Exhibit 4.20











|Affimed
                           GmbH Affimed N.V. Im Neuenheimer Feld 582 69120 Heidelberg
        
        
        
        Perceptive Credit
        Opportunities Fund, LP
        Mr. Edelman
        
        51 Astor Place
        
        10th Floor
        
        New York
        New York 10003USA | 
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 
|                                                                                                                                                                                                                                                                                                                      | 

March
29, 2016







Term Facility Agreement dated
July 24, 2014



Waiver regarding a Development
Milestone (Clause 19.2)





Dear Mr. Edelman,



We are writing to you on behalf
of Affimed GmbH and on behalf of Affimed N.V. As discussed with Sam Chawla and Sandeep Dixit, we are contemplating to discuss
with you the structure and certain terms of the Term Facility Agreement between Affimed GmbH (formerly Affimed Therapeutics AG,
the “Company”) as Borrower, Affimed N.V. as Guarantor and funds managed by Perceptive Advisors LLC –
currently Perceptive Credit Opportunities Fund, LP and PCOF Phoenix II Fund, LP – as Lenders, dated July 24, 2014 (as amended
from time to time, the “Agreement”). In connection therewith and in order to better reflect the Company’s
current development strategy, the Parties might also agree on development milestones other or different than those currently set-out
in Schedule 6 to the Agreement.



To allow
for sufficient time for the above mentioned discussions, the Lender hereby agrees to waive, up and until September 30, 2016, any
rights it may have under Section 21.13 (Events of Default, Other obligations) of the Agreement in connection with 19.2 (Development
of Milestones) and Schedule 6, No. 2 of the Agreement. For the avoidance of doubt, all other rights and obligations of the Parties
under the Agreement remain unaffected, in particular, but not limited to, the Lender’s rights under Section 21.13 (Events
of Default, Other obligations) in case of any non-compliance with any provision of the Finance Documents other than 19.2 (Development
of Milestones), Schedule 6, No. 2.



Terms defined in the Agreement
have the same meaning in this letter, unless otherwise defined herein. This letter is governed by German law.











|Affimed GmbH                |                          |                                           |                                      
|--------------------------- | ------------------------ | ----------------------------------------- | -------------------------------------
|Affimed
    N.V.            | Phone:+49 6221 65307 0   | Bankverbindung: Deutsche
    Bank         | Geschäftsführer
    der Affimed GmbH:
|Technologiepark             | Fax:+49 6221 65307 49    | IBAN  DE
    5867 2700 0300 1408 0600     | Dr. Adi Hoess                        
|Im
    Neuenheimer Feld 582 | www.affimed.com          | BIC  DEUTDESM672                          | Dr. Florian Fischer                  
|69120
    Heidelberg        | E-Mail: info@affimed.com | Sitz der Gesellschaft:
    Heidelberg     | Dr. Jens-Peter Marschner             
|Germany                     |                          | Registergericht: Amtsgericht
    Mannheim | Dr. Martin Treder                    
|                            |                          | HRB 721206 –
    VAT.Nr.: DE 206700144    | Dr. Jörg Windisch                    















Please return countersigned copies
of this letter to Affimed GmbH and to Affimed N.V. at your earliest convenience.



Kind regards





On behalf of Affimed GmbH:



March 29, 2016



Date



|/s/ Adi Hoess     |  | /s/
    Florian Fischer
|----------------- |  | -----------------------
|Dr.
    Adi Hoess |  | Dr. Florian Fischer    
|CEO               |  | CFO                    









On behalf of Affimed N.V.



March 29, 2016



Date



|/s/ Adi Hoess     |  | /s/
    Florian Fischer
|----------------- |  | -----------------------
|Dr.
    Adi Hoess |  | Dr. Florian Fischer    
|CEO               |  | CFO                    













|Affimed GmbH                |                          |                                           |                                      
|--------------------------- | ------------------------ | ----------------------------------------- | -------------------------------------
|Affimed
    N.V.            | Phone:+49 6221 65307 0   | Bankverbindung: Deutsche
    Bank         | Geschäftsführer
    der Affimed GmbH:
|Technologiepark             | Fax:+49 6221 65307 49    | IBAN  DE
    5867 2700 0300 1408 0600     | Dr. Adi Hoess                        
|Im
    Neuenheimer Feld 582 | www.affimed.com          | BIC  DEUTDESM672                          | Dr. Florian Fischer                  
|69120
    Heidelberg        | E-Mail: info@affimed.com | Sitz der Gesellschaft:
    Heidelberg     | Dr. Jens-Peter Marschner             
|Germany                     |                          | Registergericht: Amtsgericht
    Mannheim | Dr. Martin Treder                    
|                            |                          | HRB 721206 –
    VAT.Nr.: DE 206700144    | Dr. Jörg Windisch                    















Accepted and Agreed



On behalf of Perceptive Credit
Opportunities Fund, LP



And PCOF Phoenix II Fund, LP



March 29, 2016



Date





|/s/ Joseph Edelman
|------------------





Joseph Edelman



























|Affimed GmbH                |                          |                                           |                                      
|--------------------------- | ------------------------ | ----------------------------------------- | -------------------------------------
|Affimed
    N.V.            | Phone:+49 6221 65307 0   | Bankverbindung: Deutsche
    Bank         | Geschäftsführer
    der Affimed GmbH:
|Technologiepark             | Fax:+49 6221 65307 49    | IBAN  DE
    5867 2700 0300 1408 0600     | Dr. Adi Hoess                        
|Im
    Neuenheimer Feld 582 | www.affimed.com          | BIC  DEUTDESM672                          | Dr. Florian Fischer                  
|69120
    Heidelberg        | E-Mail: info@affimed.com | Sitz der Gesellschaft:
    Heidelberg     | Dr. Jens-Peter Marschner             
|Germany                     |                          | Registergericht: Amtsgericht
    Mannheim | Dr. Martin Treder                    
|                            |                          | HRB 721206 –
    VAT.Nr.: DE 206700144    | Dr. Jörg Windisch