Several hundred of you sent me links to various articles and videos in the lay press, reporters discussing the results of the recent paper in New England Journal of Medicine. I gave up acknowledging the individual emails after the first couple of dozen or so. It was good to see our members are wide awake and keeping tabs on new research that may be relevant to our community. Keep it up! In case you have been too busy following the roller coaster ride of the stock market and not paying attention to much else, here are some of the links that you can look up at your leisure. Frankly, I have stopped looking at my savings accounts – it is indeed scary and there is not a whole lot I can do about it. Any case, I would rather spend my time writing about CLL breakthroughs!
The article in NEJM is so new that PubMed has not yet caught up with it and therefore there is no official abstract. In its stead, below is the “Summary” section of the NEJM article, as well as a link where you can access the full text article for free. I must warn you, it is not easy reading since it is clearly written for a professional audience – but well worth a try if you are a science geek like me. I found it very interesting. It is credible research, published in a very credible peer-reviewed journal – definitely not snake oil. That much is clear.
New England Journal of Medicine, August 10, 2011
David L. Porter, M.D., Bruce L. Levine, Ph.D., Michael Kalos, Ph.D., Adam Bagg, M.D., and Carl H. June, M.D.
We designed a lentiviral vector expressing a chimeric antigen receptor with specificity for the B-cell antigen CD19, coupled with CD137 (a costimulatory receptor in T cells [4-1BB]) and CD3-zeta (a signal-transduction component of the T-cell antigen receptor) signaling domains. A low dose (approximately 1.5×105 cells per kilogram of body weight) of autologous chimeric antigen receptor–modified T cells reinfused into a patient with refractory chronic lymphocytic leukemia (CLL) expanded to a level that was more than 1000 times as high as the initial engraftment level in vivo, with delayed development of the tumor lysis syndrome and with complete remission. Apart from the tumor lysis syndrome, the only other grade 3/4 toxic effect related to chimeric antigen receptor T cells was lymphopenia. Engineered cells persisted at high levels for 6 months in the blood and bone marrow and continued to express the chimeric antigen receptor. A specific immune response was detected in the bone marrow, accompanied by loss of normal B cells and leukemia cells that express CD19. Remission was ongoing 10 months after treatment. Hypogammaglobulinemia was an expected chronic toxic effect.
OK, now that we have acknowledged the official paper in NEJM, as well as the TV soundbites, we can get down to business and try to make sense out of this new development. Is this a breakthrough or is it just more hype? Will we be able to declare CLL a curable cancer in the next couple of years? Below is my best understanding of the science, admittedly at first blush and short notice. I will be keeping my eyes peeled for learned discussions on this subject and if anything changes in my understanding, I will be sure to get back to you via the comments section that follows each of my reviews. In the meantime, here is a quick look-see at this interesting research.
T-cells: elite troops, serial killers
Before you can understand what this research is all about, you need to learn a little bit about T-cells, how they work, why they are so important for good health and what can go wrong with them. Bear in mind, this is indeed a cartoon version of a field of immunology that researchers spend their whole professional lives studying. But without even this bit of understanding of how T-cells work, you won’t be able to make sense of the University of Pennsylvania research results. At your leisure, you can also browse earlier articles I have written on the subject. Links are given below for your convenience.
T-cells are smart troops. In other words, they can learn from prior experiences fighting pathogens and cancerous cells, they can remember, and they can pass on their wisdom to their off-spring. T-cells (and their less numerous but even more potent side-kicks called NK Cells) are among the most important of our immune defenses against all sorts of external threats such as viral infections as well as home grown cancers.
Consider what may happen when a stray photon of UV light hits the unprotected bald spot at the top of your head, in exactly the wrong way. There you were, minding your own business and enjoying a day at the beach and soaking up a little sunshine, trying to get a tan. But as happenstance would have it, that single skin cell on top of your head got damaged by the UV photon and its DNA became messed up. Most of the time, scrambling of the DNA is serious enough that the cell dies immediately thereafter. This is the orderly process of apoptosis, cellular suicide. Without it, we will have all sorts of dysfunctional cells hanging around and gumming up the works. As it is, the dead cell does little more than contribute to a bit of dandruff, skin flakes that you brush off with hardly a second thought.
But what if the cell is damaged just enough to be dangerous? What if the DNA damage is such that it learns how to turn a deaf ear to the suicide signals it gets from its neighbors and friends? What if it continues to live in its mangled state, even thrive and grow a few babies that share its cancerous abilities of avoiding proper cell death? What you have is a microscopically small colony of newly minted skin cancer cells – a really tiny colony of basal cell or squamous cell carcinoma. Left unchecked, this little group of cancer cells would keep growing and pretty soon it would not be such a small problem anymore. That is one reason why defects in the P53 gene are so important. This gene controls the cell’s ability to commit suicide.
That is where T-cells come in. T-cells have the ability to query the cells they meet as they patrol every nook and cranny of your body. They are on the prowl for infected cells and cancer cells. In a healthy individual with properly functioning immune function, the little colony of cancerous skin cells is soon discovered. T-cells go far beyond politely asking the cancer cells to commit suicide. They actually drill holes into the cancerous cells, build a funnel (“perforin”) and pour in a particularly deadly poison (“granzyme”). Talk about irresistible and lethal force – the cancer cell that is attacked in this fashion has no chance of survival. Does it matter if the cancer cell has developed p53 defects? No, because we are not talking of suicide anymore, we are talking of execution! Carried out by T-cells. Once the target cell is dead, the T-cell moves on to the next victim, until every single cancer cell in the little colony is wiped out. T-cells are truly serial killers. A single T-cell on killing rampage can execute many target cells before it runs out of ammo (perforin and granzyme) and needs to recover, re-load as it were.
In fact, T-cells can be such dangerous killers that they have to be kept under careful check at all times. Uncontrolled, they can become hordes of killers that damage healthy tissue as well as cancer cells. For example, many forms of autoimmune disease are the result of an over enthusiastic immune system killing perfectly healthy cells. Being able to tell the difference between healthy cells and cancerous or virally infected cells – that is the fine line between health and sickness. Part of the control mechanism in preventing unwanted T-cell rampages is that they must have several different signals confirming the target cell is indeed infected or cancerous, before they can kill it. Think of it as paperwork that must be filled out in triplicate before execution can take place. This bit of cellular red-tape slows things down a bit, but it makes sure innocent cells don’t get killed for no good reason.
Smart criminals can learn to hide from smart police officers
If T-cells are so great, how come any of us get cancer? The reason is simple. In addition to learning how to turn a deaf ear to official orders to commit suicide, cancer cells can also learn stealth techniques that make them invisible to T-cells. The details are complex and I will not bore you with them. But all we need to understand is that for a cancer cell to flourish, it needs to do three things. (1) Avoid committing suicide (2) have plenty of babies just like itself (3) learn how to fool T-cells so that they cannot identify it as a cancer cell that must be killed on the spot. Remember all those careful confirmatory signals that T-cells must have before they can kill, the red tape paperwork that must be filled out before they can unleash their killing fury? That is often the basis of how cancer cells avoid getting killed. Think of it as the police department swamped in bureaucratic red tape and unable to act quickly. Criminals can learn to use that window of opportunity to flourish. Pretty soon, T-cells get so used to seeing these criminals hanging around that they stop paying any attention to them at all! This called “T-cell anergy”.
Bringing in new and better trained police officers
How about if we bring in a fresh bunch of police officers from the neighboring town? Officers who have not become blase to the presence of criminals hanging around, officers with different safety protocols that the criminals have not heard about and therefore cannot use to their advantage? Yes, that may be able to do the job – if there are enough new police officers, if they stick around long enough to do the job, if they are not overwhelmed by too many well entrenched criminals. And if the new police officers don’t kill too many innocent citizens, mistaking them for criminals.
There is a name for such a therapy. It is called a mini-allo transplant. We get rid of the existing useless police force and as many of the criminals as we can (pre-conditioning therapy), bring in new batch of police officers (graft) and hope that they will go after the criminals (graft versus leukemia effect). The single biggest problem associated with allogeneic stem cell transplant is graft-versus-host disease. Even with the best efforts to match donor to recipient, the new T-cells coming in are prone to attack healthy tissue as well as cancer cells. Graft-versus-Leukemia and graft-versus-host disease are two sides of the same coin.
Can we teach our own T-cells to be more effective?
Is there anyway of making our own T-cells work better at spotting the cancer cells? If it is our own T-cells – the term is “autologous” when the T-cells are the patient’s own, not from a donor – then there is little risk of the dreaded GVHD. Can we, for example, give them extra training to recognize a particular kind of cancer, help them recognize the cancer cells better by sharpening their focus to just that one kind of cancer cell? Can we suspend some of the safety rules and give them more discretionary power to carry out executions without having to dither and second guess themselves? You with me so far? Because that is exactly what this new bit of research attempts to do. It makes it easier for the patient’s own T-cells to recognize CLL cells, and it removes some of the hurdles T-cells have to cross before they can shoot to kill.
Autologous, B-cell targeted, rampaging T-cells
Let us take that paragraph heading, one step at a time. Autologous. In other words, T-cells from the patient’s own body are harvested and taught a few new tricks before they are infused back into the patient. B-cell targeted. T-cells are designed by nature to be general purpose smart troops, ready to identify a breast cancer cell, a skin cancer cell, a virally infected cell or whatever happens to be around. But in this case, we want them to focus on just one thing. CLL cells. All B-cells carry CD19 marker. Immature B-cells, mature B-cells, cancerous B-cells, healthy B-cells – it does not matter what kind of B-cell. Think of CD19 as the marker that defines a B-cell, its very essence, the one thing that it cannot hide. This study trains the T-cells collected from the patient to recognize CD19 as a huge red flag, a signal that cannot be ignored, in fact the only signal that matters as far as it is concerned. They did a couple more things to the T-cells. They took some of the safeties off, by providing the confirmatory signals ahead of time. Think of it as filling out the paperwork and signing the execution orders ahead of time, taking that pesky duty off the list of things T-cells have to hassle with. We now have all the ingredients necessary for effective hunting of B-cells: patient’s own home grown T-cells able and willing to recognize any cell carrying the CD19 marker (which means all B-cells), and trained to use lethal force without needing any other bits of confirmatory signals.
The U. Penn. clinical trial
Just three patients underwent this protocol so far. But the NEJM article reports the data with reference to just one patient. This is a single patient case history report, something to keep in mind as we evaluate the results.
The patient was diagnosed with CLL in 1996. After 6 years of Watch & Wait, he was treated with 2 cycles of FR and got a partial response (blood counts looked good, but there were still some swollen lymph nodes). He needed therapy again in 2006 and got 4 more cycles of FR. Same result, blood counts normalized but only a partial response in nodes. By 2009, things got a lot worse. He had rapidly progressive disease, heavily infiltrated bone marrow, and FISH test showed unequivocal deletion in the dreaded 17p region. They tried bendamustine (Rituxan had to be withheld because he developed massive allergy to the mouse juice of Rituxan) with very little to show for it.
So, we are looking at a patient with pretty bleak future: very aggressive CLL, 17p deletion, prior history of only partial responses to FR and more recently bendamustine, contra-indications for ever using Rituxan again due to hyper allergic reactions. What would you do in his situation? Campath? Revlimid? Mini-allo transplant if you somehow managed to get a good remission ahead of the transplant? Tough calls, all of them.
In Dec 2009, patient underwent procedure for T-cell collection from his own blood. While these T-cells were being modified, he underwent 11 weeks of Campath therapy. The point of the Campath therapy is to get some control over the CLL while he waited for the modified T-cells to be ready. Over the next 6 months, while he waited, his disease came roaring back. Massive bone marrow infiltration, 1-3 cm lymph nodes all over the place. By July 2010, the modified T-cells were ready. Phew. Those six months must have been tough waiting for this brave volunteer!
We will not go into details of how exactly the T-cell modification was carried out. There is no way I can make a cartoon version of that, you have to read the NEJM article if you are interested in the details. For the rest of us, just remember these T-cells are now fixated on CD19 as their target, and they are T-cells on steroids, only too anxious to kill their target cells.
Four days prior to getting the new modified T-cells, the patient got massive doses of pentostatin (another purine analog similar to fludarabine) and cyclophosphamide. The intent is not so much to kill CLL cells – but to kill of some of his remaining local defenses. Same approach is taken in mini-allo transplant, making sure that the new graft coming in is not immediately attacked and killed by the patient’s remaining immune system.
Finally, arrival of T-day. Our patient got his modified T-cells split into three doses on 3 consecutive days. 10% on the first day, 30% on the second day and 60% on the third day. The researchers were being cautious with this very new technology. No toxic effects were noted upon infusion of the souped up T-cells.
Now for the details you have been waiting for, what happened after the patient got his own modified T-cells. Frankly, nothing much happened for the first couple of weeks. I bet the researchers were disappointed, scratching their heads and wondering what they could have done better.
Fortunately for our guy, they did not stop monitoring him, they did not go off on vacation and chalk the experiment to yet another failure in the long list of unsuccessful T-cell therapy approaches. Because all hell broke loose after 14 days. It started off with low grade fever, chills, a little fatigue. All the usual symptoms that we are familiar with, for example, when we have a slight infection and T-cells are doing their thing and stamping it out.
Over the next 5 days, things got a lot more interesting. And dangerous. The chills got worse. The fever spiked to 102.5, there were rigors, nausea, diarrhea, lack of appetite. On day 22 post infusion of modified T-cells, patient was formally diagnosed with tumor lysis syndrome.
If you are inclined to dismiss this incident of TLS as not very important, please don’t. TLS is dangerous, TLS can kill. Notice the sudden spike in uric acid, creatinine and LDH (lactate dehydrogenase). All of these are waste products created when cancer cells are getting killed so fast that the debris created by their death is accumulating too fast for the kidneys to dispose of. The authors note, there was evidence of “acute kidney injury”in this patient.
I wonder if the researchers considered this possibility and had the patient pre-medicated with allopurinol. I did not see any references to that, but perhaps it is a detail they did not report. They do report that the patient was hospitalized after the diagnosis of TLS, hydrated and treated with rasburicase. This is the new drug that is used in place of allopurinol when time is of the essence – as it was in this case. Please refer to our earlier article on tumor lysis syndrome if you want to learn more about it.
Our guy was lucky. Rasburicase worked and uric acid levels came back down within 24 hours. By day 28, positive results of all the modified T-cell induced mayhem could be seen: the swollen lymph nodes were no longer felt, and there was no evidence of CLL in the bone marrow! FISH test showed no 17p deletion. Continued monitoring of the patient at 3 and 6 month post modified T-cell infusion showed no return of the cancer – no swollen nodes, no FISH defect, no bone marrow involvement. Patient had no B-cells left. As expected the CD19 targeting T-cells killed all B-cells, not just the cancerous CLL cells. It is now 10 months since start of the T-cell therapy, and the patinet’s remission is still intact.
There were no other high grade adverse effects. Lymphopenia (too few white blood cells) continues, since the bulk of white blood cells are B-cells and this patient has no B-cells left. Also a consequence of having no B-cells, patient is now low on immunoglobulins. Remember, B-cells mature to become plasma cells, which are nothing more than factories for manufacture of immunoglobulins. No B-cells means no plasma cells, which in turn means no immunoglobulins. This was an expected adverse effect and patient is now on regularly scheduled IVIG (intravenous immunoglobulin) therapy.
The gift that keeps on giving..
Several earlier attempts at using externally modified T-cells failed soon after when the newcomers gradually died away in a couple of weeks. Some of you old timers may remember all the hype associated with “XCYTE” technology that went no where fast. In a nutshell, the problem was that the modified T-cells did not hang around long enough to do much. Not so the little critters used in this trial – and that was the huge surprise.
Notice how the number of modified T-cells (“transgene copies”) shot up after the three days of infusion, by a factor of 1,000 fold! At their peak level, the modified T-cells accounted for more than 20% of all circulating lymphocytes. The timing of the peak in their concentration also coincided with the onset of tumor lysis syndrome in our patient. Makes, sense, highest number of killer T-cells going on a rampage, maximum number of B-cells killed quickly, most damage to the kidneys. The interesting thing to note that 180 days out, there are still 100 times as many modified T-cells as were initially infused. Wow. No question but these souped up T-cells are not only surviving but thriving! The graph above is with reference to whole blood. Similar trends of modified T-cell concentrations were also seen in the bone marrow.
The good news is that these new modified T-cells are able to survive and even grow their numbers by huge amounts in the patient’s body. That means there are enough of them to do the job of killing CLL cells, and they are sticking around long enough to complete the job. And if they stay around forever, the remissions will hold forever.
The bad news is that these new modified T-cells are able to survive and even grow their numbers. Controlling dosage of T-cells infused is going to be tricky. TLS will be a huge risk factor, if the numbers increase too much, too quickly, and therefore kill too many B-cells too fast for the kidneys to handle. If they hang around forever, and continue to target all CD19 carrying cells, that means the patient will continue to have zero B-cells – forever. B-cells are an important part of our immune system. Even Rituxan therapy (which targets CD20 marker) does not totally wipe out B-cell populations, and the counts recover in any any case a couple of months post Rituxan therapy. Live with no B-cells for very extended lengths of time will be tricky. For starters, patient will become dependent upon regular IVIG infusions, for the rest of his life. Even with that, long term B-cell deficiency means there will be increased risk of infections.
Down the road, more work will establish dosage, safety monitoring, better protection against TLS ahead of time. They may also build in a suicide switch into the modified T-cells, so that an externally administered signal can cause them to curl up and die, once they have finished their job and CURED the CLL. Such technology is known and has been used in other approaches. The bottom line take home point is this: in a very refractory and 17p deleted patient with few therapeutic options, they managed to actually eradicate the nasty CLL cells. That is a huge accomplishment. How can we not cheer that?
This has been a long article. So I will keep my editorial short and to the point.
- Is this “snake oil”? No.
- Is this credible research? Yes.
- In its present state, can it be dangerous? Yes.
- Is the research promising? Very.
- Is there a lot more work to do? Yes.
- Grounds for optimism? Most definitely yes.
- Will it be available to treat you in the next year or so? Not outside of carefully conducted clinical trials.
- Should we be rooting for this approach? Absolutely!
Wonderful breakthrough, lots of press visibility, kudos from their peers and patient groups like us. Did the authors thank the single patient whose life hung in the balance in this clinical trial? No. Well, that is nothing new. So, please join me in a very heartfelt round of applause for this pioneer. His courage may one day pave the way for the rest of us beating this awful cancer.