Shin-ichi Takemura

A mutated superantigen SEA D227A fusion diabody specific to MUC1 and CD3 in targeted cancer immunotherapy for bile duct carcinoma.

Abstract. In cancer immunotherapy research, many bispecific antibodies (BsAbs) have been developed for directing T cells toward tumor cells. Recent advances in genetic engineering have made it possible to prepare immunoglobulin fragments consisting of variable domains using bacterial expression systems. Therefore, recombinant BsAbs, termed diabodies, have attracted particular attention. We have previously produced an anti-MUC1 × anti-CD3 diabody (M×3 diabody) in an Escherichia coli (E. coli) expression system. In order to reinforce the antitumor effects of the M×3 diabody, mutated superantigen staphylococcal enterotoxin A (SEA) D227A was genetically fused to the M×3 diabody. The SEA D227A fusion M×3 diabody (SEA D227A-M×3 diabody) thus constructed showed remarkable MUC1-specific antitumor effects when used with effector cells (lymphokine-activated killer cells with T-cell phenotype [T-LAK] and peripheral blood mononuclear cells [PBMCs]). In the bile duct carcinoma (BDC)-xenografted severe combined immunodeficient (SCID) mouse model, it also demonstrated strong antitumor activity when administered i.v. together with T-LAK cells and interleukin-2 (IL-2). In this experiment, the complete disappearance of tumors was observed in 3 out of 6 mice, and the other 3 showed marked retardation of tumor growth. Therefore, the SEA D227A-M×3 diabody is considered to be a promising reagent in specific targeted immunotherapy for BDC and other MUC1-positive carcinomas. This is the first report on a diabody that is effective in treating human solid cancers in the xenografted SCID mouse experimental model.

Specific and effective targeting cancer immunotherapy with a combination of three bispecific antibodies.

For the purpose of establishing a new adoptive immunotherapy for bile duct carcinoma (BDC), we previously constructed two kinds of bispecific antibodies (bsAbs), anti-MUC1 x anti-CD3 (M x 3) and anti-MUC1 x anti-CD28 (M x 28), which activate T cells and form bridges between them and MUC1-expressing tumor cells. In our previous studies [Cancer Res. 56 (1996) 4205] specific targeting therapy (STT) consisting of i.v. administration of lymphokine activated killer cells with a T cell phenotype (T-LAK) sensitized with two kinds of bsAbs to human BDC-grafted severe combined immunodeficient (SCID) mice demonstrated remarkable inhibition of tumor growth. However, complete cures could not be obtained. In order to improve antitumor efficacy, we have paid attention to anti-CD2 monoclonal antibodies (mAbs), thought to play an important roles in signal transduction in T cell activation or control of T cell receptor (TCR)-driven activation. Therefore, we developed another bsAb, anti-MUC1 x anti-CD2 (M x 2), in order to examine if this would show synergism with the two previously described bsAbs. The combination of the three bsAbs (M x 3, M x 28 and M x 2 bsAbs) showed highest cytotoxicity against MUC1-expressing BDC cells when given simultaneously with peripheral blood mononuclear cells (PBMCs) or T-LAK cells in vitro. When 2 x 10(7) T-LAK cells sensitized with different combinations of bsAbs were administered four times i.v. to BDC-grafted SCID mice, the best therapeutic result was obtained with a combination of all three bsAbs. These results indicate usefulness of combination of three bsAbs for targeting cancer immunotherapy.

Mutated SEA-D227A-conjugated antibodies greatly enhance antitumor activity against MUC1-expressing bile duct carcinoma.

Abstract. For the purpose of establishing a new adoptive immunotherapy for bile duct carcinoma (BDC), we have directed our attention to superantigens (SAgs), the most potent known activators of T lymphocytes. In our previous study, staphylococcal enterotoxin A (SEA) was conjugated chemically with MUSE11 mAb, which recognizes the MUC1 cancer-associated antigen, and shown to enhance the specific cytotoxic activity of T-LAK cells against MUC1-expressing BDC cells (TFK-1) in vitro and in vivo. However, it is probable that SEA might cause side-effects because of nonspecific binding to class II positive cells. In order to overcome these, we generated mutated SEA (mSEA) by changing Asp at position 227 of native SEA to Ala, which has reduced affinity to MHC class II molecules, but retains the potential for T cell activation. When mSEA-D227A was administered to rabbits to examine effects on blood pressure, 500 times more mSEA-D227A was tolerated than native SEA. This prompted us to construct a mSEA-D227A-conjugated mAb, reactive with MUC1. It augmented the antitumor activity of T-LAK cells significantly, and furthermore, mSEA-D227A could be conjugated to two bispecific antibodies, BsAb (anti-MUC1×anti-CD3) and BsAb (anti-MUC1×anti-CD28), which in combination had greater enhancing effects than mSEA-D227A-conjugated anti-MUC1 mAb, and combination of unconjugated BsAbs. These findings indicate a utility of mSEA-D227A-conjugated antibodies for targeted cancer immunotherapy.

Functional Fv fragment of an antibody specific for CD28: Fv-mediated co-stimulation of T cells.

The most predominant co‐stimulation pathway, which is critical for T cell activation and proliferation, is the CD28‐B7 pathway. The anti‐CD28 monoclonal antibody (mAb) also provides a co‐stimulatory signal to T cells. In order to construct a functional Fv fragment (complex of VH and VL domains) of anti‐CD28 antibody using a bacterial expression system, cDNA encoding the variable regions of immunoglobulin from 15E8 hybridoma cells was cloned and expressed in Escherichia coli. The Fv fragment was obtained as a soluble protein from the periplasmic fraction and showed a binding pattern similar to parental IgG. The Fv fragment induced proliferation of peripheral blood mononuclear cells in the presence of anti‐CD3 or anti‐CD2 mAb and enhanced anti‐tumor activity of anti‐MUC1×anti‐CD3 bispecific antibody when tested with lymphokine‐activated killer cells with T cell phenotype. Thus, the anti‐CD28 Fv fragment will be promising not only for the study of co‐stimulation, but also for cancer immunotherapy.