SNLN Highland iBoxx Senior Loan

Principal Risks

When you sell Fund shares, they may be worth less than what you paid for them. Consequently, you can lose money by investing in the Fund. No assurance can be given that the Fund will achieve its investment objective, and investment results may vary substantially over time and from period to period. An investment in the Fund is not appropriate for all investors.

An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.

Industry Concentration-Healthcare Companies Risk is the risk that because the Fund normally invests at least 80% of the value of its assets in healthcare companies, the Fund’s performance largely depends on the overall condition of the healthcare industry and the Fund is more susceptible to economic, political and regulatory risks or other occurrences associated with the healthcare industry than a fund that does not focus on healthcare companies. Healthcare companies, including biotechnology companies and pharmaceutical firms, may be significantly affected by product obsolescence, thin capitalization, limited product lines and markets, civil liability claims and legislative or regulatory activities, among other factors.

Biotechnology Industry Risk is the risk that the Fund’s investments in biotechnology companies is highly dependent on the development, procurement and/or marketing of drugs and may be valued based on the potential or actual performance of a limited number of products. A biotechnology company’s valuation could be affected if one of its products proves unsafe, ineffective or unprofitable. Such companies may also be characterized by thin capitalization and limited markets, financial resources or personnel. The stock prices of companies involved in the biotechnology sector have been and will likely continue to be extremely volatile.

Convertible Securities Risk is the risk that the market value of convertible securities may fluctuate due to changes in, among other things, interest rates; other economic conditions; industry fundamentals; market sentiment; the issuer’s operating results, financial statements, and credit ratings; and the market value of the underlying common or preferred stock.

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Counterparty Risk is the risk that a counterparty (the other party to a transaction or an agreement or the party with whom the Fund executes transactions) to a transaction with the Fund may be unable or unwilling to make timely principal, interest or settlement payments, or otherwise honor its obligations.

Credit Risk is the risk that the issuers of certain securities or the counterparties of a derivatives contract or repurchase contract might be unable or unwilling (or perceived as being unable or unwilling) to make interest and/or principal payments when due, or to otherwise honor its obligations. Debt securities are subject to the risk of non-payment of scheduled interest and/or principal. Non-payment would result in a reduction of income to the Fund, a reduction in the value of the obligation experiencing non-payment and a potential decrease in the net asset value (“NAV”) of the Fund.

Currency Risk is the risk that fluctuations in exchange rates will adversely affect the value of the Fund’s foreign currency holdings and investments denominated in foreign currencies.

Debt Securities Risk is the risk associated with the fact that the value of debt securities typically changes in response to various factors, including, by way of example, market-related factors (such as changes in interest rates or changes in the risk appetite of investors generally) and changes in the actual or perceived ability of the issuer (or of issuers generally) to meet its (or their) obligations. During periods of rising interest rates, debt securities generally decline in value. Conversely, during periods of falling interest rates, debt securities generally rise in value. This kind of market risk is generally greater for funds investing in debt securities with longer maturities.

Derivatives Risk is a combination of several risks, including the risks that: (1) an investment in a derivative instrument may not correlate well with the performance of the securities or asset class to which the Fund seeks exposure, (2) derivative contracts, including options, may expire worthless and the use of derivatives may result in losses to the Fund, (3) a derivative instrument entailing leverage may result in a loss greater than the principal amount invested, (4) derivatives not traded on an exchange may be subject to credit risk, for example, if the counterparty does not meet its obligations (see also “Counterparty Risk”), and (5) derivatives not traded on an exchange may be subject to liquidity risk and the related risk that the instrument is difficult or impossible to value accurately. As a general matter, when the Fund establishes certain derivative instrument positions, such as certain futures, options and forward contract positions, it will segregate liquid assets (such as cash, U.S. Treasury bonds or commercial paper) equivalent to the Fund’s outstanding obligations under the contract or in connection with the position. In addition, changes in laws or regulations may make the use of derivatives more costly, may limit the availability of derivatives, or may otherwise adversely affect the use, value or performance of derivatives. The Fund’s ability to pursue its investment strategy, including its strategy of investing in certain derivative instruments, may be limited to or adversely affected by the Fund’s intention to qualify as a RIC, and its strategy may bear adversely on its ability to so qualify.

Emerging Markets Risk is the risk of investing in securities of issuers tied economically to emerging markets, which entails all of the risks of investing in securities of non-U.S. issuers detailed below under “Non-U.S. Securities Risk” to a heightened degree. These heightened risks include: (i) greater risks of expropriation, confiscatory taxation, nationalization, and less social, political and economic stability; (ii) the smaller size of the markets for such securities and a lower volume of trading, resulting in lack of liquidity and in price volatility; (iii) greater fluctuations in currency exchange rates; and (iv) certain national policies that may restrict the Fund’s investment opportunities, including restrictions on investing in issuers or industries deemed sensitive to relevant national interests.

Equity Securities Risk is the risk that stock prices will fall over short or long periods of time. In addition, common stocks represent a share of ownership in a company, and rank after bonds and preferred stock in their claim on the company’s assets in the event of bankruptcy.

Exchange-Traded Funds (“ETF”) Risk is the risk that the price movement of an ETF may not exactly track the underlying index and may result in a loss. In addition, shareholders bear both their proportionate share of the Fund’s expenses and similar expenses of the underlying investment company when the Fund invests in shares of another investment company.

Fixed Income Market Risk is the risk that fixed income markets may, in response to governmental intervention, economic or market developments (including potentially a reduction in the number of broker-dealers willing to engage in market-making activity), or other factors, experience periods of increased volatility and reduced liquidity. During those periods, the Fund may experience increased levels of shareholder redemptions, and may have to sell securities at times when it would otherwise not do so, and at unfavorable prices. Fixed income securities may be difficult to value during such periods.

Hedging Risk is the risk that, although intended to limit or reduce investment risk, hedging strategies may also limit or reduce the potential for profit. There is no assurance that hedging strategies will be successful.

High Yield Debt Securities Risk is the risk that below investment grade securities or unrated securities of similar credit quality (commonly known as “high yield securities” or “junk securities”) are more likely to default than higher rated securities. The Fund’s ability to invest in high-yield debt securities generally subjects the Fund to greater risk than

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Highland Funds I Summary Prospectus

October 31, 2019

securities with higher ratings. Such securities are regarded by the rating organizations as predominantly speculative with respect to capacity to pay interest and repay principal in accordance with the terms of the obligation. The market value of these securities is generally more sensitive to corporate developments and economic conditions and can be volatile. Market conditions can diminish liquidity and make accurate valuations difficult to obtain.

Illiquid and Restricted Securities Risk is the risk that the Adviser may not be able to sell illiquid or restricted securities, such as securities issued pursuant to Rule 144A of the Securities Act of 1933, at the price it would like or may have to sell them at a loss. Securities of non-U.S. issuers, and emerging or developing markets securities in particular, are subject to greater liquidity risk.

Interest Rate Risk is the risk that fixed income securities will decline in value because of changes in interest rates. When interest rates decline, the value of fixed rate securities already held by the Fund can be expected to rise. Conversely, when interest rates rise, the value of existing fixed rate portfolio securities can be expected to decline. A fund with a longer average portfolio duration will be more sensitive to changes in interest rates than a fund with a shorter average portfolio duration.

Leverage Risk is the risk associated with the use of leverage for investment purposes to create opportunities for greater total returns. Any investment income or gains earned with respect to the amounts borrowed that are in excess of the interest that is due on the borrowing will augment the Fund’s income. Conversely, if the investment performance with respect to the amounts borrowed fails to cover the interest on such borrowings, the value of the Fund’s shares may decrease more quickly than would otherwise be the case. Interest payments and fees incurred in connection with such borrowings will reduce the amount of net income available for payment to Fund shareholders.

Liquidity Risk is the risk that low trading volume, lack of a market maker, large position size, or legal restrictions (including daily price fluctuation limits or “circuit breakers”) limits or prevents the Fund from selling particular securities or unwinding derivative positions at desirable prices. At times, a major portion of any portfolio security may be held by relatively few institutional purchasers. Even if the Fund considers such securities liquid because of the availability of an institutional market, such securities may become difficult to value or sell in adverse market or economic conditions.

Management Risk is the risk associated with the fact that the Fund relies on the Adviser’s ability to achieve its investment objective. The Adviser may be incorrect in its assessment of the intrinsic value of the companies whose securities the Fund holds, which may result in a decline in the value of Fund shares and failure to achieve its investment objective. The Fund’s portfolio managers use qualitative analyses and/or models. Any imperfections or limitations in such analyses and models could affect the ability of the portfolio managers to implement strategies.

Mid-Cap Company Risk is the risk that investing in securities of mid-cap companies may entail greater risks than investments in larger, more established companies. Mid-cap companies tend to have more narrow product lines, more limited financial resources and a more limited trading market for their stocks, as compared with larger companies. As a result, their stock prices may decline significantly as market conditions change.

Non-Diversification Risk is the risk that an investment in the Fund could fluctuate in value more than an investment in a diversified fund. As a non-diversified fund for purposes of the 1940 Act, the Fund may invest a larger portion of its assets in the securities of fewer issuers than a diversified fund. The Fund’s investment in fewer issuers may result in the Fund’s shares being more sensitive to the economic results of those issuers. An investment in the Fund could fluctuate in value more than an investment in a diversified fund. This risk is particularly pronounced for the Fund, which from time to time may own a very small number of positions, each of which is a relatively large portion of the Fund’s portfolio.

Non-U.S. Securities Risk is the risk associated with investing in non-U.S. issuers. Investments in securities of non-U.S. issuers involve certain risks not involved in domestic investments (for example, fluctuations in foreign exchange rates (for non-U.S. securities not denominated in U.S. dollars); future foreign economic, financial, political and social developments; nationalization; exploration or confiscatory taxation; smaller markets; different trading and settlement practices; less governmental supervision; and different accounting, auditing and financial recordkeeping standards and requirements) that may result in the Fund experiencing more rapid and extreme changes in value than a fund that invests exclusively in securities of U.S. companies. These risks are magnified for investments in issuers tied economically to emerging markets, the economies of which tend to be more volatile than the economies of developed markets. In addition, certain investments in non-U.S. securities may be subject to foreign withholding and other taxes on interest, dividends, capital gains or other income or proceeds. Those taxes will reduce the Fund’s yield on any such securities. See the “Taxation” section below.

Operational and Technology Risk is the risk that cyber-attacks, disruptions, or failures that affect the Fund’s service providers, counterparties, market participants, or issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Options Risk is the risk associated with investments in options. Options, such as covered calls and covered puts, are subject to the risk that significant differences between the

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securities and options markets could result in an imperfect correlation between these markets.

Portfolio Turnover Risk is the risk that the Fund’s high portfolio turnover will increase the Fund’s transaction costs and may result in increased realization of net short-term capital gains (which are taxable to shareholders as ordinary income when distributed to them), higher taxable distributions and lower after-tax performance. During the last two fiscal years, the Fund experienced a high portfolio turnover rate.

Prepayment Risk is the risk that during periods of falling interest rates, issuers of debt securities may repay higher rate securities before their maturity dates. This may cause the Fund to lose potential price appreciation and to be forced to reinvest the unanticipated proceeds at lower interest rates. This may adversely affect the NAV of the Fund’s shares.

Risk of Substantial Redemptions is the risk that if substantial numbers of shares in the Fund were to be redeemed at the same time or at approximately the same time, the Fund might be required to liquidate a significant portion of its investment portfolio quickly to meet the redemptions. The Fund might be forced to sell portfolio securities at prices or at times when it would otherwise not have sold them.

Securities Lending Risk. The Fund may make secured loans of its portfolio securities. Any decline in the value of a portfolio security that occurs while the security is out on loan is borne by the Fund, and will adversely affect performance. Also, there may be delays in recovery of securities loaned, losses in the investment of collateral, and loss of rights in the collateral should the borrower of the securities fail financially while holding the security.

Securities Market Risk is the risk that the value of securities owned by the Fund may go up or down, sometimes rapidly or unpredictably, due to factors affecting particular companies or the securities markets generally. A general downturn in the securities market may cause multiple asset classes to decline in value simultaneously. Many factors can affect this value and you may lose money by investing in the Fund.

Senior Loans Risk is the risk associated with Senior Loans, which are typically below investment grade and are considered speculative because of the credit risk of their issuers. As with any debt instrument, Senior Loans are generally subject to the risk of price declines and to increases in interest rates, particularly long-term rates. Senior loans are also subject to the risk that, as interest rates rise, the cost of borrowing increases, which may increase the risk of default. In addition, the interest rates of floating rate loans typically only adjust to changes in short-term interest rates; long-term interest rates can vary dramatically from short-term interest rates. Therefore, Senior Loans may not mitigate price declines in a rising long-term interest rate environment. The secondary market for loans is generally less liquid than the market for higher grade debt. Less liquidity in the secondary trading market could adversely affect the price at which the Fund could sell a loan, and could adversely affect the NAV of the Fund’s shares. The volume and frequency of secondary market trading in such loans varies significantly over time and among loans. Although Senior Loans in which the Fund will invest will often be secured by collateral, there can be no assurance that liquidation of such collateral would satisfy the borrower’s obligation in the event of a default or that such collateral could be readily liquidated.

Short Sales Risk is the risk of loss associated with any appreciation on the price of a security borrowed in connection with a short sale. The Fund may engage in short sales that are not made “against-the-box,” which means that the Fund may sell short securities even when they are not actually owned or otherwise covered at all times during the period the short position is open. Short sales that are not made “against-the-box” involve unlimited loss potential since the market price of securities sold short may continuously increase.

Small-Cap Company Risk is the risk that investing in the securities of small-cap companies either directly or indirectly through investments in ETFs, closed-end funds or mutual funds (“Underlying Funds”) may pose greater market and liquidity risks than larger, more established companies, because of limited product lines and/or operating history, limited financial resources, limited trading markets, and the potential lack of management depth. In addition, the securities of such companies are typically more volatile than securities of larger capitalization companies.

Swaps Risk involves both the risks associated with an investment in the underlying investments or instruments (including equity investments) and counterparty risk. In a standard over-the-counter (“OTC”) swap transaction, two parties agree to exchange the returns, differentials in rates of return or some other amount calculated based on the “notional amount” of predetermined investments or instruments, which may be adjusted for an interest factor. Swaps can involve greater risks than direct investments in securities, because swaps may be leveraged and OTC swaps are subject to counterparty risk (e.g., the risk of a counterparty’s defaulting on the obligation or bankruptcy), credit risk and pricing risk (i.e., swaps may be difficult to value). Swaps may also be considered illiquid. Certain swap transactions, including interest rate swaps and index credit default swaps, may be subject to mandatory clearing and exchange trading, although the swaps in which the Fund will invest are not currently subject to mandatory clearing and exchange trading. The use of swaps is a highly specialized activity which involves investment techniques, risk analyses and tax planning different from those associated with ordinary portfolio securities transactions. The value of swaps, like many other derivatives, may move in unexpected ways and may result in losses for the Fund.

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Highland Funds I Summary Prospectus

October 31, 2019