Convertible Promissory Notes - Additional Information (Details)	1 Months Ended					3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 31, 2025 USD ($)	Nov. 30, 2024 USD ($)	Oct. 31, 2024 USD ($)	May 31, 2024 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2025 USD ($) $ / shares	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2025 USD ($) $ / shares shares	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Short-Term Debt [Line Items]
Issuance of conversion of convertible promissory notes									$ 3,695,000
Total fair value at issuance of derivative instrument					$ 2,100,000
Tranche Liability											$ 1,407,000
Kalaris Therapeutics, Inc. | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Debt instrument, converted ratio									1
Maximum | Kalaris Therapeutics, Inc.
Short-Term Debt [Line Items]
Issuance of conversion of convertible promissory notes			$ 7,500,000
Probability of Achievement | Minimum
Short-Term Debt [Line Items]
Tranche liability											0
Probability of Achievement | Maximum
Short-Term Debt [Line Items]
Tranche liability											0.80
Discount Rate
Short-Term Debt [Line Items]
Tranche liability											0.09
Tranche Liability
Short-Term Debt [Line Items]
Tranche Liability			45,900,000
2024 Convertible Promissory Note
Short-Term Debt [Line Items]
Outstanding principal amount						$ 10,000,000			$ 10,000,000
Interest rate					10.00%			10.00%
Aggregate advance				$ 10,000,000	$ 5,000,000
Maturity date					2025-03
Estimated fair value					$ 12,100,000			$ 12,100,000
Change in the fair value of derivative liability									500,000
Loss on issuance of convertible promissory notes							$ (1,300,000)		(200,000)	$ (2,100,000)
Total fair value at issuance of derivative instrument					1,100,000
Interest expense						0	500,000		800,000	600,000
Contractual interest expense							200,000		200,000	200,000
Amortization of debt discount							300,000		600,000	400,000
Total premium on debt					$ 2,100,000
Debt instrument outstanding						$ 0			0
Accrued interest									$ 900,000
Common shares issued for conversion of debt | shares									1,757,951
Conversion price per share | $ / shares						$ 6.2			$ 6.2
2024 Convertible Promissory Note | Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Percentage of conversion price					80.00%
2024 Convertible Promissory Note | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Percentage of conversion price					100.00%
2024 Convertible Promissory Note | Kalaris Therapeutics, Inc.
Short-Term Debt [Line Items]
Debt instrument, issued, principal amount	$ 3,750,000
2024 Convertible Promissory Note | Minimum
Short-Term Debt [Line Items]
Expected term (in years)								4 months 24 days
2024 Convertible Promissory Note | Minimum | Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Gross proceeds								$ 10,000,000
2024 Convertible Promissory Note | Maximum
Short-Term Debt [Line Items]
Outstanding principal amount					$ 10,000,000			$ 10,000,000
Expected term (in years)								1 year 3 months 18 days
2024 Convertible Promissory Note | Probability of Achievement | Minimum
Short-Term Debt [Line Items]
Tranche liability					0			0
2024 Convertible Promissory Note | Probability of Achievement | Maximum
Short-Term Debt [Line Items]
Tranche liability					0.90			0.90
2024 Convertible Promissory Note | Discount Rate | Minimum
Short-Term Debt [Line Items]
Tranche liability					0.123			0.123
2024 Convertible Promissory Note | Discount Rate | Maximum
Short-Term Debt [Line Items]
Tranche liability					0.187			0.187
2024 Bridge Notes
Short-Term Debt [Line Items]
Outstanding principal amount		$ 5,000,000	$ 24,500,000			$ 10,000,000			$ 10,000,000
Interest rate		8.00%
Maturity date			2025-05
Change in the fair value of derivative liability						0			500,000
Recognized gain for change in fair value of tranche liability						0			400,000
Loss on issuance of convertible promissory notes											$ (35,900,000)
Total fair value at issuance of derivative instrument			$ 1,000,000
Tranche liability			0.095
Debt instrument outstanding						$ 0			0
Accrued interest									$ 300,000
Common shares issued for conversion of debt | shares									1,660,888
Conversion price per share | $ / shares						$ 6.2			$ 6.2
Debt instrument, issued, principal amount		$ 1,000,000	$ 9,000,000
Additional draw up amount		$ 15,000,000
Tranche Liability			$ 21,400,000								400,000
Change in the fair value of the tranche liability											$ 21,000,000
2024 Bridge Notes | Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Percentage of conversion price			80.00%
Difference between the fair value at the issuance date and the principal amount of the note			$ 14,500,000
2024 Bridge Notes | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Percentage of conversion price			100.00%
2024 Bridge Notes | Minimum
Short-Term Debt [Line Items]
Expected term (in years)			4 months 24 days
2024 Bridge Notes | Minimum | Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Gross proceeds			$ 10,000,000
2024 Bridge Notes | Maximum
Short-Term Debt [Line Items]
Outstanding principal amount			$ 15,000,000
Expected term (in years)			7 months 6 days
Debt instrument, issued, principal amount			$ 25,000,000
2024 Bridge Notes | Probability of Achievement | Minimum
Short-Term Debt [Line Items]
Tranche liability			0
2024 Bridge Notes | Probability of Achievement | Maximum
Short-Term Debt [Line Items]
Tranche liability			0.60
2025 Bridge Notes
Short-Term Debt [Line Items]
Outstanding principal amount	3,900,000					$ 3,750,000			$ 3,750,000
Change in the fair value of derivative liability						$ 0			200,000
Total fair value at issuance of derivative instrument	$ 200,000
Accrued interest									$ 100,000
Per share price paid by investors	8.50%
2025 Bridge Notes | Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Difference between the fair value at the issuance date and the principal amount of the note	$ 200,000
2025 Bridge Notes | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Outstanding principal amount	$ 3,750,000
Common shares issued for conversion of debt | shares									794,499
Conversion price per share | $ / shares						$ 4.7851			$ 4.7851
2025 Bridge Notes | Minimum
Short-Term Debt [Line Items]
Expected term (in years)	2 months 12 days
2025 Bridge Notes | Maximum
Short-Term Debt [Line Items]
Expected term (in years)	3 months 18 days
2025 Bridge Notes | Probability of Achievement | Minimum
Short-Term Debt [Line Items]
Tranche liability	0.20
2025 Bridge Notes | Probability of Achievement | Maximum
Short-Term Debt [Line Items]
Tranche liability	0.80
2025 Bridge Notes | Tranche | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Additional draw up amount	$ 5,000,000
2025 Bridge Notes | First and Second Tranches | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Additional draw up amount	3,750,000
2025 Bridge Notes | Third Tranches | Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Additional draw up amount	7,500,000
2024 Bridge Notes and 2025 Bridge Notes
Short-Term Debt [Line Items]
Interest expense						$ 0	$ 0		$ 600,000	$ 0
Contractual interest expense									200,000
Amortization of debt discount									$ 400,000
January 2025 AlloVir Convertible Promissory Note
Short-Term Debt [Line Items]
Outstanding principal amount	$ 3,750,000
AlloVir Note | Kalaris Therapeutics, Inc.
Short-Term Debt [Line Items]
Common shares issued for conversion of debt | shares									160,165
AlloVir Note | Maximum
Short-Term Debt [Line Items]
Issuance of conversion of convertible promissory notes			$ 7,500,000