<PAGE>   1

                                                                   Exhibit 10.27

                                            ***Text Omitted and Filed Separately
                                                Confidential Treatment Requested
                                          Under 17 C.F.R. Sections 200.80(b)(4),
                                                            200.83 and 240.24b-2



                       FIRST AMENDMENT TO LEASE AGREEMENT


        THIS FIRST AMENDMENT TO LEASE AGREEMENT (this "Amendment") is made as of
November 10, 1998, by and between HMS GATEWAY OFFICE L.P., a Delaware limited
partnership ("Landlord"), and COULTER PHARMACEUTICAL, INC., a Delaware
corporation. ("Tenant").

                                    RECITALS

        A. Landlord and Tenant have previously entered into that certain Lease
Agreement dated November 7, 1997 (the "Lease").

        B. Pursuant to the Lease, Tenant leased from Landlord approximately
[...***...]* square feet (the "Original Premises"), which Original Premises
constitute the entire building commonly known as 600 Gateway Boulevard, South
San Francisco, California (the "Building").

        C. Landlord and Tenant desire to amend the Lease to reflect the
expansion of the Original Premises, all upon and subject to the terms, covenants
and conditions hereinafter set forth.

                                    AGREEMENT

        NOW THEREFORE, in consideration of the agreements of Landlord and Tenant
herein contained and other valuable consideration, the receipt and adequacy of
which are hereby acknowledged, Landlord and Tenant hereby agree as follows:

        1. DEFINED TERMS. Except as otherwise defined herein, capitalized terms
shall have the meaning ascribed to them in the Lease.

        2. PREMISES.

        Landlord shall lease to Tenant, and Tenant shall lease from Landlord,
the Premises on the terms and conditions set forth in the Lease and herein. From
and after the Expansion Space Commencement Date (as defined in Exhibit B-FA
attached hereto), the Premises shall mean the Original Premises and an
additional approximately [...***...] square feet (the "Expansion Space"), which
Expansion Space shall constitute the entire building to be conducted in
accordance with Exhibit A-FA and Exhibit B-FA hereto and to be commonly known as
650 Gateway Boulevard, South San Francisco, California (the "Expansion
Building").




                                       1.
<PAGE>   2


        3. MONTHLY BASE RENT FOR THE EXPANSION SPACE.

        Monthly Base Rent for the Expansion Space shall, as of the Expansion
Space Commencement Date, be [...***...]* to the applicable rate per square foot
being charged from time to time under the Lease for the Original Premises
multiplied by the square footage of the Expansion Space. The rate per square
foot being charged under the Lease for the Original Premises shall be determined
by dividing the Monthly Base Rent due for the Original Premises by the Premises
Square Footage for the Original Premises. Nothing in this Paragraph 2 shall
alter or amend the Monthly Base Rent payable under the Lease for the Original
Premises.

        4. TENANT'S PROPORTIONATE SHARE; PARKING.

        As of the Expansion Space Commencement Date and subject to the terms and
conditions set forth in the Lease, (i) Tenant's Proportionate Share of the
Project shall be [...***...], (ii) Tenant's Proportionate Share of the Building
shall remain 100% and (iii) the number of unreserved parking spaces shall be
increased to [...***...] non-exclusive and undesignated parking spaces.

        5. SECURITY DEPOSIT.

        Prior to execution of this Amendment and in satisfaction of the
condition set forth in Paragraph 52 of the Lease, Tenant has increased the
Security Deposit by [...***...] such that the total Security Deposit held by
Landlord under the Lease is [...***...]. Such increased Security Deposit is
subject to the terms and conditions of the Lease, including without limitation,
Paragraph 7 of the Lease.

        6. EXPANSION CONSTRUCTION AGREEMENTS.

        Attached hereto as Exhibit A-FA and Exhibit B-FA, respectively, are the
Expansion Construction Agreements that set forth the rights and obligations of
Landlord and Tenant with respect to the construction of the Expansion Building
and the Expansion Space. These Expansion Construction Agreements amend and
restate the Base Building Construction Agreement and the Premises Construction
Agreement currently attached to the Lease with respect to the construction of
the Expansion Building and Expansion Space only.

        7. TIME FOR PERFORMANCE.

        With respect to construction of the Expansion Space, the parties have
set forth on Exhibit H-FA hereto certain events which must occur prior to or
during the construction of the Expansion Space (each a "Condition"), together
with certain dates upon which each condition must be satisfied ("Initial Window
Date"); provided however, if Landlord is delayed in satisfying any Condition due
to Tenant Delays or Force Majeure Events (as defined in Exhibit B-FA hereto),
all of the Initial Window Dates set forth on Exhibit H-FA shall be extended for
a period equal to the length of such delay. If any Condition is not satisfied on
or before its respective Initial Window Date, as such may be so extended, Tenant
shall have the right to terminate this Lease, as to both the Original Premises
and Expansion Space, by delivering written notice to



                                       2.
<PAGE>   3


Landlord within [...***...]* business days after expiration of the applicable
Initial Window Date. If Tenant does not deliver written notice of termination to
Landlord within such [...***...] period, time being of the essence, Tenant shall
have waived its right to terminate as a result of Landlord's failure to satisfy
the particular Condition in question. If Tenant timely elects to terminate the
Lease as set forth above, the Lease, as to the Original Premises and the
Expansion Space, shall terminate.

        If Tenant timely exercises its right to terminate the Lease as provided
above, Landlord shall have the right to nullify Tenant's election to terminate
the Lease as to the Original Premises by notifying Tenant, within [...***...]
days after receipt of Tenant's election to terminate, of Landlord's election to
pay to Tenant the Relocation Costs (as defined below). In the event Landlord
nullifies Tenant's election to terminate the Lease as to the Original Premises
and Tenant (i) gives Landlord written notice within [...***...] months of such
nullification that Tenant will vacate the Original Premises and (ii) vacates the
Original Premises, Tenant shall have the right to sublease the Original Premises
as otherwise provided under Paragraph 23 of the Lease; provided however, Tenant,
in this instance, shall not be required to pay the Additional Rent required to
be paid to Landlord under Paragraph 23(c) of the Lease. Notwithstanding this
paragraph, Tenant and any guarantor or surety of Tenant's obligations under the
Lease shall at all times remain fully responsible and liable for payment of the
Rent and for compliance with all of Tenant's obligations under the Lease, as
provided in Paragraph 23(d) of the Lease.

        "RELOCATION COSTS" are defined as [...***...] of the reasonable
out-of-pocket costs that Tenant incurs to relocate from the Original Premises to
a new location. Relocation Costs shall not include any payment of rent or any
cost of tenant improvements. Prior to reimbursement of Relocation Costs by
Landlord, Tenant shall provide Landlord with back-up invoices evidencing the
costs incurred by Tenant in relocating to Tenant's new location. In no event
shall Landlord pay Relocation Costs in excess of [...***...]. Relocation Costs
shall be paid by Landlord within [...***...] days after receipt of the
above-referenced back-up invoices.

        8. CARRY COSTS.

        Notwithstanding anything in Paragraph 52(e) of the Lease to the
contrary, except for any delays in the Phase II Commencement Date due to Force
Majeure Events, Tenant shall continue to pay to Landlord the Carry Costs on the
first day of each month up to and including [...***...]. In the event of a delay
in the Phase II Commencement Date due to Force Majeure Events, Tenant shall
continue payment (prorated as appropriate) of Carry Costs for the time
attributable to such delay.

        9. TENANT MAINTENANCE.

        Notwithstanding anything in the Paragraph 13 of the Lease to the
contrary, Tenant shall be responsible for maintaining the heating, ventilating
and air-conditioning systems and the life-safety systems serving the Premises.
Tenant shall maintain these systems in good order and condition and shall, at a
minimum, follow Landlord's standard servicing guidelines for such systems.




                                       3.

<PAGE>   4

        10. R&D SPACE.

        Notwithstanding anything in Paragraph 11 of the Lease to the contrary,
Tenant shall be permitted [...***...]* square feet of R&D Space in the Expansion
Space. Tenant may not exceed such maximum square footage for R&D Space in the
Expansion Space and therefore no Conversion Allowance shall be payable by Tenant
nor shall any Converted Office Space be available to Tenant with respect to the
Expansion Space. The terms and conditions of Paragraph 11 shall remain
unmodified and continue to apply in full force and effect with respect to the
Original Premises.

        11. BROKERS.

        Landlord and Tenant each represents and warrants to the other that
neither it nor its officers or agents nor anyone acting on its behalf has dealt
with any real estate broker except the Broker(s) specified in the Basic Lease
Information in the negotiating or making of this Amendment, and each party
agrees to indemnify and hold harmless the other from any claim or claims, and
costs and expenses, including attorneys' fees, incurred by the indemnified party
in conjunction with any such claim or claims of any other broker or brokers to a
commission in connection with this Amendment as a result of the actions of the
indemnifying party. Landlord shall pay the brokerage commissions due to the
Brokers listed in the Basic Lease Information.

        12. BASIC LEASE INFORMATION.

        As of the Expansion Space Commencement Date, the Basic Lease Information
in the Lease shall be amended and restated pursuant to the Basic Lease
Information attached as Exhibit Z.

        13. RATIFICATION.

        As amended hereby, the Lease is hereby ratified and confirmed in all
respects. In the event of any inconsistencies between the terms of this
Amendment and the Lease, the terms of this Amendment shall prevail.

        14. SUCCESSORS AND ASSIGNS.

        This Amendment shall bind and inure to the benefit of Landlord and
Tenant and their respective legal representatives and successors and assigns.





                             SIGNATURES ON NEXT PAGE


* CONFIDENTIAL TREATMENT REQUESTED

                                       4.


<PAGE>   5


        IN WITNESS WHEREOF, Landlord and Tenant have executed this Amendment to
Lease as of the date first above written.



                   LANDLORD: HMS GATEWAY OFFICE, L.P.,
                          a Delaware limited liability company

                          By: Hines Gateway Office, L.P.,
                              General Partner

                              By: Hines Interests Limited Partnership,
                                  General Partner

                                  By: Hines Holdings, Inc.,
                                      General Partner

                                      By: /s/ James Buie
                                          -------------------------------------

                                      Name:  James Buie            
                                           ------------------------------------

                                      Its:  EVP
                                          -------------------------------------



                      TENANT:   COULTER PHARMACEUTICAL, INC.,
                                a Delaware corporation

                                By:  /s/ William G. Harris
                                     ----------------------------------

                                Name: William G. Harris            
                                     ----------------------------------

                                Its: Vice President and CFO        
                                     ----------------------------------




<PAGE>   6

                                  EXHIBIT A-FA

                      BASE BUILDING CONSTRUCTION AGREEMENT



        This exhibit, entitled "Base Building Construction Agreement", is and
shall constitute Exhibit A-FA to the First Amendment to Lease Agreement, dated
as of November 10, 1998, by and between Landlord and Tenant (the "First
Amendment"). The terms and conditions of this Exhibit A-FA are hereby
incorporated into and are made a part of the First Amendment. As used in this
Exhibit, the term "Lease" shall include the original Lease Agreement and the
First Amendment.

        Subject to the terms and conditions set forth herein and in the Lease,
Landlord shall cause construction of the Building in accordance with the
procedures set forth below:

        (A) DEFINITIONS.

            (1) "BASE BUILDING IMPROVEMENTS" shall mean a [...***...] story
building, containing approximately [...***...]* square feet, all exterior
surfaces, utilities, landscaping and paved parking, all in substantial
compliance with those items listed on the Preliminary Specifications as "Base
Building" and located substantially in accordance with the Site Plan.

            (2) "BASE BUILDING PLANS AND SPECIFICATIONS" is defined in Section
B. 1 below.

            (3) "BUILDING WORK COST" is defined in Section B.3 below.

            (4) "CONTRACTOR" shall mean Rudolph & Sletten.

            (5) "CONSTRUCTION WARRANTIES" is defined in Section D.2 below.

            (6) "LANDLORD'S ARCHITECT" shall mean DES Architects/Engineers or
any replacement architect selected by Landlord in Landlord's reasonable
discretion.

            (7) "LANDLORD'S CONTRACT" shall mean the construction contract
entered into by and between Landlord and the Contractor for the construction of
the Base Building Improvements and any Tenant Requested Base Building
Improvements.

            (8) "PRELIMINARY SPECIFICATIONS" shall mean those preliminary
specifications for construction of the Base Building Improvements categorized as
"Base Building" and more particularly described on the attached Schedule A-1.

            (9) "650 GATEWAY PRELIMINARY SPECIFICATIONS" shall mean those
preliminary specifications for construction of the Base Building Improvements
categorized as "Base Building" and more particularly described on the attached
Schedule A-1.

            (10) "SITE PLAN" shall mean the site plan set forth on the attached
Schedule A-2 establishing the approximate location of the Building. All details
relating to the Project



* CONFIDENTIAL TREATMENT REQUESTED

<PAGE>   7

contained on the Site Plan, including without limitation, location of the
Building, parking areas, ingress, egress, direction of driveways, and entrances
are from time to time subject to change in Landlord's discretion, upon written
consent from Tenant, which consent shall not be unreasonably withheld,
conditioned or delayed and provided further that if Tenant fails to respond
within five (5) business days following Landlord's request for consent, Tenant
shall be conclusively deemed to have given its approval to any such change.
Notwithstanding the foregoing, Landlord may, without the written consent of
Tenant, change any details relating to the Project as may be required by any
governmental agency or as necessary to comply with any governmental requirements
or to address structural or unanticipated field conditions or which, in the
reasonable discretion of Landlord, will not have a material effect on Tenant's
use of the Premises or a material effect on the aesthetic appearance or
impression relating to the area covered by the Site Plan.

            (11) "TENANT'S COSTS" is defined in Section B.6 below.

            (12) "TENANT REQUESTED BASE BUILDING IMPROVEMENTS" shall mean those
improvements requested by Tenant in accordance with this Exhibit A-FA that are
to be incorporated into the Base Building Plans and Specifications.

Capitalized terms not otherwise defined in this Exhibit A shall have the
meanings ascribed to them in the Lease.

        (B) SCHEDULE.

            (1) PLANS AND SPECIFICATIONS. At Landlord's sole cost and expense,
Landlord's Architect shall prepare, on or before November 15, 1998, plans and
specifications (the "Base Building Plans and Specifications") for construction
of the Base Building Improvements substantially in accordance with the 650
Gateway Preliminary Specifications. Tenant shall have the right to approve the
Base Building Plans and Specifications only to the extent of any material
deviations from the 650 Gateway Preliminary Specifications; provided, however,
that such approval shall not be unreasonably withheld, conditioned, or delayed
and, provided further that if Tenant fails to respond within [...***...]*
business days following Landlord's request for approval, Tenant shall be
conclusively deemed to have given its approval to the matter submitted by
Landlord. Notwithstanding the foregoing, the Base Building Plans and
Specifications are, from time to time, subject to change in Landlord's
discretion, upon written consent from Tenant, which consent shall not be
unreasonably withheld, conditioned or delayed and provided further that if
Tenant fails to respond within [...***...] business days following Landlord's
request for consent, Tenant shall be conclusively deemed to have given its
consent to any such change. Landlord may without the written consent of the
Tenant change the Base Building Plans and Specifications as may be required by
any governmental agency or as necessary to comply with any governmental
requirements or to address structural or unanticipated field conditions or
which, in the reasonable discretion of Landlord, will not have a material effect
on Tenant's use of the Premises or a material effect on the aesthetic appearance
or impression relating to the Base Building Improvements.



* CONFIDENTIAL TREATMENT REQUESTED


                                       2.
<PAGE>   8

            (2) TENANT REQUESTED BASE BUILDING IMPROVEMENTS. On or before the
date that is [...***...]* weeks after the date of this Lease, Tenant shall
deliver to Landlord's Architect detailed specifications for any Tenant Requested
Base Building Improvements. All Tenant Requested Base Building Improvements
shall be subject to review and approval by Landlord, which approval may be given
or withheld in Landlord's reasonable discretion, to ensure, among other things,
that the Tenant Requested Base Building Improvements are compatible with all
other construction and all electrical, mechanical, life safety, and other
systems within the Building. If Landlord disapproves the Tenant Requested Base
Building Improvements, then within five (5) business days thereafter, Landlord
shall meet with the Tenant's Architect (as defined in Exhibit B-FA) and Tenant
to discuss, or shall submit to Tenant's Architect and Tenant in writing, the
reasons for Landlord's disapproval. Within five (5) business days following such
meeting or submission, Tenant shall cause Tenant's Architect to revise the same
and to submit new Tenant Requested Base Building Improvements to Landlord. The
procedure set forth in this paragraph will be repeated as set forth above until
Landlord has approved the Tenant Requested Base Building Improvements.

            (3) ESTIMATE OF BUILDING WORK COSTS. Promptly after approval of the
Tenant Requested Base Building Improvements, Landlord shall furnish Tenant with
an estimate of the cost of the Tenant Requested Base Building Improvements (the
"Building Work Cost").

            (4) TENANT'S REVIEW OF BUILDING WORK COSTS. The Building Work Cost
shall be subject to Tenant's approval, which approval shall not be unreasonably
withheld, conditioned or delayed and provided further that if Tenant fails to
respond within five (5) business days following Landlord's request for consent,
Tenant shall be conclusively deemed to have given its approval to the Building
Work Costs. If Tenant timely disapproves the Building Work Cost, then within
five (5) business days thereafter, Tenant shall meet with Landlord, Contractor,
Landlord's Architect and Tenant's Architect to discuss value engineering changes
to the Tenant Requested Base Building Improvements. Within five (5) business
days following such meeting, Tenant shall cause Tenant's Architect to revise the
Tenant Requested Base Building Improvements and to submit revised Tenant
Requested Base Building Improvements for approval by Landlord in accordance with
the procedure set forth above and for a new Building Work Cost to be prepared by
Landlord. The procedure set forth in this paragraph will be repeated until
Tenant has approved the Building Work Cost.

            (5) REVISION OF PLANS & SPECIFICATIONS. Following Landlord's
approval of the Tenant Requested Base Building Improvements and Tenant's
approval of the Building Work Cost, Landlord shall cause Landlord's Architect to
revise the Base Building Plans and Specifications to incorporate the Tenant
Requested Base Building Improvements within fifteen (15) days after receipt of
Tenant's approval of the Building Work Cost.

            (6) TENANT'S RESPONSIBILITY FOR COST OF TENANT REQUESTED BASE
BUILDING IMPROVEMENTS. All costs associated with incorporating the Tenant
Requested Base Building Improvements into the Base Building Plans and
Specifications and all costs of constructing (including without limitation the
cost of obtaining all necessary city approvals and permits) the Tenant Requested
Base Building Improvements (the "Tenant's Costs") shall be the responsibility




* CONFIDENTIAL TREATMENT REQUESTED

                                       3.
<PAGE>   9


of Tenant and shall not be credited against Tenant's Allowance, as defined in
Exhibit B-FA. Tenant shall make progress payments to Landlord from time to time
as the Tenant Requested Base Building Improvements are constructed. Tenant shall
pay the portion of such progress payments attributable to Tenant's Costs to
Landlord within ten (10) days of delivery of statements from Landlord to Tenant
therefor. Upon receipt of such payments, Landlord shall make all progress
payments directly to Contractor or subcontractors, as appropriate. Landlord
shall be entitled to suspend or terminate construction of the Base Building
Improvements and to declare Tenant in default in accordance with the terms of
the Lease, if payment by Tenant to Landlord of Tenant's Costs has not been
received as required hereunder.

        (C) CONSTRUCTION.

        The Base Building Improvements shall be constructed, at Landlord's sole
cost and expense, by Contractor in accordance with the Base Building Plans and
Specifications, as the same may be amended or modified from time to time by
Landlord and, if required, as approved by Tenant in accordance with this Exhibit
A-FA. All changes to the Base Building Plans and Specifications requiring
Tenant's approval must be evidenced by a written change order executed by
Landlord and by Tenant or each of their agents, describing the change required
in the Base Building Improvements and, the cost of such changes shall be paid in
accordance with the terms of this Exhibit A-FA.

        (D) GENERAL.

            (1) RIGHT OF TERMINATION. Landlord and Tenant acknowledge that
construction of the Base Building Improvements and all matters relating thereto
are subject to Landlord obtaining all necessary governmental and private
approvals to commence construction of the Base Building Improvements. Landlord
shall use commercially reasonable efforts to obtain such approvals; however, if
Landlord is unable to obtain such approvals by [...***...], either party shall
have the right to terminate' this Lease, as to the Expansion Space only, by
delivering written notice of termination to the other party on or before
[...***...]. The Lease as to the Original Premises shall remain in full force
and effect and shall be unmodified by any termination pursuant hereto. If no
such notice of termination is given, the Lease shall remain in full force and
effect as to the Original Premises and the Expansion Space. Notwithstanding
anything herein to the contrary, Landlord shall not be liable to Tenant for any
loss or damage resulting from any delay in constructing or developing the Base
Building Improvements, nor shall such failure affect the obligations of Tenant
under the Lease, except as otherwise set forth in the Lease.

            (2) CONSTRUCTION WARRANTIES. Landlord shall obtain from Contractor,
and shall request Contractor to obtain from all subcontractors and material
suppliers, warranties (collectively, "Construction Warranties") for all
components of the Base Building Improvements for which warranties are
customarily provided in the construction industry and Landlord shall enforce the
Construction Warranties as reasonably requested by Tenant.

            (3) LANDLORD'S COVENANTS. Subject to the terms and conditions of the
Lease, Landlord covenants that (a) the Base Building Improvements shall be
constructed in compliance with all applicable building code requirements in
effect and being actively enforced by the City 



                                       4.
<PAGE>   10


of South San Francisco on the date the applicable building permits for
construction of the Base Building Improvements were issued to Contractor and
substantially in accordance with the Base Building Plans and Specifications and
(b) that the Base Building Improvements shall be free from material latent
defects in design, materials and workmanship; provided however, Landlord shall
have no liability under this paragraph unless failure to comply with the terms
hereof materially adversely affect Tenant's use of the Premises. Any claims by
Tenant under clause (a) above, shall be made in writing not later than one (1)
year after the Expansion Commencement Date and any claims by Tenant under clause
(b) above, shall be made in writing not later than the earlier of [...***...]*
years after the Expansion Commencement Date or termination of the Lease. In the
event Tenant fails to deliver a written claim to Landlord on or before such
dates, then Landlord shall be conclusively deemed to have satisfied its
obligations under this paragraph. The covenants contained in this paragraph are
subject to Paragraph 39 of the Lease and are made specifically and exclusively
for the benefit of the original Tenant.

INITIALS:

TENANT:  /s/
       ---------------------------------

LANDLORD:  /s/                              
         -------------------------------



* CONFIDENTIAL TREATMENT REQUESTED




                                       5.


<PAGE>   11


                      COULTER PHARMACEUTICAL - SCHEDULE A1
                           PRELIMINARY SPECIFICATIONS
                               COST RESPONSIBILITY



<TABLE>
<CAPTION>
                                                                                     Base        
                                  Description                                      Building       Tenant
---------------------------------------------------------------------------       ----------    -----------
<S>                                                                              <C>           <C>
Sitework

  -     All necessary fees and permits for Base Building Works.                   [...***...]   [...***...]
  -     All grading of the site to predetermined grades per DES                   [...***...]   [...***...]
        Architects plans.                                                                       
  -     Installation of all necessary underground utilities, storm drain,         [...***...]   [...***...]
        sewer, catch basins, drain inlets, common trench, water,                                
        electricity, cable televisions and gas meter per DES Architects                         
        documents.                                                                              
  -     Installation of all offsite and onsite curbs, gutters and                 [...***...]   [...***...]
        sidewalks as shown on Des Architect construction documents.                             
  -     Installation of all irrigation and landscaping per DES                    [...***...]   [...***...]
        Architect's plans.                                                                      
  o     All area drains in landscaping areas, which shall be connected to         [...***...]   [...***...]
        the storm drain system if required by DES Architect                                     
  -     Installation of separate water and electrical meters for all              [...***...]   [...***...]
        common area landscaping                                                                 
  -     Installation of code required informational and directional               [...***...]   [...***...]
        signage.                                                                                
  -     Illuminated and non-illuminated interior signage by tenant.                             [...***...]
  -     Illuminated monument signage and on building identification               [...***...]   [...***...]
        signage as reviewed by Tenant.                                                          
  -     Striping of all parking areas per DES Architects documents.               [...***...]   [...***...]
  -     Installation of all trash screens as required by Planning                 [...***...]   [...***...]
        Department of the City of South San Francisco                                           
  -     Installation of all exterior lighting with a minimum coverage in          [...***...]   [...***...]
        both parking areas and walkways of not less than one foot candle.                       
                                                                                                
Structure                                                                                       
  -     All necessary fees and permits for Base Building work.                    [...***...]   [...***...]
  -     All work necessary per code to make the Base Building handicap            [...***...]   [...***...]
        accessible.                                                                             
  -     Minimum 5" slab on grade in conformance with specifications and           [...***...]   [...***...]
        recommendations of Base Building geotechnical and engineering                           
        consultants.  Finish shall be smooth.                                                   
  -     Sand fill and moisture barrier under slab on grade as recommended         [...***...]   [...***...]
        by DES Architects.                                                                      
  -     Exterior concrete walls shall be sandblasted and sealed.                  [...***...]   [...***...]
  -     All structural steel shall be erected per DES Architect's                 [...***...]   [...***...]
        specifications.                                                                         
  -     All structural steel shall not be fireproofed unless required by          [...***...]   [...***...]
        local codes.                                                                            
  -     Second floor decking shall be galvanized metal with a lightweight         [...***...]   [...***...]
        concrete topping slab.  Finish shall be smooth.                                         
  -     All exterior vision glass shall be  1/4" thick with reflective            [...***...]   [...***...]
        coating.                                                                                
  -     Roof membrane shall be 4-ply built-up system with a mineral fiber         [...***...]   [...***...]
        cap sheet.                                                                              
  -     All required condensate lines to be installed and terminated at           [...***...]   [...***...]
        the nearest roof drain for Base Building equipment.                                     
  -     Roof drains per plan with drain lines tying into the storm drain          [...***...]   [...***...]
        system.  Scuppers for overflow to be provided if required by code.                      
  -     Convenience outlets, as required by code, on the roof.                    [...***...]   [...***...]
  -     Floor systems shall be designed to a minimum of 45 lbs. Per               [...***...]   [...***...]
        square foot for office space and a minimum of 100 lbs. Per square                       
        foot on ground floor for lab space.                                                     
</TABLE>




* CONFIDENTIAL TREATMENT REQUESTED




<PAGE>   12


                      COULTER PHARMACEUTICAL - SCHEDULE A1
                           PRELIMINARY SPECIFICATIONS
                               COST RESPONSIBILITY


<TABLE>
<S>                                                                               <C>           <C> 
  -     Roof insulation to meet minimum energy code.                              [...***...]   [...***...]
  -     Roof live load to accommodate 50 lb. dead load and necessary              [...***...]   [...***...]
        reinforcement for additional lab related mechanical equipment in                        
        areas indicated on plan.                                                                
  -     Required second floor penetrations, including blockouts, as shown         [...***...]   [...***...]
        on Tenant Improvement drawings for mechanical, electrical and                           
        plumbing trades and roof hatch.                                                         
  -     Required roof penetrations, including blockouts, as shown on base         [...***...]   [...***...]
        building for mechanical, electrical and plumbing work.                                  
  -     Top of slab on grade to top of second floor slab shall be                 [...***...]   [...***...]
        15'-0".  Top of second floor slab to top of roof trusses shall be                       
        13'-0".                                                                                 
  -     All exterior doors, except entrance doors, shall be hollow core           [...***...]   [...***...]
        metal with metal jambs as shown in schematic documents with                             
        hardware as required by Tenant.                                                         
  -     One 12'-0" x 12'-0" steel rollup door shall be installed per              [...***...]   [...***...]
        Tenant specifications for delivery area.                                                
  -     Front entry doors shall be a pair of 3'-0" x 8'-0" fully                  [...***...]   [...***...]
        supported, balanced aluminum and glass doors with hardware                              
        approved as required by Tenant.                                                         
  -     All interior stairs as required by code, but not less than two            [...***...]   [...***...]
        per building.  All stairs shall be metal pan stairs with concrete                       
        fill.                                                                                   
  -     Stair carpeting, if required, to be provided tenant.                      [...***...]   [...***...]
  -     All interior stair handrails shall be primed.  Proper backing             [...***...]   [...***...]
        shall be installed.                                                                     
  -     All stairwells shall be sheetrocked, taped and ready for paint.           [...***...]   [...***...]
  -     All stairwells shall include code required lighting.                      [...***...]   [...***...]
  -     All required base building life safety signage as required by             [...***...]   [...***...]
        code.                                                                                   
  -     All equipment platforms shall have a sheetmetal cap and minimum           [...***...]   [...***...]
        3" apron around the perimeter.  Six bay equipment platform as                           
        indicated on plan ready to receive framing for equipment.                               
  -     One hydraulic passenger elevator, including all necessary wiring          [...***...]   [...***...]
        and equipment, with a capacity of not less than 2,500 lbs. and                          
        minimum speed of 100' per minute.                                                       
  -     A complete elevator cab that is the manufacturer's standard.              [...***...]   [...***...]
  -     Base Building to accommodate a 9'-0" finished ceiling height on           [...***...]   [...***...]
        both floors.                                                                            
  -     All exterior concrete walls shall be finished on the interior             [...***...]   [...***...]
        with lightweight metal studs, insulation and sheetrock, taped                           
        with a smooth finish.                                                                   
  -     Master keyed exterior locks.                                              [...***...]   [...***...]
  -     Individual keying per tenant specifications.                              [...***...]   [...***...]
  -     A complete fire sprinkler system, sized to meet code per the              [...***...]   [...***...]
        interior improvement design. This system shall be complete and                          
        operational including required drops to the suspended ceiling in tenant               
        finished areas. The system shall include, but is not limited to, valves,
        dry stand pipes, monitoring stations, aennciators, horns and storage
        tanks, if required by code.
  -     Roof access ladder and hatch in one stairwell.                            [...***...]   [...***...]
  -     Patio furniture                                                           [...***...]   [...***...]
                                                                                                
UTILITIES AND BACKBONE SYSTEMS                                                    [...***...]   [...***...]
  -     2,000 amp. 277/480 volt, 3 phase electrical service switchgear            [...***...]   [...***...]
        and meter and switch center room.                                                       
  -     Separate electrical meter, panel and time clock for Parking lot           [...***...]   [...***...]
        lighting and irrigation.                                                                
  -     Telephone trunk lines to the interior telephone room sufficient           [...***...]   [...***...]
        in size to accommodate the buildings.                                                   
</TABLE>




* CONFIDENTIAL TREATMENT REQUESTED


                                       2.
<PAGE>   13
                      COULTER PHARMACEUTICAL - SCHEDULE A1
                           PRELIMINARY SPECIFICATIONS
                               COST RESPONSIBILITY


<TABLE>
<S>                                                                               <C>           <C> 
  -     Two PVC conduits, minimum of 4" between the first and option              [...***...]   [...***...]
        buildings for telephone and data.                               
  -     Required water service for sprinkler system.                              [...***...]   [...***...]
  -     A minimum of 2" domestic water service to building.  There shall          [...***...]   [...***...]
        be a separate meter for this water line and it shall terminate inside                 
        the building below the second floor.
  -     A minimum 4" natural gas service building.  There shall be a              [...***...]   [...***...]
        separate meter for this service and it shall terminate inside the                      
        building below the second floor.                                                       
  -     As required, a 6" cast iron, sanitary sewer gut line the entire           [...***...]   [...***...]
        length of the building.  This gut line shall have, at a minimum,                       
        one cleanout at the end of its run, one in the restroom core and                       
        one cleanout at the entrance to the building.  Exact location of                       
        this gut line shall be determined by tenant.                                           
  -     All necessary electrical and fire sprinkler rooms, sized to               [...***...]   [...***...]
        accommodate Tenant requirements, shall be completed with light                         
        weight metal studs, metal doors and jambs, required ventilation                        
        through the roof membrane, lighting, convenience outlets and                           
        sheetrock, taped and textured.                                                         
                                                                                               
MEP                                                                                            
  -     All required electrical to base building equipment.                       [...***...]   [...***...]
  -     All backboards as required by Tenant.                                     [...***...]   [...***...]
  -     All required electrical outlets and lighting to complete base             [...***...]   [...***...]
        building requirements.                                                                 
  -     Smoke detectors as required by code for Base Building                     [...***...]   [...***...]
  -     All required roof walk pads, conduit supports, and penetrations           [...***...]   [...***...]
        for Base Building equipment.                                                           
  -     All sheetmetal necessary to provide moisture protection and               [...***...]   [...***...]
        flashing details for Base Building equipment.  (None anticipated)                      
  -     All necessary seismic restraints on Base Building equipment.              [...***...]   [...***...]
        (None anticipated)                                                                     
  -     A centrally located, gas hot water heater large enough to                 [...***...]   [...***...]
        accommodate all of the tenant requirements including hot water to                      
        all labs.                                                                              
  -     A mechanical chiller system, sized to accommodate [...***...]             [...***...]   [...***...]
        square feet of office space.                                                           
  -     All ductwork and penetrations necessary to provide both supply            [...***...]   [...***...]
        and return air to each floor, elevator cores and lobby restrooms                       
        shall be provided.  All necessary fire and smoke dampers shall be                      
        included for Base Building work.  Restrooms, elevator cores,                           
        lobby and stairwells shall be complete.                                                
  -     All ductwork and roof mounted fans necessary to provide proper            [...***...]   [...***...]
        ventilation in the restrooms, electrical closets and elevator                          
        machine room.                                                                          
  -     Screening of roof mounted equipment.  Roof screen as shown on             [...***...]   [...***...]
        roof plan.                                                                             
  -     Exhaust ducts, through the roof, for lab ventilating as specified         [...***...]   [...***...]
        by Tenant.                                                                             
  -     Hose bib near delivery areas.                                             [...***...]   [...***...]
                                                                                               
LOBBY AREA                                                                                     
  -     Architect design fees associated with the lobby area.                     [...***...]   [...***...]
  -     [...***...]  story height with skylight, visibility to stairwell          [...***...]   [...***...]
        and a catwalk and overlook at the second floor level.                                  
  -     Area of Lobby to be 30' x 30'.  Landlord to contribute [...***...]        [...***...]   [...***...]
  -     All walls sheetrocked, taped with a smooth finish.  If Tenant so          [...***...]   [...***...]
        desires, all walls will be prepared and ready to accept                                
        wallcovering.                                                                          
  -     Electrical outlets, telephone outlets and data outlets necessary          [...***...]   [...***...]
        to accommodate the 
</TABLE>




* CONFIDENTIAL TREATMENT REQUESTED

                                       3.



<PAGE>   14
                      COULTER PHARMACEUTICAL - SCHEDULE A1
                           PRELIMINARY SPECIFICATIONS
                               COST RESPONSIBILITY


<TABLE>
<S>                                                                               <C>           <C> 
        Tenant's proposed lobby layout.                                     
  -     Ceramic tile entry, 8'-0" wide, from the front doors to the               [...***...]   [...***...]
        reception counter.  All other areas to be carpet, a 36 oz. loop                        
        minimum, and if desired by Tenant, with a border.                                      
  -     6" or 2" rubber base in all areas.                                        [...***...]   [...***...]
  -     Entry doors to be a pair of aluminum glass with hardware reviewed         [...***...]   [...***...]
        by Tenant.                                                                             
  -     All doors off of lobby to be wood grain, 3'-0" x 8'-0" minimum in         [...***...]   [...***...]
        height.  Hardware to be selected by tenant.                                            
  -     All HVAC to be complete.                                                  [...***...]   [...***...]
  -     All Base Building areas to be handicap accessible per code.               [...***...]   [...***...]
  -     All finishes by Tenant.                                                   [...***...]   [...***...]
  -     Ceiling to be sheetrock, taped and textured.                              [...***...]   [...***...]
  -     Lighting to include, but not be limited to, down lights, recessed         [...***...]   [...***...]
        wall washers, recessed parabolic or halogen.                                           
  -     Wallcovering on all walls if so desired by Tenant.                        [...***...]   [...***...]
  -     Fully painted to Tenant specifications.                                   [...***...]   [...***...]
                                                                                               
ELEVATOR LOBBIES                                                                               
  -     Sheetrock walls and ceiling, taped with a smooth finish.                  [...***...]   [...***...]
  -     Ceiling to have a multiple coffer with lighting behind.                   [...***...]   [...***...]
  -     Electrical outlets to support work required in the area.                  [...***...]   [...***...]
  -     Stainless steel jambs and head around elevator opening ground             [...***...]   [...***...]
        floor.                                                                                 
  -     Painted hollow metal jambs and head on 2nd floor.                         [...***...]   [...***...]
  -     Nickel/silver threshold and elevator entrance.                            [...***...]   [...***...]
  -     Grout under elevator thresholds.                                          [...***...]   [...***...]
  -     Carpet, 36 oz. loop minimum, and if desired by Tenant, with a             [...***...]   [...***...]
        border.                                                                                
  -     6" and 2" rubber base at all areas.                                       [...***...]   [...***...]
  -     Magnetic hold opens on all lobby doors if required by code.               [...***...]   [...***...]
  -     Lobby door to be wood grain, full height, with hardware reviewed          [...***...]   [...***...]
        by Tenant.                                                                             
  -     Lighting to include recessed down lights, recessed lights or wall         [...***...]   [...***...]
        washers.                                                                               
  -     Fully painted to Tenant specifications.                                   [...***...]   [...***...]
  -     All HVAC to be complete.                                                  [...***...]   [...***...]
  -     All elevator lobby areas to have a one hour rating if required by         [...***...]   [...***...]
        code.                                                                                  
                                                                                               
RESTROOMS                                                                                      
  -     Sheetrock walls taped with a smooth finish.  A cofer shall be             [...***...]   [...***...]
        installed over the vanity area.                                                        
  -     Ceiling to be drywall.                                                    [...***...]   [...***...]
  -     Ceramic tile floors and wainscot on wet wall.                             [...***...]   [...***...]
  -     All floors sloped to a floor drain.                                       [...***...]   [...***...]
  -     Light cove with egg crate louver over stalls and urinals.                 [...***...]   [...***...]
  -     Provide janitor closets on each floor adjacent to restrooms.              [...***...]   [...***...]
  -     Provide sinks in janitor closets.                                         [...***...]   [...***...]
  -     Recessed lighting at entry, sinks and outside stalls.                     [...***...]   [...***...]
  -     All partitions to be meal and hung from wall.                             [...***...]   [...***...]
  -     All toilets and urinals to be hung from wall.                             [...***...]   [...***...]
  -     Plastic laminate counter tops over moisture resistant plywood             [...***...]   [...***...]
        with 5' lipped apron 
</TABLE>




* CONFIDENTIAL TREATMENT REQUESTED

                                       4.




<PAGE>   15
                      COULTER PHARMACEUTICAL - SCHEDULE A1
                           PRELIMINARY SPECIFICATIONS
                               COST RESPONSIBILITY


<TABLE>
<S>                                                                               <C>           <C> 
        and 6" splash (to be ADA compliant).                              
  -     Full length mirror with polished stainless steel frame.                   [...***...]   [...***...]
  -     Provide insulation for hot and cold water pipes.                          [...***...]   [...***...]
  -     Minimum toilet accessories to include, but not limited to, sinks,         [...***...]   [...***...]
        stainless faucets, toilets, urinals, recessed paper towel dispensers                 
        with integral waste, counter mounted soap dispensers, sanitary napkin
        dispenser, seat cover dispenser, toilet tissue dispenser, handicap grab
        bars and partition mounted coat hooks.
  -     Paint above wainscot as directed by Tenant.                               [...***...]   [...***...]
  -     Vestibules and finishes.                                                  [...***...]   [...***...]
</TABLE>











* CONFIDENTIAL TREATMENT REQUESTED


                                       5.


<PAGE>   16

                                  SCHEDULE A-2

                                    SITE PLAN

                             [GRAPHIC - MAP OF SITE]









                                       1.
<PAGE>   17
                                  EXHIBIT B-FA

                         PREMISES CONSTRUCTION AGREEMENT



        This exhibit, entitled "Premises Construction Agreement", is and shall
constitute Exhibit B-FA to the First Amendment to Lease Agreement, dated as of
November 10, 1998, by and between Landlord and Tenant (the "First Amendment").
The terms and conditions of this Exhibit B-FA are hereby incorporated into and
are made a part of the First Amendment. As used in this exhibit, the term
"Lease" shall include the original Lease Agreement and the First Amendment.

        Subject to the terms and conditions set forth herein and in the Lease,
Landlord shall allow the construction or installation of the improvements in the
interior of the Premises in accordance with the procedures set forth below:

        (A) DEFINITIONS.

               (1) "APPROVED PLANS" is defined in Section B.6 below.

               (2) "CONTRACTOR" shall mean Rudolph and Sletten.

               (3) "ESTIMATED WORK COST" is defined in Section B.3 below.

               (4) "EXCESS TENANT IMPROVEMENTS" is defined in Section B.7 below.

               (5) "FINAL COST QUOTATION" is defined in Section B.7 below and
shall include all costs associated with the Tenant Improvements, including
without limitation, costs of all tenant improvement work; architectural and
engineering fees; governmental agency fees for permits, licenses and
inspections; construction fees, including, without limitation, general
contractors' overhead and supervision fees; Landlord's administration fee of
[...***...]; and such other costs as may be reasonably incurred by Landlord in
connection with such construction.

               (6) "PRELIMINARY PLANS" is defined in Section B. 1 below.

               (7) "TENANT'S ALLOWANCE" shall mean an amount equal to
[...***...], which amount shall, except as otherwise provided in this Exhibit
B-FA, be paid by Landlord toward the cost of completion of the Tenant
Improvements and related design, engineering, governmental, overhead,
supervision and administration fees and costs (collectively, the "Tenant
Improvement Cost"). Notwithstanding the foregoing, no portion of the Tenant's
Allowance shall be paid by Landlord toward the cost of the Tenant Requested Base
Building Improvements, or Tenant Improvements that constitute furniture,
equipment or trade fixtures or result in changes to the Base Building
Improvements. If the Tenant Improvement Cost exceeds the Tenant's Allowance, the
difference shall be paid by Tenant in accordance with this Exhibit B-FA.





* CONFIDENTIAL TREATMENT REQUESTED


                                       1.

<PAGE>   18

               (8) "TENANT'S ARCHITECT" shall mean CAS Architects, or such other
licensed architect designated by Tenant and subject to Landlord's prior
approval, which approval shall be given or withheld in Landlord's reasonable
discretion.

               (9) "TENANT'S CONTRACT" shall mean the construction contract
entered into by and between the Tenant and the Contractor for the construction
of the Tenant Improvements.

               (10) "TENANT IMPROVEMENTS" shall mean all improvements made to
the Premises pursuant to the Approved Plans.

Capitalized terms not otherwise defined in this Exhibit B-FA shall have the
meanings ascribed to them in the Lease.

        (B) SCHEDULE.

               (1) Tenant shall cause Tenant's Architect to furnish to Landlord
on or before [...***...], preliminary space plans and specifications (the
"Preliminary Plans"). Tenant shall be responsible for all costs associated with
the Preliminary Plans (collectively, the "Preliminary Design Costs"), including
any revisions required by Section B.2 hereunder; provided, however, Tenant shall
be reimbursed by Landlord out of the Tenant's Allowance for the Preliminary
Design Costs reasonably incurred upon delivery to Landlord of invoices, receipts
and other documents reasonably required to substantiate such costs.

               (2) The Preliminary Plans shall be subject to Landlord's
approval, which approval shall not be unreasonably withheld, conditioned or
delayed. If Landlord disapproves the Preliminary Plans, then within five (5)
business days thereafter, Landlord shall meet with the Tenant's Architect and
Tenant to discuss, or shall submit to the Tenant's Architect and Tenant in
writing, the reasons for Landlord's disapproval. Within five (5) business days
following such meeting or submission, Tenant shall cause the Tenant's Architect
to revise the same and to submit new Preliminary Plans to Landlord. The same
procedure set forth in this paragraph will be repeated as set forth above until
Landlord has approved the Preliminary Plans.

               (3) Promptly after approval of the Preliminary Plans, Tenant
shall cause Contractor to furnish Landlord with an estimate of the cost of the
Tenant Improvements as shown on the Preliminary Plans and Landlord shall in turn
provide Tenant with an estimate of the cost of the Tenant Improvements,
including, without limitation, estimates of the following costs: architectural
and engineering fees, governmental agency fees for permits, licenses and
inspections, overhead and supervision fees, and Landlord's administrative fees
(the "Estimated Work Cost"). The Estimated Work Cost shall separately itemize
the cost of changes to the Base Building Improvements for those Tenant
Improvements that will necessitate changes in the Base Building Improvements.

               (4) The Estimated Work Cost shall be subject to Tenant's
approval, which approval shall not be unreasonably withheld, conditioned or
delayed and provided further that if Tenant fails to respond within five (5)
business days following Landlord's delivery of the Estimated Work Cost, Tenant
shall be conclusively deemed to have given its approval of the




* CONFIDENTIAL TREATMENT REQUESTED



                                       2.
<PAGE>   19
Estimated Work Cost. If Tenant timely disapproves the Estimated Work Cost, then
within five-(5) business days thereafter, Tenant shall meet with Landlord,
Contractor and Tenant's Architect to discuss value engineering changes to the
Preliminary Plans. Within five (5) business days following such meeting, Tenant
shall cause Tenant's Architect to revise the Preliminary Plans and to submit new
Preliminary Plans for approval by Landlord in accordance with the procedure set
forth above and for a new Estimated Work Cost to be prepared by Landlord. The
procedure set forth in this paragraph will be repeated until Tenant has approved
the Estimated Work Cost.

               (5) Following Landlord's approval of the Preliminary Plans and
Tenant's approval of the Estimated Work Cost, Tenant shall cause Tenant's
Architect to prepare detailed construction drawings and specifications (the
"Working Drawings") for the Tenant Improvements based strictly upon the
Preliminary Plans, except as otherwise agreed in writing by Landlord and Tenant.
The Working Drawings shall be completed within [...***...] business days after
approval of the Preliminary Plans and Estimated Work Cost, but in no event later
than [...***...].

               (6) The Working Drawings shall be subject to Landlord's approval,
which approval shall not be unreasonably withheld, conditioned or delayed. If
Landlord disapproves the Working Drawings, then within five (5) business days
thereafter, Landlord shall meet with Tenant's Architect and Tenant to discuss,
or shall submit to the Tenant's Architect and Tenant in writing, the reasons for
Landlord's disapproval. Within five (5) business days following such meeting or
submission, Tenant shall cause Tenant's Architect to revise the same and to
submit new Working Drawings to Landlord, and the same procedure will be repeated
as set forth above until Landlord has approved the Working Drawings (the
"Approved Plans"). The reasonable costs of preparing the Working Drawings,
together with any revisions thereto, may be paid by Landlord to Tenant from
Tenant's Allowance. Upon approval of the Working Drawings, Landlord shall
deliver to Tenant a list of Tenant Improvements to be removed by Tenant, at
Tenant's cost and expense in accordance with Paragraph 11 of the Lease, upon
expiration of the Term or earlier termination of the Lease. Notwithstanding the
foregoing, during the preparation of the Working Drawings, Landlord shall, upon
Tenant's request, advise Tenant of items that will be required to be removed
pursuant to the previous sentence.

               (7) Within ten (10) business days after Landlord's approval of
the Approved Plans, Tenant shall cause Contractor to furnish to Landlord a cost
estimate for the Tenant Improvements based upon the Approved Plans and Landlord
shall in turn provide Tenant with a final cost quotation for the Tenant
Improvements (the "Final Cost Quotation"). If the Final Cost Quotation is
greater than the Tenant's Allowance, Tenant shall be responsible for the
difference between the Tenant's Allowance and the Final Cost Quotation (the
"Excess Tenant Improvements Cost").

               (8) Landlord and Tenant shall make progress payments on a pro
rata basis (in the proportion that the Tenant's Allowance paid by Landlord and
the Excess Tenant Improvements Cost paid by Tenant bear to the Final Cost
Quotation) from time to time as the Tenant Improvements are constructed in the
Premises. Tenant shall pay its pro rata share of any progress payments directly
to Contractor or subcontractors, as appropriate, and Landlord shall




* CONFIDENTIAL TREATMENT REQUESTED

                                       3.
<PAGE>   20

pay its pro rata share of any progress payments directly to Contractor or
subcontractors, as appropriate. Landlord shall be entitled to suspend or
terminate construction of the Tenant Improvements and to declare Tenant in
default in accordance with the terms of the Lease, if payment by Tenant of
Tenant's pro rata share of any progress payment has not been received by
Contractor when due, as required hereunder. Moreover, Landlord shall not be
required to pay its pro rata share of any progress payment until such time as
Landlord receives from Contractor an unconditional lien waiver as to each
progress payment and a conditional lien waiver for the next due progress
payment. All lien waivers shall comply with California law regarding materialmen
and mechanic's liens. Notwithstanding the foregoing, Tenant may, at Tenant's
option and upon reasonable prior written notice to Landlord, pay the full amount
of the progress payment and, subject to Landlord's receipt of the lien waivers
specified above, obtain reimbursement from Landlord for Landlord's pro rata
share promptly after Tenant's delivery to Landlord of a written demand for such
pro rata share owing.

        (C) TENANT IMPROVEMENT CONSTRUCTION.

            (1) All Tenant Improvements to be constructed or installed in the
Premises shall be performed by Contractor in accordance with the Approved Plans,
subject to any changes agreed to by Landlord and Tenant in writing. Landlord
shall have no obligation to Tenant for defects in design, workmanship or
materials in connection with the Tenant Improvements. Any changes to the
Approved Plans shall require the written approval of Landlord and Tenant, which
approval shall not be unreasonably withheld, conditioned or delayed. All such
changes must be evidenced by a written change order executed by Landlord and
Tenant or their agent describing the change required in the Approved Plans, and
the cost of such changes shall be paid in accordance with the terms of this
Exhibit B-FA.

            (2) Landlord shall coordinate construction of the Tenant
Improvements by Contractor with the construction of the Base Building
Improvements by Contractor in the most efficient manner reasonably possible for
the timely completion of the Base Building Improvements and the Tenant
Improvements. Landlord and Tenant shall each use good faith efforts to
reasonably resolve any issues or conflicts that may arise during the course of
constructing the Tenant Improvements and the Base Building Improvements. Entry
by Contractor in accordance with this Exhibit B-FA shall not constitute Tenant's
occupancy of the Expansion Space under Paragraph 3 of the Lease; however, all
terms and conditions of the Lease shall apply to Contractor's occupancy of and
work within the Expansion Space.

            (3) In addition to and without limitation on the requirements set
forth in the Lease, Tenant shall ensure that, with respect to the work to be
performed as part of Tenant's Contract, Contractor and all subcontractor(s)
procure and maintain in full force and effect during the course of construction
a "broad form" commercial general liability and property damage policy of
insurance naming, Landlord, Tenant and Landlord's lenders as additional
insureds. The minimum limit of coverage of the aforesaid policy shall be in the
amount of not less that [...***...] for injury or death of one person in any
one accident or occurrence and in the amount of not less than [...***...] for
injury or death of more than one person in any one accident or occurrence, and
shall contain a severability of interest clause or a cross liability
endorsement.




* CONFIDENTIAL TREATMENT REQUESTED


                                       4.


<PAGE>   21
Such insurance shall further insure Landlord and Tenant against liability for
property damage of at least [...***...].

        (D) TERM COMMENCEMENT.

            (1) Notwithstanding anything in the Lease to the contrary, except as
otherwise provided in D.2 and D.3 below, the commencement date as to the
Expansion Space (the "Expansion Space Commencement Date") shall be no later than
[...***...]. The Expansion Space Commencement Date shall not be adjusted due to
delays caused by Tenant or any employee, agent or representative of Tenant
("Tenant Delays"), including, without limitation, delays caused by (i) failure
to furnish information in accordance with this Exhibit B-FA or Exhibit A-FA of
the Lease; (ii) Tenant's request for any special, long lead time materials or
installations as part of the Tenant Improvements or the Tenant Requested Base
Building Improvements; (iii) Tenant's changes in the Approved Plans; (iv) any
changes initiated by reason of the disapproval of any plans or drawings or any
cost proposals or authorizations resulting in the preparation of revised plans,
drawings, cost proposals or authorizations beyond the second submission to
Landlord for approval; (v) field changes to construction work; (vi) the
delivery, installation or completion of the Tenant Improvements work performed
by; (vii)Tenant's request for any Tenant Requested Base Building Improvements,
as defined in Exhibit A-FA of the Lease or any delay in delivering the Tenant
Requested Base Building Improvements beyond the date set forth in Section B.2 of
Exhibit A-FA; or (viii) any other act or omission of Tenant.

            (2) Except as may be otherwise specifically provided herein or in
the Lease, time periods for either party's performance under any provisions of
this Exhibit B-FA, shall be extended for periods of time during which such party
is prevented due to circumstances beyond such party's control, including,
without limitation, strikes, embargoes, governmental regulations, delays in
obtaining permits or materials, acts of God, war, civil commotion or other
strife ("Force Majeure Events"). Each party shall use reasonable efforts to
mitigate the effect of any Force Majeure Event upon such party's performance
hereunder. In addition, if Landlord's Architect fails to complete the Base
Building Plans and Specifications on or before the date set forth in Section B.1
of Exhibit A-FA of the First Amendment for reasons other than Tenant Delays,
then the Expansion Space Commencement Date shall be delayed by one (1) day for
each day of delay in the completion of the Base Building Plans and
Specifications.

            (3) Intentionally deleted.

            (4) If, for any reason Landlord cannot perform any other covenant
contained in this Exhibit B-FA or in the Lease related to the work described in
this Exhibit B-FA, the Lease shall not be void or voidable nor shall Landlord be
liable to Tenant for any loss or damage resulting therefrom, nor shall such
failure affect the obligations of Tenant under the Lease or this Exhibit B-FA,
except as otherwise specifically provided in the First Amendment.

        (E) GENERAL.

            (1) All drawings, space plans, plans and specifications for any
improvements or installations in the Premises are expressly subject to
Landlord's prior written approval, which





* CONFIDENTIAL TREATMENT REQUESTED


                                       5.

<PAGE>   22


approval shall not be unreasonably withheld, conditioned or delayed. Any
approval by Landlord of any drawings, plans or specifications prepared on behalf
of Tenant including, without limitation, any Preliminary Plans, Working Drawings
or Approved Plans, or any revisions thereto, shall not in any way bind Landlord,
create any responsibility or liability on the part of the Landlord for the
completeness of the same, their design sufficiency or compliance with applicable
statutes, ordinances or regulations or constitute a representation or warranty
by Landlord as to the adequacy or sufficiency of such drawings, plans or
specifications, or the improvements to which they relate, but such approval
shall merely evidence the consent of Landlord to such drawings, plans or
specifications.

               (2) Any failure by Tenant to pay any amounts due hereunder shall
have the same effect under the Lease as a failure to pay Rent and any failure by
Tenant to perform any of its other obligations hereunder shall be subject to
Paragraph 24 of the Lease.




INITIALS:
         -----------------------------

TENANT: /s/
       -------------------------------

LANDLORD /s/
        ------------------------------







                                       6.

<PAGE>   23
                                  EXHIBIT H-FA

                          EXPANSION SPACE WINDOW DATES




<TABLE>
<CAPTION>
CONDITION                                                             INITIAL WINDOW DATE
---------                                                             -------------------
<S>                                                                   <C>
Certificate from Landlord's Architect that the foundation of the         [...***...]
Building has been completed.

Certificate from Landlord's Architect that the construction of           [...***...]
the Building has progressed to a "Water Tight Shell"

Temporary Certificate of Occupancy                                       [...***...]
</TABLE>




INITIALS:
         -----------------------------

TENANT: /s/
       -------------------------------

LANDLORD /s/
        ------------------------------






* CONFIDENTIAL TREATMENT REQUESTED


                                       1.

<PAGE>   24
                                    EXHIBIT Z

                             BASIC LEASE INFORMATION




<TABLE>
<S>                                              <C>                                
                                     Lease Date:  November 7, 1997; amended by First Amendment
                                                  dated November 10, 1998

                                       Landlord:  HMS Gateway Office, L.P.
                                                  a Delaware limited partnership

                             Landlord's Address:  c/o Hines Interests Limited Partnership
                                                  101 California Street, Suite 1000
                                                  San Francisco, California  94111-5848
                                                  Attn:  Tom Kruggel

                                                  All notices sent to Landlord
                                                  under this Lease shall be sent
                                                  to the above address, with
                                                  copies to:

                                                  Hines Interests Limited Partnership
                                                  101 California Street, Suite 1000
                                                  San Francisco, California  94111-5848
                                                  Attn:  Paul Paradis

                                         Tenant:  Coulter Pharmaceutical, Inc.,
                                                  a Delaware corporation

                        Tenant's Contact Person:  William G. Harris

  Tenant's Address and Telephone Number prior to  550 California Avenue
                          the Commencement Date:  Suite 200
                                                  Palo Alto, California  94306-1440
                                                  (650) 842-7300

 Tenant's Address and Telephone Number after the  600 Gateway Boulevard
                              Commencement Date:  South San Francisco, California  94080
                                                  (650) ___-__________

                         Premises Square Footage  [...***...] square feet, subject to final
                                                  determination by Landlord's Architect upon
                                                  Commencement of the Term.  Such measurement
                                                  to be made in accordance with Landlord's
                                                  Architect's standard measurement procedures
                                                  or research and development space.

                               Premises Address:  600 and 650 Gateway Boulevard
                                                  South San Francisco, California

                                        Project:  Approximately 7.85 acres of land commonly
                                                  known as Lot 2B of the Gateway Center and
                                                  referred to as the Gateway Technology Center,
                                                  together with the land and improvements on
                                                  which the Project is situated and all Common
                                                  Areas.
</TABLE>



* CONFIDENTIAL TREATMENT REQUESTED

                                       1.

<PAGE>   25
<TABLE>
<S>                                              <C> 
      Building (if not the same as the Project):  600 Gateway Boulevard
                                                  South San Francisco, California

        Tenant's Proportionate Share of Project:  [...***...] subject to adjustment in
                                                  accordance with Paragraph 4(c)(3)

       Tenant's Proportionate Share of Building:  100%

                                 Length of Term:  [...***...]

                    Estimated Commencement Date:  November 14, 1998 for the Original Premises;
                                                  September 1, 1999 for the Expansion Space

                      Estimated Expiration Date:  [...***...]

          Monthly Base Rent (Original Premises):  [...***...]

                                                  The above Monthly Base Rent
                                                  calculations are subject to
                                                  change after final
                                                  determination of the Premises
                                                  Square Footage and any such
                                                  adjustment shall be based on a
                                                  Monthly Base Rent for the
                                                  first Lease year of
                                                  [...***...] per square foot
                                                  multiplied by the Premises
                                                  Square Footage, and each
                                                  subsequent Lease Year being
                                                  [...***...] of the preceding
                                                  Lease Year's Monthly Base
                                                  Rent.

            Monthly Base Rent (Expansion Space):  Monthly Base Rent for the Expansion Space
                                                  shall, as of the Expansion Space Commencement
                                                  Date, be an amount [...***...] the applicable
                                                  rate per square foot being charged from time
                                                  to time under the Lease for the Original
                                                  Premises multiplied by the square footage of
                                                  the Expansion Space.  The rate per square
                                                  foot being charged under the Lease for the
                                                  Original Premises shall be determined by
                                                  dividing the Monthly Base Rent due for the
                                                  Original Premises by the Premises Square
                                                  Footage for the Original Premises.

                                   Prepaid Rent:  None

                        Prepaid Additional Rent:  None

                               Security Deposit:  [...***...]

                                  Permitted Use:  General office and research and development
                                                  activities associated with
                                                  biotechnology/pharmaceutical services. All uses
                                                  must be in accordance with zoning ordinances of
                                                  the City of South San Francisco.
                              
                      Unreserved Parking Spaces:  [...***...] non-exclusive and undesignated
                                                  parking spaces.
</TABLE>



* CONFIDENTIAL TREATMENT REQUESTED

                                       2.


<PAGE>   26


<TABLE>
<S>                                              <C> 
                                      Broker(s):  CB Commercial Real Estate Group, Inc.
                                                  CB Madison Advisory Group

                             Tenant's Allowance:  [...***...] with respect to the Original Premises
                                                  [...***...] with respect to the Expansion Space
</TABLE>





* CONFIDENTIAL TREATMENT REQUESTED


                                       3.