Blocking a key molecular pathway that the body uses to amplify an immune response has been found to delay disease onset and extend survival in mice with a disease that mimics human amyotrophic lateral sclerosis (ALS), say researchers at the MDA-supported ALS Therapy Development Institute (ALS TDI) in Cambridge, Mass.
The ALS TDI researchers say they found that the immune-system pathway they ultimately blocked was overactive in the SOD1 mice (mice with a familial form of ALS due to an SOD1 gene mutation) and was likewise overactive in 56 percent (35 of 63) blood samples taken from people with ALS, most of whom did not have familial ALS.
"This linkage between mouse and human data played a major role in the Institute's decision to pursue development of this molecule as a potential treatment for ALS," said Steve Perrin, the Institute's CEO and chief scientific officer, who coordinated the study.
The finding opens up new and promising avenues for treating ALS, extends understanding of the mechanisms underlying this disease, and validates methods the ALS TDI has developed for identifying these mechanisms and therapies that target them.
About ALS mechanisms
About 1 percent to 3 percent of ALS cases are caused by any of a large number of mutations in a chromosome-21 gene known as SOD1. Mice with an SOD1 mutation called G93A are a common research model of the human disease and were used in the ALS TDI experiments. The mice used in the experiments had a rapidly progressive, severe ALS-like disease.
There is a growing body of evidence that malfunction of the immune system is at least part of the ALS disease process. ALS TDI researchers and others have identified abnormal immune-system over activity in animal models of the disease, and the ALS TDI investigators have observed it in ALS patients' blood samples.
About the new findings
The MDA-supported ALS TDI team published its findings online March 28, 2010, in Nature Genetics.
The team used a strategy called "whole transcriptome analysis," which involves looking at levels of activity of all the genes in an organism during the course of a disease or under other specific conditions.
Finding that particular genes associated with the immune response were abnormally active in the SOD1 G93A research mouse, the scientists conducted further investigations and decided to try blocking the interaction between two molecules involved in the immune response: CD40 and CD40 ligand.
When the body mounts an immune response to a protein it considers threatening — an "antigen"— specialized antigen-presenting cells show the antigen to immune-system T cells. When they do this, the antigen-presenting cells have docking sites ("receptors") of a type known as CD40, which engage with correspondingly shaped pieces — CD40 ligands — on the surfaces of the T cells. These two pieces — the CD40 receptor and the CD40 ligand — fit together like a lock and key, signaling the immune system that a full-blown attack is needed.
Blocking this interaction has been found to be beneficial in animal models of tissue transplantation, where the goal is to make the animal tolerant of another animal's cells; and in animal models of autoimmune disease, in which the goal is to make the animal tolerant to its own cells, which it is mistakenly attacking.
The ALS TDI scientists decided to use a blocking protein (antibody) to the CD40 ligand to interrupt the engagement of the CD40 receptor and CD40 ligand. This antibody has been dubbed ALSTDI-00846.
They treated 44 mice with the antibody, while 45 received "empty" injections, for comparison. Compared to the untreated group, the treated mice lost body weight significantly more slowly.
In addition, anti-CD40 ligand treatment significantly delayed the onset of paralysis (by eight days) compared to paralysis onset in the untreated group. And, the antibody-treated mice survived an average of nine days longer than the untreated animals, which also was significant.
By comparison, the ALS TDI researchers have found that ALS mice that are given riluzole (the only treatment for ALS approved by the U.S. Food and Drug Administration) survive only an average of three days longer than untreated mice.
Unfortunately, when the researchers tried starting the CD40 ligand antibody treatment at day 80, after the onset of overt ALS symptoms in the mice, they saw no therapeutic effect on disease onset or progression and no extension of survival.
The need for treatment very early in the disease process, preferably before symptoms appear, could be problematic in humans, because most ALS isn't diagnosed until the disease has been progressing for some time. However, Perrin noted, the SOD1 G93A mice used in these experiments have a very severe, rapidly progressive form of the disease, and it isn't clear that such early treatment would be absolutely necessary in most people with the disease.
MDA, through its Augie's Quest initiative, began supporting the ALS TDI in 2007, making an $18 million grant to the Institute from 2007-2009 and awarding an additional $2.5 million in 2010.
The ALS patient blood samples used in these experiments were collected through several MDA/ALS Centers.
Meaning for people with ALS
This study adds to the already considerable evidence that parts of the immune system misbehave in ALS. The study goes on to show that blocking the interaction between two immune-system molecules can significantly slow the ALS disease process, at least in a mouse model.
Furthermore, the primary action of the immune system is outside the spinal cord and brain (central nervous system) and is therefore reachable by medical therapies without breaching central nervous system barriers. Therapies that require entering the central nervous system are much more challenging to develop and administer.
The CD40 ligand antibody could be developed for use in human ALS, the researchers say, and it could become one of many possible strategies for modulating the immune system. Such antibodies are being investigated for their potential to treat various diseases in which an overactive immune system plays a role, such as rheumatoid arthritis and lupus.
"The human blood work we did could be used to identify a subset of patients for a clinical trial who would be likely to respond to the CD40 ligand antibody," Perrin said. "We now have a potential set of biological disease markers that could be used by a pharmaceutical industry partner to advance trials quickly."