HLH researchers explore new drugs, gene therapy

Although science has come a long way in understanding HLH, its treatment presents significant challenges. Each step in treatment – getting the raging immune response under control, then replacing the immune system with bone marrow transplantation – wages its own set of assaults on young bodies. Cincinnati Children’s physician-researchers are working to find more effective, less toxic alternatives.

Combination Therapy

One approach is a multicenter clinical trial led by Michael Jordan, MD, of the Division of Bone Marrow Transplantation and Immune Deficiency. The trial combines two currently used approaches into a unique treatment, “hybrid immunotherapy.” It is designed to improve the first step of treating HLH – quieting the inflammatory response. The Hybrid Immunotherapy for HLH (HIT-HLH) trial is the first-ever U.S.-based trial for the condition and the only one funded by the NIH. It involves 10 centers throughout the U.S. and Canada.

“This study focuses on controlling the disease process, not fixing the underlying problem,” says Jordan. “But we believe it may give more rapid and complete control of inflammation. We hope it will be a real improvement.”

Treatment involves a combination of three drugs, anti-thymocyte globulin (ATG), etoposide and dexamethasone. The HIT-HLH trial has enrolled 12 children so far and plans to enroll up to 40 more. So far, researchers are pleased with the early results, Jordan says.

The Interferon Connection

Jordan and Lisa Filipovich, MD, also are collaborating with colleagues overseas and a Swiss pharmaceutical company on a clinical trial recently launched in Europe to test the effects of an antibody, NI-0501, on the protein gamma interferon (IFNg). This protein, crucial in the immune process, is believed to be excessively elevated in patients with HLH. NI-0501 targets and neutralizes the protein. If the theory that elevated IFNg causes HLH proves true – and data so far support it – then targeting the protein should shut down the disease process, Jordan says.

Filipovich, Jordan and others hope to approach the FDA this year for permission to test the drug in the U.S., with Cincinnati Children’s a likely trial site.

Giving Perforin a Boost

Although most children with mutations in perforin – a protein crucial to immune response – develop HLH in early infancy, some develop the disease later. Children with “later onset” HLH are able to create some perforin, though not enough to avoid eventually succumbing to the disease.

For these children, Kimberly Risma, MD, PhD, Division of Allergy and Immunology, is looking at how targeted drug therapy might boost perforin production, which could help them avoid the ravages of HLH and the rigors of bone marrow transplantation.

“The type of perforin mutations impact the age of onset,” Risma says. “So late onset — after 18 months — means a child is producing some small amount of functional protein. If onset occurs after age 5, the child is producing even more.”

Finding the ’Enhancers’

Risma has developed a unique assay to measure the killing function of cytotoxic lymphocytes. Using a high-throughput screen, she hopes to evaluate thousands of small-molecule compounds to see which might best serve to boost the lymphocytes’ killing capacity.

She will first screen FDA-approved compounds, using the resources of the University of Cincinnati’s Drug Discovery Center. She will then look for similar compounds in the Center’s library, which contains 300,000 pharmaceutical-quality compounds used by researchers nation-wide to hunt for potential treatments.

“My hope is that we will find compounds that are orally bioavailable and will have an impact on cytotoxic cells,” Risma says.

Collaboration with Great Ormond Street

Jordan, Risma and Punam Malik, MD, at Cincinnati Children’s, have also teamed with colleagues at London’s Great Ormond Street Hospital for a study of perforin gene replacement therapy to treat HLH.

The study will use perforin-deficient mice – a model developed by Jordan during his training – and inject them with healthy stem cells carrying normal perforin genes. The mice will then be infected with a virus that triggers HLH. The goal is to see if the mice begin producing perforin and are protected from getting the disease.

“If the experiment works and the mice are protected, it will be an important step forward in the development of gene therapy for perforin-deficient HLH patients,” Jordan says. “For patients who have no perforin function, there is no way to fix it apart from a bone marrow transplant, which has significant risks. If this is successful, we could fix the perforin deficiency with gene therapy, replacing it in their own cells.”

Getting the vector right

Researchers at Great Ormond Street turned to Cincinnati Children’s because of our experience producing lentiviral vectors for gene therapy and Jordan’s development of the pre-clinical mouse model for HLH. But getting it right is a painstaking process as scientists move their work from in vitro studies, conducted at Great Ormond Street, to an animal model here.

Refining the vector that will carry the perforin gene is especially complicated, says Jordan, because the vector is not a passive transport mechanism – it actually controls how much of the gene product is expressed, and when.

“Getting it controlled in the right cells at a sufficient level that can be modulated by inflammation is the ultimate goal,” Jordan says.

He is optimistic that they will get it right and the animal studies will proceed. And he is cautiously optimistic that the research could lead to a game changer for HLH. But clinical trials remain several years and a great deal of work away.

“We already know that many children with HLH do not survive bone marrow transplant,” he says. “That could change if this works.