Therapy of human non-small-cell lung carcinoma using antibody targeting of a modified superantigen

A T cell receptor β chain-directed antibody fusion molecule activates and expands subsets of T cells to promote antitumor activity

Despite the success of programmed cell death-1 (PD-1) and PD-1 ligand (PD-L1) inhibitors in treating solid tumors, only a proportion of patients respond. Here, we describe a first-in-class bifunctional therapeutic molecule, STAR0602, that comprises an antibody targeting germline Vβ6 and Vβ10 T cell receptors (TCRs) fused to human interleukin-2 (IL-2) and simultaneously engages a nonclonal mode of TCR activation with costimulation to promote activation and expansion of αβ T cell subsets expressing distinct variable β (Vβ) TCR chains. In solution, STAR0602 binds IL-2 receptors in cis with Vβ6/Vβ10 TCRs on the same T cell, promoting expansion of human Vβ6 and Vβ10 CD4+ and CD8+ T cells that acquire an atypical central memory phenotype. Monotherapy with a mouse surrogate molecule induced durable tumor regression across six murine solid tumor models, including several refractory to anti-PD-1. Analysis of murine tumor-infiltrating lymphocyte (TIL) transcriptomes revealed that expanded Vβ T cells acquired a distinct effector memory phenotype with suppression of genes associated with T cell exhaustion and TCR signaling repression. Sequencing of TIL TCRs also revealed an increased T cell repertoire diversity within targeted Vβ T cell subsets, suggesting clonal revival of tumor T cell responses. These immunological and antitumor effects in mice were recapitulated in studies of STAR0602 in nonhuman primates and human ex vivo models, wherein STAR0602 boosted human antigen-specific T cell responses and killing of tumor organoids. Thus, STAR0602 represents a distinct class of T cell-activating molecules with the potential to deliver enhanced antitumor activity in checkpoint inhibitor-refractory settings.

Apoptosis-mediated inhibition of human T-cell acute lymphoblastic leukemia upon treatment with Staphylococus Aureus enterotoxin-superantigen

Patients with relapsed T cell acute lymphoblastic leukemia (T-ALL) have limited therapeutic options and poor prognosis. The finding of efficient strategies against this refractory neoplasm is a medical priority. Superantigens (SAgs) are viral and bacterial proteins that bind to major histocompatibility complex class II molecules as unprocessed proteins and subsequently interact with a high number of T cells expressing particular T cell receptor Vβ chains. Although on mature T cells, SAgs usually trigger massive cell proliferation producing deleterious effects on the organism, in contrast, on immature T cells, they may trigger their death by apoptosis. On this basis, it was hypothesized that SAgs could also induce apoptosis in neoplastic T cells that are usually immature cells that probably conserve their particular Vβ chains. In this work, we investigated the effect of the SAg Staphylococcus aureus enterotoxin E (SEE) (that specifically interacts with cells that express Vβ8 chain), on human Jurkat T- leukemia line, that expresses Vβ8 in its T receptor and it is a model of the highly aggressive recurrent T-ALL. Our results demonstrated that SEE could induce apoptosis in Jurkat cells in vitro. The induction of apoptosis was specific, correlated to the down regulation of surface Vβ8 TCR expression and was triggered, at least in part, through the Fas/FasL extrinsic pathway. The apoptotic effect induced by SEE on Jurkat cells was therapeutically relevant. In effect, upon transplantation of Jurkat cells in the highly immunodeficient NSG mice, SEE treatment reduced dramatically tumor growth, decreased the infiltration of neoplastic cells in the bloodstream, spleen and lymph nodes and, most importantly, increased significantly the survival of mice. Taken together, these results raise the possibility that this strategy can be, in the future, a useful option for the treatment of recurrent T-ALL.

Mechanistic and pharmacodynamic studies of DuoBody-CD3x5T4 in preclinical tumor models

CD3 bispecific antibodies (bsAbs) show great promise as anticancer therapeutics. Here, we show in-depth mechanistic studies of a CD3 bsAb in solid cancer, using DuoBody-CD3x5T4. Cross-linking T cells with tumor cells expressing the oncofetal antigen 5T4 was required to induce cytotoxicity. Naive and memory CD4+ and CD8+ T cells were equally effective at mediating cytotoxicity, and DuoBody-CD3x5T4 induced partial differentiation of naive T-cell subsets into memory-like cells. Tumor cell kill was associated with T-cell activation, proliferation, and production of cytokines, granzyme B, and perforin. Genetic knockout of FAS or IFNGR1 in 5T4+ tumor cells abrogated tumor cell kill. In the presence of 5T4+ tumor cells, bystander kill of 5T4− but not of 5T4−IFNGR1− tumor cells was observed. In humanized xenograft models, DuoBody-CD3x5T4 antitumor activity was associated with intratumoral and peripheral blood T-cell activation. Lastly, in dissociated patient-derived tumor samples, DuoBody-CD3x5T4 activated tumor-infiltrating lymphocytes and induced tumor-cell cytotoxicity, even when most tumor-infiltrating lymphocytes expressed PD-1. These data provide an in-depth view on the mechanism of action of a CD3 bsAb in preclinical models of solid cancer.

Novel tri-specific tribodies induce strong T cell activation and anti-tumor effects in vitro and in vivo

Background

Immunotherapy based on Bi-specific T Cell Engagers (TCE) represents one of the most attractive strategy to treat cancers resistant to conventional therapies. TCE are antibody-like proteins that simultaneously bind with one arm to a Tumor Associated Antigen (TAA) on cancer cells and with the other one to CD3 complex on a T-cell to form a TCR-independent immune synapse and circumvent Human Leucocyte Antigen restriction. Among them, the tribodies, such as Tb535H, a bi-specific molecule, made up of a Fab and a scFv domain both targeting 5T4 and another scFv targeting CD3, have demonstrated anti-tumor efficacy in preclinical studies.

Methods

Here, we generated five novel tri-specific and multi-functional tribodies, called 53X tribodies, composed of a 5T4 binding Fab arm and a CD3 binding scFv, but differently from the parental Tb535H, they contain an additional scFv derived from an antibody specific for an immune checkpoint, such as PD-1, PD-L1 or LAG-3.

Results

Compared with the parental Tb535H bi-specific T cell engager targeting 5T4, the novel 53X tribodies retained similar binding properties of Tb535H tribody, but showed enhanced anti-tumor potency due to the incorporation of the checkpoint inhibitory moiety. In particular, one of them, called 53L10, a tri-specific T cell engager targeting 5T4, CD3 and PD-L1, showed the most promising anti-tumor efficacy in vitro and led to complete tumor regression in vivo.

Conclusions

The novel tribodies have the potential to become strong and safe therapeutic drugs, allowing to reduce also the cost of production as one single molecule contains three different specificities including the anti-TAA, anti-CD3 and anti-IC binding arms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02474-3.

High Prevalence of 5T4/Trophoblast Glycoprotein in Soft Tissue Sarcomas

The expression of 5T4/trophoblast glycoprotein was evaluated in several histological subtypes of soft tissue sarcoma (STS) to determine whether the prevalence and level of expression of this membrane-associated glycoprotein is sufficient for use in targeted therapies. Tumor tissue microarrays containing cores from different histological subtypes of STS were stained using a standardized immunohistochemical staining method to detect 5T4; the level of staining was assessed using a semi-quantitative scoring method. No 5T4 staining was seen in the angiosarcomas and liposarcomas investigated in this study. 5T4 staining in the other STS subtypes was seen in more than 50% of cases, warranting further investigation into whether this antigen could evoke an anti-tumor immune response or can be used as target for the delivery of more potent toxins through antibody drug conjugates.

Superantigen Recognition and Interactions: Functions, Mechanisms and Applications

Superantigens are unconventional antigens which recognise immune receptors outside their usual recognition sites e.g. complementary determining regions (CDRs), to elicit a response within the target cell. T-cell superantigens crosslink T-cell receptors and MHC Class II molecules on antigen-presenting cells, leading to lymphocyte recruitment, induction of cytokine storms and T-cell anergy or apoptosis among many other effects. B-cell superantigens, on the other hand, bind immunoglobulins on B-cells, affecting opsonisation, IgG-mediated phagocytosis, and driving apoptosis. Here, through a review of the structural basis for recognition of immune receptors by superantigens, we show that their binding interfaces share specific physicochemical characteristics when compared with other protein-protein interaction complexes. Given that antibody-binding superantigens have been exploited extensively in industrial antibody purification, these observations could facilitate further protein engineering to optimize the use of superantigens in this and other areas of biotechnology.

TRAIL produced by SAM-1-activated CD4+ and CD8+ subgroup T cells induces apoptosis in human tumor cells through upregulation of death receptors

Bacterial superantigens potently activate conventional T-cells to induce massive cytokine production and mediate tumor cell death. To engineer superantigens for immunotherapy against tumors in clinic, we previously generated SAM-1, a staphylococcal enterotoxins C2 (SEC2) mutant, that exhibited significantly reduced toxicity but maintained the superantigen activity in animal models. This present study aimed to investigate whether SAM-1 activates T cells and induces apoptosis in human tumor cells. We found that SAM-1 induced the maturation of dendritic cells (DCs) with upregulating expression of the surface markers CD80, CD86 and HLA-DR, which secreted high levels of IL-12p70 by activating TLR2-NF-κB signaling pathways. SAM-1 could activate human CD4⁺ subgroup T cells and CD8⁺ subgroup T cells in the presence of mature dendritic cells (DCs), leading to the productions of cytokines TRAIL, IL-2, IFN-γ and TNF-α. We observed that TRAIL mediated the apoptosis and S-phase and G2/M-phase arrest in HGC-27 tumor cells via binding to upregulated death receptors DR4 and DR5. Using shRNA knockdown in HGC-27 cells or constitutive overexpression in ES2 cells for DR4 and DR5, we demonstrated the vital requirement of DR4 and DR5 in apoptosis of tumor cells in response to TRAIL secreted from SAM-1-activated T cells. Collectively, our results will facilitate better understanding of SAM-1-based immunotherapies for cancer.

HLA class I-associated expansion of TRBV11-2 T cells in multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C), a hyperinflammatory syndrome associated with SARS-CoV-2 infection, shares clinical features with toxic shock syndrome, which is triggered by bacterial superantigens. Superantigen specificity for different Vβ chains results in Vβ skewing, whereby T cells with specific Vβ chains and diverse antigen specificity are overrepresented in the T cell receptor (TCR) repertoire. Here, we characterized the TCR repertoire of MIS-C patients and found a profound expansion of TCRβ variable gene 11-2 (TRBV11-2), with up to 24% of clonal T cell space occupied by TRBV11-2 T cells, which correlated with MIS-C severity and serum cytokine levels. Analysis of TRBJ gene usage and complementarity-determining region 3 (CDR3) length distribution of MIS-C expanded TRBV11-2 clones revealed extensive junctional diversity. Patients with TRBV11-2 expansion shared HLA class I alleles A02, B35, and C04, indicating what we believe is a novel mechanism for CDR3-independent T cell expansion. In silico modeling indicated that polyacidic residues in the Vβ chain encoded by TRBV11-2 (Vβ21.3) strongly interact with the superantigen-like motif of SARS-CoV-2 spike glycoprotein, suggesting that unprocessed SARS-CoV-2 spike may directly mediate TRBV11-2 expansion. Overall, our data indicate that a CDR3-independent interaction between SARS-CoV-2 spike and TCR leads to T cell expansion and possibly activation, which may account for the clinical presentation of MIS-C.

Design of split superantigen fusion proteins for cancer immunotherapy

Several antibody-targeting cancer immunotherapies have been developed based on T cell activation at the target cells. One of the most potent activators of T cells are bacterial superantigens, which bind to major histocompatibility complex class II on antigen-presenting cells and activate T cells through T cell receptor. Strong T cell activation is also one of the main weaknesses of this strategy as it may lead to systemic T cell activation. To overcome the limitation of conventional antibody-superantigen fusion proteins, we have split a superantigen into two fragments, individually inactive, until both fragments came into close proximity and reassembled into a biologically active form capable of activating T cell response. A screening method based on fusion between SEA and coiled-coil heterodimers was developed that enabled detection of functional split SEA designs. The split SEA design that demonstrated efficacy in fusion with coiled-coil dimer forming polypeptides was fused to a single chain antibody specific for tumor antigen CD20. This design selectively activated T cells by split SEA-scFv fusion binding to target cells.

5T4 oncofoetal antigen: an attractive target for immune intervention in cancer

The natural history of a patient's cancer is often characterised by genetic diversity and sequential sweeps of clonal dominance. It is therefore not surprising that identifying the most appropriate tumour-associated antigen for targeted intervention is challenging. The 5T4 oncofoetal antigen was identified by searching for surface molecules shared between human trophoblast and cancer cells with the rationale that they may function to allow survival of the foetus as a semi-allograft in the mother or a tumour in its host. The 5T4 protein is expressed by many different cancers but rarely in normal adult tissues. 5T4 molecules are 72 kD, heavily N-glycosylated proteins with several leucine-rich repeats which are often associated with protein-protein interactions. 5T4 expression is associated with the directional movement of cells through epithelial mesenchymal transition, potentiation of CXCL12/CXCR4 chemotaxis and inhibition of canonical Wnt/beta-catenin while favouring non-canonical pathway signalling; all processes which help drive the spread of cancer cells. The selective pattern of 5T4 tumour expression, association with a tumour-initiating phenotype plus a mechanistic involvement with cancer spread have underwritten the clinical development of different immunotherapeutic strategies including a vaccine, a tumour-targeted superantigen and an antibody drug conjugate. In addition, a chimeric antigen receptor T cell approach targeting 5T4 expressing tumour cells is in pre-clinical development. A key challenge will include how best to combine each 5T4 targeted immunotherapy with the most appropriate standard of care treatment (or adjunct therapy) to maximise the recovery of immune control and ultimately eliminate the tumour.

Naptumomab estafenatox: targeted immunotherapy with a novel immunotoxin

Improvement of cancer therapy by introducing new concepts is still urgent even though there have been major advancements lately. Immunotherapy is well on the way to becoming an established tool in the cancer treatment armory. It seems that a combination of (1) activation of immune effector cells and selective targeting of them to tumors and (2) the inhibition of immune suppression often induced by the tumor itself are necessary to achieve the therapeutic goal. The immunotoxin naptumomab estafenatox was developed in an effort to activate and target the patient’s own T cells to their tumor, by fusing a superantigen (SAg) variant that activates T lymphocytes to the Fab moiety of a tumor-reactive monoclonal antibody. Naptumomab estafenatox targets the 5T4 tumor antigen, a 72-kDa oncofetal trophoblast protein expressed on many carcinomas, including renal cell carcinoma. The therapeutic effect is associated with activation of SAg-binding T cells. The SAg-binding T lymphocytes expand, differentiate to effector cells, and infiltrate the tumor. The therapeutic efficacy is most likely related to the dual mechanism of tumor cell killing: (1) direct lysis by cytotoxic T lymphocytes of tumor cells expressing the antigen recognized by the antibody moiety of the fusion protein and (2) secretion of cytokines eliminating antigen-negative tumor cell variants. Naptumomab estafenatox has been clinically tested in a range of solid tumors with focus on renal cell carcinoma. This review looks at the clinical experience with the new immunotoxin and its potential.

Control of established colon cancer xenografts using a novel humanized single chain antibody-streptococcal superantigen fusion protein targeting the 5T4 oncofetal antigen

Superantigens (SAgs) are microbial toxins that cross-link T cell receptors with major histocompatibility class II (MHC-II) molecules leading to the activation of large numbers of T cells. Herein, we describe the development and preclinical testing of a novel tumor-targeted SAg (TTS) therapeutic built using the streptococcal pyrogenic exotoxin C (SpeC) SAg and targeting cancer cells expressing the 5T4 tumor-associated antigen (TAA). To inhibit potentially harmful widespread immune cell activation, a SpeC mutation within the high-affinity MHC-II binding interface was generated (SpeC_D203A) that demonstrated a pronounced reduction in mitogenic activity, yet this mutant could still induce immune cell-mediated cancer cell death in vitro. To target 5T4⁺ cancer cells, we engineered a humanized single chain variable fragment (scFv) antibody to recognize 5T4 (scFv5T4). Specific targeting of scFv5T4 was verified. SpeC_D203A fused to scFv5T4 maintained the ability to activate and induce immune cell-mediated cytotoxicity of colorectal cancer cells. Using a xenograft model of established human colon cancer, we demonstrated that the SpeC-based TTS was able to control the growth and spread of large tumors in vivo. This required both TAA targeting by scFv5T4 and functional SAg activity. These studies lay the foundation for the development of streptococcal SAgs as ‘next-generation’ TTSs for cancer immunotherapy.

SEA antagonizes the imatinib-meditated inhibitory effects on T cell activation via the TCR signaling pathway

The BCR-ABL kinase inhibitor imatinib is highly effective in the treatment of chronic myeloid leukemia (CML). However, long-term imatinib treatment induces immunosuppression, which is mainly due to T cell dysfunction. Imatinib can reduce TCR-triggered T cell activation by inhibiting the phosphorylation of tyrosine kinases such as Lck, ZAP70, LAT, and PLCγ1 early in the TCR signaling pathway. The purpose of this study was to investigate whether the superantigen SEA, a potent T cell stimulator, can block the immunosuppressive effects of imatinib on T cells. Our data show that the exposure of primary human T cells and Jurkat cells to SEA for 24 h leads to the upregulation of the Lck and ZAP70 proteins in a dose-dependent manner. T cells treated with SEA prior to TCR binding had increased the tyrosine phosphorylation of Lck, ZAP70, and PLCγ1. Pretreatment with SEA prevents the inhibitory effects of imatinib on TCR signaling, which leads to T cell proliferation and IL-2 production. It is conceivable that SEA antagonizes the imatinib-mediated inhibition of T cell activation and proliferation through the TCR signaling pathway.

The tumor targeted superantigen ABR-217620 selectively engages TRBV7-9 and exploits TCR-pMHC affinity mimicry in mediating T cell cytotoxicity

The T lymphocytes are the most important effector cells in immunotherapy of cancer. The conceptual objective for developing the tumor targeted superantigen (TTS) ABR-217620 (naptumomab estafenatox, 5T4Fab-SEA/E-120), now in phase 3 studies for advanced renal cell cancer, was to selectively coat tumor cells with cytotoxic T lymphocytes (CTL) target structures functionally similar to natural CTL pMHC target molecules. Here we present data showing that the molecular basis for the anti-tumor activity by ABR-217620 resides in the distinct interaction between the T cell receptor β variable (TRBV) 7-9 and the engineered superantigen (Sag) SEA/E-120 in the fusion protein bound to the 5T4 antigen on tumor cells. Multimeric but not monomeric ABR-217620 selectively stains TRBV7-9 expressing T lymphocytes from human peripheral blood similar to antigen specific staining of T cells with pMHC tetramers. SEA/E-120 selectively activates TRBV7-9 expressing T lymphocytes resulting in expansion of the subset. ABR-217620 selectively triggers TRBV7-9 expressing cytotoxic T lymphocytes to kill 5T4 positive tumor cells. Furthermore, ABR-217620 activates TRBV7-9 expressing T cell line cells in the presence of cell- and bead-bound 5T4 tumor antigen. Surface plasmon resonance analysis revealed that ABR-217620 binds to 5T4 with high affinity, to TRBV7-9 with low affinity and to MHC class II with very low affinity. The T lymphocyte engagement by ABR-217620 is constituted by displaying high affinity binding to the tumor cells (K_D approximately 1 nM) and with the mimicry of natural productive immune TCR-pMHC contact using affinities of around 1 µM. This difference in kinetics between the two components of the ABR-217620 fusion protein will bias the binding towards the 5T4 target antigen, efficiently activating T-cells via SEA/E-120 only when presented by the tumor cells.

5T4 oncofetal antigen is expressed in high risk of relapse childhood pre-B acute lymphoblastic leukemia and is associated with a more invasive and chemotactic phenotype

Although the overall prognosis in childhood acute lymphoblastic leukemia (ALL) is good, outcome after relapse is poor. Recurrence is frequently characterized by the occurrence of disease at extramedullary sites, such as the central nervous system and testes. Subpopulations of blasts able to migrate to such areas may have a survival advantage and give rise to disease recurrence. Gene expression profiling of 85 diagnostic pre-B-ALL bone marrow samples revealed higher 5T4 oncofetal antigen transcript levels in cytogenetic high-risk subgroups of patients (P<0.001). Flow cytometric analysis determined that bone marrow from relapse patients have a significantly higher percentage of 5T4-positive leukemic blasts than healthy donors (P=0.005). The high-risk Sup-B15 pre-B-ALL line showed heterogeneity in 5T4 expression, and the derived, 5T4(+) (Sup5T4) and 5T4(-) (Sup) subline cells, displayed differential spread to the omentum and ovaries following intraperitoneal inoculation of immunocompromised mice. Consistent with this, Sup5T4 compared with Sup cells show increased invasion in vitro concordant with increased LFA-1 and VLA-4 integrin expression, adhesion to extracellular matrix and secretion of matrix metalloproteases (MMP-2/-9). We also show that 5T4-positive Sup-B15 cells are susceptible to 5T4-specific superantigen antibody-dependent cellular toxicity providing support for targeted immunotherapy in high-risk pre-B-ALL.

Superantigens increase the survival of mice bearing T cell lymphomas by inducing apoptosis of neoplastic cells

Superantigens bind to major histocompatibility complex class II molecules and interact with T cells expressing a particular T cell receptor Vβ inducing a strong proliferation/deletion response of the superantigen-reactive T cells. However, there have been no attempts to investigate the ability of Sags to induce apoptosis in neoplastic T cells by signaling through the Vβ region of their TCR. In the present study we show that bacterial and MMTV-encoded superantigens induce the apoptosis of AKR/J cognate lymphoma T cells both in vitro and in vivo. The Fas-Fas-L pathway was shown to be involved in the apoptosis of lymphoma T cells induced by bacterial superantigens. In vivo exposure to bacterial superantigens was able to improve the survival of lymphoma bearing mice. Moreover, the permanent expression of a retroviral encoded superantigen induced the complete remission of an aggressive lymphoma in a high percentage of mice. The possibility of a therapeutic use of superantigens in lymphoma/leukemia T cell malignancies is discussed.

In vivo and in vitro antitumor effects of a staphylococcal enterotoxin A mutant (SEA-H61D)

In this study, we evaluated SEA-H61D, a staphylococcal enterotoxin A mutant without emetic activity, as an antitumor agent in vitro and in vivo. It showed that SEA-H61D could significantly inhibit the growth of many cancer cell lines in vitro at very low concentrations by activating human peripheral blood mononuclear cells (PBMCs). CD4+ and CD8+ T lymphocytes could be activated at a dose between 125 and 500 μg/kg. Systemic administration of SEA-H61D in vivo significantly inhibited tumor growth, with the treated group undergoing tumor necrosis and showing a strong infiltration of lymphocytes to the tumor area.

Naptumomab estafenatox: a new immunoconjugate

IMPORTANCE OF THE FIELD

New agents that specifically engage the immune system are being tested in a variety of malignancies. This review provides an overview of naptumomab, an immunotoxin, with encouraging clinical activity in Phase I trials.

AREAS COVERED IN THIS REVIEW

This review examines the preclinical and the published clinical data with regards to naptumomab.

WHAT THE READER WILL GAIN

This review provides the reader with an understanding of the mechanism of action, immunology, pharmacokinetics and clinical activity of this agent.

TAKE HOME MESSAGE

Naptumomab has a unique mechanism of action and appears to be an active agent in the treatment of refractory solid tumors such as renal cell carcinoma.

Phase I dose escalation, pharmacokinetic and pharmacodynamic study of naptumomab estafenatox alone in patients with advanced cancer and with docetaxel in patients with advanced non-small-cell lung cancer

PURPOSE

Two phase I studies were conducted of ABR-217620 alone or in combination with docetaxel. This is a recombinant fusion protein consisting of a mutated variant of the superantigen staphylococcal enterotoxin E (SEA/E-120) linked to fragment antigen binding moiety of a monoclonal antibody recognizing the tumor-associated antigen 5T4.

PATIENTS AND METHODS

Patients with non-small-cell lung cancer (NSCLC), pancreatic cancer (PC), and renal cell cancer (RCC) received 5 daily boluses of ABR-217620 (3-month cycles) in escalating doses to determine the maximum-tolerated dose (MTD; ABR-217620 dose escalation monotherapy [MONO] study). Doses were selected based on individual patient anti-SEA/E-120 titers pretreatment. Patients with NSCLC received 4 daily, escalating doses of ABR-217620 followed by docetaxel in 21-day cycles (ABR-217620 dose escalation combination with docetaxel [COMBO] study).

RESULTS

Thirty-nine patients were enrolled in the MONO study and 13 were enrolled in the COMBO study. The monotherapy MTD was 26 microg/kg (NSCLC and PC) and 15 microg/kg (RCC). Dose-limiting toxicities (DLTs) in the MONO study were fever, hypotension, acute liver toxicity, and vascular leak syndrome. In the COMBO study, the MTD was 22 microg/kg (neutropenic sepsis). Adverse events included grade 1 to 2 fever, hypotension, nausea, and chills. Treatment caused a systemic increase of inflammatory cytokines and selective expansion of SEA/E-120 reactive T-cells. Tumor biopsies demonstrated T-cell infiltration after therapy. Fourteen patients (36%) had stable disease (SD) on day 56 of the MONO study. Two patients (15%) in the COMBO study had partial responses, one in a patient with progressive disease on prior docetaxel, and five patients (38%) had SD on day 56.

CONCLUSION

ABR-217620 was well tolerated with evidence of immunological activity and antitumor activity.

Enhancement of superantigen activity and antitumor response of staphylococcal enterotoxin C2 by site-directed mutagenesis

Bacterial superantigen staphylococcal enterotoxins (SEs) tremendously stimulate polyclonal T cells bearing particular TCR Vbeta domains when binding to MHC II molecules, suggesting that they could be a candidate of new antitumor agent. SEC2, an important member of superantigen family, has been used in clinical trial as an immunotherapy agent for cancer treatment in China, and obtained some encouraging effects. However, the presence of immunosuppression and endotoxic activity limits the therapeutic dosage of SEC2, and influences its antitumor effect in clinic. Therefore, the enhancement of superantigen activity and antitumor effect of SEC2 could effectively make compensation for the disadvantages mentioned above. In this study, a superantigen SEC2(T20L/G22E) mutant was generated by site-directed mutagenesis, and efficiently expressed in E. coli BL21(DE3). The results showed that SEC2(T20L/G22E) mutant exhibited a significantly enhanced superantigen activity and antitumor response, compared with native SEC2 in vitro. Further toxicity assay in vivo indicated that SEC2(T20L/G22E) mutant had no significant increase in emetic and pyrogenic activity compared with SEC2, which suggested that the mutant SEC2(T20L/G22E) could be used as a potentially powerful candidate for cancer immunotherapy, and could make compensation for the deficiency of native SEC2 in clinic.

CD4+ T-cell recognition of human 5T4 oncofoetal antigen: implications for initial depletion of CD25+ T cells

BACKGROUND

The human 5T4 (h5T4) oncofoetal antigen is expressed by a wide variety of human carcinomas including colorectal, ovarian, gastric and renal, but rarely on normal tissues. Its restricted expression on tumour tissues as well as its association with tumour progression and bad prognosis has driven the development of a MVA-based vaccine (TroVax) which has been tested in several early phase clinical trials and these studies have led to the start of a phase III trial in renal cell carcinoma patients. We have recently shown that CD8(+) T cells recognizing h5T4 can be generated in the absence of CD4(+) T cells from peripheral blood lymphocytes of human healthy individuals.

RESULTS

We report the existence and expansion of human CD4(+) T cells against h5T4 by stimulation with autologous monocyte-derived dendritic cells infected with a replication defective adenovirus encoding the h5T4 cDNA (Ad-h5T4). The h5T4-specific T-cell responses in normal individuals are enhanced by initial depletion of CD25(+) cells (putative T regulatory cells) prior to the in vitro stimulation. We have identified a novel h5T4-derived 15-mer peptide recognized by CD4(+) T cells in HLA-DR4 positive healthy individuals. Interestingly, CD4(+) T cells spontaneously recognizing a different 5T4 epitope restricted by HLA-DR were identified in tumour-infiltrating lymphocytes isolated from a regressing renal cell carcinoma lung metastasis.

CONCLUSION

Our data show that CD4(+) T cells recognizing h5T4 can be expanded and detected in healthy individuals and a renal cell carcinoma patient. Such h5T4-specific CD4(+) T cells boosted or induced by vaccination could act to modulate both cell or antibody mediated anti-tumour responses.

Immunotherapy for gastrointestinal cancer: current status and strategies for improving efficacy

BACKGROUND

Despite improvement in conventional strategies for treating gastrointestinal (GI) carcinoma, large numbers of patients still suffer from incurable or progressive disease.

OBJECTIVE

Here we consider the prospects for circumventing limitations and maximising the efficacy of different immunotherapies.

METHODS

We summarise different cancer vaccines and targeted drugs and highlight the scientific rationale of using immunotherapy for targeting GI cancers, in addition to the potential strategies for improving immunotherapeutic efficacy.

RESULTS/CONCLUSION

Many cancer vaccines and antibody-directed therapies have been tested in early phase clinical trials and demonstrated proof of concept and safety. As yet few have been properly evaluated for clinical efficacy; although adoptive transfer of tumour-associated-antigen-specific T cells has shown dramatic clinical responses in some patients. The recognition of a role for T regulatory cells in limiting anti-tumour immunity has provided momentum for developing strategies to over-ride such immunoinhibitory effects. There is some evidence that conventional therapies may work by influencing these negative factors and allowing expression of immune control mechanisms. An important developing area for clinical evaluation is the testing of combined conventional and immunotherapeutic modalities which may provide for synergy; thereby circumventing the limitations of individualised treatments and generating additional clinical benefits.

A phase II study of a 5T4 oncofoetal antigen tumour-targeted superantigen (ABR-214936) therapy in patients with advanced renal cell carcinoma

In a phase II study, 43 renal cell carcinoma patients were treated with individualised doses of ABR-214936; a fusion of a Fab recognising the antigen 5T4, and Staphylococcal enterotoxin A. Drug was given intravenously on 4 consecutive days, treatment was repeated 1 month later. Treatment was associated with moderate fever and nausea, but well tolerated. Of 40 evaluable patients, 28 had disease control at 2 months, and at 4 months, one patient showed partial response (PR) and 16 patients stable disease. Median survival, with minimum follow-up of 26 months was 19.7 months with 13 patients alive to date. Stratification by the Motzer's prognostic criteria highlights prolonged survival compared to published expectation. Patients receiving higher drug exposure had greater disease control and lived almost twice as long as expected, whereas the low-exposure patients survived as expected. Sustained interleukin-2 (IL-2) production after a repeated injection appears to be a biomarker for clinical effect, as the induced-IL-2 level on the day 2 of treatment correlated with survival. The high degree of disease control and the prolonged survival suggest that this treatment can be effective. These findings will be used in the trial design for the next generation of drug, with reduced antigenicity and toxicity.

Combination of vaccination and chimeric receptor expressing T cells provides improved active therapy of tumors

We have generated murine T cells expressing chimeric immune receptors (CR) against human 5T4 oncofetal Ag (h5T4) and evaluated their tumor therapeutic efficacy alone and in combination with immunization using a replication-defective adenovirus encoding h5T4 (Rad.h5T4) and bone marrow-derived dendritic cells (BMDC). The h5T4-specific engineered T cells demonstrated Ag-specific, non-MHC-restricted cytolysis of h5T4-positive B16 and CT26 tumor cells in vitro by cytotoxicity assay and antitumor activity in vivo using a Winn assay. In the s.c. injected B16h5T4 melanoma model, early local but not systemic i.v. administration of syngeneic h5T4-specific CR T cells significantly increased mice survival. This improvement was further enhanced when combined with immunization with Rad.h5T4, followed by post-CR T cell treatment with BMDC in the active therapy model, possibly through mechanisms of enhancing Ag-specific cellular immune responses. This synergistic effect was lost without delivery of the BMDC. Our findings suggest that combining engineered T cells with specific vaccination strategies can improve the active tumor therapy.

Monoclonal antibodies in the treatment of lung cancer

BACKGROUND

Lung cancer is an aggressive disease and its conventional therapy is far from success. There is a strong need for new, better approaches to improve survival, symptom control and quality of life.

METHODS

The authors searched the literature for indexed articles published over the past 30 years from Pubmed concentrating on all possibilities of monoclonal antibodies in the therapy of tumours and especially of lung cancer.

RESULTS

The search resulted in more then 200 published articles. Important major reports of the pre-clinical/clinical investigations of monoclonal antibodies in the therapy of tumours, with an emphasis on lung cancer were reviewed, screened and tracked for other relevant publications and the yielded data were summarized and systematized.

CONCLUSION

It is concluded, that immunotherapy and the reviewed use of monoclonal antibodies in the therapy of tumours (including lung cancer) certainly carries a hope. However, studies of this topic are in a wide range of phases, from experiments to clinical trials, thereby their results are not comparable with each other. Based on the data available though the authors feel that active immunization with monoclonal antibodies as anti-idiotype vaccines, and antibody targeting with immunoconjugates (immunotoxins, radioimmunoconjugates and chemoimmunoconjugates) are the most promising methods. Radioimmunoguided surgery and immunoguided focal ablation are also valuable. Anti-growth factor monoclonal antibodies are the most evaluated agents so far. They certainly have an objective effect, though they are still not the 'magic bullets', waited for by many clinicians. The use of monoclonal antibodies against the escape mechanisms of tumours can be a good auxiliary method. There are too little data on the value of antibodies directly targeting tumour cells and on combined passive immunotherapy. Due to constant research, other modalities, such as prodrug activation, T cell activation, the use of intrabodies, T bodies, and conjugated antibody fragments might also prove to be valuable.

Cd8 T-cell recognition of human 5T4 oncofetal antigen

The 5T4 oncofetal antigen is expressed by a wide variety of human carcinomas, including colorectal, ovarian and gastric carcinomas. The restricted expression of 5T4 on tumor tissues as well as its implication in tumor progression and bad prognosis makes 5T4 a promising new candidate for immunotherapy. An MVA vaccine encoding 5T4 antigen has been successfully evaluated in preclinical studies in a murine tumor model. Here, we report the generation of human CD8 T cells specific for the 5T4 antigen by stimulation with autologous monocyte derived DC infected with a replication defective adenovirus encoding the 5T4 cDNA (Ad5T4). Analysis of several donors confirms a repertoire of such CD8 responses. In a parallel approach, incorporating the results of proteasome-mediated digestion of 5T4 derived 35-mer peptides and the potential high affinity epitopes predicted by a computer-based algorithm, we identified 8 putative HLA-A*0201-presented CD8 MHC class I epitopes of 5T4 antigen. Two of these generated specific CD8 T cells after restimulation with peptide loaded autologous DC and assay by cytotoxicity and IFN gamma ELISPOT. Moreover these particular peptide generated T cells recognized naturally 5T4 positive tumor cells only if they expressed HLA-A*0201 as judged by IFN gamma ELISPOT or ELISA. Also, HLA-A*0201 CD8 T cells recognized these peptides in a DC-Ad5T4 polyclonal response. In conclusion, there is a repertoire of CD8 T cell recognition of 5T4 in normal human donors and some candidate HLA-A*0201 epitopes have been identified.

Engineered antibody fragments and the rise of single domains

With 18 monoclonal antibody (mAb) products currently on the market and more than 100 in clinical trials, it is clear that engineered antibodies have come of age as biopharmaceuticals. In fact, by 2008, engineered antibodies are predicted to account for >30% of all revenues in the biotechnology market. Smaller recombinant antibody fragments (for example, classic monovalent antibody fragments (Fab, scFv)) and engineered variants (diabodies, triabodies, minibodies and single-domain antibodies) are now emerging as credible alternatives. These fragments retain the targeting specificity of whole mAbs but can be produced more economically and possess other unique and superior properties for a range of diagnostic and therapeutic applications. Antibody fragments have been forged into multivalent and multi-specific reagents, linked to therapeutic payloads (such as radionuclides, toxins, enzymes, liposomes and viruses) and engineered for enhanced therapeutic efficacy. Recently, single antibody domains have been engineered and selected as targeting reagents against hitherto immunosilent cavities in enzymes, receptors and infectious agents. Single-domain antibodies are anticipated to significantly expand the repertoire of antibody-based reagents against the vast range of novel biomarkers being discovered through proteomics. As this review aims to show, there is tremendous potential for all antibody fragments either as robust diagnostic reagents (for example in biosensors), or as nonimmunogenic in vivo biopharmaceuticals with superior biodistribution and blood clearance properties.

Embryonic expression of murine 5T4 oncofoetal antigen is associated with morphogenetic events at implantation and in developing epithelia

Overexpression of 5T4 oncofoetal antigen, an early marker of ES cell differentiation, in vitro increases cellular motility and decreases adhesion, properties relevant to development and cancer. Embryonic expression of m5T4 antigen is first detected on trophectoderm at implantation and is restricted to extra-embryonic tissues to embryonic day (E) 11.5. In the embryo, significant m5T4 expression is detected at E12.5 in hindbrain roofplate and in various epithelia derived from all germ layers. In keratin 14-expressing epithelia, there is a congruent 5T4 expression pattern with many of these cells being Ki-67 positive. In brain, expression is observed in roofplate, ependymal layers, choroid plexus, and subventricular zones of lateral ventricles at E14.5. By E17.5, expression is decreased in the subventricular zone with further restriction to choroid plexus in adult brain. Our data demonstrate a limited 5T4 expression profile during embryogenesis associated with actively cycling, undifferentiated epithelial progenitor cells that may contribute to their migration.

Preclinical evaluation of superantigen (staphylococcal enterotoxin B) in the intravesical immunotherapy of superficial bladder cancer

Superantigens are potent activators of T lymphocytes; therefore, their characteristics can be exploited in diseases where immunomodulation is known to be effective. In this study, we evaluated a new approach for the intravesical therapy of superficial bladder cancer. We investigated in coculture experiments if staphylococcal enterotoxin B (SEB)-activated PBMCs are able to induce apoptosis in human transitional cell carcinoma (TCC) cells. Additionally, we tested the toxicity and efficacy of SEB dissolved in NaCl 0.9% administered intravesically once weekly for 6 weeks in a rat bladder cancer model. To validate the coculture in vitro findings, we evaluated tumor stage, grade, apoptotic cells in the urothelium and stroma of the bladder and infiltration of the bladder wall by lymphocytes, macrophages and mononuclear cells. Coculture experiments revealed that SEB-activated PBMCs are able to kill TCC cells by inducing apoptosis. The intravesical toxicity study with a maximum dose of 100 microg/ml SEB demonstrated no side effects. In the intravesically SEB-treated animals (10 microg/ml), only 3 tumors remained vs. 15 persisting tumors in the control group. The remaining tumors of the therapy group showed a significant amount of apoptosis and granulocytes, mainly in the urothelium, whereas no relevant apoptosis or infiltration of the bladder with lymphocytes or macrophages was found in the control group. These preclinical findings suggest that SEB might be an interesting candidate for further clinical evaluation.

Vaccine and antibody-directed T cell tumour immunotherapy

Clearer evidence for immune surveillance in malignancy and the identification of many new tumour-associated antigens (TAAs) have driven novel vaccine and antibody-targeted responses for therapy in cancer. The exploitation of active immunisation may be particularly favourable for TAA where tolerance is incomplete but passive immunisation may offer an additional strategy where the immune repertoire is affected by either tolerance or immune suppression. This review will consider how to utilise both active and passive types of therapy delivered by T cells in the context of the failure of tumour-specific immunity by presenting cancer patients. This article will outline the progress, problems and prospects of several different vaccine and antibody-targeted approaches for immunotherapy of cancer where proof of principle pre-clinical studies have been or will soon be translated into the clinic. Two examples of vaccination-based therapies where both T cell- and antibody-mediated anti-tumour responses are likely to be relevant and two examples of oncofoetal antigen-specific antibody-directed T cell therapies are described in the following sections: (1) therapeutic vaccination against human papillomavirus (HPV) antigens in cervical neoplasia; (2) B cell lymphoma vaccines including against immunoglobulin idiotype; (3) oncofoetal antigens as tumour targets for redirecting T cells with antibody strategies.

Identification of the antigenic epitopes in staphylococcal enterotoxins A and E and design of a superantigen for human cancer therapy

Monoclonal antibodies have a potential for cancer therapy that may be further improved by linking them to effector molecules such as superantigens. Tumor targeting of a superantigen leads to a powerful T cell attack against the tumour tissue. Encouraging results have been observed preclinically and in patients using the superantigen staphylococcal enterotoxin A, SEA. To further improve the concept, we have reduced the reactivity to antibodies against superantigens, which is found in all individuals. Using epitope mapping, antibody binding sites in SEA and SEE were found around their MHC class II binding sites. These epitopes were removed genetically and a large number of synthetic superantigens were produced in an iterative engineering procedure. Properties such as decreased binding to anti-SEA as well as higher selectivity to induce killing of tumour cells compared to MHC class II expressing cells, were sequentially improved. The lysine residues 79, 81, 83 and 84 are all part of major antigenic epitopes, Gln204, Lys74, Asp75 and Asn78 are important for optimal killing of tumour cells while Asp45 affects binding to MHC class II. The production properties were optimised by further engineering and a novel synthetic superantigen, SEA/E-120, was designed. It is recognised by approximately 15% of human anti-SEA antibodies and have more potent tumour cell killing properties than SEA. SEA/E-120 is likely to have a low toxicity due to its reduced capacity to mediate killing of MHC class II expressing cells. It is produced as a Fab fusion protein at approximately 35 mg/l in Escherichia coli.

Linomide and Antibody-Targeted Superantigen Therapy Abolishes Formation of Liver Metastases in Mice

Hematogenous spread of tumor cells and metastasis formation in the liver are insidious aspects of cancer progression and are not frequently amenable to curative treatment. We examined the effect of Linomide and antibody-targeted therapy against the formation of hepatic metastases in vivo. For this purpose, syngenic B16 melanoma cells transfected with GA733-2 (a human colon cancer cell surface antigen) were injected into a mesenteric vein of C57/Bl6 mice. To test bacterial superantigen (Sag) targeting for immunotherapy of liver metastases, we used genetically fused proteins consisting of SEA and a Fab moiety of a GA733-2 tumor-reactive antibody (C215Fab-SEA). Linomide dose-dependently reduced hepatic metastases, and at 300 mg/kg this reduction was more than 80%. Treatment with C215Fab-SEA decreased metastases formation by 49% and the combination of Linomide and C215Fab-SEA was found to completely abolish liver metastases (>99% reduction). Taken together, our novel data suggest that Linomide and antibody-targeted superantigen therapy individually markedly reduce and together abolish liver metastases. Considering that current therapy of hepatic metastases is mainly limited to surgical resection in a subgroup of patients, these findings indicate that Linomide alone or in combination with antibody-targeted superantigen may provide a novel approach against liver metastases.

Growth and Functional Reactivity of Lymphocytes Obtained from Three Anatomic Compartments in Patients with Non–Small-Cell Lung Cancer (NSCLC)

Non-small-cell lung cancer (NSCLC) claims the lives of both men and women worldwide. In this study, we describe the ability to expand lymphocytes from solid tumor biopsies, pleural fluid, and peripheral blood of patients with NSCLC. While lymphocytes readily expanded from both solid biopsies and pleural fluids, the incidence of obtaining tumor-specific lymphocytes was low. Specific cytolytic and/or cytokine-releasing activity was observed in tumor-infiltrating lymphocytes (TIL) from 3/15 solid tumor biopsies (20%) and 2 of 4 pleural fluid samples (50%). Two of the CTL derived from solid tumor were cytolytic, one being HLA-A2 restricted while the other was either restricted at HLA-A30 or - B18. One of the pleural fluid cytotoxic T lymphocyte (CTL) was also HLA-A2 restricted. Peripheral blood from NSCLC patients was studied using mixed lymphocyte tumor cell cultures (MLTC) as reported previously. Peripheral blood lymphocytes were cultured with allogeneic NSCLC-TC line 29.7, which expressed by gene transfer the lymphocyte costimulatory molecule CD80. Of 9 HLA-A2 patient samples tested, 8 gave rise to lymphocytes, which lysed NSCLC tumor cells expressing HLA-A2 in an major histocompatibility complex (MHC)-restricted fashion. While specific CTL can be generated from all anatomic sites, for clinical trials peripheral blood appears to be the site of choice for obtaining specific precursors.

Crystal structure of a SEA variant in complex with MHC class II reveals the ability of SEA to crosslink MHC molecules

Although the biological properties of staphylococcal enterotoxin A (SEA) have been well characterized, structural insights into the interaction between SEA and major histocompatibilty complex (MHC) class II have only been obtained by modeling. Here, the crystal structure of the D227A variant of SEA in complex with human MHC class II has been determined by X-ray crystallography. SEA(D227A) exclusively binds with its N-terminal domain to the alpha chain of HLA-DR1. The ability of one SEA molecule to crosslink two MHC molecules was modeled. It shows that this SEA molecule cannot interact with the T cell receptor (TCR) while a second SEA molecule interacts with MHC. Because of its relatively low toxicity, the D227A variant of SEA is used in tumor therapy.

Targeting immune effector molecules to human tumor cells through genetic delivery of 5T4-specific scFv fusion proteins

Although several clinical trials have shown beneficial effects by targeting tumor-associated antigens (TAAs) with monoclonal antibodies, a number of issues, including poor penetration of the tumor mass and human antimouse antibody responses, remain. The use of recombinant single-chain Fv (scFv) fragments has the potential to address these and other issues while allowing the addition of different effector functions. To develop therapeutic strategies that recruit both humoral and cellular arms of the immune response, we have constructed chimeric proteins linking either the human IgG1 Fc domain or the extracellular domain of murine B7.1 to a scFv specific for the oncofetal glycoprotein, 5T4. This TAA is expressed by a wide variety of carcinomas and is associated with metastasis and poorer clinical outcome. We have engineered retroviral constructs that produce fusion proteins able to interact simultaneously with both 5T4-positive cells and with the receptor/ligands of the immune effector moieties. Genetic delivery through a murine leukemia virus vector to 5T4-positive tumor cells results in the secreted scFv fusion protein binding to the cell surface. Furthermore, the scFv-HIgG1 fusion protein is able to direct lysis of 5T4-expressing human tumor cell lines through antibody-dependent cell cytotoxicity, indicating its potential as a gene therapy for human cancers.

Recombinant antibody Fab against the hypervariable region 1 of hepatitis C virus blocks the virus adsorption to susceptible cells in vitro

Antibodies against hypervariable region 1 (HVR1) of hepatitis C virus (HCV) are putatively considered to be neutralizing. We previously found that monoclonal antibodies (mAbs) (30F1 and 30F3) against the HVR1 of HCV neutralize HCV in vitro. To develop potentially therapeutic molecules against HCV, we cloned cDNAs of antibody Fab fragments from the mouse hybridoma cells secreting these two mAbs. Fab fragments produced in Escherichia coli were purified by a single step of nickel-chelate affinity chromatography via a hexa-histidine tag. The specificity of the Fabs was confirmed by competition ELISA, BIAcore analysis, and N-terminal amino acid sequencing. The binding constant for the interaction with HVR1 was 1.39 nM for Fab 30F1 and 3.96 nM for Fab 30F3. The HCV capture assay and inhibition of HCV adsorption test demonstrated that both Fabs had neutralizing activity. The data may be useful for designing immunological therapy of HCV.

Characterization of the murine 5T4 oncofoetal antigen: a target for immunotherapy in cancer

Human 5T4 oncofoetal antigen defined by the murine 5T4 monoclonal antibody is a highly glycosylated protein expressed by trophoblast and a few specialized adult epithelia. Up-regulation of 5T4 expression in some cancers is associated with poor clinical outcome; overexpression of human 5T4 cDNA in epithelial cells can alter their morphology and motility, supporting a role for such functions in cancer and development. A murine model to study 5T4 biology and tumour immunology would be useful. The production of m5T4-specific antibodies, their use in establishing transfected cells and documenting their biological properties in vitro are described. A rat monoclonal antibody specific for mouse 5T4 molecules by ELISA, flow cytometry, immunohistochemistry and immunoprecipitation was isolated and epitope mapped. Similar to its human counterpart, murine 5T4 antigen is a 72 kDa glycoprotein (immunoprecipitation and Western blot analysis) and exhibits punctate cell surface expression, dependent upon the integrity of the actin cytoskeleton. Likewise, overexpression of autologous murine 5T4 by B16 F10 melanoma cells and A9 L fibroblasts accentuates the 5T4 phenotype, which is characterized by a spindle-like morphology, increased motility, and reduced adhesion and proliferation rate. Immunohistochemical analysis of adult mouse tissues shows a restricted pattern of expression similar to that of human 5T4 antigen. The murine 5T4 antigen-expressing cell lines and antibody reagents are now being used to explore novel immunotherapies in pre-clinical models and the biology of 5T4 in development.

Glycosylation and epitope mapping of the 5T4 glycoprotein oncofoetal antigen

The human 5T4 oncofoetal antigen is a focus for development of several antibody-directed therapies on the basis of the murine monoclonal antibody against 5T4 (mAb5T4), which recognizes a conformational epitope. 5T4 molecules are highly N-glycosylated transmembrane glycoproteins whose extracellular domain contains two regions of leucine-rich repeats (LRRs) and associated flanking regions, separated by an intervening hydrophilic sequence. Using a series of deletion and mutated cDNA constructs as well as chimaeras with the murine homologue, we have mapped the mAb5T4 epitope to the more membrane-proximal LRR2 or its flanking region. Analysis of the glycosylation of the seven consensus Asp-Xaa-Ser/Thr sites was consistent with all of the sites being glycosylated. A combination of two high-mannose chains (predominantly octasaccharide) and five mostly sialylated bi-, tri- and tetra-antennary complex chains with minor quantities of core fucose were detected. The two glycosylation sites, which are the most likely to have predominantly high-mannose chains, are in the only two regions that show significant differences between the human and the 81% identical mouse sequence. A site-directed mutation, which abolished glycosylation at one of these sites (position 192), did not alter antigenicity. The other, which is nearest to the N-terminus in the human, has an Asn-Leu-Thr to Asn-Leu-Leu conversion in the mouse, so cannot be glycosylated in the latter species. The large complex glycosylation at the other sites is likely to influence the antigenicity and tertiary structure generating the 5T4 epitope.

The development of immunotherapies for non-small cell lung cancer

Standard of care for non-small cell lung cancer (NSCLC) (surgery, chemotherapy and radiation) may enhance patient survival but the enhancement is typically transient and quite uncommon with advanced disease. Researchers and medical professionals are using new approaches to improve patient mortality and morbidity. One of these approaches, immunotherapy, seeks to stimulate antitumour immunity above a threshold level needed for tumour regression or to induce stability in the face of progression. Among the most established approaches are vaccines involving monoclonal antibodies (mAbs) or immune effector cells. These approaches stimulate the humoral and cell-mediated arms of the immune system, respectively. As the development of humanised or fully human antibodies has spurred exploration of radioimmunoconjugates and immunotoxins, mAbs have enjoyed a revival of sorts. Cell-based therapies using the tumour cell itself as a vaccine component has resulted in disease stabilisation or regression. In addition, immune cells (e.g., T-lymphocytes and dendritic cells [DCs]) are the focal point of numerous patient trials in which meaningful clinical impact was achieved. In general, there are many tactics under development for the treatment of NSCLC. This review primarily concerns immunotherapeutic cancer treatments that are either already in clinical trial or well progressed into preclinical studies.