Immunological surveillance of tumors in the context of major histocompatibility complex restriction of T cell function

CAR-T Cells in the Treatment of Urologic Neoplasms: Present and Future

In recent years, with the breakthrough of CAR-T cells in the treatment of hematological tumors, they are increasingly being used to treat solid tumors, including urologic neoplasms. There are many relatively specific targets for urologic neoplasms, especially prostate cancer. Besides, urologic neoplasms tend to progress more slowly than tumors in other organs of the body, providing ample time for CAR-T cell application. Therefore, CAR-T cells technology has inherent advantages in urologic neoplasms. CAR-T cells in the treatment of urologic neoplasms have been extensively studied and preliminary achievements have been made. However, no breakthrough has been made due to the problems of targeting extra-tumor cytotoxicity and poor anti-tumor activity. we systematacially summarized the research actuality of CAR-T cells in urologic neoplasms, discussed the potential value and difficulties of the research. The application of CAR-T cells in the treatment of urologic neoplasms requires improvement of function through screening for better targets, modification of CAR structures, or in combination with other antitumor approaches.

The Past, Present, and Future of NK Cells in Hematopoietic Cell Transplantation and Adoptive Transfer

Hematopoietic cell transplantation (HCT) has been used as a part of cancer therapy for over half a decade. Beyond the necessity for donor-derived cells to reconstitute hematopoiesis after radiation and chemotherapy, immunologic reconstitution from allogeneic cells is important for the elimination of residual tumor cells. Natural killer (NK) cells are first among lymphocytes to reconstitute post-transplant and protect against cancer relapse. In this review, we provide a historical perspective on the role of NK cells in cancer control in the transplant setting and focus on current research aimed at improving NK cell responses for therapeutic benefit.

Evasion of host immune responses by tumours and viruses

Viruses and tumours use various mechanisms to avoid immune surveillance. Oncogenic viruses have achieved a balance with the immune system through evolutionary time to ensure long-term persistence. Mutations that promote escape mechanisms favouring tumour growth to the detriment of host survival through reproductive age offer no selective advantage and will not generally be maintained in the viral genome that persists in nature. Conventional (non-oncogenic) and tumour viruses interact with various immune mediators and T cells in different ways. Oncogenic viruses cannot operate solely in the context of a lytic cycle, though this may be characteristic of the initial phase of infection that is limited by the acute immune response. Some oncogenic viruses interact with normal cellular growth control and signalling mechanisms. Synthesis of key viral proteins may be tightly controlled in replicating cells that are subject to T cell surveillance, such as basal epithelia, while productive infection occurs in non-proliferating progeny that are lost under normal physiological conditions, such as desquamating epithelia. Tumorigenesis may be an aberrant consequence of the molecular mechanisms needed to maintain this pattern of viral growth regulation in the context of the cell cycle. Vaccines designed to limit the acute phase of infection with cell-free oncogenic viruses should be as effective as those for conventional viruses.

Analyses and perspectives in cancer immunotherapy

Since the last two decades, rapid progress has been made in the field of cancer immunotherapy relevant to manipulation of adaptative cytotoxic T lymphocytes (CTLs) and innate immunity natural killer (NK) cells as well as antibodies. Many possibilities are now offered for therapeutic purposes contributing to better approaches in treatment of cancer.

Challenged by complexity: my twentieth century in immunology

My research career has focused on complex experimental systems, principally virus-induced infectious processes. I have always run my own experimental program and never had a major mentor, although I have had many great colleagues. After graduating from the School of Veterinary Science at the University of Queensland, Australia, I worked for nine years on diseases of domestic animals. During that interval I completed a part-time PhD at the University of Edinburgh while employed as an experimental neuropathologist. Returning to the John Curtin School of Medical Research in Canberra, I focused on cell-mediated immunity, started to work seriously with mice, and thus became both an immunologist and a basic medical scientist. It was there in 1973 that Rolf Zinkernagel and I discovered MHC I-restricted CD8(+) T cell recognition, a finding that, together with the "single T cell receptor/altered self" hypothesis that we developed to explain our results, led to the 1996 Nobel Prize for Physiology or Medicine. Part of my focus since then has been to communicate the societal value and power of science to the broader community. As my scientific life is not yet over, I confine the present historical account to the twentieth century.

The tumor microenvironment in the post-PAGET era

The research area of tumor microenvironment is considered, at present, to be an important factor in tumorigenesis and especially in tumor progression. The present mini review is focused on three principles characterizing the nature of the tumor microenvironment. We first discuss the regulatory functions of the tumor microenvironment and the complexity of the combinatorial signaling pathways operating in it. We then address the aspect that the tumor microenvironment incorporates both pro and anti malignancy factors and that a balance between these factors regulates tumor progression. Thirdly we provide evidence that the non-tumor cells in the tumor microenvironment and their products may be different from those of their counterparts residing in non-tumor microenvironments. The conclusion of this mini review is that the tumor microenvironment, by exerting regulatory functions and selective pressures drives cancer cells into one of several molecular evolution pathways thereby determining and shaping their malignancy phenotype.

Augmenting major histocompatibility complex class I expression by murine tumors in vivo enhances antitumor immunity induced by an active immunotherapy strategy

OBJECTIVE

Tumors down-regulate major histocompatibility complex class I expression, escaping recognition by the cellular immune response. We hypothesized that augmentation of tumor cell class I expression by interferon-gamma would enhance the cellular antitumor immune response and cure rate of an active immunotherapy strategy.

METHODS

B16.F10 tumor cells were exposed to interferon-gamma in culture, and class I expression was quantified using flow cytometry. Syngeneic mice bearing established tumors were injected with interferon-gamma (5000 U, intraperitoneal), and class I expression was assessed using immunohistochemistry. Tumor-specific cytotoxic T lymphocytes were induced in mice by an intratumoral injection of AdCD40L (5 x 10(10) particles), an adenovirus gene transfer vector-based immunotherapy strategy previously demonstrated to augment cellular antitumor immunity. A conjugate-formation assay and the enzyme-linked immunospot assay were used to evaluate the binding and activation of cytotoxic T lymphocytes, respectively. Interferon-gamma was administered to tumor-bearing mice concomitantly with intratumoral AdCD40L. End points measured included the frequencies of cytotoxic T lymphocytes using the enzyme-linked immunospot assay, tumor size, and mouse survival. The role of class I expression was further evaluated by monoclonal antibody blockade in both in vitro and in vivo experiments.

RESULTS

B16.F10 cells exposed to interferon-gamma expressed significantly more class I, both in vitro and in vivo, and were able to bind to and activate cytotoxic T lymphocytes more efficiently than untreated cells. Cytotoxic T-lymphocyte frequencies, tumor regression, and the cure rate induced by AdCD40L were augmented by the addition of a single dose of interferon-gamma in tumor-bearing mice. These in vitro and in vivo effects of interferon-gamma were attenuated by class I monoclonal antibody blockade.

CONCLUSIONS

Up-regulation of class I expression using interferon-gamma enhances the cellular antitumor immune response and cure rate of AdCD40L, an active immunotherapy strategy. This approach may be useful for human tumors that lack class I expression.

CD8+ T-cell mediated tumor protection by Pseudomonas exotoxin fused to ovalbumin in C57BL/6 mice

BACKGROUND

Pseudomonas exotoxin (PE) is a 66 kDa bacterial toxin that is able to bind to mammalian cells, undergo receptor mediated endocytosis, and translocate its C-terminal catalytic domain into the cytosol. We investigated whether PE could be used in vivo to deliver CD8+ T-cell epitopes to the MHC-class I antigen presentation pathway to trigger a specific cytotoxic T-lymphocyte (CTL) response.

METHODS

Amino acid 553 of PE was deleted to eliminate toxin catalytic activity, and amino acids 204-386 of ovalbumin were fused near the nontoxic PE C-terminus to produce PE(D)-OVA200. Mice were vaccinated with 100 microg of PE(D)-OVA200 3 times at 21 day intervals. Splenocytes were harvested 1 week later, and stimulated in vitro with ovalbumin expressing EG7 murine thymoma cells. In vivo tumor protection experiments were performed by vaccinating groups of mice as before, followed by a lethal dose of ovalbumin expressing tumor cells (MO5) injected subcutaneously.

RESULTS

Splenocytes from PE(D)-OVA200 vaccinated mice lysed (51)Cr labeled EG7 cells but not the untransfected EL4 parent cell line, whereas splenocytes from mice immunized with PBS, PE(D), or ovalbumin were unable to lyse EG7 cells. Cytotoxicity in vitro was mediated by CD8+ T-cells. PE(D)-OVA200 vaccinated mice survived (88%) a lethal subcutaneous challenge of ovalbumin expressing MO5 cells. Depletion of CD8+ cells from PE(D)-OVA200 vaccinated mice abolished this protection, indicating that this cell population is required for tumor rejection in vivo.

CONCLUSIONS

Our results indicate that PE(D) may be used as a vehicle to stimulate a protective CTL response to heterologous antigen in vivo.

Direct transfection and activation of human cutaneous dendritic cells

Gene therapy techniques can be important tools for the induction and control of immune responses. Antigen delivery is a critical challenge in vaccine design, and DNA-based immunization offers an attractive method to deliver encoded transgenic protein antigens. In the present study, we used a gene gun to transfect human skin organ cultures with a particular goal of expressing transgenic antigens in resident cutaneous dendritic cells. Our studies demonstrate that when delivered to human skin, gold particles are observed primarily in the epidermis, even when high helium delivery pressures are used. We demonstrate that Langerhans cells resident in the basal epidermis can be transfected, and that biolistic gene delivery is sufficient to stimulate the activation and migration of skin dendritic cells. RT-PCR analysis of dendritic cells, which have migrated from transfected skin, demonstrates the presence of transgenic mRNA, indicating direct transfection of cutaneous dendritic cells. Importantly, transfected epidermal Langerhans cells can efficiently present a peptide derived from the transgenic melanoma antigen MART-1 to a MART-1-specific CTL. Taken together, our results demonstrate direct transfection, activation, and antigen-specific stimulatory function of in situ transduced human Langerhans cells.

TGF-beta-based immunotherapy for cancer: breaching the tumor firewall

Many malignant cells secrete transforming growth factor-beta (TGF-beta), a potent immunosuppresant, suggesting that TGF-beta production may represent a significant tumor escape mechanism from host immunosurveillance. Establishment of a leukocyte subpopulation with disrupted TGF-beta signaling in the tumor-bearing host offers a potential means for immunotherapy of cancer. Downregulation of TGF-beta secretion in tumor cells results in restoration of immunogenicity in the host, while T-cell insensitivity to TGF-beta results in accelerated differentiation and autoimmunity, elements of which may be required in order to combat self-antigen-expressing tumors in a tolerized host. The rationale, approaches, and potential pitfalls of this strategy will be discussed.

CD8+ T cells are crucial for the ability of congenic normal mice to reject highly immunogenic sarcomas induced in nude mice with 3-methylcholanthrene

An attempt was made to identify the selection pressures put upon a growing tumour by CD8+ T cells. To this end tumours induced with 3-methylcholanthrene in T cell-deficient nude mice and in congenic T cell-competent nu/+ mice were transplanted to nu/+ recipients. The rejection rate of the sarcomas from nude mice was almost twice that of the sarcomas from nu/+ mice. Depletion of CD8+ T cells from nu/+ recipients prior to transplantation made them accept nude tumours that were consistently rejected by untreated nu/+ recipients. These findings suggest that a methylcholanthrene sarcoma during its growth in a T cell-competent host adapts to the T cell system through a selective elimination of highly immunogenic tumour cells that are susceptible to CD8+ T cell-mediated lysis.

Antibodies for transplantation

The use of antibodies in transplantation has become a clinical reality. Antibodies have been used to both dampen the recipient's immune response and to obscure the immunogenicity of the donor graft. Traditionally, antibodies have been administered to the transplant recipient to transiently inactivate the host's T cells, the lymphocytes responsible for recognizing and attacking foreign proteins, cells, and tissues. Antibodies can also be used to eliminate any highly immunogenic passenger cells from a donor graft prior to transplantation, and antibodies can mask or conceal antigens present on donor cells that might trigger rejection.

Burnet Oration: living in the Burnet lineage

Scientific discoveries are not made in isolation. Innovation depends on resources, both intellectual and physical. A primary requirement is the development and maintenance of appropriate institutions. Such structures do not emerge by chance, but arise from opportunity, political will and the continued efforts and commitment of many people over long periods. Suitable buildings, laboratories and state-of-the-art equipment are obviously necessary, but hardware alone is of little value in the absence of a vibrant research culture. The key characteristics of the latter are intellectual foment, open debate and a body of wisdom and knowledge about the particular subject area. Rolf Zinkernagel and 1 played a part in triggering a paradigm shift in the understanding of T cell recognition, a contribution recognized by the 1996 Nobel Prize for Physiology or Medicine. In our Nobel lectures, we both discussed briefly why it was that the John Curtin School of Medical Research (JCSMR) of 1973-75 provided a milieu that facilitated the emergence of the underlying experiments and ideas. My intention here is to discuss in more detail the scientific lineages that put this physical and intellectual environment in place, focusing particularly on the influence of Sir Frank Macfarlane (Sir Mac) Burnet as we celebrate his centenary year.

Gene therapy--phase I trial for primary untreated head and neck squamous cell cancer (HNSCC) UICC stage II-IV with a single intratumoral injection of hIL-2 plasmids formulated in DOTMA/Chol

Recombinant IL-2 protein has shown many immunostimulatory effects in a variety of human tumors. However, the clinical use of rIL-2 is limited by common and serious side effects after systemic administration. IL-2 expression plasmids may circumvent these drawbacks, producing high local IL-2 concentrations that cause limited or no systemic side effects. Due to the superficial growth of squamous cell carcinoma of the head and neck (HNSCC) are readily accessible for direct intratumoral injection and therefore an optimal target for such a gene therapy approach. There has been evidence for local and systemic activation of immune cells by peritumoral injections of IL-2 in patients with advanced HNSCC (Whiteside et al. 1993; Cortesina et al. 1994; De Stefani et al. 1996). We now perform a placebo-controlled, dose-rising study of the safety and tolerability of a single intratumoral injection of hIL-2 plasmid at four dose levels formulated in DOTMA/Chol in patients with primary untreated head and neck squamous cell cancer (HNSCC) TNM stage II-IV. The patients will be monitored for the occurrence of any adverse reactions to the given medication. In addition, we will determine whether the intratumoral administration of the plasmid induces and or enhances tumor-specific host responses at the immunological and or clinical level.

Vaccination with dendritic cells inhibits the growth of hepatic metastases in B6 mice

Dendritic cells (DC) are specialized antigen-presenting cells that can activate naive and mature T-cells, induce cellular immunity, and stimulate strong antitumor reactions in vivo. This study was undertaken to examine the function of DC vaccines in suppressing the growth of hepatic metastases in C57BL/6 mice. Experimental mice received two i.v. doses of 1 x 10(6) bone marrow-derived DC, either unpulsed or pulsed with MCA-106 fibrosarcoma cell lysates, on days -14 and -7. Controls were injected with HBSS. Hepatic metastases were established on day 0 through intrasplenic injections of 1 x 10(5) MCA-106 tumor cells. Animals were sacrificed on day 21 and their livers were excised to assess tumor burden. Splenocytes from DC-treated groups were cytotoxic against MCA-106 cells, but not against the L929 and CT26 (syngeneic fibroblast and colon tumor, respectively) cell lines. All control mice developed grossly evident hepatic metastases, while 62 and 44% of the mice receiving MCA-106 cell lysate-pulsed DC and unpulsed DC vaccines, respectively, were completely free of tumor. Mean hepatic mass for the controls, including tumor, was almost double that for treated animals. Antibody depletion of either CD4+ or CD8+ lymphocytes abrogated the protective effect of the vaccine. This study demonstrates that immunization with DC confers cellular immunity, with both CD4+ and CD8+ T-cells playing a significant role, and impedes the subsequent establishment and growth of hepatic metastases in mice. The antitumor capabilities of DC justify their use in immunotherapeutic vaccines against human cancers.

Epidermal dendritic cells induce potent antigen-specific CTL-mediated immunity

Professional antigen-presenting cells (APCs) are required for the initiation of an immune response. Dendritic cells (DCs) are the most potent APCs identified thus far and can present antigen in the context of co-stimulatory signals required for the stimulation of both primed and naïve T cells. Cytotoxic T lymphocytes (CTLs) are critical to the immune response against tumors or virally infected cells. Optimal stimulation of antigen-specific CTLs is the goal of evolving immunization strategies for the prevention or therapy of viral infections and tumors. Epidermal dendritic cells (eDCs), or Langerhans cells, can present antigens for the stimulation of CD4+ T cell dependent anti-tumor immunity and may play a role in tumor surveillance. The capacity of eDCs to induce tumor-specific CD8+ CTL immunity has not been determined. We have previously shown that DCs derived from bone marrow precursors (BmDCs) under the influence of cytokines can induce protective, antigen-specific CTL-mediated anti-tumor immunity. Here we show that subcutaneous immunization with ovalbumin (OVA) peptide (SIINFEKL(257-264))-pulsed eDCs induced OVA-specific, CD8+ CTLs that lyse the OVA-expressing target. Furthermore, mice vaccinated with OVA peptide-pulsed eDCs were completely protected from subsequent challenge by the OVA-expressing melanoma MO5. The capacity of peptide-pulsed eDCs to induce CTL-mediated immunity is directly dependent on the dose of eDCs administered. Importantly, the APC capacity of eDCs is comparable to that of BmDCs, as mice immunized with eDC populations containing at least as many class II+/B7.2+ cells as populations of BmDCs were equally protected against challenge with MO5. These results demonstrate that eDCs can be potent inducers of antigen-specific CD8+ CTL-mediated immunity. They suggest that eDCs may be important targets for antigen delivery strategies aimed at inducing antiviral or anti-tumor immunity.

DNA-based immunization by in vivo transfection of dendritic cells

Delivery of antigen in a manner that induces effective, antigen-specific immunity is a critical challenge in vaccine design. Optimal antigen presentation is mediated by professional antigen-presenting cells (APCs) capable of taking up, processing and presenting antigen to T cells in the context of costimulatory signals required for T-cell activation. Developing immunization strategies to optimize antigen presentation by dendritic cells, the most potent APCs, is a rational approach to vaccine design. Here we show that cutaneous genetic immunization with naked DNA results in potent, antigen-specific, cytotoxic T lymphocyte-mediated protective tumor immunity. This method of immunization results in the transfection of skin-derived dendritic cells, which localize in the draining lymph nodes. These observations provide a basis for further development of DNA-based vaccines and demonstrate the feasibility of genetically engineering dendritic cells in vivo.

Methylcholanthrene-induced sarcomas in nude mice have short induction times and relatively low levels of surface MHC class I expression

In order to study the role of the T-cell-mediated immune defense in tumor development, a total of 93 sarcomas were induced using different doses (8 micrograms (0.1%), 40 micrograms (0.5%) and 400 micrograms (5%)) of 3-methylcholanthrene in athymic nude Balb/c mice and phenotypically normal immunocompetent Balb/c mice. A shorter tumor induction time and a higher tumor incidence after treatment with low doses of methylcholanthrene were seen in nude mice than in immunocompetent mice, indicating that they have a lower resistance to the carcinogen. Contrary to expectations we found that the MHC class I expression of tumors from nude mice was lower than that of tumors from normal mice. Higher surface expression of MHC class I was demonstrated on high dose tumors from normal mice than on low dose tumors from normal mice. The cellular composition of the individual tumors raised in nude mice was more heterogeneous with respect to MHC class I expression. Since the mice differ genetically only with respect to the nu gene, these results indicate that a lack of T-cell-mediated defense mechanisms may confer upon the bearer a lower resistance to 3-methylcholanthrene and a different MHC profile of the ensuing tumor.

Natural resistance against tumors grafted into the brain in association with histocompatibility-class-I-antigen expression

The role of MHC-class-I-antigen expression in intracerebral anti-tumor natural resistance was examined using MHC-positive Lym+ and MHC-negative Lym- lymphoma cell lines. Lym+ was sensitive to MHC-class-I-restricted CTL-mediated lysis, while lym- was resistant. Both lines were susceptible to NK-cell-mediated lysis. There was no difference in in vitro growth rate of in vivo intraperitoneal tumorigenicity between them. Inoculation of Lym+ cells into the brain caused upregulation of the intracellular MHC mRNA to the same level as after treatment with interferon-gamma, resulting in an increase in cell-surface MHC expression. Although inoculated Lym- cells also underwent an increase in cytosolic MHC mRNA, the cell-surface MHC expression remained negative. Immunoprecipitation revealed that the terminal glycosylation did not occur normally in Lym-. An in vivo intracerebral tumorigenicity assay, using 2 groups of untreated and NK-cell-depleted syngeneic mice, showed that Lym+ was less tumorigenic than Lym-. In T-cell-depleted mice, however, no difference was detected between them. In addition, when Lym+ and Lym- cells were inoculated into the brain of allogeneic or syngeneic preimmunized mice (immunized with tumor cells), Lym+ was rejected, while Lym- was accepted. When allogeneic mice had received treatment for T-cell depletion before intracerebral inoculation, no rejection was observed in Lym+. On the other hand, Lym- cells, when injected i.p. into NK-depleted mice, had greater killing activity than Lym+ cells, while in T-cell-depleted mice Lym- was less tumorigenic than Lym+. These results suggest that MHC-positive tumor cells grafted into the brain may be rejected by CTL in an MHC-dependent manner, whereas MHC-negative tumor cells can escape from T-cell-mediated immunosurveillance and grow progressively in the brain, due to absence of intracerebral natural resistance mediated by NK cells.

Cancer cell progression and chemoimmunotherapy--dual effects in the induction of resistance to therapy

To determine whether resistance to chemoimmunotherapy is acquired during therapy, we investigated the effects of chemotherapeutic agents and anti-tumour polysaccharide, lentinan, on the progression of Rous sarcoma virus-induced S908.D2 fibrosarcomas. The chemoimmunotherapy was effective against the parental S908.D2-bearing mice. Nearly all the mice that were treated with cyclophosphamide (CY) and lentinan achieved complete tumour regression. Only a few of the mice that achieved complete regression of the primary tumours showed a recurrence of the tumour in regional lymph nodes. S908.D2-vp.1 was established from metastatic tumours that developed in the regional lymph nodes of parental S908.D2-bearing mice during therapy. S908.D2-vp.2-or vp.3 cells were sequentially derived in a similar way from S908.D2-vp.1-or-vp.2-bearing mice respectively, in which complete tumour regression at each primary site was achieved during therapy. These lines acquired resistance to CY and lentinan and also to 5-fluorouracil (5-FU)/5'-deoxy-5-fluorouracil and lentinan. No significant difference in either the sensitivity to 5-FU or 4-deoxycyclophosphamide in vitro or in the susceptibility to immune effector cells was observed between the parental and progressed lines (S908.D2-vp1 -vp3). There was an increase in the level of prostaglandin E2 (PGE2) in the progressed lines during repeated therapy (parental, 1171 pg ml(-1); vp.1, 2199 pg ml(-1); vp.2, 5500pg ml(-1); vp3, 16187 pg ml(-1)). There was no significant increase in the production of transforming growth factor beta (TGF-beta). The amount of interleukin-2 (IL-2) produced by spleen cells isolated from the S908.D2-vp.2-bearing mice was decreased compared with the amount produced by the parental S908.D2- bearing mice. Furthermore, combination therapy with lentinan and IL-2 achieved complete tumour regression in all the mice transplanted with S908.D2 progressed tumour lines, although IL-2 alone did not show any anti-tumour effects in either the S908.D2 parental or progressed lines. The findings suggest that the reduced production of IL-2 induced an increase in the production of the PGE2 by progressed tumour lines is involved in the acquisition of resistance.

Peptide-pulsed dendritic cells induce antigen-specific CTL-mediated protective tumor immunity

Cytotoxic T lymphocytes (CTLs) are a critical component of the immune response to tumors. Tumor-derived peptide antigens targeted by CTLs are being defined for several human tumors and are potential immunogens for the induction of specific antitumor immunity. Dendritic cells (DC) are potent antigen-presenting cells (APCs) capable of priming CTL responses in vivo. Here we show that major histocompatibility complex class I-presented peptide antigen pulsed onto dendritic APCs induces protective immunity to lethal challenge by a tumor transfected with the antigen gene. The immunity is antigen specific, requiring expression of the antigen gene by the tumor target, and is eliminated by in vivo depletion of CD8+ T cells. Furthermore, mice that have rejected the transfected tumor are protected from subsequent challenge with the untransfected parent tumor. These results suggest that immunization strategies using antigen-pulsed DC may be useful for inducing tumor-specific immune responses.

Perforin dependence of natural killer cell-mediated tumor control in vivo

Adaptive immune surveillance by T cells against infections and tumors depends on the presence of antigenic peptides presented by major histocompatibility complex (MHC) molecules. If antigenic tumor-specific peptides or MHC class I molecules are absent, the adaptive T cell immune response fails. Natural killer (NK) cells seem to complement the specific T cells by recognizing target cells lacking MHC class I (e.g. RMA-S). The role of perforin, which is crucially involved in T cell and NK cell-mediated target cell lysis, was evaluated in mice lacking perforin with respect to their capacity to eliminate a syngeneic lymphoid tumor. Here, we show that growth of MHC class I RMA-S tumor cells in unprimed mice was controlled by NK cells through perforin-dependent cytotoxicity.

Beta 2-microglobulin expression of AIDS-related and classical Kaposi's sarcoma

The expression of beta 2-microglobulin, the invariable light chain of HLA class I molecules, of Kaposi's sarcoma from 11 AIDS patients and from 11 patients without known immunodeficiency was studied by immunohistochemistry using a polyclonal antibody to beta 2-microglobulin. The staining intensity of spindle cells in these lesions was scored in a semiquantitative system. We found that the spindle cells of Kaposi's sarcomas from AIDS patients showed significantly increased staining intensity for beta 2-microglobulin compared to those of Kaposi's sarcomas from non-AIDS patients. The results may indicate that Kaposi's sarcomas developing in immunocompromised individuals, such as AIDS patients, are not subject to immune selection by T cells eliminating HLA class I high-expressing tumor cells, while this may be the case in non-AIDS patients. Alternatively, the results may be caused by differences in the activity of cytokines, which upregulate the expression of HLA class I molecules on the cell surface.

Targeting antigen into the phagocytic pathway in vivo induces protective tumour immunity

Cytotoxic T lymphocytes (CTLs) kill neoplastic or virally infected cells after recognizing on their surface antigenic peptides bound to major histocompatibility complex class I molecules. These peptides are derived from antigens that are degraded in the cytosol of the affected cell. Because exogenous proteins cannot enter the cytosol, immunizations with killed pathogens or their proteins do not generally elicit CTLs. However, antigens that are internalized into phagocytic cells can enter the cytosol and be processed for class I presentation. Here we show that immunization with a purified antigen on an avidly phagocytized particle primes CTLs, which in turn protect animals from subsequent challenge with tumours transfected with the antigen gene. Interestingly, these animals also become immune to other antigens expressed by the tumour. This approach could be exploited to develop tumour and viral vaccines.

Major histocompatibility complex antigens in normal, acanthotic and neoplastic ovine skin: an association been tumor invasiveness and low level MHC class I expression

The distribution and density of ovine MHC class I and class II antigens in normal, acanthotic and malignantly transformed ovine skin was investigated using monoclonal antibodies and an immunoperoxidase technique. The subjects were sheep that had been exposed to high levels of sunlight for more than 6 years. The expression of MHC class II antigens in the plasma membrane of cells within the normal epidermis was restricted to basally located dendritic and mononuclear cells. Normal keratinocytes did not express MHC class II antigens. However, we observed low levels of intracellular MHC class II expression in both acanthotic and neoplastic keratinocytes. Expression of MHC class I antigens was variable in normal and acanthotic epithelium; it was usually present, but of low intensity in very early ovine squamous cell carcinoma and was increased in small, but morphologically typical, tumors. Tumors originating on the nose, which are more invasive than those on the ear, were found to express significantly less MHC class I (P < 0.05). Thus, an association between tumor invasiveness and low level expression of MHC class I was apparent. This may have diagnostic value and highlights a mechanism by which neoplastic cells may evade immune surveillance by T cells.

Metastasis of mouse T lymphoma cells is controlled by the level of major histocompatibility complex class I H-2Dk antigens

In vivo inoculation of a low metastatic BW 5147 derived T-cell lymphoma variant into syngeneic mice, had led to the generation of a highly metastatic variant. The shift towards a more metastatic phenotype is accompanied by an increase in major histocompatibility class I H-2Dk antigen expression. This suggests that H-2Dk antigens may control the metastatic potential of BW T lymphoma cells. Our present findings indicate that H-2Dk expression is directly correlated with the metastatic potential of BW cells. We have confirmed such correlation by specifically altering the level of H-2Dk expression by: 1) FACS analysis, 2) IFN-gamma treatment, 3) H-2Dk gene transfection. Cells sorted for low H-2Dk expression had a significantly reduced metastatic potential. Induction of H-2Dk expression on these cells by either IFN-gamma treatment or H-2Dk gene transfection concomitantly led to increased metastasis. We also assessed metastatic potential of BW cells in irradiated, immunocompromised recipients. Our results show that the immune system is implicated and we further tested which immune effectors are involved. In vivo depletion of natural killer (NK) and CD8+ T-cells revealed that the difference in metastatic potential of the H-2Dk variants relies upon an NK-dependent mechanism, whereas CD8+ T-cells are not implicated. Our observations suggest that highly metastatic cells, expressing a high level of H-2Dk antigens are more resistant to NK-cell-mediated cytotoxicity in vivo. We have confirmed our in vivo results by in vitro cytotoxicity assays using poly I:C induced NK and IL-2 activated LAK cells. We conclude that a NK-dependent mechanism accounts for the association between differential H-2Dk antigen expression and metastasis.

Both major and minor peptide-binding pockets in HLA-A2 influence the presentation of influenza virus matrix peptide to cytotoxic T lymphocytes

Most of the polymorphic residues in class I MHC molecules are concentrated in the alpha 1- and alpha 2-domains with their side chains pointing towards the antigen peptide site. Previous crystal structure analysis revealed six pockets inside the peptide-binding groove and the "extra" electron density in some of the pockets indicated that the pockets are involved in direct peptide binding. In order to investigate the functional role of individual positions from each pocket in antigen presentation, 37 HLA-A2 variants with single amino acid substitution in the peptide-binding groove were generated and used to analyse the specificity of influenza A virus matrix peptide-specific, HLA-A2-restricted CTL. The ability to present peptide by each variant was studied in detail by peptide titration, cold target inhibition, time course and limiting dilution analysis. The direct effect on peptide binding by these substitutions was determined by cell surface class I MHC molecule reconstitution analysis. The results demonstrated that each of the six peptide binding pockets plays a role in T cell recognition. Substitutions introduced into pocket F had less effect on CTL recognition than substitutions introduced in other pockets. With the exception of Tyr substitution for Phe9, single amino acid substitutions in the peptide-binding groove had only minor effects on peptide binding. Therefore, the impact of the substitutions in altering the epitopes recognized by CTL seems to be mediated through an alteration in the conformation of the bound peptide.

T-cell based cancer immunotherapy: direct or redirected tumor-cell recognition?

In development of strategies for immunotherapy of cancer a new emphasis is emerging, termed T-cell retargeting, which involves artificial redirection of cytotoxic T lymphocytes (CTL) against cancer cells, using bispecific reagents. In this article, Gideon Beun, Cornelis van de Velde and Gert Jan Fleuren evaluate this potential strategy for cellular immunotherapy, and propose how the gap between in vitro results and clinical application might be bridged.

Tumorigenicity of mouse T lymphoma cells is controlled by the level of major histocompatibility complex class I H-2Kk antigens

We have previously found that an increased tumorigenicity and spontaneous metastatic potential of BW5147-derived T lymphoma cells was associated with a decrease in major histocompatibility complex (MHC) class I H-2Kk antigen expression. This suggested that H-2Kk antigens may control the tumorigenic potential of BW T lymphoma cells. Our current experiments aimed to prove this association by specifically altering H-2Kk expression by gene transfection. Transfected cells expressing a high level of H-2Kk antigens were significantly less tumorigenic and metastatic after subcutaneous inoculation. However, there was selection in vivo for cells expressing a reduced level of H-2Kk antigens, which concomitantly led to an increased tumorigenicity. These data further confirmed the strong association between H-2Kk expression and tumorigenicity. We subsequently tested whether the immune system is implicated in this phenomenon by inoculating the H-2Kk transfectants into irradiated, immunocompromised recipients. Our results indicate that the reduced tumorigenicity of the BW H-2Kk transfectants is due to an immune rejection mechanism, mediated by CD8+ immune effector cells, as revealed by in vivo depletion experiments with anti-CD8 antibodies. Hence, we hereby demonstrated that H-2Kk antigens increased the immunogenicity of BW cells, via a CD8-dependent mechanism, which consequently reduced their tumorigenicity.

Control of metastatic properties of BL6 melanoma cells by H-2Kb gene: immunological and nonimmunological mechanisms

The effect of class I H-2 antigen expression on the metastatic properties of BL6 melanoma cells was investigated. The BL6-8 clone isolated from the highly metastatic BL6 melanoma did not express H-2Kb gene. Following transfection with the H-2Kb gene, BL6-8 cells displayed a low metastatic potential in the immunocompetent as well as immunosuppressed (X-irradiated) or triple-immunodeficient mice with impaired T, B and natural killer (NK) cells function. The expression of H-2Kb gene and the low metastatic ability of transfected BL6 melanoma cells were associated with appearance of cell membrane soybean agglutinin (SBA) and Griffonia simplicifolia 1B4 (GS1B4) lectin-binding carbohydrates. These alterations in cell surface carbohydrates were found to be a result of reduction in sialylation of SBA binding sites and upregulation of the alpha 1.3 galactosyltransferase (alpha 1.3GT) gene. To assess the importance of H-2Kb-induced alterations in cell surface carbohydrates for metastasis formation, BL6-8 melanoma cells were transfected with H-2Kb gene without neor gene cotransfection and selected for adherence to SBA-lectin-conjugated agarose beads. The transfected clones that expressed SBA and GS1B4 lectin-binding carbohydrates were low metastatic. Further analysis of these clones showed that presence of SBA and GS1B4 lectin-binding carbohydrates rather than expression of H-2Kb molecules per se might be responsible for low metastatic potentials of H-2Kb-transfected cells in the immunocompromised mice. Studies of the possible mechanisms responsible for low metastatic ability of H-2Kb-transfected melanoma cells revealed that these cells displayed a reduced ability to adhere to murine pulmonary endothelial cells as well as to laminin and collagen IV. We hypothesized that the observed nonimmunological effects of H-2Kb gene in BL6 melanoma cells is a result of an interaction between the H-2Kb gene and B16 melanoma-specific ecotropic retrovirus. It results in inhibition of this retrovirus production with consecutive alteration in the expression of cellular genes controlling cell surface glycosylation and adhesion properties essential for the metastatic phenotype of BL6 melanoma.

Decreased adhesion to endothelial cells and matrix proteins of H-2Kb gene transfected tumour cells

Transfection of murine metastatic B78H1 cells (derived from B16 melanoma) with a syngeneic H-2Kb gene was used to study the effect of Major Histocompatibility Complex (MHC) gene products on tumour cell adhesion to endothelial cells and matrix proteins and the involvement in the metastatic process. H-2Kb-expressing transfectants showed a reduced adhesion to endothelial surfaces of different origin (four murine endotheliomas and human umbilical vein endothelial cells) when compared to parental B78H1 cells and to controls transfected with pSV2neo alone. On the average a 50-70% reduction in adhesion to endothelial cells was observed among H-2Kb transfectants. H-2Kb transfectants had a reduced expression of the alpha 4 integrin subunit, moreover the adhesion of Neo-transfected clones to endothelial cells was reduced to the levels of H-2Kb transfectants by antibodies directed against the beta 1 subunit and the endothelial VCAM-1 molecule, thus suggesting an impairment of the VLA-4/VCAM-1 interaction in H-2Kb transfectants. Adhesion to extracellular matrix components was also strongly decreased: in general the adhesion of H-2Kb cells showed a 50-75% inhibition with respect to Neo or parental controls. The highest difference was observed in adhesion to vitronectin and laminin, the lowest in adhesion to fibronectin. Reduction in adhesive properties of H-2Kb-expressing transfectants could be involved in the reduced metastatic ability, evaluated by means of intravenous injection of cells: H-2Kb transfectants yielded less than ten lung colonies, while all controls produced more than 100. Our data indicate that expression of a single class I MHC gene can significantly alter the metastatic phenotype of MHC-negative tumour cells and this could be related to a general alteration of tumour cell adhesive interactions.

A tumor escape variant that has lost one major histocompatibility complex class I restriction element induces specific CD8+ T cells to an antigen that no longer serves as a target

After loss of expression of a major histocompatibility complex class I Kk allele, the escape variant of an immunogenic tumor grows progressively in normal mice. This progressor variant is resistant to killing by cytotoxic T lymphocytes (CTLs) directed against the A and B antigens presented by Kk. Although the variant retains the expression of the Dk allele and is sensitive to CTLs directed against the C antigen presented by Dk, the variant failed to induce CTLs to this antigen in vivo. Instead, the variant induced CD8+ T cells directed to the A antigen. This was shown at the molecular level by T cell receptor beta chain sequence analysis of the responding cells. Further evidence for the presence of A antigen in the variant came from the finding that spleen cells of mice injected intraperitoneally with the variant tumor cells were primed for an anti-A CD8+ CTL response in vivo. Thus, in contrast to other variants that lost a target antigen and induced a CTL response to remaining target antigens, the Kk loss variant continued to induce an immune response to a tumor antigen that is no longer presented on the tumor cell surface. Even though the variant escapes in a single step because an effective CTL response to secondary antigens is prevented, these secondary antigens remain as potential targets of immunotherapy on the variant's cell surface.

Identification of H-2Kb-, Db- and Dd-binding peptides derived from amino acid sequences of polyoma virus T antigens

Viral and tumor antigens are presented to cytotoxic T cells (CTL) in the form of short peptides. The peptide antigen is transported to the cell surface in conjunction with molecules encoded by the major histocompatibility complex (MHC). Different methods have recently been described for the analysis of the MHC-class-I binding ability of synthetic peptides. Here, we describe a protocol, based on intact RMA-S cells cultured at 26 degrees C in the presence of synthetic peptides, which gives an allele-specific peptide binding pattern with high resolution. This allowed an analysis of the H-2Kb-, Db- and Dd-binding capacity of a panel of synthetic peptides with amino acid (aa) sequences derived from polyoma (py) virus large-, middle- and small-T (LT, MT and ST) antigens, previously used in immunization experiments against py-virus-induced tumors. Eight single aa mutants and a deletion mutant of one peptide with an ability to bind both to H-2Kb and to Db were also analyzed. We foresee that the present protocol, or variants thereof, may serve as a simple and rapid assay for the systematic screening of the class-I binding ability of large sets of synthetic peptides in vitro. Such analysis may facilitate the search for viral or tumor peptide epitopes that are recognized by CTL.

Efficient major histocompatibility complex class I presentation of exogenous antigen upon phagocytosis by macrophages

Antigens in extracellular fluids can be processed and presented with major histocompatibility complex (MHC) class I molecules by a subset of antigen presenting cells (APCs). Chicken egg ovalbumin (Ova) linked to beads was presented with MHC class I molecules by these cells up to 10(4)-fold more efficiently than soluble Ova. This enhanced presentation was observed with covalently or noncovalently linked Ova and with beads of different compositions. A key parameter in the activity of these conjugates was the size of the beads. The APC that is responsible for this form of presentation is a macrophage. These cells internalize the antigen constructs through phagocytosis, since cytochalasin B inhibited presentation. Processing of the antigen and association with MHC class I molecules appears to occur intracellularly as presentation was observed under conditions where there was no detectable release of peptides into the extracellular fluids. When injected in vivo in C57BL/6 mice, Ova-beads, but not soluble Ova, primed CD4- CD8+ cytotoxic T lymphocytes (CTLs). Similar results were obtained in BALB/c mice immunized with beta-galactosidase-beads. The implications of these findings for development of nonliving vaccines that stimulate CTL immunity are discussed.

Expression of beta 2m-free HLA class I heavy chains in neuroblastoma cell lines

Flow cytometry with the specific monoclonal antibody (MoAb) L31 was used to analyse the expression of HLA class I heavy chains not bound with beta 2-microglobulin (beta 2m) by neuroblastoma (NB) cell lines IMR-32 and LA-N-1. The cells, which express barely detectable amounts of beta 2m-free (L31-positive molecules) and beta 2m-complexed HLA class I antigens (W6.32- and BBM.1-reactive molecules), expressed MHC class I molecules not bound to light chains upon differentiation with either retinoic acid or serum starvation. The expression was not accompanied by an increase of surface heterodimers. Conversely, recombinant interferon-gamma (rIFN-gamma) treatment led IMR-32 and LA-N-1 cells to almost exclusively express beta 2m-complexes HLA class I heavy chains. Surface beta 2m-free MHC class I molecules displayed a molecular mass of approximately 45 kDa and did not bind exogenously added beta 2m. No changes in the synthesis of either HLA class I and beta 2m mRNAs or of L31 proteins were observed in differentiated NB cells, thus suggesting that the surface exposure of unusual HLA class I antigens is regulated post-translationally. These findings indicate that, in addition to activated lymphocytes, the surface expression of beta 2m-free class I heavy chains is a feature of other cell types, such as NB cells.

Increased projection of MHC and tumor antigens in murine B16-BL6 melanoma induced by hydrostatic pressure and chemical crosslinking

The B16-BL6 melanoma, like most spontaneously arising tumors, is poorly immunogenic and expresses low levels of major histocompatibility complex (MHC) antigens. Treatment of cells of this tumor in vitro by hydrostatic pressure in the presence of adenosine 2',3'-dialdehyde (oxAdo), a membrane-impermeant crosslinker, caused elevated projection of MHC and a specific tumor antigen as demonstrated by flow-cytometric analysis. Maximum projection of both the MHC and the tumor antigens could be reached by application of 1200 atm for 15 min in the presence of 20 mM oxAdo. It is not yet clear whether this passive increase in availability of antigens on the cell surface originated from a dormant pool of antigens in the plasma membrane or from pressure-induced fusion of antigen-rich intracellular organelles (e.g. the endoplasmic reticulum). The immunogenic properties of the antigen-enriched B16-BL6 cells are described in the following paper.

Tumors developing in nude mice express unusually large amounts of MHC class I antigens

Tumors were induced in athymic, T-cell-deficient nude mice and in syngeneic normal haired mice by treatment with low doses of 3-methylcholantrene (MCA). The tumors were studied for tumor cell expression of MHC class I molecules and for immunogenicity by transplantation to syngeneic haired recipients. Ten tumors were obtained by the MCA treatment, six from nude and four from haired mice. They were all fibrosarcomas as judged from their microscopic appearance. Five of the "nude" tumors expressed measurable amounts of MHC class I molecules and two of them expressed high amounts. Both were immunogenic in the sense that they evoked a cytotoxic T-cell response in transplanted haired recipients. Only one of the four "haired" tumors expressed measurable amounts of MHC class I, and none of them were immunogenic. These findings support the concept that some tumors are immunoselected at an early point of time in their existence in a host with a normal immune system and that this results in an elimination of tumor cell variants which are highly immunogenic for the T-cell system, leaving the low or non-immunogenic variants. These take over and grow and kill their host. The results suggest that tumor cell variants expressing high amounts of MHC class I are important targets in the immunoselection in hosts with a normal immune system.

HLA antigen expression and malignant mesothelioma

The expression of HLA antigens by a tumor may determine its progression and metastatic potential by influencing the immune response to that tumor. The upregulation of HLA antigen expression on some cell types by interferons (IFNs) may contribute to their antitumor activity. Malignant mesothelioma (MM) is a tumor that has a poor prognosis and is unaffected by conventional therapy, although immunotherapy has not been adequately assessed. In this study, we have examined the constitutive and IFN-inducible expression of class I and class II HLA antigens on MM cell lines using indirect immunofluorescence and Northern blotting. All MM cell lines constitutively expressed class I, but not class II, surface antigen, and all three class I loci (HLA-A, HLA-B, and HLA-C) were expressed. The MM cell lines were heterogeneous in their response to the IFNs. Treatment with IFN-alpha marginally increased class I surface expression, but not class II. Class I mRNA was, however, clearly increased in all cell lines after IFN-alpha treatment, suggesting that class I surface antigen was already maximally expressed. IFN-gamma increased class I mRNA expression in all but one cell line and induced DR expression on three of the cell lines. DQ-beta, but not DQ-alpha, mRNA was inducible in the same three cell lines, but DQ surface antigen was never demonstrable.(ABSTRACT TRUNCATED AT 250 WORDS)

Promotion of tumor growth by transfecting antisense DNA to suppress endogenous H-2Kk MHC gene expression in AKR mouse thymoma

Many AKR spontaneous thymomas are reported to express different amounts of the major histocompatibility complex class I H-2Kk molecules. Moreover, H-2Kk-deficient AKR tumor cells are found to be more malignant when compared to tumor cells that express abundant levels of the H-2Kk molecules. To corroborate further the role of H-2Kk in tumorigenesis of AKR leukemia, we have, in this study, expressed antisense H-2Kk RNA in a high-H-2Kk-expressing and poorly tumorigenic AKR thymoma cell line 369. The down-regulation of H-2Kk molecules in the transfected 369 clones rendered them more tumorigenic in syngeneic AKR/J mice. The increase in oncogenicity correlates well with a concomitant reduction in their susceptibility to tumor-specific cytotoxic T lymphocytes in vitro. These results suggest the relevance of H-2Kk molecules in the immune surveillance of AKR tumors.

Class I-induced resistance to natural killing: identification of nonpermissive residues in HLA-A2

Structural characteristics of major histocompatibility complex class I antigens associated with natural killer (NK)-resistance phenomena were examined. Previous research has shown that transfection of class I genomic DNA clones into class I-deficient, NK-sensitive target cell lines results in transfectants exhibiting class I+, NK-resistant phenotypes. In contrast to the HLA-A3, -B7, -B27, and -Bw58 class I molecules, the HLA-A2 class I molecules were shown not to protect target cells from NK activity. Here we show that this nonprotective phenotype maps to the alpha 1 domain of the HLA-A2 molecule by examining the NK-protective capacity of the natural interdomain recombinant HLA-Aw69 molecule. HLA-Aw69, which consists of an alpha 1 domain exhibiting homology with HLA-Aw68, and alpha 2/alpha 3/transmembrane-cytoplasmic domains, exhibiting homologies with HLA-A2, mimics HLA-Aw68 and provides HLA-A,B null target cell (C1R) transfectants with increased resistance to NK. Further, the inability of transfected HLA-A2 to confer protection against NK activity can be completely attributed to the expression of a "nonpermissive" residue at position 74 in the alpha 1 domain. Site-directed mutation of the His-74 residue in HLA-A2 to the Asp-74 (HLA-A3, -Aw68, -Aw69, -B7) residue generates a mutant that provides C1R cell line transfectants an NK-resistant phenotype. As His-74 blocks access to a side pocket in the HLA-A2 antigen-binding cleft, these results support the critical involvement of residues within the peptide-binding groove of class I molecules in determining the NK susceptibility phenotype of class I+ target cells.

Prevention of xenograft rejection by masking donor HLA class I antigens

Destruction of target cells by cytotoxic T lymphocytes requires the presence of HLA (human lymphocyte antigen) class I antigens on the target cells for adhesion as well as for triggering of the antigen-specific T cell receptor. Rejection of xenogeneic human pancreatic islets and liver was circumvented by masking, before transplantation, donor antigens with F(ab')2 antibody fragments to HLA class I or tissue-specific epitopes. This strategy eliminated the need for recipient immunosuppression and allowed islet xenograft survival beyond 200 days, as demonstrated functionally by C peptide secretion as well as by histology. These in vivo observations are consistent with the importance of donor HLA class I in eliciting graft rejection and have potential applicability to the successful transplantation of other HLA class I-bearing donor tissues.