Before you invest, you may want to
review the Portfolio’s prospectus, which contains more information about the Portfolio and its risks. You can find the
Portfolio’s prospectus, reports to shareholders, and other information about the Portfolio online at www.nmseriesfund.com.
You can also get this information at no cost by calling (866) 910-1232 or by sending an e-mail request to
sfprospectus@northwesternmutual.com. The current prospectus and statement of additional information, each dated May 1, 2026,
along with the Portfolio’s most recent annual report dated December 31, 2025, are incorporated by reference into this
Summary Prospectus. The Portfolio’s statement of additional information and annual report may be obtained, free of charge, in the same manner
as the prospectus.
The Securities and Exchange Commission has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.
The investment objective of the Portfolio is to pursue total return using a strategy that seeks to protect against U.S. inflation.
FEES AND EXPENSES OF THE PORTFOLIO
The table below describes the fees and expenses that you may pay when you buy, hold, and
sell interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable
life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity
contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance
policies were included, the fees and expenses shown in the table and the Example would be higher.
Example
This Example is intended to help you compare the cost of investing
in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold
all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same.
The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the
investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would
be:
Portfolio Turnover
The Portfolio pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 42% of
the average value of its portfolio.
PRINCIPAL
INVESTMENT STRATEGIES
The Portfolio invests substantially all of its
assets in investment-grade debt securities. To help protect against U.S. inflation (as measured by the change in the Consumer Price Index over time),
under normal conditions, the Portfolio will invest over 50% of its net assets (plus any borrowings for investment purposes) in inflation-indexed debt
securities. These securities include inflation-indexed U.S. Treasury Securities, inflation-indexed securities issued by U.S. government agencies and
instrumentalities other than the U.S. Treasury, and inflation-indexed securities issued by domestic and foreign corporations and governments, and may
include those located in emerging markets. Inflation-indexed securities are designed to protect the future purchasing power of the money invested in them. The Portfolio also may invest in fixed income securities that are not inflation-indexed. Such investments may include other investment grade debt securities, including collateralized mortgage obligations, mortgage-backed securities, including commercial mortgage-backed securities and agency mortgage-backed securities, and asset-backed securities, including collateralized loan obligations, whether issued by the U.S. government, its agencies or instrumentalities, corporations or other non-governmental issuers, or foreign governments. Investment grade securities are generally securities rated investment grade by major