<PAGE>

                                                                   Exhibit 10.28

               Alteon Severance Plan and Summary Plan Description

The following is the Alteon Severance Plan ("Severance Plan"), effective June 1,
2005 (the "Effective Date"). This Severance Plan supersedes any and all
previously communicated severance policies, plans and arrangements of Alteon.
All such previously communicated Alteon severance policies or plans are, as of
the Effective Date, terminated, unless part of an express written agreement
applicable to only the employee and Alteon and signed by each.

This Severance Plan may be amended, modified or terminated by the Company, in
its discretion, at any time.

This document serves as the Severance Plan document and your Summary Plan
Description.

Alteon ("Alteon" or the "Company") recognizes and values your contributions to
this Company. The Severance Plan, as explained more fully below, is designed to
reaffirm Alteon's desire to retain you as part of our team and to provide
increased economic security and assurances as we continue to work together to
develop alagebrium chloride.

On rare occasions, at the sole and unfettered discretion of Company management,
additional or alternate severance may be offered to certain employees when
employment with the Company is terminated. Such severance is independent of the
Severance Plan and is not intended to be covered by its terms.

The Severance Plan details are as follows:

1.   Eligibility

If you are employed by Alteon and have been provided with notice of your
eligibility to the Severance Plan by the Company, otherwise meet the eligibility
requirements, and your employment with the Company is involuntarily terminated
under limited, specified circumstances (as described in Section 2 of this
Severance Plan), you will be eligible to receive Severance Payments and Benefits
under Section 3 of this Severance Plan, provided, however, that your notice of
eligibility may be rescinded at any time in the Company's sole discretion,

As a condition of eligibility for severance under this Severance Plan, you must
be actively employed by the Company on the date of the triggering event under
Section 2 of this Severance Plan. You also will be required to execute a
separation agreement and/or confirmation of non-compete agreement prepared by
the Company which may include, among other things, a general release of all
claims against the Company, its affiliates, successors or assigns. If you are
required to sign an agreement as a condition to receiving severance and do not
sign or if you revoke your acceptance, you will not be eligible to receive
severance benefits.

2.   Triggering Event

If you are an eligible employee whose position is eliminated as the result of
Alteon's decision to restructure the organization, close a facility or otherwise
reduce the workforce, and you remain with the Company through the effective date
of such elimination (a "Triggering Event"), you will qualify for the Severance
Payments and Benefits described in Section 3 of this Severance Plan. If the
Company or its assets are sold, you will not be eligible for severance unless
you are terminated from your employment as a result of such sale. Whether you
are being terminated as a result of a sale of the Company or its assets, this
will be determined by the Company, in its sole discretion, in its capacity as
Plan Administrator and such decision shall be final and binding as set forth in
Section 9 hereof. Employees who leave their jobs voluntarily or

<PAGE>

who are terminated for "cause" or any reason other than those identified above
will not be eligible for benefits under this Severance Plan.(1)/

3.   Severance Payments and Benefits

     A.   Up to six (6) months of salary payments following Triggering Event

If you are eligible for benefits, and experience a Triggering Event, under this
Severance Plan, you shall be entitled to up to 6 months of severance salary
payments paid in installments according to your current pay schedule at the time
of separation. Payments shall be based on your base pay only at the time of
termination (excluding bonus, overtime and anything other than base pay). All
payments made pursuant to this Severance Plan shall be subject to all applicable
taxes and withholding, as required by law, and shall be offset by amounts, if
any, that you may owe to the Company at the time of your termination.

These severance payments are intended to provide financial support during a
period of employment transition. If you secure other employment during the
6-month period following the Triggering Event, the Company's obligation to pay
you severance payments will end. It is your duty to inform the Company
immediately once such new employment of any kind is secured. If you fail to
notify the Company of your acceptance of such employment immediately, you will
forfeit your right to any and all payments made pursuant to this Severance Plan
and the Company shall be entitled to reimbursement for all payments made to you
hereunder.

     B.   Up to three (3) months COBRA payments for medical and dental benefits
          following Triggering Event

If you are (i) eligible for benefits and experience a Triggering Event under the
terms of this Severance Plan, and (ii) entitled to, and elect, to continue your
health care coverage under COBRA, upon your enrollment the Company will pay your
COBRA premiums for up to 3 months following the Triggering Event, provided that
you do not have other employment. If you secure other employment during the
3-month period following the Triggering Event, the Company's obligation to pay
your COBRA premiums will immediately end. You will, however, have the right to
continue on COBRA at your own expense to the extent permitted under applicable
law.

4.   Status of the Severance Plan

This Severance Plan is a welfare benefit plan, as defined in Section 3(1) of the
Employee Retirement Income Security Act of 1974, as amended ("ERISA") and shall
be construed and interpreted in accordance with such section of ERISA.

5.   Funding of Plan Obligations

All payments under Section 3 of this Severance Plan shall be made solely from
the general assets of the Company at such time as those payments may become due.

6.   No Assignment

Unless and until otherwise paid to you pursuant to the terms of this Severance
Plan, benefits payable to you under this Severance Plan may not be anticipated,
assigned (either at law or in equity), alienated, pledged, encumbered or
subjected to attachment, garnishment, levy, execution or other legal or
equitable process.

----------
(1)/ For the purpose of this Agreement, "cause" is as defined in the Alteon
     Associate Handbook.


                                       2

<PAGE>

7.   Amendment, Termination and Modification

This Severance Plan may be amended, modified or terminated by the Company, in
its discretion, at any time.

8.   No Contract of Employment

This Severance Plan does not constitute a contract of employment and nothing
herein shall affect the Company's right to terminate an employee's employment at
any time, with or without cause.

9.   Plan Administrator

The Company or its designee shall serve as Plan Administrator of the Severance
Plan. The Plan Administrator shall be responsible for administering the
Severance Plan and shall have absolute discretion to make all determinations,
both factual and legal, with respect to the operation of the Severance Plan,
including but not limited to determinations regarding participation, eligibility
and benefits calculations. The Plan Administrator's decisions will be final and
binding and shall be subject to review only for an abuse of discretion.

10.  Claims Procedures

Any request for benefits (a "Claim") by you or your authorized representative (a
"Claimant") must be filed in writing with the Plan Administrator. Within ninety
(90) days after receipt of a Claim, the Plan Administrator will provide written
notice to any Claimant whose Claim has been wholly or partly denied, including:

     (i)  the reasons for the denial;

     (ii) the Plan provisions on which the denial is based;

     (iii) any additional material or information necessary to perfect the Claim
          and the reasons it is necessary; and

     (iv) the claims review procedure.

Any Claimant whose application for benefits is denied, in whole or in part, may
appeal from such denia1 to the Plan Administrator for a review of the decision
by submitting to the Plan Administrator within sixty (60) days after receiving
written notice from the Plan Administrator of the denial of the Claim a written
statement:

     (i)  requesting a review of the application for benefits by the Plan
          Administrator;

     (ii) setting forth all of the grounds upon which the request for review is
          based and any facts in support thereof; and

     (iii) setting forth any issues or comments which the Claimant deems
          relevant to the application.

The Plan Administrator shall act upon each such application within sixty (60)
days after either receipt of the Claimant's request for review by the Plan
Administrator or receipt of any additional materials reasonably requested by the
Plan Administrator from such Claimant, whichever occurs later.

The Plan Administrator shall, in its discretion, make a full and fair review of
each such Claim and any written materials submitted by the Claimant or the
Company in connection therewith and may require the Company or the applicant to
submit within a reasonable number of days after receiving a written notice


                                       3

<PAGE>

from the Plan Administrator such additional facts, documents or other evidence
as is deemed necessary or advisable in the sole discretion of the Plan
Administrator in making such a review. On the basis of the review, the Plan
Administrator shall make an independent determination of the applicant's
eligibility for benefits under the Plan. The decision of the Plan Administrator
on any application for benefits shall be final and conclusive upon all persons.
If the Plan Administrator denies an appeal application in whole or in part, the
Plan Administrator shall give written notice of the decision to the Claimant
setting forth the specific reasons for such denial and specific references to
the pertinent Plan provisions on which the Plan Administrator's decision is
based. Such written notice shall be given within sixty (60) days of the date the
appeal was filed; provided, however, the Plan Administrator may extend the
period for providing notice hereunder for up to an additional sixty (60) days if
the Plan Administrator determines it is necessary and notifies the applicant in
writing prior to the expiration of the initial sixty (60) day period.

11.  ERISA Rights

As a participant in the Severance Plan you are entitled to certain rights and
protections under ERISA. ERISA provides that all Severance Plan participants
shall be entitled to:

     A.   Receive Information About Your Plan and Benefits

Obtain, upon written request to the Plan Administrator, copies of documents
governing the operation of the Plan. The Plan Administrator may make a
reasonable charge for the copies.

     B.   Prudent Actions by Plan Fiduciaries

In addition to creating rights for Plan participants, ERISA imposes duties upon
the people who are responsible for the operation of the employee benefit plan.
The people who operate your Plan, called "fiduciaries" of the Plan, have a duty
to do so prudently and in the interest of you and other Plan participants and
beneficiaries. No one, including your employer, your union, or any other person,
may fire you or otherwise discriminate against you in any way to prevent you
from obtaining a welfare benefit or exercising your rights under ERISA.

     C.   Enforce Your Rights

If your claim for a severance benefit is denied or ignored, in whole or in part,
you have a right to know why this was done, to obtain copies of documents
relating to the decision without charge, and to appeal any denial, all within
certain time schedules.

Under ERISA, there are steps you can take to enforce the above rights. For
instance, if you request a copy of Plan documents or the latest annual report
from the Plan and do not receive them within 30 days, you may file suit in a
Federal court. In such a case, the court may require the Plan administrator to
provide the materials and pay you up to $110 a day until you receive the
materials, unless the materials were not sent because of reasons beyond the
control of the Plan Administrator. If you have a claim for benefits which is
denied or ignored, in whole or in part, you may file suit in a state or Federal
court. In addition, if you disagree with the Plan's decision or lack thereof
concerning the qualified status of a domestic relations order or a medical child
support order, you may file suit in Federal court. If it should happen that Plan
fiduciaries misuse the Plan's money, or if you are discriminated against for
asserting your rights, you may seek assistance from the U.S. Department of
Labor, or you may file suit in a Federal court. The court will decide who should
pay court costs and legal fees. If you are successful the court may order the
person you have sued to pay these costs and fees. If you lose, the court may
order you to pay these costs and fees, for example, if it finds your claim is
frivolous.

     D.   Assistance with Your Questions

If you have any questions about your Plan, you should contact the Plan
Administrator. If you have any questions about this statement or about your
rights under ERISA, or if you need assistance in obtaining


                                       4

<PAGE>

documents from the Plan Administrator, you should contact the nearest office of
the Employee Benefits Security Administration, U.S. Department of Labor, listed
in your telephone directory or the Division of Technical Assistance and
Inquiries, Employee Benefits Security Administration, U.S. Department of Labor,
200 Constitution Avenue NW, Washington, D.C., 20210. You may also obtain certain
publications about your rights and responsibilities under ERISA by calling the
publications hotline of the Employee Benefits Security Administration. You may
also visit their website at www.dol.gov/ebsa.

12.  General Information

Name and Identification of Plan:

Alteon Severance Plan
Plan No. 502

Plan Sponsor:

Alteon
6 Campus Drive
Parsippany, New Jersey 07054
EIN: 13-3304550

Plan Administrator and Agent for Service of Process:

Alteon
6 Campus Drive
Parsippany, New Jersey 07054
(201) 934-5000
Attention: Human Resources

The Plan Year for the Plan is the twelve-month period ending each December 31.


                                       5