Enzon Acquires Global Rights from NatImmune for Oncology Product

Enzon Pharmaceuticals, Inc. (Nasdaq: ENZN) and theDanish biotech company, NatImmune A/S today announced that they haveentered into a license agreement for NatImmune's lead developmentproduct, recombinant human Mannan-Binding Lectin (rhMBL), a proteintherapeutic being developed for the prevention of severe infections inMBL-deficient individuals undergoing chemotherapy. Under theagreement, Enzon receives exclusive worldwide rights, excluding theNordic countries, and is responsible for the development, manufacture,and marketing of rhMBL. NatImmune will receive an upfront payment of$10 million and is eligible to receive additional payments upon thesuccessful completion of certain clinical development, regulatory, andsales-based milestones. NatImmune is also eligible to receiveroyalties from any future product sales of rhMBL by Enzon and retainscertain rights to develop a non-systemic formulation for topicaladministration of MBL.

Mannan-Binding Lectin (MBL) is a naturally occurring human plasmaprotein that plays a key role in the immune system's first-linedefense against infections. MBL binds to a wide range of invadingorganisms, including bacteria, fungi, viruses, and parasites andactivates the lectin pathway of the complement system, an importantdefense mechanism of the immune system.

Numerous studies have found a strong correlation betweenMBL-deficiency and an increased susceptibility to infections inpatients with a suppressed immune system, such as cancer patientsundergoing treatment with chemotherapy. In addition, a number ofpublications have also highlighted the potentially important futurerole of MBL replacement therapy in preventing serious infections inother critical care areas associated with immunodeficiency.

"Today's announcement underscores our commitment to rebuilding ourclinical pipeline with promising product development opportunities,"said Jeffrey H. Buchalter, Enzon's chairman and chief executiveofficer. "Given the vital role MBL plays in the immune system, thiscompound represents an exciting opportunity for us to bring asubstantial clinical advantage to patients who are susceptible toserious infections."

"We believe Enzon's extensive experience in developing andcommercializing therapeutics for patients with cancer and otherimmunodeficiency disorders makes them an ideal partner to advance thishigh-potential therapeutic," said Dr. Martin Bonde NatImmune's chiefexecutive officer. "Further, we will also work together to leverageEnzon's long-standing skills in developing optimized versions ofprotein-based therapeutics through PEGylation to potentially explore anext-generation compound."

In December 2004, NatImmune completed Phase 1 clinical trials thatevaluated the safety and pharmacokinetic profile of single and multidose intravenous administration of rhMBL in 28 MBL-deficientvolunteers. Results from the Phase 1 trials demonstrated that rhMBLreplacement therapy is safe and has an attractive pharmacokineticprofile. NatImmune has also completed a prospective correlation studyof 250 hematological cancer patients that documented MBL-deficientpatients have a significantly higher risk of severe infectionsfollowing chemotherapy compared to patients with sufficient MBLlevels. These results confirmed previous clinical correlation studiespublished in the Lancet in August 2001.

About Enzon

Enzon Pharmaceuticals, Inc. is a biopharmaceutical companydedicated to the development and commercialization of therapeutics totreat patients with cancer and other life-threatening diseases.Enzon's specialized sales force markets ABELCET(R), ONCASPAR(R),ADAGEN(R), and DEPOCYT(R) in North America. In addition, Enzon alsoreceives royalties on sales of PEG-INTRON(R), marketed bySchering-Plough Corporation, and MACUGEN(R), marketed by EyetechPharmaceuticals and Pfizer Inc. Enzon's product-driven strategyincludes an extensive drug development program that leverages itsproprietary technologies, including a next-generation PEGylationplatform that utilizes linkers designed to release compounds at acontrolled rate. Enzon complements its internal research anddevelopment efforts with strategic initiatives, such as partnershipsdesigned to broaden its revenue base or provide access to promisingnew technologies or product development opportunities. Furtherinformation about Enzon and this press release can be found on theCompany's web site at www.enzon.com.

About NatImmune

NatImmune A/S is a biotech company focused on the development oftherapeutic proteins. Based in Symbion Science Park, the Company wasfounded in 2000 and has 22 employees. NatImmune's lead product, MannanBinding Lectin (MBL), has completed Phase 1 clinical trials and isbeing developed under a global licensing agreement with the U.S.biopharmaceutical company, Enzon Pharmaceuticals, Inc. NatImmune hasretained certain rights to develop a non-systemic formulation for thetopical administration of MBL. In addition, the Company's pipelinealso includes antibodies for the treatment of colorectal cancer(COU-I) and cardiovascular diseases (MASP-2). Further informationabout NatImmune can be found at the Company's web site atwww.natimmune.com.

There are forward-looking statements contained herein that are notbased on historical fact, including without limitation statementscontaining the words "believes," "may," "plans," "will," "estimate,""continue," "anticipates," "intends," "expects," and similarexpressions. Such forward-looking statements involve known and unknownrisks, uncertainties and other factors that may cause actual results,events or developments to be materially different from the futureresults, events or developments discussed above. Such factors include,but are not limited to the timing of, success, and cost of clinicalstudies; the ability to obtain regulatory approval of products; andthose described in Enzon's Form 10-K and Forms 10-Q on file with theUnited States Securities and Exchange Commission and NatImmune'spublicly filed reports. These factors should be considered carefullyand readers are cautioned not to place undue reliance on suchforward-looking statements. All information in this press release isas of October 3, 2005 and Enzon and NatImmune undertake no duty toupdate this information.