Business Wire - July 9, 2003

Data from several published preclinical studies (Journal of Infectious Diseases 2002; 186:1098-1105, Vaccine 2002, 20:2684-92, & 2000, 18:1081-1087, Journal of Human Virology 2001, 4:39-43) have demonstrated that combining The Immune Response Corporation's whole-killed HIV vaccine with immunostimulatory CpG oligonucleotides elicits greatly enhanced HIV-specific CD4+ and CD8+ T cell responses, indicating the potential for a therapeutic as well as a preventive vaccine.

"These responses are thought to be key components of the immune system's ability to combat HIV infection," stated Dorothy Bray, Ph.D., Clinical Development Advisor to The Immune Response Corporation. "Hybridon's IMO candidates have promising immunostimulatory properties useful in combination with a vaccine, and we are enthusiastic about initiating testing on this vaccine candidate."

"We believe that our whole-killed HIV antigen technology combined with Hybridon's state-of-the-art IMO technology could produce the next-generation HIV vaccine," said Georgia Theofan, Ph.D., vice president of Clinical Development of The Immune Response Corporation. "We plan to continue the development of REMUNE while rapidly moving forward with the evaluation of a potential 2nd generation vaccine."

"Hybridon is pleased that The Immune Response Corporation has selected a candidate from our IMO technology as a potential adjuvant for a next generation HIV vaccine," said Stephen R. Seiler, chief executive officer of Hybridon, Inc. "The published data on REMUNE plus CpG oligos demonstrates HIV specific CD4+ and CD8+ T-cell responses that are compelling. We believe that adjuvants are key components in making vaccines more effective."

The Immune Response Corporation has initiated the basic preclinical studies necessary to evaluate of a 2nd generation vaccine product. The Immune Response Corporation and Hybridon have entered into a non-binding agreement for The Immune Response Corporation to negotiate a license from Hybridon to use Hybridon's IMO technology in combination with The Immune Response Corporation's HIV vaccine. There can be no assurance that the parties will enter into a license agreement or that the results of The Immune Response Corporation's evaluation will warrant such a license.

About The Immune Response Corporation and REMUNE

Co-founded by medical pioneer Dr. Jonas Salk and headquartered in Carlsbad, California, The Immune Response Corporation is a biopharmaceutical company dedicated to treating HIV and AIDS through the development of REMUNE. REMUNE is an immune-based therapeutic vaccine designed to induce an HIV-specific immune response and boost the body's natural defense mechanisms in order to slow the virus' progression. REMUNE is comprised of HIV that has been chemically killed and inactivated so that it is non-infectious. During the inactivation process, the HIV outer envelope, which is prone to rapid mutations, is removed. REMUNE is then emulsified in Incomplete Freund's Adjuvant, an agent that elicits a more potent immune response by drawing the immune system's attention to the inactivated virus.

HIV, the human immunodeficiency virus, is the virus that causes AIDS, a condition that slowly destroys the body's immune system, making it vulnerable to infections. More than 60 million people have been infected with HIV since it was first recognized in 1981. Today, 40 million people around the world are living with HIV.

About Hybridon

Hybridon, Inc. is a leader in the discovery and development of novel therapeutics and diagnostics, based on synthetic DNA. The Company now has four technology platforms: 1) Synthetic immunomodulatory oligonucleotide (IMO) motifs that act to modulate responses of the immune system; 2) Antisense technology which uses synthetic DNA to block the production of disease-causing proteins at the cellular level; 3) Synthetic DNA drug candidates that enhance the antitumor activity of certain marketed anticancer drugs, thereby increasing their effectiveness; and 4) Cyclicon(TM) probes, novel synthetic DNA structures for identifying gene function, which can be used for target validation and drug discovery as well as for PCR-based gene amplification.

This press release contains forward-looking statements concerning Hybridon that involve a number of risks and uncertainties. For this purpose, any statements contained herein that are not statements of historical fact may be deemed to be forward-looking statements. Without limiting the foregoing, the words, "believes," "anticipates," "plans," "expects," "estimates," "intends," "should," "could," "will," "may," and similar expressions are intended to identify forward- looking statements.

There are a number of important factors that could cause Hybridon's actual results to differ materially from those indicated by such forward-looking statements including risks as to whether the patent and patent applications owned or licensed by Hybridon will protect the Company's technology and prevent others from infringing it, and such other important factors as are set forth under the caption "Risk Factors" in Hybridon's Quarterly Report on Form 10-Q for the quarter ended March 31, 2003, which important factors are incorporated herein by reference.

These forward-looking statements should not be relied upon as representing Hybridon's views as of any date subsequent to the date of this release and Hybridon disclaims any obligation to update these forward-looking statements.

This news release contains forward-looking statements. Actual results could vary materially from those expected due to a variety of risk factors, including whether The Immune Response Corporation and Hybridon, Inc. will enter into a license agreement or successfully develop a HIV vaccine, whether The Immune Response Corporation will continue as a going concern and successfully raise proceeds from financing activities sufficient to fund operations and additional clinical trials of REMUNE, the uncertainty of successful completion of any such clinical trials, whether REMUNE will be effective as either a preventive or therapeutic vaccine, whether future trials will be conducted and whether the results of such trials will coincide with the results of REMUNE in preclinical trials. These risks, among others, are set forth in The Immune Response Corporation's SEC filings including, but not limited to, its Annual Report on Form 10-K for the year ended December 31, 2002, and subsequent Quarterly Reports on Form 10-Q. The Immune Response Corporation undertakes no obligation to publicly release the results of any revisions to these forward-looking statements, which may be made to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

REMUNE is a registered trademark of The Immune Response Corporation.

IMO is a registered trademark of Hybridon, Inc.

CONTACT: The Immune Response Corporation

Kathy Lane, 760/771-2236 (Investors)

info@imnr.com

or

for The Immune Response Corporation

Betsey Wann, 916/554-3409 (Media)

Cell: 916/207-2600

or

Hybridon, Inc.

R. Russell Martin, 617/679-5500 ext. 5593 (Investors)

rmartin@hybridon.com

or

Noonan Russo Presence

Robert Stanislaro, 212/845-4268 (Media)

SOURCE: The Immune Response Corporation

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