Cancer/Testis Antigen Expression on Mesenchymal Stem Cells Isolated from Different Tissues

Background/Aims: The expression of cancer/testis antigens (CTAs) on additional normal tissues or stem cells may restrict their use as cancer targets. The objective of the present study was to evaluate the mRNA levels of some CTAs in a variety of tissues. Materials and Methods: mRNA of pericytes, fibroblasts and mesenchymal stem cells (MSCs) derived from adult and fetal tissues, human umbilical vein endothelial cells, MSC-derived adipocytes, selected normal tissues and control cancer cell lines (CLs) were extracted and quantitative polymerase chain reaction was performed for MAGED1, PRAME, CTAG1B, MAGEA3 and MAGEA4. Results: MAGED1 was expressed in all normal tissues and cells evaluated. CTAG1B was expressed at levels comparable to control CLs on MSCs derived from arterial, fetal skin, adipose tissue and saphenous vein, heart, brain and skin tissues. MAGEA4 was detected only in fibroblasts and differentiated adipocytes from MSCs, at levels comparable to the control CLs. Conclusion: The potential use of CTAs in immunotherapy should take into account the potential off-target effects on MSCs.

HIGH EXPRESSION OF CANCER TESTIS ANTIGENS MAGE-A, MAGE-C1/CT7, MAGE-C2/CT10, NY-ESO-1, AND GAGE IN ADVANCED SQUAMOUS CELL CARCINOMA OF THE LARYNX

Background. Despite diagnostic and therapeutic advances in head and neck cancer, the 5-year survival of patients with laryngeal cancer has not improved in the last 30 years. Several recent studies indicate that specific targets for immunotherapeutic approaches can be useful in the control of cancer. There is considerable interest in the expression of cancer testis antigens in human cancers since they may serve as the basis for an immunologic approach to therapy. Methods. We evaluated by immunohistochemical analysis the expression of cancer testis antigens MAGE-A4 (57B), MAGE-C1 (CT7-33), MAGE-A1 (MA454), MAGE-A3 (M3H67), MAGE-C2 (CT10.5), NY-ESO-1 (E978), and GAGE (GAGE) in squamous cell carcinoma (SCC) of the larynx. Results. A total of 63 cases (57 men and 6 women) of laryngeal SCC were available for this study. The findings were correlated with the clinical course and laboratory data. Expression of at least 1 cancer testis antigen was detected in 42 of 63 of the laryngeal SCCs (67%). In 34 of 42 of the positive cases (81%) there was simultaneous expression of >= 2 cancer testis antigens. There was significant correlation between antigen expression and advanced tumor stage (stage III/IV) in cases with reactivity to only 1 antibody (p = .01) as well as in the cases with reactivity to >= 2 primary antibodies (>= 2 mAbs, p = .04). There was no association between survival and expression of any of the analyzed antigens. Conclusions. We find a high incidence of cancer testis antigen expression in SCCs of the larynx, which was correlated with advanced clinical stage. Our data indicate that cancer testis antigens could be valuable vaccine targets in laryngeal tumors, especially in those with a worse prognosis. (C) 2010 Wiley Periodicals, Inc. Head Neck 33: 702-707, 2011

Effect of BCG stimulus on proinflammatory cytokine production in laryngeal cancer

Background Evaluate the production of TNF and IL-6 in the supernatant of peripheral blood mononuclear cell (PBMC) cultures of patients with supraglottic laryngeal cancer before and after surgical treatment. Materials and methods Adherent cell cultures were stimulated with LPS and BCG. Fourteen patients with advanced supraglottic laryngeal cancer were studied. Cytokine concentration was determined by ELISA in supernatants of mononuclear cell cultures. Results In non-stimulated cultures, lower TNF cytokine levels were detected during the late postoperative (LP) period compared to control (P = 0.02). LP TNF and IL-6 levels were high in cultures stimulated with LPS compared with the preoperative period (PREOP) (P = 0.007; P = 0.008, respectively). Stimulation with BCG led to increased levels of TNF and IL-6 during the LP period compared to control (P = 0.001; P = 0.04, respectively). Conclusions BCG is able to modulate the immune response of patients with advanced supraglottic laryngeal cancer in vitro, increasing the secretion of TNF and IL-6 by macrophages during the postoperative period.

Metastatic lesions in the joint associated with acute inflammatory arthritis after dendritic cell immunotherapy for metastatic melanoma

A 47 year old man undergoing immunotherapy for metastatic melanoma with autologous dendritic cells pulsed with autologous tumour peptide and hepatitis a surface antigen developed acute left ankle arthritis. Gout and acute infection were excluded, and an autoimmune aetiology or occult metastasis were considered. The arthritis initially subsided with indomethacin, but the symptoms recurred 2 months later, and magnetic resonance imaging demonstrated metastatic melanoma of the left talus. Immunohistochemical staining of a cerebral metastatic deposit biopsied 1 week after the onset of arthritis demonstrated T-cell and macrophage infiltration of the tumour. In addition, the patient developed melanoma-specific delayed type hypersensitivity and cytotoxic T-cell responses after vaccination. Thus, the monoarthritis represented an 'appropriate' inflammatory response directed against metastatic melanoma. (C) 2001 Lippincott Williams & Wilkins.

Donor-derived b2a2-specific T cells for immunotherapy of patients with chronic myeloid leukemia

The BCR-ABL fusion proteins, b2a2 and b3a2, are potential targets for a beneficial graft-versus-leukemia (GVL) effect after allogeneic stem cell transplantation for chronic myeloid leukemia (CML). This study demonstrates that CD4(+) T cells specific to the b2a2 peptide can be generated from a normal allogeneic stem cell transplant donor after stimulation with monocyte-derived dendritic cells (Mo-DC) using culture conditions applicable to clinical use. Stimulation of donor T-cell enriched mononuclear cells (MNC) with b2a2-pulsed Mo-DC produced approximately 3 x 10(9) b2a2-specific CD4(+) T cells. The CD4(+) T cells were HLA-DR7 restricted. These results confirm that the generation of donor derived b2a2-specific T cells for clinical use is feasible and warrants clinical testing after stem cell transplantation.

Macrophages as biomarkers in BCG treatment response in bladder cancer

Bladder cancer is a common urologic cancer and the majority has origin in the urothelium. Patients with intermediate and high risk of recurrence/progression bladder cancer are treated with intravesical instillation with Bacillus Calmette-Guérin, however, approximately 30% of patients do not respond to treatment. At the moment, there are no accepted biomarkers do predict treatment outcome and an early identification of patients better served by alternative therapeutics. The treatment initiates a cascade of cytokines responsible by recruiting macrophages to the tumor site that have been shown to influence treatment outcome. Effective BCG therapy needs precise activation of the Th1 immune pathway associated with M1 polarized macrophages. However, tumor-associated macrophages (TAMs) often assume an immunoregulatory M2 phenotype, either immunosuppressive or angiogenic, that interfere in different ways with the BCG induced antitumor immune response. The M2 macrophage is influenced by different microenvironments in the stroma and the tumor. In particular, the degree of hypoxia in the tumors is responsible by the recruitment and differentiation of macrophages into the M2 angiogenic phenotype, suggested to be associated with the response to treatment. Nevertheless, neither the macrophage phenotypes present nor the influence of localization and hypoxia have been addressed in previous studies. Therefore, this work devoted to study the influence of TAMs, in particular of the M2 phenotype taking into account their localization (stroma or tumor) and the degree of hypoxia in the tumor (low or high) in BCG treatment outcome. The study included 99 bladder cancer patients treated with BCG. Tumors resected prior to treatment were evaluated using immunohistochemistry for CD68 and CD163 antigens, which identify a lineage macrophage marker and a M2-polarized specific cell surface receptor, respectively. Tumor hypoxia was evaluated based on HIF-1α expression. As a main finding it was observed that a high predominance of CD163+ macrophage counts in the stroma of tumors under low hypoxia was associated with BCG immunotherapy failure, possibly due to its immunosuppressive phenotype. This study further reinforces the importance the tumor microenvironment in the modulation of BCG responses.

Response of high-risk of recurrence/progression bladder tumours expressing sialyl-Tn and sialyl-6-T to BCG immunotherapy

High risk of recurrence/progression bladder tumours is treated with Bacillus Calmette-Guérin (BCG) immunotherapy after complete resection of the tumour. Approximately 75% of these tumours express the uncommon carbohydrate antigen sialyl-Tn (Tn), a surrogate biomarker of tumour aggressiveness. Such changes in the glycosylation of cell-surface proteins influence tumour microenvironment and immune responses that may modulate treatment outcome and the course of disease. The aim of this work is to determine the efficiency of BCG immunotherapy against tumours expressing sTn and sTn-related antigen sialyl-6-T (s6T). METHODS: In a retrospective design, 94 tumours from patients treated with BCG were screened for sTn and s6T expression. In vitro studies were conducted to determine the interaction of BCG with high-grade bladder cancer cell line overexpressing sTn. RESULTS: From the 94 cases evaluated, 36 had recurrence after BCG treatment (38.3%). Treatment outcome was influenced by age over 65 years (HR=2.668; (1.344-5.254); P=0.005), maintenance schedule (HR=0.480; (0.246-0.936); P=0.031) and multifocality (HR=2.065; (1.033-4.126); P=0.040). sTn or s6T expression was associated with BCG response (P=0.024; P<0.0001) and with increased recurrence-free survival (P=0.001). Multivariate analyses showed that sTn and/or s6T were independent predictive markers of recurrence after BCG immunotherapy (HR=0.296; (0.148-0.594); P=0.001). In vitro studies demonstrated higher adhesion and internalisation of the bacillus to cells expressing sTn, promoting cell death. CONCLUSION: s6T is described for the first time in bladder tumours. Our data strongly suggest that BCG immunotherapy is efficient against sTn- and s6T-positive tumours. Furthermore, sTn and s6T expression are independent predictive markers of BCG treatment response and may be useful in the identification of patients who could benefit more from this immunotherapy.

The predominance of M2-polarized macrophages in the stroma of low-hypoxic bladder tumors is associated with BCG immunotherapy failure

OBJECTIVE: Bacillus Calmette-Guérin (BCG) immunotherapy is the gold standard treatment for superficial bladder tumors with intermediate/high risk of recurrence or progression. However, approximately 30% of patients fail to respond to the treatment. Effective BCG therapy needs precise activation of the type 1 helper cells immune pathway. Tumor-associated macrophages (TAMs) often assume an immunoregulatory M2 phenotype and may directly interfere with the BCG-induced antitumor immune response. Thus, we aim to clarify the influence of TAMs, in particular of the M2 phenotype in stroma and tumor areas, in BCG treatment outcome. PATIENTS AND METHODS: The study included 99 patients with bladder cancer treated with BCG. Tumors resected before treatment were evaluated using immunohistochemistry for CD68 and CD163 antigens, which identify a lineage macrophage marker and a M2-polarized specific cell surface receptor, respectively. CD68+ and CD163+ macrophages were evaluated within the stroma and tumor areas, and high density of infiltrating cells spots were selected for counting. Hypoxia, an event known to modulate macrophage phenotype, was also assessed through hypoxia induced factor (HIF)-1α expression. RESULTS: Patients in whom BCG failed had high stroma-predominant CD163+ macrophage counts (high stroma but low tumor CD163+ macrophages counts) when compared with the ones with a successful treatment (71% vs. 47%, P = 0.017). Furthermore, patients presenting this phenotype showed decreased recurrence-free survival (log rank, P = 0.008) and a clear 2-fold increased risk of BCG treatment failure was observed in univariate analysis (hazard ratio = 2.343; 95% CI: 1.197-4.587; P = 0.013). Even when adjusted for potential confounders, such as age and therapeutic scheme, multivariate analysis revealed 2.6-fold increased risk of recurrence (hazard ratio = 2.627; 95% CI: 1.340-5.150; P = 0.005). High stroma-predominant CD163+ macrophage counts were also associated with low expression of HIF-1α in tumor areas, whereas high counts of CD163+ in the tumor presented high expression of HIF-1α in tumor nests. CONCLUSIONS: TAMs evaluation using CD163 is a good indicator of BCG treatment failure. Moreover, elevated infiltration of CD163+ macrophages, predominantly in stroma areas but not in the tumor, may be a useful indicator of BCG treatment outcome, possibly owing to its immunosuppressive phenotype.

Thomsen-Friedenreich antigens in bladder cancer: evaluation of their prognostic value

RESUMO: Introdução. O cancro de bexiga é uma patologia comum que representa o 6° e o 5° cancro mais incidente em Portugal e na Itália, respetivamente. Em mais de metade dos casos ocorre reincidência durante o primeiro ano, requerendo acompanhamento clínico ao longo da vida. A instilação intravesical de Bacillus Calmette-Guérin (BCG) (uma estirpe atenuada do Mycobacterium bovis) representa uma imunoterapia eficaz no combate ao cancro de bexiga, no entanto, muitos aspetos da interação de BCG com as células tumorais bem como com as células do sistema imunitário permanecem por desvendar. As células tumorais de bexiga expressam frequentemente as formas sialiladas dos antigénios de Thomsen-Friedenreich (TF), i.e., sialil-T (sT) e sialil-Tn (sTn). Contudo ainda se desconhece o significado da sua expressão na malignidade tumoral e se afeta a eficácia da terapêutica BCG. Objetivo do estudo. Investigar o papel dos antigénios sT e sTn no fenótipo maligno de células de cancro de bexiga bem como na resposta mediada pelo sistema imunitário à terapia com BCG. Metodologia. Para tal, foram utilizadas as linhas celulares de cancro da bexiga HT1376 e MCR, geneticamente modificadas por transdução com vetores codificantes para as sialiltransferases ST3GAL1 ou ST6GALNAC1, de forma a expressar homogeneamente os antigénios sT ou sTn respetivamente. Estes modelos celulares foram estudados após confronto com BCG. O nível de BCG internalizado foi avaliado por citometria de fluxo. O perfil global de expressão genética dos modelos celulares antes e após incubação com BCG foi analisado pela tecnologia de microarray. O perfil de citocinas secretadas pelos modelos celulares após incubação com BCG, bem como de macrófagos estimulados pelo secretoma de células de cancro de bexiga que por sua vez foram estimuladas previamente por BCG, foi estudado pelo sistema multiplex de “imuno-esferas”. Resultados. A análise do transcritoma dos modelos celulares revelou que grupos de genes envolvidos em funções específicas foram modulados em paralelo nos dois modelos celulares, após transdução, independentemente da sialiltransferase expressa. Ou seja, em células que expressavam a sialiltransferase ST3GAL1 ou ST6GALNAC1, os genes envolvidos na regulação da segregação cromossómica e na reparação do DNA foram consistentemente regulados negativamente. Genes descritos na literatura como marcadores para o cancro de bexiga foram também modulados. A incubação com BCG resultou numa tendência ao aumento da expressão de genes relevantes na preservação e estabilidade genómica e menor malignidade, no entanto, apenas em células que expressavam sT ou sTn. Entre as dez citocinas testadas, apenas a IL-6 e IL-8 foram expressas pelas linhas celulares de cancro da bexiga, com indução destas após estimulação com BCG, e principalmente em células que expressavam ST3GAL1 ou ST6GALNAC1. Em macrófagos, citocinas inflamatórias, tais como IL-1β, IL-6 e TNFα, e a citocina anti-inflamatória IL-10, foram induzidas apenas pelo secretoma de células de cancro da bexiga confrontadas com BCG, com maior relevância quando estas expressavam ST3GAL1 ou ST6GALNAC1, prevendo a estimulação de macrófagos semelhantes aos de tipo M1 e uma melhor resposta à terapia com BCG. Conclusões. O efeito geral da expressão destas sialiltransferases e dos produtos enzimáticos sT ou sTn nas células de cancro de bexiga conduz a um fenótipo de maior malignidade. Contudo, a maior avidez de estas na produção de citocinas inflamatórias após confronto com BCG, bem como a maior capacidade de estimulação de macrófagos, predirá uma resposta à terapia com BCG mais eficaz em tumores que expressem os antigénios de TF sialilados. Tais conclusões são totalmente concordantes com os nossos mais recentes dados clínicos obtidos em colaboração, que mostram que em doentes com cancro de bexiga que expressam sTn respondem melhor a terapia BCG. ----------ABSTRACT: Background. Bladder cancer is a common malignancy representing the 6th and the 5th most incident cancer in Portugal and in Italy, respectively. More than half of the cases relapse within one year, requiring though a lifelong follow-up. Intravesical instillation of Bacillus Calmette-Guérin (BCG) (an attenuated strain of Mycobacterium bovis) represents an effective immunotherapy of bladder cancer, although many aspects of the interaction of BCG with cancer cells and host immune cells remain obscure. Bladder cancer cells often express the sialylated forms of the Thomsen-Friedenreich (TF), i.e., sialil-T (sT) e sialil-Tn (sTn). However, it’s still unknown the sense of such expression in tumour malignancy and in the BCG therapy efficacy. Aim of the study. To investigate the role of the sT and sTn antigens on the malignant phenotype of bladder cancer cells and the immune mediated response to BCG therapy. Experimental. We have utilized populations of the bladder cancer cell lines HT1376 and MCR, genetically modified by transduction with the sialyltransferases ST3GAL1 or ST6GALNAC1 to express homogeneously sT or sTn antigens. The level of BCG internalized was assessed by flow cytometry. The whole gene expression profile of BCG-challenged or unchallenged bladder cancer cell lines was studied by microarray technology. The profile of cytokines secreted by BCG-challenged bladder cancer cells and that of macrophages challenged by the secretome of BCG-challenged bladder cancer cells was studied by multiplex immune-beads assay. Results. Transcriptome analysis of the sialyltransferase-transduced cells revealed that groups of genes involved in specific functions were regulated in parallel in the two cell lines, regardless the sialyltransferase expressed. Namely, in sialyltransferase-expressing cells, genes involved in the proper chromosomal segregation and in the DNA repair were consistently down-regulated, while genes reported in literature as markers for bladder cancer were modulated. BCG-challenging induced a tendency to up-regulation of the genes preserving genomic stability and reducing malignancy, but only in cells expressing either sT or sTn. Among the ten cytokines tested, only IL-6 and IL-8 were expressed by bladder cancer cell lines and up-regulated by BCG-challenging, mainly in sialyltransferases-expressing cells. In macrophages, inflammatory cytokines, such as IL-1β, IL-6 and TNFα, and the antinflammatory IL-10 were induced only by the secretome of BCG-challenged bladder cancer cells, particularly when expressing either sialyltransferase, predicting the stimulation of M1-like macrophages and a better response to BCG therapy. Conclusions. The general effect of the expression of the two sialyltransferases and their products in the bladder cancer cells is toward a more malignant phenotype. However, the stronger ability of sialyltransferase expressing cells to produce inflammatory cytokines upon BCG-challenging and to stimulate macrophages predicts a more effective response to BCG in tumours expressing the sialylated TF antigens. This is fully consistent with our recent clinical data obtained in collaboration, showing that patients with bladder cancer expressing sTn respond better to BCG therapy.

Theranostic applications of phage display to control leishmaniasis: selection of biomarkers for serodiagnostics, vaccination, and immunotherapy

AbstractPhage display is a high-throughput subtractive proteomic technology used for the generation and screening of large peptide and antibody libraries. It is based on the selection of phage-fused surface-exposed peptides that recognize specific ligands and demonstrate desired functionality for diagnostic and therapeutic purposes. Phage display has provided unmatched tools for controlling viral, bacterial, fungal, and parasitic infections, and allowed identification of new therapeutic targets to treat cancer, metabolic diseases, and other chronic conditions. This review presents recent advancements in serodiagnostics and prevention of leishmaniasis -an important tropical parasitic disease- achieved using phage display for the identification of novel antigens with improved sensitivity and specificity. Our focus is on theranostics of visceral leishmaniasis with the aim to develop biomarker candidates exhibiting both diagnostic and therapeutic potential to fight this important, yet neglected, tropical disease.

Harmonization guidelines for HLA-peptide multimer assays derived from results of a large scale international proficiency panel of the Cancer Vaccine Consortium.

PURPOSE: The Cancer Vaccine Consortium of the Cancer Research Institute (CVC-CRI) conducted a multicenter HLA-peptide multimer proficiency panel (MPP) with a group of 27 laboratories to assess the performance of the assay. EXPERIMENTAL DESIGN: Participants used commercially available HLA-peptide multimers and a well characterized common source of peripheral blood mononuclear cells (PBMC). The frequency of CD8+ T cells specific for two HLA-A2-restricted model antigens was measured by flow cytometry. The panel design allowed for participants to use their preferred staining reagents and locally established protocols for both cell labeling, data acquisition and analysis. RESULTS: We observed significant differences in both the performance characteristics of the assay and the reported frequencies of specific T cells across laboratories. These results emphasize the need to identify the critical variables important for the observed variability to allow for harmonization of the technique across institutions. CONCLUSIONS: Three key recommendations emerged that would likely reduce assay variability and thus move toward harmonizing of this assay. (1) Use of more than two colors for the staining (2) collect at least 100,000 CD8 T cells, and (3) use of a background control sample to appropriately set the analytical gates. We also provide more insight into the limitations of the assay and identified additional protocol steps that potentially impact the quality of data generated and therefore should serve as primary targets for systematic analysis in future panels. Finally, we propose initial guidelines for harmonizing assay performance which include the introduction of standard operating protocols to allow for adequate training of technical staff and auditing of test analysis procedures.

Rapid evolution of cancer/testis genes on the X chromosome.

BACKGROUND: Cancer/testis (CT) genes are normally expressed only in germ cells, but can be activated in the cancer state. This unusual property, together with the finding that many CT proteins elicit an antigenic response in cancer patients, has established a role for this class of genes as targets in immunotherapy regimes. Many families of CT genes have been identified in the human genome, but their biological function for the most part remains unclear. While it has been shown that some CT genes are under diversifying selection, this question has not been addressed before for the class as a whole. RESULTS: To shed more light on this interesting group of genes, we exploited the generation of a draft chimpanzee (Pan troglodytes) genomic sequence to examine CT genes in an organism that is closely related to human, and generated a high-quality, manually curated set of human:chimpanzee CT gene alignments. We find that the chimpanzee genome contains homologues to most of the human CT families, and that the genes are located on the same chromosome and at a similar copy number to those in human. Comparison of putative human:chimpanzee orthologues indicates that CT genes located on chromosome X are diverging faster and are undergoing stronger diversifying selection than those on the autosomes or than a set of control genes on either chromosome X or autosomes. CONCLUSION: Given their high level of diversifying selection, we suggest that CT genes are primarily responsible for the observed rapid evolution of protein-coding genes on the X chromosome.

Pattern and clinical significance of cancer-testis gene expression in head and neck squamous cell carcinoma.

Cancer-testis (CT) antigens comprise families of tumor-associated antigens that are immunogenic in patients with various cancers. Their restricted expression makes them attractive targets for immunotherapy. The aim of this study was to determine the expression of several CT genes and evaluate their prognostic value in head and neck squamous cell carcinoma (HNSCC). The pattern and level of expression of 12 CT genes (MAGE-A1, MAGE-A3, MAGE-A4, MAGE-A10, MAGE-C2, NY-ESO-1, LAGE-1, SSX-2, SSX-4, BAGE, GAGE-1/2, GAGE-3/4) and the tumor-associated antigen encoding genes PRAME, HERV-K-MEL, and NA-17A were evaluated by RT-PCR in a panel of 57 primary HNSCC. Over 80% of the tumors expressed at least 1 CT gene. Coexpression of three or more genes was detected in 59% of the patients. MAGE-A4 (60%), MAGE-A3 (51%), PRAME (49%) and HERV-K-MEL (42%) were the most frequently expressed genes. Overall, the pattern of expression of CT genes indicated a coordinate regulation; however there was no correlation between expression of MAGE-A3/A4 and BORIS, a gene whose product has been implicated in CT gene activation. The presence of MAGE-A and NY-ESO-1 proteins was verified by immunohistochemistry. Analysis of the correlation between mRNA expression of CT genes with clinico-pathological characteristics and clinical outcome revealed that patients with tumors positive for MAGE-A4 or multiple CT gene expression had a poorer overall survival. Furthermore, MAGE-A4 mRNA positivity was prognostic of poor outcome independent of clinical parameters. These findings indicate that expression of CT genes is associated with a more malignant phenotype and suggest their usefulness as prognostic markers in HNSCC.

Redirecting anti-viral CTL against cancer cells by surface targeting of monomeric MHC class I-viral peptide conjugated to antibody fragments.

To combine the advantage of both the tumor targeting capacity of high affinity monoclonal antibodies (mAbs) and the potent killing properties of cytotoxic T lymphocytes (CTL), we investigated the activity of conjugates made by coupling single Fab' fragments, from mAbs specific for tumor cell surface antigens, to monomeric HLA-A2 complexes containing the immunodominant influenza-matrix peptide 58-66. In solution, the monovalent 95 kDa Fab-HLA-A2/Flu conjugates did not activate influenza-specific CTL. However, when targeted to tumor cells expressing the relevant tumor-associated antigen, the conjugates induced CTL activation and efficient tumor cell lysis, as a result of MHC/peptide surface oligomerization. The highly specific and sensitive in vitro cytotoxicity results presented suggest that injection of Fab-MHC/peptide conjugates could represent a new form of immunotherapy, bridging antibody and T lymphocyte attack on cancer cells.