Taysha Gene Therapies, Inc. (TSHA) Q1 2022 Earnings Call Transcript

Taysha Gene Therapies, Inc. (TSHA -1.63%)
Q1 2022 Earnings Call
May 16, 2022, 8:00 a.m. ET

Contents:

• Prepared Remarks
• Questions and Answers
• Call Participants

Prepared Remarks:

Operator

Good morning. Welcome to Taysha Gene Therapies first quarter 2022 financial results and corporate update conference call. [Operator instructions] I'll now turn the call over to Dr. Kimberly Lee, chief corporate affairs officer.

Please go ahead.

Kimberly Lee -- Chief Corporate Affairs Officer

Good morning, and welcome to Taysha's first quarter 2022 financial results and corporate update conference call. Joining me on today's call are RA Session II, Taysha's president, founder, and CEO; Dr. Suyash Prasad, chief medical officer and head of R&D and Kamran Alam, chief financial officer. After formal remarks, we will conduct a question-and-answer session, and instructions will follow at that time.

Earlier today, Taysha issued a press release announcing financial results for the first quarter ended March 31, 2022. A copy of this press release is available on the company's website and through our SEC filings. Please note that on today's call, we will be making forward-looking statements, including statements relating to the safety and efficacy and the therapeutic and commercial potential of our investigational product candidates. These statements may include the expected timing and results of clinical trials for our product candidates.

Our expectations regarding the data necessary to support regulatory approval of TSHA-120 and the regulatory status and market opportunities for those programs, as well as Taysha's manufacturing plans. This call may also contain forward-looking statements relating to Taysha's growth and future operating results, discovery and development of product candidates, strategic alliances and intellectual property, as well as matters that are not of historical facts or information. Various risks may cause Taysha's actual results to differ materially from those stated or implied in such forward looking-statements. These risks include uncertainties related to the timing and results of clinical trials and preclinical studies of our product candidates, or dependence upon strategic alliances and other third-party relationship, our ability to obtain patent protection for discoveries, limitations imposed by patents owned or controlled by third parties, and the requirement of substantial funding to conduct our research and development activities.

For a list and discussion of the various uncertainties that we face, please see the reports we have filed with the Securities and Exchange Commission. This conference call contains time-sensitive information that is accurate only as of today of this live broadcast, May 16, 2022. Taysha undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date of this conference call, except as may be required by applicable securities law. I would now like to turn the call over to our president, founder, and CEO, RA Session II.

RA?

RA Session -- President, Founder, and Chief Executive Officer

Thank you, Kim. Good morning, and welcome, everyone, to our first quarter 2022 financial results and corporate update conference call. Since our last update, we have continued to advance our core development programs with particular focus on giant axonal neuropathy, or GAN, and Rett syndrome. In March, we were pleased to initiate clinical development of TSHA-102, under a CTA approved by Health Canada, for the first and only gene therapy in clinical development for Rett, which affects over 350,000 patients worldwide.

We look forward to reporting preliminary phase 1/2 clinical safety and efficacy data by year end. We were also pleased to recently receive orphan drug designation for TSHA-120 for giant axonal neuropathy from the European Commission, further highlighting the unmet need for treatment options in GAN and the potential of TSHA-120 to provide a disease-modifying treatment for these patients. We look forward to providing a regulatory update by mid-2022. As we look ahead, we remain focused on executing on our strategic pipeline prioritization initiatives and expect our current capital resources, along with full access to our existing term loan facility, to fund operating expenses and capital requirements into the fourth quarter of 2023.

I will now turn the call over to Suyash to provide a more detailed update on our clinical programs. Suyash, please go ahead.

Suyash Prasad -- Chief Medical Officer and Head of R&D

Thanks, RA. As RA noted, we have made significant recent progress in advancing our clinical programs for GAN and Rett syndrome, and expect exciting milestones throughout the remainder of the year. I will begin with Rett syndrome. TSHA-102 delivers a transgene for MECP2, which is a protein essential for neuronal development and function.

The challenging gene replacement therapy of MECP2 is finding the appropriate balance of sufficient physiological expression to correct the deficiency, while also avoiding overexpression and the associated toxicity. To do this, TSHA-102 regulates the expression of MECP2 using a novel microRNA-Responsive Auto-Regulatory Element platform, known as miRARE, that is exclusively licensed to Taysha and developed by Dr. Sarah Sinnett and Steven Gray of UT Southwestern Medical Center. miRARE provides a sophisticated regulation of transgene expression on a cell-by-cell basis, ensuring controlled expression that avoids excessive levels of MECP2.

We recently initiated clinical development of TSHA-102 under an approved CTA by Health Canada. And further supporting this promising program, we presented positive IND/CTA-enabling preclinical data at the International Rett Syndrome Foundation Scientific Conference and ASCENT Rett Syndrome National Patient Advocacy Summit. These data supported the CTA acceptance, including a pharmacology study in Rett's knockout mice, assessing the efficacy of TSHA-102 and a six-month GLP toxicology study in nonhuman primates, exploring the safety by distribution and mechanism of action of TSHA-102. Collectively, these preclinical results confirm the ability of TSHA-102 to regulate transgene expression to within appropriate physiological levels.

This week, we will have a presence at the 25th annual meeting of the American Society of Gene and Cell Therapy, or ASGCT, while we will be presenting the safety and biodistribution data in NHPs, as well as safety data in rats. These presentations will further support the ability of our miRARE platform to control gene expression and address the challenge of ensuring appropriate levels of MECP2 expression that have limited, effective therapeutic development with other gene replacement strategies. As already indicated, there are over 350,000 patients estimated to suffer from Rett syndrome worldwide, spanning patients as young as six months into adulthood. Currently, there are no disease-modifying therapies to treat this devastating condition.

We are excited to advance TSHA-102 in their REVEAL phase 1/2 clinical trial of the first gene therapy in clinical development for Rett syndrome. The REVEAL study is an open-label dose escalation randomized multicenter study that will examine the safety and efficacy of TSHA-102 in adult female patients with Rett syndrome. Up to 18 patients will be enrolled. in the first cohort, a single 5e14 total vg dose of TSHA-102 will be given intrathecally.

The second cohort will be given 1e15 total vg dose of TSHA-102. Key assessments will include Rett-specific clinical global assessments, quality of life, biomarkers, and neurophysiology and imaging assessments. Sainte-Justine Mother and Child University Hospital Center in Montreal, Quebec, Canada has been selected as the initial clinical trial site, under the direction of Dr. Elsa Rossignol, assistant professor, neuroscience and pediatrics, and principal investigator.

We look forward to reporting preliminary first-in-human data by the end of 2022. TSHA-102 has been granted rare pediatric disease designation and orphan drug designation from the FDA, and more recently, orphan drug designation from the European Commission. Turning to TSHA-120 for the treatment of GAN, earlier this year, we reported positive clinical efficacy and safety data for the high-dose cohort of 3.5E-14 total vg delivered intrathecally, as well as long-term safety and durability across all therapeutic doses. Treatment with TSHA-120 achieved a clinically meaningful and statistically significant slowing or halting of disease progression across all therapeutic dose cohorts that was further confirmed by long-term data, demonstrating sustained durability.

Notably, no biopsy data provided new evidence of reactive regeneration of nerve fibers following treatment with TSHA-120. In addition, we observed preservation of visual acuity as measured by the log mass scale and optical coherence tomography. There were no significant safety issues, no increase in adverse events at high doses, and no dose-limiting toxicities. All adverse events related to immunosuppression or study procedures were comparable to other gene therapies and transient in nature.

Lastly, there was no evidence of dorsal root ganglia inflammation or thrombocytopenia. We recently completed a commercially representative GMP batch for TSHA-120, and release testing for this batch is currently underway. Also, in April, TSHA-120 received orphan drug designation from the European Commission, further supporting a large unmet need for treatment options in GAN and potentially expediting support and regulatory approval. As a reminder, TSHA-120, previously received orphan drug and rare pediatric disease designations from the FDA.

Partnerships with genetics testing leader GeneDx to sponsor the inclusion of a genetic marker for GAN testing and the GeneDx routine hereditary neuropathy screening panel free of charge are ongoing, as well as a collaboration with the Hereditary Neuropathy Foundation and the Charcot-Marie-Tooth Association Centers of Excellence, healthcare professionals, and patient advocacy groups to help raise awareness on the early diagnosis of GAN. We remain well-positioned to further advance TSHA-120 through regulatory approval and believe the comprehensive gene therapy dataset generates the data in GAN offers TSHA-120 a potentially derisk regulatory path that meets most registration requirements of the FDA and EMA. We look forward to our continued discussions with major regulatory agencies on potential registration pathways for TSHA-120 and anticipate providing a regulatory update by mid-2022. At the upcoming ASGCT meeting, Dr.

Rachel Bailey, assistant professor in the department of pediatrics at UTSW, will be presenting data on vagus nerve delivery of TSHA-120 to treat the autonomic nervous system dysfunction in GAN. There will also be other presentations on some of our earlier stage programs, including preclinical data on tauopathy, Prader-Willi syndrome, and Angelman syndrome. There will also be a symposium on innovative approaches and translational strategies in gene therapy development. In addition to expected regulatory feedback for TSHA-120 and GAN by mid-2022 and first-in-human preliminary phase 1/2 safety and efficacy data for TSHA-102 in Rett syndrome by year end, we remain focused on continued clinical development of the first-generation constructs for CLN7 disease, in partnership with UT Southwestern and under the leadership of Dr.

Ben Greenberg, vice chair of clinical and translational research, and principal investigator, during the course of 2022. Clinical development of TSHA-118 in CLN1 disease also remains ongoing, and we intend to initiate clinical development for our small proof of concept study for TSHA-105 in SLC138A5 deficiency. With that, I'll turn the call over to Kamran to review our financial results. Kamran?

Kamran Alam -- Chief Financial Officer

Thank you, Suyash. This morning I will discuss key aspects of our financial results for the first quarter ended on March 31, 2022. More details can be found in our Form 10-Q, which will be filed with the SEC shortly. As indicated in our press release today, research and development expenses were $37.8 million for the three months ended March 31, 2022, compared to $23.9 million for the three months ended March 31st, 2021.

The $13.9 million increase was primarily attributable to an increase of $9.3 million in employee compensation, which included $2.2 million of severance and one-time termination costs in connection with the strategic reprioritization of programs completed in March 2022 and $1 million of noncash stock-based compensation. Additionally, in the three months ended March 31, 2022, we incurred an increase of $2.9 million of expenses in research and development, manufacturing, and other raw material purchases. We also incurred an increase of $1.7 million in third-party research and development consulting fees, primarily related to GLP toxicology studies and clinical study activities. General and administrative expenses were $11.5 million for the three months ended March 31, 2022, compared to $8.2 million for the three months ended March 31, 2021.

The increase of approximately $3.3 million was primarily attributable to $2.9 million of incremental compensation expense, which included $0.4 million of severance and one-time termination cost and $0.7 million of noncash stock-based compensation. We also incurred an increase of $0.4 million in professional fees related to insurance, investor relations, communications, accounting, and market research. Net loss for the three months ended March 31, 2022, was $50.1 million or $1.31 per share, as compared to a net loss of $32 million or $0.87 per share for the three months ended March 31, 2021. As of March 31, 2022.

Taysha had $96.6 million in cash and cash equivalents. This cash balance excludes $12 million in gross proceeds generated from the sale of common shares under our existing aftermarket facility, or ATM, in April. Current cash and cash equivalents, along with full access to our existing term loan facility, is expected to fund operating expenses and capital requirements into the fourth quarter of 2023. And with that, I will hand the call back to RA.

RA Session -- President, Founder, and Chief Executive Officer

Thanks, Kamran. Our focus for 2022 continues to be on executing across our core development programs, and I am extremely proud of our team's progress and accomplishments this quarter. We continue to maintain a strong cash position that should provide runway into the fourth quarter of 2023. We would like to thank our Taysha employees, board of directors, scientific advisory board, collaborators, and the patients and advocates for their ongoing support of our mission to develop curative gene therapies to eradicate devastating monogenic CNS disease.

I will now ask the operator to begin our Q&A session. Operator?

Questions & Answers:

Operator

[Operator instructions] Our first question comes from the line of Joon Lee with Truist Securities. Please proceed with your question.

Unknown speaker -- Truist Securities -- Analyst

Hi. Good morning, and thank you for taking my question. This is Matthew on for Joon. So what is the probability by which you think FDA might ask you to have efficacy data on new patients using commercial grade material? And how long would you take -- will you think it takes to provide such data? Thank you.

RA Session -- President, Founder, and Chief Executive Officer

Hey, good morning, Matthew. Thank you for the question. You know, I think we've gone through this when we actually presented the definitive data set earlier this year, really around kind of the current scenarios and how we look at them. We essentially, you know, cut them in two parts, one being ex-U.S., one being the U.S.

Particularly for the FDA, that breaks down to about three scenarios. The first being able to immediately file off the data that we've generated thus far. Again, we've reported data from all therapeutic dose cohorts, including the high dose of 3.5e to the 14 earlier this year, where we really see really nice efficacy and safety durability. And now, we have really nice pathological data with the biopsy showing nerve fiber regeneration, which essentially we view as a game changer.

And so, we're pretty excited about this data set, not only because we show clinical, but -- we show really nice clinical data, but also safety and efficacy data, but also really the biopsy data and the natural history, which essentially has been going on for close to 10 years. And each patient rolling over from their natural history study provides three levels of control. The patient has a comparison between their own pretreatment and post-treatment performance. Because of such a large natural history study, over 50 patients at this point were able to show age-matched controls.

And then you're able to compare the entire cohort to a patient's performance. So, we're really excited, again, about the breadth of this data. As I mentioned, our base case is most likely that the FDA would ask you to dose a few more patients using the commercial grade material. And this is a similar pathway of what they have asked us to do during the registration of Zolgensma.

Most likely, it would be, you know, what we would consider a handful of patients, you know, somewhere between probably three to five patients. Those patients are already identified. So, from a timing perspective, this would shorten any type of recruitment effort to get these patients into the study because essentially, they would roll over from the natural history study. So, these patients are already identified in our partners at the NIH under the leadership of Carsten Bonneman, who have done a fantastic job keeping that study moving and the wealth of data that we've generated from that study.

So, we really see the difference between filing immediately based off the current data set and dosing a few more patients. We're probably looking at about a six-month time difference. It's not a huge time difference because, again, we don't have to go out and identify patients. Those patients are already identified.

And so, we think by dosing a few more patients, that would probably set us up for an approval toward the end of 2023. This would again be the FDA scenario. The EMA, our going-in position is that we meet all the requirements for conditional approval, and the hope is to initiate EMA filing by the end of the year. We would also ask -- just shifting focus back to the FDA, based off the current data set, we would ask the FDA, as a default, to initiate a rolling submission based on the data that we've generated.

The preclinical data won't change. The clinical data set is -- it would be near-final. If they asked us to dose a few more patients, so we would be able to start the review of the current data set. And obviously, we would have completed the release testing and the analytical panel for our commercial-grade material, which we've already completed the manufacturer of this currently undergoing release testing.

And we're quite excited about, not only the yield, but also the product purity from that run. So, that's kind of our going-in strategy. We're going to go in and ask for approval based off the current data set. But our base case would be dosing a few more patients that would immediately roll over from the NIH natural history study.

And so, this is something we previously stated before, and it continues to be our base case.

Operator

Thank you. Our next question comes from the line of Gil Blum with Needham and Company. Please proceed with your question.

Gil Blum -- Needham and Company -- Analyst

Good morning, and thanks for taking our question. Another quick one on TSHA-120. So, what more is there to do on your commercial-grade product? And, you know, what more things do you need to do there? And maybe you can give us an idea of how many patients are going to be treated with this batch. Thank you.

RA Session -- President, Founder, and Chief Executive Officer

Yeah, no, it's actually a really good question, Gil. Thanks. Thanks for asking. And I'll start, and, Suyash, please chime in if you'd like.

But essentially, there's not much more to do on this commercial-grade material. We initiated the manufacturing run earlier this year. We have now completed that manufacturing run. It was quite successful, both from a yield perspective and a purity perspective.

The current analytic that we've run around comparability to the original clinical material are spot-on. And those tests continue to be ongoing. The team -- Suyash's team, along with Fred's team, are continue to work on key assays, key relief assays that will support the BLA, including the definitive potency assay, which the team has made significant progress on, which I'm quite pleased about. And just to give you an idea on just the yields from this run, the team has done just a fantastic job around manufacturability.

And depending on the dose, and I'll just go with the high dose of 3.5E to the 14, we're over 50 patients worth of drug. And so, that gives you an idea around just, one, the strength of our platform. This is using our HEK293 suspension triple plasmid transfection platform that we use across the entire portfolio, but also just really the strength of the team that we have in CMC. So, I couldn't be even more proud.

So, what we'll do is the -- this run will continue to go -- undergo release testing, stability testing, and whatnot. And the team will continue to gather data to support the BLA. But really, the progress that the team has made as the manufacturer of this commercial-grade material has gone -- it's gone even better as we could imagine. So, I'll stop there.

Suyash, do you have anything to add?

Suyash Prasad -- Chief Medical Officer and Head of R&D

No. You know, I think I would just echo the fact that, you know, the batch is made. There was plenty of product made in the high-yielding run. And release testing is underway, looking at the characterization of the product.

And it's all looking very promising thus far. RA's quite correct. The only thing outstanding is to finalize the potency assay. And just to remind you, you know, potency assay essentially exists to demonstrate that the molecule that we're administering closely mimics and works effectively in a clinical setting, as it does in a lab setting.

And, you know, every lot needs to be tested and certain predefined acceptance character that need to be met. And the FDA and the regulators are pretty keen to ensure, obviously, the product we make on an ongoing basis is consistent and highly -- you know, the appropriate level of quality. And as RA said, we have made a lot of progress in finalizing that potency assay. So, everything is looking great, or at least testing is on the way.

And drugs are going to be available to treating patients imminently.

Operator

Thank you. Our next question comes from the line of Salveen Richter with Goldman Sachs. Please proceed with your question.

Elizabeth Webster -- Goldman Sachs -- Analyst

Hey, good morning, guys. And thank you for taking our question. This is Elizabeth on for Salveen. Maybe just switching over to Rett, if you could comment on the nature of the first clinical data we expect to see and how many patients we can expect to see data from.

And then a second one from us are what kind of assumptions have been baked into the for 4Q '23 cash runway guidance. Thank you.

Suyash Prasad -- Chief Medical Officer and Head of R&D

Sure. Let me take the question about the clinical trial, and then Kamran or I can handle the second question. So, with regard to the Rett clinical trial, this is a trial in adult females with Rett syndrome. To remind you, we just felt -- you know, just given the concerns about potential overexpression, which we show, actually downregulate very nicely in our NHP data, we still wanted to be a little bit conservative.

And so, we're starting off in adults. And the plan will be to move into children, pediatric females with the Rett at some point thereafter. And then we also plan a small study in boys, the very rare population of boys with Rett shortly thereafter. Now, in terms of expectations with regard to what we're going to have coming out of the clinical trial data for the adult study, which we anticipate sharing data from by the end of the year, the likelihood is going to be safety data and perhaps some preliminary efficacy data.

We're not sure at the moment. We will, as is the case, for these first enhanced studies with these innovative products, we have to stagger-dosing. We can't dose several questions all at once. We have to dose one patient, leave it a period of time and then dose the second patient after DMC review and then leave it a period of time before dosing the next patient.

So, my guess is it's going to be small number of patients' safety data by the end of this year, potentially some preliminary efficacy data if we start to see some early signs of that. But I think that's why we're -- that's where we're focusing on for the clinical trials in line with this. With regard to assumptions, I'll let RA and Kamran take that question.

RA Session -- President, Founder, and Chief Executive Officer

Sure. And thanks, Liz, for the question. I was actually talking on mute. So, just to reiterate what Suyash mentioned, you know, we're quite excited about the Rett data, the preclinical data set that supports the CTA and again are really excited about what this means to the Rett community being the first and only gene therapy actually in clinical development for Rett syndrome.

And I think just to echo what Suyash mentioned, it'll really be on the totality of data, the amount of -- the amount of endpoints that are being collected are immense, both from physician reported Rett syndrome outcomes, patient-reported outcomes, respiratory measures, obviously some neurodevelopmental measures, as well as movement. So it's really going to be a, you know, a whole host of endpoints that we'll share, including safety. And safety is going to be probably one of the most important ones because there's always this notion around overexpression. And the data from our NHP study, our NHP tox study, not only demonstrated the safety of our construct at doses up to fourfold above what the starting dose will be in the clinical setting, but also proof of mechanism, the ability to downregulate the expression of MECP2 in the presence of wild type MECP2.

And so, again, for us it's quite exciting. But certainly this is one of the reasons why we decided to start into adult. So, I would probably characterize it similarly the way that's Suyash did. And it'll be on the totality of data, it'll be safety with some preliminary efficacy in there.

From an assumption perspective, on cash runway, the way that we're thinking about this is we have -- you know, with the full drawdown of our current term loan facility from Silicon Valley Bank, we have the ability to be able to extend runway into Q4 of 2023 with our -- along with our existing cash. And that's kind of the assumption, the base case assumption, that's gone in. As you are aware, we executed on a pipeline prioritization exercise earlier this year, which we announced at our year-end earnings call, which also included a rep of 35% and essentially kind of a rightsizing based on the clear focus on two key programs. And that's our Rett syndrome program and our giant axonal neuropathy program, which we're both quite excited about.

And then taking two of the additional clinical development assets and moving those from more of a registration-directed trial to more of a proof of -- kind of small proof of concept studies, that being CLN1 and then SLC13A5. What I would also say, though, is, again, I'm quite excited about the progress that the team has made, just in this short period of time and really the ability to be able to get to this prioritization analysis and kind of refocus company and still execute is just been something that I've been immensely proud of. It's not easy for anyone out there in biotech and particularly in gene therapy, but the team is really nose to the grind and executing. And so, for us, all of this has been baked into our cash analysis.

And we continue to look at ways to augment and extend runway.

Operator

Thank you. Our next question comes from the line of Kevin DeGeeter with Oppenheimer and Company. Please proceed with your question.

Kevin DeGeeter -- Oppenheimer and Company

Hey, great. Thanks for taking our questions. Just on GAN regulatory update. RA, can you comment on your confidence sort of above that mid-2022 update timeline? I guess, sort of underlying this question is, is it reasonable to, you know, conclude that you had the necessary meetings with FDA and other regulatory agencies and are waiting for feedback at this point? Are there kind of open scheduling, you know, components that could impact that timeline and cause some uncertainty there?

RA Session -- President, Founder, and Chief Executive Officer

Yeah. Thanks, Kevin, for the question. Good morning. So, I think we're confident in reiterating that guidance around the mid-2022 from a from a regulatory feedback perspective.

Again, I think, you know, most people going to have conversations with the FDA and the EMA in a COVID environment, and other regulatory agencies in a COVID environment. You know, obviously, there's been a little bit of flex in scheduling. But with that being said, we're quite excited in the promise of the dataset that we've presented thus far, the reproducibility of that data, you know, and the fact of the matter that the product is not only efficacious but durable and safe at multiple doses, including a really robust natural history study, and now, a really -- now the beginnings of what would be a really nice data package from a Module 3 perspective from a CMC comparability. So, we're going to go in with that dataset.

And obviously, our going-in strategy is to be able to file off of the current dataset. And as the default base case, we essentially default to being prepared to dose a few more patients with the commercial grade material. So, we are reiterating that guidance. We've done that in our communications and look forward to updating you guys here closer to later this year.

But again, mid-year 2022 is our guidance around having that feedback in here.

Operator

Thank you. Our next question comes from the line of Jack Allen with Baird. Please proceed with your question.

Jack Allen -- Baird -- Analyst

Hi. Thank you so much for taking the questions, and congratulations on all progress. I wanted to shift gears back to Rett really briefly and talk about the dose there. I know you mentioned that you're starting at 5e to the 14 total vg and then moving up to 1e to the 15.

And that, I guess the preclinical package showed safety at 4x the first dose. I was just curious, was there a dose in the preclinical package where you did see tolerability issues? And how much coverage do you think you have to dose escalate as we move through the study based on the existing preclinical package?

RA Session -- President, Founder, and Chief Executive Officer

Thanks, Jack. Great question, and good morning. I'll turn it over to Suyash to answer that question.

Suyash Prasad -- Chief Medical Officer and Head of R&D

Yeah. Hi, Jack. Thanks for the question. So, it's a really important question.

Those selection for the clinical trial for a gene therapy study, getting the dose right the first time is really important, because you've got to make sure you give enough drug to make sure the drugs are effective, but also make sure that there's no safety or tolerability issues. Because once you've give them the gene therapy drugs, you can't take it away again. So, it's a really critical decision that needs to be made. And in particular, for Rett, where there is this risk of overexpression toxicity, so you have to get the amount of protein being produced appropriate within these appropriate physiological limits, enough to make sure you're having efficacy but not so much protein that it causes toxic side effects.

Because of that, we actually did a very, very disciplined preclinical package, which included a mouse pharmacology study. So, a mouse model pharmacology study. We did a Rett toxicology study. We did an NHP toxicology study.

All of the studies were very extensive and very comprehensive. The mouse study was over 250 mice. The Rett study was over 120 Retts. The NHP study was 24 NHPs.

And the mouse pharmacology study is where you look for a dose that's going to be efficacious. And we're able to -- we were able to identify that very clearly in terms of demonstrating enough drug, causing an improvement in survival, motor assessments, respiratory assessments and other assessments. So, the 5e14 total vg dose is above that level. And then on the other end, both in the Rett talks, and the NHP tops, we tested doses up to an equivalent of 2e15 total VG human equivalent.

So, that's fourfold of the starting dose. And to answer your question, specifically, there was no adverse events of any note at the 2e15 dose. So, it's possible we could go even higher from that. We didn't test higher than that, because we didn't think there would be a need to go higher than 2e15, simply because we saw efficacy at a much lower amount in the national pharmacology study.

And I think it was that combination of studies that really persuaded Health Canada to allow the CTA to be opened. And I think there is one other important piece around this NHP study that is really, really important. And I will actually be discussing this post-presentation at the ASGCT. I think it's tomorrow, tomorrow, Wednesday.

I think it's Tuesday, actually, yeah. Presenting it Tuesday. I actually presented the state of the big Rett syndrome scientific conference that's organized by the IRSF about three or four weeks ago. And the NHP tox study does three things.

It shows a full absence of any kind of toxic effects, which is important fourfold higher clinical dose. It also shows really excellent biodistribution from an intrathecal dose throughout the brain and the spinal cord. So, you are getting back to copy numbers in a very nice range, one to two copies particular genome in different parts of the brain, and the spinal cord, and the ganglia and the peripheral nervous system. And it also shows correspondingly low levels of RNA.

And don't forget, these are wild type NHPs. So, what that means is you are getting great delivery of drug into the brain and spinal cord, but actually very high downregulation, meaning not much RNA being produced, which is appropriate given this a wild type animal. So, that NHP study shows safety, it shows biodistribution, but importantly, mechanism of action. And as I said, I will be going through that data in more detail in the ASGCT meeting tomorrow.

So, that group of studies together was really very persuasive to Health Canada to allow us to work in a CTA.

Operator

Thank you. Our next question comes from the line of Yun Zhong with BTIG. Please proceed with your question.

Yun Zhong -- BTIG -- Analyst

Hi. Thank you very much for taking the question. This is actually a follow-up question on just what you said, just now, Suyash. So, on Rett syndrome, has anyone looked at comparability between nonhuman primates and human patients in terms of biodistribution? And also, given that this is not cross correction to be expected, so are there any data to suggest the transduction efficiency? Or do you have any estimate on how many cells will need to be transduced to see reasonable efficacy?

Suyash Prasad -- Chief Medical Officer and Head of R&D

Two very good questions. So, the first question was about the translatability of NHP biodistribution to human. You know, it's a good question. No one has done it specifically in Rett.

What we have done is we have shown very nice biodistribution with our Rett program with an intrathecal dose into an NHP, which is of course smaller than the human being. But the anatomy is very similar. And it's probably the best corollary looking at biodistribution in any animal model to the human. And we get really nice biodistribution throughout the brain and the spinal cord with the intrathecal dose of injection.

Now, in the human setting, the only way to really ascertain biodistribution is in a sad situation, if the patient was to pass away, and to look at DNA and RNA and protein in that individual. And that did happen very early on in one of the GAN patients. One of the low-dose GAN patients who sadly passed away through progression of disease, this data has been presented by Carsten Bonneman and Steven Gray at the ASGCT meeting a few years ago. And they showed that with an intrathecal dose of AAV9 gene therapy for GAN, you actually got nice biodistribution.

Although it's a low level, but it was a low dose throughout all target organ tissues. And the other thing I will say that we learned from the GAN program -- and don't forget GAN is AAV9, is HEK293, and intrathecally delivered, so lots of similarities to the Rett program. The other thing I will say about GAN is that we have demonstrated more recently in our January presentation that we see improvements in the peripheral nerves in the nerve biopsies. Now, these are nerve biopsies that are performed in the radial superficial nerve, which is a nerve in the wrist.

And what this means is that drug is getting down into the peripheral nerve system, down to the wrist, from an intrathecal dose of injection. So, for those reasons, we are confident that intrathecal dose of drug will actually deliver drug in the Rett syndrome very nicely to all the tissues that needs to be transfused which are brain in particular and the spinal cord and brainstem. That's answer of the first question. The second question you had was about, you know, what proportion of cells need to be transduced.

And it's difficult to know, but we certainly believe that, with this 50-50 ratio of mosaics versus non-mosaics -- sorry, wild type versus null cells in the mosaic setting, we certainly know that if we transduce some of the cells, you are going to get some clinical benefit. And the likelihood is, the more cells that are now being transduced, the better clinical benefit you get. So, our approach, once again, is to give a high dose of drug intrathecally to enhance biodistribution. And we know we have confidence, that giving high doses of drug, you still see a nice downregulation of the protein being produced, which for the wild type cells.

So, once again, we don't know exactly how many cells need to be transduced. But I think a small number will give you some benefit. A large number may give you more benefits. But we are quite confident giving high doses to enhanced biodistribution because we see our downregulation package working nicely.

Hopefully, that answers your question, Yun?

RA Session -- President, Founder, and Chief Executive Officer

The only thing that I would add, Suyash, to what you mentioned are just two examples. You know, I would say, the preclinical data set that we have been able to generate, particularly the NHP data set, really gives us the opportunity to maximize transduction efficiency. And Suyash mentioned this before, I just wanted to reiterate this. The fact of the matter is that we didn't see -- we didn't observe tox at any dose that was actually given including to 2e15.

You always have the ability to be able to increase dose to really maximize transduction efficiency and to be able to get really nice biodistribution. We see nice biodistribution at the levels that we're starting at. But again, if we wanted to be able to maximize that, we obviously have the ability to be able to go higher. The second point that I just wanted to make and I think it's something that does get overlooked is a nice correlation to our CLN7 study, which is being done under a collaboration with our partners at UT Southwestern.

This is again a membrane bound protein similar to MECP2. So, it's not -- there is no cross correction here. And we have shown the ability to be able to dose patients up to 1e to the 15 and to be able to do that successfully and safely. So, some of that early preliminary data was presented at World Symposium earlier this year.

And since that data has been presented, there has been an additional patient that has been dosed at the high dose which is 1e to the 15. So, again, I think I like to remind the field around the number of firsts that's really come out of this collaboration with Taysha and UT Southwestern, where you have the first centrifugally dose gene therapy in history. That's our giant axonal neuropathy study, the first gene therapy in development for Rett syndrome. You now have the first gene therapy with the self-regulatory feedback loop in clinical development to control expression on a cell-by-cell basis.

The first to be able to dose intrathecally at 1e to the 15 and to be able to do that safely and to demonstrate safety of an AAV9 construct. So, just in the short period of time that the company has been in existence, there has been a number of firsts that have been generated. And it's something that I am very proud of. And I always remind our employees to be proud of the number of firsts for the field of gene therapy that's been generated by the company and our partners at UT Southwestern.

Operator

Thank you. Our next question comes from a line of Laura Chico with Wedbush Securities. Please proceed with your question.

Laura Chico -- Wedbush Securities -- Analyst

Hey. Good morning, guys. Thanks for taking the question. I wanted to circle back with regards to the spend.

I am wondering if you can offer a little bit more clarity on perhaps the breakdown between R&D and G&A. And, RA, I think you made an earlier comment too, about kind of exploring additional channels for monetization. Just wondering if you could kind of expand on that a little bit. Thanks, guys.

RA Session -- President, Founder, and Chief Executive Officer

Sure. Thanks Laura. Good morning. So, I will start with your last question first, really around just ways that we are thinking about extending cash runway.

Obviously, you know, having business development opportunities continue to remain an opportunity for us to be able to go and bring in nondilutive forms of capital. What I would say to that is that, we are constantly looking at potential strategic collaborations with parties, whether those are regional collaborations or collaboration around specific assets. You know, but it's something that we consistently look at, and we have been fortunate to essentially get a lot of calls after we have made our announcement at the year-end earnings call. And so, we continue to explore those as a potential way of bringing in nondilutive capital.

What I would also say is, again, we look very carefully around which programs that, you know, would continue in, and what the company would actually focus on from a clinical development perspective. And essentially, what we decided to do is once, you know, for programs that have hit proof of concept, we have essentially, you know, ceased with those. And for -- and again, for the ones that are currently in clinical development and haven't yet hit proof of concept, we will continue to move forward with those until we hit that milestone, particularly with a focus on CLN1 and SLC13A5, going away from that registration -- speed-to-registration pathway, which is going to be a lot more expensive from a CMC perspective and a clinical development perspective and really just begin continuing to validate the platform from a proof of concept perspective. And then still focus with our two lead programs on the fastest pathway to approval.

And that's our giant axonal neuropathy in our Rett syndrome program, which we continue to be all-in on, but still doing from a totality of our portfolio, really looking with an eye to preserve cash and long-term runway and so that's the way that that we are kind of looking at looking at this. I think, again, as I mentioned earlier, we executed on a strategic pipeline prioritization earlier this year, which is starting to play out where essentially we pause, work on a lot of our preclinical programs, and essentially kind of begin reconstituted a number of our clinical programs continuing to move them forward done for an effort to preserve cash runway. And I think you will start to see R&D expense come down over the next few quarters and start to get to a certain runway as we get into the second half of the year, that we will be able to hold constant. Ways to augment that, obviously, if there is a turnaround in the capital markets, you know, we should be able to go in and raise capital through our currently available ATM, which we have already done.

Since our year-end earnings call, we have been able to successfully draw down some capital from that ATM, that extended cash runway. And we will continue to be strategic in the way that we look at that. But I would probably say nondilutive forms of capital. Our current term loan facility, which again allows us to have cash into Q4 2023 and then, obviously, the ability to be able to tap our ATM, which we have already done.

I think all of those things being consistent are ways that we would look to extend runway. Maybe, Kamran, you would want to comment on just the breakdown between R&D and G&A.

Kamran Alam -- Chief Financial Officer

Yes. Sure. Happy to. Thanks, RA.

And thanks for the question, Laura. So, over 75% of our operating expenses are R&D related. And as RA mentioned, because of their strategic pipeline prioritization efforts, we will be able to reduce that R&D expense burn significantly over the next coming quarters as a result of pausing research and development activities on our preclinical programs, as well as significant reduction in our CMC expenses. Ultimately, as a reminder, we conducted six GMP batches last year, some of which were completed in Q1 of this year in terms of product release.

And we are only doing GMP manufacturing on our GAN program this year. So, you can expect a significant reduction in our CMC expense year over year and in subsequent quarters as a result. So, again, a lot of a lot of nice work to really focus our resources and our efforts, primarily on of course, GAN and Rett.

RA Session -- President, Founder, and Chief Executive Officer

Thanks, Kamran.

Operator

Thank you. Our next question comes from line of Yanan Zhu with Wells Fargo. Please proceed with your question.

Yanan Zhu -- Wells Fargo Securities -- Analyst

Hi. Thanks for taking my questions. A couple on the Rett syndrome clinical trial. What is the waiting period for safety observation once patient one is dosed? And how would you ascertain whether there is MECP2 overexpression associated toxicity, given that the MECP2 duplication syndrome share a lot of the same manifestations with Rett syndrome? Thank you.

RA Session -- President, Founder, and Chief Executive Officer

Hi Yanan. Good morning. I will turn that question over to Suyash to provide some context. Suyash?

Suyash Prasad -- Chief Medical Officer and Head of R&D

Sure. So, the staggering specifically is eight weeks. So, after patient is dosed for a review of the eight-week time point and discussions with [Inaudible] with the absence of any safety issues, we will then go ahead and dose the next patient. But that's between patients one and two.

As time progresses, the staggering changes in the clinical trial course. And we do less staggering as the study progresses. Specifically, with regard to signs of over-expression toxicity, it's a good question. And it's one we have discussed at length, both with regulators and with key opinion leaders.

And the bottom line is this. Most patients, in fact, all patients in the adult study certainly, unlike in the pediatric study, will be in the phase 3 of Rett syndrome, i.e., they are stable and not declining. You may recollect that there is four phases to the clinical progress of patients with Rett. The first is where they get the diagnosis.

The phase 2 is when there is a rapid decline in functionality. Phase 3 is the one they are in a stable phase, i.e., stable with the right complex level of functioning. And then there can be a phase for years, sometimes decades, and then they end up into a deterioration phase. To all patients who have struggled in the Phase 3, i.e., they are stable.

So, what we are looking for clinically is any kind of deterioration, OK, because there is such a poor state. They have been stable for a while. If there is any deterioration seen in terms of Rett syndrome-type behaviors or other neurological features, it's likely to be due to overexpression than a progression of Rett syndrome. Now, will we miss a definite? No, we wouldn't, because we can't biopsy brain tissue, of course, in the clinical trial in patients.

But the way we are observing specifically MECP2 over especially toxicity is by looking for a change in the mental status and the change of neurological status, and your behavioral status, and central nervous system, peripheral nervous system, deterioration after dosing with a gene therapy, because that's unlikely be due to progression of Rett. It's likely to be due to over a special toxicity of MECP2. Having several of that, we anticipate that's highly unlikely given NHP tox data and our Rett tox data where we gave very high doses of the drug fourfold of the present clinical dose, and so no toxicity even at that high level.

RA Session -- President, Founder, and Chief Executive Officer

Thanks, Suyash.

Operator

Thank you. Ladies and gentlemen, we have come to the end of our time allowed for questions. I will turn the floor back to Mr. Session for any final comments.

RA Session -- President, Founder, and Chief Executive Officer

Thank you, operator. And again, thank you for everybody for joining our Q1 call today. As we iterated earlier, the company has performed quite nicely coming out of Q1 and our strategic pipeline prioritization. Also, refocus on continuing to move forward our GAN program, our Rett program, from a speed to registration aspect, and then morphing some of our earlier clinical programs to more proof-of-concept studies.

I couldn't be prouder of the execution of the team. I couldn't be prouder of the focus of the team. And we continue to invite you guys to follow the progress that the company continues to make strides later this year. With that, I wish you guys a wonderful week.

Many of us will be at ASGCT. So, I would ask you guys to come by and say hi. And I look forward to seeing many of you there. With that, we will end today's call.

Thank you.

Operator

[Operator signoff]

Duration: 57 minutes

Call participants:

Kimberly Lee -- Chief Corporate Affairs Officer

RA Session -- President, Founder, and Chief Executive Officer

Suyash Prasad -- Chief Medical Officer and Head of R&D

Kamran Alam -- Chief Financial Officer

Unknown speaker -- Truist Securities -- Analyst

Gil Blum -- Needham and Company -- Analyst

Elizabeth Webster -- Goldman Sachs -- Analyst

Kevin DeGeeter -- Oppenheimer and Company

Jack Allen -- Baird -- Analyst

Yun Zhong -- BTIG -- Analyst

Laura Chico -- Wedbush Securities -- Analyst

Yanan Zhu -- Wells Fargo Securities -- Analyst

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