TWST: Please begin with a brief historical sketch of the company and a picture of the things you are doing now.

Dr. Siegall: Seattle Genetics just hit its 10-year anniversary. We were founded in 1998 by myself and Dr. Perry Fell. We started the company for the purpose of making antibody-based therapeutics for cancer patients. Since day one that's been our goal and it remains our goal. We have since developed a number of clinical-stage product candidates as well as antibody-drug conjugate, or ADC, technology to empower antibodies. We currently have three products that are in multiple clinical trials and three lead preclinical product candidates that we intend to bring forward to clinical testing, one each over the next three years.

TWST: Would you go into detail on some of these product candidates?

Dr. Siegall: SGN-40 is a humanized antibody that's targeted to CD40. CD40 is expressed on hematologic malignancies, including multiple myeloma and non- Hodgkin lymphoma. We are evaluating this antibody for patients with relapsed or refractory disease, meaning they have received at least one and often several approved and/or experimental drugs previously. These patients typically have very few treatment options remaining. We have reported multiple objective antitumor responses, including complete and partial responses to therapy at well-tolerated doses in patients with non-Hodgkin lymphoma. In January 2007, we entered into a worldwide collaboration with Genentech for the development and commercialization of SGN-40. Genentech is based in South San Francisco and is the world's leading company developing antibodies for cancer. This deal is lucrative to Seattle Genetics with $60 million upfront, over $800 million in potential milestone payments plus increasing double-digit royalties on net sales that start in the mid-teens. Importantly, Genentech is paying for development, manufacturing and clinical costs, including reimbursing Seattle Genetics for the work it performs on the program. In addition to the upfront payment, in the first year of the collaboration we've received $20 million of milestone payments from Genentech. The program is doing extremely well and advancing in a broad way. There are a total of six clinical trials in multiple myeloma and non- Hodgkin lymphoma, both as a single-agent and in combination with standard treatment regimens that we have planned under the joint development team between Seattle Genetics and Genentech. Four of those trials are underway now and the other two trials will be underway within the next few months. We're delighted to have a strong partnership and relationship with Genentech on this program.

TWST: What are your other product candidates?

Dr. Siegall: The second product candidate in our pipeline is SGN-33. This is a humanized antibody that targets CD33, which is highly expressed on myeloid tumors such as acute myelogenous leukemia, or more commonly referred to as AML. The other indication that we are pursuing is myelodysplastic syndromes, or MDS, which is a condition that often leads to AML. About two thirds of all patients with AML are first diagnosed over 60 years old, and the disease can be life threatening for these patients. For older patients that are diagnosed with AML who cannot tolerate chemotherapy, there's a median survival of less than six months. AML is a disease in which malignant cells, called tumor blast cells, enter the bloodstream and bone marrow. They crowd out the normal blood cells that are needed and make patients very weak and frail. Once they crowd out enough of the cells, the patient needs regular blood transfusions. The goal with SGN-33 is to eliminate the tumor blast cells and allow normal red blood cells and white blood cells to re-populate the bloodstream and bone marrow. AML is a very painful and debilitating disease, and it is very hard for patients, especially older patients, to tolerate any type of cytotoxic treatment or intensive chemotherapy. SGN-33, an antibody that targets these leukemic cells in AML or the myeloid cells in MDS, has been well tolerated. In our Phase I, single-agent clinical trial, we've shown multiple responses including many complete remissions. We've been pleased with our data and are doing further single agent work in larger clinical trials. We are also doing trials of SGN-33 in combination with chemotherapies that are used to treat AML and/or MDS. Our goal is to develop an antibody that could be used independently or with other drugs to help patients with AML and MDS, specifically by extending survival and improving quality of life without introducing the types of toxicities that you normally see with chemotherapy.

TWST: Do you have any idea how long that survival could be in different cases?

Dr. Siegall: I mentioned that the average survival for older AML patients is less than six months. We've had patients on treatment for a year now in some of our studies. We are very pleased with that and we will be reporting more data from our clinical trials later in 2008 at clinical conferences.

TWST: Would go on to describe some of the other product candidates?

Dr. Siegall: The third and last of our clinical-stage programs is called SGN-35. SGN-35 is different from SGN-40 and SGN-33 in that it is an antibody-drug conjugate or ADC. Our ADC technology enhances the potency of an antibody by attaching it to a cell-killing payload. SGN-35 is an ADC that targets CD30. CD30 is on Hodgkin lymphoma cells and on T-cell lymphomas. It's very different from CD40, the target of SGN-40, which is on myeloma and B-cell lymphomas, and from SGN-33, which is on myeloid diseases. These three programs do not overlap; they are different drugs for different indications. SGN-35 is in an ongoing Phase I clinical trial. We've reported interim data showing that SGN-35 can induce objective responses at well-tolerated doses. We are planning to report additional data in the first half of 2008 at an appropriate medical conference such as ASCO, which is American Society of Clinical Oncology. We are looking forward to bringing SGN-35 into further clinical trials and to moving this product towards approval. Later in 2008, we will be detailing our registration pathway for this agent. SGN-35 is important to us for two reasons. One is it's a drug on its own that could be important for patients and the second is it's the first drug that we've developed using our proprietary ADC technology. This technology is, like I said, a way to empower antibodies by attaching a potent cell-killing drug to an antibody using a stable linker. In addition to our internal development of ADCs, other companies have been very interested in our technology. As a result we have done a number of ADC technology deals with other companies to make their internal antibodies more powerful. Those deals generate upfront payments, milestone payments, and ultimately may pay us royalties on sales of products using our technology. Through our ADC technology deals we have brought in more than $65 million to date, and that does not count a very high number of future progress-dependent milestone payments that we may receive, as well as possible royalties.

TWST: What about SGN-30, 70 and 75?

Dr. Siegall: We aren't currently sponsoring clinical trials with SGN-30. SGN-30 is the unconjugated antibody that's used in SGN-35. We conducted Phase I and Phase II trials with SGN-30 and found that it was safe and induced objective responses in patients with T-cell lymphomas. But we have chosen to focus corporate development on the empowered form of SGN-30, which we call SGN-35. Our clinical trials with SGN-35 demonstrate that it has stronger antitumor activity, particularly in Hodgkin lymphoma, than we saw with SGN-30. As for SGN-70 and SGN-75, this is a pair of therapies targeted to CD70. SGN-70 is a humanized antibody and SGN-75 is an ADC. We plan to initiate clinical trials with SGN-70 for the purpose of developing this product in autoimmune disease based on its properties and our preclinical data. SGN-75 is an empowered antibody that takes the same antibody and links it to a potent drug payload utilizing our ADC technology. In preclinical models such as renal cancer, SGN-75 is very effective. We are going to develop SGN-75 for cancer. Those two molecules should be put into clinical trials over the next two years, SGN-70 starting in 2008 and SGN-75 starting in 2009.

TWST: What possible challenges or obstacles might arise over the next few years?

Dr. Siegall: I think that an obstacle that faces any company that develops therapeutic products is clinical data. We have a broad array of clinical trials that we've initiated and that are advancing well, so we feel favorable about our future prospects. But our clinical data will need to continue to be exciting and supportive of future development. Another area we think about is the manufacturing and scale-up of our product candidates. Seattle Genetics does not own manufacturing facilities. We manufacture our products through other companies contract manufacturing organizations. We develop our own antibodies, establish processes for how to manufacture them, and put the QC/QA parameters in place, but we contract with people for their manufacturing capacity. We've not had any limitations in hiring contractors to make bulk amounts of our antibodies, but it is expensive and it's something we focus on.

TWST: What is the picture that you would hope to see for Seattle Genetics in, say, three to four years?

Dr. Siegall: In three to four years we hope to be a company that has commercialized one or potentially two products in the United States. We may consider some aspect of partnering in the rest of the world for commercializing products, or we may consider doing it ourselves, although that is a tough challenge for a small biotech company like Seattle Genetics. More likely, within three to four years I envision Seattle Genetics having multiple products in clinical trials, and one or two products approved and being sold commercially, with Seattle Genetics doing a big share of the commercial sales. In addition, I see us having a big pipeline behind that with strong technology.

TWST: What might be some year-by-year milestones that investors could look for?

Dr. Siegall: For 2008, we have a number of clinical milestones that investors should expect for SGN-33, SGN-35 and SGN-40. We plan to report clinical data at appropriate medical conferences such as ASCO and ASH, which is the American Society of Hematology, and at other specialty conferences as well. Along the way, in 2008 we plan to initiate many clinical trials with each of our lead drugs. Then going into 2009 and 2010, it would really be once again our clinical data, including from later-stage trials. Those are the things that are critical. I also think that entering into manufacturing contracts for commercial scale manufacturing is important for investors, as that is a sign that the company is excited about the program and willing to invest in it.

TWST: Would you tell us about your own background and expertise and the same for one or two of your colleagues?

Dr. Siegall: I have a PhD in Genetics and I trained in making targeted drugs for cancer patients at the National Cancer Institute. Then I worked for Bristol- Myers Squibb in a number of capacities over a seven-year period before I co- founded Seattle Genetics. Tom Reynolds, our Chief Medical Officer, has a, MD and PhD from Stanford. Tom has worked in several biotech companies, most recently Zymogenetics here in Seattle. Tom was integral to their filing of the product that just got approved, called RecoThrom. Tom is a very skilled and highly trained clinical manager. Another person who I would point out is Eric Dobmeier, our Chief Business Officer. Eric leads all of our business functions and much of our corporate strategy. Eric is an attorney by training and has a JD from Cal Berkeley Boalt School of Law, and undergraduate from Princeton. Eric is one of the brightest people I have ever met. He has an affinity for biotechnology, and runs all of our legal, business development, communications and marketing functions, as well as many other operational items within the company. For example, Eric negotiated and completed the deal with Genentech, which is the single largest deal that Seattle Genetics has ever done.

TWST: How many employees do you have?

Dr. Siegall: Just over 200.

TWST: Would you tell us about the culture and about how the people go about their work?

Dr. Siegall: We have very bright people working here. The culture hinges on teamwork; it's collaborative, upbeat and fun. I think the morale here is excellent. We have a very low turnover rate. We try to do the best we can for our employees. Just an example is that every Friday morning the entire company gets together. We provide breakfast, and each week there is a presentation. We alternate among groups within the organization, so that everyone in the company has an idea and knowledge of what goes on in the whole company, providing visibility and transparency. We strive not to have any silos or things that are sectioned off. As far as teams, there are some people who focus on just one project because it requires so much of their time and expertise. But there are other people who have responsibility that touches on multiple projects.

TWST: I believe that you did a recent $90 million offering?

Dr. Siegall: Yes, in January we completed an offering that raised a net amount of $97.5 million. This additional capital puts us in a very strong position to continue advancing and investing in our promising pipeline.

TWST: Will you be taking any further steps within the next few years to improve your capital situation?

Dr. Siegall: We ended 2007 with over $129 million in cash. With the recent financing, we have more than $220 million. That should take us forward for many years. However, biotechnology is a capital-intensive business and we are always mindful about maintaining a strong financial position.

TWST: Would you tell us about your investor base?

Dr. Siegall: Our investor base is heavily weighted toward institutional stockholders. Our investors include some of the biggest mutual funds, such as Fidelity, T. Rowe Price and Oppenheimer. We are delighted with the investor base that we have been able to attract.

TWST: What would be the two or three best reasons for the long-term investor to look very closely at Seattle Genetics?

Dr. Siegall: I would say that the depth of our clinical pipeline is the single best reason. We have three product candidates with data demonstrating their potential in the treatment of cancer, three lead preclinical programs advancing toward clinical trials over the course of the next three years, and multiple early-stage programs that will ensure continued pipeline strength. The second reason is our ADC technology, which has come of age and is doing well in treating patients and eliciting antitumor responses.

TWST: You must be feeling very good about the things you have accomplished with the company.

Dr. Siegall: Seattle Genetics is a company that's no longer a startup company; I would categorize us as an emerging company. We do not feel that we are a successful company yet. We think success is in our future. While we are excited about our prospects, all of us here are working very hard to become successful.

TWST: Is there anything that you would like to add, especially regarding strategies, long-term objectives and reasons for investors to look at the company?

Dr. Siegall: I would add one comment and that is when I look at the competitive landscape of biotechnology companies, I don't view that any of them are our competitors. I view that cancer is our competitor, and every day we get up in the morning and come to work to compete against cancer.

TWST: Thank you. (MC)

CLAY SIEGALL President & CEO Seattle Genetics, Inc. 21823 30th Drive SE Bothell, WA 98021 (425) 527-4000 (425) 527-4001 FAX www.seattlegenetics.com e-mail: contact@seagen.com