Market Interest Rates: Rising interest rates generally decrease bond prices, as newly issued bonds offer higher yields, making existing lower-yielding bonds (like those held in SPNNX.US) less attractive.

Credit Quality of Holdings: Downgrades in the credit ratings of bonds held by the fund can negatively impact its price, as the perceived risk of default increases.

Economic Conditions: A weakening economy could lead to increased default rates on bonds, affecting the fund's value. Strong economic growth might put upward pressure on interest rates.

Inflation Expectations: Rising inflation erodes the purchasing power of fixed income, prompting investors to demand higher yields, thus lowering bond prices in SPNNX.US.

Supply and Demand for Fund Shares: Increased demand for SPNNX.US shares can drive up its price, while higher supply (due to increased selling) can push it down.

Fund Management Decisions: The fund manager's decisions on which bonds to buy or sell, and how to manage the fund's duration and credit risk, can impact its performance and price.