Urologic Oncology

SLIDES & TRANSCRIPTS
Saturday, December 14, 2002

Dendritic Cell Therapy for GU Malignancies

Johannes Vieweg, M.D.

Slide 1:

Thanks, Marty, for the introduction.

Jeff Schlom has shown you very nicely that antigenic peptides exist which can elicit an antigen-specific anti-tumor response. What you have to know though is that peptides alone don't elicit anti-tumor immunity. The antigen has to be processed and presented. What I show here on this slide is the cells, which are responsible for antigen presentation and antigen processing, these are dendritic cells.

These dendritic cells have a pivotal role in the induction of all immune responses in the human body. They are able to induce or pass on the message of the antigen to cytotoxic T lymphocytes, which are considered to be the executive organs of the anti-tumor response, and lead to tumor cell killing in an antigen-specific fashion.

Slide 2:

The central role of dendritic cells is underscored here in this cartoon, where you can see that dendritic cells, assuming we have the appropriate co-stimulation, are able to prime both arms of the immune system, T helper cells, as well as cytotoxic T cells. And we strongly believe in our laboratory, that both components of this immune response are needed to have a clinical effect. I think will explain more about this in the following slides.

Slide 3:

What we have developed over the last I would say almost 8-10 years is a platform, which I believe is very versatile, and is a vehicle to show proof of concept in cancer immunotherapy.

What we have done is we have provided dendritic cells, which I have shown in the previous slide, with antigens encoded by RNA. And this platform, I believe, resulted now in an abundance of clinical trials. And I would like to show a couple of slides on this. These are targeted therapies with high specificity and low toxicity. We can target multiple antigens, avoiding immune escape.

And RNA has the advantage that it can be further purified by selective hybridization, or it can be amplified by PCR. So unlike with tumor-based antigens like tumor-derived materials or tumor extracts, we never run out of antigen using RNA.

Slide 4:

Here I show some patients we have treated in our first proof of principle trial using a PSA RNA transfected dendritic cells. We chose PSA for safety reasons, not because I'm convinced this is the best antigen we have to date, but I think it was a safe choice in these patients mainly with hormonal affected prostate cancers, as you can see here.

I think only in one patient were we unable to process sufficient numbers of dendritic cells for the study, which was designed as a safety trial, with a dose escalation up to 5 times 10 to the 7th cells, applied in three cycles.

Slide 5:

These are part of the vaccine characteristics before we transfect with RNA, which shows these are immature dendritic cells we generate, which have the following features: MHC class high, linage marker negative, and activation markers are low to intermediate, prior to RNA transfection.

Slide 6:

However, after we transfect with RNA, I think we have a dose dependent increase in activation markers such as CD83, dependent on the RNA dose. So in conclusion, I think we have semi-activated dendritic cells, which are not optimized, but can still do their job, as I show.

Slide 7:

These are the immunological data from the first PSA trial, what we have done. And I think what we should focus on is the difference between the blue columns, which are nonexistent, and the red columns, which shows a dramatic increase in the frequencies of PSA specific T cells in the peripheral blood of cancer patients after three vaccination cycles.

And this response was specific for PSA. We also used kilocurie(?) controls. As you know, killikrein is very closely related to PSA structurally and may share some epitopes, but apparently did not.

So we also see a dose dependent effect, which is remarkable considering that these first three patients were treated on the low dose, these on the medium dose, and two patients on the high dose. There is actually data on another patient treated on the high dose, which had a similar increase in T cell frequencies.

Slide 8:

We also showed that with vaccination, although unexpected, it may have some impact on disease progression. In the majority of patients what we treated in these protocols, you can see we made a significant dent in the PSA progression curve of most of these patients, 5 out 7 subjects on trial.

This is remarkable considering that hormone refractory cancer patients, only a minority of the cells, I guesstimate about 20 percent, express PSA. So by design, the response that you would expect from these vaccines can be only partial. And I am very pleased to see this kind of PSA progression curve.

Slide 9:

Another observation we made is a reduction or clearance of circulating tumor cells, which were pre-existing prior to treatment. As you can see here, vaccination leads either to partial, followed by relapse, or more stable clearance, which was actually always associated with either relapse or rather stable disease.

We have further validated this now in over 20 patients with similar observations, and trying to correlate whether the magnitude of clearance, and the duration of the clearance of circulating tumor cells may allow us to model our vaccines toward improved efficacy.

Slide 10:

A second trial, which is currently unpublished, which was conducted in metastatic renal cell carcinoma, showed similar results.

Slide 11:

I think this is a very interesting result on its own. Here we can see in virtually all patients, again, we have an increase of high frequencies of tumor specific T cells. On the other hand, when we look at an increase of specificities directed against housekeeping genes like OFA, telomerase, or G2-50, I think these increases are rather modest.

What that suggests is that a patient or an individual vaccine may contain actually the more appropriate antigens. And conceivably these are patient-specific antigens, which are largely unknown. And that shared antigens may be weaker antigens in this response, which was our hypothesis before we started the trial.

Slide 12:

This is expected curve in survival. This is the Gleave study, which was published in the New England Journal of Medicine. I'm just superimposing, this is not comparative, and I don't want to mislead you about the survival data of our patients that we had on this trial.

But there is one observation that I'm trying to convey to you is that although most patients die, or will die actually later on, I think there is a remarkable time period of stable disease over a prolonged time period in patients treated with three cycles of RNA loaded dendritic cells.

Slide 13:

So if this is true, and this a hypothesis, then I think we can have a partial success with these vaccines. And I think this is the establishment of a chronic disease state which will eventually, like in HIV, hopefully lead to the cure of cancer over the long run once we have further optimized our vaccines.

Slide 14:

So in summary, I think we show a proof of principle. We show safety, bioactivity, and immunogenicity. We show these are prevalent in the vaccine, and that stable disease may be a hallmark of the response that we can expect with these vaccines.

Slide 15:

The last comment was rather speculative. On the other hand, what I wanted to show you is that in our hands, we have a clinical trial system, which allows clinical trials, which will allow the development of second generation vaccines with even higher chances of clinical success.

Slide 16:

How we want to do this, I have shown this here in three slides -- improve activation of Antigen specific T cells, expansion and survival, and maybe combining immunotherapy with other modalities.

Slide 17:

We first focused on maturation, which is critically important now for activation of dendritic cells. I think we have two trials ongoing right now with rather spectacular results using fully mature DC.

Slide 18:

These DCs create potent DTH reactions where the immature DC did not.

Slide 19:

What I show also is that we have improved our transfection methods by better expression of protein after electroporation.

Slide 20:

I think what is very exciting is the in vivo migration of dendritic cells, which we have studied recently. These are inguinal injection sites, and migration to inguinal lymph nodes, which we can show here with mature dendritic cells only. But, not with immature DC, which further validates our new platform.

Slide 21:

I would like to spend two slides on something new and exciting what we are doing at the moment. I think this will also be another milestone in the development of our vaccines. We know that regulatory T cells of the CD4 C25 phenotype exist that suppress immune responses to viral and tumor antigens.

And some studies, and actually our own experience suggests that these regulatory T cells are increased, particularly in renal cancer patients. And methods exist now to actually block these cells in the tumor-bearing host before we apply immunotherapy.

Slide 22:

What we are doing right now is we have focused on a fusion protein, which contains the diphtheria toxin fused to the receptor of the CD25 with a high affinity IL-2 receptor. And upon internalization, this fusion protein kills regulatory T cells in a CD25 specific fashion. Although these slides are kind of complicated, what we show is that if you deplete in vivo, you get a better immune response with your vaccine.

This last bar also shows that actually the timing of the depletion is critical. You cannot deplete during your vaccination cycles, and you have to restrict depletion just prior to your vaccination phase, because you not only kill regulatory T cells, but also actually your de novo induced cells is what you would like to generate with your vaccine.

So this is a suitable reagent to do these things, and we show that we actually can increase immunity with this strategy, which has now resulted in an ongoing trial in renal cancer. Where we deplete first,

Slide 23:

and then apply dendritic cells in the second arm. Actually, we use renal tumor agents and dendritic cells alone.

Slide 24:

This is our long-term goal. At the moment we are focusing actually on optimization of immunization protocol using different strategies, here listed from one to five. On the other hand, we have recently established actually a new program here, which focuses on the identification of the appropriate antigenic targets.

I cannot show slides because of time reasons, but we have very exciting data targeting anti-antigenic products like VEGF or metalloproteinases using T cell therapy. And this may overcome the obstacles of what we currently have with small molecules, which are semi-effective, and in combination might be more effective using these approaches. And of course, active immunization can be combined with adoptive T cell therapy.

With all these things in mind, and we have established a key elements to come closer to eventually solve the cancer puzzle. And I think this is our long-term goal.

Thanks for the attention.

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Slide 26: