<PAGE>

                                                                    Exhibit 10.4


                              PURCHASE AGREEMENT


     AGREEMENT dated as of June 13, 1996 by and among ImmunoTherapeutics, Inc.,
a Delaware corporation (the "Company"), Dominion Resources, Inc., a Delaware
corporation ("Seller") and The Aries Fund, a Series of the Aries Trust, a Cayman
Island Trust (the "Trust") and The Aries Domestic Fund, L.P., a Delaware limited
partnership (the "Partnership") (herein the Trust and the Fund are collectively
referred to as the "Purchasers").

                                  WITNESSETH:

     WHEREAS, the Seller desires to sell to Purchasers, at a price of $.10 per
share, 4,000,000 shares of the Company's Common Stock (the "Shares"); and

     WHEREAS, the Purchasers desire to purchase the Shares upon and subject to
the terms and conditions hereinafter set forth; and

     WHEREAS, such shares were purchased by the Seller from the Company pursuant
to a Purchase Agreement dated March 1, 1996 (the "March Purchase Agreement") (a
copy of which is attached hereto as Exhibit "All); and

     WHEREAS, the Company has been joined with and made a party to this
Agreement for the purpose of confirming the transfer of the Shares and the
assignment by the Seller to the Purchasers of certain rights (the "Rights")under
the March Purchase Agreement;

     NOW, THEREFORE, in consideration of the premises and the mutual agreements
contained herein, the parties hereto hereby agree as follows:

     1.   Purchase and Sale,-of the shares. Subject to the terms and conditions
set forth herein, the Seller hereby agrees to sell and transfer to Purchasers,
and Purchasers hereby agree to purchase from the Seller, in the amounts set
forth on Exhibit "B" hereto, the Shares at the Closing (as such term is defined
in Section 2.1 hereof). The purchase price for the Shares sold pursuant to this
Agreement shall be $.10 per Share, together with the assignment of the Rights.

     2.   Closing; Termination.

     2.1  Closing. The closing of the purchase and sale of the Shares will take
place at the offices of Purchasers at 375 Park Avenue, Suite 1501, New York, New
York. Such closing (the "Closing") will take place at 11:00 A.M., local time, on
June 13, 1996. Such Closing may take place at such other time and place or on
such later date as may be mutually agreeable to the parties hereto. At such
Closing, the Seller will deliver to Purchasers certificates for the Shares
purchased as not forth in Section I hereof, against payment of the purchase
price therefor by Purchasers, by wire transfer or certified check payable to the
Seller. The Shares shall be registered in Purchasers, name or the name of the
nominee of Purchasers in such denominations as Purchasers shall request
according to their instructions delivered to the Seller not less than two (2)
days prior to the Closing.

     2.2  Termination. In the event that the transactions contemplated by this
Agreement to take place at or prior to the Closing have not been consummated by
June 29, 1996, this Agreement shall, at the option of Purchasers, terminate and
be of no further force and effect, and any payment made by Purchasers to Seller
shall be refunded to Purchasers by Seller, and there shall be no further
liability on the part of any party hereto except for breaches of this Agreement
prior to the time of such termination.

     3.   Conditions to the Obligations of Purchasers at the Closing. The
obligation of Purchasers to purchase and pay for the Shares to be purchased by
Purchasers at the Closing is subject to the satisfaction on or prior to June 29,
1996 of the following conditions, satisfaction of which conditions shall not be
deemed waived unless waived in writing by Purchasers:
<PAGE>

     3.1  Opinion of Counsel to the Company. Purchasers shall have received from
William S. Clarke, P.A., counsel for the Company, its opinion dated the date of
the Closing substantially in the form of Exhibit B hereto.

     3.2  Representations And Warranties. All of the representations and
warranties of the Company contained in the March Purchase Agreement shall
continue to be true and correct on the Closing as of the date made.

     3.3  Performance of Covenants. All of the covenants and agreements of the
Seller contained in this Agreement and required to be performed on or prior to
the date of the Closing shall have been performed in a manner reasonably
satisfactory in all respects to Purchasers.

     3.4  Legal Action. No action or proceeding before any court or governmental
body shall be pending or threatened wherein an unfavorable judgment, decree or
order would prevent the carrying out of this Agreement or any of the
transactions contemplated hereby, declare unlawful the transactions contemplated
by this Agreement or cause such transactions to be rescinded.

     3.5  Consent. The Seller and the Company shall have obtained in writing all
consents required to enable each of them to observe and comply with all of their
respective obligations under this Agreement and to consummate the transactions
contemplated hereby.

     3.6  Board and committee Representation. The person designated by
Purchasers shall have been elected as a member of the Company's Board of
Directors and William McManus shall have resigned as a Director of the Company.

     3.7  Closing Documents.

          (a)  The Company shall have delivered to Purchasers a certificate
executed by the President of the Company dated the date of the Closing stating
that the conditions set forth in Sections 3.2 through 3.6 hereof as applicable
to the Company have been satisfied, and

          (b)  the Seller shall have delivered to Purchasers a certificate
executed by the President of the Seller dated the date of the Closing stating
that the conditions set forth in Sections 3.2 through 3.6 hereof am applicable
to the Sellers have been satisfied, and

          (c)  Purchasers shall have received such certificates, assignments of
the Rights, other documents and instruments as Purchasers may reasonably request
in connection with, and to effect, the transactions contemplated by this
Agreement.

     3.8  Proceedings. All corporate and other proceedings taken or to be taken
in connection with the transactions contemplated hereby to be consummated at the
Closing and all documents incident thereto shall be reasonably satisfactory in
form and substance to Purchasers.

     3.9  Redemption of Rights. The Board of Directors shall redeem prior to the
Closing all of the Company' a outstanding rights pursuant to Section 24(a)(i) of
the Rights Agreement dated as of September 23, 1994 between the Company and
American Stock Transfer and Trust Company.

     4.   Conditions to the Obligations of the Seller, at the Closing. The
obligation of the Seller to sell the Shares to Purchasers as set forth herein at
the Closing is subject to the satisfaction on or prior to the date of the
Closing of the following conditions, any of which may be waived by the Company:

     4.1  Representations and Warranties. The representations and warranties of
Purchasers contained in this Agreement shall be true and correct at and as of
the date of the Closing with the same effect as if made on the date of the
Closing, except to the extent of changes caused by the transactions contemplated
hereby.

     4.2  Legal Action. No action or proceeding before any court or governmental
body shall be pending or threatened wherein an unfavorable judgment, decree or
order
<PAGE>

would prevent the carrying out of this Agreement or any of the transactions
contemplated hereby, declare unlawful the transactions contemplated by this
Agreement or cause such transactions to be rescinded.

     4.3  Proceedings. All proceedings taken or to be taken by Purchasers in
connection with the transactions contemplated hereby shall be reasonably
satisfactory in form and substance to the Company.

     5.   Conditions to the Obligations of the Company at the Closing. The
obligation of the Company to fulfill the conditions to the Closing at the
Closing is subject to the satisfaction on or prior to the date of the Closing of
the following conditions, any of which may be waived by the Company:

     5.1  Representations and Warranties. The representations and warranties of
Purchasers contained in this Agreement shall be true and correct at and as of
the date of the Closing with the same effect au if made on the date of the
Closing, except to the extent of changes caused by the transactions contemplated
hereby.

     5.2  Performance of Covenants. All of the covenants and agreements of the
Purchasers and the Seller contained in this Agreement and required to be
performed an or prior to the date of the Closing shall have been performed in a
manner reasonably satisfactory in all respects to the Company.

     5.3  Board and Committee Representation. The person designated by
Purchasers shall have been elected as a member of the Company's Board of
Directors and William McManus shall have resigned as a Director of the Company.

     5.4  Legal Action. No action or proceeding before any court or governmental
body shall be pending or threatened wherein an unfavorable judgment, decree or
order would prevent the carrying out of this Agreement or any of the
transactions contemplated hereby, declare unlawful the transactions contemplated
by this Agreement or cause such transactions to be rescinded.

     5.5  Proceedings. All proceedings taken or to be taken by Purchasers in
connection with the transactions contemplated hereby to be consummated at the
Closing and all documents incident thereto shall be reasonably satisfactory in
form and substance to the Company.

     6.   Representation and Warranties of the Seller. The Seller hereby
represents and warrants to Purchasers au follows:

     6.1  Organization of Seller. The Seller is duly organized, validly
existing, and in good standing under the laws of the jurisdiction of its
incorporation.

     6.2  Authorization. The Seller has full corporate power and authority to
execute and deliver this Agreement and to perform its obligations hereunder.
This Agreement constitutes the valid and legally binding obligation of the
Seller, enforceable in accordance with its terms and conditions. The Seller need
not give any notice to, make any filing with, or obtain any authorization,
consent, or approval of any government or governmental agency in order to
consummate the transactions contemplated by this Agreement.

     6.3  Non-Contravention. Neither the execution and the delivery of this
Agreement, nor the consummation of the transactions contemplated hereby, will
(a) violate any provision of Seller's charter or by-laws, or (b) conflict with,
result in a breach of, constitute a default under, result in the acceleration
of, create in any party the right to accelerate, terminate, modify, or cancel,
or require any notice under any agreement, contract, lease, license, instrument,
or other arrangement to which the Seller is a party or by which it is bound or
to which any of its assets is subject.

     6.4  Brokers' Fees. The Seller has no liability or obligation to pay any
fees or commissions to any broker, finder, or agent with respect to the
transactions contemplated by this agreement for which the Purchasers could
become liable or obligated.
<PAGE>

     6.5  Shares. The Seller holds of record and owns -beneficially the Shares,
free and clear of any restrictions on transfer (other than any restrictions
under the Securities Act and state securities laws), taxes, security interests,
options, warrants, purchase rights, contracts, commitments, equities, claims,
and demands. The Seller is not a party to any option, warrant, purchase right,
or other contract or commitment that could require the Seller to sell, transfer,
or otherwise dispose of any capital stock of the Company (other than this
Agreement) . The Seller is not a party to any voting trust, proxy, or other
agreement or understanding with respect to the voting of any capital stock of
the Company. All of the Shares are validly issued, fully paid and non-
assessable.

     7.   Representations and Warranties of the Company. The Company hereby
represents and warrants to the Purchasers as follows:

     7.1  Organization of the Company. The Company is duly organized, validly
existing, and in good standing under the laws of the jurisdiction of its
incorporation.

     7.2  Authorization. The Company has full corporate power and authority to
execute and deliver this Agreement and to perform its obligations hereunder.
This Agreement constitutes the valid and legally binding obligation of the
company, enforceable in accordance with its terms and conditions. The Company
need not give any notice to, make any filing with, or obtain any authorization,
consent, or approval of any government or governmental agency in order to
consummate the transactions contemplated by this Agreement.

     7.3  Non-Contravention. Neither the execution and the delivery of this
Agreement, nor the consummation of the transactions contemplated hereby, will
(a) violate any provision of the Company's charter to by-laws, or (b) conflict
with, result in a breach of, constitute a default under, result in the
acceleration of, create in any party the right to accelerate, terminate, modify,
or cancel, or require any notice under any agreement, contract, lease, license,
instrument, or other arrangement to which the Company is a party or by which it
is bound or to which any of its assets is subject.

     7.4  March Purchase Agreement. All of the representations and warranties of
the company contained in Section 6 of the March Purchase Agreement are true and
correct on the date of this Agreement.

     7.5  Assignment of Rights. The Rights assigned and transferred by Seller to
the Purchasers pursuant to this Agreement will be, upon consummation with the
Closing, enforceable against the Company by the Purchasers as assignee of Seller
after the date of the Closing in accordance with the terms thereof.

     8.   Representations and Warranties of the Purchasers. The Purchasers
jointly and severally represent and warrant to Seller and the Company as
follows:

     8.1  Organization of the Purchasers. Each of the Purchasers are entities
duly organized or created, validly existing, and in good standing under the laws
of the jurisdiction of its incorporation.

     8.2  Authorization. Each of the Purchasers has full corporate power and
authority to execute and deliver this Agreement and to perform its obligations
hereunder. This Agreement constitutes the valid and legally binding obligation
of each of the Purchasers, enforceable in accordance with its terms and
conditions. Each of the Purchasers need not give any notice to, make any filing
with, or obtain any authorization, consent, or approval of any government or
governmental agency in order to consummate the transactions contemplated by this
Agreement.

     8.3  Non-Contravention. Neither the execution and the delivery of this
Agreement, nor the consummation of the transactions contemplated hereby, will
(a) violate any provision of either of Purchasers' organizational documents
(which includes all documents pursuant to which Purchasers were organized or
created), or (b) conflict with, result in a beach of, constitute a default
under, result in the acceleration of, crate in any party the right to
accelerate, terminate, modify, or cancel, or require any notice under any
agreement, contract, lease, license,
<PAGE>

instrument, or other arrangement to which either of Purchasers is a party or by
which either is bound or to which any of its assets is subject.

     8.4  Brokers' Fees. Neither of the Purchasers has any liability or
obligation to pay any fees or commissions to any broker, finder, or agent with
respect to the transactions contemplated by this Agreement for which Seller
could become liable or obligated.

     8.5  Investment. Purchasers are not acquiring the Shares with a view to or
for sale in connection with any distribution thereof within the meaning of the
Securities Act of 1933. Each of Purchasers is acquiring the Shares to be
purchased by it for its own account, beneficially and not as a nominee for or
for the account of any other person.

     9.   Covenants of the Seller. The Seller covenants and agrees with
Purchasers and the Company as follows:

     9.1  Assignment of Rights. Concurrently with and subject to consummation of
the Closing, the Seller has assigned to the Purchasers the following Rights
under the March Purchase Agreement: (i) all rights of Dominion to the
performance of those obligations of the Company set forth in Section 8 of the
March Purchase Agreement, (ii) all rights of Dominion, if any, to enforce any
claims of Dominion against the Company for breach of any representation or
warranty against the Company set forth in Section 6 of the March Purchase
Agreement, and (iii) the rights, as a holder of Securities under Section 9 of
the March Purchase Agreement, to registration of the shares under the Securities
Act of 1933, as amended.

     10.  Covenants of the Company. The Company covenants and agrees with the
Seller and the Purchasers as follows:

     10.1 Consent to Assignment of the Rights. The Company herewith consents to
the assignment of the Rights and agrees that such Rights shall be enforceable by
the Purchasers as set forth in Section 9.1 hereof.

     11.  Miscellaneous.

     11.1 Survival of Representations, warranties and Covenants. All
representations, warranties, covenants and agreements contained in this
Agreement, or in any document, exhibit, schedule or certificate by any party
delivered in connection herewith shall survive the execution and delivery of
this Agreement and the date of each Closing and the consummation of the
transactions contemplated hereby, regardless of any investigation made by any
party or on its behalf, provided that, such representations and warranties shall
survive until December 31, 1996.

     11.2 Expenses. The Seller agrees to pay, and save Purchasers harmless
against liability for the payment of (a) fees and expenses (including, without
limitation, attorneys' fees) incurred with respect to any amendments or waivers
(whether or not the same shall become effective) under or with respect to this
Agreement and the transactions contemplated hereby, (b) stamp and other taxes
which may be payable in respect of the execution and delivery of this Agreement
and the consummation of the transactions contemplated hereby including the
issuance, delivery and acquisition of the Shares, and (c) fees and expenses
(including, without limitation, reasonable attorneys' fees) incurred in respect
of the enforcement of the rights granted under this Agreement and the
transactions contemplated hereby.

     11.3 Amendments and Waivers. This Agreement and all exhibits and schedules
hereto set forth the entire agreement and understanding among the parties as to
the subject matter hereof and merges and supersedes all prior discussions,
agreements and understandings of any and every nature among them. This Agreement
may be amended, the Company may take any action herein prohibited or omit to
take any action herein required to be performed by it, and any breach of any
covenant, agreement, warranty or representation may be waived, only if the
Company has obtained the written consent or waiver of (a) Purchasers, if the
amendment, action, omission or waiver is one which affects their rights or
obligations under this Agreement and (b) the holders of 51% of the Shares then
outstanding if the amendment, action, omission or waiver is one which affects
their rights or
<PAGE>

obligations under this Agreement. No course of dealing between or among any
persons having any interest in this Agreement will be deemed effective to
modify, amend or discharge any part of this Agreement or any rights or
obligations of any person under or by reason of this Agreement.

     11.4  Successors and Assigns. This Agreement may not be assigned by the
Company except with the prior written consent of the holders of 51% of the
Shares then outstanding. This Agreement shall be binding upon and inure to the
benefit of each of the Company and Seller and their respective permitted
successors and assigns and Purchasers and their successors and assigns. The
provisions hereof which are for Purchasers, benefit as purchasers or holders of
the Shares, are also for the benefit of, and enforceable by, any subsequent
holder of such Shares.

     11.5  Notices. All notices, demands and other communications to be given or
delivered under or by reason of the provisions of this Agreement shall be in
writing and shall be deemed to have been given personally or when mailed by
certified or registered mail, return receipt requested and postage prepaid, and
addressed to the addresses of the respective parties set forth below or to such
changed addresses as such parties may have fixed by notice; provided, however,
that any notice of change of address shall be effective only upon receipt:

               To the Purchasers:
               Aries Financial Services, inc.
               375 Park Avenue - Suite 1501
               New York, New York 10152

               With a Copy to:
               David Walner, Esquire
               375 Park Avenue - Suite 1501
               New York, New York 10152

               To the Company:
               ImmunoTherapeutics, Inc.
               3233 Fifteenth Street South
               Fango, North Dakota 58104
               Attention: Dr. Gerald Vesica

               With a Copy to:
               William S. Clarke, P.A.
               5 Independence way
               Princeton, New Jersey 08540

               To the Seller:
               Dominion Resources, inc.
               The Abbey
               355 Madison Avenue
               Morristown, New Jersey 07960

               With a Copy to:
               William E. McManus, III, Esquire Spencer's Corner
               90 Main Street - Suite 211
               Centerbrook, Connecticut 06409-1058


     11.6  Governing Law. The validity, performance, construction and effect of
this Agreement shall be governed by the internal laws of the State of New Jersey
without giving effect to principles of conflicts of law.

     11.7  Counterparts. This Agreement may be executed in any number of
counterparts and, notwithstanding that any of the parties did not execute the
same counterpart, each of such counterparts shall, for all purposes, be deemed
an original, and all such counterparts shall constitute one and the same
instrument binding on all of the parties thereto.

     11.8  Headings. The headings of the Sections hereof are inserted as a
matter of convenience and for reference only and in no way define, limit or
describe the scope of this Agreement or the meaning of any provision hereof.
<PAGE>

     11.9  Severability. In the event that any provision of this Agreement or
the application of any provision hereof is declared to be illegal, invalid or
otherwise unenforceable by a court of competent jurisdiction, the remainder of
this Agreement shall not be affected except to the extent necessary to delete
such illegal, invalid or unenforceable provision unless the provision held
invalid shall substantially impair the benefit of the remaining portion of this
Agreement.
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the date and year first above written.


                                        ImmunoTherapeutics, Inc.



                                        By: __________________________________
                                            Name:
                                            Title:



                                        Dominion Resources, Inc.



                                        By: __________________________________
                                            Name:
                                            Title:




                                        The Aries Fund, a Series of
                                              the Aries Trust



                                        By: __________________________________
                                            Name:
                                            Title:



                                        The Aries Domestic Fund, L.P.



                                        By: __________________________________
                                            Name:
                                            Title:

<PAGE>

                                  EXHIBIT "B"



The ARIES Fund,                         3,000,000
A Series of the ARIES TRUST



The Aries Domestic Fund, L.P.           1,000,000