Quite a storm has been raised by a paper in Blood from Alan Rickinson's unit in Birmingham. I have known Alan for about 30 years. He runs the premier Herpes virus lab in the UK. Herpes viruses include Herpes Simplex, Zoster, CMV and Epstein-Barr virus. Epstein was Professor of Pathology in Bristol when I was a medical student and a junior doctor.
Herpes viruses have this in common: once you have them, you never lose them. CLL patients will know that they are prone to shingles attacks. Most people have chicken-pox as children - it's caused by the same virus. After recovery from chicken-pox the virus lodges in the spinal cord and at times of immunodeficiency (or other 'stress') it migrates down a peripheral nerve to infect the skin covered by that nerve. Likewise, as those who suffer from cold sores can testify, being 'run-down', getting a cold or exposure to sunlight can awaken the sleeping virus around the mouth.
I have been interested in EBV for many years and have written a few papers about it. In one of them I postulated that patients reacted to the infection in different ways, some made a rapid recovery, some a slow recovery and some kept getting recurrent symptoms. We were able to show a difference between T cell receptors in the different groups. Of course, in 1983 the methods were unbelievably crude compared with what can be done today, but I was interested to read the paper by Sauce et al in Blood . They studied the IL-7 and IL-15 receptors on CD8+ T cells in patients who had EBV infections.
Interleukin-7 and interleukin-15 are both pro-inflammatory cytokines, both having many targets and functions, but united in their ability to support and activate CD8+ cytotoxic T lymphocytes (CTL), the cells believed to be responsible for killing both tumor cells and virus infected cells. CD8+ T cells have receptors for both cytokines on their surface. These receptors are complicated affairs. In common with IL-2 and IL-12 they both use the common gamma chain as part of the receptor. This is what is missing in those 'boys in the bubble' who suffer from severe immunodeficiency syndrome (SIDS), and who have recently been treated by gene therapy (three of who have subsequently developed a T-cell leukemia). In the case of the IL-15 receptor it also shares the beta subunit with the IL-2 receptor, but also has a private alpha chain that is wholly its own. IL-7 on the other hand has only one other chain, an alpha chain that at least has a number, CD127.
Signaling through these receptors makes use of the JAK-STAT pathway. (Some may be familiar with this from all the publicity about JAK2 mutations in patients with polycythemia; in this case JAK1 or JAK3 are involved rather than JAK2). In mice both the IL-7 and IL-15 receptors are altered in response to a viral infection, IL-15R being upregulated and IL-7R being downregulated. The Birmingham study looked at these receptors in patients who had glandular fever.
Strictly speaking glandular fever and infections mononucleosis may not be quite the same thing, but the terms are used interchangeably. Glandular fever refers to the enlarged lymph nodes in the neck together with the fever; infectious mononucleosis refers to the presence in the blood of large numbers of mononuclear cells, which are now known to be CD8+ CTLs reacting to virally infected B cells. Although EBV is the commonest cause of this syndrome other viruses like CMV can produce a similar disease, as can the protozoan toxoplasma gondii.
They followed patients who developed glandular fever over a two year period. At first the T cells had no IL-7R alpha, but as time past this receptor appeared and after 2 years the level was back to normal. In contrast, the IL-15R alpha chain not only disappeared with the infection, but remained absent 2 years later. They were also able to study individuals in whom there was serological evidence of an EBV infection, but no history of any clinical disease - people who had had a silent infection. These individuals had normal levels of both IL-7R and IL-15R.
Thus the suggestion is that people who have glandular fever damage their CTLs for at least 2 years after the event, whereas those who have a subclinical infection with EBV recover normal CTLs. Is this defect permanent? It may be, though the evidence for this is not clear. One individual who had had glandular fever 14 years previously still had the IL-15R alpha defect, and there may be others in whom the effect was long lasting, but we are not given details in the paper. Is it specific for EBV? It would seem so because patients whose infectious mononucleosis was caused by CMV recover their IL-15R in a parallel way to the recovery of the IL-7R. Was there a defect in IL-15R in the first place that caused the patient to have a clinical rather than sub-clinical infection? That's a possibility because they were not able to study any of the patients' T cells from before their infection, but they did look at 30 individuals who had never been exposed to EBV and all of these had normal expression of IL-15R alpha. It would be very unlikely that there is a population of IL-15R alpha deficient individuals waiting to get a severe attack of glandular fever that would not be detected among 30 normal individuals.
Does the loss of the receptor matter? They did experiments to show that loss of receptor correlates with loss of function. Cells that lacked IL-15R alpha were 20 times less responsive to IL-15 than normal cells.
What does it all mean? It looks as though transient down regulation of IL-7 and IL-15 alpha receptors is a normal physiological response to viral infection and there for a purpose. The idea is that it regulates the response to that particular virus, so that the whole T cell repertoire isn't subverted by the immune response by non-specific cytokine stimulation, only those T cells designed to react with the particular virus. But in infectious mononucleosis the IL-15R alpha fails to recover even after many years. Does this matter? In mice this defect can be by-passed by monocytes capturing the IL-15 on their surface and presenting it to CD8+ T cells via the IL-15 beta and gamma receptor sub-units which are not affected by the virus infection. There is evidence that this does not happen in humans.
We do know, however, that post-IM patients maintain high levels of EBV-specific CD8+ T cells in their circulation and that these cells lack IL-15R alpha. Often patients continue to shed virus long after the attack and sometimes there are clinical recurrences. It seems that there is a precarious balance between virus and host after an attack.
We also know that in instances of immunosuppression EBV-related lymphomas may occur (after stem cell transplant or indeed any type of transplant, or after fludarabine or Campath). In Richter's syndrome EBV is often implicated. However, without such immunosuppression EBV-related lymphomas are not known to occur.
CLL Forum has wondered whether CLL might occur more frequently in people who have had a clinical rather than subclinical attack of EBV infection. They are conducting a survey. However, these sorts of data are very difficult to determine and interpret. Patients often believe that they have had glandular fever but never had a blood test to confirm it. Doctors sometimes tell patients that they have had glandular fever to fob them off. Patients with CLL need an explanation and their memories may deceive them. The comparator is difficult to assess. Normal individuals forget particular infections. I can't remember whether I have had mumps or not. Sore throats often go uninvestigated.
Although this story is stimulating and interesting, it is premature to draw conclusions just yet.
5 comments:
Terry,
The CLL Forum poll is a straw poll, absolutely unscientific. And, yes, memories can be deceiving. But maybe there is something there; the only way we patients have to gather this sort of information is anecdotally.
It is, of course, premature to draw conclusions. And the devil is always in the details.
But there is enough out there to make one at least take some pause. I think further serious study is warranted by those with the money and capability to take it on.
David
Terry:
I am delighted this topic has received the attention it has in the past few days, ever since the publication of our article "The enemy within" on www.clltopics.org .
I have received emails from 35 patients who have had clinically diagnosed infectious mononucleosis (IM) as kids or young adults. I have not counted in this number the patients who did not sound quite sure. These 35 cases had massive fatigue associated with them, and bed rest that stretched from a couple of weeks to a few months. I was intrigued that among these 35 cases of CLL with prior history of IM, there were 4 sets of familial CLL.
If one were to assume these 35 cases were indeed EBV driven infectious mononuclosis (your point on lack of quality control in IM diagnosis is well taken), then the incidence of IM in CLL patients is much higher than in the general population.
We estimate our article was read by about 1,500 people. Even if we assume each and every person who did not respond did not have IM in their past, this adds up to more than 2% of CLL patients with IM, versus 0.045% for the general public. It is reasonable that the 2% number is a tremendous underestimation, since many people who read our article and had IM in their past may not have bothered to write back. This was a "straw poll" on our website, not intended to be a scientific or rigorous survey.
My interest in IM stems from the observed increasing incidence of secondary aggressive lymphomas (Richeter's transformation) seen in CLL patients in recent years. EBV is clearly implicated in post transplant lymphomas (PTLPD), and situations where the patients have undergone very immunosuppressive therapies.
So, the million dollar question from patient's perspective is this: if the higher incidence of Richter's transformation is due to the advent of new and more aggressive therapy regimens that are likely to facilitate EBV reactivation, are CLL patients with a prior documented case of infectious mononucleosis more at risk from these therapies?
Making therapy choices is always a matter of balancing risks versus rewards. Very recently, we have learnt that there is not much point in putting 17p deleted patients through fludarabine therapy. They will not respond to the therapy, there is no bang for the buck in this situatin. We are also extra careful when administering Campath therapy to patients who are positive for cytomegalovirus (CMV) since a number of CMV reactivations have been documented following Campath therapy. Are we now on the threshold of learning that for patients with a potentially larger window of vulnerability to EBV (as demonstrated by prior IM) there is need to be extra careful about immne suppressive therapies, since this may give the old enemy (EBV) a chance to grow out of control? Richter's transformation carries a massive penalty, median survival is measured in months and not years.
Sometimes the choices CLL patients face are between the devil and the deep blue sea, and we cannot avoid therapies that may be dangerous but are necessary / essential to control a more immediate threat of CLL. But surely we need to take a closer look at patients with prior history of IM before signing them up for aggressive immune suppressive therapies as front-line first options? If regimens containing high doses of fludarabine, Campath or even high dose steroids are unavoidable, should we be developing "Best Practices" guidelines on how to protect particularly EBV-vulnerable patients as they go through these therapies? We have done that for CMV and Campath. Perhaps the time has come to see what needs to be done about protecting against EBV reactivation as well.
If any of the CLL researchers out there are willing and able to do a scientifically valid and statistically rigorous survey that sheds light on this issue, we at CLL Topics will support such an effort all the way. Heck, I am willing to go on record right now, we will even help fund and sponsor such an effort. No one has more at stake in learning about these issues than our patients, our very lives depend on it. I dount such an effort will get funding from drug companies!
Thank you for letting me use your soap box!
Chaya
The poll on CLLForum is recording 11 out of 41 respondents being ill in bed with IM.
Of course people who know or think they had IM would vote where others may not.
So if we use the total membership of over 600 and 11 have had IM (resulting in bed rest)this is still vastly more than one would expect to see.
Using Chaya's 0.045% in the general community or 1 in 2200 we should expect to see this result if we had 24,200 members not 629.
Not at all scientific I realise but very interesting.
My experience with EBV started in 1973 where it was confirmed by the only test available at the time a Paul Bunnel test (I think this was the name, whoever he is?) I was told that there were many false negatives with this test but that I was positive.
Until this infection I was obscenely healthy, I was playing professional football and had just been selected to play for my state. I was never able to play competitive sport again and have had recurring symptoms of IM ever since (every 12-18 months)
I have been recently tested for CMV and declared negative.
Just my story that proves absolutely nothing but I thought I would share :)
Actually, Steve, the Paul Bunnell test was a pretty good test. Many patients did not even get that. It would be interesting if the tendncy to get severe could be traced to a polymorphism on the IL-15R alpha receptor. Whether this defect in T cell function would make people prone to CLL is difficult to say as there is no evidence that CLL is common in people with other forms of immunodeficiency. A recent paper in Blood suggests that familial tendenmcy to CLL may be related to defects in the ATM-CHK2-BRA2 pathway.
Post a Comment