Breakthroughs in T-cell therapy
Some of you may have read about the University of Pennsylvania researchers treating a very small number of CLL patients with very advanced disease, using a novel T-cell therapy. All of the lay-press carried reports of this new development and for a change the hype was almost justified. We reported on it as well in an earlier article, hopefully with a more readable and balanced description of the technology and its potential value to us down the road.
While the approach was indeed an exciting development, there were some clear problems associated with it as well. Now we are beginning to see modifications that may get around the potential pitfalls. Combining potent therapies such as the new family of kinase inhibitors such as PCI-32765 with T-cell immunotherapies such as this may indeed make chemotherapy obsolete in the lifetime of patients reading this review. This is important stuff – and therefore, I hope you will bear with me as I walk you through the logic of how it is all supposed to work. As always, I will attempt to make the science and jargon a lot less heavy-handed and therefore more user friendly. In the process, I know I will be sacrificing some of the technical detail. Those of you who are up to it are always welcome to read the professional articles for yourselves.
Limitations of conventional chemotherapy
Before we discuss the benefits of T-cell immunotherapy, it might help to highlight the short-comings of conventional chemotherapy.
While different chemotherapy drugs have different mechanisms, by and large they work by damaging and poisoning cancer cells to such a extent that the cells die. Sounds good, but for a small fly in the ointment. The toxicity of chemotherapy drugs is not strictly restricted only to cancer cells. A certain percentage of perfectly healthy cells are also damaged in the process. The differential between the toxicity of the drug on cancer cells versus healthy cells is called the therapeutic window. A good chemotherapy drug is one that has a wide therapeutic window, in that it kills a lot of cancer cells while damaging and killing only a small number of healthy cells.
It always boils down to balancing risks and rewards. Unless the chemotherapy drug kills most or all the cancer cells, relapse is likely. Higher doses generally achieve more cell kill. But if the dosage is increased to improve the percentage of cancer cells killed, it is very likely the toxicity to healthy cells will increase too. In the extreme case, it is possible to give such a high dose of chemotherapy drug that almost all of the CLL cells are killed -probably at the expense of killing the patient too – a case of death by therapy. We cured the CLL, but unfortunately the patient died.
Another limitation of chemotherapy is that very often the drugs are ineffective against CLL cells that are nicely tucked away in enlarged lymph nodes, infiltrated bone marrow or enlarged spleen, liver. Larger percentage of CLL cells in such protected locations survive chemotherapy – one reason why it is relatively easy to clear the blood of CLL cells, but it is a lot harder to eradicate them in enlarge nodes or bone marrow – and these survivors can not only grow back to trigger a full-fledged relapse, the survivors are also likely to have learned how to avoid getting killed the next time around. Drug resistance is a major problem with most chemotherapy drugs. We see it all the time in CLL patients. Over time, patients develop resistance to most of the major drugs available to us, resulting in ever shorter list of therapy options.
Autologous T-cell Immunotherapy
The label given to this kind of therapy is important. It is immunotherapy – suggesting it is therapy based on your own immune system – and therefore very different from standard chemotherapy. It uses T-cells as the smart troops, hopefully on a house-to-house search for cancer cells where ever they try to hide in the body. It is autologous, meaning the T-cells used are harvested from the patient himself.
You have probably heard of another T-cell based therapy that has the ability to cure CLL patients, one that has been around for quite some time. I am talking about mini-allo transplants. In that case, the T-cells are allogeneic, meaning they are derived from the stem cells of the matched donor. The killing of CLL cells by the newly grafted T-cells (and other components of the donted immune system) is called “graft-versus-leukemia” effect. Sometimes, when the GVL is not sufficiently potent, the patient is given an extra dose of donor T-cells to get the job done (DLI – donor lymphocyte infusion). While GVL is very much the desired effect since it is the lynch-pin that brings about the hoped for cure, there is another side to this coin – graft-versus-host disease (GVHD) – which can be potentially dangerous. In fact, GVHD contributes major share of sickness and death in mini-allo transplants. We have yet to figure out exactly how to preserve and increase the GVL effect, but not at the expense of increased GVHD. These two effects, GVHD and GVL, are two sides of the same coin.
All that becomes a moot point when we talk of using autologous T-cells. Since the T-cells are obtained from the patient himself, there is little reason to expect that they would find the patient’s body “foreign” and therefore there is every reason to hope GVHD is no longer an issue. Unlike conventional chemotherapy, it is hoped that autologous T-cell therapy would spare healthy tissue, killing only the cancer cells and thereby toxicity to healthy tissue should be vastly decreased. But how to get the patient’s own T-cells to go after the CLL cells, when clearly they had been sleeping on the job up to that point – the reason why CLL had a chance to establish itself in the first place? That is the million dollar question of all autologous T-cell therapy approaches. Last but not least, it is hoped that the modified T-cells will stay vigilant and on the job for a long time. We need these vigilant smart troops to survive and hang around long enough to finish the job, get the patient into a 100% cure with no CLL cells left behind to trigger relapse.
The game plan boils down to this:
- We need to harvest sufficient number of T-cells from the patient. This is not hard to do.
- The next step is to vastly increase their number in the lab by encouraging them to grow and have lots of babies.
- We need to tweak the armies of T-cells so that they are now monomaniacal killers fixated on killing CLL cells – and nothing else.
- As with the University of Pennsylvania study, it is probably necessary to treat the patient with some chemotherapy regimen ahead of injecting back the doctored T-cell troops. This is necessary to reduce the number of cancer cells in the body to manageable levels. If the newly engineered T-cells infused back into the patient face an overwhelming army of cancer cells that outnumber and outgun them, chances of success become that much slimmer.
- There is another reason for this high impact chemotherapy ahead of infusing back the engineered T-cells. As most of you know by know, chemotherapy damages the immune system. In this case, that is what we want the preconditioning chemotherapy to do. We do not want the patient’s immune system still feisty enough to try and kill off all the newly engineered T-cells when they come back. Same logic is used in mini-allo transplants as well, pre-transplant chemo conditioning is an essential feature. Without it the new graft is quickly killed and the patient is back to square one.
There have been earlier autologous T-cell therapy experiments that met with scant success. Some of you old timers may remember a company called Xcyte. They too grew huge armies of the patient’s own T-cells in the lab and infused them back into the patient. The problem was these were not specially trained to seek and kill CLL cells. Nor were they given sufficient self-protection capabilities. All too soon, the precious new comer T-cells were quickly killed off by the host immune system. The over hyped early phase clinical trials at UCSD (and elsewhere) came to nothing and the company went bankrupt.
University of Pennsylvania – a genuine breakthrough
So, what has changed from the prior generation T-cell attempts? What the U. Penn folks were able to demonstrate is new technology that gave the engineered T-cells the ability to survive – even thrive and grow their numbers once they are infused back into the patient. The prior heavy duty chemotherapy was important too, by softening up the host immune system. For the first time, the engineered T-cells were still around and doing their job months after their infusion back into the patient. The other important thing they were able to do is channel the killing power of the new T-cells into a narrow focus. They were able to graft a specific search / identify tool onto the T-cells, such that they could identify all cells carrying a particular marker, and kill them on the spot. This identification tool is called a chimeric antigen receptor (“CAR”) and the hope is that CARs technology will allow us to engineer T-cells to target different cell types by appropriately chosen tumor markers.
U. Penn folks chose CD19 as the marker on which to focus the T-cell killers. All B-cells carry the CD19 marker; not just CLL cells but healthy B-cells as well. As expected, once they are infused back into the patient the CD19 targeted CARs T-cells killed every CD19 carrying cell they found in the body. As hoped for, the new T-cells not only survived but even increased their numbers over time – a first step if this therapy is to work at all. And they did indeed kill each and every cell they came across that carried the CD19 marker. A couple of patients with very advanced and refractory CLL saw almost miraculous clearance of their CLL tumor load. That is the good news, and it is indeed very encouraging news.
But there were problems as well. Since the new CD19 targeted CARs T-cells killed all B-cells, pretty soon there were no B-cells of any kind. B-cells are an important part of the immune system. They also go on to become plasma cells, which manufacture immunoglobulins. The constant and continuing surveillance of the killer CARs T-cells kept B-cell counts close to zero – which meant no plasma cells down the road, and therefore no immunoglobulins either. Ig levels plummeted and patients undergoing this therapy are committed to a life time of dependence on intravenous immunoglobulin (IVIG) therapy. Immunoglobulin therapy is based on careful collection of these precious bits of protein from huge quantities of donated blood – not a cheap process. IVIG therapy is quite expensive and the product is often in short supply. Long term, this is not a viable approach for large groups of patients, since there is no way we can maintain all of them on regular IVIG therapy for the rest of their lives.
Building upon success
Any number of research groups are looking to see how to tweak the U.Penn CARs approach so as to keep the good parts going but fix the problem areas. Using a different target for the T-cells – something other than CD19 – so that they kill only the cancerous B-cells and spare the healthy B-cells is very much desired. A number of options are being considered and I have no doubt that we will build on the success of the ground breaking success of the U. Penn team.
M. D. Anderson and others are looking at something called ROR1. What makes this marker hugely attractive is that it is expressed by CLL cells – but not healthy B-cells. IF everything goes according to plan, the hope is that ROR1 targeted T-cells will survive long enough in the body to kill each and every CLL cell in the body, but not damage the healthy B-cells. In other words, the patient is cured of CLL and yet healthy B-cell populations can recover and go on to produce plasma cells, immunoglobulins etc. By using ROR1 as the target of the killing power of the engineered T-cells, we can hope for avoiding the IVIG dependence baked into the cake of the U. Penn approach.
The B-cell tumor-associated antigen ROR1 can be targeted with T cells modified to express a ROR1-specific chimeric antigen receptor.
Hudecek M, Schmitt TM, Baskar S, Lupo-Stanghellini MT, Nishida T, Yamamoto TN, Bleakley M, Turtle CJ, Chang WC, Greisman HA, Wood B, Maloney DG, Jensen MC, Rader C, Riddell SR.
Clinical Research Division, Program in Immunology, Fred Hutchinson Cancer Research Center, Seattle, WA, USA. firstname.lastname@example.org
Monoclonal antibodies and T cells modified to express chimeric antigen receptors specific for B-cell lineage surface molecules such as CD20 exert antitumor activity in B-cell malignancies, but deplete normal B cells. The receptor tyrosine kinase-like orphan receptor 1 (ROR1) was identified as a highly expressed gene in B-cell chronic lymphocytic leukemia (B-CLL), but not normal B cells, suggesting it may serve as a tumor-specific target for therapy. We analyzed ROR1-expression in normal nonhematopoietic and hematopoietic cells including B-cell precursors, and in hematopoietic malignancies. ROR1 has characteristics of an oncofetal gene and is expressed in undifferentiated embryonic stem cells, B-CLL and mantle cell lymphoma, but not in major adult tissues apart from low levels in adipose tissue and at an early stage of B-cell development. We constructed a ROR1-specific chimeric antigen receptor that when expressed in T cells from healthy donors or CLL patients conferred specific recognition of primary B-CLL and mantle cell lymphoma, including rare drug effluxing chemotherapy resistant tumor cells that have been implicated in maintaining the malignancy, but not mature normal B cells. T-cell therapies targeting ROR1 may be effective in B-CLL and other ROR1-positive tumors. However, the expression of ROR1 on some normal tissues suggests the potential for toxi-city to subsets of normal cells.
As expected, the abstract above reports ROR1 is nicely expressed by CLL cells, mantle cell lymphoma cells and fetal embryonic cells – but not healthy adult cells. (In other words, this approach is a definite no-no if you are pregnant or likely to be pregnant in the near future). Healthy B-cells do not express it. In fact, the only group of cells that express it other than CLL cells and MCL cells are adipose cells (fat cells) and pancreatic cells. The expression of ROR1 on fat cells and pancreatic cells is lower than its expression on CLL cells.
That ROR1 gene is expressed to any level by adipose cells and pancreatic cells may pose a problem with this technology. In fact, one of the Canadian doctors at the conference asked Dr. Keating this question. Is he worried that administration of ROR-1 targeted CARs T-cells will not only attack CLL cells, but pancreatic cells as well? I thought this was a clearly relevant question. And I was very chagrined that Dr. Keating brushed off the question with a joke. He said that since ROR1 is also expressed by fat cells, a side effect of the ROR-1 based CARs technology may be that heavy patients with a few pounds to lose may find themselves getting slender, since their adipose cells express ROR1 as well and therefore targeted.
Well. He was kidding, of course. But the prospect scares the heck out of me. One of the major (and I mean life threateningly major) risk factors of the U. Penn study was tumor lysis syndrome. When too many cells are killed at a rapid pace, the quantity of debris created by the dead and dying cells can become a huge problem. Eventually, all this stuff must be handled by the body’s garbage handling systems. TLS can become life threatening if the load becomes more than the kidneys can handle. Even with urgently initiated dialysis, kidney failure can kill patients a whole lot faster than CLL.
So, how would you like to get slender at the risk of TLS? Notice, the U. Penn researchers deliberately set out to reduce the tumor load in their patients by means of pre-conditioning chemotherapy. The idea was to decrease the number of CLL cells left over for the CD19 targeted CAR T-cells to kill. Even with that precaution, TLS was an issue with their patients. Each and every one of us has adipose tissue – fat cells – in our bodies. Some of us have more than others, but there is no way of taking adipose tissue to zero levels ahead of CARs therapy. Is there a risk of TLS as the engineered T-cells go after fat cells, even though they express only low levels of ROR1? This would not be my chosen way of losing a few pounds. Along the same lines, pancreatic inflammation if the ROR1 targeted T-cells go after pancreatic cells would not be a trivial matter either. The question asked at the conference was quite valid and I wish Dr. Keating had chosen to answer it seriously.
Case report of a serious adverse event following the administration of T cells transduced with a chimeric antigen receptor recognizing ERBB2.
Morgan RA, Yang JC, Kitano M, Dudley ME, Laurencot CM, Rosenberg SA.
Surgery Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA. email@example.com
In an attempt to treat cancer patients with ERBB2 overexpressing tumors, we developed a chimeric antigen receptor (CAR) based on the widely used humanized monoclonal antibody (mAb) Trastuzumab (Herceptin). An optimized CAR vector containing CD28, 4-1BB, and CD3zeta signaling moieties was assembled in a gamma-retroviral vector and used to transduce autologous peripheral blood lymphocytes (PBLs) from a patient with colon cancer metastatic to the lungs and liver, refractory to multiple standard treatments. The gene transfer efficiency into autologous T cells was 79% CAR(+) in CD3(+) cells and these cells demonstrated high-specific reactivity in in vitro coculture assays. Following completion of nonmyeloablative conditioning, the patient received 10(10) cells intravenously. Within 15 minutes after cell infusion the patient experienced respiratory distress, and displayed a dramatic pulmonary infiltrate on chest X-ray. She was intubated and despite intensive medical intervention the patient died 5 days after treatment. Serum samples after cell infusion showed marked increases in interferon-gamma (IFN-gamma), granulocyte macrophage-colony stimulating factor (GM-CSF), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and IL-10, consistent with a cytokine storm. We speculate that the large number of administered cells localized to the lung immediately following infusion and were triggered to release cytokine by the recognition of low levels of ERBB2 on lung epithelial cells.
As you can see in the discussion and abstract above, CARs technology is immensely powerful. It has the ability to cure, but it also has the ability to kill just as quickly. We are in early stages of developing this technology, we need to build careful understanding of the science, so that we can benefit from the curative potential but avoid its lethal power that can cause mayhem. Full fledged late stage clinical trials using ROR1 marker (and other target candidates being explored by other researcher groups) are several years out. I have no doubt that down the road high powered immunotherapy regimens using this and similar approaches will finally cure CLL and many other presently lethal cancers. Will we get there in the next 2-3 years? Will chemotherapy become passe and CLL patients cured in droves in the optimistic time frame Dr. Keating mentioned at the conference? I am willing to bet several dollars to a single high fat donut that the vast majority of CLL patients will still have to deal with less than perfect chemotherapy options for many years yet.
When pressed on the time horizons, Dr. Keating said we as patients and patient advocates can help the process by getting regulatory agencies off his back. He said, and I quote, the only animal experiments he wants to do are in human animals . I beg to differ, humbly but quite vehemently. Without proper pre-clinical work in the lab and appropriate animal studies, in my layperson opinion it would be highly unethical to recruit “human animals” for the studies. A couple of well publicized disasters where patients died as a result of poorly vetted technological errors can also set the whole field back for years. All of us want success, all of us want it yesterday. But there is good reason for the checks and balances in place to protect human subjects volunteering for such cutting edge technologies. When is it OK to sacrifice the lives of early volunteers, cut corners on safety concerns so that we can speed up the process for folks further back in the line?
Never, not on my watch, not if I have to say anything about it. There are these little things called the Helsinky Accord and the Nuremberg Code that were established soon after the second world war. In 1948, German physicians who conducted deadly or debilitating experiments on concentration camp prisoners underwent criminal proceedings in the Nuremberg Trials. That same year, following the Nuremberg Trials, the Nuremberg Code was established. The Nuremberg Code was the first international document that supported the concept that “the voluntary consent of the human subject is absolutely essential”. The emphasis that was placed on individual consent in the Nuremberg Code was aimed at keeping participants informed of the risk-benefit outcomes of experiments. No, I will not support “human animal experiments”, not without due diligence to scope out the risks and rewards through well conducted pre-clinical work and animal studies. Not one of my members is expendable, not in this way.
You know my thoughts about patient volunteers who participate in cutting edge clinical trials. Progress is not possible without their courage and generosity. But precisely for that reason, it is our sacred duty not to sacrifice their lives without doing what needs to be done to protect them as well as possible. Informed consent is the at the heart of human clinical trials. How can consent be informed if we do not have a good handle on the possible risks and rewards? I doubt ROR1 based CARs technology will ever get FDA approval as a way of controlling obesity. The flip comment may be OK as a one-liner to lighten a speech and introduce a bit of humor to spice up a talk to cancer patients, but dismantling regulatory and ethical oversight in order to speed up development of a pet theory – that may or may not pan out – is not something I will support. There have been plenty of other sure-fire sounding medical theories that have not done so well in actual practice. Trust but verify, be hopeful but don’t buy every pig in a poke, be generous in volunteering for clinical trials but be damned sure you have a pretty good handle on the risks involved – this is my advice.
What say you?