<PAGE>
MFS(R) INTERMEDIATE INVESTMENT GRADE BOND FUND AND MFS(R) RESEARCH BOND FUND
Supplement to the January 1, 1999 Prospectus and
Statement of Additional Information (As revised February 1, 1999)
The following information should be read in conjunction with the Fund's
Prospectus and Statement of Additional Information ("SAI"), dated January 1,
1999, and contains a description of Class I shares.
Class I shares are available for purchase only by certain investors as
described under the caption "Eligible Purchasers" below.
EXPENSE SUMMARY
<TABLE>
<CAPTION>
<S> <C> <C>
Investment Research
Grade Bond Bond
Fund Fund
Annual Operating Expenses of the Funds (as a percentage of average net assets):
Management Fees (after fee reduction)(1)............................................... 0.00% 0.00%
Rule 12b-1 Fees........................................................................ None None
Other Expenses (after expense limitation)(2) (3)....................................... 0.00% 0.00%
---- -----
Total Operating Expenses (after fee reduction and expense limitation)(4)............... 0.00% 0.00%
</TABLE>
- ------------------
(1) The Adviser will, during the Funds' current fiscal year, waive its right to
receive management fees from each Fund. Absent this waiver, "Management
Fees" would be as follows:
Investment Grade Bond Fund Research Bond Fund
0.50% 0.60%
(2) Each Fund has an expense offset arrangement which reduces the Fund's
custodian fee based upon the amount of cash maintained by the Fund with its
custodian and dividend disbursing agent, and may enter into other such
arrangements and directed brokerage arrangements (which would also have the
effect of reducing the Fund's expenses). Any such fee reductions are not
reflected under "Other Expenses."
(3) The Adviser has agreed to bear the Funds' expenses, such that "Other
Expenses" do not exceed 0.00% per annum of the Fund's average daily net
assets during the current fiscal year. Otherwise, "Other Expenses" for
Investment Grade Bond Fund and Research Bond Fund would be 1.68% and 1.72%
per annum respectively.
(4) Absent any fee waivers and expense reductions, "Total Operating Expenses"
for each Fund would be as follows:
Investment Grade Bond Fund Research Bond Fund
2.18% 2.32%
Example of Expenses
An investor would pay the following dollar amounts of expenses on a $1,000
investment in Class I shares of the Fund, assuming (a) a 5% annual return and
(b) redemption at the end of each of the time periods indicated:
<TABLE>
<CAPTION>
<S> <C> <C>
Period Investment Grade Bond Fund Research Bond Fund
1 year..................... $0 $0
3 years.................... 0 0
</TABLE>
The purpose of the expense table above is to assist investors in
understanding the various costs and expenses that a shareholder of a Fund will
bear directly or indirectly. A more complete description of each Fund's
management fee is set forth under the caption "Management of the Fund" in the
Prospectus.
The "Example" set forth above should not be considered a representation of past
or future expenses of a Fund; actual expenses may be greater or less than those
shown.
<PAGE>
ELIGIBLE PURCHASERS
Class I shares are available for purchase only by the following purchasers
("Eligible Purchasers"):
(i) certain retirement plans established for the benefit of employees of
Massachusetts Financial Services Company ("MFS"), each Fund's investment
adviser, and employees of MFS' affiliates; and
(ii) any fund distributed by MFS Fund Distributors, Inc. ("MFD"), the Fund's
distributor, if the fund seeks to achieve its investment objective by
investing primarily in shares of the Fund and other funds distributed by
MFD.
In no event will the Fund, MFS, MFD or any of their affiliates pay any sales
commissions or compensation to any third party in connection with the sale of
Class I shares; the payment of any such sales commission or compensation would,
under each Fund's policies, disqualify the purchaser as an eligible investor of
Class I shares.
SHARE CLASSES OFFERED BY THE FUND
While each Fund has four classes of shares (Class A, Class B, Class C and
Class I shares), Class A and Class I shares are the only classes presently
available for sale. Class I shares are available for purchase only by Eligible
Purchasers, as defined above, and are described in this Supplement. Class A
shares, Class B shares and Class C shares are described in the Fund's
Prospectus. Class A shares are available for purchase by employees of MFS and
its affiliates and certain of their family members who are residents of The
Commonwealth of Massachusetts, and members of the governing boards of the
various funds sponsored by MFS.
Class A shares are offered at net asset value plus an initial sales charge
up to a maximum of 4.75% of the offering price (or a contingent deferred sales
charge (a "CDSC") upon redemption of 1.00% during the first year in the case of
purchases of $1 million or more and certain purchases by retirement plans), and
are subject to an annual distribution fee and service fee up to a maximum of
0.35% per annum. Class B shares are offered at net asset value without an
initial sales charge but are subject to a CDSC upon redemption (declining from
4.00% during the first year to 0% after six years) and an annual distribution
fee and service fee up to a maximum of 1.00% per annum; Class B shares convert
to Class A shares approximately eight years after purchase. Class C shares are
offered at net asset value without an initial sales charge but are subject to a
CDSC upon redemption of 1.00% during the first year and an annual distribution
fee and service fee up to a maximum of 1.00% per annum. Class I shares are
offered at net asset value without an initial sales charge or CDSC and are not
subject to a distribution or service fee. Class C and Class I shares do not
convert to any other class of shares of the Funds.
OTHER INFORMATION
Eligible Purchasers may purchase Class I shares only directly through MFD.
Eligible Purchasers may exchange Class I shares of a Fund for Class I shares of
any other MFS Fund available for purchase by such Eligible Purchasers at their
net asset value (if available for sale), and may exchange Class I shares of a
Fund for shares of the MFS Money Market Fund (if available for sale), and may
redeem Class I shares of a Fund at net asset value. Distributions paid by a Fund
with respect to Class I shares generally will be greater than those paid with
respect to Class A shares, Class B shares and Class C shares because expenses
attributable to Class A shares, Class B shares and Class C shares generally will
be higher.
The date of this Supplement is January 1, 1999.
(As revised February 1, 1999)
<PAGE>
MFS(R) INTERMEDIATE INVESTMENT GRADE BOND FUND
MFS(R) RESEARCH BOND FUND
Supplement to the January 1, 1999 Prospectus
The sections of the prospectus entitled "Expense Summary" and "Information
Concerning Shares of the Funds - Expenses" are hereby deleted and replaced with
the following:
<TABLE>
<CAPTION>
<S> <C> <C> <C>
1. EXPENSE SUMMARY
Shareholder Transaction Expenses: Class A Class B Class C
Maximum Initial Sales Charge Imposed
on Purchases of each Fund's Shares (as
a percentage of offering price)................................ 4.75% 0.00% 0.00%
Maximum Contingent Deferred Sales Charge (as
a percentage of original purchase price or
redemption proceeds, as applicable)............................ See Below(1) 4.00% 1.00%
</TABLE>
Annual Operating Expenses (as a percentage of average net assets):
Class A Shares
<TABLE>
<CAPTION>
<S> <C> <C>
Investment Grade Research
Bond Fund Bond Fund
Management Fees (after fee reduction)(2).............................. 0.00% 0.00%
Rule 12b-1 Fees (after fee reduction)(3).............................. 0.00% 0.00%
Other Expenses (after expense limitation)(5)(6)....................... 0.00% 0.00%
----- -----
Total Operating Expenses (after fee reduction and
expense limitation)(7)............................................. 0.00% 0.00%
</TABLE>
Class B Shares
<TABLE>
<CAPTION>
<S> <C> <C>
Investment Grade Research
Bond Fund Bond Fund
Management Fees (after fee reduction)(2).............................. 0.00% 0.00%
Rule 12b-1 Fees(4).................................................... 1.00% 1.00%
Other Expenses (after expense limitation)(5)(6)....................... 0.00% 0.00%
----- -----
Total Operating Expenses (after fee reduction
and expense limitation)(7)......................................... 1.00% 1.00%
</TABLE>
Class C Shares
<TABLE>
<CAPTION>
<S> <C> <C>
Investment Grade Research
Bond Fund Bond Fund
Management Fees (after fee reduction)(2).............................. 0.00% 0.00%
Rule 12b-1 Fees(4).................................................... 1.00% 1.00%
Other Expenses (after expense limitation)(5)(6)....................... 0.00% 0.00%
----- -----
Total Operating Expenses (after fee reduction and
expense limitation)(7)............................................. 1.00% 1.00%
</TABLE>
- -----------------
(1) Purchases of $1 million or more and certain purchases by retirement plans
are not subject to an initial sales charge; however, a contingent deferred
sales charge ("CDSC") of 1% will be imposed on such purchases in the event
of certain redemption transactions within 12 months
<PAGE>
following such purchases. See "Information Concerning Shares of the
Funds- Purchases" below. (2) The Adviser intends, during the Funds'
current fiscal year, to waive its right to receive management fees from
each Fund. Absent this waiver, "Management Fees" would be as follows:
Investment Grade Research
Bond Fund Bond Fund
0.50% 0.60%
(3) Each Fund has adopted a distribution plan for its shares in accordance
with Rule 12b-1 under the Investment Company Act of 1940, as amended (the
"1940 Act") (the "Distribution Plan"), which provides that it will pay
distribution/service fees aggregating up to (but not necessarily all of)
0.35% per annum of the average daily net assets attributable to Class A
shares. Class A distribution and service fees under the Distribution Plan
are currently being waived on a voluntary basis and, while they may be
imposed at the discretion of MFD at any time, MFD currently intends to
waive these fees during the Funds' current fiscal year. Distribution
expenses paid under the Plan, together with the initial sales charge, may
cause long-term shareholders to pay more than the maximum sales charge
that would have been permissible if imposed entirely as an initial sales
charge. See "Information Concerning Shares of the Funds - Distribution
Plan" below.
(4) Each Fund's Distribution Plan provides that it will pay
distribution/service fees aggregating up to (but not necessarily all of)
1.00% per annum of the average daily net assets attributable to Class B
shares and Class C shares, respectively. Distribution expenses paid under
the Distribution Plan with respect to Class B or Class C shares, together
with any CDSC payable upon redemption of Class B and Class C shares, may
cause long-term shareholders to pay more than the maximum sales charge
that would have been permissible if imposed entirely as an initial sales
charge. See "Information Concerning Shares of the Funds Distribution Plan"
below.
(5) The Adviser has agreed to bear the Fund's expenses, such that "Other
Expenses" do not exceed 0.00% per annum of each Fund's average daily net
assets during the current fiscal year. Otherwise, "Other Expenses" for
each class of shares for Investment Grade Bond Fund and Research Bond Fund
would be 1.68% and 1.72% per annum, respectively.
(6) Each Fund has an expense offset arrangement which reduces the Fund's
custodian fee based upon the amount of cash maintained by the Fund with
its custodian and dividend disbursing agent, and may enter into other such
arrangements and directed brokerage arrangements (which would also have
the effect of reducing the Fund's expenses). Any such fee reductions are
not reflected under "Other Expenses."
(7) Absent any fee waivers and expense reductions, "Total Operating Expenses,"
expressed as a percentage of average daily net assets, would be as
follows:
Investment Grade Research
Bond Fund Bond Fund
Class A......................... 2.53% 2.67%
Class B......................... 3.18% 3.32%
Class C......................... 3.18% 3.32%
<PAGE>
Example of Expenses
An investor would pay the following dollar amounts of expenses on a $1,000
investment in each Fund, assuming (a) 5% annual return and unless otherwise
noted, (b) redemption at the end of each of each of the time periods indicated:
Class A Shares
Investment Grade Research
Bond Fund Bond Fund
1 year .......................... $48 $48
3 years.......................... $48 $48
Class B Shares
(Assumes Redemption)
Investment Grade Research
Bond Fund Bond Fund
1 year ........................... $50 $50
3 years........................... $62 $62
Class B Shares
(Assumes No Redemption)
Investment Grade Research
Bond Fund Bond Fund
1 year ........................... $10 $10
3 years........................... $32 $32
Class C Shares
(Assumes Redemption)
Investment Grade Research
Bond Fund Bond Fund
1 year ............................. $20 $20
3 years............................. $32 $32
Class C Shares
(Assumes No Redemption)
Investment Grade Research
Bond Fund Bond Fund
1 year ............................. $10 $10
3 years............................. $32 $32
The purpose of the expense table above is to assist investors in understanding
the various costs and expenses that a shareholder of a Fund will bear directly
or indirectly. More complete descriptions of the following
<PAGE>
Fund expenses are set forth in the following sections: (i) varying sales charges
on share purchases - "Purchases"; (ii) varying CDSCs - "Purchases"; (iii)
management fees - "Investment Adviser"; and (iv) Rule 12b-1 (i.e., distribution
plan) fees - "Distribution Plan."
The "Example" set forth above should not be considered a representation of past
or future expenses of the Fund; actual expenses may be greater or less than
those shown.
2. INFORMATION CONCERNING SHARES OF THE FUNDS - EXPENSES
Effective as of February 1, 1999, the following language shall replace the
paragraph in the section entitled "Information Concerning Shares of the Fund -
Expenses" on Page 24 of the Prospectus as follows:
Subject to termination or revision at the sole discretion of MFS, MFS has
agreed to bear the Fund's expenses such that the Fund's "Other Expenses," which
are defined to include all Fund expenses (after taking into effect any
compensating balance and offset arrangements), except for management fees, Rule
12b-1 fees, taxes, extraordinary expenses, brokerage and transaction costs and
class specific expenses, do not exceed 0.00% per annum of its average daily net
assets (the "Maximum Percentage"). The obligation of MFS to bear the Fund's
Other Expenses pursuant to this arrangement may be terminated at MFS' discretion
at anytime.
The date of this Supplement is February 1, 1999.
