Greetings and welcome to X4 Pharmaceuticals Fourth Quarter Financial and Operating Results Conference Call. At this time all participants are in a listen-only mode. A question-and-answer session will follow the formal presentation. As a reminder this conference call is being recorded. It is now my pleasure to introduce your host, Dan Ferry of LifeSci Advisors. Please begin.

Thank you, Operator. And good morning everyone. Thanks so much for joining us. Presenting on today's call will be X4’s Chief Executive Officer, Dr. Paula Ragan, and the company’s Chief Financial Officer, Adam Mostafa. Following prepared remarks by each, we'll open up the call to your questions. And we’ll be joined by Dr. Diego Cadavid, Chief Medical Officer, Art Taveras, Chief Scientific Officer and Mary DiBiase, Senior Vice-President, technical operations and quality. As a reminder on today's call, we'll be making forward-looking statements regarding regulatory and product development plans, as well as research activities. These statements are subject to risks and uncertainties that may cause actual results to differ from those forecasted. The descriptions of these risks can be found in X4’s most recent filing with the SEC. I'd now like to turn the call over to Paula Ragan. Paula?

Thanks Dan, and thank you all for joining us on the call this morning. We hope that you are all safe and healthy. As with many companies, 2020 drew some unexpected and significant challenges our way, certainly with the COVID pandemic being chief among them. Working within our company were many patients that were immunocompromised which resulted in challenges for the enrollment of our clinical trials. However, I’m extremely proud of the work done by our team in mitigating these obstacles. We made significant progress in the clinical development of our lead candidate mavorixafor and have an experienced leadership team in place to execute on our 2021 goals and beyond. As a reminder, mavorixafor is our first-in-class small molecule antagonist of the chemokine receptor, CXCR4 that is being developed as a once-daily oral therapy to treat a number of conditions caused by excessive signaling in the CXCR4, CXCR12 pathway. Our most advanced mavorixafor program is in WHIM syndrome. As you may recall, WHIM is a rare inherited primary immunodeficiency disease caused by gain of function CXCR4 mutations that prevents the healthy trafficking of immune cells and effective immune surveillance. We believe mavorixafor has the potential to be the first disease-modifying therapy for the more than 3,500 estimated diagnosed and undiagnosed WHIM patients in the U.S. We are currently conducting a global Phase 3 clinical trial in WHIM syndrome. The 4WHIM trial is a randomized double-blinded placebo-controlled multi-center study designed to evaluate the safety and efficacy of mavorixafor in genetically confirmed WHIM patients. The primary efficacy endpoints for the trial will compare the level of circulating these results relative to a clinically meaningful threshold in response to treatment with mavorixafor versus placebo, measured over the course of 52 weeks. Secondary endpoints include infection rates, work burden, and assessments of immune system function and quality of life. Given the current pace of enrollment, and the fact that this is a 52-week study, we continue to anticipate top line data from this Phase 3 trial in 2022. Notably, during the fourth quarter of 2020, we received both fast track and rare pediatric designations from the FDA for mavorixafor for the treatment of WHIM syndrome. These FDA designations further recognize WHIM as a serious condition with a clear unmet need in both adult and pediatric populations and underscore the importance of our efforts to advance this program as rapidly as possible. Through the fast track program, we will be eligible for more frequent meetings with the FDA to discuss the drug development plan, protocols and the clinical data that would support mavorixafor for its potential approval for WHIM. As you may recall, mavorixafor was previously granted breakthrough therapy designation by the FDA, as well as orphan drug status by the FDA and the European Commission for the treatment of WHIM syndrome. With the rare pediatric designation, we may qualify in the future for a priority review voucher, which, if awarded, could potentially be monetized. In the meantime, we expect additional data this year to further support our confidence in the outcome of the 4WHIM trial. Notably, the open-label extension of our Phase 2 clinical trial in WHIM has continued to dose patients. We anticipate presenting detailed updated results from the study within the next year. Since we expect that mavorixafor will be used as a chronic therapy, if approved, these long-term data are quite meaningful to the patient and physician communities. We are also continuing our research into WHIM prevalence, characterizations of specific WHIM mutations, and compelling patient case studies, as well as potential presentations at upcoming medical conferences and other venues in 2021 and beyond, again, with a goal of better understanding the WHIM market for future commercialization and also increasing our visibility in the WHIM patient, physician and KOL communities. Turning now to our other ongoing mavorixafor clinical programs, enrollment is progressing in our Phase 1b trial investigating the safety and efficacy of mavorixafor in combination with ibrutinib for the treatment of a subset of CXCR4 mutant patients with Waldenström’s Macroglobulinemia, a rare form of non-Hodgkin lymphoma. We look forward to presenting initial data from the study in the first half of 2021, with a more robust data set expected to be presented later this year. As previously discussed, Waldenström results from a somatic mutation in the MYD88 gene that is prevalent in more than 90% of patients. Approximately 30 to 40% of these patients have a second mutation in the CXCR4 gene. These double mutant patients with both the MYD88 and CXCR4 mutations typically present with a more severe disease profile and do not achieve the same depth and robustness of responses as patients with a single MYD88 mutation treated with the current standard of care. We are targeting the high need double mutant subset of Waldenström patients as we assess the potential of mavorixafor treatment in combination with ibrutinib in our ongoing Phase 1b trial. The Phase 1b multicenter open-label dose escalation clinical trial is expected to enroll approximately 12 to 18 patients. In addition to safety, dose and pharmacodynamic markers, the study is designed to evaluate changes in serum immunoglobulin M and hemoglobin from baseline, both key biomarkers of clinical response in Waldenström patients. Lastly, regarding our Phase 1b trial in severe congenital neutropenia, we continue to anticipate initial Phase 1b data from the study later in 2021. As you can see, we expect that 2021 will be a year of key value-driving catalysts for X4 across clinical data readouts, enrollment completions, and breadth of opportunity initiatives. On our last call, we briefly introduced you to Dr. Art Taveras, who had just joined as our new Chief Scientific Officer. As he mentioned, he has a wealth of experience in discovering and developing novel next-generation CXCR2 antagonists which makes him an ideal fit to lead our R&D initiatives and has already had a significant positive impact on our research activities and on our earlier stage pipeline initiatives. Following Art’s joining in November, we also welcomed Dr. Diego Cadavid as our new Chief Medical Officer. Having previously served in key senior medical leadership roles at Fulcrum Therapeutics and Biogen, Diego has brought us broad and deep clinical experience in the rare disease space. He has also proven invaluable to us already as we continue to advance our multiple clinical programs in parallel and further advance our preclinical pipeline towards the clinic. With that summary, I'll now turn the call over to Adam to discuss our financial results for the quarter. Adam?

Thanks, Paula. And thanks to all of you on the call today. As presented in our press release this morning, I will summarize our financial activities and results for the fourth quarter and full year ended December 31, 2020. As of the end of the year, X4 had $80.7 million in cash, cash equivalents and restricted cash. We continue to expect that our cash and cash equivalents will fund our operations into 2022. Research and development expenses were $12.3 million and $41.9 million for the fourth quarter and full year ended December 31, 2020 respectively, as compared to $7.1 million and $30.2 million for the comparable periods in 2019 respectively. General and administrative expenses were $5.4 million and $20.9 million for the fourth quarter and full year ended December 31, 2020 respectively, as compared to $3.9 million and $17.6 million for the comparable periods in 2019 respectively. Finally, X4 reported net losses of $18.4 million and $62.1 million for the fourth quarter and full year 2020 as compared to net losses of $10.8 million and $52.8 million for the comparable periods in 2019, respectively. Let's now open up the call for questions.

Thank you. Please stand by while we compile the Q&A roster. Our first question comes from Stephen Willey, with Stifel. Your line is now open.

Yes, good morning, guys. Thanks for taking the question. I guess, Paula, can you just kind of frame up expectations for us in terms of what this first WHIM or Waldenström’s disclosure might look like just in terms of, I guess, maybe timing. And there's a couple of potential venues on the medical conference front in the first half of the year. What we might be able to expect in terms of just patient numbers, and then also what a median duration of follow up in those patients might look like?

Sure, thanks, Steve. So the plan is to present the data at a medical conference. Of course, that's not always in our control. But we are likely to aim for one of the more visible conferences like EHA. There are some other conferences around that same timeframe that could be a good fit as well. In terms of the data, it's an open-label Phase 1b as you know, with three different cohorts. So we'll present the data, which will support a demonstration of obviously safety and dose escalation. Patients have joined the trial at various time points, so we will be providing a range of treatment times for that initial cohort of patients and will also be providing IgM changes as well as hemoglobin changes, which are indicative of activity. I think the most important thing for people to recognize is that we'll aim to provide some relevant benchmarks so people can put our data in context with standard-of-care. And so I think that's the plan at this point.

Okay, that's helpful. And I guess as you continue to characterize some of these additional CXCR4 mutations, have you gained any insight as to whether or not certain mutations within Waldenström’s are more oncogenic just in terms of pathogenicity?

Yes, there are, there's one reference in the literature that talks about sort of two different buckets of mutations in Waldenström, some possibly a little bit more impactful than others. We certainly reflect on that and think that's important information to be tracking. At this point, we're tracking that within our patients, but we'll use our own data set to better inform us on how to think about variant mutations and how they may or may not impact clinical outcomes. I think just overall, the data are still early across the board. We look forward to contributing that to the total data set with our own study.

Okay, and then just lastly, do you maybe just talk about some of the pediatric work that you may have planned for when, I guess, specifically in the context of having the voucher now potentially available? And I think the age cut-off for WHIM is 12 years, if I remember correctly?

Yes, that's right. So the ongoing study does capture the adolescent population. In terms of expanding our studies beyond the age of 12, we're currently evaluating that. Certainly, our goal is to always move forward in a safe way for patients and then expand as appropriate. So we're learning that certainly on our near-term list of priorities, and we'll be glad to update you when we have better clarity on how we'll be initiating studies in younger populations.

All right. Thanks for taking the questions.

Thanks, Steve.

Thank you. Our next question comes from Joel Beatty with Citi. Your line is now open.

Hi, thanks for taking the questions. First one is, could you compare the expectations for this Phase 1 data from Waldenström that are coming around later in the first half, with what to expect in the data set that's expected towards the end of 2021?

Sure, so most Phase 1b studies in Waldenström, obviously are focused on safety and dose. Predictably, they also are assessing changes in IgM, as well as hemoglobin as a measure of activity against the disease. So in the early part of this year, we'll be looking at changes in those two metrics, in addition to safety and dose over time. The longer-term outcomes enable us to measure response rates, which are more robust in terms of their requirements. Typically, that includes imaging for patients who have systemic disease, as well as bone marrow assessments. So the end of the year will include response rate information because the study will be much more mature across a broad number of our patients; the earlier data will be the leading indicators that are certainly highly correlated with response rates. For example, IgM is one of the major components of response rates. So it’s a nice correlation for the long-term outcomes.

Okay, great. And then for WHIM syndrome, can you help us think about the enrollment speed? It seems to be a little bit slower than first expected. Can you share how to think of it in light of what that may mean for patient interests? As you've done a lot of work characterizing the size of the patient population out there, it seems like there are more than 3,500 patients in the U.S. alone, and there are no approved targeted therapies like this. It seems like, perhaps, the need for interest enrollment might be a little bit faster than what we've been seeing. So can you help us reconcile those two thoughts? Thanks.

Sure. No, it's a great question. I wish enrollment would correlate with patient numbers. Unfortunately, that's not the case. Patients in sites need to be lined up. The lead time for opening sites in a geographic region that supports patients and minimizes their travel requirements, especially during the COVID pandemic was set before COVID hit us. So really, this is a story of matching patients to open sites supporting their travel and risk profiles for COVID. We identified patients well in advance of opening our space to make sure we could optimize across the globe in terms of how we would logistically open these trials. I don't have anything to offer other than to suggest that the connectivity is not there for the industry. And unfortunately, it's not there for us as well. The good news is we've known our patients now for quite a period of time. They're ready, they're there, and 2021 will be the year we successfully enroll this trial and communicate that to the industry.

Great, thank you very much.

Thank you. Our next question comes from Leland Gershell with Oppenheimer. Your line is now open.

Hey, good morning, Paula and Adam. Thanks for taking the question. I just want to ask in terms of the open-label update in the Phase 2 in WHIM, will you also be targeting EHA or would it be later in the year? I just want to have some color around the timing of that. Also want to ask just in terms of the earlier pipeline, just wanted to check in and see how any progress may be going with some of the earlier candidates you have in the pipeline? Thank you.

Sure. Diego, would you like to comment on the open-label extension? And then, Art would you like to comment on the pipeline? Go ahead, Diego.

Yes, thank you, Paula. Yes, we are planning for a later disclosure of the Phase 2 WHIM open-label extension, and not at EHA, but most likely later in the year or early next year. Art, would you like to comment on the pipeline?

Sure. Thank you, Diego. Thank you, Paula. Hi. Yes, the pipeline actually, I'm pretty excited about where we're going with them. We've been looking at some of the profiles of various molecules, we have pre-very deep target series, and we're looking for opportunities. This year, I think we're going to be able to push something into the IND enabling studies with the hope of getting something into the clinic next year. That's the goal. We got some pretty good profiles that we're able to penetrate. I think that leaves us with opportunities for some brain-related diseases that are associated with the CXCR4 regulation. Then we have compounds that look like they target various lymphocyte populations. So there are opportunities for lymphocytopenia type diseases. More to come, and I'll disclose a lot more information as we get it.

Excellent. Thank you for taking the questions. Congratulations.

Thank you. Our next question comes from RK with H.C. Wainwright. Your line is open.

Thank you. Good morning, Paula, and a couple of quick questions. The first one on Waldenström. I think since ibrutinib got approved as the combination therapy as well, along with the detection app in 2018, the combination has been moving more into the first-line therapy, but you're doing your study, just a combination with ibrutinib. How do you see your combination working within the therapeutic paradigm for this disease?

Thanks, RK. I appreciate the question. I think there are some geographic differences. What we've been hearing is certainly that ibrutinib is still used as a single agent, sometimes in the frontline setting, and in the second line setting in the U.S. and has some shifts to do that as well as in Europe. We recognize the ibrutinib plus Rituximab sort of frontline paradigm. If you look at the data, and also we hear some input from our ex-U.S. clinicians, I think most people experience that Rituximab offers very little to the combination and effectively are prioritizing ibrutinib in that frontline setting. I think that could actually bode well for us. It is still early, and you mentioned 2018, it's really only about two years into it. It does take some time for the paradigm to settle in. I think we're actually in very good shape with initially partnering with ibrutinib. Even in the event of a paradigm shift, I think CXCR4 antagonism partners more broadly with other types of mechanisms and agents in Waldenström's and even more broadly in lymphoma. So in either regard, I think we're well positioned with this early data set to just show the power of CXCR4 antagonism and move forward from there.

Great, thank you for that. The second question is on SCN. Just as you discussed a little bit more in terms of better expectations from the other indication in the middle of the year for Waldenström. Here in SCN, I know you're not telling us specifically when in 2021, but what sort of efficacy data, safety, and dose escalation that we'll see?

Sure, let me just remind you of the strategic importance of SCN. Severe Congenital Neutropenia is ideally what we hope, assuming WHIM is approved. We would certainly like to explore the application of mavorixafor in other patients with these profound neutropenia and lymphopenias, and SCN is a natural first place to explore. So strategically, the timing on the data continues to fit well with the overall timing of our global efforts around mavorixafor. As we think about the data this year, the SCN trial has probably been the most complicated due to COVID because of the duration of the trial. It is a two-week dosing period, which offers little opportunity to provide clinical benefit for patients. We respect that. It is really a translational study that will correlate a piece of genetic profile with a response after two weeks of dosing. At the end of the day, we need to be respectful of the patient dynamics, given the global and once-in-a-century pandemic that we're all experiencing. We will have some initial data towards the end of the year and will provide more color on that as we gain better clarity.

Perfect, thank you very much. Good luck.

Thank you so much, RK.

Thank you. Our next question comes from Mayank Mamtani with B. Riley Securities. Your line is now open.

Hi, good morning team. This is a question for Mayank. Congrats on all the progress. I have a couple of brief questions. Could you discuss the IgM response kinetics and how you see the levels potentially evolving over time from this initial readout compared to what we can expect at the end of the year? Also, regarding WHIM, could you provide some insight into the enrollment dynamics in terms of the U.S. versus outside the U.S., and any considerations related to the pandemic that might have affected the SCN program, particularly regarding missed doses?

Sure, I think the first question was about IgM level kinetics and benchmarks. I want to ensure that I catch that correctly?

Yes, exactly.

Okay. So I'll begin and then I'll ask Diego to also chime in. There are actually some very good references. Ibrutinib has been well studied in the Waldenström population. Dr. Steve Treon is considered one of the global experts in this area, and thankfully, he is one of the key investigators on our trial. Dr. Treon’s translational work has shown that patients with the CXCR4 mutations have IgM drops that are dramatically different from those patients without CXCR4. There’s a great publication by Dr. Treon and Blood of 2017, that actually splits up the kinetics of IgM versus time for the two different types of populations. So it will be a great benchmark for us, because we understand what patients do on ibrutinib, with the CXCR4 mutation and without. Ideally, our treatment with mavorixafor could correct for that and change these patients from double mutants to look more like the kinetics of single mutants. That’s part of the efforts we are working on now to measure and benchmark. I hope that was helpful. The second question was a little bit around the pandemic's impact on the WHIM trial. There are differences there. Certainly, the WHIM trial provides the potential for clinical benefit. If we reflect on our Phase 2 data that's been published, it has certain strong suggestions of reductions in infection rates and improvements in the quality of life for patients with WHIM syndrome. There's reason to be motivated and committed to this trial, which we've seen our break patients step forward with. We feel like our relationships with the patient community are still strong, which support hitting our enrollment targets, which are nicely on track for this year.

It's very helpful. Thanks for taking our question.

Absolutely.

Thank you. Our next question comes from Zegbeh Jallah with Roth Capital Partners. Your line is now open.

Good morning, guys. Just wanted to quickly confirm, Paula, if we're going to see any kind of highlights from the larger interim data before a presentation at our medical meeting and then also are we to expect any updates or data progress in your partnership with Abbisko this year?

So why don't I invite Diego to comment about our plans around the Waldenström data given his connection with our investigators, and then I'll take the other question.

Yes, thank you, Paula. We are looking to do an initial, public disclosure of the Waldenström Phase 1b data towards the end of H1, most likely at EHA, where we will report on initial safety PK, and pharmacodynamic markers. We have a very good pharmacodynamic marker and some initial data on the Serum IgM and hemoglobin, which are really helpful biomarkers. Later in the year, most likely at ASH, we plan to have a second presentation shooting to more patients, and longer follow-up including an assessment of responses including bone marrow and whole body CTs. Both of these presentations will be able to be compared with the benchmarks from ibrutinib monotherapy in double mutant populations. So we believe that will help us assess the emerging efficacy of mavorixafor in this type of lymphoma, which has a high unmet need. We'll use that information to decide on next steps. Regarding the partnership with Abbisko, Paula, could you take that one?

Oh, thank you Diego. Yes, the Abbisko partnership is advancing. I would bet that we'll be able to provide more clear updates towards the end of 2021. It's launching nicely. And as we gain clarity, we'll look forward to sharing more details at a future point.

Got it Paula, and thanks for all the updates.

Thank you.

Thank you. I'm not showing any further questions at this time. I would now like to turn the call back over to Paula Ragan for closing remarks.

Thank you so much for joining everyone this morning. I hope you all continue to remain safe and healthy. If you have any follow-up questions, we'd be happy to answer those offline. Thank you again and I hope you enjoy the rest of your day. Goodbye.

Ladies and gentlemen, this concludes today's conference call. Thank you for participating. You may now disconnect.