A new study finds that HIV infection may significantly reduce the risk of MS.
The research team, including Prof. Julian Gold of The Albion Centre at the Prince of Wales Hospital in Sydney, Australia, says if their findings are confirmed, this could hold important implications for the treatment of multiple sclerosis (MS) - a disabling disease of the central nervous system.
Combined, there are more than 1 million peer-reviewed studies documenting HIV and MS. Among these, there has only ever been one case report of an individual with both conditions who was treated with HIV antiretroviral drugs. After 12 months of treatment, the patient's MS symptoms disappeared.
In this particular case report, Danish researchers hypothesized that antiretroviral therapy for HIV could be coincidentally treating MS or halting its progression. In this latest study, Prof. Gold and colleagues wanted to further investigate this theory.
Patients with HIV '62% less likely to develop MS'
The team analyzed data from English Hospital Episode Statistics between 1999 and 2011, involving 21,207 patients in England with HIV and more than 5 million controls.
For 7 years, all patients were monitored for development of MS. The researchers calculated the number of expected MS cases among HIV patients and controls, and compared these numbers with the actual number of cases.
During follow-up, there were 18 expected MS cases among HIV patients and only seven actual cases. Based on this, the team calculated that patients with HIV were 62% less likely to develop MS, compared with control patients.
In addition, the researchers found that the possible protective effect of HIV against MS appears to be stronger the more time that elapses between diagnosis of each condition.
Based on 16 expected MS cases and four actual MS cases among patients who were diagnosed with HIV more than 1 year ago, the researchers calculated that these patients were 75% less likely to develop MS. Those who were diagnosed with HIV more than 5 years ago were 85% less likely to develop MS, based on 6.5 expected cases of MS among these patients and only one actual case.
Prof. Gold and colleagues say their findings are consistent with the theory previously presented by the Danish researchers, but that this latest research shows statistical significance.
They stress, however, that these results are purely observational and further studies are needed, but that they could hold important implications for MS development and treatment if confirmed:
"If subsequent studies demonstrate there is a causal protective effect of HIV and/or its treatment, and if the magnitude of it proves to be similar [...] this would be the largest protective effect of any factor yet observed in relation to the development of MS."
Why does HIV appear to protect against MS?
The research team points out some theories that may explain the observed protective effect of HIV against MS.
For example, they say that immunodeficiency triggered by HIV, even without antiretroviral treatment, could prevent development of MS. "HIV impairs immune cell homoeostasis and targets a wide range of immune cells and signaling pathways overlapping with MS pathogenesis," they explain.
Furthermore, they note that antiretroviral drugs used to treat HIV may also curb other pathogens linked to MS, such as herpes viruses and human endogenous retroviruses (HERVs).
Fast facts about MS
- It is estimated that around 400,000 people in the US are living with MS
- Onset of MS is most common between the ages of 20 and 40
- What causes MS is unclear, although past research has suggested the disease occurs when the immune system launches a defensive attack against its own tissues.
"If having HIV is associated with a signiﬁcantly lower risk of subsequent MS and the association is in the causal chain, it is either because of some biological effect of HIV itself on the pathogenesis of MS, or because the treatments for HIV are coincidentally also treating or preventing development of MS," the team says.
"Unfortunately," they add, "neither this study nor any study design that is feasible at present can prove which mechanism may be correct."
They point out that their research is subject to a number of limitations. For example, they lacked data on how many individuals were exposed to antiretroviral treatment and the exact combination of drugs that were used in such treatment, which could have influenced the results. They also note that they lacked information on the ethnicity of patients.
In an editorial linked to the study, Mia van der Kop, an epidemiologist at the University of British Columbia in Vancouver, Canada, notes that despite the limitations of this study, the researchers have made a "significant contribution" to past research suggesting HIV may protect against MS.
"However, additional work is required to move beyond hypothesis generation," she adds. "A logical next step would be to directly examine the association between exposure to antiretroviral therapy and the development of MS."
Earlier this year, Medical News Today reported on a study published in Stem Cell Reports, which detailed how researchers implanted human stem cells in the spinal cords of mice with MS, restoring their ability to walk and run.