Loss of an HLA haplotype in pancreas cancer tissue and its corresponding tumor derived cell line

Transcriptome-based identification of tumor-reactive and bystander CD8+ T cell receptor clonotypes in human pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is generally refractory to immune checkpoint blockade, although patients with genetically unstable tumors can show modest therapeutic benefit. We previously demonstrated the presence of tumor-reactive CD8+ T cells in PDAC samples. Here, we charted the tumor-infiltrating T cell repertoire in PDAC by combining single-cell transcriptomics with functional testing of T cell receptors (TCRs) for reactivity against autologous tumor cells. On the basis of a comprehensive dataset including 93 tumor-reactive and 65 bystander TCR clonotypes, we delineated a gene signature that effectively distinguishes between these T cell subsets in PDAC, as well as in other tumor indications. This revealed a high frequency of tumor-reactive TCR clonotypes in three genetically unstable samples. In contrast, the T cell repertoire in six genetically stable PDAC tumors was largely dominated by bystander T cells. Nevertheless, multiple tumor-reactive TCRs were successfully identified in each of these samples, thereby providing a perspective for personalized immunotherapy in this treatment-resistant indication.

The association between CD3+ and CD8+tumor-infiltrating lymphocytes (TILs) and prognosis in patients with pancreatic adenocarcinoma

BACKGROUND

Pancreatic adenocarcinoma (PDAC), with more than 250,000 deaths each year, is the eighth leading cause of death worldwide, with a five-year survival of less than 5% and a median recurrence time between 5 and 23 months. The association between PDAC and CD3⁺/CD8⁺ tumor-infiltrating lymphocytes (TILs) and the extent of tumor spread and clinical outcomes has been recently shown. This study aimed to determine and compare the density of TILs and their association with disease prognosis in patients with PDAC.

MATERIALS AND METHODS

In this study, we collected PDAC tissues and corresponding adjacent normal tissues from 64 patients with TIL-positive PDAC. The immunohistochemistry method was used for the detection of the expression levels of CD3⁺ and CD8⁺ TILs in PDAC tissues. Also, the completed follow-up history was evaluated for at least five years.

RESULTS

The frequency of intratumoral and peritumoral TILs was 20 (31.2%) and 44 (68.8%), respectively. The mean density of CD3⁺ TILs and CD8⁺ TILs was 67.73%±20.17% and 69.45%±17.82%, respectively. The density of CD3⁺ TILs and CD8⁺ TILs was not associated with overall survival nor metastasis-free survival of the patients and tumor grade. However, the density of TILs was significantly lower in those patients who experienced tumor recurrence than those without this recurrence.

CONCLUSION

TILs density was high in patients with PDAC. The density of both CD3⁺ and CD8⁺ TILs was significantly lower in patients who experienced tumor recurrence. Thus, this study suggests that tracking and determining the density of CD3⁺ and CD8⁺ TILs might be effective in predicting PDAC recurrence.

Copy Neutral LOH Affecting the Entire Chromosome 6 Is a Frequent Mechanism of HLA Class I Alterations in Cancer

Total or partial loss of HLA class I antigens reduce the recognition of specific tumor peptides by cytotoxic T lymphocytes favoring cancer immune escape during natural tumor evolution. These alterations can be caused by genomic defects, such as loss of heterozygosity at chromosomes 6 and 15 (LOH-6 and LOH-15), where HLA class I genes are located. There is growing evidence indicating that LOH in HLA contributes to the immune selection of HLA loss variants and influences the resistance to immunotherapy. Nevertheless, the incidence and the mechanism of this chromosomal aberration involving HLA genes has not been systematically assessed in different types of tumors and often remains underestimated. Here, we used SNP arrays to investigate the incidence and patterns of LOH-6 and LOH-15 in a number of human cancer cell lines and tissues of different histological types. We observed that LOH in HLA is a common event in cancer samples with a prevalence of a copy neutral type of LOH (CN-LOH) that affects entire chromosome 6 or 15 and involves chromosomal duplications. LOH-6 was observed more often and was associated with homozygous HLA genotype and partial HLA loss of expression. We also discuss the immunologic and clinical implications of LOH in HLA on tumor clonal expansion and association with the cancer recurrence after treatment.

The prevalence of HLA-I LOH in Chinese pan-cancer patients and genomic features of patients harboring HLA-I LOH

HLA-I LOH may facilitate immune evasion. However, large population studies on the prevalence of HLA-I LOH across different cancer types and in relation to mutational profiles are lacking, in particular, in the Chinese population. In this study, analysis was performed in 1504 advanced pan-cancer patients and 134 early-stage non-small-cell lung cancer patients using a 1021-gene panel. The consistency between the 1021-gene panel and whole-exome sequencing was evaluated in 45 samples, where concordant results were obtained in 95.6% (43/45) of the samples. Analytical results revealed that the prevalence of HLA-I LOH in tumor tissue presents considerable differences across cancer types. HLA-I LOH was relevant to genomic instability, reflected in higher tumor mutation burden level. HLA-I LOH occurs more frequently in MSS samples than in MSI-H samples. The alteration frequencies of p53 pathway, RTK/RAS pathway, Notch pathway, Hippo pathway, and Nrf2 pathway in HLA-I LOH group were significantly higher than that in HLA-I stable group (p < .0001, p < .0001, p = .032, p = .013, p = .003, respectively). In DNA damage response pathways, alterations in the checkpoint factor pathway and Fanconi anemia pathway are enriched in HLA-I LOH group (p < .0001, p = .023, respectively). Besides, HLA-I LOH was accompanied by higher mutation rates of several tumor suppressors, including TP53 and LRP1B. These results may shed light on follow-up tumor immunology research.

The interplay between innate and adaptive immunity in cancer shapes the productivity of cancer immunosurveillance

The immune system is a vital determinant of cancer and shapes its trajectory. Notably, the immune reaction to cancer harbors dual potential for suppressing or promoting cancer development and progression. This polarity of the immune response is determined, in part, by the character of the interplay between innate and adaptive immunity. On the one hand, the innate immune compartment is a necessary proponent of cancer immunity by supporting an immunostimulatory state that enables T cell immunosurveillance. However, in the setting of cancer, innate immune cells are commonly polarized with immune-suppressive properties and as a result, orchestrate a tolerogenic niche that interferes with the cytotoxic potential of tumor antigen-specific T cells. Here, we discuss the role of innate immunity as a positive and negative regulator of adaptive immunosurveillance; moreover, we highlight how tumor cells may skew leukocytes toward an immunosuppressive state and, as such, subvert the phenotypic plasticity of the immune compartment to advance disease progression. These observations establish the precedent for novel therapeutic strategies that aim to restore the tumor microenvironment to an immunoreactive state and, in doing so, condition and maintain the immunogenicity of tumors to yield deep and durable responses to immunotherapy.

B Cells in the Gastrointestinal Tumor Microenvironment with a Focus on Pancreatic Cancer: Opportunities for Precision Medicine?

We review state-of-the-art in translational and clinical studies focusing on the tumor microenvironment (TME) with a focus on tumor-infiltrating B cells (TIBs). The TME is a dynamic matrix of mutations, immune-regulatory networks, and distinct cell-to-cell interactions which collectively impact on disease progress. We discuss relevant findings concerning B cells in pancreatic cancer, the concepts of "bystander" B cells, the role of antigen-specific B cells contributing to augmenting anticancer-directed immune responses, the role of B cells as prognostic markers for response to checkpoint inhibitors (ICBs), and the potential use in adoptive cell tumor-infiltrating lymphocyte (TIL) products.

MHC/HLA Class I Loss in Cancer Cells

In this chapter I describe Tumour Immune Escape mechanisms associated with MHC/HLA class I loss in human and experimental tumours. Different altered HLA class-I phenotypes can be observed that are produced by different molecular mechanisms. Experimental and histological evidences are summarized indicating that at the early stages of tumour development there is an enormous variety of tumour clones with different MHC class I expression patterns. This phase is followed by a strong T cell mediated immune-selection of MHC/HLA class-I negative tumour cells in the primary tumour lesion. This transition period results in a formation of a tumour composed only of HLA-class I negative cells. An updated description of this process observed in a large variety of human tumors is included. In the second section I focus on MHC/HLA class I alterations observed in mouse and human metastases, and describe the generation of different tumor cell clones with altered MHC class I phenotypes, which could be similar or different from the original tumor clone. The biological and immunological relevance of these observations is discussed. Finally, the interesting phenomenon of metastatic dormancy is analyzed in association with a particular MHC class I negative tumor phenotype.

Gemcitabine alters the proteasome composition and immunopeptidome of tumour cells

The antigenic makeup of tumour cells can have a profound effect on the progression of cancer and success of immunotherapies. Therefore, one strategy to improve the efficacy of cancer treatments is to augment the antigens displayed by tumours. The present study explores how the recognition of tumour cells may be altered by non-cytotoxic concentrations of gemcitabine (GEM). Testing a panel of chemotherapeutics in human cancer cell lines in vitro, it was found that GEM increased surface expression of HLA-A,B,C and that underlying this were specific increases in β-2-microglobulin and immunoproteasome subunit proteins. Furthermore, the peptide antigen repertoire displayed on HLA class I was altered, revealing a number of novel antigens, many of which that were derived from proteins involved in the DNA-damage response. Changes in the nature of the peptide antigens eluted from HLA-A,B,C after GEM treatment consisted of amino acid anchor-residue modifications and changes in peptide length which rendered peptides likely to favour alternative HLA-alleles and increased their predicted immunogenicity. Signalling through the MAPK/ERK and NFκB/RelB pathways was associated with these changes. These data may explain observations made in previous in vivo studies, advise as to which antigens should be used in future vaccination protocols and reinforce the idea that chemotherapy and immunotherapy could be used in combination.

Enhanced killing of chordoma cells by antibody-dependent cell-mediated cytotoxicity employing the novel anti-PD-L1 antibody avelumab

Chordoma, a rare bone tumor derived from the notochord, has been shown to be resistant to conventional therapies. Checkpoint inhibition has shown great promise in immune-mediated therapy of diverse cancers. The anti-PD-L1 mAb avelumab is unique among checkpoint inhibitors in that it is a fully human IgG1 capable of mediating antibody-dependent cell-mediated cytotoxicity (ADCC) of PD-L1-expressing tumor cells. Here, we investigated avelumab as a potential therapy for chordoma. We examined 4 chordoma cell lines, first for expression of PD-L1, and in vitro for ADCC killing using NK cells and avelumab. PD-L1 expression was markedly upregulated by IFN-γ in all 4 chordoma cell lines, which significantly increased sensitivity to ADCC. Brachyury is a transcription factor that is uniformly expressed in chordoma. Clinical trials are ongoing in which chordoma patients are treated with brachyury-specific vaccines. Co-incubating chordoma cells with brachyury-specific CD8⁺ T cells resulted in significant upregulation of PD-L1 on the tumor cells, mediated by the CD8⁺ T cells' IFN-γ production, and increased sensitivity of chordoma cells to avelumab-mediated ADCC. Residential cancer stem cell subpopulations of chordoma cells were also killed by avelumab-mediated ADCC to the same degree as non-cancer stem cell populations. These findings suggest that as a monotherapy for chordoma, avelumab may enable endogenous NK cells, while in combination with T-cell immunotherapy, such as a vaccine, avelumab may enhance NK-cell killing of chordoma cells via ADCC.

Are changes in HLA Ags responsible for leukemia relapse after HLA-matched allogeneic hematopoietic SCT?

Loss of heterozygosity (LOH) has been shown to be associated with leukemia relapse after haploidentical transplantation. Whether such changes are an important cause of relapse after HLA-matched transplantation remains unclear. We retrospectively HLA-typed leukemic blasts for 71 patients with AML/myelodysplastic syndrome obtained from stored samples, and the results were compared with those obtained at diagnosis and/or before the transplant. No LOH or any other changes in HLA Ag were found in any of the samples tested post transplant as compared with pretransplant specimens. One patient had LOH in HLA class I Ag (HLA-A,-B and -C); however, these changes were present in the pretransplant sample indicating that they occurred before the transplant. We concluded that, in contrast with haploidentical transplantation, HLA loss does not have a major role as a mechanism of relapse after allogeneic transplantation with a closely HLA-matched donor.

MHC class I antigen processing and presenting machinery: organization, function, and defects in tumor cells

The surface presentation of peptides by major histocompatibility complex (MHC) class I molecules is critical to all CD8(+) T-cell adaptive immune responses, including those against tumors. The generation of peptides and their loading on MHC class I molecules is a multistep process involving multiple molecular species that constitute the so-called antigen processing and presenting machinery (APM). The majority of class I peptides begin as proteasome degradation products of cytosolic proteins. Once transported into the endoplasmic reticulum by TAP (transporter associated with antigen processing), peptides are not bound randomly by class I molecules but are chosen by length and sequence, with peptidases editing the raw peptide pool. Aberrations in APM genes and proteins have frequently been observed in human tumors and found to correlate with relevant clinical variables, including tumor grade, tumor stage, disease recurrence, and survival. These findings support the idea that APM defects are immune escape mechanisms that disrupt the tumor cells' ability to be recognized and killed by tumor antigen-specific cytotoxic CD8(+) T cells. Detailed knowledge of APM is crucial for the optimization of T cell-based immunotherapy protocols.

Targeting T cells with bispecific antibodies for cancer therapy

Bispecific antibodies (BiAbs) offer a unique opportunity to redirect immune effector cells to kill cancer cells. BiAbs combine the benefits of different binding specificities of two monoclonal antibodies (mAbs) into a single construct. This unique feature of BiAbs enables approaches that are not possible with single mAbs. Advances in antibody engineering and antigen profiling of malignant cells have led to the development of a number of BiAb formats and their combinations for redirecting effector cells to tumor targets. There have been significant advances in the design and application of BiAbs for intravenous and local injection.The initial barrier of cytokine storm has been partially overcome by more recent constructs that have improved clinical effectiveness without dose-limiting toxicities. Since the recent revival of BiAbs, there has been multiple, ongoing, phase I/II and III trials, and some promising clinical outcomes have been reported in completed clinical studies. This review focuses on arming T cells with BiAbs to create the 'poor man's cytotoxic lymphocyte'.

Adoptive T cell therapy promotes the emergence of genomically altered tumor escape variants

Adoptive T cell therapy has been proven effective against melanoma in mice and humans. However, because most responses are incomplete or transient, cures remain rare. To maximize the efficacy of this therapy, it will be essential to gain a better understanding of the processes which result in tumor relapse. We studied these processes using B16ova murine melanoma and adoptive transfer of OT-I T cells. Transfer of T cells as a single therapy provided a significant survival benefit for mice with established subcutaneous tumors. However, tumors which initially regressed often recurred. By analyzing tumors which emerged in the presence of a potent OT-I response, we identified a novel tumor escape mechanism in which tumor cells evaded T cell pressure by undergoing major genomic changes involving loss of the gene encoding the target tumor antigen. Furthermore, we show that these in vivo processes can be recapitulated in vitro using T cell/tumor cell co-cultures. A single round of in vitro co-culture led to significant loss of the ova gene and a tumor cell population with rapidly induced and diverse karyotypic changes. Although these current studies focus on the model OVA antigen, the finding that T cells can directly promote genomic instability has important implications for the development of adoptive T cell therapies.

False homozygosity results in HLA genotyping due to loss of chromosome 6 in a patient with acute lymphoblastic leukemia

Loss of heterozygosity (LOH) in chromosome 6p has been reported in a number of tumors and some hematologic malignancies, including ALL. LOH in chromosome 6p, on which the HLA genes are located, can give rise to false homozygosity results in HLA genotyping of patients with hematologic malignancies. Here we report false homozygosity results in HLA genotyping due to the loss of whole chromosome 6 in the neoplastic cells of a patient with ALL. A 33-yr-old Korean female patient was admitted for the evaluation of leukocytosis detected during a workup for headache. Her initial white blood cell count was 336.9×10(9)/L with 84% of blasts in the differential count. Precursor-B lymphoblastic leukemia was diagnosed from a subsequent bone marrow study. HLA high-resolution genotyping of the patient was requested at the time of diagnosis for possible hematopoietic stem cell transplantation. Homozygosity results (A(*)02:01, B(*)54:01, C(*)08:01, DQB1(*)04:01) were obtained, except for the DRB1 locus (DRB1(*)04:05, DRB1(*)11:01), in sequence-based typing. Conventional karyotyping of bone marrow metaphase cells revealed chromosomal abnormalities, with loss of multiple chromosomes including chromosome 6, and reduplication of the remaining chromosomes: 29,X,+X,+8,inv(9)(p11q13),+10,+14,+18,+21[15]/58,idemX2[3]/46,XX,inv(9)[2]. LOH at the HLA region was suspected and HLA genotyping was repeated with the peripheral blood in remission state after induction chemotherapy. All 5 HLA loci were typed as heterozygous (A(*)02:01, A(*)02:06, B(*)40:01, B(*)54:01, C(*)03:04, C(*)08:01, DRB1(*)04:05, DRB1(*)11:01, DQB1(*)03:01, DQB1(*)04:01). To avoid false HLA typing results in patients with hematologic malignancies, clinicians, as well as laboratory personnel, need to be aware of such problems and take appropriate precautions.

Loss of expression of antigen-presenting molecules in human pancreatic cancer and pancreatic cancer cell lines

Tumours evade immune recognition and destruction through loss or down-regulation of expression of antigen processing and antigen-presenting molecules such as the human leucocyte antigen (HLA class I) and transporter for antigen presentation (TAP). This study examined the expression of HLA class I, class II and TAP in human pancreatic carcinoma tissue and 19 immortalized pancreatic cancer lines using a panel of antibodies directed against allele-specific as well as monomorphic determinants of these molecules. In tissue samples, reduction or loss of HLA class I and TAP was observed in 76% of cases, loss or down-regulation of TAP expression in 53%. In pancreatic cell lines down-regulation or loss of class I and TAP expression was also observed frequently. However, reductions in class I and TAP expression were reversible upon exposure to interferon-gamma in vitro, suggesting a regulatory rather than structural defect in these genes. De novo class II expression was observed in 26% of tumours and 42% of cell lines and may reflect the differentiation status of the cells. The high rate of class I and TAP loss has implications for immunotherapy strategies for pancreatic cancer, as such changes could facilitate a selective growth advantage for malignant cells. However, the reinduction of expression of these molecules with cytokines such as interferon-gamma may ultimately allow their cytotoxic T cell-mediated destruction.

Loss or down-regulation of HLA class I expression at the allelic level in freshly isolated leukemic blasts

Loss or down-regulation of human leukocyte antigen (HLA) class I expression has been demonstrated in a variety of solid tumors. To date, such altered HLA expression has not been studied extensively in freshly isolated leukemic blasts. If it occurs, leukemic cells could escape T-cell surveillance as a consequence. Genotypes of nine leukemic cell lines were determined using a polymerase chain reaction for HLA classes I and II. Cells were also examined for HLA beta2-microglobulin, and allele-specific HLA protein expression using flow cytometry. Next, 44 samples of freshly isolated leukemic blasts from 43 patients with malignant hematological diseases were examined for allele-specific HLA expression using flow cytometry. Microsatellite analysis was performed to determine heterozygosity in the HLA region on chromosome 6. Genotype analysis for HLA class I together with microsatellite analysis demonstrated loss of HLA haplotype in HL-60 cells. No loss of HLA haplotype was observed in 44 samples of freshly isolated leukemic blasts. As reported previously, flow cytometric analysis rarely demonstrated loss or down-regulation of HLA expression at initial diagnosis (3/39; 7.7%); however, this was evident in two of five cases in relapse (40.0%), which contrasts with previous reports. In one patient with acute leukemia, HLA-A2 cell surface expression was present at initial diagnosis, lost at relapse, and completely restored after 48 h of culture in the presence of interferon-gamma. These results suggest loss of allele-specific HLA expression may be involved in the pathogenesis of relapse in patients with leukemia. The findings should be valuable in designing new strategies for clinical immunotherapy.

MHC Class I Antigens and Immune Surveillance in Transformed Cells

MHC class I antigens play a crucial role in the interaction of tumor cells with the host immune system, in particular, in the presentation of peptides as tumor-associated antigens to cytotoxic lymphocytes (CTLs) and in the regulation of cytolytic activity of natural killer (NK) cells. In this review we discuss the role of MHC class I antigens in the recognition and elimination of transformed cells and in the generation of tumor immune escape routes when MHC class I losses occur in tumors. The different altered MHC class I phenotypes and their distribution in different human tumors are the main topic of this review. In addition, molecular defects that underlie MHC alterations in transformed cells are also described in detail. Future research directions in this field are also discussed, including the laboratory analysis of tumor MHC class I-negative variants and the possible restoration of MHC class I expression.

Prospects for vaccine therapy for pancreatic cancer

Vaccine therapy is being tested for many forms of cancer. The identification of immunogenic target molecules in pancreatic cancer is providing candidates for new vaccines targeting this cancer. Early clinical trials have demonstrated safety for all vaccines tested. Immunogenicity has been variable, but some vaccines have induced responses in a high proportion of vaccinated patients. Most trials have to some extent been able to document increased survival associated with immune responses. Based on this, several vaccines are now entering controlled trials. Recent feasibility studies have demonstrated that vaccination can be combined with standard chemotherapy and indicate that some synergy effects are to be expected. This has paved the way for larger clinical studies combining gemcitabin with cancer vaccination. Characterization of regulatory pathways involved in negative control of the immune system and development of new drugs to intercept such pathways has opened for ways to manipulate the immune response in the clinical setting. Vaccination therapy for pancreatic cancer is moving into an exiting area with opportunities to attack not only the tumour as such, but also to deal with important regulatory mechanisms that have negatively influenced clinical efficacy so far.

Loss of human leucocyte antigen class I and gain of class II expression are early events in carcinogenesis: clues from a study of Barrett's oesophagus

BACKGROUND

Human leucocyte antigen (HLA) expression is altered in oesophageal carcinomas compared with normal tissue. It is unclear, however, whether this phenotype precedes malignant transformation or results as a consequence of it.

AIM

To investigate HLA class I and II expression in Barrett's oesophagus and normal squamous oesophageal tissue.

METHODS

Asian patients with Barrett's oesophagus (n = 64) and a control group (n = 60) with a normal oesophagus but without reflux symptoms were recruited using endoscopic and histopathological criteria. Tissue samples were stained with monoclonal antibodies specific for HLA-ABC, HLA-DR alpha chain or HLA-DP/DQ/DR, and scored semiquantitatively. The results of immunohistochemical staining were correlated with clinical and histopathological characteristics of patients.

RESULTS

Marked expression of HLA-ABC was observed in 50% of Barrett's oesophagus sections as compared with 68.3% of controls (p = 0.038). HLA-DR staining was seen in 51.6% of Barrett's oesophagus samples versus 11.7% of controls (p<0.001). Expression of HLA-DP/DQ/DR was evident in 73.4% of oesophageal intestinal metaplasia tissue as opposed to 18.3% of controls (p<0.001). Importantly, a total loss of HLA-ABC and a concomitant gain of HLA-DP/DQ/DR expression were seen in 37.5% of patients with Barrett's oesophagus but in none of the controls (p<0.001). Interestingly, this phenotype was associated positively with dysplasia (adjusted p, p* = 0.031) but negatively with non-steroidal anti-inflammatory drug use (p* = 0.004).

CONCLUSIONS

HLA class I expression is down regulated and class II expression is up regulated in Barrett's oesophagus. As these changes predate malignant transformation, altered major histocompatibility complex expression may be a key event in disease progression, possibly in facilitating evasion from immune surveillance.

Mechanisms of tumor evasion

The results from in vitro immunological experiments, murine tumor models and patients with cancer clearly demonstrate that tumors have multiple mechanisms to evade the immune response. During the early stages of tumor development malignant cells can be poor stimulators, present poor targets or become resistant to the innate immune response, while at later stages, progressively growing tumors impair the adaptive immune response by blocking the maturation and function of antigen presenting cells and causing alterations in T cell signal transduction and function. Preliminary results also suggest a correlation between some of these changes and an increased metastatic potential of the tumor cells, a diminished response to immunotherapy, and poor prognosis. Carefully coordinated basic research studies and clinical immunotherapy trials will be required to fully determine the impact on the outcome of the disease and the response to treatment. However, understanding the mechanisms used by tumor cells to evade the immune system could result in new therapeutic approaches for preventing and/or reversing these immune alterations and have the potential of improving the current results of immunotherapy trials.

Classical and nonclassical HLA class I antigen and NK Cell-activating ligand changes in malignant cells: current challenges and future directions

Changes in classical and nonclassical HLA class I antigen and NK cell-activating ligand expression have been identified in malignant lesions. These changes, which are described in this chapter, are believed to play a major role in the clinical course of the disease since both HLA class I antigens and NK cell-activating ligands are critical to the interaction between tumor cells and components of both innate and adaptive immune systems. Nevertheless, there is still debate in the literature about the biologic and functional significance of HLA class I antigen and NK cell-activating ligand abnormalities in malignant lesions. The reasons for this debate are reviewed. They include (i) the incomplete association between classical HLA class I antigen changes and the clinical course of the disease; (ii) the relatively limited number of malignant lesions that have been analyzed for nonclassical HLA class I antigen and NK cell-activating ligand expression; and (iii) the conflicting data regarding the role of immunoselection in the generation of malignant cells with HLA antigen and NK cell-activating ligand abnormalities. The technical limitations associated with the assessment of HLA antigen and NK cell-activating ligand expression in malignant lesions as well as the immunological and nonimmunological variables that may confound the impact of HLA antigen and NK cell-activating ligand changes on the clinical course of the disease are also discussed. Future studies aimed at overcoming these limitations and characterizing these variables are expected to provide a solution to the current debate regarding the significance of HLA class I antigen and NK cell-activating ligand abnormalities in malignant lesions.

High frequency of homozygosity of the HLA region in melanoma cell lines reveals a pattern compatible with extensive loss of heterozygosity

Malignant transformation of cells is frequently associated with abnormalities in human leukocyte antigen (HLA) expression. MHC class I loss or down-regulation in cancer cells is a major immune escape route used by a large variety of human tumours to evade antitumour immune responses mediated by cytotoxic T lymphocytes. The goal of our study was to explore HLA genotyping and phenotyping in a variety of melanoma tumour cell lines. A total of 91 melanoma cell lines were characterised for HLA class I and II genotype. In addition, 61 out of the 91 cell lines were also analysed for HLA class I and II cell surface molecule expression by flow cytometry. Unexpectedly, we found that 19.7% of the melanoma cell lines were homozygous for HLA class I genotypes, sometimes associated with HLA class II homozygosity (8.79%) and sometimes not (10.98%). The frequency of homozygosity was significantly higher compared with the control groups (1.6%). To identify the reasons underlying the high frequency of HLA homozygosity we searched for genomic deletions using eight pairs of highly polymorphic microsatellite markers covering the entire extended HLA complex on the short arm of chromosome 6. Our results were compatible with hemizygous deletions and suggest that loss of heterozygosity on chromosome arm 6p is a common feature in melanoma cell lines. In fact, although autologous normal DNA from the patients was not available and could not be tested, the retention in some cases of heterozygosity for a number of microsatellite markers would indicate a hemizygous deletion. In the rest of the cases, markers at 6p and 6q showed a single allele pattern indicating the probable loss of part or the whole of chromosome 6. These results led us to conclude that loss of heterozygosity in chromosome 6 is nonrandom and is possibly an immunologically relevant event in human malignant melanoma. Other well-established altered HLA class I phenotypes were also detected by flow cytometry that correspond to HLA class I total loss and HLA-ABC and/or specific HLA-B locus down-regulation.

Control of T-Cell–Mediated Immune Response by HLA Class I in Human Pancreatic Carcinoma

Purpose: Cell surface HLA class I molecules present peptides derived from human cellular proteins to T cells. In the present study, we investigated the expression of HLA class I in human pancreatic carcinoma.

Experimental Design: The expression of HLA class I antigen and the extent of tumor infiltration by T cells were investigated in 46 primary tumors and in 14 metastases of pancreatic cancer by standard immunohistochemistry.

Results: The locus-specific expression of HLA I was reduced in 61% of primary tumors and in 93% of metastases. The total loss of this molecule complex was detected in 6% of primary tumors and in 43% of metastases. Pancreatic carcinoma and peritumoral tissue showed a significantly higher infiltration by CD3+, CD4+, and CD8+ T-cells compared with the tumor-distant pancreatic tissue. The negative expression of HLA class I was uniformly accompanied by a low density of tumor-infiltrating cytotoxic T-cells whereas the HLA class I–positive tumors were characterized by a substantial lymphocyte accumulation. However, the infiltration by cytotoxic T-cells was not correlated with the density of tumor cells. Patients with a high accumulation of cytotoxic cells showed a longer median survival.

Conclusions: Pancreatic carcinoma frequently induces a cellular immune response that results in intratumoral and peritumoral T-cell infiltration. The expression of HLA class I is frequently lost in pancreatic carcinoma, which represents an effective mechanism to escape the tumor infiltration by cytotoxic T-cells. However, the infiltration by cytotoxic cells represents a favorable prognostic sign in pancreatic cancer patients.

Retargeting T cells and immune effector cells with bispecific antibodies

The development of BiAbs for therapeutic applications in cancer shows promise. As our understanding of effector cell receptor biology for triggering of cytotoxic functions improves and the behavior of TAA and the targeting antibody engagement is elucidated, customized BiAb reagents can be engineered to optimize in vivo or ex vivo arming of T cells for targeting tumors. Additionally, other variables that require consideration in the equation for successful T cell immunotherapy include: the type of effector cells, their state of activation, the type of effector receptor being activated or tareeted. the presence of Tregs, the affinity of the anti-effector cell antibody and the anti-TAA antibody, the type of BiAb (mouse, humanized, or human), the number of binding sites for the T cells or TAA, the presence or absence of decoy antigen, whether the TAA modulates after being engaged by antibody, the type of tumor, the tumor burden, and last, but not least, the amount of 'immunologic' space available for the adoptively transferred cells to expand and function.

Loss of heterozygosity in the HLA class I region in human pancreatic cancer

An altered human leukocyte antigen (HLA) class I expression constitutes an important tumor-escape mechanism counteracting T-cell mediated immune responses. We utilized the technique of microsatellite analysis to characterize the loss of heterozygosity (LOH) in the HLA class I region in 24 samples of patients with human ductal pancreatic carcinoma. The expression of HLA class I and the infiltration by T cells were studied in parallel by standard immunohistochemistry. The present study demonstrates LOH in the HLA class I region in five patients with pancreatic carcinoma. Immunohistochemical analysis showed that pancreatic carcinomas were frequently characterized by a total or partial loss of expression in HLA class I antigen. The positive or negative LOH status corresponded with the expression analysis in eight cases. Reduction of HLA class I expression without LOH was found in 14 cases. Lymphocyte infiltration with CD3+, CD4+, and CD8+ T cells did not show significant differences between LOH-positive and LOH-negative tumors. In conclusion, LOH does not seem to be the only factor for the reduced expression of HLA class I antigen as well as for the T-cell infiltration in this type of tumor.

A comprehensive in vitro characterization of pancreatic ductal carcinoma cell line biological behavior and its correlation with the structural and genetic profile

There are a large number of stable pancreatic ductal carcinoma cell lines (PDCL) that are used by researchers worldwide. Detailed data about their differentiation status and genetic alterations are present in the literature, but a systematic correlation with cell biological behavior is often lacking. PDCL ( n=12) were clustered by source of tumor cell (ascites, primary tumor, metastasis), and the data of functional cell biology were correlated with the reported structural and genetic profiles. Major histocompatibility complex expression, chemosensitivity and aneuploidia appeared to be related to the source of PDCL, and proliferative capacity appeared to be related to the grade of differentiation. No correlation between genetic/structural features of PDCL and biological behavior was found. All the cell lines appeared generally insensitive to in vitro treatment with 5-fluorouracil and showed variable degrees of susceptibility to gemcitabine, raltitrexed and oxaliplatin. All the PDCL showed resistance to Fas-mediated apoptosis but were significantly sensitive to the pro-apoptotic effect of inflammatory cytokines [interleukin (IL)-1beta, tumor necrosis factor (TNF)alpha and interferon gamma]. PDCL were characterized for the secretion of several factors relevant to the tumor-immune cross talk. Vascular endothelial growth factor, CCL2, CCL5 and transforming growth factor beta were the factors most frequently released; less frequent was the secretion of CXCL8, CCL22, IL-6 and sporadically CXCL12, IL-10 and hepatocyte growth factor. The cytokines IL-1beta and TNFalpha were always undetectable. In conclusion, a clear correlation between structural/genetic features and function could not be detected, suggesting the weakness of a "morphological" classification for the in vitro studies of pancreatic cancer.

Expression of HLA class I/II antigens and T cell immune response in human neuroendocrine tumors of the pancreas

Peptide presentation by HLA class I and II antigens regulates specific antigen recognition by T cells. The present study aimed to investigate T cell infiltration and its relation to HLA antigen expression in pancreatic neuroendocrine tumors. Fresh tissue samples were collected from five insulinomas and six other neuroendocrine tumors (one gastrinoma, one glucagonoma, two carcinoid, and two neuroendocrine carcinomas). Normal pancreatic and splenic tissue samples were used as controls. Investigation of infiltrating lymphocyte populations, as well as staining of HLA class I and II antigens, were performed by standard immunohistochemistry. The majority of investigated tumors demonstrated an intratumoral infiltration by CD3+, CD4+ and CD8+ T cells that was significantly higher than in normal pancreatic islets. Only a minority of tumor-infiltrating T cells showed the CD45RO+ phenotype. The expression of HLA class I antigen was altered in 10 of 11 tumors. A loss of beta-2microglobulin represented the most frequent type of alteration to HLA class I expression, although the total loss of HLA class I was found in only one case of neuroendocrine carcinoma. HLA class II molecules were expressed by endothelial and lymphoid cells and not by tumor cells. In conclusion most neuroendocrine pancreatic tumors induce a T cell mediated immune response resulting in an intratumoral infiltration with CD3+, CD4+ and CD8+ T cells. Loss of beta-2microglobulin is a frequent alteration in these tumors, which may influence the normal function of the HLA class I antigen complex. In contrast to malignant tumors of the exocrine pancreas, expression of HLA class II was absent in neuendocrine pancreatic tumor cells.

Tumour immunology, vaccination and escape strategies

Our increasing knowledge of the mechanisms by which tumour cells escape immune effector cells is helping to establish new approaches to therapeutic vaccination against tumour development. One of the escape mechanisms used by tumour cells is the generation of multiple variants with different HLA phenotypes. These MHC class I phenotypic alterations play a key role in the tumour-host scenario, as they are crucial molecules for antigen presentation to T cells and modulation of natural killer (NK) cell activity. This review presents evidence indicating that tumours develop sophisticated MHC phenotypes that allow them to escape immune surveillance. We evaluate the importance of these alterations in terms of the potential development of therapeutic approaches to immune vaccination.

MHC class I antigens, immune surveillance, and tumor immune escape

Oncogenic transformation in human and experimental animals is not necessarily followed by the appearance of a tumor mass. The immune system of the host can recognize tumor antigens by the presentation of small antigenic peptides to the receptor of cytotoxic T-lymphocytes (CTLs) and reject the nascent tumor. However, cancer cells can sometimes escape these specific T-cell immune responses in the course of somatic (genetic and phenotypic) clonal evolution. Among the tumor immune escape mechanisms described to date, the alterations in the expression of major histocompatibility complex (MHC) molecules play a crucial step in tumor development due to the role of MHC antigens in antigen presentation to T-lymphocytes and the regulation of natural killer cell (NK) cell function. In this work, we have (1) updated information on the mechanisms that allow CTLs to recognize tumor antigens after antigen processing by transformed cells, (2) described the altered MHC class I phenotypes that are commonly found in human tumors, (3) summarized the molecular mechanisms responsible for MHC class I alteration in human tumors, (4) provided evidence that these altered human leukocyte antigens (HLA) class I phenotypes are detectable as result of a T-cell immunoselection of HLA class I-deficient variants by an immunecompetent host, and (5) presented data indicating the MHC class I phenotype and the immunogenicity of experimental metastatic tumors change drastically when tumors develop in immunodeficient mice.

Complete loss of HLA class I antigen expression on melanoma cells: a result of successive mutational events

Alterations in the surface expression of HLA class I molecules have been described as a strategy of tumors to evade recognition by cytotoxic T cells. We detected complete loss of HLA class I antigen presentation for 2 tumor cell lines from 1 melanoma patient, the first originated from a regional lymph node lesion diagnosed simultaneously with the primary tumor and the second established 8 months later from a metastatic pleural effusion sample. Antigen presentation was not inducible with IFN-gamma but could be restored after transfection of tumor cells with b2m cDNA, indicating a defect in b2m expression. Analysis of the nature of this defect revealed that it originated from at least 2 mutational events affecting both copies of the b2m gene: a microdeletion of 498 bp in one b2m gene, including its entire exon 1, and a macrodeletion involving the entire copy of the second b2m gene. Microsatellite analysis pointed to the macrodeletion by demonstrating LOH for several specific markers on the long arm (q) of chromosome 15. Structural imbalance of 15q was verified by FISH. FISH studies also indicated the coexistence of a structurally abnormal variant of chromosome 15q with 2 apparently entire chromosomes 15q harboring the homozygous b2m microdeletion. Block of b2m expression in tumor cells builds a barrier to immunotherapy of cancer patients, and its early incidence should be of major consideration in the development and design of immunotherapeutic strategies.

Analysis of HLA-E expression in human tumors

Downregulation of MHC class Ia molecule expression is a widespread mechanism used by tumor cells to escape antitumor T-cell-mediated immune responses. However, it is not known why NK cells cannot lyse these MHC class-Ia-deficient tumor targets. Tumors must select additional routes of escape from NK cells. An attractive hypothesis is that the aberrant expression of nonclassical HLA class Ia molecules in tumors provides the required inhibitory signal to NK cells, rendering tumor cells resistant to NK lysis. To analyze the possible role of HLA-E molecules in providing tumor cells with an NK escape mechanism, we studied the cell surface expression of this HLA class Ib molecule in a variety of tumor cell lines with well-defined HLA class Ia alterations. Tests were done with the monoclonal antibody 3D12 recognizing cell surface HLA-E molecules. Our results indicate that HLA-E was mainly detected in leukemia-derived cell lines. In addition, HLA-E was detected in tumor cell lines of different origin. This expression was related with the availability of free beta(2)-microglobulin (beta(2)m) in the cytoplasm of tumor cells. Expression was detected in tumor cell lines showing an imbalance in heavy chain/beta(2)m expression, particularly in tumor cell lines with alterations in the expression of heavy-chain genes. Several lines of evidence favor these conclusions: (1) In the FM55 and NW145 melanoma tumor systems, the reduction in HLA class Ia expression paralleled the increased cell surface detection of HLA-E. (2) A cervical tumor (808) and a melanoma cell line (R22.2) expressing a single HLA-A1 allele also expressed HLA-E. (3) The addition of human beta(2)m to tumor cell lines that expressed the HLA-E(G) allele increased HLA-E cell surface expression. (4) There was no HLA-E cell surface expression in tumor cell lines with total loss of HLA class Ia expression, including cell lines with low transcription of HLA class I heavy chains or with beta(2)m mutations. Our findings suggest that the biological consequences of these cumulative genetic and molecular changes in tumor cells lead to the appearance of HLA-E in a limited number of tumor cell lines with peculiar phenotypic and genotypic characteristics, namely: HLA-class Ia downregulation, free beta(2)m and HLA-E(G) genotype. The aberrant HLA-E expression might be of particular biological relevance in those HLA tumor phenotypes that express a single HLA-A allele when NK inhibition is markedly reduced due to the downregulation of HLA-B and -C alleles.

Hemizygous deletions in the HLA region account for loss of heterozygosity in the majority of diffuse large B-cell lymphomas of the testis and the central nervous system

Loss of heterozygosity (LOH) is a major mechanism for inactivation of tumor-suppressor genes and has been observed in various solid tumors and lymphomas. The human leukocyte antigen (HLA) region is located at chromosome band 6p21.3, and loss or alteration of this region may provide tumor cells with a mechanism to escape from the immune system. We previously identified small homozygous deletions within the HLA class II region in many of the diffuse large B-cell lymphomas (DLCLs) of the central nervous system (CNS) and the testis. In the present study, we focused on the mechanism leading to LOH in the HLA region. Twenty microsatellite markers, of which 12 were specific for HLA, were applied on 11 extranodal DLCLs of the CNS and 28 of the testis. Additionally, fluorescence in situ hybridization with seven HLA-specific probes and a centromere 6-specific probe was performed on 20 cases to study the mechanism of LOH. In contrast to previously published data on spontaneously mutated lymphoblastoid cell lines, intrachromosomal hemizygous deletion, not mitotic recombination, was the major cause of LOH of the HLA region in these lymphomas. However, opposed to data in colorectal cancer, these deletions were rarely (one of nine cases) associated with an interchromosomal rearrangement such as a translocation.

Frequency and genetic basis of MHC, beta-2-microglobulin and MEMO-1 loss of heterozygosity in sporadic breast cancer

The Human Leukocyte Antigen (HLA) class I molecules are critical factors in T cell recognition of abnormal, including neoplastic, cells. Loss of HLA class I expression phenotypes, as defined by immunohistochemistry-based tests, have been previously described in many types of cancer. Here we describe a microsatellite marker DNA-based loss of heterozygosity (LOH) analysis of three distinct chromosomal regions which have been implicated in HLA class I expression on a cohort of 99 unselected sporadic breast cancer samples. These regions comprise the 4Mb major histocompatibility complex (MHC) region on chromosome 6p, which contains the HLA class I heavy chain loci and other genes responsible for antigen processing, the HLA class I light chain (beta-2-microglobulin, beta2m) gene on chromosome 15q, and the putative HLA class I modifier of methylation gene (MEMO-1) on chromosome 1p. Additional chromosome 6 markers were also employed to determine the likely genetic mechanism for MHC loss. We show that 25/99 (25%) of samples show allelic loss within the MHC, 28/95 informative samples (29%) show allelic loss of beta2m and 21/76 informative samples (28%) show allelic loss of MEMO-1. Approximately half of the samples are predicted to have compromised HLA class I gene expression due to LOH at one and/or other of these three loci. Sequencing of the remaining beta2m allele in samples displaying beta2m LOH failed to detect any additional intragenic mutations. Analysis of the frequency of samples showing LOH at either 0, 1, 2 or 3 of the genomic regions analyzed suggested clustering of tumors into either 'no loci loss' or '3 loci loss' categories. These results reveal major underlying genetic causes for the high level of HLA class I expression loss seen in breast cancer.

Impaired surface antigen presentation in tumors: implications for T cell-based immunotherapy

The identification of tumor-associated antigens has suggested new possibilities for cancer therapy. However, multiple mechanisms may contribute to the ability of tumor to escape antitumor immune responses. Tumor antigen heterogeneity, modulation of HLA expression and immune suppressive mechanisms may occur at any time during tumor cell progression, and can affect the outcome of therapeutic immune intervention. In particular, the appearance of altered HLA class I phenotypes during tumor development may have important biological and medical implications due to the role of these molecules in T and NK cell functions. Exhaustive tumor tissue studies are necessary before deciding whether a particular patient is suitable for inclusion in T cell-based immunotherapy protocols.

Tumor-specific cytotoxic T lymphocyte responses against chondrosarcoma with HLA haplotype loss restricted by the remaining HLA class I allele

Although loss of HLA expression by malignant cells has also been demonstrated, it has not been clarified how the loss of HLA expression observed in vitro actually results in immune escape. We demonstrated two major findings: (i) a part of chromosome 6 coding for HLA haplotypes was deleted from the genome of chondrosarcoma cell line, OUMS-27; furthermore, immunohistostaining for HLA-A11 showed that the original chondrosarcoma tissue lost the expression of HLA-A11, implicating that HLA haplotype loss was already present in the original tumor tissue and (2) HLA class I-restricted and autologous tumor-specific cytotoxic T cells (CTL) were generated from peripheral blood lymphocytes of the patient with chondrosarcoma, from whom OUMS-27 originated. This CTL line was maintained by weekly stimulation with OUMS-27, and lysed OUMS-27 in an HLA-A24 dependent manner but did not either K562 or autologous (EBV)-transformed B cells. These observations indicated that OUMS-27 and its original tumor are still immunogenic and can present antigen peptides with the remaining HLA-A24, even if HLA expression is partially lost. Tumor specific immunotherapy can be applied to the treatment of malignancies, even if HLA expression is partially lost.

Analysis of HLA class I expression in different metastases from two melanoma patients undergoing peptide immunotherapy

We characterized the HLA class I alterations in five metastases obtained from two patients with melanoma immunized with Melan A/MART-1, tyrosinase and gp100 tumor peptides. All three metastases analyzed in the first patient (NW145) showed a similar HLA class I alteration with a dual population of melanoma cells. One population was HLA class I antigen positive and the other had loss of heterozygosity (LOH) in the short arm of chromosome 6 leading to an HLA haplotype loss (A02011, B4007, Cw1). The absence of HLA-A2 antigen may explain why this patient did not develop HLA-A2 restricted, Melan A/MART-1 specificity immunization, since this HLA molecule is the restriction element for the tumor peptides used. However, this HLA-deficient population was not selected after peptide immunotherapy. The primary tumor in this patient presented LOH in region 6q, but only in the vertical growth phase of the lesion, whereas LOH at 6p was observed only in DNA from metastatic material. The second patient (NW16) also presented two metastatic lesions with an identical HLA molecular defect, i.e. HLA B locus downregulation (HLA B51011: serological B51; B1503: serological B70). One lesion expressed the tumor antigen (Melan A/ MART-1), but the other did not. Interestingly, the antigen-positive metastasis regressed after peptide immunotherapy, whereas the other progressed rapidly. These findings provide the first indication that multiple metastases generated in the same host can have identically altered HLA class I phenotypes.

Investigation of HLA class I downregulation in breast cancer by RT-PCR

Downregulation of HLA class I antigen expression has been reported in a significant proportion of primary breast carcinomas suggesting an escape mechanism from CTL mediated lysis leading to tumor dissemination and metastasis. We have previously reported the biochemical and immunohistochemical analysis of HLA total class I (W6/32 mAb), alpha-chain (Q1/28,TP25.99 mAbs) and beta(2)-microglobulin (Namb-1 mAb) subunits expression in 25 primary breast carcinomas. This study at protein level resulted in the observation of three different HLA class I expression patterns by both techniques: high, low, and absent downregulation patterns. To better characterize the HLA class I antigens downregulation we extended such analysis also at RNA level by RT-PCR using HLA-A, HLA-B, HLA-C, and beta(2)-microglobulin specific primers either in breast cancer or normal tissues derived from the same patient. None (100%) of the alpha-chain genes analyzed in patient tumor tissues showed significant reduction of expression. In 10 patients out of 25 (40%) the beta(2)-microglobulin gene showed complete loss of expression compared with the corresponding normal tissue counterpart, which showed a constitutive expression, whereas in 2 patients (12.5%) its expression was comparable with the normal counterpart. Sequence analysis at genomic level revealed no defects affecting beta(2)-microglobulin gene in those patients showing lack of expression. Also TAP1 and TAP2 genes expression were investigated in order to confirm or exclude involvement of the MHC class I molecules assembling machinery. The RT-PCR approach mainly confirmed our beta(2)-microglobulin biochemical analysis indicating that in breast cancer specimens it is possible to address the HLA class I gene downregulation as a phenomenon occurring at post-transcriptional level mainly affecting the beta(2)-microglobulin gene expression.

Immunoselection by T lymphocytes generates repeated MHC class I-deficient metastatic tumor variants

Alteration of MHC class I molecule expression is a widespread mechanism used by tumor cells to evade T cell responses. It has long been proposed that the origin of these MHC class I-negative or -deficient tumor variants is T cell immune selection. However, there are no experimental or clinical data to substantiate this hypothesis, and this issue is currently the subject of debate. Here we report that an H-2 class I-negative fibrosarcoma tumor clone generated MHC class I-negative spontaneous lung metastases in immunocompetent syngeneic BALB/c mice. Interestingly, the same B9 clone generated MHC class I-positive metastatic nodes, under basal conditions, in athymic nu/nu BALB/c mice. This phenomenon was observed in the metastatic nodules generated after a period of in vivo growth but not in the primary tumors growing locally in the footpad. These findings support the hypothesis that the H-2 phenotype of metastatic nodes is influenced by the T cell repertoire of the host, since in the absence of this T cell pressure (i.e., in nude mice) the metastatic nodes 'recovered' H-2 class I expression. In addition, 2 different phenotypes were found when the metastatic nodules obtained from immunocompetent mice were treated with IFN-gamma. One phenotype, present in 83% of the colonies, was characterized by resistance of the Ld molecule to IFN-gamma induction, due to a deletion involving the Ld gene. The second phenotype (17% of the colonies) was similar to the original B9 clone and was characterized by the response of K, D and L class I genes to IFN-gamma. These data provide evidence that the changes in MHC class I expression during tumor development might not be random but could be predictable.

C-terminal epitope tagging facilitates comparative ligand mapping from MHC class I positive cells

Purification of specific class I molecules prior to peptide ligand characterization is complicated by the presence of multiple class I proteins in most cell lines. Immortalized B, T, and tumor cell lines typically express endogenous HLA-A, -B, and -C; and most individuals from which the cell lines are derived are heterozygous at these loci. Antibodies specific for a particular HLA molecule may be used for purification, but allele-specific antibodies can be biased by ligands occupying the peptide-binding groove. Through the use of C-terminal tagging, we have developed a method of soluble HLA production such that downstream purification does not skew the peptide analysis of the examined molecule. Comparison of peptides eluted from HLA class I molecules with and without C-terminal tags demonstrates that addition of a tag does not abrogate the peptide binding specificity of the original molecule. Both pooled Edman sequencing and mass spectrometric sequencing identified no substantial differences in peptides bound by untailed, 6-HIS-tailed, and FLAG-tailed class I molecules, demonstrating that the peptide specificity of a given molecule is not distorted by either tag. This production methodology bypasses problems with isolation of specific molecules and permits ligand mapping and epitope discovery in a variety of pathogen-infected and tumor cell lines.

Extensive genetic alterations of the HLA region, including homozygous deletions of HLA class II genes in B-cell lymphomas arising in immune-privileged sites

In B-cell lymphomas, loss of human leukocyte antigen (HLA) class I and II molecules might contribute to immune escape from CD8+ and CD4+ cytotoxic T cells, especially because B cells can present their own idiotype. Loss of HLA expression and the possible underlying genomic alterations were studied in 28 testicular, 11 central nervous system, and 21 nodal diffuse large B-cell lymphomas (DLCLs), the first two sites are considered as immune-privileged sites. The analysis included immunohistochemistry, loss of heterozygosity analysis, and fluorescent in situ hybridization (FISH) on interphase cells and isolated DNA fibers. Total loss of HLA-A expression was found in 60% of the extranodal cases and in 10% of the nodal cases (P < .01), whereas loss of HLA-DR expression was found in 56% and 5%, respectively (P < .01). This was accompanied by extensive loss of heterozygosity within the HLA region in the extranodal DLCLs. In 3 cases, retention of heterozygosity for D6S1666 in the class II region suggested a homozygous deletion. This finding was confirmed by interphase FISH that showed homozygous deletions in the class II genes in 11 of the 18 extranodal lymphomas but in none of the 7 nodal DLCLs (P < .001). Mapping by fiber FISH showed variable deletions that always included HLA-DQ and HLA-DR genes. Hemizygous deletions and mitotic recombinations often involving all HLA genes were found in 13 of 18 extranodal and 2 of 7 nodal lymphomas. In conclusion, a structural loss of HLA class I and II expression might help the B-cell lymphoma cells to escape from immune attack.

Extensive genetic alterations of the HLA region, including homozygous deletions of HLA class II genes in B-cell lymphomas arising in immune-privileged sites

In B-cell lymphomas, loss of human leukocyte antigen (HLA) class I and II molecules might contribute to immune escape from CD8+ and CD4+ cytotoxic T cells, especially because B cells can present their own idiotype. Loss of HLA expression and the possible underlying genomic alterations were studied in 28 testicular, 11 central nervous system, and 21 nodal diffuse large B-cell lymphomas (DLCLs), the first two sites are considered as immune-privileged sites. The analysis included immunohistochemistry, loss of heterozygosity analysis, and fluorescent in situ hybridization (FISH) on interphase cells and isolated DNA fibers. Total loss of HLA-A expression was found in 60% of the extranodal cases and in 10% of the nodal cases (P &lt; .01), whereas loss of HLA-DR expression was found in 56% and 5%, respectively (P &lt; .01). This was accompanied by extensive loss of heterozygosity within the HLA region in the extranodal DLCLs. In 3 cases, retention of heterozygosity for D6S1666 in the class II region suggested a homozygous deletion. This finding was confirmed by interphase FISH that showed homozygous deletions in the class II genes in 11 of the 18 extranodal lymphomas but in none of the 7 nodal DLCLs (P &lt; .001). Mapping by fiber FISH showed variable deletions that always included HLA-DQ and HLA-DR genes. Hemizygous deletions and mitotic recombinations often involving all HLA genes were found in 13 of 18 extranodal and 2 of 7 nodal lymphomas. In conclusion, a structural loss of HLA class I and II expression might help the B-cell lymphoma cells to escape from immune attack.

From the study of tumor cell immunogenicity to the generation of antitumor cytotoxic cells in non-Hodgkin's lymphomas

The question of the immunogenicity of non-Hodgkin's lymphoma (NHL) B cells has been investigated in an attempt to support the development of new immunotherapeutic treatments for this disorder, which remains resistant to conventional treatments in most cases. In the present review, we report and discuss our new findings in the field of NHL B cell immunogenicity. One aspect of our work is the description of the expression and functions of membrane molecules associated with antigen presentation. The expression levels of adhesion molecules was measured, and the relevance of this expression to the sensitivity of malignant B cells to cell-mediated lysis was studied. Since the T cell response relies on the expression of both HLA class I and II molecules, we also investigated whether or not these molecules were present at the surface of NHL B cells. Subsequently, we asked whether antitumor CTL and LAK cells could be developed and analyzed the mechanisms of cell lysis involved. Since the generation of a T cell response requires the expression of the costimulatory molecules CD80 and CD86, we investigated their in vivo expression and their modulation in vitro during contact with responding T lymphocytes. The understanding of the immunogenicity of NHL B cells has enabled us to develop a new culture protocol to induce antitumor specific autologous CTL. The originality of NHL B cells--unlike most other tumor cells--is to be able to function as antigen presenting cells (APC) and to activate a T cell response in the absence of other professional APC. Over the next few years, these findings should allow the generation of anti-NHL specific T cells for adoptive immunotherapy and for the identification of NHL-associated antigens.

Selective upregulation of MHC class I expression in metastatic colonies derived from tumor clones of a murine fibrosarcoma

Eighteen metastatic nodes derived from the wild-type (GR9) and from 4 different clones (G2, D8, B10, and B9) obtained from a fibrosarcoma were analyzed for H-2 class I and II expression, as well as for adhesion molecules (CD44, CDIIb, CD18, CD49, and CD54). When metastatic nodes were cultured, typed for H-2 antigens, and compared with the H-2 expression of the inducing tumor cell, H-2 Kd and Dd class I expression was greater in most nodes analyzed. In contrast, the Ld molecule remained negative, or showed a minor increase. Class II expression was negative in the wild-type and the tumor clones, and remained so in the metastatic colonies. Analysis of the adhesion molecules revealed no differences between the inducing tumor cells and the metastatic nodes. The only molecule expressed was CD44, which was present in all cells studied and was also inducible by interferon-gamma. The increase in H-2K and H-2D expression was associated with resistance to natural killer cytotoxicity, as observed in the G2 tumor clone and some autologous metastases, such as B9MP2, G2MK2, and G2MLI. In three independent clones of this tumor system (D8, BIOMP6, and B9MP6) we found that tumor cells treated with interferon-gamma had the same altered phenotype, i.e., a selective lack of response of the Ld molecule to induction. These findings add a cautionary note to the well-established idea that tumor cells may lose all class I antigens during tumor progression, and suggest that sometimes this may not be the case. The selective downregulation of Ld and upregulation of Kd and Dd class I expression may give some tumor cells means of escaping both cytotoxic lymphocyte and natural killer immune surveillance.

Biochemical analysis of HLA class I subunits expression in breast cancer tissues

The expression of HLA class I alpha-chain and beta(2)-m subunits was studied at the protein level by a semiquantitative Western blot (WB) approach, in 25 primary breast tumors. The results indicated three pathways of alterations defined comparing the tumor WB gel band with the corresponding PBL gel band: (i) high downregulation pattern (the tumor WB gel band was < or =50% relative to the PBL band), which was found in 44% and 36% of tumors for alpha-chain and beta(2)-m, respectively; (ii) low downregulation pattern (the tumor gel band was between 51% and 75%), which was found in 24% and 20% of tumors for alpha-chain and beta(2)75%), which was found in 32% and 44% of tumors for alpha-chain and beta(2)-m, respectively. The concordance rate with immunohistochemistry (IHC) performed on the same tissue samples was 72% for alpha-chain and 64% for beta(2)-m. This study shows that the use of a semiquantitative WB technique can well define the levels of HLA class I antigens in an autologous setting allowing the biochemical analysis of HLA class I downregulation directly in solid tumor tissues. In addition, the WB technique can be a valuable tool to objectively support the IHC method.

Multiple genetic alterations cause frequent and heterogeneous human histocompatibility leukocyte antigen class I loss in cervical cancer

The nature and frequency of human histocompatibility leukocyte antigen (HLA) class I loss mechanisms in primary cancers are largely unknown. We used flow cytometry and molecular analyses to concurrently assess allele-specific HLA phenotypes and genotypes in subpopulations from 30 freshly isolated cervical tumor cell suspensions.Tumor-associated HLA class I alterations were present in 90% of the lesions tested, comprising four altered pheno/genotype categories: (a) HLA-A or -B allelic loss (17%), mostly associated with gene mutations; (b) HLA haplotype loss, associated with loss of heterozygosity at 6p (50%). This category included cases with additional loss of a (third) HLA-A or -B allele due to mutation, as well as one case with an HLA class I-negative tumor cell subpopulation, caused by a beta2-microglobulin gene mutation; (c) Total HLA class I antigen loss and retention of heterozygosity (ROH) at 6p (10%); and (d) B locus or HLA-A/B downregulation associated with ROH and/or allelic imbalance at 6p (10%). Normal HLA phenotypes and ROH at 6p were observed in 10% of the cases. One case could not be classified (3%). Altered HLA class I antigen expression occurs in most cervical cancers, is diverse, and is mainly caused by genetic changes. Combined with widespread tumor heterogeneity, these changes have profound implications for natural immunity and T cell-based immunotherapy in cervical cancer.

HLA class I expression on human cancer cells. Implications for effective immunotherapy

Early studies demonstrated the role of cytotoxic T cells as an immune defence mechanism against tumour cells. The demonstration of tumour antigen peptides and their presentation to T cells on major histocompatibility complex class I molecules highlighted the importance of these molecules in effective anti-tumour responses. It is well established that many tumours escape T cell recognition by loss or down regulation of class I molecule expression on the cell surface of tumour cells. Tumours which have lost class I expression are immunoselected and as a result have a propensity for growth and metastatic spread. With the development of cancer vaccine strategies for clinical use, there will be a future role for histocompatibility laboratories in determining class I expression on tumour cells in individual patients. These studies of expression will require not just the demonstration of total class I expression but the demonstration of locus and allele specific class I molecules involved in the relevant tumour peptide presentation. These studies will be pivotal in tailoring individual patient therapies. The identification of appropriate monoclonal antibody reagents for class I expression and techniques used on different kinds of tissue sections will be a component of the forthcoming 13th International Histocompatibility Workshop.