<TABLE> <S> <C>
<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
CONDENSED FINANCIAL STATEMENTS OF AVANT IMMUNOTHERAPEUTICS, INC. FOR THE SIX
MONTHS ENDED JUNE 30, 2000 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<CURRENCY> U.S. DOLLARS
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> DEC-31-2000
<PERIOD-START> JAN-01-2000
<PERIOD-END> JUN-30-2000
<EXCHANGE-RATE> 1
<CASH> 16,058,500
<SECURITIES> 0
<RECEIVABLES> 0
<ALLOWANCES> 0
<INVENTORY> 0
<CURRENT-ASSETS> 16,946,000
<PP&E> 4,798,100
<DEPRECIATION> (3,725,500)
<TOTAL-ASSETS> 21,517,600
<CURRENT-LIABILITIES> 1,979,000
<BONDS> 0
0
0
<COMMON> 50,200
<OTHER-SE> 16,600,300
<TOTAL-LIABILITY-AND-EQUITY> 21,517,600
<SALES> 0
<TOTAL-REVENUES> 307,700
<CGS> 0
<TOTAL-COSTS> 5,698,800
<OTHER-EXPENSES> 0
<LOSS-PROVISION> 0
<INTEREST-EXPENSE> 0
<INCOME-PRETAX> (4,847,300)
<INCOME-TAX> 0
<INCOME-CONTINUING> (4,847,300)
<DISCONTINUED> 0
<EXTRAORDINARY> 0
<CHANGES> 0
<NET-INCOME> (4,847,300)
<EPS-BASIC> (0.10)
<EPS-DILUTED> (0.10)
</TABLE>