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                                                                   Exhibit 10.16

[ACTIVBIOTICS(R) LOGO]

February 27, 2005

Suzanne Cadden, M.Sc.
2782 Termini Terrace
Mississauga, Ontario L5M 5S3

Dear Suzanne:

1 am pleased to offer you the position of VICE PRESIDENT, REGULATORY AFFAIRS AND
CANADIAN OPERATIONS, with ActivBiotics (Canada) Inc., on the following terms and
conditions:

Your start date will be March 21, 2005, which shall be your service date for all
purposes. You acknowledge and agree that there is no recognition of service with
your previous employer for any purpose.

In this position, you will report to Steven C. Gilman, Ph.D, PRESIDENT. You will
be responsible for all aspects of global regulatory affairs as well as for
managing the Company's operations with respect to ongoing or planned clinical
studies and contract manufacturing activities in Canada. You may be assigned
other duties from time to time commensurate with your position. Your principal
work location will be in your home office in Toronto, Canada, but you may be
required to travel from time to time for the purposes of carrying out your
duties and responsibilities, including, but not limited to, being present at the
ActivBiotics (US) Inc. facility located in Lexington, MA. We expect your
maximum time commitment to be present at the US facility in Lexington, MA will
be 2 full days/week for the first 4 weeks and thereafter for 2 full days every
other week.

Your annual base salary will be $210,000 payable in semi-monthly installments of
$8,750.00 in accordance with the Company's normal payroll practice. You will
also participate in our annual bonus program, wherein you will be eligible to
earn up to 25% of your annual base salary. Any bonus payout will be based upon
your individual performance against agreed upon objectives, as well as company
and management team performance against objectives. Bonus is entirely
discretionary on the part of the Company and there is no guarantee of a bonus in
any particular year. Under no circumstances is the bonus to be considered part
of your base salary or other regular employment income. If your employment
ceases for any reason, you will not be entitled to any bonus payable after your
last day or active service. Bonus payments may be made in cash, stock or a
combination of both, at the discretion of the Board of Directors. Any bonus
payment applicable to 2005 shall be pro-rated based on your start date with the
Company.

You will also be eligible to participate in the Company's stock option plan (the
"Plan") with an initial grant of an option exercisable for 580,000 shares (the
"Option"). The Plan, and this initial grant, including the strike price thereof,
is subject to the approval of the Company's Board of Directors. If approved, the
Option will be subject to the terms and conditions of the Plan. The Stock Option
Agreement that you will be required to sign as a condition of participation in
the

     ActivBiotics, Inc. 128 Spring Street, Lexington, MA 02421 781-372-4800
                                Fax 781-274-9129

                              www.activbiotics.com

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Plan (the "Option Agreement") will include, among other things, a vesting
schedule stating that the Option will vest 25% on the anniversary of the date
you commence employment with the Company, and then annually thereafter over a
period of three years from such anniversary, provided you remain actively
employed with the Company on each applicable vesting date. Should the Company
dissolve or otherwise cease to exist for any reason, your entitlements relative
to the Options shall be governed by the Plan terms, including any entitlement to
convert Company common stock owned to ActivBiotics (US) Inc. common stock in
certain circumstances. Any additional Options granted will be subject to their
applicable option agreement and the option plan then in effect. Suzanne, this
award represents an important equity position in the Company and we look forward
to working together to continue build the value of this company.

You will be eligible to participate in a comprehensive benefits package
commensurate with the benefits presently by employees of ActivBiotics, Inc.,
including with respect to:

-    Health and dental insurance

-    Long and short term disability insurance

-    8 fixed and 4 floating holidays

-    Membership in a 401K retirement plan (or equivalent)

-    Direct deposit of payroll (OPTIONAL)

-    Four (4) weeks (20 days) paid vacation time per year (pro-rated for 2005
     based on your start date).

Your employment with the Company may be terminated for Cause at any time. In
such event you will not be entitled to receive any further compensation or
benefits whatsoever other than those which are accrued but unpaid up to the date
of notice of termination.

     For purposes of this letter:

     "Cause" shall include, but not be limited to, any one or more of the
following: (i) your substantial and continuing failure to perform the material
responsibilities of your position in a competent manner, provided you first
receive notice from the Board or the President of such failure and such failure
is not corrected within 30 days of such notice; (ii) your willful misconduct
fraud, or material dishonesty that results in material harm to the Company;
(iii) your breach of fiduciary duty to the Company; (iv) your disregard of the
rules or policies of the Company or directions from the Board or the President
of the Company, which results in material harm to the Company; (v) your
commission of an act which constitutes unfair competition with the Company or
which induces any customer or supplier to breach a contract with the Company;
(vi) your material breach of the Invention and Non-Disclosure agreement or any
other agreement executed by you with the Company; or (vii) any other grounds at
common law for which an employer is entitled to dismiss an employee summarily.

Should the Company terminate your employment due to its dissolution or
discontinuation of operations, we fully expect to discuss with you employment
opportunities that may be available with ActivBiotics (US) Inc. However, nothing
in this preceding statement should be considered as a binding obligation or
entitlement to provide you alternative employment, benefits, salary or any
compensation whatsoever should the Company dissolve or otherwise discontinue its
operations.

If your employment is terminated by the Company without Cause, the Company shall
provide you a separation package ("Separation Package") whereby the Company
shall pay you, in accordance with its normal payroll practice, an amount
equivalent to your base salary at the base salary rate in effect as of the date
you are notified of termination from now until the earlier of: 5 months from
your termination date and the date you obtain alternate employment ("Salary

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Continuance Period"). Alternate employment shall mean full-time employment in
the pharmaceutical industry in a position comparable to your position with the
Company. However, under no circumstances shall the Separation Package be less
than the greater of: (i) an amount equivalent to 3 months' base salary at the
base salary rate as of the date you are notified of termination; or (ii) the
minimum amounts required to be paid under applicable employment standards
legislation. As part of the Separation Package, benefits coverage shall be
continued for the minimum period required by applicable employment standards
legislation. Other than the salary and benefits continuation described in this
paragraph, you will not be entitled to any other compensation or benefits of
employment during the Salary Continuance Period, including, without limitation,
vacation pay, bonus, and the issuance or vesting of stock options.

You agree that the Separation Package described above is reasonable notice of
termination and specifically includes all amounts owing for termination and/or
severance pay under any contract, statute, common law or otherwise. You further
agree that you will execute a general release in a form and substance that is
reasonable and satisfactory to the Company prior to you receiving any payments
under the Separation Package.

Prior to your start date, you must verify that the performance of your position
at the Company does not and will not breach any agreement entered into by you
prior to employment with the Company (i.e., you have not entered into any
agreements with previous employers that are in conflict with your obligations to
the Company.) Your employment is conditional upon the absence of any such
conflicting agreements. Please provide us with a copy of any potentially
conflicting agreements for our review. You will also be required to sign the
Company's standard Invention and Non-Disclosure Agreement (INA), which is
enclosed. Your execution of and continued compliance with the INA is also a
condition of your employment with the Company.

Upon commencement of employment on your start date under the terms of this
letter, you shall be entitled to a signing bonus of $5,000, which shall be paid
to you within 30 days of your start date.

All payments and benefits described in this letter are in Canadian Dollars and
are subject to standard and applicable withholdings and deductions.

This employment offer letter and the INA attached hereto supersedes and replaces
all prior negotiations and/or agreements made between you and the Company,
whether oral or written and your agreement to the terms and conditions in this
employment offer and signing of this letter has not been induced by, nor do you
rely upon or regard as material any representations or writings whatsoever not
incorporated into and made a part of this employment offer letter.

Suzanne, we are confident that you will make important contributions to
ActivBiotics (Canada) Inc., and we look forward to working with you. This offer
will be open for acceptance until March 4, 2005. Please do not hesitate to
contact me if you have any questions. In order to accept the position as
offered, please sign this letter, the attached INA and application for
employment for our records, and return both to me.

Sincerely,

/s/ Steven C. Gilman
-------------------------------------
Steven C. Gilman, PhD
President
ActivBiotics (Canada) Inc.

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I have received a copy of this letter. I have read, considered and understood
and hereby accept its terms and conditions. I acknowledge having been given an
opportunity to obtain legal consultation and advice with respect to the terms
and conditions contained in this letter, and execute this agreement freely and
voluntarily with full understanding of its contents. I agree to sign and be
bound by the attached Invention and Non-Disclosure Agreement. This employment
offer and my employment hereunder have not been induced by any representations
of the Company not contained herein.

/s/ Suzanne Cadden
-------------------------------------
Suzanne Cadden<Page>

                                                                   Exhibit 10.17
                                                                        ORIGINAL

[ACTIVBIOTICS LOGO]

January 17, 2006

Dr. Constantine E. Anagnostopoulos
435 Dockside Drive, #902
Naples, Florida 34110

Dear Dr. Anagnostopoulos:

On behalf of the Board of Directors of ActivBiotics (the "Company"), I am
pleased to offer you a position as a member of the Board of Directors, effective
December 30, 2005.

As an independent member of the Board, we offer you the following compensation
package:

CASH COMPENSATION: $10,000 annual compensation, payable in 4 quarterly
installments.

STOCK OPTIONS: You will be eligible to receive periodic grants of stock options,
as recommended by the ActivBiotics Board of Directors Compensation Committee,
(once this committee is newly constituted) and upon approval by the full Board
of Directors. These option grants will vest in equal monthly installments over a
four-year period from the date of grant, so long as you continue to serve as a
Director, at an exercise price equal to the Fair market value of the Company's
Common Stock on the date of the grant.

EXPENSES. The Company will reimburse you for all reasonable and necessary
out-of-pocket expenses incurred by you in connection with the performance of
your duties as a Director.

INDEMNIFICATION. The Company shall, to the fullest extent permitted by Delaware
General Corporation law as then in effect, indemnify you if as a result of your
position as a director of the Company you are involved in any manner (including,
without limitation, as a party or a witness) or are threatened to be made so
involved in any threatened, pending or completed investigation, claim, action,
suit or proceeding, whether civil, criminal, administrative or investigative
(including, without limitation, any action, suit or proceeding by or in the
right of the Company to procure a judgment in its favor) (a "Proceeding")
against all expenses (including reasonable attorneys' fees), judgments, fines
and amounts paid in settlement actually and reasonably incurred by you in
connection with such Proceeding. Such indemnification shall be a contract right
and shall include the right to receive payment in advance of any expenses
incurred by you in connection with such Proceeding.

     ActivBiotics, Inc. 110 Hartwell Avenue, Lexington MA 02421 781-372-4800
                                Fax 781-274-8638
                              www.activbiotics.com

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INSURANCE. The Company is covered by Directors and Officers Liability and
Reimbursement Insurance issued by Carolina Casualty Company with a $5,000,000
liability limit

Costas, ActivBiotics has an exciting future, but of course faces many challenges
in realizing its ultimate potential. We can only achieve our vision for the
Company with the help of individuals like you who have a significant breath and
depth of experience, demonstrated talent and personal commitment. To that end, I
welcome you to join the ActivBiotics Board of Directors.

Sincerely,

/s/ Dr. Alan Dunton, MD
----------------------------------------
Dr. Alan Dunton, MD
Chairman, ActivBiotics

I hereby accept my election as a member of the Board of Directors of
ActivBiotics, effective December 30, 2005.

/s/ Constantine E Anagnostopoulos
----------------------------------------
Constantine E Anagnostopoulos

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