EXHIBIT 1

AGREEMENT REGARDING JOINT FILING OF SCHEDULE 13G

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13G need be filed with respect to the ownership by each of the undersigned of shares of Common Stock of Principia Biopharma Inc.

Date: February 12, 2019

NEW LEAF VENTURES II, L.P.
By:	NEW LEAF VENTURE ASSOCIATES II, L.P.
	Its General Partner
	By:	NEW LEAF VENTURE MANAGEMENT II, L.L.C.
		Its General Partner
		By:	/s/ Craig L. Slutzkin
			Craig L. Slutzkin
			Chief Financial Officer
NEW LEAF VENTURE ASSOCIATES II, L.P.
By:	NEW LEAF VENTURE MANAGEMENT II, L.L.C.
	Its General Partner
	By:	/s/ Craig L. Slutzkin
		Craig L. Slutzkin
		Chief Financial Officer
NEW LEAF VENTURE MANAGEMENT II, L.L.C.
By:	/s/ Craig L. Slutzkin
	Craig L. Slutzkin
	Chief Financial Officer
*
Vijay K. Lathi
*
Ronald M. Hunt
*
Liam T. Ratcliffe
*
Daniel J. Becker
*
Isaac A. Manke

/s/ Craig L. Slutzkin

* Craig L. Slutzkin

As attorney-in-fact

* This Schedule 13G was executed by Craig L. Slutzkin on behalf of the individuals listed above pursuant to Powers of Attorney. Note that copies of the applicable Powers of Attorney are already on file with the appropriate agencies.

NEW LEAF BIOPHARMA OPPORTUNITIES II, L.P.
By:	NEW LEAF BPO ASSOCIATES II, L.P.
	Its General Partner
	By:	NEW LEAF BPO MANAGEMENT II, L.L.C.
		Its General Partner
		By:	/s/ Craig L. Slutzkin
			Craig L. Slutzkin
			Chief Financial Officer
NEW LEAF BPO ASSOCIATES II, L.P.
By:	NEW LEAF BPO MANAGEMENT II, L.L.C.
	Its General Partner
	By:	/s/ Craig L. Slutzkin
		Craig L. Slutzkin
		Chief Financial Officer
NEW LEAF BPO MANAGEMENT II, L.L.C.
By:	/s/ Craig L. Slutzkin
	Craig L. Slutzkin
	Chief Financial Officer