UPDATED: February 16, 2012, at 9:55 p.m.

Allan M. Brandt announced Wednesday that he will be stepping down from his role as dean of the Graduate School of Arts and Sciences due to health considerations stemming from a recently diagnosed illness.

“I am deeply grateful for the opportunity I have had to know and collaborate with all of you,” Brandt wrote in an email to his GSAS colleagues. “The core mission you have worked hard to support will continue unchanged.”

Noting his leadership capacity and positive energy, faculty members said news of Brandt’s decision was unexpected and sobering.

“We were devastated,” said Garth O. McCavana, GSAS dean for student affairs. “We were very sad...that he is stepping down, because he is such a great leader.”

Faculty of Arts and Sciences Dean Michael D. Smith highlighted Brandt’s accomplishments in pedagogical innovation, diversity at the Ph.D. level, and student support in an email that he sent to FAS faculty members and staff on Thursday.

“In the five admissions cycles he has overseen, the quality of our entering Ph.D. and A.M. [Masters of Arts] classes has risen to unprecedented heights, as have the number of applications to GSAS,” Smith wrote.

In addition to developing the student body of GSAS, Brandt launched Graduate Seminars in General Education—a program through which graduate students help design undergraduate courses.

“He sees undergraduate and graduate education as part of the same seamless fit,” said classics professor Richard F. Thomas, who serves as the classics department’s director of graduate studies.

Colleagues praised Brandt for increasing the accessibility of graduate education at Harvard.

Applications to GSAS—including those from underrepresented minorities—have increased consistently during his tenure.

And in the midst of the financial downturn since 2008, Brandt has continued to fund graduate stipends and student support programs.

“He has created an unbelievably collaborative and communicative environment among the directors of graduate studies,” said Marie D. Dahleh, director of graduate studies for engineering and applied sciences. “We’ve been getting together more frequently...to discuss concerns that go beyond departmental boundaries.”

Brandt also made an effort to interact with the Graduate Student Council—the school’s representative student body.

Council President Cammi N. Valdez said that Brandt’s dedication to graduate students went “above and beyond” the call of duty. “Finding someone who is as committed to graduate students as Dean Brandt is rare,” Valdez said.