Ladies and gentlemen, thank you for standing by, and welcome to the Atara Biotherapeutics Q3 2019 financial results call. At this time, all participants' lines are in a listen-only mode. After the speaker's presentation, there will be a question and answer session. To ask a question during the session, you will need to press star one on your telephone. Please be advised that today's conference is being recorded. If you require any further assistance, please press star and then zero. I'd now like to hand the conference over to your speaker today, Dr. John Craighead, Vice President of Investor Relations and Corporate Communications of Atara Biotherapeutics. Please go ahead, sir.
Thank you, operator. Good morning, everyone, and welcome to Atara's third quarter 2019 conference call. On today's call, we plan to discuss our third quarter financial results, as well as recent clinical, operational, and strategic progress. Earlier this morning, we issued a press release providing an overview of the company's third quarter 2019. This press release, as well as an updated investor presentation, are available in the investor and media section of atarabio.com. I'm joined on today's call by Dr. Pascal Touchon, president and chief executive officer, Utpal Koppikar, chief financial officer, and Dr. AJ Joshi, chief medical officer. We'll begin with prepared comments from Pascal, and then open the call for your questions. We'd like to remind listeners that the company's management will be making forward-looking statements.
Actual results could differ materially from those stated or implied by our forward-looking statements due to risks and uncertainties associated with the company's business. These forward-looking statements are qualified in their entirety by the cautionary statements contained in today's press release and the company's SEC filings. These statements are made as of today's date, and the company undertakes no obligation to update these statements. Now, I'd like to turn the call over to Atara's President and Chief Executive Officer, Pascal Touchon. Pascal?
Thank you, John, and thank you, everyone, for joining us this morning. Before we begin our discussion on our recent progress, I want to reinforce how proud I am of the advances we've made toward a vision of delivering an off-the-shelf allogeneic T-cell immunotherapy to every patient in need at any time. We know that lives depend on us achieving this vision, and our team is strongly motivated every day to deliver meaningful results for patients and the company. During today's call, we will provide context surrounding our new strategic priorities, recent clinical and operational progress, and upcoming milestones. First, I would like to update you on Atara's strategic objective and priority following the extensive review of technologies, assets, resources, and organization that I have conducted during my first month as CEO.
Objective moving forward is to become the leading off-the-shelf allogeneic T-cell immunotherapy company, transforming the lives of patients with cancer, autoimmune, and viral diseases. We are planning to accomplish this objective over the next three years by executing resolutely on four strategic priorities. First and foremost, file and launch tabelecleucel or tab-cel for patients with relapsed refractory EBV positive PTLD in the U.S. and Europe, as well as develop tab-cel for other indications. Second, achieve clinical proof of concept with ATA188 or allogeneic MS-specific EBV T-cell immunotherapy. Third, advance our mesothelin programs with autologous ATA2271 and allogeneic ATA3271. Fourth, develop ATA3219 or allogeneic CD19 CAR T to clinical proof of concept in B-cell malignancies. In parallel, we'll continue to leverage the capabilities and expertise of external partners for autologous CAR T immunotherapy development.
Starting with tabelecleucel, we are very pleased to share exciting long-term outcome data from a multi-center expanded access program following acceptance of an abstract for presentation at ASH 2019. I would like particularly to highlight the long-term outcomes in a subgroup of 22 stem cell and solid organ transplant patients with relapsed refractory EBV positive PTLD treated with tabelecleucel, who would likely have been eligible for our ongoing phase III study. These results demonstrate tabelecleucel was generally well-tolerated, with overall response rates of 55% in HCT and 82% in SOT patients. Estimated two-year overall survival was 79% for HCT and 81% for SOT. With such a larger number of patients and longer duration follow-up, these data are consistent with previous studies showing a well-tolerated safety profile, high response rates, and durable overall survival at two years.
They do reinforce our clinical development and regulatory strategy for patients with relapsed refractory EBV+ PTLD. These new data also confirm that tab-cel is potentially a transformative off-the-shelf allogeneic T-cell immunotherapy with compelling value for patient, physician, and payers in this often deadly ultra-rare cancer. Turning to our pivotal clinical development program for tab-cel, we remain on track to initiate a tab-cel BLA submission for patients with EBV+ PTLD in the second half of 2020. We now have 35 sites available for enrollment in the U.S. and Australia, and plan to continue to open additional sites at transplant centers in the U.S. and Canada over the coming months. We also plan to file the clinical trial application, or CTA, in several European countries by the end of this year, and to open study sites there next year.
Meanwhile, we are engaged in discussions with the EMA. The outcome of these discussions will determine the timing of the tabelecleucel EU conditional marketing authorization application for patients with EBV positive PTLD. Our BLA submission guidance takes into account the recruitment constraints inherent in our pivotal study due to the nature of PTLD as an ultra-rare and rapidly progressing disease. Our phase III studies are also only open at about 10% of transplant sites in the U.S. There are a number of competing, although less advanced, clinical trials. Since July, we have upgraded the way we are addressing these constraints. Importantly, we believe these development constraints should have limited impact on the tabelecleucel business case for PTLD. Indeed, the value to individual patients will be high with such a potentially transformative T-cell immunotherapy.
tab-cel could be delivered within three days of order to any center to an appropriate patient's need. If tab-cel becomes the first approved treatment for PTLD, it will likely be supported by patients and physicians based on proven efficacy and safety. The potential U.S. market size for this first tab-cel indication is several hundred patients per year. Taken together with a potential tab-cel opportunity in Europe, we believe there is a strong and profitable business case for Atara to commercialize tab-cel in the relapsed refractory EBV positive PTLD in these geographies. We're also advancing studies in potential additional indication for tab-cel. We continue to enroll patients in our phase I-II clinical study of tab-cel in combination with anti-PD-1 therapy in patients with platinum-resistant or recurrent EBV-associated NPC.
We also expect to start enrollment in a phase II clinical study targeting other EBV-positive cancer in the second half of 2020 to continue expanding the value proposition of tab-cel. Overall, these value studies show the potential opportunity for tab-cel as an ultra-rare disease pipeline in a product. Turning to our second corporate priority, ATA188. We reported encouraging data at ECTRIMS in September in patients living with progressive MS. Recently, we reviewed the 6-month follow-up data of our cohort 3 dose. Based on this data, we are pleased to share that we have selected this cohort 3 dose to initiate the phase I-B portion of the study.
The decision to initiate the phase I-B was based on achieving in cohort 3 our predetermined criteria of a continued well-tolerated safety profile and at least 50% of patients experiencing clinical improvement based on the multi-scale assessment defined at ECTRIMS, with improving patients coming from more than one clinical study site. Recognizing these are early data and incorporating input from external experts, we believe these results merit the acceleration of ATA188 development for progressive MS patients who have limited treatment options and in whom continuous decline is expected. Enrollment in a fourth and final planned phase I dose escalation cohort is complete. Six months data from cohort 4 will be mature in April 2020. We plan to present then all cohort data in detail at an appropriate congress in 2020.
Following such encouraging ATA188 results, in line with our strategic focus on allogeneic T-cell therapy, we have decided not to move forward with a phase II study for ATA190 or autologous product in MS. This decision will allow us to focus our resources on ATA188 to ensure efficient study execution as well as reduce autologous operating complexity and associated manufacturing cost. We'll continue to evaluate strategic options for ATA190. Our third strategic priority is around the mesothelin CAR T programs, ATA2271 and ATA3271. ATA2271 is an autologous CAR T for mesothelin-associated solid tumors, for which an IND is planned in 2020. ATA2271 will enter the clinic first while we work to advance development of ATA3271, our allogeneic mesothelin targeted CAR T, leveraging our EBV-T cell platform.
Both of these programs have great potential due to the incorporation of a novel 1XX costimulatory domain and a PD-1 dominant negative receptor. Finally, Atara's fourth strategic priority is ATA3219, our internal allogeneic CD19 CAR T. This asset is currently in preclinical study and will later be brought to IND with the goal to demonstrate clinical proof of concept for our EBV CAR T-cell platform. Here we intend to show that allogeneic EBV CAR Ts are safe, expand in vivo, traffic to tumor sites, and persist sufficiently to obtain high response rate and durability of responses. Turning to a few operational updates, facility commissioning and qualification activities to support clinical development at our operations and manufacturing facility, ATOM, are complete. Commercial production qualification activities are progressing well and align with our commercial strategy.
As would be expected by a new CEO focused on maximizing Atara's operational efficiency, I am now in the process of adapting my leadership team to our new strategic priorities. This effort includes active searches for a new global head of research and development, a head of commercial, and a general counsel. Before opening the call to questions, I would like to comment on our third quarter 2019 financial results. We ended the quarter with cash balance of $282.9 million, reflecting proceeds from our recent secondary follow-on financing. We continue to expect to have cash to fund ongoing operations into 2021. I would like now to turn the call back over to the operator so we can go ahead and take your questions. Operator?
Thank you. As a reminder, to ask a question, you will need to press star one on your telephone. To withdraw your question, please press the pound key. Please stand by while we compile the Q&A roster. Our first question comes from Anupam Rama from JP Morgan. Your line is now open.
Hey, guys. Thanks for taking the question. Congrats on all the progress. In the past, we've talked about, in PPMS, the need to follow patients long-term to truly kind of understand the emerging clinical profile of ATA188. What are you seeing at the six-month time point in cohort 3 dose that's really giving you the confidence to move forward here, given the 12-month, 18-month time points are not available? Thanks so much.
Thank you, Anupam, for your question. I will start, and maybe AJ will chime in there. Clearly, we had predetermined criteria for moving forward to the phase I-B. This phase I-A study, as you know, is built as a one-year study with different time points for assessment of the clinical evaluation of the patients there. We have reached that particular situation with cohort 3 dose, having data at six months that shows that not only we have this well-accepted safety profile, but we have also this clinical improvement in at least 50% of the patients coming from more than one site.
When we have this result in hand, we believe these results merit acceleration of our decision to move to the phase I-B while we are, of course, pursuing the phase I-A, and we will have more mature data on these different cohorts, particularly cohort four, for which we don't have yet the six months data. AJ, do you want to comment on that?
Sure. Anupam, just recalling the criteria that we used, we specifically set those criteria up to try to find early signals. To your point, it does take a longer timeframe to really have some of the EDSS and other style endpoints. Again, this approach specifically looked for early signals. Now, based on the approach, when we talk about 50% having clinical improvement, the bar was relatively high because there were seven different scales we used, and we required an improvement on two separate scales at consecutive time points. That means we measured at three months and six months. Those were our time points. You'd have to have improvement on two scales at each of those time points for the patient. When we discussed that with the thought leaders, they thought that was a relatively high bar for us to hit.
We also said, "You know what? It's an open label study. We want to make sure that these improvements are happening at more than one site." The 50% target that we hit was 50% improvers, plus it was at two different sites. The intent was to set a high bar using this kind of early signal detection, and that's what gives us the confidence, because it was a high bar, and we did have that early detection.
Yeah. As we say, there will be additional details to be shown at appropriate scientific congress in 2020.
Great. Thanks so much, and congrats on all the progress.
Thank you, Anupam.
Thank you. Once again, ladies and gentlemen, if you would like to ask a question at this time, you may press star and then one on your touch tone telephone. Our next question comes from John Newman from Canaccord. Your line is now open.
Hi. Thanks for taking my question. This is Chris on the phone for John. I just wanted to ask if we could get any additional color on enrollment. You've also mentioned opening more clinical sites in Canada and the U.S. Just wondering what that timeline would look like and how many sites you guys are thinking about.
Thank you for your question, Chris. In terms of enrollment, the enrollment is progressing as planned to be aligned with our guidance for initiating the BLA submission in second half of 2020. We mentioned earlier on, part of the challenge in recruiting more patients in this study is the need to expand our number of sites, because today we are only in about 10% of transplant sites in the U.S. This is done in two ways. In the U.S., we are continuously increasing the number of sites. This takes the necessary time for these sites to be open and running. We've obtained, in July, the approval from the Canadian authorities to start opening sites in Canada, and that's why we're now moving into Canada. We had already opened sites in the past in Australia.
The next stage will really be Europe, where we're going to file a CTA in several European countries by the end of the year to be able to open site next year once the usual process of review of the CTA has gone through in these specific countries.
Got it. Thank you very much.
You're welcome.
Thank you. Our next question comes from Salim Syed from Mizuho Securities. Your line is now open.
Hey, guys. Thanks so much for taking my question, and congrats on the progress. Just a couple from me. When you were thinking about Cohort 3 and making the decision to either move Cohort 3 forward or waiting for Cohort 4, was there a reason why you decided not to wait for Cohort 4 here, specifically, theoretically, or with actual data? Also just on ATA190, when you say you're not developing it at this time and you're evaluating strategic options, can you just give us a little more color? Does that mean you're planning to sell the product, or are you holding on to it? Do you no longer think that it can address a different part of the commercial market? Thanks so much.
Thanks, Salim, for your good questions. Maybe, AJ, you can start with the first one, and we'll take the second one.
Sure. It's a good question, Salim. I think when we had our predetermined criteria for go, no go, as I mentioned earlier, it was a relatively high bar. To some extent, actually, some of our thought leaders didn't think we'd hit that. They thought we'd be kind of in a middle zone. We hit it pretty nicely with Cohort 3. The decision was that, you know what? The Cohort 3 dose looks good. Because there's such a high unmet need here for these patients, remember, this is a baseline decline population, and we should expect decline everywhere, right? The measures that we use should pick those things up. Even despite that concept, we have those three patients have clinical improvement. It made sense to move forward with the Cohort 3 dose.
We've also left ourselves some optionality because as we get the data, and the six-month data will mature for the Cohort 4 dose in the April timeframe. As we get those data in, if we're seeing a signal that suggests we need to actually take a look at Cohort 4, we've already set up a plan to adapt our protocol to allow for that dose to be evaluated as well. For us, we feel like we have a good dose now. We may have a better dose, and we leave ourselves with options to go for both, but no sense in holding back given the high unmet medical need here.
To your second question, Salim. Clearly, with these two assets, ATA190 and ATA188, they were about at the same stage of development. I would even say that ATA188 was a bit more advanced, being in this program of phase I-A followed by phase I-B. We were ready to start phase II for ATA190, as we had explained in the past. Having these encouraging results, we say, let's focus on the allogeneic T-cell therapy there. Clearly, for this type of disease, a chronic disease, where we're going to bring, for the first time ever, we believe, a T-cell therapy, allogeneic offers significant advantage compared with autologous there. We don't see what autologous could bring right now in terms of advantages, but we also want to focus our resources on delivering rapidly some clear proof of concept from the phase I-B in a double-blind, randomized, placebo-controlled way.
We will keep the ATA190 in our portfolio and review strategic options. There are other ideas that we are considering right now, but we want really to focus and to execute resolutely on this development because the phase I-B is truly the key element of value creation for the company and for patients once we have these results. The more we can accelerate based on proper achievement of predetermined criteria and with the support of external experts, the better for the patient and for the company.
Great. Thanks so much, guys.
Yeah, fine.
Yeah, that's perfect. Thanks so much, Pascal. Thanks so much, guys.
Thank you. Our next question comes from Phil Nadeau from Cowen and Company. Your line is now open.
Good morning. Thanks for taking my questions. A few on tab-cel. I guess first, a follow-up to an earlier question. You mentioned that you're in 10% of U.S. centers now. I guess the question is, why is it just 10% of U.S. centers? Trial's been open for, I think, close to two years, so what has been the hold-up in getting more sites on board in the U.S.?
Yeah, thank you. AJ, do you want to answer that?
Yeah. I think I wouldn't necessarily call it a hold-up. We are kind of focused in on the centers that we feel like are going to be the best geographically suited and the ones that are going to be seeing the most patients. We have a kind of a secondary structure that for the centers where we're not in, we've actually hired a fairly decently sized medical science liaison team to reach out to those additional centers where if there are patients being found at those centers, we're able to refer them in to the 35 or so that we have now. There's over 300 transplant centers in the country. There's not an intent to be at 300 transplant centers. It's really to try to zone in and optimize the centers that we're at now. Doesn't mean we're not going to continue.
We are continuing to add centers, but we'd really never try to get to, whatever, 200 centers. The goal would be to be at the top centers, to refer patients in when they're found from the other centers. Of course, the geographic expansion through Canada and Europe will be the next key part of it.
I would add, Phil, that since July, we have also added additional MSL to continue to increase awareness and interaction with HCP at transplant centers. We're also starting to use artificial intelligence technology to evaluate claims data to identify potential patients suitable for non-enrollment. We've upgraded our efforts there. It's not only the number of centers, it's all the efforts we've done and accelerated since July to be able to recruit in line with our guidance.
Okay, that makes sense. Second is on the U.S. filing guidance. You mentioned the filing will be initiated in the second half of 2020. What modules will be filed first? Do you have a sense or some guidance for when the filing will be completed?
As we said last time, this initiation of filing will be based on an interim analysis that has been pre-specified in our protocol. That's why we're mentioning this word of initiation of the BLA filing there. At this stage, there is some very specific requests from the FDA in terms of follow-up of the patient. I think we shared that with you last time, that the FDA is asking for a 6 months following response. Response usually is being identified at 2 months after the first infusion. 2 months plus 6 months, about 8 months of follow-up from the last patient being enrolled there. That's an important aspect to take into account.
Our guidance has been clear that we will be able to initiate this BLA filing in the second half of 2020, based on one hand on the interim analysis for part of the total population. On the other hand, of course, on all the CMC and other aspect that is needed for the filing. This is on track, on schedule. There is absolutely no issue there. The limiting factor for the timing is really the recruitment and enrollment of patients and achieving a predetermined, pre-specified number of patients for the interim analysis there.
When will a PDUFA date be given to you by the FDA? Will it be upon the initiation of the filing, or do you have to get that six-month follow-up data in first?
This is truly a review process because as expected, we will go to a Pre-BLA meeting with the FDA and discuss with them how they see our data so far and what is the best possible way to move forward for these patients. I would like to say that the FDA has been very constructive in our discussions so far. We're very optimistic there that we will find the best possible way to bring this transformative therapy to U.S. patients if indeed the results are at the level we believe they could be.
Great. One last question from me. Just on the EU, can you give us an update on the issues that you continue to discuss with the regulators and any guidance for when you can get clarity from the EMA and what will be necessary for a European filing?
Yeah. We're not going to give a guidance on timing. I would say we are really discussing with them. We are, as you know, in a PRIME system in the EU, which is a system that for transformative therapies allows also some interactive dialogue with a PRIME rapporteur that is designated by the EMA. This dialogue is a constructive dialogue, and the importance there is to agree specifically on the SOT, because that's where we've changed following alignment with the FDA, the previous protocol in terms of joining the two cohort in one, and we want to make sure that this type of change is fully supported by the EMA through the PRIME system of interaction with the EMA. We will inform you when we make progress there and when we have a clear view on when we believe we can file in Europe for conditional approval.
Perfect. Thanks for taking my questions.
Thank you. Our next question comes from Tony Butler from Roth Capital. Your line is now open.
Thank you very much. AJ, you made reference to ATA188 to an earlier question that early signals gave you confidence to move forward in the phase I-B portion of the study. What I'm about to ask you is more theoretical and clearly not known, but the question is: do those early signals tell you something about the duration that a patient may see on therapy? Second, with that stated, do you think that as the patient progresses on study, that their EDSS scores actually improve beyond that initial signal? The question is more about what happens in the future if you have a view. My second question, if I may, Pascal, could you maybe provide us with some of the criteria you think about when you're looking at a head of R&D?
How you might think about those criteria when you want to hire that person? Appreciate the time.
Sure. As you might imagine, guessing into the future is always going to be a little bit difficult. Maybe just to give you an overall perspective, because when you think about clinical improvements, this is what we're really talking about now. People have not really thought about clinical improvement in MS. There's very few companies, very few products or programs that have ever looked at that. The ones that have looked at it have anticipated that, yes, over time, you would see some kinds of improvements in a variety of disability measures. When they've looked, they haven't looked just at EDSS, they've looked at a variety of disability measures, sometimes separately, sometimes as composites. If you think about, okay, we would look at our product in a similar fashion. If you're looking for improvement, you'd look for something like that.
Maybe that's the best way I can answer it. Obviously, we're going to have 12 months of data that's going to continue to mature over time. We'll be presenting that style of 12-month data in 2020. We'll have a cleaner view on it, so we won't be just guessing into the future. That's the best I can do in terms of expectations. I hope that answered the question.
I appreciate you.
One other point, actually. Sorry. I would like to say sorry, Pascal. Is that, for the phase I-A portion of the study, we are continuing an open label extension. We will be having annual dosing, and that way we'll also get some additional long-term information on this entire group of phase I-A, 24 patients.
That's exactly the point I wanted to add. On the 1-A, it will continue and will continue to inform us and physician and experts about the durability of response there.
Thank you, sir.
Now, Tony.
Yes, sir.
On your second question there. I think clearly, I have in mind, and we have in mind the ideal profile, and that's what we are looking for, is to try to be as close as possible from that ideal profile. By that I mean, a clear scientist physician, ideally an MD PhD, who is knowledgeable about cell therapy, who has been a clinician in oncology, ideally a transplanter as well. We also have developed products, particularly in oncology, to the finish post in terms of getting FDA approval and EMA approval. Someone who has worked in both large company and biotech companies and has been a true leader in bringing project forward and excellent execution and operational execution there in bringing project forward to the finish line. That's really what we have in mind.
I've been starting to meet with potential candidates, there is a lot of excitement for these type of individuals in the sense that the scientific basis of our platform, the technology that we have at our disposal now through the various collaboration, the way we've developed these technologies, but also the quality of the team is amazing at Atara. That's something that I would like to insist upon, that we are benefiting, and I'm benefiting myself from what I would call a very strong bench of experienced leaders with our CMO, head of clinical development, AJ Joshi, who is with us today. We've our head of regulatory affairs, Renu Vaish, and our head of preclinical and translational research, Blake Aftab. A very strong bench, very capable leaders, very knowledgeable and experienced people there that are supporting our various development.
We also benefit from direct support to our pipeline and technologies, not only from Christopher Haqq, our former CSO, who is continuing in an advisory role with the company, but with key academic experts in the field. Michel Sadelain and Prasad Adusumilli, Richard Andre from MSK on our different programs there, Marco Davila from Moffitt, Rajiv Khanna from QIMR. We are really strongly supported by these experts who are taking active part in our discussion related to our science and technology. We add to that also some key advisors, especially in MS, where we are working with key experts of the field, not only from Australia, but from U.S. and more and more from Europe as well. I hope I answered your question.
Yes, sir, you did. Thank you, Pascal.
Thank you. Our next question comes from Salveen Richter from Goldman Sachs. Your line is now open.
Good morning. Thanks for taking my questions. Two from me, I guess, Pascal. One is a strategic question here. As you look to creating your allogeneic CAR T pipeline, just a question as to why you would go into the CD19 space, just given the crowded nature there, versus maybe going after some other targets apart from mesothelin. A second question, just following up on what Phil said. What gives you the confidence, just given that you have only 10% of transplant sites in the U.S. open for the EBV program, that you can hit this second half 2020 BLA submission?
Thank you for your question. I'll start with the first one. There is one slide in our new investors deck that I recommend you maybe to have a look to, slide 40. That's trying to explain how we see the different assets for the different CAR T that we have right now. We have clearly a need to accelerate the clinical stage development of ATA2271 or mesothelin autologous CAR T. As you know, we are also actively developing at a preclinical stage our allogeneic version of the mesothelin CAR T, ATA3271. Now, the reason we are pursuing the development of a CD19 allogeneic EBV-based CAR T, ATA3219, is really because we can go there faster to get to the clinical stage, where we can compare what we will get there with currently approved products in that space, which are autologous.
Also some clinical results that start to appear with some other allogeneic type of platform there. We strongly believe that our EBV-based allogeneic T-cell as CAR T could lead to not only a very safe and well-tolerated way to treat these patients, but the level of expansion, trafficking, and persistence that is needed to have a significant level of response and durable response there. Persistence is one of the key aspects, I believe there. I think that has been one of the challenges of many other allogeneic type of platform. We have data, as you know, from our tab-cel experience that shows that the cells are persisting and in different type of patients, and are persisting long enough to have durable remission there.
We would like to show the same with the CD19 construct. That we believe will be the definite proof of concept that not only we have a feasible platform for allogeneic CAR T, but we have a better platform for allogeneic CAR T than any other platform that exists right now. Again, that's why we are in that program. It's really to have proof of concept that will support all of our other efforts in terms of allogeneic CAR T, and ability to do so in a rapid way, and to do so in a particular type of disease, B-cell malignancies, where the existing data from autologous and some other early data from other allogeneic platform will help us to be able to compare the type of results we get, and hopefully, as we believe, to show how we could be superior to other approaches there.
I hope I answered your question on that one.
Yes, thank you.
On the number of sites, as we said, we are in about 10% of the sites. As you can imagine from what we've said, the increased number of sites in the U.S., in Canada, later on in Europe, all of this will play a significant role in terms of enrolling and recruiting new patients in that pivotal study. We are, of course, benefiting here from the work that has been done. The guidance we're giving about the second half of 2020 is based on a reasonable enrollment rate in line with what we're seeing right now. That's something important. It's a reasonable estimate in terms of what we're seeing right now. Any increase in number of sites is going to help us to continue the work to be able to be in line with that guidance, which is our objective.
We want to be able to execute as expected, and really to deliver as expected, what we would like to do for patients and for our shareholders.
Thank you.
Thank you. Our next question comes from Ben Burnett from Stifel. Your line is now open.
Great. Thanks so much. Congrats on the progress. I have a question about the tab-cel expanded access program. I guess specifically the stem cell transplant group that you reported on yesterday. I think the ORR that was reported yesterday was 55%, which is a bit lower than a previous analysis of 80%. Obviously, there are more patients, but I was wondering if there's any notable differences between the six new patients that enrolled into the EAP and were included in this analysis versus the original, I think five, just in terms of disease severity or baseline characteristics.
Thank you, Ben, for your question. AJ, do you want to take that one?
Yeah. I wouldn't say that there's a significant difference. As you see in the abstract, the HCT patients in general did have kind of an intermediate to high risk. A higher proportion of them were intermediate to high risk relative to the SOT group. They were generally a bit sicker patients, but honestly, it's a small number of patients, so at least from our read, I wouldn't overread that. I think the key point for us has been that these data are pretty consistent with almost everything we've presented. We've generally had a 50% to a little bit over 80% ORR across all of the different study populations we've reported on. For me, it's still a fairly consistent view.
I think also the durability of response is something that is very important there. The fact that we have the 79%-81%, by the way, on the full population there, is extremely encouraging there in terms of overall survival at two years.
Great. That's helpful. Okay. If I could just ask one more, maybe just to follow up on Salim's question. Could you just maybe articulate a little bit more on the strategy with regard to the mesothelin asset? ATA2271 is autologous, so I guess is there a planned shift away from this asset at some point to focus on ATA3271? Thanks so much.
Thank you for your question. Here we have, as we said, our priority is on both assets. We want to go to the clinic with ATA2271. We believe it's going to offer superiority potentially to the first generation due to the integration of this 1XX costimulatory domain, which is going to have an impact, we believe, from preclinical data from Michel Sadelain on persistence. A more physiologic way of addressing the target there through the activation of the T cell of the CAR T. Adding also the PD-1 DNR with its intrinsic ability to address the immunosuppressive environment that the CAR T is encountering in this type of disease there. We're very confident on this as autologous CAR T. It's going to the clinic next year. The idea is to pursue that.
We start with 13 human, titrating the dose, and moving into, hopefully, proof of concept. If we could accelerate to a pivotal study, we will do so. That's really our aim, is to accelerate not only moving to the clinic, but ideally moving to a product that could be approved there. The allogeneic version is behind in terms of timing, for good reasons, and we are pursuing that and accelerating that because ultimately, we believe that having an allogeneic CAR T that is able to offer at least the same efficacy and safety and some significant advantages in terms of the delivery to patients within three days from our inventory, as well as, of course, cost of goods will be significant in terms of what we can achieve in that particular space.
Clearly, ATA2271 is a priority for us to move as fast as possible to the clinic, to proof of concept, and ideally, to some type of pivotal study.
Got it. That's helpful. Okay, thanks. Congrats to you on the progress.
Thank you.
Thank you. Our next question comes from Maury Raycroft from Jefferies. Your line is now open.
Hi, everyone. Good morning, and thanks for taking my questions. I just had a question on the early access and single-patient use program for tab-cel. Just wondering if you could provide an update on how many patients you've treated with tab-cel in those programs. Are you acquiring specific data from these patients, and do you plan on providing an update on those patients at some point? Could you provide a general update on the patients now?
Sure. In terms of kind of the total number of patients across all groups, we're probably not going to be giving exact numbers there. What I will tell you, though, is a couple of different things about this, for example, this 201 Expanded Access Program. You talked about are we going to be providing data on some of the other patients. Yeah. At a future congress, we do plan on talking about some of the other populations that we're seeing.
I think the important thing to understand off of the 201 data that's not PTLD patients that we've got is that those are data that we've utilized to plan for our multi-cohort study, the 205 study that we've talked about, because it's the information that we've gained in that 201 study that's actually given us the necessary requirements to figure out how we want to do the 205. The data that we've gotten is useful, and we will be presenting that at some future point.
Great. Thanks for taking my question.
Thank you. That concludes our question and answer session for today. I'd like to turn the conference back to Pascal Touchon for closing remarks.
Thank you, everyone on the call today. It's been a great pleasure talking with you. We look forward to finishing the year very strong and hope to see many of you in Orlando at ASH. Have a very nice day. Bye.
Ladies and gentlemen, this concludes today's conference call. Thank you for participating, and you may now disconnect.