Document:

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EXHIBIT 10.63

                        AGREEMENT REGARDING PAY-TO-STAY

         This Agreement is entered into as of April 28, 2000, by and between
Aastrom Biosciences,  Inc., a Michigan corporation ("Employer"),  and R. Douglas
Armstrong, Ph.D. ("Employee"), with respect to the following facts:

                                   RECITALS

         A. Employer currently employs Employee.

         B. In the Fall of 1999, Employer was experiencing severe financing
difficulties, such that Employer needed to substantially reduce operations and
the number of its employees, and Employer was seeking to be acquired by a third
party. Under these circumstances, Employer found it to be necessary to offer and
enter into a "Pay to Stay Severance Agreement" with Employee, in order to induce
Employee to remain employed by Employer through April 30, 2000.

         C. Pursuant to the Pay to Stay Severance Agreement, Employee is
entitled to receive a twelve month salary severance payment (the "Payment Sum")
upon termination of employment, so long as Employee remains employed through
April 30, 2000. Since the Fall of 1999, Employer's financing position has
improved, such that Employer's current focus is on growing and developing its
business, rather than to principally pursue an acquisition transaction.
Accordingly, Employer would like the employment of Employee to continue, and
Employer does not want Employee to have an incentive to terminate employment in
order to obtain the Payment Sum or to obtain full vesting of Employee's stock
options.

         D. In view of the fact that Employee has been willing to remain in the
employment of Employer during the past difficult months, and the fact that
Employee has been supportive and instrumental in helping Employer attain its
current position, Employer has concluded that Employee has now fully earned the
Payment Sum.

         E. Pursuant to the Pay to Stay Severance Agreement, Employee was also
entitled to an "Incentive Sale Bonus" based upon the net sales proceeds from a
third party acquiring Employer.

         WHEREFORE, the parties hereto mutually agree as follows:

         1. Severance Pay.  For and in consideration of the matters set forth
            -------------
herein, Employer hereby agrees to pay to Employee within the next thirty days
the Payment Sum, less applicable payroll deductions.
<PAGE>

         2.  Incentive Sale Bonus.  Employer and Employee hereby acknowledge and
             --------------------
agree (i) that the Incentive Sale Bonus remains in effect and applicable to
Employer being acquired by (by sale or merger) another company and provided that
Employee remains an employee of Employer through the completion of the
acquisition transaction, (e.g. through approval by the shareholders of the
merger transaction) excepting however, that such continued employment shall not
be required or applicable if Employer terminates Employee's employment without
cause.

         3.  Stock Vesting.  The parties reaffirm and agree that for all
             -------------
unvested stock options granted by Employer to Employee prior to the date of this
agreement, and for all stock subject to Employer's buy back right, there shall
be accelerated and immediate vesting upon the date of this agreement.

         4.  Prior Agreement.  The parties acknowledge and agree that the prior
             ---------------
Executive Retention and Severance Agreement, dated February 2, 1999, pursuant to
which Employee is entitled to certain severance pay, remains in full force and
effect.

         5.  Acknowledgment of No Claims.  Employee hereby acknowledges and
             ---------------------------
confirms that Employee has no claims against Employer, or any director, officer,
shareholder or agent of Employer, with respect to any employment matters (except
as set forth in this Agreement, and for ordinary course of business salary,
fringe benefits, accrued vacation leave and reimbursement of customary business
expenses incurred on behalf of Employer, all in the ordinary course of
business). Further, Employee acknowledges and confirms that Employee's
employment with Employer continues on an "at will" basis, with no expressed or
implied continued duration of employment.

         6.  General.
             -------

             a.  Excepting Section 2 ("Incentive Sale Bonus") as provided in
Section 2 of the Pay to Stay Severance Agreement entered into the Fall of 1999,
the Pay to Stay Severance Agreement is hereby terminated in its entirety.

             b.  This Agreement shall bind and inure to the benefit of the
parties' successors, assigns, heirs and legal representatives.

             c.  This Agreement may be modified, amended or superseded only by a
written document signed by both parties.

             d.  Employee acknowledges that this Agreement confers significant
legal rights on Employee, and also involves Employee waiving other potential
rights he/she might have under other agreements and laws. Employee acknowledges
that Employer has encouraged Employee to consult with Employee's own legal, tax
and financial advisors before signing this Agreement, and Employee acknowledges
that Employee has had an adequate time to do so before signing this Agreement.

             e.  This Agreement may be executed in counterparts, each of which
shall be deemed an original, and all of which taken together will constitute one
and the same instrument.

         IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Agreement as of June 18, 2000.
<PAGE>

                                          EMPLOYER:

                                              Aastrom Biosciences, Inc.

                                              By: /s/ Arthur F. Staubitz
                                              --------------------------

                                          EMPLOYEE:

                                              /s/ R. Douglas Armstrong
                                              --------------------------
                                              Print Name: R. Douglas Armstrong<PAGE>

Exhibit 10.64

                        AGREEMENT REGARDING PAY-TO-STAY

         This Agreement is entered into as of June 30, 2000, by and between
Aastrom Biosciences, Inc., a Michigan corporation ("Employer"), and Todd E.
Simpson ("Employee"), with respect to the following facts:

                                   RECITALS

         A. Employer currently employs Employee.

         B. In the Fall of 1999, Employer was experiencing severe financing
difficulties, such that Employer needed to substantially reduce operations and
the number of its employees, and Employer was seeking to be acquired by a third
party. Under these circumstances, Employer found it to be necessary to offer and
enter into a "Pay to Stay Severance Agreement" with Employee, in order to induce
Employee to remain employed by Employer through April 30, 2000.

         C. Pursuant to the Pay to Stay Severance Agreement, Employee is
entitled to receive a six month salary severance payment (the "Payment Sum")
upon termination of employment, so long as Employee remains employed through
April 30, 2000. Since the Fall of 1999, Employer's financing position has
improved, such that Employer's current focus is on growing and developing its
business, rather than to principally pursue an acquisition transaction.
Accordingly, Employer would like the employment of Employee to continue, and
Employer does not want Employee to have an incentive to terminate employment in
order to obtain the Payment Sum or to obtain full vesting of Employee's stock
options.

         D. In view of the fact that Employee has been willing to remain in the
employment of Employer during the past difficult months, and the fact that
Employee has been supportive and instrumental in helping Employer attain its
current position, Employer has concluded that Employee has now fully earned the
Payment Sum.

         E. Pursuant to the Pay to Stay Severance Agreement, Employee was also
entitled to an "Incentive Sale Bonus" based upon the net sales proceeds from a
third party acquiring Employer.

         WHEREFORE, the parties hereto mutually agree as follows:

         1. Severance Pay.
            -------------

            a.  For and in consideration of the matters set forth herein,
Employer hereby agrees to pay to Employee within the next thirty days the
Payment Sum, less applicable payroll deductions.

         2. Incentive Sale Bonus.  Employer and Employee hereby acknowledge and
            --------------------
agree (i) that the Incentive Sale Bonus remains in effect and applicable to
Employer being acquired by (by sale or merger) another company and provided that
Employee remains an employee of Employer through the completion of the
acquisition transaction, (e.g. through approval by the
<PAGE>

shareholders of the merger transaction) excepting however, that such continued
employment shall not be required or applicable if Employer terminates Employee's
employment without cause.

         3. Stock Vesting.  The parties agree that for all unvested stock
            -------------
options granted by Employer to Employee prior to the date of this agreement,
there shall be accelerated and immediate vesting as of the date of this
agreement.

         4. Prior Agreement.  The parties acknowledge and agree that the prior
            ---------------
Supplemental Agreement to Employment Agreement, dated September 24, 1999,
pursuant to which Employee is entitled to certain severance pay, remains in full
force and effect.

         5.  Acknowledgment of No Claims. Employee hereby acknowledges and
             ---------------------------
confirms that Employee has no claims against Employer, or any director, officer,
shareholder or agent of Employer, with respect to any employment matters (except
as set forth in this Agreement, and for ordinary course of business salary,
fringe benefits, accrued vacation leave and reimbursement of customary business
expenses incurred on behalf of Employer, all in the ordinary course of
business). Further, Employee acknowledges and confirms that Employee's
employment with Employer continues on an "at will" basis, with no expressed or
implied continued duration of employment.

         6.  General.
             -------

             a.  Excepting Section 2 ("Incentive Sale Bonus") as provided in
Section 2 of the Pay to Stay Severance  Agreement entered into the Fall of 1999,
the Pay to Stay Severance Agreement is hereby terminated in its entirety.

             b.  This Agreement shall bind and inure to the benefit of the
parties' successors, assigns, heirs and legal representatives.

             c.  This Agreement may be modified, amended or superseded only by a
written document signed by both parties.

             d.  Employee acknowledges that this Agreement confers significant
legal rights on Employee, and also involves Employee waiving other potential
rights he/she might have under other agreements and laws. Employee acknowledges
that Employer has encouraged Employee to consult with Employee's own legal, tax
and financial advisors before signing this Agreement, and Employee acknowledges
that Employee has had an adequate time to do so before signing this Agreement.

             e.  This Agreement may be executed in counterparts, each of which
shall be deemed an original, and all of which taken together will constitute one
and the same instrument.

         IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Agreement as of June 30, 2000.

                                          EMPLOYER:

                                                Aastrom Biosciences, Inc.
<PAGE>

                                                By: /s/ R. Douglas Armstrong
                                                ----------------------------

                                          EMPLOYEE:

                                                 /s/ Todd E. Simpson
                                                 -------------------
                                                 Print Name: Todd E. Simpson

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