Xcyte Therapies, Inc. Presents Results of Phase I/II Clinical Trial of Xcellerated T Cells in Chronic Lymphocytic Leukemia at American Society of Hematology Meeting.

SEATTLE -- Discusses Plans for Phase II/III Trial

Xcyte Therapies, Inc. ("Xcyte") (Nasdaq:XCYT) announced today that results from a Phase I/II clinical trial of Xcellerated T Cells in patients with chronic lymphocytic leukemia (CLL) were presented at the American Society of Hematology meeting in San Diego yesterday. Xcyte also discussed its plans for a Phase II/III clinical trial of Xcellerated T Cells in patients who have received Campath (alemtuzumab), which will be named the X-CLL Trial.

In the Phase I/II clinical trial, 17 patients received a single infusion of Xcellerated T Cells without other treatment for their leukemia. In CLL, leukemic cells infiltrate the lymph nodes, spleen and blood, leading to enlargement of the lymph nodes and spleen and increased numbers of leukemic cells in the blood. Following the infusion of Xcellerated T Cells, 12 (71%) of 17 patients demonstrated a 50% or greater decrease in the size of their enlarged lymph nodes. Eleven (85%) of the 13 patients with an enlarged spleen demonstrated a 50% or greater reduction in spleen size as determined by physical examination. Decreases in leukemic cell counts in the blood were not observed. Sustained increases in T lymphocytes as well as in neutrophil and platelet counts were seen, suggesting that Xcellerated T Cells may also have positive effects on many kinds of blood cells. Observed side effects thought to be related to the therapy were low-grade, and included fever, chills and headache associated with the infusion.

Six patients received a second infusion of Xcellerated T Cells from 6 to 11 (median 10) months after the first infusion. Five of the 6 patients had measurable disease in their lymph nodes and spleen at the time of the second infusion. In four of these patients, there was a decrease in the size of the involved organs. Decreases in leukemic cell counts were not observed.

"Based on the reduction in the size of lymph nodes and spleen infiltrated with leukemic cells, we are encouraged to move forward with the clinical development of Xcellerated T Cells in patients with CLL," said Mark Frohlich, M.D., Medical Director and Vice President of Xcyte Therapies. "We are planning to initiate a Phase II/III trial in patients with CLL who have received Campath (alemtuzumab), which we have named the X-CLL Trial. Currently, patients with CLL who fail treatment with Campath have no approved therapeutic options, and these patients have a significant unmet medical need."

"Campath is a standard treatment for advanced CLL, but it increases the risk of infection because it eradicates nearly all T cells for several months after treatment," continued Dr. Frohlich. "In addition, although Campath can decrease leukemic cell counts in the blood, it has less therapeutic activity in the lymph nodes and spleens of CLL patients. Accordingly, we believe there is a strong clinical rationale for using Xcellerated T Cells after Campath therapy."

In the planned X-CLL Trial, patients who are refractory to fludarabine or have received at least two prior chemotherapy regimens, including at least one nucleoside analog-containing regimen, will be eligible for the trial. Following leukapheresis, a procedure to collect white blood cells to initiate the Xcellerate Process, patients will be treated with Campath. Those patients who fail to respond will enter one component of the X-CLL Trial and receive Xcellerated T Cells. The primary endpoint of the X-CLL Trial will be the response rate in these patients. Those patients who respond to Campath will be eligible to enter a second component of the X-CLL trial.

"We discussed our plans for this Phase II/III trial with the Food and Drug Administration (FDA) at an End of Phase II meeting in September," said Ron Berenson, M.D., President and Chief Executive Officer of Xcyte Therapies. "We are currently working with the FDA to finalize the X-CLL Trial protocol and to review our manufacturing plans for this trial. We intend to manufacture Xcellerated T Cells for this trial in our newly completed manufacturing facility in Bothell, Washington. If the FDA accepts our protocol and manufacturing plans, we expect to enroll our first patient in the X-CLL trial by the end of the second quarter of 2005."

Note: Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the therapeutic potential of Xcellerated T Cells, used alone or in combination with Campath, and our ability to initiate the X-CLL Trial on time or at all. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include risks related to adverse clinical results as our product candidates move into and advance in clinical trials, risks that the FDA may not agree with our clinical or manufacturing plans and failure by Xcyte Therapies to secure or maintain relationships with collaborators. Results obtained in early stage clinical trials may not be predictive of results obtained in larger trials intended to demonstrate the safety and efficacy of Xcellerated T Cells. More information about the risks and uncertainties faced by Xcyte Therapies is contained in our filings with the Securities and Exchange Commission. Xcyte Therapies disclaims any intention or obligation to update or revise any forward-looking statement, whether as a result of new information, future events or otherwise.

Xcyte Therapies, Inc. is a biotechnology company developing a new class of therapeutic products designed to enhance the body's natural immune responses to treat cancer, infectious diseases and other medical conditions associated with weakened immune systems. Xcyte derives its therapeutic products from a patient's own T cells, which are cells of the immune system that orchestrate immune responses and can detect and eliminate cancer cells and infected cells in the body. Xcyte uses its patented and proprietary Xcellerate(TM) Technology to generate activated T cells, called Xcellerated T Cells(TM), from blood that is collected from the patient. Activated T cells are T cells that have been stimulated to carry out immune functions. The Xcellerate(TM) Technology is designed to rapidly activate and expand the number of the patient's T cells outside of the body. Xcyte is currently conducting clinical trials of Xcellerated T Cells(TM) in patients with chronic lymphocytic leukemia, non-Hodgkin's lymphoma, and multiple myeloma.

Xcyte(TM), Xcyte Therapies(TM), Xcellerate(TM) and Xcellerated T Cells(TM) are trademarks of Xcyte Therapies, Inc. Campath(R) is a registered trademark of ILEX Oncology, Inc.