Morphological appearance, content of extracellular matrix and vascular density of lung metastases predicts permissiveness to infiltration by adoptively transferred natural killer and T cells

We have recently shown that adoptively transferred, IL-2-activated natural killer (A-NK) cells are able to eliminate well-established B16-F10.P1 melanoma lung metastases. However, some B16-F10.P1 lung metastases were resistant to infiltration by the A-NK cells and also resistant to the A-NK cell treatment. The infiltration-resistant (I-R) B16-F10.P1 metastases had a unique "compact" morphology compared to the "loose" morphology of the infiltration-permissive (I-P) metastases. Here, we show that I-P loose tumors and I-R compact tumors are also found in lung metastases of mouse Lewis lung carcinoma (3LL), MCA-102 sarcoma, and MC38 colon carcinoma as well as rat MADB106 mammary carcinoma origin. Furthermore, the infiltration resistance of the compact tumors is not restricted to A-NK cells, since PHA and IL-2 stimulated CD8+ T-cells (T-LAK cells) also infiltrated the compact tumors poorly. Analyses of tumors for extracellular matrix (ECM) components and PECAM-1(+) vasculature, revealed that the I-R lesions are hypovascularized and contain very little laminin, collagen and fibronectin. In contrast, the I-P loose tumors are well-vascularized and they contain high amounts of ECM components. Interestingly, the distribution pattern of ECM components in the I-P loose tumors is almost identical to that of the normal lung tissue, indicating that these tumors develop around the alveolar walls which provide the loose tumors with both a supporting tissue and a rich blood supply. In conclusion, tumor infiltration by activated NK and T cells correlates with the presence of ECM components and PECAM-1(+) vasculature in the malignant tissue. Thus, analysis of the distribution of ECM and vasculature in tumor biopsies may help select patients most likely to benefit from cellular adoptive immunotherapy.

[Life-threatening serotonin syndrome following a single dose of a serotonin reuptake inhibitor during maintenance therapy with a monoamine oxidase inhibitor]

A 72-year-old man presented to the emergency clinic with motor restlessness and diminished consciousness 24 hours after he had mistakenly been given venlafaxine. He was referred from the psychiatric clinic where he was treated with tranylcypromine. Shortly after arrival, a severe serotonin syndrome developed with generalised myoclonic seizures, hyperreflexia, hypertonia, a rapid increase in temperature to 40.9 degrees C, hypertension, tachycardia, respiratory insufficiency, hyperkalaemia and metabolic acidosis. The patient was treated with the sedative propofol and the muscle relaxant rocuronium, followed by intubation and artificial respiration. He was cooled on a cooling mattress. Twenty-four hours later the airway tube could be removed and after 48 hours he was returned to the psychiatric ward in good condition. Tranylcypromine is a monoamine oxidase inhibitor and venlafaxine is a serotonin and noradrenaline reuptake inhibitor. When two serotoninergic agents are combined, the serotonin syndrome may develop, and this may be life-threatening. The treatment of this syndrome with propofol and rocuronium can be given quickly and safely in practically every hospital.

Membrane-bound complement regulatory proteins inhibit complement activation by an immunotherapeutic mAb in a syngeneic rat colorectal cancer model

MAb-mediated immunotherapy offers a potential tool for destroying metastasizing colorectal tumor cells. Promising results have been obtained by using xenograft models. However, overexpression of membrane-bound complement regulatory proteins (mCRP) impedes complement-mediated destruction of tumor cells in vitro. mCRP operate in a species selective manner. Therefore a syngeneic animal model is needed to investigate the contribution of mCRP in mAb-mediated immunotherapy. Here we present a syngeneic rat colorectal carcinoma model, which fulfills the conditions necessary to investigate the effect of mCRP expression on mAb-mediated immunotherapy of metastases of solid tumors.CC531 rat colorectal cancer cells were injected subcapsularly into the liver of syngeneic WAG/Rij rats. Four mAb (MG1(IgG2a), MG2(IgG2a), MG3(IgG3) and MG4(2a)(IgG2a)) directed against CC531 cells, were tested for their complement activating abilities in vitro and tumor homing capacities in vivo. Only MG4(2a) was found to activate complement in vitro and home to the tumor cells in vivo. This mAb induced C3-deposition and C-mediated lysis of CC531 cells in vitro when the effects of the C-inhibitors Crry/p65 and CD59 were neutralized. This implies an important role for these mCRP in restricting the effector functions of tumor-associated mAb on these cells. Although C activation could be induced by MG4(2a) in situ on tumor tissue sections, no deposition of C3 could be found on the tumor cells positive for MG4(2a) in vivo. This suggests that complement activation in vivo was inhibited by mCRP. The results indicate the suitability of this syngeneic animal model for studying the effects of mAb immunotherapy. However, the effect of mCRP on tumor cells need to be overcome, e.g. by the use of mAb against tumor antigens and mCRP.

Role of NK cells in adoptive immunotherapy of metastatic colorectal cancer in a syngeneic rat model

This article reviews our immunotherapy research with natural killer (NK) cells in a syngeneic rat colorectal cancer liver and lung metastasis model. Using adoptive transfer of interleukin (IL)-2-activated NK cells, NK cells were shown to selectively infiltrate the tumors. More NK cells were found in tumors when the NK cells were directly injected into tumor-draining blood vessels than when the cells were injected in systemic blood vessels. Under optimal conditions, a limited, though significant, effect of adoptively transferred NK cells on tumor growth was shown. We observed that both endogenous and adoptively transferred NK cells were predominantly present in the stroma surrounding the tumor cell nodules. It is possible that they did not penetrate the nodules containing the tumor cells because of the presence of a basal membrane-like structure around these nodules. Adoptively transferred NK cells may initiate elimination of tumor cells by activating other effector cells, whereas some may eliminate tumor cells by direct cell-cell contact. A diverse array of molecules was shown to be involved in this process. CD45 on NK cells was found to be important in initiating the lysis-inhibitory signal upon binding of 'self' major histocompatibility complex (MHC) class I on potential target cells. Our results indicate that NK-cell cancer therapy is still promising and needs improvement.

The development of novel mouse monoclonal antibodies against the CC531 rat colon adenocarcinoma

In this paper we describe 4 new monoclonal antibodies to be applied in rat models for cancer. The monoclonal antibodies were obtained by immunizing Balb/c mice with CC531 rat colon adenocarcinoma cells. Hybridomas were produced and 4 were selected for their reactivity with CC531 in vitro (MG1, 2, 3 and 4). All 4 antibodies recognized other rat tumour cell lines and showed limited cross-reactivity with normal rat tissues. Intraperitoneally injected MG1, 2 and 4 homed to in vivo growing, artificially induced CC531 liver metastases. In these in vivo experiments, limited cross-reactivity with normal rat tissues, predominantly of the gastro-intestinal tract, was found. MG4 was found to enhance lysis of CC531 tumour cells mediated by IL-2 activated, cultured natural killer cells. These antibodies are potentially useful for antibody-based laboratory techniques and for investigation of antibody-based immunotherapy of cancer in a rat model.

The microscopic anatomy of experimental rat CC531 colon tumour metastases: consequences for immunotherapy?

The colon adenocarcinoma cell line CC531 was adopted as a model for immunotherapeutical treatment of experimental colorectal metastases in a syngeneic rat model. We studied the presence and localization of T and natural killer cells, vessels and matrix proteins in in vivo growing CC531 tumours by immunohistochemistry. CC531 tumours were induced either in the lungs by injecting CC531 tumour cells into a tail vein or in the liver by injection of CC531 tumour cells under the liver capsule or into a mesenteric vein. All 3 tumour types were composed of islets of tightly apposed tumour cells surrounded by abundantly present tumour-stroma which contained tumour vessels and matrix proteins. Some of these matrix proteins, especially laminin and collagen IV formed a basal membrane-like structure around the tumour nodules. This structure was most pronounced in mesenteric vein-induced liver tumours and less prominent in subcapsular-induced liver tumours and tail vein-induced lung tumours. Tumour-infiltrating lymphocytes of both T and natural killer cell origin were found in the tumours, but predominantly in the tumour stroma, separated from the islets of tumour cells by the basal membrane-like structure. We hypothesize that the matrix proteins of these tumours play an ambivalent role: they may provide a substratum for migration of effector cells into the tumour stroma but may also provide a barrier preventing direct contact between tumour target cells and immune effector cells.

Administration of BiMAb-retargeted T cells in a rat hepatic metastases colon tumour model results in T-cell tumour infiltration independent of the route of administration

In this study, cultured T cells, pre-incubated with the bispecific monoclonal antibody (BiMAb) R73IgG1 x CC52IgG1 were adoptively transferred, via systemic and regional routes, to rats bearing day 10 hepatic metastases of the CC531 adenocarcinoma of the colon to investigate the role of the route of administration in tumour infiltration by these BiMAb-retargeted effector cells. The BiMAb, directed against the T-cell receptor and the tumour-associated antigen CC52, were used to crosslink CC531 tumour cells and T cells to induce tumour cell lysis. Retargeted T cells were administered via the jugular vein, hepatic artery or the portal vein. The number of BiMAb-retargeted T cells that reached the liver tumours was independent of the route of administration. There was also no difference between the number of T cells that reached the portal tracts, central veins of parenchyma of the liver, after loco-regional or systemic administration. These findings are in contrast to the interleukin (IL)-2 activated NK (A-NK) cells biodistribution studies earlier performed in the same animal model in our laboratory. Compared with A-NK cells, a lower number of BiMAb-retargeted T cells reached the tumours, irrespective of their route of administration while for A-NK cells, there was an advantage of administration via the hepatic artery.

Tumor structure and extracellular matrix as a possible barrier for therapeutic approaches using immune cells or adenoviruses in colorectal cancer

In this article we report about the role that tumor structure and extracellular matrix (ECM) may play in immunotherapy and in gene therapy using adenoviruses. We performed studies in a rat model for colorectal cancer, CC531, and in specimens of human colorectal cancer. The tumors were composed of two compartments, tumor cell nests surrounded by stromal cells. ECM proteins were expressed in the stromal part, where the blood vessels were also located. Furthermore, in several tumors, the tumor cell nests were surrounded by basal membrane-like structures. Therefore, in vascular approaches to treat cancer, therapeutic agents on their route to tumor cells may be hampered by ECM to reach tumor cells. We found that immune cells were abundantly present in tumors from colorectal origin. These cells were, however, not found in direct contact with tumor cells, but mainly in the stromal part of the tumor. Adenoviruses, when intravascularly injected, did not reach tumor cells in the CC531 rat model. Tumor cells were only infected, and even then in limited numbers, in cases of intratumoral injection. We hypothesize that ECM in a tumor is a barrier both for immune cells and for adenoviruses to make direct contact with these tumor cells, and thus limits colorectal tumor therapy.

NK cells modulate MHC class I expression on tumor cells and their susceptibility to lysis

Cytotoxicity and production of cytokines are two important functions of NK cells. These two different NK functions were studied in a syngeneic rat model in relation to MHC class I expression. We focussed on the mechanism by which NK cells modulate MHC class I expression on target cells and how this interferes with NK cell-mediated lysis. Using transfection experiments an inhibitory role on NK cell cytotoxicity for expression of target cells of RT1.A, rat MHC class I, was found. Co-culturing syngeneic tumor cells and NK cells resulted in enhanced MHC class I expression on the surviving tumor cell fraction, which was less susceptible to NK lysis. Increased tumor cell MHC class I was due to production of a soluble factor by NK cells, most likely interferon gamma. The regulatory function of NK cells shows here, that the enhancing of MHC class I expression on tumor cells in vitro and in vivo, results in downregulation of their target cell killing, but at the same time may facilitate the cytotoxic T cell function.

Expression profile of saccharide epitope CaMBr1 in normal and neoplastic tissue from dogs, cats, and rats: implication for the development of human-derived cancer vaccines

CaMBr1 is a blood group-related tumour-associated antigen, whose pattern of expression provides a therapeutic window for passive or active immunotherapy and points to the promise of a vaccine against carcinomas overexpressing this antigen. In this context, an animal model that closely mimics the human situation would be extremely useful. We, therefore, utilised the murine monoclonal antibody MBr1, which defines CaMBr1, as a useful probe to detect the molecule targeted for vaccine development on canine and feline spontaneous breast and uterus tumours and on their normal counterparts, and on rat normal tissues and carcinoma cell lines. Immunoperoxidase staining of cryostat sections revealed homogeneous CaMBr1 expression only in normal feline uterus and a uterus papilloma, whereas MBr1 reactivity was very weak and heterogeneous in normal (1/3 and 1/3) and tumour (1/10 and 1/6) breast tissues from dogs and cats, respectively. In contrast, the data obtained in rat tissues were reproducible in the strains tested and showed that CaMBr1 was expressed in all epithelial tissues of the digestive tract, although with variable intensities. Monoclonal antibody staining appeared to correspond to membrane-bound structures as well as mucinous secretions. Similarly, secretion products of lactating mammary glands expressed CaMBr1. The spectrum of expression on rat digestive tract was broader than that in humans but the specificity of MBr1 reactivity was confirmed by competition assay with a synthetic tetrasaccharide that mimics the CaMBr1 antigen. On FACS analysis, only one of two clonal derivatives of the rat breast carcinoma line RAMA 25 expressed CaMBr1, and a negative cell subset was evident in repeated experiments. By contrast, both colon carcinoma lines, DHD/K12 and CC531, showed staining with MBr1, albeit at different levels of intensity, and no evidence of a negative subset. The cell line CC531 maintained or even increased CaMBr1 expression levels following transplantation in syngeneic immunocompetent animals. Our data suggest the usefulness of the rat as a test model for vaccines against human cancers overexpressing the CaMBr1 antigen.

Bispecific antibodies in cancer therapy, from the laboratory to the clinic

Bispecific monoclonal antibodies (BiMAb) have been shown to be able to contribute to an immunological approach in cancer therapy. In this review, essential aspects regarding the production of BiMAb and modes to apply them in immunotherapy for cancer are discussed. The pros and cons of BiMAb are considered, and the development from application in animal models to clinical studies is reviewed. The most important clinical trials are summarized, and the different problems encountered are discussed. Provided some crucial problems can be overcome, BiMAb will have a place in the treatment of cancer, especially in the setting of minimal residual disease.

The development of a bi-specific anti-CD161A x anti-tumor antibody for rat NK cell targeting

In order to improve the therapeutic efficacy of adoptive immunotherapy of cancer using IL-2-activated NK (A-NK) cells, we developed a bi-specific monoclonal antibody (BimAb) 3.2.3xCC52. One specificity of the BimAb (mAb 3.2.3) was directed against rat CD161A (NKR-P1A) which has been shown to be an activation structure on rat NK cells involved in lysis of target cells and cytokine secretion. The other specificity (mAb CC52) was directed against a tumor associated antigen on the rat colon adenocarcinoma cell line CC531. The hybridomas producing 3.2.3 and CC52 were fused, resulting in a quadroma producing the desired 3.2.3xCC52 BimAb. The hybridomas produced antibodies of different isotypes (IgG2b and IgG1 respectively) which enabled us to pre-select quadromas with a high likelihood for production of BimAb, through testing for the production of bi-isotypic antibodies. Production of functional BimAb by the selected quadromas was demonstrated in an assay showing enhanced conjugate formation between CD161A+ cells and CC531 tumor cells. We also tested the 3.2.3xCC52 BimAb for its capacity to enhance NK cell-mediated lysis of CC531 tumor cells in 4 h and 19 h 51Cr release assays; in a prolonged (2 day) tumor neutralization assay using a tetrazolium salt (MTT)-based assay; and in tests for apoptosis using Annexin V-FITC. Although this BimAb was not demonstrated to cause enhanced lysis of CC531 cells by CD161A+ effector cells in vitro, it might be a useful tool to enhance the number of NK cells at the tumor site and/or prolong contact between tumor cells and NK cells in vivo, thereby probably enhancing the therapeutic efficacy of NK cells.

Characteristics of tumor infiltration by adoptively transferred and endogenous natural-killer cells in a syngeneic rat model: implications for the mechanism behind anti-tumor responses

Interleukin-2-activated, cultured NK cells (A-NK) cells were adoptively transferred into a syngeneic rat liver-tumor model. The kinetics of tumor infiltration by NK cells, originating either from adoptively transferred or from endogenous sources, the localization of these cells in the tumor, and their interactions with extracellular-matrix proteins were studied by immunohistochemistry and transmission-electron microscopy. The adoptive transfer of A-NK cells via the hepatic artery and s.c. injections of IL-2 into rats bearing subcapsularly induced CC531 liver tumors, but also IL-2 monotherapy, resulted in a significant increase of the number of NK cells both at the tumor border and in the tumor center. The majority of tumor-infiltrating NK cells was present in the tumor stroma and only occasionally was an NK cell observed in a tumor nodule in direct contact with tumor cells. Observations by electron microscopy suggested that matrix proteins, abundantly present in the tumor stroma but absent in the tumor nodules, provide a substrate for migration of infiltrating cells, whereas tight structures of matrix proteins surrounding tumor nodules provide a barrier for establishment of direct NK-cell-to-tumor-cell-contact. Our results suggest that direct NK-cell-to-target-cell-contact-mediated lysis is of minor importance for attaining an anti-tumor effect in this model. We hypothesize that treatment of tumor-bearing rats with A-NK cells and/or IL-2 initiates a cascade of events (e.g., secretion of tumor-killing cytokines and/or infiltration of other immune cells) ultimately leading to tumor regression.

Regional administration of natural killer cells in a rat hepatic metastasis model results in better tumor infiltration and anti-tumor response than systemic administration

A syngeneic rat liver metastasis model, the CC531 colon carcinoma cell line in Wag rats, was used to study the homing properties and anti-tumor effects of adoptively transferred, interleukin-2 (IL-2)-activated, cultured natural killer (A-NK) cells. To identify the route of administration that gives the highest tumor infiltration, 1.5 x 10(8) A-NK cells were dyed with fluorescent rhodamine and injected via 4 different routes into rats, bearing subcapsularly induced (day 10) liver metastases. The routes chosen were: jugular vein, portal vein, hepatic artery and directly into the peritoneal cavity (i.p). The rats were sacrificed 20 hr after administration of A-NK cells. The highest (p < 0.05) infiltration of tumors by A-NK cells was found both at the tumor border and in the tumor center after injection via the hepatic artery: 65 +/- 7 A-NK cells/mm2 at the tumor border and 26 +/- 14 A-NK cells/mm2 in the center of the tumor (jugular vein infusion: 32 +/- 10 and 9 +/- 5 A-NK cells/mm2, respectively; portal vein infusion: 36 +/- 13 and 7 +/- 4 A-NK cells/mm2, respectively). No A-NK cells were detected in the liver after i.p. injection. Rats bearing day 5 tumors were injected with 1.5 x 10(8) A-NK cells via the hepatic artery or via the jugular vein (n = 5 and n = 6 respectively). Regional administration of A-NK cells via the hepatic artery resulted in a significant (p < 0.05) lower weight (35 +/- 23 mg) of tumors than did systemic administration (70 +/- 10 mg). Our results suggest that both the level of tumor infiltration by adoptively transferred A-NK cells and the therapeutic outcome depend on the route of administration.