ISF35: CLL “Vaccine”

ISF35 is called a vaccine. In some ways that is not quite right, since it does not prevent anyone from contracting CLL, the usual reason why people get vaccine shots. What it is targeted to do however is to make the CLL cells easier to kill by waking up the patient’s own immune defenses – and that is similar to what vaccines do. So, the title of “vaccine” is not too far off the mark.

“Gene Therapy”

Back in August 2003 I wrote about a “gene therapy” clinical trial pioneered at UCSD. With some rather subtle but important modifications / improvements, ISF35 vaccine technology is  similar to the earlier “gene therapy”. You have to admit, these guys know how to give their projects sexy titles. I will try to explain the science behind this technology in rather simple terms. If you wish to read more detailed and technically correct version of it, I recommend the plenary paper published by Dr. Kipps et al in “Blood”, November 2000. A whole decade has passed since that seminal paper. That makes it all the more appropriate to take stock where the technology is at today.

Cool Science

When everything is working the way it should, a healthy immune system can spot pathogens or even the body’s own cells that have gone rogue and kill them before they can do much harm. Obviously, since you have CLL, things are not working quite the way they should, CLL cells are accumulating in your body even as we speak.

The interesting thing about CLL is that the  rampant run-away population growth is not  because the cancer cells are having babies a whole lot faster than they should. In fact CLL cells have only a modestly faster rate of reproduction than normal cells.  That is why it is called an indolent leukemia. The accumulation is due to the other side of the equation, the ability of CLL cells to resist dying. They can block out polite signals from the body to commit suicide, and they can hide from death enforcers like T-cells and NK-cells. If babies continue to be born into a society where death of older folks is abolished, you can see this leads to a population explosion. That is the driving force behind the steady growth of your cancerous CLL  counts.

Our immune system’s killing power can be very dangerously if it is left uncontrolled. In order to avoid “Oops! Friendly Fire Accident!” type of situations where perfectly law abiding cells are killed by an immune system gone berserk, our bodies have developed a number of complex protocols before T-cells and NK-cells can let loose their lethal fire power. All the paperwork has to be done right, filed in triplicate etc before executions can take place. One of the necessary conditions is that the cell targeted for killing must display certain markers – sort of a “Kill me, please” signal on their surfaces. As you can guess, CLL cells skip this important step, and thereby avoid getting killed. ISF35 (and their gene therapy before it) focus on making it harder for CLL cells to hide from the killing wrath of T-cells and NK-cells, by means of painting a huge bull’s-eye on the cancerous cells.

The markers that paint a “Kill me” bulls-eye on cancerous B-cells are called CD154 and its soul mate (“ligand”) CD40. Memgen has engineered an improved version of human CD154 that is even better than the natural variety at locking on to CD40 on B-cells. This is how it works: blood is withdrawn from the patient and mononuclear cells (including CLL cells) are separated from it. To deliver the payload of their powerful version of CD154 molecule to latch on to malignant B lymphocytes, Memgen uses an adenovirus. Think of the adenovirus as a sort of Trojan horse, it’s stealthy job is to deliver the CD154 protein and thereby infects the leukemic cells. This is the kind of thing viruses are good at! The game plan is that once there is stable expression of the CD154 (ISF35) molecule on the cell surface, the cancer cells cannot hide any longer.  It triggers powerful immune attack on the marked cells, leading to their death.  Pretty cool stuff.

Here are a couple of details that are rather important. The adenovirus used as the Trojan horse is “replication defective” variety. In simple English, what this means is that the virus cannot get out of control and grow unchecked, thereby creating new problems all by iteself. This approach, using a “neutered” virus that cannot make copies of itself, is a time-honored approach in gene therapy. Barring a few scary episodes early in the history of gene therapy, this approach has now withstood the test of time. That does not mean there will never be any accidents to worry about, but my sense of it is that it is now pretty mature technology.

The other thing to understand is that even though only a very small percentage of CLL cells are withdrawn from the patient and infected with Memgen’s ISF35 and then injected back into the patient, there seems to be a by-stander effect. The ISF35 infected cancer cells seem to cause other CLL cells in the neighborhood to light up as well, become more visible targets for the immune system. In other words, the effect of ISF35 is amplified many times over by means of this by-stander effect – which is very important.

This is no more than a mere cartoon version of some pretty cool and complicated science. You can find a lot more information about the science of “Gene Therapy” and “ISF35 vaccine therapy” on the web and in professional journal articles. But I will stop the science lecture at this point and proceed with a more pragmatic evaluation of the technology, from patients’ perspective. Does it work? Is it likely to become commercial? How long is that going to take? Should I hold my breath and avoid chemotherapy because a successful ISF35 vaccine is just around the corner? You know, the usual life-and-death questions pesky patients like to ask.

Active ISF35 Clinical Trials lists two ongoing clinical trials for ISF35 treating CLL patients. Please refer to their full citations and details by clicking on the links below.



I was surprised to see both are listed as “active” but “not recruiting”. What gives? Perhaps they already have all the volunteers they need.

The first study (NCT00772486) started in September of 2008, expected to recruit 12 patients. It is very early stage trial, a Phase-I trial, designed to test safety and tolerability of the new drug. Patients get three infusions of ISF35, followed by three cycles of standard issue FCR therapy. Patients recruited must be refractory, resistant and/or have high risk 17p deleted variety of CLL. The researchers reported on the status of this trial at the recent ASH2010 conference.

  • Four patients have completed treatment thus far.
  • Two of these have achieved “CR”, one of whom got the coveted MRD negative response.
  • One patient got a partial response.
  • One patient had progressive disease in spite of therapy

I have a hard time evaluating this information. For starters, just four patient responses is no more than a tad better than single person anecdotal stories. This does not begin to reach statistical credibility. Second, I have no way of telling how much of this response is due to ISF35 and how much of it is due to FCR. After all, FCR is pretty potent all by itself.

In any case, the follow-up time for all four patients is a medial of 18 months – not long enough to know if the protectiveness of the ISF35 vaccine is long lasting or whether the CLL will sneak back as soon as the effects of FCR has worn off. I was also taken aback that the clinical trials citation says while the study is on-going, they are not recruiting patients at this time. Does this mean the remaining 8 patients are gradually working their way through the process and we will hear about their response in future publications, or have they stopped recruiting short of the planned 12 volunteers for some reason? In any case, a single arm early phase – I trial with only a dozen patients recruited makes it very hard to separate out the benefits of ISF35 from those of FCR used in this clinical trial protocol.

The second trial (NCT00849524) started in January 2009, just about 2 years ago. 28 patients are planned to be recruited in this Phase-II trial. The protocol calls for up to 6 direct injection of the ISF35 vaccine into a single lymph node chosen for each patient.  However, ASH2010 abstract below reports on only 10 patients who went through this process.

  • All patients were chemo-naïve but their CLL had progressed to the point where therapy was indicated. There do not seem to have been much by way of toxicity, barring flu-like symptoms.
  • Seven out of 10 patients had at least 50% reduction in their blood CLL counts.
  • Eight out of the 10 patients had 50% or more reduction in the targeted lymph node.
  • Seven out of 10 patients had 50% or better reduction in their swollen spleens.
  • Overall response rate was only 30%;  3 patients with a PR (partial response), 4 patients with stable disease and 3 patients with progressive disease.

I was really hoping that even though they targeted only a single node in each patient’s case, that the vaccine effect would spread like wild fire and shrink other nearby nodes as well. That does not seem to be the case. There were, at best, only 3 partial responses in the whole bunch.

Where is this technology going?

This is the million dollar question, both for Memgen and patients anxiously waiting for big breakthroughs of non-toxic and effective therapy choices.

I will be the first to admit, the analysis below is just my two cents – I seem to have misplaced my crystal ball recently and I have no way of predicting the future with certainty. No doubt Memgen would have a different take on things, and may be rightly so. In other words, you need to take this evaluation at face value, no more and no less than the opinion of a layperson patient advocate.

Several things bother me about where this technology stands, ten years almost to the day when Dr. Kipps et al wrote about the scientific underpinnings in their famous Blood plenary paper.

  • Ten years out, we are still talking about early Phase – I or II trials, single arm trials with just a handful of patients recruited.
  • The only center where ISF35 trials are offered is UCSD  – makes sense, Dr. Thomas Kipps is the inventor, this is his brain-child, he is still officially connected to Memgen, the company that makes ISF35.  I believe that in addition to UCSD the earlier Gene therapy trial was also offered at M. D. Anderson (Dr. Wierda of MDA was part of the team at UCSD back when this science was being explored at UCSD). None of the other centers seem to have picked it up.
  • The two clinical trials listed as “ongoing” are also shown as “not recruiting”. I wonder why. Perhaps they have already recruited all they are going to recruit. Or perhaps things are grinding to a halt. I do not know.
  • ASH has a nifty way or prioritizing papers at its conference. The high profile and important papers are given slots for oral presentation, where the researchers get to talk about their findings in front of a live audience. These oral presentations generate a lot of buzz, questions and feedback. Papers that are lower on the pecking order get a slot in the “Poster Presentation” section. I have been to enough ASH conferences to know what that looks like. A really gigantic room with literally hundreds (thousands?) of posters, a truly bewildering maze. Researchers stand in front of their poster, waiting for anyone interested to stop by and ask questions. It surprised me that both of the ISF35 papers merited only “Poster Presentations”.
  • I have become cynical in my old age. Sexy new approaches like this – especially the ones that require patient customized approaches – generally cost an arm and a leg. Anyone remember the old Genitope saga? That too was a customized patient vaccine, but a very different approach. Unless the early trials just about hit the ball out of the ball-park, it is hard to maintain momentum and in-flow of funds from anxious  investors.  Genitope did not meet its goals and it did not survive.
  • It bothers me that ten years of replication restricted adenovirus transfected CD154 vaccine / gene therapy approach has not made it into large scale, multi-center, double arm trials.
  • Last but not least, in an earlier review we reported on a very interesting recent article in Blood authored by Dr. John Byrd et al suggesting the same effect of painting a “Kill me” bulls-eye of CD154/CD40 can be achieved by treatment with Revlimid. Let’s see: one requires high tech single patient customized gene therapy / vaccine manufacture. The other requires patient swallow a pill at home.
  • Revlimid is not cheap, and Celgene is likely to fight hard to maintain its (egregious, in my opinion) monopoly pricing capability. But heck, Revlimid is not a complicated molecule. Any reasonably competent organic chemist with a good lab can make it. As you would expect, a generic version of Revlimid from India has been in the news. How long before Celgene’s pricing policy comes under pressure? And where does that leave very high tech customized vaccine approaches that may be targeting the same pathway?

Some of you old timers may remember Lise Rasmussen. She was a good friend. She was one of the patients we featured in our “Patient Profiles” when we were no more than a Yahoo discussion group. Back in 2000 she was not at all in favor of chemotherapy, she hung in there until the Gene Therapy trial started at UCSD and she was among the first batch of patients recruited.

In my opinion (and it is just my opinion), she waited too long to initiate therapy. After going through the Gene Therapy clinical trial, she ended up getting every chemotherapy drug known to man, followed by not one but two mini-allo transplants. She lucked out, her sister was a good match and was willing to donate again when the first transplant failed. There was significant loss of quality of life before she passed away. In her case, Gene Therapy was just not enough to control her CLL. In my opinion (and once again, it is just my opinion), it cost Lise a window of opportunity when she could have had more joy with better understood therapy choices initiated earlier, when they may have worked better.

So, bottom line, if your CLL has progressed and you are ready for therapy now, should you hold your breath for a commercially available version of ISF35 vaccine therapy? In my humble opinion, you would be ill advised to do so.

That evaluation should not come as a surprise to anyone.  Early phase trials are for the purpose of learning more about dosages, toxicity, method of administration, efficacy etc.  Your participation in such trials is of immense value to future generations of patients and something that I salute. But you need to have a clear understanding of your own motives, and what you expect to get from your participation.  Expecting therapeutic benefit for yourself and a miraculous cure from participating in such early stage trials would be wishful thinking.  As I have said before, informed consent needs to be truly informed.  Do it with your eyes wide open.

ASH2010 Abstracts

Ad-ISF35– Transduced Autologous Cells Promote In Vitro and In VivoChemosensitization to FCR and Durable Complete Responses In Patients with Del(17p)/P53 Defective Chronic Lymphocytic Leukemia.

Januario E Castro, M.D*,1, Johanna Melo-Cardenas, B.Sc*,1,Juan Sebastian Barajas-Gamboa, M.D*,1,Mauricio Urquiza, PhD*,1, Mark J. Cantwell, PhD*,2 andThomas J. Kipps, MD, PhD3

1 Division of Hematology and Oncology, Moores-UCSD Cancer Center, University of California, San Diego, San Diego, CA, UCSD, La Jolla, CA, USA,

2 Memgen, LLC, Dallas, TX, USA,

3 The University of California, San Diego, La Jolla, CA, USA

Abstract 1472

Background: Chronic lymphocytic leukemia (CLL) cells with del(17p) typically have loss of functional P53, rendering them refractory to chemotherapeutic agents. However, del(17p) CLL cells activated by CD40L (CD154)are induced to express pro-apoptotic factors that re-sensitize cells to the cytotoxic activity of P53-dependent drugs, such as fludarabine (F-ara-A). Chemotherapy re-sensitization is mediated in part by induction of p73, a p53-related transcription factor. To examine whether a CD154-based therapeutic strategy can be developed in vivo for del(17p) and/or fludarabine refractory CLL, a phase 1b clinical study evaluating an autologous cellular gene immunotherapy is being conducted. Autologous CLL cells transduced ex vivo with a replication defective adenovirus vector encoding a membrane-stable, re-engineered form of CD154 (Ad-ISF35) are administered, followed by standard courses of FCR in subjects with high-risk fludarabine refractory and/or del(17p) CLL.

Methods: Subjects with fludarabine refractory and/or del(17p) receive three IV doses (one dose every two weeks) of 3×108 autologous CLL cells that have been transduced ex vivo with Ad-ISF35. Two weeks following the third dose of Ad-ISF35-transduced cells, subjects receive standard monthly cycles of fludarabine, cyclophosphamide and rituximab (FCR). Study endpoints include analysis of safety and efficacy. Correlative analyses are conducted for evidence of drug re-sensitization, regulation of apoptotic pathways, cytokine analysis, and humoral immune responses to the adenovirus vector and ISF35 transgene.

Results: To date, four patients have completed treatment. Two patients have achieved a compete response, one of them without detectable minimal residual disease (MRD) by sensitive multiparameter flow cytometry of marrow mononuclear cells after completion of treatment. These responses have been durable after a median follow up of 18 months. One patient achieved a partial response with complete resolution of lymphocytosis, lymphadenopathy and splenomegaly, but residual CLL in the bone marrow. The remaining patient had progressive disease despite an initial response to both infusion of Ad-ISF35-transduced cells and FCR chemoimmunotherapy. Infusion of Ad-ISF35transduced cells has been well tolerated. Overall, the most common adverse events have been transient fever, malaise and fatigue associated with infusion of Ad-ISF35-transduced cells and cytopenias after treatment with FCR. Prior to ISF35 treatment, CLL cells from patients were resistant to F-ara-A induced apoptosis (IC50 > 10µM). However, one day following the first infusion of Ad-ISF35-transduced CLL cells, patient cells became sensitive to F-ara-A (IC50 0.3–1 µM). In addition, pro-apoptotic factors, including Bid, DR5, CD95, and P73 were induced in the non-transduced “bystander” CLL population following ISF35 infusion. These pro-apoptotic effects persisted 2 weeks following IV infusion. The sera from treated patients showed increase in IL-6 and IFN- after infusion of Ad-ISF35 transduced CLL cells. Despite evidence of anti-adenovirus antibody responses in the treated patients, there was no detectable anti-human CD154 production before or after ISF35 treatment.

Conclusions: The results indicate that Ad-ISF35-cell-gene therapy can sensitize P53-deficient CLL to “P53-dependent” cytotoxic agents in vivo, allowing for effective and durable clinical responses. These data are very encouraging and suggest that this unique chemoimmunotherapy re-sensitization strategy could offer a valuable treatment option for patients who otherwise would be resistant to standard forms of therapy.

Disclosures: Cantwell: Memgen: Employment. Kipps: Memgen, LLC: Membership on an entity’s Board of Directors or advisory committees.


Immune Gene Therapy for Patients with CLL Using Repeat Dose Intranodal Injection of Ad-ISF35, a Replication Incompetent Vector Expressing a Membrane-Stable CD40 Binding Protein.

Januario E Castro, M.D*,1, Johanna Melo-Cardenas, B.Sc*,1,Juan Sebastian Barajas-Gamboa, M.D*,1,Ramin Sean Pakbaz, M.D*,2, Mauricio Urquiza, PhD*,1 andThomas J. Kipps, MD, PhD3

1 Division of Hematology and Oncology, Moores-UCSD Cancer Center, University of California, San Diego, San Diego, CA, UCSD, La Jolla, CA, USA,

2 Division of Radiology University of California, San Diego, San Diego, CA, UCSD, San Diego, CA, USA,

3 The University of California, San Diego, La Jolla, CA, USA

Abstract 1476

Ad-ISF35 is a replication-defective adenovirus (Ad) vector that encodes ISF35, which is a potent immuno-stimulatory CD40 binding protein designed to maximize stable, high-level cell-surface expression of this molecule.ISF35 can induce expression of costimulatory and death receptor molecules on chronic lymphocytic leukemia (CLL) cells in vitro and in vivo.

Ad-ISF35 has shown to be safe and to have potential activity in two clinical studies in CLL patients, one using infusions of autologous CLL cells trasduced ex-vivo with Ad-ISF35 and the second one using a single intranodal injection of Ad-ISF35. From this second study we have observed that the maximum tolerated intranodal dose (MTD) was 3.3 x 1010 viral particles (vp) due to development of asymptomatic and transient hypophosphatemia,SGOT/AST elevation and neutropenia in some patients treated with higher doses.

Using this MTD dose (3.3 x 1010 vp), we designed a clinical study to evaluate the toxicity and efficacy of repeat doses of intranodal Ad-ISF35 administration in CLL patients. Ten patients with median age of 66 years (range 56–74, 80% male and 20% female), with progressive CLL (Rai stage III and IV) and median leukemia-cell doubling times of 6 months participated in this repeat dose intranodal administration study involving up to six biweekly injections with a fixed dose of 3.3 x1010 vp. Intranodal Ad-ISF35 injections were done into pathologically enlarged lymph nodes accessible by palpation using ultrasound guidance.

Repeat dose intranodal administration of Ad-ISF35 was well tolerated by the majority of patients. The median number of injections was 5. One patient developed transient and asymptomatic Grade III hyponatremia after injection #4 considered to be a dose-limiting toxicity (DLT). No dose adjustments were required in any of the patients and we have not observed cumulative dose effect or long-term toxicities after a median follow up of 14 months. Other adverse events included erythema, swelling and/or pain at the site of injection and “flu-like symptoms”, which occurred primarily during the first 24 hours after each injection and were self-limited.

The majority of patients experienced >50% reduction in leukemia cell counts (70% of patients), lymphadenopathy (80% of patients) and/or splenomegaly (70% of patients) during the course of treatment. Response assessment based on IW-CLL-08 criteria showed and overall response rate of 30% with 3 patients achieving a partial response, 4 patients with stable disease and 3 patients with disease progression.

Although we have no evidence of Ad-ISF35 vector expression beyond the injected lymph node, we observed upregulation of death receptors, immune costimulatory molecules, and pro-apoptotic proteins in the circulating, non-transduced CLL cells of the treated patients suggesting a bystander effect. Cytokine expression analysis in the sera of treated patients showed increased levels of interferon-gamma and interleukin-6 beginning 8 hours after injection. In addition, we observed evidence of antibody production against Ad-ISF35 with the ability in some cases to neutralize vector transduction in vitro. However, we did not see antibody formation against human CD154.

In summary, we found that repeat dose Ad-ISF35 intranodal administration via direct injection in patients with CLL was well tolerated and had systemic biologic and clinical activity that appears to be mediated by the effect of non-transduced bystander cells. These data suggest that intranodal administration of Ad-ISF35 may be safe and potentially effective in the treatment of patients with CLL or other B-cell lymphomas.

Disclosures: Kipps: Memgen, LLC: Membership on an entity’s Board of Directors or advisory committees.

A Different Perspective

After publication of my review above, I received a letter from the management of Memgen, the company that manufactures ISF35.  As you would expect, their take on the future of ISF35 technology is quite a bit different from mine. They did not disagree with any of the factual content of my review. I am publishing their letter to me below, verbatim – but only after getting their explicit permission to do so.  We take confidentiality very seriously on this website, no emails get published without prior permission.

I think it is only fair that you should get both viewpoints, the glass half full and the glass half empty. Call it hubris or ego, I am still willing to bet dollars to donuts I called this one right.  Only time will tell which of us is more prescient, Mark or me.

Dear Chaya,

On behalf of Memgen, I’d like to thank you for your article on ISF35. I also wanted to take this opportunity to provide an update for you on the ISF35 development program.

To date, 38 subjects with CLL have participated in ISF35 clinical studies. Study NCT00772486 (ISF35 plus FCR study at UCSD) has expanded into a multi-center study, including Moffitt Cancer Center and The West Clinic in Memphis, TN. Four new patients have begun participation in this study within the last two months. We look forward to presenting updated trial results at the ASCO conference in June 2011.

Memgen is now transitioning ISF35 to an international, multi-center phase 2 study for refractory CLL. This study is designed to be a proof of concept of direct intranodal injections of ISF35 in combination with bendamustine and rituximab (BR). The intranodal route of administration has a very similar mechanism of action to that of Ad-ISF35-transduced cells and it offers considerable advantages to patients and doctors in terms of the scheduling of patients and the ease of administration.

Memgen’s clinical trials and correlative analysis have demonstrated that ISF35 induces significant changes in the patient’s CLL cells and immune system, thereby making it possible to overcome resistance to chemoimmunotherapy. ISF35 induces p53-independent pathways and increases expression of pro-apoptotic genes, enhancing sensitivity to chemotherapy-based apoptosis of CLL cells. The previous M.D. Anderson and the UCSD clinical trial support this combination effect: of eight patients with high-risk CLL that received ISF35 plus chemotherapy, 7 responded: 4 complete responses, 1 MRD-negative response and 2 partial responses. Remarkably, the six patients with del(17p) achieved 2 complete responses (including 1 MRD-negative), 1 nodular partial response, and 2 partial responses.

Also, I’d like to note that ISF35 was selected for two oral presentations last year:

• At ASCO 2009, final results from the phase 1 ISF35 intranodal injection were selected for oral presentation: Link to abstract; Link to oral session

• At ASH 2009, interim results from the phase 1b study evaluating ISF35-transduced cells in combination with FCR were selected for oral presentation: Link to abstract; Link to oral session

In addition, results from the earlier study conducted at M.D. Anderson were published in Leukemia this year (link to abstract).

Again, thank you for taking the time to research and write about ISF35. We think very highly of you and your work and know that many CLL patients rely on what you say. We hope that you can in some way provide your many readers with this updated information. If I can be of any help in answering your questions, please call me.

Best regards,

Mark Cantwell

Mark J. Cantwell, Ph.D

Vice President Research & Development

Memgen, LLC

5950 Berkshire Lane, Suite 540

Dallas, TX 75225

Phone: 214-731-3170

Cell: 858-967-0387

Corporate Office: 214-731-3141