Altered Genes Used To Deliver Antitumor Cytokine Therapy

MONTREAL-Altering genes to express therapeutic cytokines may representan improved approach to direct delivery of these increasinglyutilized recombinant proteins, Michael T. Lotze, MD, said duringa plenary session at the 19th International Congress of Chemotherapy(ICC).

Although cytokines will be among the most useful agents for clinicaltreatment of a multitude of infectious diseases and malignanciesin the future, he predicted, many of these products are currentlyassociated with considerable toxicities.

Dr. Lotze and his colleagues in the Department of Surgery, Universityof Pittsburgh Medical Center, are exploring techniques by whichgenes that control expression of appropriate proteins may be introducedinto cells. It is hoped that antitumor cytokines, for example,expressed by cells with altered genes, will exert their effectswith reduced toxicity.

According to Dr. Lotze, T-cell growth factors may be thought ofas either "growth factors" (ie, IL-2) or "die factors"(antiapoptosis factors, ie, IL-10, IL-12, interferon-gamma).And while different cytokines sometimes share common receptors,intracellular signaling may be quite distinct.

Some cytokines, such as IL-10, are considered to have immunosuppressiveproperties, while others enhance cellular reactivity. Many cytokinescan have both immunosuppressive and immunostimu-lating properties,depending on how the proteins are generated, he said.

In their own preclinical studies, Dr. Lotze and his colleaguesobserved that IL-4 promoted cellular activity. The
combination of IL-1 plus IL-4 had excellent antitumor activity;and despite toxicity (capillary leak syndrome), the combinationof IL-2 plus IL-4 was also active against tumors.

Based on these findings, Dr. Lotze and his colleagues developeda cancer vaccine protocol using IL-4 transfected autologous fibroblasts.A total of 18 patients were treated with high levels of IL-4,delivered into the skin of patients' backs via transfected fibroblasts.

Interim findings of the study include expression of message forup to 7 days, induction of VCAM and E-selectin on dermal epithelium,generation of tumor-specific CD4+ cells in patients with melanoma,profound lymphocytic infiltration, and correlation of VCAM expressionwith S100+ dendritic cell infiltration, Dr. Lotze said.

He also described a new protocol involving IL-12 delivered withretroviral vectors that was designed to administer high doseswithout the severe toxicities associated with direct IL-12 treatment.Studies of IL-12 have demonstrated enhanced tumor immunogenicity,delayed tumor progression, and increased survival in animals.

Gene Transport Systems

Viral vectors have been widely used over the past few years totransport genes in gene therapy protocols. "Over millionsof years," Dr. Michael Lotze said in his talk at the ICC(see story above), "microbes have waged war on the humanimmune system. Somewhere along the line, they learned how to getin."

Many viruses have the ability, for example, to subvert interferonfunctions or downstream events, he said. Ironically, researchersare now trying to harness these microbes, using them to penetrateand ultimately enhance the human immune system.

Nonviral methods for transferring genetic information into cellsinclude liposomal delivery, intramuscular injection of naked DNA,and "bioballistic," or gene-gun, devices, which shoottiny gold beads containing genetic material into a target.