CytRx Reports Successful Completion of Phase I HIV Vaccine Clinical Trial; Data Indicates Favorable Safety and Immune Responses; ABL and UMMS Investigators Expect to File Final Trial Results with the FDA in August.

LOS ANGELES -- CytRx Corporation (Nasdaq:CYTR) today announced completion of the Phase I clinical trial of the novel HIV DNA + protein vaccine that it has exclusively licensed. Analysis of the unblinded data confirmed previous preliminary conclusions that the HIV vaccine formulation DP6-001 was generally well tolerated in volunteers receiving lower vaccine doses and was effective at eliciting both HIV-specific T-cell and antibody immune responses. A summary of the Phase I trial results will be filed with the U.S. Food and Drug Administration (FDA) in August 2006 and manuscripts that provide additional detailed results are being prepared to submit for publication in peer-reviewed journals and presentations at scientific conferences.

DP6-001 was developed by researchers at University of Massachusetts Medical School (UMMS) and Advanced BioScience Laboratories (ABL), and exclusively licensed to CytRx. The vaccine initially "primes" the subject's immune system through the injection of DNA that causes the subject's own cells to produce the HIV "envelope" and "gag" proteins, followed by protein "boosts" from an injection that contains the corresponding HIV envelope proteins.

"We are very encouraged that analysis of the unblinded data confirms that DP6-001 is among the first experimental HIV vaccines to produce antibody responses with neutralizing activity against multiple HIV strains in humans," said Steven A. Kriegsman, President and CEO of CytRx. "The favorable priming of T- and B-cell immune responses to the vaccine also raises hope that this approach may produce a 'memory' immune response that may be sufficiently robust to protect against the HIV virus over time."

The Phase I trial, initiated in April 2004, was conducted at UMMS. Trial enrollment of 34 healthy volunteers was completed in March 2005, six months ahead of schedule, and follow up was completed in March 2006. The trial was divided into three arms: Group A received the DNA vaccine three times under the skin, and Groups B and C received the DNA vaccine three times in muscle, with Group C receiving a six-fold higher DNA dose compared with Groups A and B. All subjects were subsequently "boosted" by injection with a mixture of envelope protein antigens.

Low grade adverse events typical of vaccination, and classified by the investigators as "related to the vaccine", were commonly observed in Groups A and B. The most common adverse event was pain and redness at the injection site, and less often mild body ache and low grade fever were reported. Subjects in the high dose Group C who received one protein boost experienced higher grade adverse events, including muscle aches and malaise. One volunteer in Group C also developed an inflammation of small blood vessels in the skin, a condition called leukocytoclastic vasculitis, following the first protein antigen boost. These observations led to the decision to discontinue further boosting of subjects in Group C. These results suggest that future clinical trials may benefit by using a lower dose of DNA or proteins or a modified form of the protein boost.

DP6-001 met the objective of stimulating a balanced immune response that generated high titer antibody and broad cell mediated immune responses against several subtypes of primary HIV isolates. The data demonstrated potent responses to viral protein antigens in the vaccine, including the envelope protein, which is part of HIV. The envelope antigen is a critical protein on the surface of the AIDS virus that facilitates the infectivity of HIV in humans.

Further analysis of the antibody responses demonstrated that the vaccine was able to induce cross-clade neutralizing antibodies against a wide range of HIV envelope antigens. The titer of these neutralizing antibodies was relatively low, suggesting that the main task for future development of the vaccine will be to improve the strength of these neutralizing antibodies.

In general, injection of the DNA vaccine into muscle (Groups B and C) resulted in better cell mediated responses compared with injection under the skin (Group A). Additionally, as might be expected, the highest dosage of the DNA vaccine (Group C) generally elicited improved cell mediated and antibody responses compared to the low dose groups. These results may help the design of future clinical trials to safely maximize the immune response.

The Phase I study was funded under a $16 million, five-year HIV Vaccine Design and Development Team contract from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH).

HIV Background

HIV, the virus that leads to acquired immune deficiency syndrome (AIDS), remains a global epidemic. World health officials estimate 39 million people are now infected with HIV. Some 3 million people died of AIDS last year, worldwide, and millions more are expected to die from AIDS this year. With the rate of infection accelerating in many parts of the world, the search for an effective HIV vaccine is one of the highest public health priorities. Development of an HIV vaccine has been challenging because of the virus' extraordinary degree of genetic diversity. HIV mutates rapidly in the environment making it an elusive target for traditional vaccine strategies.

About DP6-001

DP6-001 is composed of a polyvalent DNA primer followed by a multivalent gp120 protein boost. The HIV vaccine formulation is based on multiple strains of HIV collected from infected people living in different parts of the world, representing five different strains of the virus. The vaccine contains elements from selected HIV genes, not the live virus, and therefore individuals receiving inoculations cannot get HIV from the vaccine.

About CytRx Corporation

CytRx Corporation is a biopharmaceutical research and development company engaged in the development of high value human therapeutics. The Company owns three clinical-stage compounds based on its small molecule "molecular chaperone" co-induction technology (CCI), as well as a targeted library of 500 small molecule CCI analogs. CytRx has initiated a Phase II clinical trial with its lead CCI small molecule product candidate arimoclomol for the treatment for amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease). Arimoclomol has received Orphan Drug status and Fast Track designation from the FDA. CytRx has previously announced that a novel polyvalent HIV DNA + protein vaccine exclusively licensed to CytRx and developed by researchers at UMMS and Advanced BioScience Laboratories, and funded by the National Institutes of Health, demonstrated very promising interim Phase I clinical trial results that indicate its ability to produce potent antibody responses with neutralizing activity against multiple HIV viral strains. CytRx also has a broad-based strategic alliance with UMMS to develop novel compounds in the areas of ALS, obesity, type 2 diabetes and cytomegalovirus (CMV) using RNAi technology. The Company has a research program with Massachusetts General Hospital, Harvard University's teaching hospital, to use RNAi technology to develop a drug for the treatment of ALS. CytRx Drug Discovery division, located in Worcester, MA focuses on the use of RNAi technologies to develop small molecule and RNAi therapeutics to treat obesity and type 2 diabetes. For more information, visit CytRx's Web site at www.cytrx.com.

About the University of Massachusetts Medical School

The University of Massachusetts Medical School, one of the fastest growing academic health centers in the country, has built a reputation as a world-class research institution, consistently producing noteworthy advances in clinical and basic research. The Medical School attracts more than $174 million in research funding annually, 80% of which comes from federal funding sources. Research funding enables UMMS scientists to explore human disease from the molecular level to large-scale clinical trials. Basic and clinical research leads to new approaches for diagnosis, treatment and prevention of disease. Visit www.umassmed.edu for additional information.

About Advanced BioScience Laboratories

Advanced BioScience Laboratories, Inc. (ABL) located in Kensington, Md., is a biomedical research, development and manufacturing company focusing on human retroviral diseases. ABL has been a leader in HIV-1 research for more than two decades and has been involved in the development of methods to both prevent and treat HIV-1 infection.

Forward-Looking Statements

This press release may contain forward-looking statements within the meaning of Section 21E of the Securities Exchange Act of 1934, as amended. Examples of such statements include, but are not limited to, statements relating to the expected timing, scope and results of our clinical development and research programs, including the results of a Phase I HIV clinical trial, and statements regarding the potential benefits of our drug and vaccine candidates. Such statements involve risks and uncertainties that could cause actual events or results to differ materially from the events or results described in the forward-looking statements, including risks or uncertainties regarding regulatory approvals for clinical testing and the scope of the clinical testing that may be required by regulatory authorities for our vaccine and molecular chaperone co-induction drug candidates and other products, and the timing and outcomes of those tests, the need to license the adjuvant used in the Phase I HIV clinical trial from a third party, CytRx's need for additional capital to fund its ongoing working capital needs, including any further clinical development of its HIV vaccine, uncertainties related to the early stage of CytRx's diabetes, obesity, cytomegalovirus and ALS research, the need for future clinical testing of any RNAi-based products and small molecules that may be developed by CytRx, the significant time and expense that will be incurred in developing any of the potential commercial applications for CytRx's RNAi technology or small molecules, risks relating to the enforceability of any patents covering CytRx's products and to the possible infringement of third party patents by those products, and the impact of third party reimbursement policies on the use of and pricing for CytRx's products. Additional uncertainties and risks are described in CytRx's most recently filed SEC documents, such as its most recent annual report on Form 10-K, all quarterly reports on Form 10-Q and any current reports on Form 8-K filed since the date of the last Form 10-K. All forward-looking statements are based upon information available to CytRx on the date the statements are first published. CytRx undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.