Generation of monoclonal antibodies specific for human kallikrein 2 (hK2) using hK2-expressing tumors

Generation and preclinical characterization of an antibody specific for SEMA4D

Semaphorin 4D (SEMA4D or CD100) is a member of the semaphorin family of proteins and an important mediator of the movement and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. Blocking the binding of SEMA4D to its receptors can result in physiologic changes that may have implications in cancer, autoimmune, and neurological disease. To study the effects of blocking SEMA4D, we generated, in SEMA4D-deficient mice, a panel of SEMA4D-specific hybridomas that react with murine, primate, and human SEMA4D. Utilizing the complementarity-determining regions from one of these hybridomas (mAb 67-2), we generated VX15/2503, a humanized IgG4 monoclonal antibody that is currently in clinical development for the potential treatment of various malignancies and neurodegenerative disorders, including multiple sclerosis and Huntington's disease. This work describes the generation and characterization of VX15/2503, including in vitro functional testing, epitope mapping, and an in vivo demonstration of efficacy in an animal model of rheumatoid arthritis.

A critical role of non-classical MHC in tumor immune evasion in the amphibian Xenopus model

Non-classical class Ib (class Ib) genes are found in all jawed vertebrates, including the amphibian Xenopus, which possesses at least 20 distinct Xenopus non-classical class Ib genes (XNCs). As an immune evasion strategy, tumors often downregulate surface expression of classical major histocompatibility complex class Ia molecules. In contrast, cancers commonly express class Ib molecules, presenting an alternative for tumor immune recognition. We characterized a novel XNC, XNC10, functionally similar to CD1d from a class Ia-deficient thymic lymphoid tumor (15/0), which grows aggressively in Xenopus LG-15 cloned animals. To investigate the roles of XNC10 in antitumor immunity, we generated stable 15/0-transfectants with silenced XNC10 mRNA and protein expression. Notably, XNC10 silencing resulted in acute tumor rejection by naturally class Ia-deficient syngeneic tadpoles, with greater potency of rejection in tumors with more efficient XNC10 knockdown. In vivo killing assays shows that the rejection of XNC10-deficient tumors is due to a cell-mediated cytotoxic immune response elicited by the tadpole host. Importantly, priming enhances XNC10-deficient tumor rejection. Flow cytometry reveals that XNC10-deficient tumor rejection is associated with an accumulation of XNC10-restricted invariant T cells and conventional CD8 T cells as well as other leukocytes. Similarly, semisolid tumor grafts in tadpoles also exhibit leukocytes infiltration. These findings suggest that XNC10 allows the 15/0-tumor to escape immune recognition and class Ia-independent cytotoxicity, thus emphasizing the critical roles of class Ibs in tumor immunity.

Development of an attenuated interleukin-2 fusion protein that can be activated by tumour-expressed proteases

The ability to alter the cytokine microenvironment has the potential to shape immune responses in many physiological settings, including the immunotherapy of tumours. We set out to develop a general approach in which cytokines could be functionally attenuated until activated. We report the development and initial characterization of fusion proteins in which human or mouse interleukin-2 (IL-2), a potent growth factor for immune cells, is joined to a specific IL-2 inhibitory binding component separated by a protease site. The rationale is that upon cleavage by a protease the cytokine is free to dissociate from the inhibitory component and becomes biologically more available. We describe the successful development of two attenuation strategies using specific binding: the first uses the mouse IL-2 receptor alpha chain as the inhibitory binding component whereas the second employs a human antibody fragment (scFv) reactive with human IL-2. We demonstrated that the fusion proteins containing a prostate-specific antigen or a matrix metalloproteinase (MMP) protease cleavage site are markedly attenuated in the intact fusion protein but had enhanced bioactivity of IL-2 in vitro when cleaved. Further, we showed that a fusion protein composed of the IL-2/IL-2 receptor alpha chain with an MMP cleavage site reduced tumour growth in vivo in a peritoneal mouse tumour model. This general strategy should be applicable to other proteases and immune modulators allowing site-specific activation of immunomodulators while reducing unwanted side-effects.

IDENTIFYING THE COMBINATION OF THE TRANSCRIPTIONAL REGULATORY SEQUENCES ON PROSTATE SPECIFIC ANTIGEN AND HUMAN GLANDULAR KALLIKREIN GENES

PURPOSE

The combination of prostate specific antigen (PSA) and human glandular kallikrein (KLK2) promoters and/or enhancers was used to establish a new model to determine the feasibility of tissue specific expression for prostate cancer.

MATERIALS AND METHODS

In vitro studies used the construction of PSA and KLK2 promoters/enhancers vectors to elucidate the link between the promoter/enhancer of PSA and KLK2. Reverse transcriptase-polymerase chain reaction assays were used to determine cell specific expression. Therefore, an attractive tissue specific expression vector for PSA and KLK2 gene was identified.

RESULTS

The reporter vectors driven by KLK2 promoter had much lower luciferase activities than those of the reporter vectors driven by PSA promoter in LNCaP cells. Furthermore, the most efficient and cell specific reporter activity after 5alpha-androstan-17beta-ol-3-one treatment among the reporter vectors constructed in this study was that of pKLK2EPSABHE, which was driven by KLK2 enhancer and PSA promoter/enhancer. The pKLK2EPSABHE reporter vector could induce 800-fold higher than the KLK2 basic promoter and its reporter activity was 16 times that of the enhancer/promoter element of KLK2 following induction by androgen.

CONCLUSIONS

The results verify that the PSA promoter/enhancer must be combined with KLK2 to ensure the full activity and cell specificity of the gene. These expressions coupled with mechanic target validation yield valuable clues regarding the model of action of complex mixtures. This model is a potentially useful tool in gene therapy for metastatic prostate cancer.