Exhibit 10.10  AGREEMENT
TO PARTICIPATE IN THE FACET
BIOTECH CORPORATION RETENTION
AND SEVERANCE PLAN Effective December 18, 2008  In consideration of the benefits provided by the Facet
Biotech Corporation Retention and Severance Plan (the Plan), the undersigned employee of Facet Biotech
Corporation (the Company)
and the Company agree that, as of the date written below, the undersigned shall
become a Participant in the Plan and shall be fully bound by and subject to all
of its provisions, subject to the modification of Section 4.1(b)(4) thereof,
titled Involuntary Termination Absent a Change in Control  Severance Benefits
 Acceleration of Vesting of Equity Awards, set forth in Appendix A attached
hereto.  All references to a Participant
in the Plan shall be deemed to refer to the undersigned.  The undersigned employee acknowledges that the Plan
confers significant legal rights and may also constitute a waiver of rights
under other agreements with the Company; that the Company has encouraged the
undersigned to consult with the undersigneds personal legal and financial
advisors; and that the undersigned has had adequate time to consult with the
undersigneds advisors before executing this agreement.  The undersigned employee acknowledges that he or she
has received a copy of the Plan and has read, understands and is familiar with
the terms and provisions of the Plan. 
The undersigned employee further acknowledges that (1) by accepting
the arbitration provision set forth in Section 13 of the Plan, the undersigned
is waiving any right to a jury trial in the event of any dispute covered by
such provision and (2) except as otherwise established in an employment
agreement between a member of the Company Group and the undersigned, the
employment relationship between the undersigned and the Company Group is an at-will
relationship.  Executed on December 18, 2008.  Participant
  
  Facet Biotech Corporation/s/ Andrew Guggenhime
  
  By:
  /s/ Francis SarenaAndrew GuggenhimeAddress:
  
  Name:
  Francis Sarnea[***]Title:
  Vice President, General
  Counsel and Secretary  1


APPENDIX
A TO AGREEMENT TO PARTICIPATE IN THE FACET BIOTECH CORPORATION RETENTION AND SEVERANCE PLAN OF Andrew Guggenhime  For all purposes of the participation of Andrew Guggenhimein
the Facet Biotech Corporation Retention and Severance Plan (the Plan), Section 4.1(b)(4) of
the Plan shall be deemed to include the following additional subsection (vi):  (vi)Additional
Acceleration of Vesting of Stock Options Upon Involuntary Termination Absent a
Change in Control Occurring On or Before December 31, 2009.  If the Participants Involuntary Termination
Absent a Change in Control occurs on or before December 31, 2009, then the
additional vesting of each stock option held by the Participant to which the
Participant is entitled, as determined in accordance with subsection (i),
subsection (ii) or subsection (iii) above, as applicable, shall
be further increased by an amount equal to twenty-five percent (25%) of the
total number of shares originally subject to such stock option, provided that
the resulting total number of vested shares subject to such stock option shall
not exceed one hundred percent (100%) of the total number of shares originally
subject to such stock option.  For the
purposes of this subsection, the total number of shares originally subject to
such stock option shall take into account any adjustments for changes in the
capital structure of the Company determined in accordance with the equity award
plan and award agreement governing such stock option.  2