Screening human antibody libraries against carcinoma cells by affinity purification and polymerase chain reaction.

Bacterial scFv clones from a naïve antibody library have been isolated against cancer cell antigens with AffiSelect, a novel screening method that indirectly identifies candidate library members via an antigen reporter gene. The first step is the coating of carcinoma cell surface epitopes (antigen) with either mAbs, scFvs or phages (library members). Upon binding to a cell surface ligand, the library member generates a linking moiety. This facilitates magnetic affinity purification of the antibody-cancer cell complexes, detected by the polymerase chain reaction (PCR) using the beta-actin gene of the cancer cell as the target. Combining these well-known methods resulted in a higher resolution than a comparable cell-based ELISA method of detection. We have isolated human scFv antibodies against surface antigens of a lung carcinoma cell line. These were identified from a polyclonal mixture of phage display-enriched library clones comparing PCR patterns of the carcinoma cell line with the two negative cell types, HUVEC and peripheral blood cells (PBLs). The positive clones were sequenced and verified by FACS.

Combined effect of recombinant CD19 x CD16 diabody and thalidomide in a preclinical model of human B cell lymphoma.

Combining different treatment strategies offers the possibility of improving treatment results for cancer patients. The aim of our study was therefore to investigate the combination of treatment of established s.c. human B non-Hodgkin's lymphoma in severe immune deficient mice using a recombinant bispecific CD19 x CD16 diabody (targeting natural killer cells to CD19 cells) and the angiogenesis inhibitor thalidomide. Monotherapy with either thalidomide or diabody caused an approximate 50% reduction in tumor growth rate. The combined treatment showed evidence for a synergistic effect resulting in a 74% reduction in median tumor size. In the combined treatment group, two of five animals had complete remissions of their s.c. tumor. These results suggest that a combination treatment with recombinant diabodies and angiogenesis inhibition represents a useful approach in cancer therapy.

Effect of domain order on the activity of bacterially produced bispecific single-chain Fv antibodies.

Bispecific single-chain Fv antibodies comprise four covalently linked immunoglobulin variable (VH and VL) domains of two different specificities. Depending on the order of the VH and VL domains and on the length of peptides separating them, the single-chain molecule either forms two single-chain Fv (scFv) modules from the adjacent domains of the same specificity, a so-called scFv-scFv tandem [(scFv)(2)], or folds head-to-tail with the formation of a diabody-like structure, a so-called bispecific single-chain diabody (scBsDb). We generated a number of four-domain constructs composed of the same VH and VL domains specific either for human CD19 or CD3, but arranged in different orders. When expressed in bacteria, all (scFv)(2) variants appeared to be only half-functional, binding to CD19 and demonstrating no CD3-binding activity. Only the diabody-like scBsDb could bind both antigens. Comparison of the scBsDb with a structurally similar non-covalent dimer (diabody) demonstrated a stabilizing effect of the linker in the middle of the scBsDb molecule. We demonstrated that the mechanism of inactivation of CD19xCD3 diabody under physiological conditions is initiated by a dissociation of the weaker (anti-CD3) VH/VL interface followed by domain swapping with the formation of non-active homodimers. The instability of one homodimer makes the process of diabody dissociation/reassociation irreversible, thus gradually decreasing the fraction of active molecules. The structural parameters influencing the formation of functional bispecific single-chain antibodies are indicated and ways of making relatively stable bispecific molecules are proposed.

Synergistic antitumor effect of bispecific CD19 x CD3 and CD19 x CD16 diabodies in a preclinical model of non-Hodgkin's lymphoma.

To target NK cells against non-Hodgkin's lymphoma, we constructed a bispecific diabody (BsDb) with reactivity against both human CD19 and FcgammaRIII (CD16). Bacterially produced CD19 x CD16 BsDb specifically interacted with both CD19(+) and CD16(+) cells and exhibited significantly higher apparent affinity and slower dissociation from the tumor cells than from effector cells. It was able to induce specific lysis of tumor cells in the presence of isolated human NK cells or nonfractionated PBLs. The combination of the CD19 x CD16 BsDb with a previously described CD19 x CD3 BsDb and CD28 costimulation significantly increased the lytic potential of human PBLs. Treatment of SCID mice bearing an established Burkitt's lymphoma (5 mm in diameter) with human PBLs, CD19 x CD16 BsDb, CD19 x CD3 BsDb, and anti-CD28 mAb resulted in the complete elimination of tumors in 80% of animals. In contrast, mice receiving human PBLs in combination with either diabody alone showed only partial tumor regression. These data clearly demonstrate the synergistic effect of small recombinant bispecific molecules recruiting different populations of human effector cells to the same tumor target.

Analysis of the antibody repertoire of astrocytoma patients against antigens expressed by gliomas.

The molecular characterization of antigens preferentially or exclusively expressed by astrocytomas and recognized by the autologous immune system are a prerequisite for the development of specific vaccines. To identify such antigens, we screened 5 cDNA expression libraries derived from astrocytomas and other gliomas for reactivity with high-titered IgG antibodies in the sera of astrocytoma patients using SEREX, the serologic identification of antigens by recombinant cDNA expression cloning. Autologous and allogeneic SEREX analysis of >5 x 10(6) clones with the sera of 18 astrocytoma patients revealed 10 antigens: the differentiation antigen glial fibrillary acidic protein (GFAP), Bax-inhibitor 1 (which was overexpressed in all glioma samples tested), 3 other molecules involved in the regulation of gene expression and proliferation (the nm23-H2-encoded nucleoside diphosphate kinase B, the Ran binding protein-2 and a DNA binding protein encoded by the son gene), SP40,40 (a complement inhibitory molecule), the chaperonin TCP-1, calnexin and 2 new gene products. No immune responses were detected against the "shared tumor" or "cancer testis antigens" that are regularly expressed in gliomas. Antibody responses in astrocytoma patients against antigens expressed by gliomas were rare and, with the exception of Bax-inhibitor 1 and the product of the son gene, were also found in apparently healthy controls. We conclude that although astrocytomas express a broad spectrum of antigens, they elicit antibody responses only rarely, most likely because of their intrinsic immunosuppressive effects.

Oral DNA vaccination: antigen uptake and presentation by dendritic cells elicits protective immunity.

Melanoma differentiation antigens, such as glycoprotein 100 (gp100), have been shown to induce both cellular and humoral immune responses against melanoma in mouse and man. They are therefore considered as potential targets for melanoma immunotherapy. In this study, we have used the attenuated auxotrophic mutant strain SL7207 of Salmonella typhimurium as vehicle for a human gp100 (hgp100) DNA vaccine against melanoma. In vitro studies indicate that Salmonella/pCMV-hgp100 is efficiently scavenged by dendritic cells, resulting in the expression of the hgp100 transcription unit in the DC. In addition, oral administration of Salmonella/pCMV-hgp100 results in the expression of hgp100 RNA and protein by cells exhibiting DC-morphology in mesenteric lymph nodes as soon as 3 days after vaccination. Analysis of the efficacy of the Salmonella/pCMV-hgp100 vaccine in the B16/hgp100 model demonstrated the induction of strong anti-hgp100 CTL responses and protective immunity in 70% of the vaccinated mice, but not in control mice. Based on these data, we consider S. typhimurium as a useful vehicle for the design of recombinant DNA based anti-cancer vaccines.

Recombinant chimeric OKT3/IgM antibodies for immune suppression: evaluation in a human CD3 transgenic mouse model.

ScOKT3-gammaDeltaIgM VAEVD is a recombinant chimeric anti-CD3 antibody variant consisting of the light and heavy variable binding domains of the OKT3 monoclonal antibody and the CH3 and CH4 domains of a human IgM mutation linked by a human IgG3 hinge region. Due to the IgM Fc domains, scOKT3-gammaDeltaIgM VAEVD antibodies are able to form polymeric structures. Independent of their polymerization state, they possess in vitro CD3 modulating and immunosuppressive properties while inducing only minimal T cell activation compared to their monoclonal counterpart. To evaluate the in vivo efficacy of the antibodies, an adjuvant-induced chronic inflammation was established in human CD3 transgenic mice. Administration of four doses of 15 microg of isolated scOKT3-gammaDeltaIgM VAEVD monomers and pentamers significantly reduced diameters of inflamed ankle joints in a manner comparable to the monoclonal antibody OKT3. Additionally, the antibody treatment lead to a significant reduction of the cytokine levels (IL-2, TNF-alpha and INF-gamma) in the mice's sera. These results suggest that scOKT3-gammaDeltaIgM VAEVD antibodies may provide a useful alternative to the OKT3 mAb for clinical immunosuppressive treatment for auto-aggressive diseases or for organ-transplantation.