Guggenheim Defined Portfolios, Series 2121 S-6/A Registration of securities by unit investment trust (amended)

 EXHIBIT 4.1

Consent of Independent Registered Public Accounting Firm

We consent to the reference to our firm under the caption “Experts-Independent Registered Public Accounting Firm” and to the use of our report dated April 29, 2021 in the Amendment No. 1 to the Registration Statement (File No. 333-253251) and related Prospectus of Guggenheim Defined Portfolios, Series 2121.

/s/ Grant Thornton LLP____________

GRANT THORNTON LLP

Chicago, Illinois

April 29, 2021