Exhibit 99.1


REPLIGEN                                        Repligen Corporation
                                                117 Fourth Avenue
                                                Needham, Massachusetts 02494

                                                Telephone:  781-449-9560
                                                Telefax:    781-453-0048


CONTACT:
     WALTER C. HERLIHY, PH.D.                              JONATHAN FASSBERG
                                   (INVESTORS)
     PRESIDENT AND CHIEF EXECUTIVE OFFICER                  THE TROUT GROUP
     (781) 449-9560, EXT. 2000                         (212) 477-9007, EXT. 16


        REPLIGEN ACQUIRES CTLA4 PATENT RIGHTS FROM TOLERANCE THERAPEUTICS

NEEDHAM, MA -- MAY 18, 2000 -- Repligen Corporation (Nasdaq: RGEN) announced
today that it has acquired rights to a U.S. patent application broadly claiming
the use of CTLA4-Ig in immune-based diseases and organ transplantation. The
rights were acquired from Tolerance Therapeutics, LLC, a company formed by Dr.
Jefferey Bluestone, a named inventor on the application.

Dr. Bluestone was the first investigator to demonstrate that CTLA4-Ig was
effective in an animal model of disease. In a seminal paper published in SCIENCE
in 1992 (v. 257, pp. 789-792) Bluestone transplanted insulin-producing cells
from healthy mice into diabetic mice and monitored their ability to control
blood sugar. Untreated mice rejected the transplant within one week; however,
mice treated with CTLA4-Ig for two weeks showed no sign of rejection even after
the CTLA4-Ig treatment was discontinued. These data demonstrated for the first
time that CTLA4-Ig has the potential to be used as an immunosuppresive drug and
that it may induce tolerance - maintenance of the immune suppression after
withdrawal of the drug.

Following these initial observations, CTLA4-Ig has been shown by numerous
research groups to have activity in animal models of solid organ transplantation
(heart and kidney), bone marrow transplantation and autoimmune diseases such as
lupus and multiple sclerosis. In 1999 Repligen announced the results of a Phase
1 clinical trial in which CTLA4-Ig was shown to block rejection (Graft versus
Host Disease) in bone marrow transplantation.

"This acquisition strengthens our CTLA4-Ig patent position," said Walter C.
Herlihy, Ph.D., President and CEO of Repligen. "CTLA4 is acknowledged as a key
mediator of the immune response and may be capable of inducing tolerance, a long
sought goal not possible with current immuosuppressive agents. We are currently
planning expanded testing of CTLA4-Ig in Phase 2 clinical trials."





CTLA4-Ig is a derivative of a natural immune cell protein (CTLA4), which is
capable of blocking immune responses. A key characteristic which distinguishes
CTLA4-Ig from other approaches to immune suppression is its ability to induce
tolerance to specific immune responses. Induction of tolerance may allow for the
treatment of immune disorders without globally compromising the ability of the
immune system to mount a response to an infection.

Additional inventors named on this patent application include scientists from
Bristol-Myers Squibb Corporation (BMS). If a patent is issued, it will be
jointly owned by Repligen and BMS and both parties will have unrestricted rights
to practice the invention without obligation to the other.

Repligen Corporation develops new drugs for autism, organ transplant and cancer.
Repligen also manufactures and markets a set of patented products based on
Protein A, which are used by the pharmaceutical industry to produce therapeutic
antibodies. Its corporate headquarters are located at 117 Fourth Avenue, Needham
MA, 02494. Additional information may be requested from www.repligen.com.

This press release contains forward-looking statements based on current
management expectations. There are certain key factors which could cause future
results to differ materially from those anticipated by management. Such factors
include, but are not limited to: uncertainty in the realization of future
revenues, the uncertain timeline for clinical activity, results of pending or
future clinical trials, the Company's ability to continue to establish
collaborative arrangements with third parties, the Company's ability to maintain
financial stability, the technical risks associated with development and
manufacture of clinical products, the fact that there can be no assurances that
patents relating to the Company's potential products will afford adequate
protection to the Company, the risks of technological change and competition,
and the competitive environment of the biotechnology and pharmaceutical
industries. These factors are more fully discussed in the Company's periodic
filings with the Securities and Exchange Commission.

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