Sensitization of tumour cells to lysis by virus-specific CTL using antibody-targeted MHC class I/peptide complexes

Redirector of Vaccine-induced Effector Responses (RoVER) for specific killing of cellular targets

BACKGROUND

In individuals with malignancy or HIV-1 infection, antigen-specific cytotoxic T lymphocytes (CTLs) often display an exhausted phenotype with impaired capacity to eliminate the disease. Existing cell-based immunotherapy strategies are often limited by the requirement for adoptive transfer of CTLs. We have developed an immunotherapy technology in which potent CTL responses are generated in vivo by vaccination and redirected to eliminate target cells using a bispecific Redirector of Vaccine-induced Effector Responses (RoVER).

METHODS

Following Yellow fever (YF) 17D vaccination of 51 healthy volunteers (NCT04083430), single-epitope YF-specific CTL responses were quantified by tetramer staining and multi-parameter flow cytometry. RoVER-mediated redirection of YF-specific CTLs to kill antigen-expressing Raji-Env cells, autologous CD19+ B cells or CD4+ T cells infected in vitro with a full-length HIV-1-eGFP was assessed in cell killing assays. Moreover, secreted IFN-γ, granzyme B, and TNF-α were analyzed by mesoscale multiplex assays.

FINDINGS

YF-17D vaccination induced strong epitope-specific CTL responses in the study participants. In cell killing assays, RoVER-mediated redirection of YF-specific CTLs to autologous CD19+ B cells or HIV-1-infected CD4+ cells resulted in 58% and 53% killing at effector to target ratio 1:1, respectively.

INTERPRETATION

We have developed an immunotherapy technology in which epitope-specific CTLs induced by vaccination can be redirected to kill antigen-expressing target cells by RoVER linking. The RoVER technology is highly specific and can be adapted to recognize various cell surface antigens. Importantly, this technology obviates the need for adoptive transfer of CTLs.

FUNDING

This work was funded by the Novo Nordisk Foundation (Hallas Møller NNF10OC0054577).

A New Class of Bifunctional Major Histocompatibility Class I Antibody Fusion Molecules to Redirect CD8 T Cells

Bifunctional antibody fusion proteins engaging effector T cells for targeted elimination of tumor cells via CD3 binding have shown efficacy in both preclinical and clinical studies. Different from such a polyclonal T-cell recruitment, an alternative concept is to engage only antigen-specific T-cell subsets. Recruitment of specific subsets of T cells may be as potent but potentially lead to fewer side effects. Tumor-targeted peptide-MHC class I complexes (pMHCI-IgGs) bearing known antigenic peptides complexed with MHC class I molecules mark tumor cells as antigenic and utilize the physiologic way to interact with and activate T-cell receptors. If, for example, virus-specific CD8(+) T cells are addressed, the associated strong antigenicity and tight immune surveillance of the effector cells could lead to efficacious antitumor treatment in various tissues. However, peptide-MHC class I fusions are difficult to express recombinantly, especially when fused to entire antibody molecules. Consequently, current formats are largely limited to small antibody fragment fusions expressed in bacteria followed by refolding or chemical conjugation. Here, we describe a new molecular format bearing a single pMHCI complex per IgG fusion molecule characterized by enhanced stability and expression yields. This molecular format can be expressed in a full immunoglobulin format and can be designed as mono- or bivalent antibody binders. Mol Cancer Ther; 15(9); 2130-42. ©2016 AACR.

Antibody-peptide-MHC fusion conjugates target non-cognate T cells to kill tumour cells

Attempts to generate robust anti-tumour cytotoxic T lymphocyte (CTL) responses using immunotherapy are frequently thwarted by exhaustion and anergy of CTL recruited to tumour. One strategy to overcome this is to retarget a population of virus-specific CTL to kill tumour cells. Here, we describe a proof-of-principle study using a bispecific conjugate designed to retarget ovalbumin (OVA)-specific CTL to kill tumour cells via CD20. A single-chain trimer (SCT) consisting of MHCI H-2K(b)/SIINFEKL peptide/beta 2 microglobulin/BirA was expressed in bacteria, refolded and chemically conjugated to one (1:1; F2) or two (2:1; F3) anti-hCD20 Fab' fragments. In vitro, the [SCT × Fab'] (F2 and F3) redirected SIINFEKL-specific OT-I CTL to kill CD20(+) target cells, and in the presence of CD20(+) target cells to provide crosslinking, they were also able to induce proliferation of OT-I cells. In vivo, activated OT-I CTL could be retargeted to kill [SCT × Fab']-coated B cells from hCD20 transgenic (hCD20 Tg) mice and also EL4 and B16 mouse tumour cells expressing human CD20 (hCD20). Importantly, in a hCD20 Tg mouse model, [SCT × Fab'] administered systemically were able to retarget activated OT-I cells to deplete normal B cells, and their performance matched that of a bispecific antibody (BsAb) comprising anti-CD3 and anti-CD20. [SCT × Fab'] were also active therapeutically in an EL4 tumour model. Furthermore, measurement of serum cytokine levels suggests that [SCT × Fab'] are associated with a lower level of inflammatory cytokine release than the BsAb and so may be advantageous clinically in terms of reduced toxicity.

Viral specific cytotoxic T cells inhibit the growth of TfR-expressing tumor cells with antibody targeted viral peptide/HLA-A2 complex

A fusion protein of single chain antibody (scFv) specific for transferrin receptor (TfR, CD71) and viral peptide/HLA-A2 complex was prepared in this study to redirect cytotoxic T cells (CTLs) of viral specificity to tumor cells by attaching the ligand of T cell receptor (TCR) to tumor cells via binding of TfR scFv to TfR. The results demonstrate that the fusion protein can attach the active virus-peptide/HLA-A2 complex to HLA class I-negative, TfR-expressing K562 cells through binding of TfR scFv to TfR, and mediate cytotoxicity of viral peptide-specific CTLs against K562 cells in vitro. In addition, the fusion protein can induce inhibition of solid tumor formation and improve survival time in tumor xenograft nude mouse with the injection of the sorted viral peptide-specific CTLs generated by co-culture of peripheral blood lymphocytes from HLA-A2 positive donors with inactivated T2 cells pulsed with the viral peptide.

Redirecting NK cells mediated tumor cell lysis by a new recombinant bifunctional protein

Natural killer (NK) cells are at the crossroad between innate and adaptive immunity and play a major role in cancer immunosurveillance. NK cell stimulation depends on a balance between inhibitory and activating receptors, such as the stimulatory lectin-like receptor NKG2D. To redirect NK cells against tumor cells, we designed bifunctional proteins able to specifically bind tumor cells and to induce their lysis by NK cells, after NKG2D engagement. To this aim, we used the 'knob into hole' heterodimerization strategy, in which 'knob' and 'hole' variants were generated by directed mutagenesis within the CH3 domain of human IgG1 Fc fragments fused to an anti-CEA or anti-HER2 scFv or to the H60 murine ligand of NKG2D, respectively. We demonstrated the capacity of the bifunctional proteins produced to specifically coat tumor cells surface with H60 ligand. Most importantly, we demonstrated that these bifunctional proteins were able to induce an NKG2D-dependent and antibody-specific tumor cell lysis by murine NK cells. Overall, the results show the possibility to redirect NK cytotoxicity to tumor cells by a new format of recombinant bispecific antibody, opening the way of potential NK cell-based cancer immunotherapies by specific activation of the NKG2D receptor at the tumor site.

Novel antibodies as anticancer agents

In recent years antibodies, whether generated by traditional hybridoma technology or by recombinant DNA strategies, have evolved from Paul Ehrlich's 'magic bullets' to a modern age 'guided missile'. In the recent years of immunologic research, we are witnessing development in the fields of antigen screening and protein engineering in order to create specific anticancer remedies. The developments in the field of recombinant DNA, protein engineering and cancer biology have let us gain insight into many cancer-related mechanisms. Moreover, novel techniques have facilitated tools allowing unique distinction between malignantly transformed cells, and regular ones. This understanding has paved the way for the rational design of a new age of pharmaceuticals: monoclonal antibodies and their fragments. Antibodies can select antigens on both a specific and a high-affinity account, and further implementation of these qualities is used to target cancer cells by specifically identifying exogenous antigens of cancer cell populations. The structure of the antibody provides plasticity resonating from its functional sites. This review will screen some of the many novel antibodies and antibody-based approaches that are being currently developed for clinical applications as the new generation of anticancer agents.

Disulfide bond engineering to trap peptides in the MHC class I binding groove

Immunodominant peptides in CD8 T cell responses to pathogens and tumors are not always tight binders to MHC class I molecules. Furthermore, antigenic peptides that bind weakly to the MHC can be problematic when designing vaccines to elicit CD8 T cells in vivo or for the production of MHC multimers for enumerating pathogen-specific T cells in vitro. Thus, to enhance peptide binding to MHC class I, we have engineered a disulfide bond to trap antigenic peptides into the binding groove of murine MHC class I molecules expressed as single-chain trimers or SCTs. These SCTs with disulfide traps, termed dtSCTs, oxidized properly in the endoplasmic reticulum, transited to the cell surface, and were recognized by T cells. Introducing a disulfide trap created remarkably tenacious MHC/peptide complexes because the peptide moiety of the dtSCT was not displaced by high-affinity competitor peptides, even when relatively weak binding peptides were incorporated into the dtSCT. This technology promises to be useful for DNA vaccination to elicit CD8 T cells, in vivo study of CD8 T cell development, and construction of multivalent MHC/peptide reagents for the enumeration and tracking of T cells-particularly when the antigenic peptide has relatively weak affinity for the MHC.

Active antiviral T-lymphocyte response can be redirected against tumor cells by antitumor antibody x MHC/viral peptide conjugates

PURPOSE

To redirect an ongoing antiviral T-cell response against tumor cells in vivo, we evaluated conjugates consisting of antitumor antibody fragments coupled to class I MHC molecules loaded with immunodominant viral peptides.

EXPERIMENTAL DESIGN

First, lymphochoriomeningitis virus (LCMV)-infected C57BL/6 mice were s.c. grafted on the right flank with carcinoembryonic antigen (CEA)-transfected MC38 colon carcinoma cells precoated with anti-CEA x H-2D(b)/GP33 LCMV peptide conjugate and on the left flank with the same cells precoated with control anti-CEA F(ab')(2) fragments. Second, influenza virus-infected mice were injected i.v., to induce lung metastases, with HER2-transfected B16F10 cells, coated with either anti-HER2 x H-2D(b)/NP366 influenza peptide conjugates, or anti-HER2 F(ab')(2) fragments alone, or intact anti-HER2 monoclonal antibody. Third, systemic injections of anti-CEA x H-2D(b) conjugates with covalently cross-linked GP33 peptides were tested for the growth inhibition of MC38-CEA(+) cells, s.c. grafted in LCMV-infected mice.

RESULTS

In the LCMV-infected mice, five of the six grafts with conjugate-precoated MC38-CEA(+) cells did not develop into tumors, whereas all grafts with F(ab')(2)-precoated MC38-CEA(+) cells did so (P = 0.0022). In influenza virus-infected mice, the group injected with cells precoated with specific conjugate had seven times less lung metastases than control groups (P = 0.0022 and P = 0.013). Most importantly, systemic injection in LCMV-infected mice of anti-CEA x H-2D(b)/cross-linked GP33 conjugates completely abolished tumor growth in four of five mice, whereas the same tumor grew in all five control mice (P = 0.016).

CONCLUSION

The results show that a physiologic T-cell antiviral response in immunocompetent mice can be redirected against tumor cells by the use of antitumor antibody x MHC/viral peptide conjugates.

Immunotherapy with Antibody-Targeted HLA Class I Complexes: Results of in vivo Tumour Cell Killing and Therapeutic Vaccination

BACKGROUND

The delivery of antibody-targeted major histocompatibility complex (MHC) class I complexes containing immunogenic peptides to the surface of tumour cells allows cytotoxic T lymphocytes (CTLs) of non-tumour specificity to recognise and kill the tumour cell. Previous studies have demonstrated the activity of this system in vitro and in a simple pre-clinical model. This system has also been shown to be an effective method of expanding antigen-specific CTLs in vitro when used to target MHC class I complexes to the surface of B cells.

METHODS

Mice were immunised with ovalbumin and the survival of EL4Hu20 lymphoma cells targeted with H2-D(b)/Ova complexes and control MHC complexes was compared by FACS analysis. A tumour protection assay was performed where immunised mice were injected B16Hu20 melanoma cells targeted with H2-K(b)/Ova or control complexes. T cell expansion in vivo was examined by administering B cells targeted with MHC class I/peptide complexes and assessing T cell expansion by tetramer analysis.

RESULTS

In vivo killing of H2-D(b)/Ova-targeted lymphoma cells in the immunised mice was demonstrated with these cells present at only 12% of the level of the control cells. In contrast, in non-immunised mice the survival of H2-D(b)/Ova-targeted and control cells was comparable. In the tumour protection assay, injection of melanoma cells targeted with H2-K(b)/Ova complexes resulted in the development of only a solitary metastasis in each mouse. This compared to an average of 130 metastases in the control mice injected with B16Hu20 cells targeted with a control MHC peptide complex. In vivo CTL expansion was demonstrated after a single intravenous administration of Daudi B cells coated with H2-D(b)/Uty complexes produced an increase in the proportion of Uty-reactive CTLs from 3.3 to 21.5%.

CONCLUSION

This study supports the development of antibody-delivered MHC complexes as a method of producing CTL-mediated lysis of cancer cells in vivo. As a therapeutic vaccine, the system may provide an effective approach for expanding oligoclonal T cell responses in vivo in the treatment of malignancy and infectious diseases.

Malignant melanoma and bone resorption

The cellular and humoral mechanisms accounting for osteolysis in skeletal metastases of malignant melanoma are uncertain. Osteoclasts, the specialised multinucleated cells that carry out bone resorption, are derived from monocyte/macrophage precursors. We isolated tumour-associated macrophages (TAMs) from metastatic (lymph node/skin) melanomas and cultured them in the presence and absence of osteoclastogenic cytokines and growth factors. The effect of tumour-derived fibroblasts and melanoma cells on osteoclast formation and resorption was also analysed. Melanoma TAMs (CD14+/CD51-) differentiated into osteoclasts (CD14-/CD51+) in the presence of receptor activator for nuclear factor kappaB ligand (RANKL) and macrophage-colony stimulating factor. Tumour-associated macrophage-osteoclast differentiation also occurred via a RANKL-independent pathway when TAMs were cultured with tumour necrosis factor-alpha and interleukin (IL)-1alpha. RT-PCR showed that fibroblasts isolated from metastatic melanomas expressed RANKL messenger RNA and the conditioned medium of cultured melanoma fibroblasts was found to be capable of inducing osteoclast formation in the absence of RANKL; this effect was inhibited by the addition of osteoprotegerin (OPG). We also found that cultured human SK-Mel-29 melanoma cells produce a soluble factor that induces osteoclast differentiation; this effect was not inhibited by OPG. Our findings indicate that TAMs in metastatic melanomas can differentiate into osteoclasts and that melanoma fibroblasts and melanoma tumour cells can induce osteoclast formation by RANKL-dependent and RANKL-independent mechanisms, respectively.

MHC class I-related chain A conjugated to antitumor antibodies can sensitize tumor cells to specific lysis by natural killer cells

PURPOSE

As a first step for the development of a new cancer immunotherapy strategy, we evaluated whether antibody-mediated coating by MHC class I-related chain A (MICA) could sensitize tumor cells to lysis by natural killer (NK) cells.

EXPERIMENTAL DESIGN

Recombinant MICA (rMICA) was chemically conjugated to Fab' fragments from monoclonal antibodies specific for tumor-associated antigens, such as carcinoembryonic antigen, HER2, or CD20.

RESULTS

Flow cytometry analysis showed an efficient coating of MICA-negative human cancer cell lines with the Fab-rMICA conjugates. This was strictly dependent on the expression of the appropriate tumor-associated antigens in the target cells. Importantly, preincubation of the tumor cells with the appropriate Fab-rMICA conjugate resulted in NK cell-mediated tumor cell lysis. Antibody blocking of the NKG2D receptor in NK cells prevented conjugate-mediated tumor cell lysis.

CONCLUSIONS

These results open the way to the development of immunotherapy strategies based on antibody-mediated targeting of MICA.

Selective antibody-mediated targeting of class I MHC to EGFR-expressing tumor cells induces potent antitumor CTL activityin vitro andin vivo

Epidermal growth factor receptor (EGFR) is highly overexpressed in many tumor types. We present a new fusion molecule that can target solid tumors that express EGFR. The fusion molecule combines the advantage(s) of the well-established tumor targeting capabilities of high affinity recombinant fragments of antibodies with the known efficient, specific and potent killing ability of CD8 T lymphocytes directed against highly antigenic MHC/peptide complexes. A recombinant chimeric molecule was created by the genetic fusion of the scFv antibody fragment derived from the anti-EGFR monoclonal antibody C225, to monomeric single-chain HLA-A2 complexes containing immunodominant tumor or viral-specific peptides. The fusion protein can induce very efficiently CTL-dependent lysis of EGFR-expressing tumor cells regardless of the expression of self peptide-MHC complexes. Moreover, the molecule exhibited very potent antitumor activity in vivo in nude mice bearing preestablished human tumor xenografts. These in vitro and in vivo results indicate that recombinant scFv-MHC-peptide fusion molecules might represent a novel and powerful approach to immunotherapy of solid tumors, bridging antibody and T lymphocyte attack on cancer cells.

Antibody-mediated targeting of human single-chain class I MHC with covalently linked peptides induces efficient killing of tumor cells by tumor or viral-specific cytotoxic T lymphocytes

Soluble forms of human MHC class I HLA-A2 were produced in which the peptide binding groove was uniformly occupied by a single tumor or viral-derived peptides attached via a covalent flexible peptide linker to the N terminus of a single-chain beta-2-microglobulin-HLA-A2 heavy chain fusion protein. A tetravalent version of this molecule with various peptides was found to be functional. It could stimulate T cells specifically as well as bind them with high avidity. The covalently linked single chain peptide-HLA-A2 construct was next fused at its C-terminal end to a scFv antibody fragment derived from the variable domains of an anti-IL-2R alpha subunit-specific humanized antibody, anti-Tac. The scFv-MHC fusion was thus encoded by a single gene and produced in E. coli as a single polypeptide chain. Binding studies revealed its ability to decorate Ag-positive human tumor cells with covalent peptide single-chain HLA-A2 (scHLA-A2) molecules in a manner that was entirely dependent upon the specificity of the targeting Antibody fragment. Most importantly, the covalent scHLA-A2 molecule, when bound to the target tumor cells, could induce efficient and specific HLA-A2-restricted, peptide-specific CTL-mediated lysis. These results demonstrate the ability to generate soluble, stable, and functional single-chain HLA-A2 molecules with covalently linked peptides, which when fused to targeting antibodies, potentiate CTL killing. This new approach may open the way for the development of new immunotherapeutic strategies based on antibody targeting of natural cognate MHC ligands and CTL-based cytotoxic mechanisms.

Autologous cytomegalovirus-specific T cells as effector cells in immunotherapy of B cell chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (B-CLL) cells express low levels of co-stimulatory molecules and therefore fail to induce activation and differentiation of tumour-specific T cells. We have shown that patients with B-CLL have considerably expanded numbers of cytomegalovirus (CMV) reactive CD8(+) T cells. This study demonstrated that B-CLL cells loaded with CMV peptide not only promoted the ex vivo expansion of autologous, in vivo-generated virus-specific T cells, but also constituted excellent target cells for these cytotoxic T cells, even without ex vivo re-stimulation. Directing virus-specific T cells to B-CLL may overcome the inadequate immunostimulatory capacity of these cells, which could be exploited for T-cell mediated immunotherapy.

Tumor-specific Ab-mediated targeting of MHC-peptide complexes induces regression of human tumor xenografts in vivo

A cancer immunotherapy strategy is described herein that combines the advantage of the well established tumor targeting capabilities of high-affinity recombinant fragments of Abs with the known efficient, specific, and potent killing ability of CD8 T lymphocytes directed against highly antigenic MHC-peptide complexes. Structurally, it consists of a previously uncharacterized class of recombinant chimerical molecules created by the genetic fusion of single-chain (sc) Fv Ab fragments, specific for tumor cell surface antigens, to monomeric scHLA-A2 complexes containing immunodominant tumor- or viral-specific peptides. The fusion protein can induce very efficiently tumor cell lysis, regardless of the expression of self peptide-MHC complexes. Moreover, these molecules exhibited very potent antitumor activity in vivo in nude mice bearing preestablished human tumor xenografts. These in vitro and in vivo results suggest that recombinant scFv-MHC-peptide fusion molecules could represent an approach to immunotherapy, bridging Ab and T lymphocyte attack on cancer cells.

Kaposi's sarcoma as a model for cancer immunotherapy

Physicians have, for over a century, attempted to harness the potential therapeutic power of the immune system to treat patients with cancer. The discovery that cancer regression can be achieved by immune rejection of tumour antigens theoretically allows the eradication of neoplastic cells without toxicity to normal tissues. An understanding of the mode of presentation of tumour antigens, including those complexed to heat shock proteins by major histocompatibility complex (MHC) class I and class II molecules, and their recognition by CD8(+) and CD4(+) T cells, respectively, has further delineated the potential cancer rejection pathways involved. This also enables the sustained induction and expansion of specific anti-tumour T cells with cytolytic activity.

MHC/peptide tetramer-based studies of T cell function

Direct visualization and quantification of antigen-specific T cells using major histocompatibility complex (MHC)/peptide tetramer technology offers a powerful means to study specific T cell populations of interest. In combination with functional assays, this technology has already provided many new insights into several long-standing immunological concepts in basic science as well as clinical settings.

Induction of viral and tumour specific CTL responses using antibody targeted HLA class I peptide complexes

The production of cytotoxic T cells with specificity for cancer cells is a rapidly evolving branch of cancer therapeutics. A variety of approaches aim to amplify anti-tumour cytotoxic T cell responses using purified peptides, tumour cell lysates or recombinant HLA/peptide complexes in differing antigen presenting systems. Using a two-step biotin-streptavidin antibody targeting system, recombinant HLA-class I/peptide complexes were attached to the surface of B cells via the anti-CD20 B9E9-scFvSA antibody-streptavidin fusion protein. Flow cytometry with a conformation dependant monoclonal antibody to HLA class I indicated that targeted HLA-class I/peptide complexes remain on the surface of B cells in culture for periods in excess of 72 h. PBMCs were stimulated in vitro for 8-14 days using the autologous B cells as antigen presenting cells. Following a single cycle of stimulation specific cytotoxic T cell responses to targeted HLA-A2 complexes containing the M1, BMLF1 and Melan A peptides could be demonstrated by tetramer staining and Cr release assays. With the HLA-A2/BMLF1 complex up to 2.99% of CD8+ve cells were tetramer positive producing 20% lysis (E : T 10 : 1) of CIR-A2 target cells in an in vitro cytotoxicity assay compared to baseline levels of 0.09% tetramer +ve and 2% lysis in the unstimulated population. PBMCs from a healthy donor treated with two cycles of stimulations with targeted HLA-A2/Melan A complexes, demonstrated expansion of the melanA tetramer +ve population from 0.03% to 1.4% producing 15% lysis of Melan A pulsed target cells. With further consideration to the key variables of HLA/peptide complex density, the ratio of stimulator to effector cells and optimum cytokine support, this system should offer an easy and effective method for the in vitro amplification of specific cytotoxic T cell responses and warrants development for the in vivo induction of cytotoxic T cell responses in cancer therapy.

Anti-viral cytotoxic T cells inhibit the growth of cancer cells with antibody targeted HLA class I/peptide complexes in SCID mice

A number of experimental antibody mediated cancer therapies aim to redirect cytotoxic T cells (CTLs) of non-tumour specificity to cancer cells. It has been previously demonstrated that cancer cells targeted with recombinant HLA-class I/viral peptide complexes via antibody delivery systems can be killed by virus specific CTLs. This novel therapeutic system has been developed with a simple pre-clinical model using the recombinant anti-CD20 B9E9 scFvSA fusion protein to target HLA-A2/peptide complexes to CD20 +ve Daudi lymphoma cells. In vitro data confirmed that, although binding of the B9E9 scFvSA fusion protein alone to Daudi cells had no effect on their growth, effective CTL mediated killing of Daudi cells could be achieved by targeting with B9E9 sfvScSA and recombinant HLA-A2/MI complexes at dilutions as low as 100 pg/ml. In contrast the free HLA-A2/MI complexes only significantly inhibited CTL activity at concentrations in excess of 100 ng/ml. The in vivo tumour protection assays in SCID mice demonstrated that only 1 of the 4 mice that received anti-HLA-A2/M1 CTLs and Daudi cells targeted with the B9E9 scFvSA fusion protein and HLA-A2/M1 complexes developed a tumour. In contrast in the control mice that received CTL and native Daudi cells all 4 developed tumours, as did all 4 that received targeted Daudi cells but no CTLs. Similar results were obtained in a parallel experiment using Daudi cells targeted with B9E9 scFvSA and HLA-A2/BMLF1 complexes and a CTL line to HLA-A2/BMLF1. The demonstration of in vivo activity for targeted HLA class I/peptide complexes combined with anti-viral T cells, supports the further clinical development of the system where it may be combined with autologous CTLs produced by vaccination or ex vivo expansion.

Peptides as receptor ligand drugs and their relationship to G-coupled signal transduction

Peptides act as effector agents that regulate and/or mediate physiological processes, serving as hormones, neurotransmitters and signal transducing factors. The low molecular weight peptides affect receptor-mediated events, which influence cardiovascular, gastrointestinal and neurocranial systems. While some peptides have been marketed as drugs, many have served as leads or templates for the development of non-peptide drugs that mimic peptide actions. This review presents the advantages and disadvantages of using peptides as drugs that bind as ligands to cell-surface receptors and considers their applications in such events. The value of both the peptides and their mimics is based on their participation in the biomodulation of physiological processes, which frequently employ scaffolding proteins acting in a cascading sequence of protein-to-protein interactions. The peptides bind to G-coupled surface receptors to initiate a signal that is transduced to the interior of the cell through multiple layers of phosphorylating enzymes and binding proteins. Peptides have been further employed to identify the molecular targets of signal transduction, the uncoupling of which might provide a means for various disease therapies. The exploitation of such peptide-mediated signal pathways, which are of primary importance to tumour cells, may provide an attractive strategy for anticancer therapy in the future.