; and (2) require such auction to include a process that minimizes the risk to the Federal Government of the Federal guarantee involved by allowing bidders for a BioBond to compete against each other by bidding on the percentage of the Federal guarantee under subsection (b) with respect to the BioBond, with the bid for the lowest percentage winning the auction, taking into account other terms and conditions set by the issuer to ensure the lowest total cost to the Federal Government. (d) Portfolio diversity With respect to an issuance of BioBonds and the loans collateralizing such issuance, not greater than 15 percent of the principal amount of such issuance may relate to a group of related diseases or disabilities (as defined by the Secretary of Health and Human Services). (e) Prioritization of taxpayer interests All proceeds received from Biobond issuance shall be invested in obligations of the Federal Government in order to ensure a revenue stream in addition to loan repayment that protects taxpayers. All BioBonds shall be structured to give first priority to protecting the interests of the United States by ensuring that— (1) all cash proceeds received from the repayment of a BioBond and income derived from loan-proceed reinvestment are first used to reduce the amount of principal guaranteed by the Secretary of the Treasury; (2) the Secretary of the Treasury has a senior claim on all assets and collateral under a BioBond to the extent the guarantee provided by the Secretary is not extinguished