Friday, 24 October 2014

What remyelinates

Xing YL, Röth PT, Stratton JA, Chuang BH, Danne J, Ellis SL, Ng SW, Kilpatrick TJ, Merson TD. Adult neural precursor cells from the subventricular zone contribute significantly to oligodendrocyte regeneration and remyelination. J Neurosci. 2014 ;34(42):14128-46.

Parenchymal oligodendrocyte progenitor cells (pOPCs) are considered the principal cell type responsible for oligodendrogenesis and remyelinaton in demyelinating diseases. Recent studies have demonstrated that neural precursor cells (NPCs) from the adult subventricular zone (SVZ) can also generate new oligodendrocytes after demyelination. However, the relative contribution of NPCs versus pOPCs to remyelination is unknown. 

We used in vivo genetic fate mapping to assess the behavior of each progenitor type within the corpus callosi (CCs) of mice subjected to cuprizone-induced demyelination. Nestin-CreER(T2) and Pdgfra-CreER(T2) transgenic mice were crossed with fluorescent Cre reporter strains to map the fate of NPCs and pOPCs respectively. In cuprizone-challenged mice, substantial numbers of NPCs migrated into the demyelinated CC and contributed to oligodendrogenesis. This capacity was most prominent in rostral regions adjacent to the SVZ where NPC-derived oligodendrocytes significantly outnumbered those generated from pOPCs. Sixty-two percent of all nodes of Ranvier in this region were flanked by at least one paranode generated from an NPC-derived oligodendrocyte. Remarkably, g-ratios (ratio of the axon diameter to the diameter of the axon plus myelin sheath) of myelinated axons in regions subject to significant NPC-derived remyelination were equivalent to those of unchallenged controls, and immunoelectron microscopy revealed that NPC-derived myelin was significantly thicker than that generated by pOPCs, regardless of axonal caliber. We also demonstrate that a reduced efficiency of remyelination in the caudal CC was associated with long-term impairment in the maturation of oligodendrogenic NPCs but only transient delay in pOPC differentiation. Collectively, our data define a major distinct role for NPCs in remyelination, identifying them as a key target for enhancing myelin repair in demyelinating diseases.

You can all read the post. It is typically stated that remyelination produces thinner myelin so the D above would be less and the g would therefore be bigger. In this instance there was normal myelination

ClinicSpeak: PML and dimethyl fumarate (Tecfidera)

How should we deal with the PML risk in patients on Tecfidera? #ClinicSpeak #MSBlog #MSResearch

"Apologies about using email as a tool to blog. I am currently at a meeting in Dubai and can't use  the normal blogger platform as Google has set it to the local custom in Arabia of writing from right to left. This policy has  something to do with Google's censorship policy in the region. As soon as I get back to Europe I will edit the post and add hyperlinks and embed important documents."

"Progressive multifocal leukoencephalopathy or PML is classed as an opportunistic infection and typically occurs in patients who are immunosuppressed as a result of cancers, in particular haematological malignancies, immunosuppression from medication or specific diseases such as HIV.  The fact that Biogen-Idec reported a case of PML on their formulation of dimethyl fumarate or DMF (Tecfidera) two days ago appears to have triggered a panic response. My email inbox is full of queries from anxious patients and colleagues about what we should do. I note a spike in Google Trends when using the search terms 'Tecfidera and PML'. The questions I have been asked are:

1.      Should we treat the risk of PML on DMF in the same way do as natalizumab? 

Obviously not; we need to take a step back and think rationally about things.  DMF has been around for decades as a treatment for psoriasis. If DMF was a major risk factor for PML we would have seen far more cases in patients with psoriasis. I have posted on the latter before and we got Professor Gold, who looked after one of the psoriasis PML cases to comment as well. In summary and to the best of my knowledge there have been 5 PML reports in patients with psoriasis on DMF. All but one of the cases had been on multiple immunosuppressive therapies that are known risk factors for PML. The one patient who developed PML on DMF monotherapy has a very low lymphocyte count for several years before developing PML. The latter seems to be the same as the reported patient with MS. This patient had been on DMF as part of the clinical trial programme for 4-and-a-half years and had a persistent lymphopaenia for 3-years before developing PML. The questions I have asked Biogen-Idec to answer are: (1) how severe was that lymphopaenia?; (2) why was he/she left on DMF; (3) when DMF was stopped did the lymphocyte counts recover? ; (4) were there any other risk factors for PML, for example previous use of immunosuppressants? Until we have more information it would be foolish to speculate. What is clear is that PML on DMF is likely to be very rare considering the psoriasis data set. The one proviso is that the dermatologists tend not to use DMF as a continuous long-term therapy in psoriasis so the situation in MS may be different. Therefore in the short-term what we need to do is be more vigilant about lymphopaenia and if someone on DMF develops a persistently low lymphocyte count the drug will need to be stopped. Until we get more data I would suggest anyone with a lymphocyte count less than 800/mm3, or 0.8x10**9/L, takes a drug holiday for several weeks until their lymphocyte counts recover above 1200/mm3, or 1.2x10**9/L; if the lymphocyte counts don't recover, or drop below this proposed threshold on restarting DMF the drug will need to be stopped. Please note that a threshold or cut-off of 800 (WHO grade 1 lymphopaenia) is very conservative and we may be able in the future to set the cut-off at 500 (WHO grade 2 lymphopaenia). Setting cut-offs like this will need to be data driven. 

We will also need to be more vigilant about screening for lymphopenia in patients on DMF. The EMA summary of product characteristics states: 'Tecfidera may decrease lymphocyte counts (see section 4.8). Tecfidera has not been studied in patients with pre-existing low lymphocyte counts and caution should be exercised when treating these patients. Prior to initiating treatment with Tecfidera, a recent complete blood count (i.e. within 6 months) should be available.  Assessments of complete blood counts are also recommended after 6 months of treatment and every 6 to 12 months thereafter and as clinically indicated'. I would suggest that we now institute 6 monthly monitoring as we do for patients on interferon-beta.

2.      Should we stop DMF in patients who are JCV positive? 

Clearly not. The risk factor for PML is not the DMF, but the lymphopaenia. Therefore if you are JCV positive on DMF and have a normal lymphocyte count there is nothing to worry about. I am not aware that there is anything in the mode of action of DMF, outside of the lymphopaenia, that specifically puts you at risk of PML. This situation is unlike natalizumab in which we know that the PML risk is linked to the mode of action of natalizumab, i.e. its stops trafficking of lymphocytes into the brain and reduces immune surveillance for infections.

3.      Should we start routine JCV testing in patients about to start DMF or who are on DMF? 

No I don't think this is necessary. The only situation I envisage this happening is if someone is doing well on DMF and has a lymphopaenia and wants to stay on the drug. Being JCV seronegative may give this person and their clinician more confidence in leaving them on DMF. 

4.      Should we not start someone on DMF if they already have a lymphopaenia? 

This will depend on the cause of the lymphopaenia. If for example they are switching from fingolimod, that causes a reversible lymphopaenia, it would seem reasonable to check lymphocyte counts after 8 weeks to make sure they have recovered.  If the cause of lymphopaenia is due to previous immunosuppression, for example secondary to corticosteroids, cladribine, alemtuzumab, mitoxantrone, teriflunomide, etc. I would be more careful. In this situation a decision will need to be made once considering the level of lymphopaenia and how active the patients MS is. This may be one situation were a JCV serology may help. Please note that prior immunosuppressive  therapies is in itself a major risk factor for PML ; therefore if the patient is JCV seropositive you will need to be more careful.

5.      Is there something specific about DMF that causes PML? 

As I have alluded to above there is nothing in the known mode of action of DMF that would implicate DMF, outside of the lymphopaenia, as a high risk drug for PML. This may change with future knowledge.
We mustn't get distracted from the fact that this is a personal tragedy. Someone with MS has died as a direct result of a treatment for MS. My condolences go out to the family and friends of this patient. From my perspective as an MSologist this complication may have been preventable, which is the main reason for this post. We must also not forget that this patient participated in the DMF clinical trial programme and without his/her participation other MSers would not be benefiting from this drug. "

CoI: multiple

Detecting JC virus

Lanzillo R, Liuzzi R, Vallefuoco L, Moccia M, Amato L, Vacca G, Vacchiano V, Portella G, Brescia Morra V. JC virus antibody index in natalizumab-treated patients: correlations with John Cunningham virus DNA and C-reactive protein level. Ther Clin Risk Manag. 2014;10:807-14. 

Natalizumab-treated patients have a higher risk of developing progressive multifocal leukoencephalopathy. Exposure to John Cunningham virus (JCV) is a prerequisite for PML (progressive multifocal leukoencephalopathy). To assess JCV exposure in multiple sclerosis patients, we performed a serological examination, obtained the antibody index, performed real-time polymerase chain reaction (PCR) to detect JCV DNA in plasma and urine, and investigated the role of ultrasensitive C-reactive protein (usCRP) as a possible biological marker of JCV reactivation. We retrospectively analyzed consecutive natalizumab-treated multiple sclerosis patients who underwent a JCV antibody test through a two-step enzyme-linked immunosorbent assay (STRATIFY test) to the measure of serum usCRP levels, and to perform blood and urine JCV PCR. The studied cohort included 97 relapsing-remitting patients (60 women). Fifty-two patients (53.6%) tested positive for anti-JCV antibodies. PCR showed JCV DNA in the urine of 30 out of 83 (36.1%) patients and 28 out of 44 seropositive patients (63.6%), with a 6.7% false-negative rate for the STRATIFY test. Normalized optical density values were higher in urinary JCV DNA-positive patients (P<0.0001). Interestingly, the level of usCRP was higher in urinary JCV DNA-positive patients and correlated to the number of DNA copies in urine (P=0.028). As expected, patients' age correlated with JCV seropositivity and with JC viruria (P=0.02 and P=0.001, respectively). JC viruria was significantly correlated with a high JCV antibody index and high serum usCRP levels. We suggest that PCR and usCRP might be useful as markers of JCV reactivation, and that patients should be monitored between STRATIFY assessments.

C-reactive protein (CRP) is an annular (ring-shaped), pentameric protein found in the blood plasma, the levels of which rise in response to inflammation (i.e., C-reactive protein is an acute-phase protein). Its physiological role is to bind tophosphocholine expressed on the surface of dead or dying cells (and some types of bacteria) in order to activate the complement system

CRP is synthesized by the liver in response to factors released by macrophages and fat cells. C-reactive protein is a pattern recognition receptor (PRR). These are proteins expressed by cells of the innate immune system to identify pathogen-associated molecular patterns (PAMPs), which are associated with microbial pathogens or cellular stress, as well as damage-associated molecular patterns (DAMPs), which are associated with cell components released during cell damage due to infection. In this study they assayed the presence of c reactive protein with ultra sensitive measurement to link this to infection with JC virus. The used polymerase chain reaction to detect the virus. PCR is a technique where you amplify DNA from low levels to high levels so you can see if it is present.

If you have high levels of  Viral DNA you are much more likely to be  Antibody positive and this occurs in about 50% of people and is more robust that looking for viral DNA however there are some false negatives.