Exhibit 4.3


 


FORM OF DEBT SECURITY


 


[Face of Security]


 


PASSAGE BIO, INC.


 


[If applicable, insert—FOR PURPOSES
OF THE ORIGINAL ISSUE DISCOUNT PROVISIONS OF THE INTERNAL REVENUE CODE OF 1986, THE ISSUE PRICE OF THIS SECURITY IS         %
OF ITS PRINCIPAL AMOUNT AT STATED MATURITY SET FORTH BELOW (ITS “PRINCIPAL AMOUNT”), THE AMOUNT OF ORIGINAL ISSUE DISCOUNT
IS         % OF ITS PRINCIPAL AMOUNT, THE YIELD TO MATURITY IS         %
AND THE ISSUE DATE IS             ]


 


[IF THE SECURITY IS A GLOBAL SECURITY, INSERT—THIS
NOTE IS A GLOBAL SECURITY. IT IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY (AS HEREINAFTER
DEFINED) OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES HEREINAFTER DESCRIBED AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE
BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE
DEPOSITARY OR BY THE DEPOSITARY OR A NOMINEE OF THE DEPOSITARY TO A SUCCESSOR OF THE DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR
DEPOSITARY.]


 


	No.	 	$            
	 	 	CUSIP No.


 


Passage Bio, Inc., a Delaware corporation
(herein called the “Company”, which term includes any successor corporation under the Indenture referred to on the
reverse hereof), for value received, hereby promises to pay to, or registered assigns, the principal sum of                 
Dollars on                  [if Security is to
bear interest prior to maturity, insert—, and to pay interest thereon from                 
or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on                 
and                  in each year, commencing                 ,
at the rate of         % per annum, until the principal hereof is paid or made available
for payment [if applicable, insert—, provided that any principal and premium, and any such installment of interest, which
is overdue shall bear interest at the rate of % per annum (to the extent that the payment of such interest shall be legally enforceable),
from the dates such amounts are due until they are paid or made available for payment, and such interest shall be payable on demand]].
The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture,
be paid to the Person in whose name this Security (or one or more predecessor Securities) is registered at the close of business
on the record date for such interest, which shall be the                 
or                  (whether or not a Business
Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided
for will forthwith cease to be payable to the Holder on such record date and may either be paid to the Person at the time this
Security (or one or more predecessor Securities) is registered at the close of business on a special record date for the payment
of such defaulted interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not
less than 10 days prior to such special record date, or be paid at any time in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required
by such exchange, all as more fully provided in said Indenture. [If the Security is not to bear interest prior to maturity, insert—The
principal of this Security shall not bear interest except in the case of a default in payment of principal upon acceleration, upon
redemption or at Stated Maturity and in such case the overdue principal and any overdue premium shall bear interest at the rate
of         % per annum (to the extent that the payment of such interest shall be legally
enforceable), from the dates such amounts are due until they are paid or made available for payment. Interest on any overdue principal
or premium shall be payable on demand. [Any such interest on overdue principal or premium which is not paid on demand shall bear
interest at the rate of         % per annum (to the extent that the payment of such interest
on interest shall be legally enforceable), from the date of such demand until the amount so demanded is paid or made available
for payment. Interest on any overdue interest shall be payable on demand.]].


 


Payment of the principal of (and premium,
if any, on) and [any such] interest on this Security will be made at the office or agency of the Company maintained for that purpose
in                  in such coin or currency of
[the United States of America] as at the time of payment is legal tender for payment of public and private debts[; provided, however,
that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto
as such address shall appear in the register of the Security maintained by the Registrar].





 


Reference is hereby made to the further
provisions of this Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect
as if set forth at this place.


 






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Unless the certificate of authentication
hereon has been manually executed by or on behalf of the Trustee under the Indenture referred to on the reverse hereof, this Security
shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.


 


IN WITNESS WHEREOF, the Company has caused
this instrument to be duly executed under its corporate seal.


 


	Dated:	Passage Bio, Inc.
	 	 	 
	 	By	 
	 	 	[Title]


 


	Attest and Countersign	 
	 	 
	 	 
	Secretary	 





 






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[Reverse of Security.]


 


PASSAGE BIO, INC.


 


This Security is one of a duly authorized
issue of securities of the Company (herein called the “Securities”), issued and to be issued in one or more series
under an Indenture dated as of                 ,
(herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Company
and                 , as trustee (herein called
the “Trustee”, which term includes any successor trustee under the Indenture), to which the Indenture and all indentures
supplemental thereto reference is hereby made for a statement of the respective rights, limitations or rights, duties and immunities
thereunder of the Company, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are
to be, authenticated and delivered. This Security is one of the series designated on the face hereof [, limited in aggregate principal
amount to $                ].


 


[If the Security is to be subordinated,
insert—The indebtedness evidenced by this Security is, to the extent and in the manner set forth in the Indenture, expressly
subordinated and subject in right of payment to the prior payment in full of all senior Indebtedness (as defined in the Indenture)
of the Company. This Security is issued subject to such provisions of the Indenture, and each Holder of this Security, by accepting
the same, agrees to and shall be bound by such provisions and authorizes and directs the Trustee on the Holder’s behalf to
take such action as may be necessary or appropriate to acknowledge or effectuate such subordination as provided in the Indenture
and appoints the Trustee such Holder’s attorney-in-fact for any and all such purposes.]


 


The Securities of this series are subject
to redemption upon not less than 30 days’, and no more than 60 days, notice provided in the manner set forth in the Indenture,
[(1) on in any year commencing with the year and ending with the year at the Redemption Price (as indicated below) equal to
100% of the principal amount, and (2)] at any time [on or after], as a whole or in part, at the election of the principal the following
Redemption Prices (expressed as percentages of the principal amount, as indicated below): If redeemed [on or before ,         %,
and if redeemed] during the 12-month period beginning of the years indicated,


 


	Year	 	Redemption Price	 	 	Year	 	 	Redemption Price	 
	 	 	 	 	 	 	 	 	 	 	 	 	 
	 	 	 	 	 	 	 	 	 	 	 	 	 
	 	 	 	 	 	 	 	 	 	 	 	 	 



 


and thereafter at a Redemption Price equal to % of the principal
amount together in the case of any such redemption with accrued interest to the Redemption Date, but interest installments whose
Stated Maturity is on or prior to such Redemption Date will be payable to the Holders of such Securities of record at the close
of business on the relevant record dates referred to on the face hereof, all as provided in the Indenture.


 


[If the Security is to be redeemable in
part, insert—In the event of redemption of this Security in part only, a new Security or Securities of this series for the
unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.]


 


[If the Security is to be subject to repayment
at the option of the Holder, insert—To be repaid at the option of the Holder, the Company must receive this Security, with
the form of “Option to Elect Repayment” hereon duly completed, at an office or agency of the Company maintained for
that purpose in (or at such other place of which the Company shall from time to time notify the Holder of this Security) not less
than nor more than days prior to the Repayment Date (as defined therein). The exercise of the repayment option by the Holder shall
be irrevocable.]


 


[If the Security is not to be subject to
redemption at the option of the Company, insert—The Securities are not redeemable at the option of the Company prior to Maturity.]


 


[If the Security is not to be an Original
Issue Discount Security, insert—If an Event of Default with respect to Securities of this series shall occur and be continuing,
the principal of the Securities of this series may be declared due and payable in the manner and with the effect provided in the
Indenture.]


 


The Indenture permits, with certain
exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Company and
the rights of the Holders of the Securities of each Series under the Indenture to be affected at any time by the Company with
the consent of the Holders of not less than a majority in aggregate principal amount of the Securities then outstanding of
each Series to be affected.


 






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The Indenture also contains provisions permitting the Holders
of a majority in principal amount of the Securities of any Series then outstanding, on behalf of the Holders of all Securities
of such series, to waive compliance by the Company with certain provisions of the Indenture and certain past Defaults or Events
of Default with respect to such Series under the Indenture and their consequences. Any such consent or waiver by the Holder of
this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security
issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent
of waiver is made upon this Security.


 


As provided in and subject to the provisions
of the indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture
or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given
the Trustee written notice of a continuing Event of Default with respect to the Securities of this series, the Holders of not less
than 25% in aggregate principal amount of the Securities of this series then outstanding shall have made written request to the
Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity reasonably satisfactory
to the Trustee, and the Trustee shall not have received from the Holders of a majority in aggregate principal amount of Securities
of this series then outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding,
for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted
by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after
the respective due dates expressed herein.


 


No reference herein to the Indenture and
no provision of this Security or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional,
to pay the principal of (and premium, if any, on) and interest on this Security at the times, place and rate, and in the coin or
currency, herein prescribed.


 


[If the Security is to be in registered
form, insert—As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security
is registrable in the register of the Registrar, upon surrender of this Security for registration of transfer at the office or
agency of the Company in any place where the principal of (and premium, if any, on) and interest on this Security are payable,
duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar duly
executed by, the Holder hereof or his attorney duly authorized in writing, and, thereupon one or more new Securities of this series,
of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.]


 


[The Securities of this series are issuable
only in registered form in denominations of $       [and any integral multiple] [or increments of $       in excess] thereof. As
provided in the Indenture and subject to certain limitations therein set forth, Securities of this series are exchangeable for
a like aggregate principal amount of Securities of this series of a different authorized denomination, as requested by the Holder
surrendering the same.]


 


[No service charge shall be made for any
such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental
charge payable in connection therewith.]


 


[Prior to due presentment of this Security
for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may treat the Person in whose
name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the
Company, the Trustee nor any such agent shall be affected by notice to the contrary.]


 


[If the Security is a Global Security,
insert—“Global Security” and “Global Securities” means a Security or Securities evidencing all or
a part of a series of Securities, issued to the Depositary (as hereinafter defined) for such Series or its nominee, and registered
in the name of such Depositary or its nominee. “Depositary” means, with respect to the Securities of any series issuable
or issued in whole or in part in the form of one or more Global Securities, the person designated as the Depositary by the Company.


 


No holder of any beneficial interest in
this Security held on its behalf by a Depositary or a nominee of such Depositary shall have any rights under the Indenture with
respect to such Global Security, and such Depositary or nominee may be treated by the Company, the Trustee, and any agent of the
Company or the Trustee as the owner of such Global Security for all purposes whatsoever. Notwithstanding the foregoing, nothing
herein shall impair, as between a Depositary and such holders of beneficial interests, the operation of customary practices governing
the exercise of the rights of the Depositary as Holder of any Security.


 


This Security is exchangeable, in
whole but not in part, for Securities registered in the names of Persons other than the Depositary or its nominee or in the
name of a successor to the Depositary or a nominee of such successor depositary only if (i) the Depositary notifies the
Company that it is unwilling or unable to continue as Depositary for this Note or if at any time such Depositary ceases to be
a clearing agency registered under the Securities Exchange Act of 1934, as amended, and, in either case, a successor
depositary is not appointed by the Company within 90 days, (ii) the Company in its discretion at any time determines not
to have all of the Securities of this series represented by one or more Global Security or Securities and notifies the
Trustee thereof, or (iii) an Event of Default has occurred and is continuing with respect to the Securities of this
series. If this Security is exchangeable pursuant to the preceding sentence, it shall be exchangeable for Securities issuable
in authorized denominations and registered in such names as the Depositary holding this Security shall direct. Subject to the
foregoing, this Security is not exchangeable, except for a Security or Securities of the same aggregate denominations to be
registered in the name of such Depositary or its nominee or in the name of a successor to the Depositary or a nominee of such
successor depositary.]


 






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[The Indenture entitles Holders to receive
annual reports with respect to the Trustee’s eligibility and qualifications to serve as Trustee by filing their names and
addresses with the Trustee for that purpose within two years preceding and mailing of any such annual report.]


 


No recourse shall be had for the payment
of the principal of (and premium, if any, on) or interest on this Security, or for any claim based hereon, or otherwise in respect
hereof, or based on or in respect of the Indenture of any indenture supplemental thereto, against any incorporator, stockholder,
officer or director, as such, past, present or future, of the Company or any successor corporation, whether by virtue of any constitution,
statute or rule of law, or by the enforcement of any assessment or penalty or otherwise, all such liability being, by the
acceptance hereof and as part of the consideration for the issue hereof, expressly waived and released.


 


All terms used in this Security which are
defined in the Indenture shall have the meanings assigned to them in the Indenture.


 


This Security, including without limitation
the obligation of the Company contained herein to pay the principal of (and premium, if any, on) and interest on this Security
in accordance with the terms hereof and of the Indenture, shall be construed in accordance with and governed by the laws of the
State of New York.


[Trustee’s Certificate
of Authentication.]


 


This is one of the Securities of the series designated herein
referred to in the within-mentioned Indenture.


 


                                                                  , as


[Authenticating Agent for] the Trustee 




 


	By	 	 
	 	Authorized Officer	 


 






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