Targeted Therapy by Using Tissue Specific Promoter and Granules as Storage Compartments for Therapeutic Proteins in Hematopoietic Cells.

Abstract 4508

Systemic administration of immunotherapeutics often give rise to severe side effects. A local deposition, using secretory lysosomes of hematopoietic cells as vehicles for delivery, may overcome this problem. Our research regarding sorting mechanisms of granule proteins have led to a new therapeutic idea – targeted therapy with hematopoietic cells as carriers. Exogenous proteins are expressed, and the gene product is directed for secretory lysosome or granule storage. These organelles are unique storage compartments in neutrophils for biological active proteins, designated for inflammatory foci. The exogenous proteins, would accordingly, be locally released at the site of inflammation. Our model construct, soluble TNF receptor 1 (sTNFR), can be directed for storage by adding a transmembranous region and a sorting signal. We have earlier shown that this construct, retrovirally expressed in murine hematopoietic progenitor cells, are destined for granule targeting. Furthermore, we have transplanted transduced murine progenitor cells with modified granule content, and found stable expression and inducible release of sTNFR1 in vivo. Our goal is cell linage specific expression in order to selectively express sTNFR1 with a transmembranous region and a signal peptide for granule targeting. To achieve this, lactoferrin, perforin and MPO promoters, including regulatory elements, have been inserted into vectors (we use a retroviral vector with self-inactivating LTRs). The vectors is retrovirally transduced into murine hematopoietic progenitor cells, and the cells are cultured during cytokine driven differentiation and analyzed by FACS and Western blotting. Our results suggest that a concept of using secretory organelles of hematopoietic cells as vehicles for therapeutic agents in vivo may become feasible. It will be possible to test this principle by experiments in animal models of inflammatory and malignant diseases. Likewise, development of this concept may give new information on secretory lysosome function and secretion at inflamed/malignant sites.