Optimism after much pessimism: what next?

The Modified Vaccination Technique

In addition to active and passive immunizations, there is a third method of immunization, the modified vaccination technique, which is based on injecting a combination of target antigens and antibodies against this antigen. The vaccine is essentially comprised of immune complexes with pre-determined immune-inducing components. When such an immune complex (target antigen × antibody against the target antigen) with a slight antigen excess is administered, it evokes a corrective immune response by the production of the same antibody with the same specificity against the target antigen that is present in the immune complex (pre-determined immune response).

A novel modified vaccination technique produces IgG antibodies that cause complement-mediated lysis of multiple myeloma cells carrying CD38 antigen

Objectives were to: 1) induce a lytic IgG antibody (ab) response (via the so called `third vaccination method') against CD38 antigen (ag) residing on the extra-cellular domain of multiple myeloma (MM) cells in recipient rabbits, by combining the CD38 ag with donor-derived anti-CD38 ag lytic IgG ab into an immune complex (IC); and 2) determine whether abs produced would cause complement-mediated lysis (in vitro) of human MM cells containing CD38 ag. The vaccine was created in a two-step process. First, ab (rabbit anti-CD38 ag IgG ab) was raised in donor rabbits by injections of low molecular weight soluble CD38 ag in Freund's complete adjuvant (FCA) and aqueous solution. Second, transfer of pathogenic lytic IgG ab response into recipient rabbits was achieved by injections of ICs composed of CD38 ag and homologous anti-CD38 ag IgG ab. Consequently, recipient rabbits produced the same ab with the same specificity against the target ag as was present in the inoculum, namely agglutinating, precipitating and lytic (as demonstrated in vitro). In an in vitro study, in the presence of complement, donor and recipient rabbits' immune sera caused lysis of CD38 ag associated human MM cells. The most effective lytic ab response causing sera were those from donor rabbits injected with CD38 ag in FCA and those from rabbits injected with ICs, especially when they were administered in adjuvants. These results provided proof of concept that the third vaccination method has good potential as a stand-alone and efficacious method of controlling cancer.

Functional and clinical relevance of chondroitin sulfate proteoglycan 4

The lack of effective conventional therapies for the treatment of advanced stage melanoma has stimulated interest in the development of novel strategies for the management of patients with malignant melanoma. Among them, immunotherapy has attracted much attention because of the potential role played by immunological events in the clinical course of melanoma. For many years, T cell-based immunotherapy has been emphasized in part because of the disappointing results of the monoclonal antibody (mAb)-based clinical trials conducted in the early 1980s and in part because of the postulated major role played by T cells in tumor growth control. More recently, mAb-based therapies have gained in popularity given their clinical and commercial success for a variety of malignant diseases. As a result, there has been increased interest in identifying and characterizing antibody-defined melanoma antigens. Among them, the chondroitin sulfate proteoglycan 4 (CSPG4), also known as high molecular weight-melanoma associated antigen (HMW-MAA) or melanoma chondroitin sulfate proteoglycan (MCSP), has attracted much attention in recent years because of the growing experimental evidence that it fulfills two requirements for immunotherapy to be therapeutically effective: (1) targeting of cancer stem cells (CSC) and (2) development of combinatorial therapies to counteract the escape mechanisms driven by the genetic instability of tumor cells. With this in mind, in this chapter, we have reviewed recent information related to the distribution of CSPG4 on various types of tumors, including CSC, its expression on pericytes in the tumor microenvironment, its recognition by T cells, its role in cell biology as well as the potential mechanisms underlying the ability of CSPG4-specific immunity to control malignant cell growth.

Tumor targeting properties of indium-111 labeled genetically engineered Fab' and F(ab')2 constructs of chimeric tumor necrosis treatment (chTNT)-3 antibody

Genetic engineering techniques have allowed the construction of Fab' and F(ab')2 constructs of chimeric tumor necrosis treatment antibody (chTNT-3), a chimeric monoclonal antibody (MAb) that targets necrotic regions of solid tumors. The purpose of this study is to evaluate the in vitro and in vivo properties of Fab' and F(ab')2 constructs radiolabeled with indium-111 (111In) using diethylentriamine pentaacetic acid (DTPA) conjugation to develop a clinically useful imaging agent for the detection of necrosis in solid tumors. Optimization of the MAb-to-DTPA ratio showed that a 1:2 ratio gave the best immunoreactivity while providing good radiolabeling efficiency and high specific activity for all three DPTA conjugates. In addition, 111In-labeled Fab' and F(ab')2 conjugates were found to have faster whole body clearance times and better biodistribution profiles compared to parental 111In-labeled chTNT-3 in tumor-bearing mice. Although radiolabeled Fab' and F(ab')2 constructs showed lower tumor uptake than radiolabeled chTNT-3, biodistribution results showed that these constructs had significantly lower uptake in liver, spleen, and other normal organs (except the kidney), and therefore had higher tumor-to-organ ratios. In addition, a comparison of all derivatives showed that the F(ab')2 reagent gave the best results in tumor imaging studies. These results demonstrate that stable, a genetically engineered F(ab')2 construct can be successfully radiolabeled with 111In to produce potential imaging reagents for the imaging and monitoring of tumor necrosis.

HLA class I antigen loss, tumor immune escape and immune selection

Poor clinical response rates have been observed in the majority of the T cell-based immunotherapy clinical trials conducted to date. One reason might be the presence of abnormalities in HLA class I antigen presentation in malignant lesions. An increased frequency of HLA class I abnormalities has been observed in malignant lesions from patients treated with T cell-based immunotherapy and in lesions which have recurred in patients who had experienced clinical responses following T cell-based immunotherapy. These observations are compatible with the possibility that the outgrowth of a patient's tumor reflects immune selection of tumor cells which have acquired escape mechanisms from immune recognition.

A carcinoembryonic antigen-specific diabody produced in tobacco

The feasibility of using tobacco for production of a recombinant antibody (T84.66/GS8 diabody) directed against the carcinoembryonic antigen (CEA) and used for tumor imaging was investigated. Two constructs were generated for targeting the protein either to the apoplast or to the endoplasmic reticulum. Expression of the diabody in tobacco leaves after vacuum-assisted infiltration of engineered Agrobacteria (agro-infiltration) and in regenerated transgenic tobacco plants was analyzed and compared. Results in terms of protein expression and accumulation between both systems showed a good correlation. His6-tagged T84.66 diabody was readily purified from agro-infiltrated tobacco leaves and from transgenic plants by immobilized metal ion affinity chromatography. The purified protein was analyzed by polyacrylamide gel electrophoresis, Western blot, gel filtration, electrospray mass spectrometry, direct and competition ELISA, electrophoretic mobility shift assay, and staining of CEA-positive colon adenocarcinoma cell line LS174T. Our results demonstrate that tobacco is a competent production system for this clinically relevant diabody.

Stable, genetically engineered F(ab')(2) fragments of chimeric TNT-3 expressed in mammalian cells

F(ab')(2) fragments are desirable structural derivatives of monoclonal antibodies (MAbs) because of their pharmacokinetic properties and bivalent binding to antigen. Production of these fragments, however, has proven difficult because of the variable sensitivity of intact antibodies to proteolytic enzymes, which can result in very low yields and unstable product. To circumvent these problems, we attempted to apply genetic engineering methods to generate stable F(ab')(2) fragments in NSO murine myeloma cells using the glutamine synthase expression system. For these studies, the chimeric MAb, chTNT-3, directed against necrotic regions of solid tumors, was used to generate several F(ab')(2) variants, which contained between one and three cysteine residues at the end of the hinge region. In addition, two different affinity tags (his tag, streptactin tag) were used with each variant to determine the best tag for purification procedures. Stability was measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and by antigen binding studies and the constructs were tested in vivo to measure their pharmacokinetic properties and biodistribution in normal organs and tumor. The results of these studies show that 3 cysteine residues are required to produce stable F(ab')(2) fragments and that either purification tag can be used with this variant to produce suitable reagents for in vivo studies. Those constructs containing one or two cysteines were found to be unstable and broke down to Fab fragments regardless of the purification tag used. These studies demonstrate that stable, clinically useful F(ab')(2) fragments of chTNT-3 can be produced in mammalian cells by genetic engineering methods.

CD20 antibody (C2B8)-induced apoptosis of lymphoma cells promotes phagocytosis by dendritic cells and cross-priming of CD8+ cytotoxic T cells

C2B8 (Rituximab, MabThera) is a chimeric mouse/human monoclonal antibody (mAb) directed against the human B cell-restricted cell surface antigen CD20 which is used as an alternative medication in the treatment of B cell non-Hodgkin lymphomas (NHL). Treatment of CD20+ B cells with C2B8 triggers different cell damaging effects including complement-dependent lysis of tumor cells, antibody-dependent cellular cytotoxicity and induction of apoptosis. Dendritic cells (DC) have recently been shown to ingest cell debris and to present associated antigens even on MHC class I molecules, a mechanism called cross-presentation. In this study, we investigated whether C2B8 treatment of lymphoma promotes the induction of CD8+ T cell responses against lymphoma cell-associated antigens via, cross-presentation. We used Daudi lymphoma cells as a model system in our studies and could demonstrate, that C2B8-treated Daudi cells undergo apoptosis, are phagocytosed by DC and induce in DC typical features of maturation; among them, the induction of CD83 expression as well as the up-regulation of prominent accessory molecules (CD40, CD86) and MHC molecules. Importantly, upon co-culture of such lymphoma cell-pulsed DC with autologous T cells, we could induce efficient cytotoxic T cell (CTL) responses against Daudi cell-associated antigens. These findings suggest that antibody treatment of tumor cells can, in addition to its direct cell damaging effects, under certain conditions, contribute to an induction of potentially protective cytotoxic T cell responses.

Active specific immunotherapy of malignant melanoma and peptide mimics of the human high-molecular-weight melanoma-associated antigen

The realization that tumor cells utilize multiple mechanisms to escape from immune recognition and destruction has stimulated interest in developing and applying immunotherapeutic strategies which target both humoral and cellular immunity to malignant cells. As a result, the tumor-associated antigens (TAA) used as targets have to be expressed on the cell surface membrane of malignant cells. Furthermore, since most of the TAA used for active specific immunotherapy are self-antigens, a challenge facing tumor immunologists is to develop strategies which are effective in breaking tolerance to self-antigens. This chapter describes one strategy which relies on the use of peptide mimics of the human high-molecular-weight melanoma-associated antigen (HMW-MAA) as immunogens to implement active specific immunotherapy in patients with malignant melanoma. These mimics, which are isolated from phage display peptide libraries by panning with anti-HMW-MAA monoclonal antibodies, are expected to induce both humoral and cellular anti-HMW-MAA immunity.