discrepancies ranged from 0.6% at DPB1 to 5.1% at DQB1 in Phase 1. The majority of discrepancies, 62%, resulted from human error such as sample handling, result interpretation, or clerical errors. Alleles that are frequently discrepant have been identified in this predominantly white population.

New HLA haplotype frequency reference standards: high-resolution and large sample typing of HLA DR-DQ haplotypes in a sample of European Americans.

A collaborative study involving a large sample of European Americans was typed for the histocompatibility loci of the HLA DR-DQ region and subjected to intensive typing validation measures in order to accurately determine haplotype composition and frequency. The resulting tables have immediate application to HLA typing and allogeneic transplantation. The loci within the DR-DQ region are especially valuable for such an undertaking because of their tight linkage and high linkage disequilibrium. The 3798 haplotypes, derived from 1899 unrelated individuals, had a total of 75 distinct DRB1-DQA1-DQB1 haplotypes. The frequency distribution of the haplotypes was right skewed with haplotypes occurring at a frequency of less than 1% numbering 59 and yet constituting less than 12% of the total sample. Given DRB1 typing, it was possible to infer the exact DQA1 and DQB1 composition of a haplotype with high confidence (>90% likelihood) in 21 of the 35 high-resolution DRB1 alleles present in the sample. Of the DRB1 alleles without high reliability for DQ haplotype inference, only *0401, *0701 and *1302 were common, the remaining 11 DRB1 alleles constituting less than 5% of the total sample. This approach failed for the 13 serologically equivalent DR alleles in which only 33% of DQ haplotypes could be reliably inferred. The 36 DQA1-DQB1 haplotypes present in the total sample conformed to the known pattern of permissible heterodimers. Four DQA1-DQB1 haplotypes, all rare, are reported here for the first time. The haplotype frequency tables are suitable as a reference standard for HLA typing of the DR and DQ loci in European Americans.

Immunization with dendritic cells pulsed with tumor extract increases survival of mice bearing intracranial gliomas.

The purpose of this study is to investigate the efficacy of dendritic cell-mediated immunotherapy against intracranial gliomas. Cloned DC2.4 dendritic cells originating from C57BL/6 mice were pulsed with glioma GL261 cell extracts and administered i.p. to C57BL/6 mice with intracranial GL261 gliomas. The survival of mice with and without pulsed dendritic cells was monitored after intracranial implantation of the GL261 glioma cells. Fluorescence activated cell sorting (FACS) analysis showed that DC2.4 cells express high levels of MHC class I and class II molecules, costimulatory molecules B7-1 and B7-2, and the cell adhesion molecule ICAM-1. Antigen-presenting capabilities in these dendritic cells were initially characterized in vitro by a mixed lymphocyte reaction, showing that Balb/c CD4+ and CD8+ T cells were able to generate allogeneic responses to DC2.4 cells. Tumor extract-pulsed DC2.4 dendritic cells were then used for the treatment of C57BL/6 mice with syngeneic GL261 gliomas. Animals with intracranial GL261 gliomas and vaccinated i.p. with pulsed DC2.4 dendritic cells exhibited significantly enhanced survival, relative to animals treated with saline or non-pulsed DC2.4 cells alone. In addition, cured animals showed an increased delayed-type hypersensitivity response to GL261 cells and survived when rechallenged with intracranial GL261 gliomas. In summary these results indicate that dendritic cells pulsed with tumor extract can enhance immune responses to tumor antigen and therefore represent a potential immunotherapeutic approach for treating patients with intracranial gliomas.